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RENDICONTI Online
Società Geologica Italiana
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Volume 9
POSTER
NATURA E GEODINAMICA
DELLA LITOSFERA NELL'ALTO ADRIATICO
VENEZIA, PALAZZO LOREDAN, 5-6 NOVEMBRE 2009
COMITATO ORGANIZZATORE
G.V. Dal Piaz (coordinatore), C. Doglioni, A. Mottana, G. Panza, A. Rinaldo e F.P. Sassi
Società Geologica Italiana – Roma
Ottobre 2009
www.socgeol.it
Rendiconti online Soc. Geol. It., Vol. 9 (2009), 71
Struttura della litosfera della zona italica
ENRICO BRANDMAYR (*), MARCO ZURI (*), FABIO ROMANELLI (*), GIULIANO F. PANZA (*,**),
CHIARA D’AMBROGI (***) & CARLO DOGLIONI (****)
ABSTRACT
STRUCTURE OF THE LITHOSPHERE IN THE ITALIC REGION
The study of the structure of the lithosphere in Italy and its
surroundings is important for the understanding of the
geodynamic setting of the region; furthermore, the structural
models for the crust and uppermost mantle (lithosphereasthenosphere system) represent a major input for the
determination of earthquake source mechanisms, for reliable
geodynamic modelling and for the evaluation of seismic hazard
using advanced methodologies like the neo-deterministic
seismic hazard assessment (NDSHA).
An important goal was obtained with the determination of
structural models for the lithosphere-asthenosphere system,
obtained from surface wave tomography and non-linear
inversion of dispersion curves, for 1°x1° cells in the whole
Italic region. All the solutions for each cell are processed with
an optimizing method (LSO) with the aim to define a smooth
3D model of the lithosphere-asthenosphere system, in
agreement with the concept of Occam razor. In fact, the criteria
of optimization will help choose, for each cell, as
representative solution the one that minimizes the local lateral
velocity gradient. One motivation for seeking smooth global
models is that to avoid the introduction of heterogeneities that
can eventually arise from a subjective choice. In fact some of
the models obtained in each cell could be solutions only for the
mathematical model. Moreover, the presence of a lateral
boundary condition, in velocity-wave equations when a threedimensional velocity model is constructed, starting from the
cellular-shaped models, is not consistent with the basic
theoretical assumption, i.e. the infinite lateral extension of the
model’s layers. Hence the choice of the smoothest solution is
needed to keep the final result as close as possible to the
conditions of validity of the used surface wave propagation
theory. LSO optimization has been applied to the whole Italic
region and the resulting 3D structural model is presented. Each
cellular model is then complemented with Vp data, properly
_________________________
(*) Dipartimento di Scienze della Terra, Università degli Studi di Trieste
(**) The Abdus Salam International Centre for Theoretical Physics, Trieste
(***) Servizio Geologico d'Italia – ISPRA
(****) Dipartimento di Scienze della Terra, Università La Sapienza di
Roma
Lavoro eseguito nell’ambito del progetto DPC-INGV S1 “Determinazione
del potenziale sismogenetico in Italia per il calcolo della pericolosità
sismica”
processing the relative models supplied by P wave
tomographic studies.
A preliminary attempt to elaborate and represent this set of
geophysical data using 3D graphics is performed and supplies
a 3D imagery of the lithosphere-astenosphere system for the
study region. For each 1°x1° cell a conversion from spherical
to metric coordinates has been carried out to enable the
integration of geophysical lithospheric data, with other ones,
mainly geological, into a comprehensive and multi-scale 3D
model. Volumes characterized by the thickness (h), Vs, Vp and
Density (ρ) values assigned to the corresponding layer in the
original dataset, describing the main characteristics of
lithosphere-asthenosphere system are built.
In the description of the lithosphere-asthenosphere system
of the Italic region the lithospheric thickness has been defined
according to the distribution of seismicity.
The properties of earthquakes sources are studied, in order
to obtain a constraint to the geodynamic modelling, using an
advanced waveform inversion technique (INPAR) that allows
the retrieving of the full earthquake moment tensor. INPAR
allows the use of relatively short period waveforms,
significantly improving the reliability of depth determination
for shallow events, usually fixed by CMT and RCMT. This
lead to a drastic relocation and change of mechanism of a
major event of Umbria Marche 1997 seismic sequence, and
provided new constraints to the geological setting and local
stress field. The major results enlighten from the 3D structural
model obtained from the structural inversion and from the
distribution and description of focal mechanisms obtained
through INPAR, allow us to add new constraints to
geodynamical description of Appenninic subduction and retroarc expansion of Thyrrenian basin, along the Crop-03 seismic
experiment profile. In particular the structural model shows
clear evidences of crustal doubling at the eastern margin of
Corsica, probably a fragment of Alpine-Betic Orogen, involved
in the subsequent expansion process. Moreover the presence of
frequent seismicity at intermediate depths (20-50 km) near to
the Apennines compressive front is a robust constraint to the
location of the subducting slab.
The data from 8 contiguous cells, along a section WSWENE oriented, are processed in order to highlight the
consistency between geological interpretations and geophysical
data.
Key words: Dispersion, Non-linear inversion, Seismicity.
Rendiconti online Soc. Geol. It., Vol. 9 (2009), 72-75
The Dinaric thrusts in the Gulf of Trieste (Northern Adriatic)
BUSETTI MARTINA (*), VOLPI VALENTINA (*), NICOLICH RINALDO (**) BARISON ERIKA (**), BARADELLO LUCA
(*), BRANCATELLI GIUSEPPE (**), MARCHI MAURIZIO (*), ROMEO ROBERTO (*) & WARDELL NIGEL (*)
RIASSUNTO
I sovrascorrimenti Dinarici nel Golfo di Trieste (Adriatico Settentrionale)
L’analisi di profili sismici multicanale acquisiti nel Golfo di Trieste ha
permesso di definire l’estensione e l’attività tettonica del fronte esterno delle
Dinaridi e le strutture ad essa legate. Il Golfo di Trieste fa parte dell’avampaese
adriatico, costituito dalla piattaforma carbonatica Paleocenica-Mesozoica,
sovrastata dai depositi di avanfossa del Flysch eocenico e dai sedimenti Plioquaternari recenti. Il dataset utilizzato è costituito da 244 km di profili sismici
multicanale e 16 km di profili sismici monocanale ad alta risoluzione acquisiti
a mare, e 5 km di profili sismici multicanale acquisiti a terra a partire dal 2003.
Le principali strutture tettoniche identificate nell’area di studio sono: a) la
Faglia di Trieste, costituita da un sistema di sovrascorrimenti dinarici che ha
prodotto nei carbonati un rigetto verticale complessivo di circa 1400 m, con
possibile attività neotettonica; b) l’attività dei sovrascorrimenti del fronte
dinarico esterno, evidente del Golfo di Trieste e nella Bassa Pianura Friulana,
con deformazione del Flysch ed presenza nei carbonati di faglie a basso
angolo; e c) sistema di faglie ad orientazione NE-SO che segmentano i
sovrascorrimenti dinarici.
Key words: Dinaric thrusts, Gulf of Trieste, North Adriatic.
INTRODUCTION
The Gulf of Trieste, together with its surrounding onshore
areas, the Friuli Plain, the Karst and the Istria, belongs to the
Adriatic Apulian foreland. It is composed of the Mesozoic
Adriatic Carbonate Platform, Paleocene-Eocene carbonates and
Eocene Flysch, outcropping in the Karst and Istria, and buried
below the Late Cenozoic sediments of the Friuli Plain (Fig. 1).
The building of the south-west vergent belt of Dinarides
provided the tilting of the Friuli Carbonate Platform (the
carbonate platform buried below the Friuli Plain and the Gulf
of Trieste), presently being 300-500 m depth at the shelf
margin in the western part of the gulf, and going down to more
than 1200 m b.s.l. close to the coast of the Karst (Busetti et al.,
in press), and the filling of the foredeep by the Eocene Flysch
and Paleocene-Early Eocene carbonates. Further, the South
Alpine compressional phase provided the tilting of the Friuli
Carbonate Platform, down to over 3500 m b.s.l., towards the
North/North-West, at the front of the Alpine thrusts (Nicolich
et al., 2004) and the filling of the foredeep during the Late
Oligocene - Miocene by the continental to coastal deposit of
the Cavanella (Aquitanian to Langhian) and Molassa (Late
Miocene).
The Messinian marine regression provided the development
of a marked erosive surface in the Flysch (Busetti et al., in
press), and a complex morphology with valleys and highs
characterised by terraces and escarpments (Mosetti and Morelli
1968). During the Pliocene marine transgression terrigenous
and marine sediments were deposited, and a further erosive
episode in the Early Pliocene took place (Fantoni et al., 2002).
Dinaric structures are present onland (Fig. 1):
a) in the Eastern Friuli Plain the buried thrust of the Panzano
Line (Carulli et al., 1980; Nicolich et al., 2004);
b) at the Karst coastal front occurs the Trieste Fault, that Del
Ben et al. (1991) considered the result of transpressive
deformation with consistent dextral strike-slip component,
generated in Middle-Alpine orogeny (Paleogene) and
reactivated during the Neo-Alpine phase. Busetti et al. (in
press) inferred from seismic data that the Karst coastal front
and the 2-3 km offshore belt, can be regarded as an
accommodation zone of the Karst Dinaric thrust system with a
vertical component of about 1400 m;
c) in the Istria peninsula with the Ćrni Kal Thrust, that Placer
(2008) hypothesizes as the continuatuon of the Trieste Fault,
the Hrastovlje and Gračišče Thrust within the Flysch (Placer
2007), and the Buzet Thrust, again in the Flysch, hypothesized
by Placer et al., 2004, to be the outermost SW margin of the
Karst Thrust Edge (Fig. 1).
The Dinaric thrusts are displaced by NE-SW faults, as the
_________________________
(*) Istituto Nazionale di Oceanografia e di Geofisica Sperimentale,
Borgo Grotta Gigante 42/c, 34010 Sgonico, Trieste, Italy
(**) Università degli Studi di Trieste, Dipartimento di Ingegneria Civile e
Ambientale, Via Valerio, 10, 34127 Trieste, Italy
Lavoro eseguito nell’ambito della convenzione n. 8443/Rep. Dd.24/11/2004
- Studio della risorsa geotermica regionale, con il contributo finanziario
della Regione Autonoma Friuli Venezia Giulia - Direzione Centrale
Ambiente e Lavori Pubblici – Servizio Geologico.
Fig. 1 – Position map of the multichannel (MC) seismic lines acquired
offshore and onshore (black line) and the high resolution (HR) seismic
collected near the coast (grey line).
TITOLO DEL LAVORO (STILE: INTEST. DISPARI)
73
Fig. 2 – Multichannel seismic profile G05-4bis across the Gulf of Trieste (modified after Busetti et al., in press). The Friuli Carbonate Platform (top reflector
indicated by “C”) is flexured below the External Dinarides frontal ramp down to 900 ms (about 1200 m). The Friuli Carbonate Platform is overlain by the
Eocene Flysch terrigenous sequence ”f”, filling the Dinaric foredeep and affected by thrusts. Plio-Quaternary marine sediments drape the Messinian erosional
surface “M” in the western part, while an erosional episode “P”, due to the Pliocene marine regression, affected the overall area, as the final PliocenePleistocene marine transgressional phase (modified after Busetti et al., in press). Onshore geological section modified after Carulli (2006).
Sistiana and Monte Spaccato Faults present at the northern and
southern part of the Karst respectively (Cavallin et al., 1978;
Carobene and Carulli, 1981).
The present study investigates the tectonic structures of the
Gulf of Trieste, in particular the Dinaric thrusts identified
offshore and related to the onshore features.
THE SEISMIC DATA
The seismic data set includes 250 km of multichannel
seismic (MCS) profiles and 16,2 km of high resolution (HR)
single-channel seismic profiles (Fig. 1). The MCS profiles
consists of: a) 218 km acquired by R/V OGS Explora in the
Gulf of Trieste and 26 km acquired across the Lagoon of
Grado and Marano by OGS, all collected in 2005; b) 4 km
collected on land by the University of Trieste, in 2005; and c)
1,1 km onland seismic profile collected by OGS in 2007.
The off-shore MCS profiles (Busetti et al., in press) were
calibrated with the exploration wells Cavanella-1, Cesarolo-1,
and Amanda-1bis (AGIP 1972, 1977 and 1994), together with
published oil exploration seismic profiles (Amato et al., 1977;
Casero et al., 1990) and the deep crustal seismic profile CROP
M-18 (Fantoni et al., 2003; Finetti and Del Ben, 2005; Scrocca
et al., 2003).
The onland MCS profiles were calibrated with the Grado-1
well, drilled in 2008. The well recovered Mesozoic carbonates
from bottom depth of 1103 to 1001 m, Paleocene-Eocene
carbonates from 1001 to 616,5 m, the presumed Miocene
Fig. 3 – Offshore multichannel seismic profiles across the tectonic
Molassa
from 616,5 to 280 m and, above, Quaternary
deformation of the Flysch sequence “f”. The underlying Friuli Carbonate
sediments.
main fracture
zone,
at 736-740
to angle
the bottom
Platform (topAreflector
“C”), exhibits
a gentle
fold withmlow
faulting.
depth
was “f”
found
(DellabyVedova
et the
al.,detachment
in 2008).level along “C”. The
The Flysch
is affected
thrusts with
erosion
“P”, that
includes
the Messinian
Lower Pliocene
erosive
The surface
16,2 km
of HR
single
channel and
profiles,
recorded
by
phases,inin a)
is affected
fault escarpment
up toclose
30 m high.
OGS
2003
withbya a boomer
source,
to the coast of
Trieste, were calibrated with four 14-27 meter long cores
(Romeo, 2009). The cores recovered marine sediments, and, at
the bottom, Flysch.
RESULTS AND DISCUSSION
The tectonic setting of the Gulf of Trieste is characterised
by Dinaric thrust systems segmented by faults with NE-SW
orientation with normal and transcurrent components. Three
main Dinaric thrust systems have been identified (Fig. 4):
a) the Trieste Fault, the Dinaric frontal ramp located from
the Karst coastal front to 2-3 km offshore, with an overall
vertical component of about 1400 m (Busetti et al., in press).
The top of the Flysch, in the HR seismic profiles collected near
the coast and calibrated with the cores, shows a morphology
characterised by erosional surfaces some hundred meters wide
and escarpment about 15 meters high with inverse faults
disrupting the Flysch and probably also the onlapping the Late
Quaternary sediment (Romeo, 2009). These evidences provide
recent tectonic activity of the Trieste Fault.
74
P. AUTORE ET ALII
(STILE: INTEST. PAGINE PARI)
The Trieste Fault is linked to the Panzano Line but
displaced by the NE-SW Sistiana Fault with a left transcurrent
component with 1-2 km of offset. The Trieste Fault, the
Panzano Line and Ćrni Kal Thrust could be considered as
belonging to the same thrust system, the Dinaric frontal ramp
located at the Karst front, overthrusting the foredeep Flysch
units, and displaced by NE-SW faults;
b) the Dinaric thrust system across the Gulf of Trieste (Fig.
3). The structure is characterised by fault-bend folds up to 1
km wide and up to some hundred meters high within the
Flysch with the detachment level coincident with the top of the
carbonates, and low angle thrusts in the carbonates. Most of
the thrusts are westward vergent, while eastward vergent
backthrusts occur mainly in the north-western part. More
intense and recent deformation is present in the north-western
part, where fault escarpments of about 30 meters cut the
Messinian/Early Pliocene erosional surface. These thrust
system should represents the westernmost Dinaric frontal
thrust in the Gulf of Trieste.
The feature is probably displaced of about 1 km by a NESW transcurrent fault located in the middle of the Gulf, that
separated two zones with different tectonic regime: the
northern part with more intense and recent deformation and
NW dipping thrusts and SE dipping backthrusts, from the
southern part with mainly NW dipping thrusts. In addition, the
morphology of the top of the Flysch (Morelli and Mosetti,
1968) shows two highs in correspondence of the northern and
southern part of the thrust respectively, that are separated by a
valley. The valley could be a further evidence of the
hypothesized NE-SW fault.
The Dinaric orientation and dip of the faults are the same as
the Hrastovlje Thrust in Istria within the Flysch (Placer, 2005),
from which is offset by the NE-SW Monte Spaccato Fault,
located at the eastern Istria coast and crossing the Karst coast.
The normal fault in the coastal area of Debelj Rtič and Punta
Sottile, was hypothesized as the continuation of the right
transcurrent Monte Spaccato Fault in the Karst (Cavallin et al.
1978 and Carobene and Carulli, 1981). The seismic data
confirm this hypothesis, as onland the top hill of the thrust
have about 200 m of elevation while offshore the top of the
Flysch lies at about 120 m depth. Part of these difference in
elevation could be related to tectonic activity;
c) the westernmost frontal Dinaric thrust across the Grado
Lagoon limiting the Flysch basin to the West and probably
overthrusting the Flysch units on the Molassa deposits.
Onland, the MCS profiles, exhibit at 600-800 m depth, high
amplitude subparallel horizons acoustically similar to the top
of the carbonate in the offshore profile. These reflectors are
probably the Paleocene-Eocene carbonates occurring in the
Grado-1 well. In the 4 km long E-W line A1, the top of the
carbonate horizons are gentle folded and faulted whereas in the
1,1 km long N-S profile UD-07-06 these horizons are gentle
dipping northward and without significant deformation. The
acoustic facies between the carbonates and the Pliocene
unconformity presents different seismic character along the
two profiles: a) in the western line A1 is characterized by low
amplitude and high frequency reflectors, possible Miocene
Molassa deposits, with two structural highs in the eastern and
western part, respectively, with gentle folds and faults; b) on
the eastern profile UD-07-06 is characterised by high
amplitude reflectors affected by thrusts, more similar to the
Flysch sequence occurring offshore. The data suggest the
occurrence of a main tectonic deformation associated to
overthrust of the Flysch on the Miocene sediment, and low
angle faulf in the carbonate. This thrust system is probably
linked with those shown by the Grado-1 well, where both the
Mesozoic and Eocene carbonates are fractured.
These thrust system should represents the westernmost
Dinaric frontal thrust below the Friuli Plain.
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AGIP (1972) - Acque dolci sotterranee. Ed. AGIP, 914 pp.
AGIP (1977) - Temperature sotterranee. Ed. AGIP, 1390 pp.
AGIP (1994) - Acque dolci sotterranee. Aggiornamento dati
dal 1971 al 1990. Ed. AGIP, 515 pp.
AMATO A., BARNABA P.F., FINETTI I., GROPPI G., MARTINIS B.
& MUZZIN A. (1977) - Geodynamic Outline and Seismicity
of Friuli Venetia Julia Region. Boll. Geof. Teor. Appl.
19(72), 217-256.
BUSETTI M., VOLPI V., BARISON E., GIUSTINIANI M., MARCHI
M., RAMELLA R., WARDELL N. & ZANOLLA C.; MesoCenozoic seismic stratigraphy and the tectonic setting of
the Gulf of Trieste (northern Adriatic). Proc. of the Adria
2006, International Geological Congress on the Adriatic
Region, 19-20 June 2006, Urbino (Italy), GeoActa, in
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Fig. 4 – Tectonic sketch map of the Gulf of Trieste and surrounding areas
with the Dinaric Thrust system and the NE-SW faults.
CAROBENE L. & CARULLI G.B. (1981) - Foglio 40A Gorizia e
53A Trieste. In: Castellarin A. (ed.) Carta tettonica delle
Alpi Meridionali. CNR Geodinamica, Pubbl. 441, 8-13.
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CARULLI G.B. (2006) - Carta Geologica del Friuli Venezia
Giulia. Ed. Reg. Aut. Friuli Venezia Giulia, Direzione
Centrale Ambiente e Lavori Pubblici, Servizio Geologico.
CARULLI G.B., CAROBENE L., CAVALLIN A., MARTINIS B.,
ONOFRI R., CUCCHI F. & VAIA F. (1980) - Evoluzione
strutturale Plio-Quaternaria del Friuli e della Venezia
Giulia. In: Contributi alla Carta Neotettonica d’Italia. CNR
- Progetto Finalizzato Geodinamica, Pubbl. 356, 488-545.
CASERO P., RIGAMONTI A. & IOCCA M. (1990) Paleogeographic relationship during Cretaceous between
the Northern Adriatic area and the Eastern Southern Alps.
Mem. Soc. Geol. It., 45, 807-814.
CATI A., SARTORIO D. & VENTURINI S. (1987) - Carbonate
Platforms in the Subsurface of the Northern Adriatic Area.
Mem. Soc. Geol. It., 40, 295-308.
CAVALLIN A., MARTINIS B., CAROBENE L. & CARULLI G.B.
(1978) - Dati preliminari sulla Neotettonica dei Fogli 25
(Udine) e 40A (Gorizia). In: Contributi preliminari alla
realizzazione della carta neotettonica d'Italia. CNR Progetto Finalizzato Geodinamica, Pubbl. 155, 189-197.
DEL BEN A., FINETTI I., REBEZ A. & SLEJKO D. (1991) Seismicity and seismotectonics at the Alps-Dinarides
contact. Boll . Geofis. Teor. Appl., 32 (130-131), 155-176.
DELLA VEDOVA B., CASTELLI E., CIMOLINO A., VECELLIO C.,
NICOLICH R. & BARISON E. (2008) - La valutazione e lo
sfruttamento delle acque geotermiche per il riscaldamento
degli edifici pubblici. Rassegna Tecnica del Friuli Venezia
Giulia, 6/2008, 16-19.
FANTONI R., CATELLANI D., MERLINI S., ROGLEDI S. &
VENTURINI S. 2002 - La registrazione degli eventi
deformativi cenozoici nell’avampaese veneto-friulano.
Mem. Soc. Geol. It., 57, 301-313.
FANTONI R., DELLA VEDOVA B., GIUSTINIANI M., NICOLICH R.,
BARBIERI C., DEL BEN A., FINETTI I. & CASTELLARIN A.
(2003) - Deep seismic profiles through the Venetian an
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NICOLICH R., DELLA VEDOVA B., GIUSTINIANI M. & FANTONI
R. (2004) - Carta del sottosuolo della Pianura Friulana
(Map of subsurface of the Friuli Plain). Reg. Aut. Friuli
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Kozina-Koper. [Kraški rob (landscape term). Geological
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PLACER L., KOŠIR A., POPIT T., ŠMUC A., & JUVAN G. (2004) The Buzet Thrust Fault in Istria and overturned carbonate
megabeds in the Eocene Flsych of the Dragonja Valley
(Slovenia). Geologija 47 (2), 193-198.
ROMEO R. (2009) - Studio geofisico integrato ad alta
risoluzione dei depositi marini e della struttura del
substrato della Riviera di Miramare (Golfo di Trieste).
Ph.D thesis, Univ. degli Studi di Trieste, 174 pp., 13 plates.
SCROCCA D., DOGLIONI C., INNOCENTI F., MANETTI P.,
MAZZOTTI A., BERTELLI L., BURBI L. & D’OFFIZI S. (Eds.)
(2003) - CROP Atlas, Seismic Reflection Profiles of the
Italian Crust. Mem. Descr. Carta Geol. d’It., LXII, 193
pp., 71 plates.
New evidence of the outer Dinaric deformation front in the Grado
area
CIMOLINO AURÉLIE (*), DELLA VEDOVA BRUNO (*), NICOLICH RINALDO (*), BARISON ERIKA (*),
MELIS ROMANA (**) & BRANCATELLI GIUSEPPE (*)
RIASSUNTO
Nuove evidenze del fronte deformativo delle Dinaridi esterne nell’area di
Grado
Il pozzo Grado-1 ha raggiunto 1108 m di profondità nei calcari
della piattaforma mesozoica che con i suoi alti strutturali
interessa l’area di Lignano – Grado. Il pozzo è stato eseguito
su finanziamento della regione Friuli Venezia Giulia – Servizio
Geologico ed ha avuto lo scopo di caratterizzare la risorsa
geotermica presente nella Basa Pianura Friulana e nella fascia
lagunare, coronando i pluriennali studi svolti dall’Università di
Trieste – Dipartimento di Ingegneria Civile e Ambientale. Il
pozzo è stato completato con logs geofisici, eseguiti dalla
Baker-Atlas nel tratto a foro aperto da 700 a 1008 m, ed ha
incontrato i calcari a nummuliti di piattaforma del Paleogene a
-616,5 m e quelli del Mesozoico (Creta Sup.) a -1001 m. I
calcari paleogenici, analoghi a quelli presenti nel nord
dell’Istria e nei pozzi petroliferi nell’offshore della Dalamzia
settentrionale, sono interessati da fratture aperte collegate a
faglie di sovrascorrimento con direzione dinarica e fanno
ritenere la presenza di un loro raddoppio. Detto
sovrascorrimento rappresenta il fronte più esterno dei sistemi
dinarici ed appare ancora attivo. La risorsa geotermica
rinvenuta è costituita da acque salmastre a temperatura di circa
42° C con portata di 25 l/s e pressione di 2,8 bar, contenute
principalmente entro le fratture dei carbonati paleogenici.
Key words: Biostratigraphy, Dinaric thrust, Exploration well,
Geophysical logs, Seismic reflection profiles.
THE GRADO-1 WELL
The Department of Civil and Environmental Engineering
(University of Trieste) conducted several studies, sponsored by
Friuli Venezia Giulia Region Geological Survey, aimed to
characterize the Friuli Plain geothermal resources (NICOLICH et
alii, 2008). Anomalous geothermal gradient areas are located
in correspondence of morphological-structural culminations in
the carbonatic basement buried beneath Dinaric Flysch
(Paleogene) and Alpine Molasse (from Oligo-Miocene) (Fig.
1). Quality, quantity and extent of geothermal resources were
defined by an 1108 m exploration borehole, which enabled to
verify also geothermal heating system feasibility (DELLA
VEDOVA et alii, 2008).
New findings concerning the Grado-1 well (Fig. 2):
• geophysical logs, acquired in openhole interval (from 700 m);
• biostratigraphic analysis on cuttings and cores, compared to
geological outcropping features and wells datings supported
by:
- public, industrial and high resolution reflection profiles,
offshore and on land;
- gravity data, acquired by DICA (DELLA VEDOVA et alii,
1988) and integrated with ENI data;
- Friuli plain and Croatia offshore oil and water wells provide
new evidences of an important regional tectonic feature in
Grado area, turned out to be the outer Dinaric deformation
front.
Biostratigraphic data and geophysical logs define stratigraphic
- structural constrains, besides lithology, porosity, resistivity
and elastic moduli. The terrigenous cover is composed by PlioPleistocene series, a Neogene marly-sandy succession, rich in
external neritic faunas, and pelagic faunas Paleogene
turbidites. The carbonates, reached at 616.5 m, present both
Alveolinidae - Nummulitidae - Orbitolites Paleogene and
Rudist rich Upper Cretaceous intervals. Carbonates are
fractured and interested by tectonic redouble; discontinuity
families are diversified according to orientation, genesis and
intensity. The sequence can be directly correlated to northern
Istria geological setting and to northern Dalmatia offshore well
stratigraphies and logs. On the contrary, the top of the nearby
Lignano platform is characterized by the Lower Cretaceous
formations, covered directly by Lower Miocene Cavanella
Group (Cesarolo-1 well; NICOLICH et alii, 2004).
Seismic sections and water wells stratigraphies have been
calibrated with Grado-1. Bouguer gravity map evidences the
carbonate basement culminations. The Grado high is NW-SE
oriented and delimited by Dinaric and anti-Dinaric structures,
whereas a SW-NE orientation dominates the Lignano-Cesarolo
area. Isobaths maps of the Quaternary base and top of
carbonates are presented, with delimitation of westward
extension of Flysch and of the eastern limit of the Pliocene
deposits.
We assume that the Grado culmination has been interested by
SW-verging Dinaric compressive structures, which involve
both Paleogene and Cretaceous carbonates, as well as Dinaric
and Alpine clastics. Quaternary sediments are locally interested
by minor structures, up to surface. This framework sets up the
_________________________
(*)Dipartimento di Ingegneria Civile e Ambientale, Università di Trieste
(**)Dipartimento di Scienze Geologiche Ambientali e Marine, Università di
Trieste.
NEW EVIDENCE OF THE OUTER DINARIC DEFORMATION FRONT IN THE GRADO AREA
77
Fig. 1 – Isobaths, 50 m contours, of the top of the Paleogene-Mesozoic Carbonates. Grado-1 well location. The western limit of the Flysch is signed.
outer Dinaric deformation front which is reactivating
stratigraphy unconformities and local extensive systems and it
results still active. The westward continuation of the Dinaric
thrust system has been evidenced in the Gulf of Trieste by
BUSETTI et alii, 2009. The seismic lines show the inversion of
the Eocene Flysch deposits filling the basin generated by the
carbonates basement flexure. The thrusts in the Flysch
sequences are re-organized by folds in the upper carbonates
units where also the presence of low angle thrust faults is
hypothesized.
The geothermal waters were found in the Carbonates Platform,
mainly inside the open fracture of the Paleogene limestones,
with a temperature of about 42 ° C and a pressure of 2,8 bars.
REFERENCES
BUSETTI M., VOLPI V., NICOLICH R., BARISON E., ROMEO R.,
BARADELLO L., BRANCATELLI G., GIUSTINIANI M., MARCHI
M., ZANOLLA C., NIETO D., & WARDELL N. (2009) - Dinaric
tectonic features in the Gulf of Trieste. Bollettino di
Geofisica Teorica e Applicata, in press.
DELLA VEDOVA B., MARSON I. & PALMIERI F. (1988) - Gravity
study of a low enthalpy hydrothermal area: Grado Lagoon
– NE Italy. European Geophysical Society - XIII General
Assembly, Annales Geophysicae, Special Issue 1988, 27.
DELLA VEDOVA B., CASTELLI E., CIMOLINO A., VECELLIO C.,
NICOLICH R. & BARISON E. (2008) - La valutazione e lo
sfruttamento delle acque geotermiche per il riscaldamento
degli edifici pubblici. Rassegna Tecnica del Friuli Venezia
Giulia, 6/2008, 16-19.
NICOLICH R., DELLA VEDOVA B., CIMOLINO A. & BARISON E.
(2008) - Le acque calde della bassa pianura friulana e la
loro potenzialità. Rassegna Tecnica del Friuli Venezia
Giulia, 3/2008, 8-12.
NICOLICH R., DELLA VEDOVA B., GIUSTINIANI M., & FANTONI
R. (2004) - Carta del sottosuolo della Pianura Friulana.
Note illustrative e 4 mappe. RFVG – Direzione Centrale
Ambiente e Lavori Pubblici, Litografia Cartografica,
Firenze, 32 pp., 4 Tav.
78
CIMOLINO ET ALII
Fig. 2– Grado-1 well stratigraphy and logs (from DELLA VEDOVA et alii, 2008).
Petrological characteristics of the Adriatic/North Africa lithospheric
mantle: inferences from Cenozoic magmatism and mantle xenoliths
1
BECCALUVA L., 1,2BIANCHINI G., 1BONADIMAN C., 1COLTORTI M., 1SIENA F.
RIASSUNTO
Caratteristiche petrologiche del mantello litosferico Adriatico/Nord
Africano dedotte dal magmatismo Cenozoico e xenoliti di mantello
Vengono riportate le caratteristiche petrologiche del mantello litosferico
Adriatico/Nord Africano desunte dal vulcanismo entroplacca Cenozoico, e
dagli xenoliti di mantello associati, delle Province Vulcaniche del Veneto e
degli Iblei. Tale mantello litosferico risulta, soprattutto nelle sue porzioni
inferiori, arricchito da processi metasomatici da parte di fusi Na-alcalini con
affinità geochimica isotopica di tipo HIMU (Fig. 2). Da un confronto regionale
risultano evidenti importanti differenze geochimiche con il mantello Europeo
sottostante i massicci Varisici che risulta invece caratterizzato da una
componente EMI in aggiunta all’HIMU (es. Sardegna).
Key words: Adriatic/North Africa lithospheres, Cenozoic
magmatism, Mantle xenoliths, Metasomatism, Isotopes
INTRODUCTION
The composition of basic magmas generated in intra-plate
settings is strongly constrained by the geochemical evolution,
particularly the enrichment processes by sublithospheric fluids,
which affected their mantle sources. The associated mantle
xenoliths, in turn, represent a further opportunity to study the
compositional evolution of the lithospheric mantle related to: i)
depletion events by partial melting and extraction of basic
magmas, ii) enrichment processes due to the interaction
between the pristine mantle parageneses and percolating
metasomatizing melts of sublithospheric provenance
In this paper which is an abridged version of Beccaluva et
al. (2005), the main petrological features of volcanic rocks and
entrained mantle xenoliths from the Veneto and Iblean districts
are summarized with the aim to provide basic information on
the lithospheric mantle in the Adriatic and North Africa
domains.
This may also contribute to highlight regional analogies
and differences between”African” and “European” lithospheric
domains which face in the central Mediterranean.
VOLCANISM AND MANTLE XENOLITHS FROM
THE ADRIA PLATE (VENETO PROVINCE)
In the Adria Plate the most relevant volcanic activity is
_________________________
(1) Dipartimento di Scienze della Terra, Università di Ferrara, Italia
(2) School of Geology, Geography and the Environment, Kingston
University, UK
represented by the Veneto Volcanic Province (VVP), of late
Paleocene to late Oligocene age (De Vecchi & Sedea, 1995),
extending over an area of about 1500 km2, with a number of
eruptive centres mostly aligned along NNW-SSE tectonic
trends. Magma generation appears to have been triggered by
decompression events related to tensional tectonics which
affected the South Alpine foreland in response to Alpine
collisional events (Milani et al., 1999; Bonadiman et al., 2001;
Beccaluva et al., 2007a). Geophysical data indicate a Moho
culmination of 28 km below the area, and a lithosphere
thickness of about 100 km (Panza & Suhadolc, 1990).
VVP lavas are mostly basic in composition, and encompass
a wide range of serial affinities comprising mela(M)nephelinites, basanites, alkaline and transitional basalts,
olivine(ol)- and quartz(qz)-tholeiites, as observed in lowvolcanicity rifts (Barberi et al., 1982). Nephelinites and
basanites often carry spinel-peridotite mantle xenoliths.
Remarkably differentiated products only occur in the Euganean
complex, where transitional basalts to quartz-trachytes and
rhyolites predominate (Milani et al., 1999).
Primitive mantle-normalized incompatible element
distribution for basic magmas show sub-parallel patterns which
become gradually more enriched from tholeiites to basanites.
In terms of geochemical components (Zindler & Hart, 1986;
Weaver , 1991), these patterns have intermediate
characteristics between HIMU (High U/Pb) and EMII
(Enriched Mantle II) of Ocean Island Basalt (OIB) endmembers. The petrological modelling of primary magmas
indicates that tholeiites to M-nephelinites may have been
generated by decreasing degrees of partial melting (~25 to
~3%) of spinel-peridotite mantle sources at increasing depths
(30 to ~100 km) (Bonadiman et al., 2001; Beccaluva et al.,
2007a). These magma sources have to be lherzolites bearing
metasomatic amphibole (± phlogopite) for tholeiites to
basanites, whereas cpx-rich lherzolites (or even wehrlites),
metasomatized also by carbonatitic components, are required
to generate the M-nephelinites.
Sr, Nd, and Pb isotopic data suggest that a previously
Depleted Mantle (DM) was subsequently affected by
metasomatic enrichment(s) with a prevalent HIMU signature
and the subordinate contribution of the EMII component,
particularly for tholeiitic lavas. In fact, the following isotopic
ranges are recorded: for alkaline lavas, with the exception of
one sample, 87Sr/86Sr 0.70315-0.70344, 143Nd/144Nd 0.5129020.512976, and 206Pb/204Pb 19.348-19.789; for tholeiitic lavas
87
Sr/86Sr 0.70325-0.70387, 143Nd/144Nd 0.512858-0.512894,
and 206Pb/204Pb 19.202-19.219.
80
P. AUTORE ET ALII
New trace element and isotopic data from the Eocene M.
Queglia lamprophyric dike (Barbieri & Ferrini, 1984) and the
Paleocene Pietre Nere alkaline subvolcanic body (De Fino et
al., 1981) show similar prevailing HIMU isotopic signature
(Bianchini et al., 2008)
In the VVP, peridotite xenoliths consist of four phase
predominant spinel lherzolites and minor harzburgites,
showing . superimposed metasomatic (pyrometamorphic)
textures consisting of secondary minerals (ol, cpx + feldspar),
spongy clinopyroxene, and variably recrystallized glassy
patches (Siena & Coltorti, 1989 and 1993; Coltorti et al., 2000;
Beccaluva et al., 2001).
A continuous depletion trend is recorded from
clinopyroxene-rich lherzolites to harzburgites, which is
chemically reflected in the gradual decrease of the most fusible
elements such as Al2O3, CaO and TiO2 and the parallel
increase of Ni and mg# (Mg/(Mg+Fe)*100), as commonly
observed in mantle rocks progressively depleted by extraction
of basaltic melts. Moreover, both lherzolites and harzburgites
and their constituent clinopyroxenes, are variably enriched in
light (L)-REE, suggesting post-depletion enrichments related
to metasomatic processes.
Major and trace element mass balance calculations were
carried out (Beccaluva et al., 2001) to quantitatively model the
metasomatic parageneses by the addition of 1-6% of Naalkaline basic melt/s. The modelled metasomatic agents
strongly resemble the late Cretaceous lamprophyric dikes of
the South-Alpine domain, as well as some VVP alkaline basic
lavas. The Sr-Nd isotope compositions of VVP mantle
xenoliths (whole rocks and cpx separates) range between the
depleted mantle (DM) and the HIMU components, suggesting
that the latter represents the isotopic signature of the
metasomatizing agent.
VOLCANISM AND MANTLE XENOLITHS FROM
THE NORTH AFRICAN PLATE (IBLEAN PROVINCE)
In south-eastern Sicily, south of Etna, Miocene and
Pliocene-Pleistocene volcanics cover an area of about 500
km2. Fissural activity, with subaerial and submarine eruptions,
produced tholeiitic to nephelinitic lavas along a regional NESW lithospheric wrench fault system (Beccaluva et al., 1993;
Di Grande et al., 2002). The oldest and volumetrically
predominant products of the Pliocene activity are tholeiites,
followed in order of decreasing abundance by basanites, alkalibasalts + hawaiites, transitional basalts and nephelinites .
Primitive mantle-normalized incompatible element patterns
for the Iblean basic lavas display intermediate characteristics
between HIMU and EMII OIB end-members, and are closely
comparable to those observed in lavas from the VVP area. The
available Sr-Nd-Pb isotope data for the Iblean magmas range
from the depleted mantle (DM) to the HIMU component
(Beccaluva et al., 1998; Bianchini et al., 1998; 1999; Trua et
al., 1998). In particular, subalkaline lavas display a more
depleted character (87Sr/86Sr 0.70271 – 0.70302 and
143
Nd/144Nd 0.51325 – 0.51299), whereas alkaline lavas are
more enriched (87Sr/86Sr 0.70287 – 0.70327 and 143Nd/144Nd
0.51302 – 0.51291).
It should be emphasised that the trace element and Sr-NdPb isotopic compositions of volcanic rocks from the Sicily
Channel (Linosa and Pantelleria) show striking analogies with
comparable Iblean lavas, consistently indicating the prevalence
of the HIMU metasomatic components in magma sources of
this sector of the African Plate (Esperanca & Crisci, 1995;
Civetta et al., 1998).
Petrogenetic modelling (Beccaluva et al., 1998) has shown
that the Iblean magmas were generated within the spinel
peridotite lithospheric mantle (30 to ca. 90 km depth) from
progressively deeper sources, from tholeiites to nephelinites,
with a parallel decrease in the degree of melting (≈ 30 to ≈
3%). The modelled mantle sources were: i) lherzolites bearing
amphibole + phlogopite for the generation of tholeiites, alkali
basalts and basanites, ii) clinopyroxene-rich lherzolites (or
even wehrlites) bearing amphibole + phlogopite + carbonatitic
components for nephelinitic magmas.
In the Iblean volcanic province, spinel-peridotite mantle
xenoliths with a typical four-phase mineral assemblage are
sometimes included in nephelinitic Miocene diatremes (Di
Grande et al., 2002 and references therein). They range in
composition from lherzolites to rare harzburgites, recording
their common and gradual depletion in the most fusible
elements. Textures vary from protogranular to porphyroclastic,
with superimposed pyrometamorphic features - consisting of
secondary phases (including rare phlogopite and feldspars),
spongy borders in pyroxenes and variably recrystallized glassy
patches - which testify to metasomatic processes.
Chondrite-normalized REE distributions of bulk rock and
clinopyroxenes suggest widespread reactions between
metasomatic agent(s) and the mantle peridotite matrix.
Accordingly, variable LREE enrichments are recorded in
whole rock, and in constituents clinopyroxenes. New Sr-Nd
isotopic data (Bianchini et al., 2009) on cpx separates cluster
around the HIMU component (87Sr/86Sr from 0.70288 to
0.70309, and 143Nd/144Nd from 0.51287 to 0.51292), thus
suggesting that the latter represents the geochemical signature
of the Iblean metasomatizing agents, in analogy with what
observed for VVP xenoliths.
DISCUSSION AND CONCLUSIONS
As shown in the previous sections, the compositional
characteristics of the parental basic magmas for both the
Veneto and the Iblean provinces are compatible with their
segregation from the lithospheric mantle between about 30 and
100 km depth. In fact, their P-T segregation conditions show a
reasonable agreement with phase equilibria constraints for
shallow silica-saturated to deep strongly silica-undersaturated
basic melts (Falloon & Green, 1988; Falloon et al., 1988;
Hirose & Kushiro, 1993; Hirose & Kawamoto, 1995):
tholeiitic basalts, 10-16 kb, 1150-1250°C; alkali-basalts, 14-22
kb, 1200-1280°C; basanites and nephelinites, > 22 kb, 12501350°C. The P-T segregation trend plots between the
experimental dry and hydrated-carbonated mantle solidi, in
agreement with petrological modelling which invariably
requires significant amounts (5-10%) of volatile- bearing
phases (mostly amphibole) in all the modelled sources. This
trend is also fairly close to the regional geotherm inferred for
the central-western Mediterranean area (Fig. 1), thus
suggesting that partial melting processes could be easily
triggered by local decompression effects related to a limited
intra-plate tensional regime.
Incompatible
element
distributions and
isotopic
characteristics suggest that parental magmas were produced
from alkali silicate-metasomatized lithospheric mantle sources,
Fig. 1 – P-T conditions of segregation of basic magmas from Veneto,
Iblean and Sardinian volcanic provinces, calculated according to
Albarede (1992) algorithm (from Beccaluva et al., 2005). The
experimental mantle peridotite solidi for anhydrous (1) and hydratedcarbonated (2) conditions are reported after Green et al. (1987) and
Wyllie (1987). The inferred regional conductive geotherm for the CentralWestern Mediterranean area is also shown, based on P-T equilibration of
associated selected mantle xenoliths from Sardinia, Veneto, and Iblei,
using the geothermomether of Brey & Koehler (1990) and the
geobarometer of Koehler & Brey (1990).
which were also enriched by carbonatitic components in the
deeper portions where nephelinites were generated. In each
investigated province, the alkaline and deeper magmas show a
more marked HIMU signature compared to the sub-alkaline
basalts; this suggests a more intensive, and probably more
recent enrichment, of the deeper lithospheric mantle sources (>
60-70 km, i.e. in the Thermal Boundary Layer, TBL: Latin et
al., 1990; Anderson, 1994) by the alkaline metasomatizing
agents with HIMU signature.
Mantle xenoliths associated to alkaline lavas in both the
Veneto and Iblean provinces, generally represent shallow
portions of the lithospheric mantle column (< 40-50 km depth)
according to thermobarometric estimates and rheologic
characteristics (Verde, 1996). Petrological data invariably
indicate that these mantle xenoliths underwent a complex
compositional evolution, characterized by at least two different
types of processes: 1) depletion(s) by extraction of basic
magmas, mostly occurring in the pre-Palaeozoic, testified by
both major element variations and progressive HREE depletion
81
in whole rocks and constituent clinopyroxenes; 2) reaction(s)
between sub-lithospheric metasomatizing
agents and
previously depleted lithospheric mantle (DM), resulting in
variable enrichments of the most incompatible elements (e.g.
LREE, LFSE, etc). The resulting isotopic signatures conform
well those of the host magmas, being dependent on the variable
contribution of DM, HIMU and minor EMII components.
Comparison at a circum-Mediterranean scale highlights the
remarkable compositional similarities between Veneto and
Iblean districts and the rest of the stable North-African domain,
such as Hoggar (Beccaluva et al., 2007b), Gharjan (Beccaluva
et al., 2008), Mid-Atlas (Raffone et al., 2009), Canary Islands
(Siena et al., 1991), and Jebel Marra, Sudan (Lucassen et al.,
2008). By contrast they show important differences with the
Sardinian mantle where a predominant EMI component, in
addition to HIMU, is observed: in fact, Sardinia mantle
xenoliths share geochemical characteristics with many other
European xenolith suites, such as those from the Massif
Central (Zangana et al., 1997), Eifel (Witt-Eischen et al.,
2003), and Tallante (Southern Spain; Beccaluva et al., 2004).
The same geochemical signatures (i.e. predominant EMI in
addition to HIMU) have been recognized in Cenozoic
anorogenic magmas located within the Variscan basement of
Western-Central Europe (Wilson & Downes, 1991; Cebrìa &
Wilson, 1995).
On the basis of the available data we propose a
compositional evolution of the European (Sardinia) and
Adriatic/North African (Veneto and Iblei) lithospheric mantle
(Fig. 2). Both lithospheres are characterized by a pristine DM
signature, but a distinct EMI metasomatic component is
recorded, at least since the mid-Mesozoic, in the European
mantle underlying the Variscan basement. On the other hand,
the HIMU component seems to have been effective in both
European and African lithospheres since the Late Cretaceous
(Wilson & Bianchini, 1999; Bianchini et al., 2008). Seismic
tomography suggests that this component, referred to as the
European Asthenospheric Reservoir (EAR: Cebrià & Wilson,
1995) or Low Velocity Component (LVC) could be related to a
common sheet-like (Hoernle et al., 1995) or diapir-like (Granet
et al., 1995) upper mantle region, extending from the Eastern
Atlantic to Central Europe and circum Mediterranean areas.
More recently this component has been also related to a
dynamic response to subduction processes that mobilized
ancient material (Wilson, 2007). The stress difference (σ1- σ3)
estimated from the grain size of European and North African
xenoliths (Verde, 1996) indicates their common provenance
from the Mechanical Boundary Layer (MBL < 60-70 km; Viti
et al., 1997). The MBL is therefore to be considered a more
appropriate long-term reservoir for preserving the older
metasomatic components (e.g. EMI and EMII) which affected
the pristine DM lithosphere. Conversely, the deeper Thermal
Boundary Layer may represent an effective transient reservoir
for more recent metasomatic agents (e.g. HIMU) rising directly
from the convecting asthenospheric mantle (Wilson et al.,
1995; Beccaluva et al., 1998).
P. AUTORE ET ALII
82
Fig. 2 – Schematic model for the compositional evolution of the European (Sardinia) and Adriatic-African (Veneto and Iblei) lithospheric mantle (from Beccaluva
et al., 2005). EMI metasomatic component is recorded mainly in the mantle sections underlying the European Variscan basement, where it could have been
effective since the pre-middle Mesozoic. In both the African and European lithospheres, the effect of HIMU component decreases (see arrow thickness) from the
thermal to the mechanical boundary layer, and could be related to the Cenozoic sublitospheric mantle region extending from the Eastern Atlantic to Central Europe
and Western Mediterranean.
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The tholeiitic Magmatism of Jabuka, Vis and Brusnik Islands: a
Carnian magmatism in the Adria Plate
(1)
DE MIN A., (2)JOURDAN F., (3)MARZOLI A., (2)RENNE P.R., & (4)JURAČIĆ M.
RIASSUNTO
GEODYNAMICAL OUTLINES
Il Magmatismo tholeiitico delle isole di Jabuca, Vis e Brusnik : nuove
evidenze di un evento magmatico di età Carnica nella placca Adria
Le isole croate di Jabuka, Brusnik e parte dell’isola di Vis sono formate da
magmatiti tholeiitiche da intrusive fino ad effusive. I nuovi dati 40Ar/39Ar
ottenuti su plagioclasi (Jabuka e Brusnik) indicano età comprese tra 227±5 e
219±3Ma e attribuiscono quindi l’evento magmatico al Carnico.
Sebbene il chimismo di tali rocce possa essere compatibile con un evento
subduttivo, essi contrastano con quanto proposto recentemente da Stampfli et
al. (2002 a) per il Sud Alpino - il quale suggerisce, come causa scatenante il
magmatismo Ladinico-Carnico di Italia, Grecia e Turchia, una subduzione
verso l’attuale Sud dell’ oceano Meliata (Vardar) - e sembrano essere associati
ad un momento di generale tettonica estensionale (Stampfli e Borel (2002b),
Csontos e Voros (2004), Schmid (2008), Grandic et al., (1997).
In quest’ottica, va segnalata sia la presenza di magmi transizionalisubalcalini coevi (ca. 217 Ma) affioranti nella zona di Brescia, che l’
indicazione di un evento termico a 220 Ma registrato da alcuni zirconi nei
dicchi tholeiitici piemontesi. I magmi studiati sembrerebbero quindi indicare,
piuttosto che un evento subduttivo, l’ estensione in sede continentale di un
sistema di ridge come quello proposto da Smidh et al., (2008) per l’apertura nel
Carnico dell’oceano da lui indicato come Neotetide-Meliata-Maliac.
According to Stampfli et al. (2002a) the Triassic
magmatism on the Adria Plate is related to a subduction,
verging North to South, of the Meliata Ocean, one of the three
Neotethyian oceanic branches which were formed as NW-SW
oriented back arc structures during the Permian subduction and
developed into oceanic extensional basins. In opposition,
Schmid et al. (2008) recognize one ocean (named Meliata
Meliac Vardar) which should represent the southern part of the
Neotethys. For these authors only extensional structure
interested the area in Triassic times. Finally, Stampfli & Borel
(2002b) suggest a South – North subduction, active only
during the Ladinian while Csontos & Voros (2004) suggested a
northward oblique subduction which started in the Permian and
ended in Ladinian. For the last authors, in Carnian the
subduction evolved with the back arc opening (Pindos Sea) of
an oceanic branch paralleling the actual Croatia coast.
Key words: Adriatic sea, Jabuka, Brusnik, tholeiites, Carnian.
INTRODUCTION
Paleogeographical reconstructions of the South Alpine area in
Triassic times are still not clear and the geodynamic meaning
of Triassic magmatism is still debated. Only recently available
geochronological data where carried out on such igneous rocks
and these seem to locally indicate the presence of different
moments of magmatic activities which partially contrast with
the most recent plate reconstructions.
In the present paper we will focus on subalkaline rocks
outcropping in central Adriatic Sea islands (Jabuka, Brusnik
and Vis) with the aim to evaluate the main geodynamic
models.
_________________________
(1)Dipartimento Scienze della Terra – Univ. Trieste
(2) Berkeley Geochronology Center; Department of Earth and Planetary
Science, University of California, Berkeley
(3) Dipartimento di Geoscienze – Univ. Padova
(4) Department of Geology – University of Zagreb
Lavoro eseguito bell’ambito del progetto PRIN 2005
PETROGRAPHY
The Jabuka samples show a coarse grain size with an
ipidiomorphic texture. The samples are slightly altered and
plagioclase is often veined by sericitic products;
notwithstanding large portions of the crystals (both core and
rim) appear to be fresh. Pyroxene appears as augites and
pigeonites.
The rocks from Brusnik are fresher, holocrystalline and
show an intergranular-doleritic texture. Plagioclase is often
idiomorphic, slightly zoned and little altered in sericitic
products. Pyroxene is present as idiomorphic and “spinifex”like crystals. Ca-rich and Ca-poor pyroxenes are both present
.Sometimes, vacuoles filled by secondary zeolites occur.
Vis magmatic products are represented by small outcrops
of aphyric or slightly plagioclase-phiric and by super altered
and vesicular flows filled by prehnite.
In all the rocks, opaques are scarce. Zircon and apatite are
present as accessory phases.
Fresh plagioclase show An content ranging from 38 to 70
while analyzed pyroxenes are mainly represented by augites.
Ca poor pyroxene are less represented.
40
AR/39AR AGES
Two new
40
Ar/39Ar plateau ages on Jabuka and Brusnik
P. AUTORE ET ALII
86
Fig. 1 Apparent age spectra of plagioclase separated respectively from samples BR3 (Brusnik Island) and BKA (Jabuka Shoal). The 2σ errors include analytical
uncertainty in neutron fluence parameter Ј value
igneous rocks have been obtained analyzing plagioclase
sam ple/chondrite
100
10
Eu/Eu* = 0.78
La/SmCn = 2.18 - 2.95
La/YbCn = 3.59 - 8.74
Dy/YbCn = 1.10 - 1.29
1
La Ce Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Fig. 2 REE patterns normalized to Boynton, 1984. White
symbols (Diamond = Vis; triangle = Brusnik; circle = Jabuka)
refer to the analyzed samples; black cyrcle = Upper Crust
(Rudnik, 2004); grey circles = unpublished Ladinian andesite
from Mulat Mountain.
tholeiites according to AFM and SiO2 vs FeOt/MgO diagrams
of Miyashiro (1974). All the rocks are Qz and Hy normative.
The mg# [Mg/(Mg+Fe2+) = 0.36-0.43] and Ni values (2025 ppm) indicate that all the studied rock types are quite
evolved. The high Al2O3 content (17.99 to 19.36 wt %)
identify the samples as High Alumina basalts.
All the samples are characterized by enriched geochemical
signatures, such as significatively fractionated LREE followed
by a flat HREE pattern. Notably, La/Sm (3.0) Sm/Yb (8.7) and
Dy/Yb (1.3) ratios are similar to those of shoshonitic –
andesitic magmas with Ladinian age from the Dolomiti
Mountains.
1000
samples/primitive mantle
100
separates, following methods described by Jourdan et al.
(2009). All the errors are at the 2σ of confidence level, the ages
have been calculated for an age of 28.02 Ma for the FCs
monitor (Renne et al., 1998). Brusnik yielded a plateau ages of
219.5 ±2.5 Ma, for a P ≥0.69 and an isochron age of 218±3
Ma.
Jabuka, which appears chemically indistinguishable,
yielded a slightly older mini-plateau age at 227 ±5 Ma defined
by about 50% of the released 39Ar and associate to a P ≥ 0.84.
The isochron age is 226±3 Ma and the integrated age
approaches the Brusnik plateau age (220±7 Ma). Such data
attribute the studied rock to the Carnian (Gradstein et al.,
2004).
GEOCHEMISTRY
Using a R1-R2 classification diagram (not shown) the
analyzed rock plot in the andesi-basalt, latibasalt fields and are
10
1
Rb Ba
K
Nb La Ce
Sr
Nd
P
Zr
Ti
Y
Fig.3 Incompatible element pattern normalized to Primitive
Mantle of McDonough & Sun (1995) symbols as in Fig.2.
Multielemental patterns are characterized by high LILE and
by an evident negative Nb anomaly (Nb/La = 0.17 – 0.27) well
comparable with that of the Ladinian andesites. The Adriatic
tholeiites yield also 100*Th/Zr (8 vs 6) and 100*Nb/Zr (4 vs 7)
values which, according to Beccaluva et al. (1991) should
indicate an orogenic signature. In few samples, Sr shows a
very little positive anomaly probably due to LILE mobilization.
87
Cycles or, according to Stampfly et al., (2002b), more
recently.
DISCUSSION
The presence of a Carnian sub-alkaline magmatism placed
south of the Dolomiti area (where a potassic magmatism
occurred in Ladinian times) and well inside the Adria Plate can
not be related to one South-North or North-South subductive
Ladinian-Carnian event. Moreover, in Late Triassic there is a
general agreement about the presence of extensional
movements which, according to Csonts & Voros (2004) and
Schmid et al. (2008) are consistent with a moment of
oceanization which could be related (or not) with a back arc
structure. Notably, in an extensive setting, coeval rock types
(basalts and andesites) outcrop in the Brescian Alps (Cassinis
et al., 2008) and a thermal event of 220 Ma was registered by
zircons in Ivrea Verbano basaltic dykes (Peressini, personal
communication). These considerations suggest, for the studied
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Fig.4 100*Nb/Zr vs 100*Th/Zr plot tectonomagmatic diagram
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Calc. = High –K calcalkaline magmatism; EI = Aeolian Islands;
CSNE = Central and Southern New Hebrides; TK = Tonga
Kermadec.
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STAMPFLI GM, BOREL G.D., MARCHANT R & MOSAR J.
(2002a) Western Alps geological constrain on Western
Tethyan reconstructions Jour. of Virt. Exp. 7, 75-104
STAMPFLI GM, BOREL G.D. (2002b). A plate tectonic model
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From field geology to earthquake mechanics: the case of the Gole
Larghe Fault Zone (Italian Southern Alps)
GIULIO DI TORO (*,**), GIORGIO PENNACCHIONI (**) & STEFAN NIELSEN (*)
RIASSUNTO
Contributo della geologia allo studio della meccanica dei terremoti: un
esempio dalle Alpi Meridionali (Italia)
Le informazioni sulla meccanica di un terremoto sono in genere ottenute
mediante indagini sismologiche (sismogrammi e tecniche di inversione) e
geofisiche (GPS, inSAR). Questo approccio offre un contributo limitato alla
comprensione della meccanica dei terremoti, poiché i processi chimico-fisici
attivi su di una superficie di faglia durante la propagazione della rottura sono al
di sotto della risoluzione della tecnica impiegata.
Un approccio alternativo consiste, partendo dall’analisi geologicostrutturale di grandi esposizioni di faglie sismogenetiche esumate, di unire studi
di terreno di dettaglio con (i) osservazioni microstrutturali e analisi
mineralogiche-geochimiche dei materiali di faglia, (ii) esperimenti di
laboratorio che riproducono le condizioni di deformazione tipiche di un
terremoto e (iii) modelli numerici e teorici che combinano le informazioni di
terreno e sperimentali in un modello unitario di propagazione della rottura
sismica.
In questo contributo descriveremo i principali risultati (ottenuti grazie a
questo approccio metodologico) di uno studio iniziato 10 anni fa e ancora in
atto, partendo dall’analisi strutturale degli eecezionali affioramenti della Faglia
delle Gole Larghe in Adamello (Alpi Meridionali).
Key words: earthquakes, faults, fault rocks, Adamello, rock
friction, experiments, numerical models.
Large earthquakes critical for human activities nucleate at ~
7-15 km depth [SCHOLZ, 2002]. The sources of these
earthquakes and the process of rupture propagation can be
investigated by geophysical monitoring of active faults from
the Earth’s surface or by interpretation of seismic waves: most
information on earthquake mechanics is retrieved from
seismology [LEE ET AL., 2002]. However, these indirect
techniques yield incomplete information on fundamental issues
of earthquake mechanics [e.g., the dynamic fault strength and
the energy budget of an earthquake during seismic slip remain
unconstrained, KANAMORI AND BRODSKY, 2004] and on the
physical and chemical processes active during the seismic
cycle.
_______________________
(*)Istituto Nazionale di Geofisica e Vulcanologia, Via di Vigna Murata
605, 00143 Roma, Italy.
(**) Dipartimento di Geoscienze, Università degli Studi di Padova, Via
Giotto 1, 35137 Padova, Italy
Lavoro eseguito nell’ambito del progetto di Eccellenza Fondazione
CA.RI.PA.RO e del progetto European Research Council Starting Grant
205175 USEMS.
To gain direct information on seismogenic sources, faultdrilling projects have been undertaken in several active faults,
e.g., the Nojima Fault in Japan [OHTANI ET AL., 2000;
BOULLIER ET AL., 2001], the Chelungpu Fault in Taiwan [MA
ET AL., 2006] and the San Andreas Fault in USA [HICKMAN ET
AL., 2004]. Fault drilling allows integration of real-time in situ
measurements (strain rate, pore pressure, etc.) and sampling
with high-quality seismological data, collected by
seismometers located at depth, and geodetic data at the surface
(GPS, inSAR, etc.). However, fault drilling has several
limitations: (i) to date, drilling is confined to shallow depths (<
3 km); (ii) the investigated fault volume is too small to provide
representative 3D information on fracture networks and fault
rock distribution (i.e., large earthquakes rupture faults with
areas > 100 km2), and iii) high costs.
An alternative and complementary approach to gain direct
information about earthquakes is the investigation of exhumed
faults showing evidence of ancient seismic ruptures (a direct
approach to the earthquake engine). However, the use of
exhumed faults to constrain the mechanics of earthquakes has
also limitations: (i) alteration during exhumation and
weathering may erase the pristine coseismic features produced
at depth; (ii) reactivation of a fault zone by repeated seismic
slip events may render difficult or impossible to distinguish the
contribution of individual ruptures; (iii) single faults may
record seismic and aseismic slip and there might be the need to
distinguish between microstructures produced during the
different stages of the seismic cycle (co-seismic, post-seismic,
interseismic, etc); (iv) the microstructural proxies to recognize
the coseismic nature of a fault rock have not yet identified with
certainty except in some cases; (v) the ambient (e.g., pressure,
temperature) conditions and the stress tensor coeval with
seismic faulting are often difficult to estimate with precision.
Therefore the use of exhumed faults to retrieve information
on earthquakes rely on (i) the recognition of faults rocks
produced during seismic slip which have escaped significant
structural overprinting and alteration until exhumation to the
Earth’s surface and, (ii) the presence of tight geological
constraints that allow the determination of ambient conditions
during seismic faulting. Up to date the only fault rock
recognized as a signature of an ancient earthquake is
pseudotachylyte [COWAN, 1999]. Pseudotachylyte is the result
of solidification of friction-induced melt produced during
seismic slip [SIBSON, 1975; SPRAY, 1995].
In this contribution we will describe an exceptional outcrop
FROM FIELD GEOLOGY TO EARTHQUAKE MECHANICS
of the Gole Larghe Fault zone (Southern Alps, Italy) which
satisfies the above conditions and allows to infer information
on earthquake mechanics [DI TORO ET AL., 2005A; 2005B; DI
TORO ET AL., 2006; PENNACCHIONI ET AL., 2006; DI TORO ET
AL., 2009].
The Gole Larghe Fault Zone is a strike-slip exhumed (from
about 10 km depth) structure crosscutting the periadriatic
Adamello tonalitic batholith [Italian Alps, VENTURELLI ET AL.,
1984] and forming a southern branch of the Tonale line, a
segment of the Periadriatic Lineament (i.e., the major fault
system of the Alps, Fig. 1a). The Gole Larghe fault zone is
exposed in large glacier-polished un-weathered outcrops which
allow a 3-dimensional investigation of the structures (Fig. 1b)
and where single faults can be mapped in detail (Fig. 1c-d).
The fault zone hosts a large number of pseudotachylytes which
have largely escaped alteration and structural reworking during
the exhumation to the Earth’s surface and therefore preserve an
intact record of the coseismic processes that occurred at depth.
At the same time, the fault zone contains hundreds of faults
which possibly record different seismic slip increments thus
forming a statistically representative population of earthquakes
89
occurring under identical ambient conditions and
geological context.
It will be shown that a multidisciplinary approach, which
includes field and laboratory study of the natural
pseudotachylytes integrated with theoretical and rock friction
experiments, may yield information on earthquake mechanics
and complementary to seismological investigations. Within
some of the results discussed here, the conclusion that some
fault zones (like is the case for the Gole Larghe Fault) may
record a dominant rupture directivity, which has implications
in earthquake hazard evaluation [DI TORO ET AL., 2005B], or
the recognition of fault lubrication operated by frictional melts
during earthquakes. An outcome of melt lubrication is the
occurrence of large dynamic stress drops, especially at depth
[DI TORO ET AL., 2006; 2009; NIELSEN ET AL., 2008].
It follows that the multidisciplinary approach suggested
here may exploit the extraordinary wealth of information
frozen in large exposures of pseudotachylyte-bearing fault
networks and yields a new vision of earthquake mechanics
based on the physical processes occurring at seismogenic
depth.
Fig. 1 – A natural laboratory of a seismogenic fault zone: The Gole Larghe Fault Zone in the Adamello batholith (Italy). (a) Tectonic sketch map of the
Adamello region showing the location of the Gole Larghe Fault, and of the glaciated outcrops (star) analyzed in detail in this contribution. (b) Field view of
the exposures of the Gole Larghe Fault Zone. Presence of deep creeks allows a 3-dimensional view of the fault zone. The fault zone is made of about 200
sub-parallel strike slip faults (some indicated by arrows). (c) Photomosaic showing a pseudotachylyte-bearing fault zone. The excellent exposure allows the
detailed mapping of the pseudotachylyte vein network. (d) Drawing of the pseudotachylytes from the photomosaic of Fig c. The orientation of the fractures
filled by pseudotachylyte was used to reconstruct the seismic rupture directivity.
G. DI TORO ET ALII
90
REFERENCES
BOULLIER, A.M., T. OHTANI, K. FUJIMOTO, H. ITO AND M.
DUBOIS (2001) - Fluid inclusions in pseudotachylytes from
the Nojima Fault, J. Geophys. Res., 106, 21965-21977.
LEE, W.H., KANAMORI, H., JENNINGS, P.C. & KISSLINGER C.,
(Eds.) (2002) - Earthquake & Engineering Seismology.
Vol. 1 & 2, Academic Press, Amsterdam.
COWAN D. (1999) - Do faults preserve a record of seismic
faulting? A field geologist’s opinion. J. Struct. Geol., 21,
995-1001.
MA K.F. ET ALII (2006) - Slip zone and energetics of a large
earthquake from the Taiwan Chelungpu-fault Drilling
Project (TCDP). Nature, 444, 473-476.
DI TORO G., PENNACCHIONI G. & TEZA G. (2005A) - Can
pseudotachylytesbe used to infer earthquake source
parameters? An exampleof limitations in the study of
exhumed faults. Tectonophysics, 402, 3-20.
NIELSEN S., DI TORO G., HIROSE T., SHIMAMOTO T. (2008) -.
Frictional Melt and Seismic Slip. J. Geophys. Res., 113,
doi:10.1029/2007JB005122.
DI TORO G., NIELSEN S. & PENNACCHIONI G. (2005B) –
Earthquake rupture dynamics frozen in exhumed ancient
faults. Nature, 436, 1009-1012.
DI TORO G., HIROSE T., NIELSEN S., PENNACCHIONI G. &
SHIMAMOTO T. (2006) - Natural and experimental evidence
of melt lubrication of faults during earthquakes. Science,
311, 647-649.
DI TORO G., PENNACCHIONI G. & NIELSEN S. (2009) Pseudotachylytes and Earthquake Source Mechanics. In:
“Fault-zone Properties and Earthquake Rupture Dynamics”,
Ed. Eiichi Fukuyama, published by the International
Geophysics Series, Elsevier, pp. 87-133
HICKMAN S.H., ZOBACK M. & ELLSWORTH W. (2004) Introduction to special session: Preparing for the San
Andreas Fault observatory at depth. Geophys. Res. Lett.,
31, doi:10.1029/2004GL020688.
KANAMORI H., & BRODSKY E., (2004) - The physics of
earthquakes, Rep. Prog. Phys. 67, 1429–1496
OHTANI, T., K. FUJIMOTO, H. ITO, H. TANAKA, N. TOMIDA, AND
T. HIGUCHI (2000) - Fault rocks and past to recent fluid
characteristics from the borehole survey of the Nojima fault
ruptured in the 1995 Kobe earthquake, southwest Japan. J.
Geophys. Res., 105, 16161–16171.
PENNACCHIONI G., DI TORO G., BRACK P., MENEGON L. &
VILLA I.M. (2006) - Brittle-ductile-brittle deformation
during cooling of tonalite (Adamello, Southern Italian
Alps). Tectonophysics, 427, 171-197.
SCHOLZ, C.H., (2002) - The mechanics of earthquakes and
faulting. Cambridge University Press, Cambridge, USA,
439 pp.
SIBSON R.H. (1975) - Generation of pseudotachylyte by ancient
seismic faulting, Geophys. J. R. Astr. Soc., 43, 775-794.
SPRAY J.G. (1995) - Pseudotachylyte controversy: fact or
friction? Geology, 23, 1119-1122.
VENTURELLI G., THORPE R.S., DAL PIAZ G.V. & POTTS P.J.
(1984) - Petrogenesis of calc-alkaline, shoshonitic and
associated ultrapotassic Oligocene volcanic rocks from the
northwestern Alps, Italy. Contributions to Mineralogy and
Petrology 86, 209-220.
Rendiconti online Soc. Geol. It., Vol. 9 (2009),91-93
Late Quaternary evolution of the Venetian-Friulian plain
ALESSANDRO FONTANA (*), PAOLO MOZZI (*) & ALDINO BONDESAN (*)
RIASSUNTO
Evoluzione tardoquaternaria della pianura Veneto-Friulana
La dettagliata cartografia geologica e geomorfologica realizzata negli
ultimi anni ha consentito di analizzare nel loro complesso le pianure alluvionali
dell'Italia nord-orientale, individuando le principali fasi evolutive avvenute
dalla fine del Pleistocene medio. I maggiori periodi di aggradazione sono
coincisi con le fasi di stazionamento dei ghiacciai alpini allo sbocco delle valli.
Una notevole fase di incisione fluviale si è verificata invece tra la fine del
LGM e l'inizio dell'Olocene e, solo dopo il raggiungimento della fase di high
stand, una nuova aggradazione ha interessato la pianura costiera. Negli ultimi
millenni lungo il tratto terminale dei fiumi alpini si sono formati dossi ben
evidenti e la loro formazione è stata influenzata anche dall'attività antropica.
Key words: Alluvial megafans, Holocene, Late Pleistocene, NE
Italy.
INTRODUCTION
In the last decade stratigraphic researches and detailed
geological surveys considered almost completely the VenetianFriulian Plain, specially its distal and coastal sectors (e.g.
BONDESAN et alii, 2004; 2008; TOSI et alii, 2007; ZANFERRARI
et alii, 2008). Some cartographic projects, founded by local
administrations, allowed to depict the general stratigraphic
setting which characterize the late Quaternary sequences and to
reconstruct a number of high-resolution profiles down to a
depth of 10-30 meters. These data have a large importance for
the comprehension of the properties of the deposits bearing
shallow hydrogeological bodies, potentially affected by
pollutants and involved in geotechnical problems.
ALLUVIAL MEGAFANS
The present surface of the Venetian-Friulian Plain is
characterized by the presence of alluvial megafans related to
the main Alpine fluvial systems (FONTANA et alii, 2008; in the
subsoil previous generations of megafans could be identified
through long-core analyses. Since middle Pleistocene the
_________________________
(*) Dipartimento di Geografia "G. Morandini" - Università degli Studi di
Padova.
alternation between glacial and interglacial periods has exerted
a major control on the evolution of alluvial systems in NE
Italy. In the distal sector of the plain, vertically stacked
trangressive-regressive sequences are recorded and they are
characterized
by the alternations of shallow-marine to
continental deposits.
PRE-LGM EVOLUTION
During main glacial periods, as the Last Glacial Maximum
(LGM, 30.0-17.0 ka cal. BP) and the MIS 6 (166-132 ka BP),
the glaciers hosted in the Alpine valleys debouched into the
plain feeding large fluvio-glacial systems (ZANFERRARI et alii,
2008). Along the coastal plain an important litho-stratigraphic
unit is represented by the MIS 5.5 highstand deposits (132-116
ka BP). These consist of a deltaic-lagoon sedimentary wedge
onlapping the MIS 6 alluvial plain, up to 25 km from the
present coastline. These paralic deposits are encountered in the
subsurface of the SW Venetian plain at depths of 60-110 m,
whereas east of Venice they occur at depths of 40-70 m
(MASSARI et alii, 2004; ANTONIOLI et alii, 2009). The sandy,
shoreface facies of this phase are quite extent and have a very
good lateral continuity.
LGM AGGRADATION
After a long period of scarce sedimentation or non
deposition, the plain experienced a major phase of aggradation
during the LGM. As during the MIS 6, the lowstand deposits
related to this phase are represented by 15-35 m thick megafan
bodies, made up of vertically stacked, amalgamated gravels in
the proximal sectors and mud-prone deposits at distal locations
(FONTANA et alii, 2008). These latter consists of a
characteristic alternation of overbank and natural-levee
deposits, with common thin peat intercalations and fine-sand
channel bodies with a thickness of 0.5-1.5 m. A remarkably
different framework characterizes the central part of the Venice
Lagoon, where the sandy channel bodies may reach a thickness
of 10-15 m (BONDESAN et alii, 2008).
POST-LGM FLUVIAL INCISIONS
Since the end of LGM a strong erosive phase developed; in
the distal sectors of Isonzo, Tagliamento and Piave megafans
the LGM fine sediments were cut by valleys which have a
depth of 15-30 m and a width of 600-2000 m. The studied
92
P. AUTORE ET ALII
Fig. 1 – Age of the alluvial surfaces in the Venetian-Friulian Plain (modified from FONTANA et alii, 2008). (1) river, (2) bathimetric lines, (3) fluvial scarp, (4)
upper limit of the spring belt, (5) interpreted limit of maximum Holocene transgression at 6.0 ka BP ca., (6) tectonic terraces, (7) pre-LGM, (8) LGM endmoraines systems, (9) LGM, (10) post-LGM. Fig. 1 – Age of the alluvial surfaces in the Venetian-Friulian Plain. (1) river, (2) bathimetric lines, (3) fluvial scarp,
(4) upper limit of the spring belt, (5) interpreted limit of maximum Holocene transgression at 6.0 ka BP ca., (6) tectonic terraces, (7) pre-LGM, (8) LGM endmoraines systems, (9) LGM, (10) post-LGM.
incised-valley fills (IVF) display a similar internal architecture,
characterized by coarse gravel deposits at bottom and a general
fining-upward trend.
Several phases of abandonment and re-activation are
recorded, but gravels are almost lacking in the upper part of the
IVF and their diameter is considerably finer than the basal
gravel.
Fluvial entrenchment and coarse-gravel transport occurred
during Lateglacial and early Holocene and stopped around 8.07.0 ka cal. BP. Since 7.0 ka cal. BP coastal aggradation started
along the present coastline and some abandoned incisions were
partly filled by lagoon/estuarine sediments.
In the distal sector of the plain the post-LGM deposits are
separated by the LGM sediments by a well recognized
unconformity that in the interfluves between the incised valleys
is marked by the paleosol locally named "caranto" (MOZZI et
alii, 2003; TOSI et alii, 2007; AMOROSI et alii, 2008). This is
characterized by indurated horizons with mottling features and
carbonate concretions and generally represents an impermeable
layer.
LATE HOLOCENE AGGRADATION
In the distal sector of the plain fluvial ridges have been
forming along the Alpine rivers for the last 4.5-3.0 ka. These
relief features have a general with of 1-3 km and they are 2-6
m higher than the surrounding floodplain (BONDESAN et alii,
2008). Probably their construction is mainly related to climate
and eustasy, but also the anthropic activity seems to have
played a significative role (CARTON et alii, 2009).
REFERENCES
AMOROSI A., FONTANA A., ANTONIOLI F., PRIMON S. &
BONDESAN A. (2008) - Post-LGM sedimentation and
Holocene shoreline evolution in the NW Adriatic coastal
area. GeoActa, 7, 41-67.
BONDESAN A., MENEGHEL M., ROSSELLI R. & VITTURI A.
(Eds.) (2004) - Geomorphological Map of the Province of
Venice, scale 1:50.000. LAC, Firenze, 4 sheets.
BONDESAN A., BASSAN V., FONTANA A., MENEGHEL M.,
MOZZI P., ABBA' T., BISAZZA A., VITTURI A. (2008) - Carta
delle unità geologiche della provincia di Venezia, scala
1:50.000. Cierre, Verona, 2 sheets.
CARTON A., BONDESAN A., FONTANA A., MENEGHEL M.,
MIOLA A., MOZZI P., PRIMON S. & SURIAN N. (2009) Geomorphological evolution and sediment transfer in the
Piave River watershed (north-eastern Italy) since the LGM.
Géomorphologié: Relief, Processus, Environment, 3, 37-58.
FONTANA A., MOZZI P. & BONDESAN A. (2008) - Alluvial
megafans in the Veneto-Friuli Plain: evidence of aggrading
93
and erosive phases during Late Pleistocene and Holocene.
Quaternary International, 189, 71-89.
MASSARI, F., D. RIO, R. SERANDREI BARBERO, R., ASIOLI, A.,
CAPRARO, L., FORNACIARI, E. & VERGERIO, P.P. (2004) The environment of Venice area in the past two million
years.
Palaeogeography,
Palaeoclimatology,
Palaeoecology, 202, 273-308.
MOZZI P., BINI C., ZILOCCHI L., BECATTINI R & MARIOTTI
LIPPI M. (2003) - Stratigraphy, palaeopedology and
palinology of late Pleistocene and Holocene deposits in the
landward sector of the lagoon of Venice (Italy), in relation
to caranto level. Il Quaternario, 16 (1bis): 193-210.
TOSI L., RIZZETTO F., BONARDI M., DONNICI S., SERANDREI
BARBERO R. & TOFFOLETTO F. (2007) - Carta Geologica
d’Italia alla scala 1:50.000. 128 - Venezia. APAT,
Dipartimento Difesa del Suolo, Servizio Geologico d’Italia,
SystemCart, Roma, 164 pp., 2 sheets.
ZANFERRARI A., AVIGLIANO R., FONTANA A. & PAIERO G.
(2008) - Carta Geologica d’Italia alla scala 1:50.000:
Foglio 087 “San Vito al Tagliamento”. Graphic Linea,
Tavagnacco, Udine.
Late-Holocene sea level change between Sistiana and Duino
(Gulf of Trieste, Italy): tectonic implications
STEFANO FURLANI (*), SARA BIOLCHI (*), GIOVANNA BURELLI (*) & FABRIZIO ANTONIOLI (°)
RIASSUNTO
Variazioni di livello marino tardo-oloceniche tra Sistiana e Duino (Golfo
di Trieste): implicazioni tettoniche
Vengono presentate le nuove misure effettuate su solchi e terrazzi
sommersi nel settore nord-orientale del Golfo di Trieste, tra Sistiana e Duino.
Inoltre, grazie ai nuovi dati emersi da un rilevamento subacqueo di dettaglio,
discutiamo l’evoluzione tardo-Olocenica di questo tratto di costa.
Key words: Sea level change, notch, shore platforms, tectonic
downlift, Gulf of Trieste.
INTRODUCTION
Notches and shore platforms represent one of the most
useful geomorphological markers to study sea level changes.
The main geological features of this sector have been described
by CUCCHI (1986) and CARULLI & CUCCHI (1991). GIORGETTI
(1967) and BRAMBATI & CATANI (1988) studied the coastal
sediments between Miramare and Duino, but, despite a detailed
surveying, no underwater investigations have been performed.
MORELLI & MOSETTI (1968) suggested the occurrence of
submerged flysch terraces, inferred from geophysical
surveying, at depths ranging from -20 m to -200 m.
Actual and palaeo-shore platforms in the Gulf of Trieste
have been studied by FURLANI (2003). Recently, the GeoCGT
Project (1:10.000 maps), promoted by the Geological Survey of
the Friuli Venezia Giulia Region and Interreg Project ItaliaSlovenia allowed a detailed geological and geomorphological
surveying of the Flysch in the Trieste area (BENSI et alii, 2007,
2009). Moreover, BRAITENBERG et alii (2005) suggested a SENW tilting versus of the coast of Trieste, probably still active.
We provide new data on submerged notch and shore
platforms between Sistiana and Duino and we aim at discuss
the late-Holocene evolution of the studied area.
ANTONIOLI et alii (2004, 2007) surveyed the lacking of the
present day notch and the occurence of a well-carved
_________________________
(*) Dipartimento di Scienze Geologiche, Ambientali e Marine, Università
degli Studi di Trieste, Italy
(**) ENEA, ACS, Roma, Italy
submerged notch in the Gulf of Trieste. Its depth ranges
between –0.65 m on the Miramare olistoliths and –0.9 m at the
Canovella de’ Zoppoli beach. Northward the depth of the notch
increases from –1.3 m to –2.55 m from Sistiana to Duino. The
submerged notch has the same amplitude of the local tide.
The Sistiana-Duino shoreline is characterised by 70-meterhigh limestone plunging cliffs, composed of pure and compact
limestones belonging to Upper Cretaceous and Eocene and
whose stratification varies from strongly inclined to subvertical, sometimes tending to capsizing. At the base of the
limestone plunging cliff a flysch outcrop occurs and it
represents the first discovered submerged in the coastal sector
between Sistiana and Duino. The analysis of nannoplankton
associations in the silty-marls terms suggested that samples are
upper Lutetian in age. The contact between limestones and
Flysch is a paraconformity. The coastal sector is displaced by
several right and left strike slip faults and some minor fractures
with a dominant N-S.
Fig. 1 – The study area is located in the northernmost sector of the Gulf of
Trieste
The flysch outcrop can be considered a shore platform Type
B (SUNAMURA, 1992). ANTONIOLI et alii (2007) suggested very
high downlift rates (0.77 mm/yr) in the Gulf of Trieste.
Probably this structural trend is higher in Sistiana-Duino area,
where the submerged notch, post-roman in age (FAIVRE et alii,
2009), was surveyed at -1.5 m vs -0.65 m southward from
Trieste.
S. FURLANI ET ALII
95
Fig. 2 Submerged sea level markers: a) flysch beds on the submerged platform; b) wall-like sandstone blocks; c, d) submerged notches; g) mushroom-like
sandstone block
The seaward edge of the platform is constituted by a
sandstone bed resulting in a wall-like morphology,
characterised by several mushroom-like blocks.
physical/chemical environmental situation more erosive than
actual.
ACKNOWLEDGEMENTS
DISCUSSION AND TECTONIC IMPLICATIONS
The evolution of the area can be divided into three steps: 1)
flysch platform widening resulted from cliff recession and it
developed during the late-Holocene. In the Gulf of Trieste cliff
recession has been estimated at 10-20 mm/yr on flysch
lithologies and 0.14 mm/yr on limestones (FURLANI et alii,
2009), so the platform widening advanced quickly up till high
resistant limestone vertical beds; 2) platform development
stopped because of relative sea level rise (ANTONIOLI et
alii,2007). At the same time the notch started to be cut on
limestone cliffs; 3) the coastal sector downlifted. The notch and
the shore platform are submerged because of tectonic downlift
caused by a creeping along pre-existent discontinuites. Notch
age suggests that the creeping acts and maybe is still acting
since post-roman. The genesis of the notch could be due to an
increasing of denudation rates, perhaps related to a
We are grateful to Bruno Benvenuto, Stavros Frenopoulos
and Giulio Radivo for underwater surveyings and to Sara Bensi
for geological discussions. Very special thanks to Prof. Franco
Cucchi, director of the “Dipartimento di Scienze Geologiche,
Ambientali e Marine” of the University of Trieste for the
critical reading of this work.
REFERENCES
ANTONIOLI F., CARULLI G.B., FURLANI S., AURIEMMA R. &
MAROCCO R. (2004) - The enigma of submerged marine
notches in northern Adriatic sea. Quaternaria Nova, 8, 263275
ANTONIOLI F., ANZIDEI M., AURIEMMA R., GADDI D., FURLANI
S., LAMBECK K., ORRÙ P., SOLINAS E., GASPARI, A.,
96
TITOLO LATE-HOLOCENE SEA LEVEL CHANGE BETWEEN SISTIANA AND DUINO: TECTONIC IMPLICATIONS
KARINJA, S., KOVAČIĆ V & SURACE L. (2007) - Sea level
change during holocene from Sardinia and Northeastern
Adriatic from archaeological and geomorphological data.
Quaternary Science Review, 26 (19-21), 2463-2486.
BENSI S., FANUCCI F., PAVSIC J., TUNIS G. & CUCCHI F. (2007)
- Nuovi dati biostratigrafici, sedimentologici e tettonici sul
Flysch di Trieste. Rend. Soc. Geol. It., 4 (2007), Nuova
Serie, 145.
BRAITENBERG C., NAGY I., ROMEO G. & TACCETTI Q. (2005) The very broad-band data acquisition of the long-base
tiltmeters of Grotta Gigante (Trieste, Italy). Journal of
Geodynamics, 41, 164-174.
BRAMBATI A. & CATANI G. (1988) - Le coste e i fondali del
Golfo di Trieste dall’Isonzo a Punta Sottile: aspetti
geologici, geomorfologici, sedimentologici e geotecnica.
Hydrores, 6, 13-28.
CARULLI G.B. & CUCCHI, F. (1991) - Proposta di
interpretazione strutturale del Carso Triestino. Atti Tic. Sc.
Terra, 34 (1991), 161-166.
CUCCHI F. 1986 - Considerazioni sulla tettonica dell’area di
Sistiana (Carso Triestino). Quaderno del Museo GeologiPaleontologico di Monfalcone, Numero Speciale: 9-11
FAIVRE S., FOUACHE E., GHILARDI M., ANTONIOLI F., FURLANI
S. & KOVAČIĆ V. (2009) – Relative sea level change in
Istria (Croatia) during the last 5 ka. Geoitalia 2009,
Epitome, 152-153.
FURLANI S., 2003 - Shore platforms along the Northwestern
istrian coast: an overview. Annales Ser. Hist. Nat., 13 (2),
247-256.
FURLANI S., CUCCHI F., FORTI F. & ROSSI A. (2009) Comparison between coastal and inland Karst limestone
lowering rates in the northeastern Adriatic Region (Italy
and Croatia). Geomorphology, 104, 73-81.
GEO-CGT PROJECT – Convenzione per la realizzazione di una
Carta di Sintesi Geologica alla scala 1:10000 – Regione
Autonoma Friuli Venezia Giulia, Direzione Centrale
Ambiente e Lavori Pubblici.
GIORGETTI F. (1967) – Nota sue sedimenti costieri lungo la
falesia a nord e nord ovest di Trieste. Boll. Soc. Adriat. Di
Sci., 55 (1): 12-17.
MORELLI C. & MOSETTI F. (1968) – Rilievo sismico continuo
nel Golfo di Trieste. Andamento della formazione arenacea
(Flysch) sotto il fondo marino nella zona tra Trieste,
Monfalcone e Grado. Boll. Soc. Adriat. Di Sci., 56 (1): 4257.
SUNAMURA, T. (1992) – Geomorphology of Rocky Coasts.
Wiley, Chichester, 302
Seismogenic sources of the Adriatic domain: an overview from the
Database of Individual Seismogenic Sources (DISS 3.1.0)
VANJA KASTELIC (*), PAOLA VANNOLI (*), PIERFRANCESCO BURRATO (*), SALVATORE BARBA (*), ROBERTO
BASILI (*), UMBERTO FRACASSI (*), MARA MONICA TIBERTI (*) & GIANLUCA VALENSISE (*)
RIASSUNTO
Sguardo d’insieme sulle sorgenti sismogenetiche della regione adriatica
dal Database delle Sorgenti Sismogenetiche Individuali (DISS 3.1.0)
Il Database delle Sorgenti Sismogenetiche Individuali (DISS) contiene
sorgenti capaci di generare terremoti con Mw > 5.5 e fornisce una visione
sinottica della sismogenesi in Italia e nelle aree limitrofe. In questo lavoro
presentiamo un dettaglio sulle sorgenti dell’alto Adriatico, che possono essere
visionate in dettaglio sul sito web e scaricate nei principali formati GIS
(http://diss.rm.ingv.it/diss). DISS è per sua natura aperto a continui
aggiornamenti tecnologici e soprattutto scientifici, pertanto beneficia di tutti gli
input provenienti dalla comunità scientifica, nazionale ed internazionale.
Key words: Adria microplate, active tectonics, Seismogenic
Sources.
We present an overview of the seismogenic sources
belonging to the interior and the border zones of the Adriatic
microplate, included in the latest version of the Database of
Individual Seismogenic Sources (DISS, v. 3.1.0; DISS
WORKING GROUP, 2009).
DISS is a large repository of geologic, tectonic and active
fault data on Italy and surrounding areas (Fig. 1) that result
from its authors’ first-hand experience and from a large
amount of literature data (BASILI et alii, 2008).
Fig. 1: Screenshot of the web-page of the DISS,
http://diss.rm.ingv.it/diss.
The main content of DISS is the Seismogenic Source. DISS
Seismogenic Sources are active faults capable of generating
Mw > 5.5 earthquakes. We distinguish three main categories of
Seismogenic Sources (BASILI et alii, 2008):
- the “Individual Seismogenic Sources” are obtained from
geological and geophysical data and are characterized by a full
set of geometric (strike, dip, length, width and depth),
kinematic (rake) and seismological parameters (average
displacement, magnitude, slip rate, recurrence interval).
Individual Seismogenic Sources are assumed to exhibit
“characteristic” behaviour with respect to rupture length/width
and expected magnitude. These Sources are tested against
worldwide databases for internal consistence in terms of
length, width, average displacement and magnitude, and can be
complemented with information on fault scarps when present.
This category of sources favours accuracy of the information
supplied over completeness. As such, they can be used for
deterministic assessment of seismic hazard, for calculating the
probability of the occurrence of strong earthquakes for the
sources themselves (AKINCI et alii, 2008), for calculating
earthquake and tsunami scenarios (LORITO et alii, 2008;
TIBERTI et alii, 2008), and for tectonic and geodynamic
investigations (e.g. BURRATO & VALENSISE, 2008).
- the “Composite Seismogenic Sources” are obtained from
geological and geophysical data and are characterized by
geometric (strike, dip, width, depth) and kinematic (rake)
parameters, but their length is more loosely defined and spans
an unspecified number of Individual Sources. They are not
assumed to be capable of a specific earthquake but their
potential can be derived from existing earthquake catalogues.
A Composite Source is essentially identified on the basis of
regional surface and subsurface geological data. This category
of sources favors completeness of the record of potential
earthquake sources over accuracy of source description. In
conjunction with seismicity and modern strain data, Composite
Sources can thus be used for regional probabilistic seismic
hazard assessment and for investigating large-scale
geodynamic processes (e.g. BARBA et alii, 2008; MELETTI et
alii, 2008).
_________________________
(*) Istituto Nazionale di Geofisica e Vulcanologia,
Via di Vigna Murata, 605 – 00143 Roma, Italy.
- “Debated Seismogenic Sources”; these are active faults
that have been proposed in the literature as potential
seismogenic sources but were not yet considered reliable
enough to be included in the database. They may include:
98
V. KASTELIC ET ALII
- sources for which only minimal surface evidence is supplied
in the literature;
- sources based on inherently ambiguous geological evidence;
- sources for which the literature offers highly contrasting
views;
- sources that occur in low or very low seismicity areas;
- sources whose characteristics are in open contrast with those
of nearby, better known and established sources, or that violate
established tectonic and seismological evidence.
Fig. 2 Overview of the seismogenic sources of the Adria
microplate included in DISS 3.1.0. The Individual
Seismogenic Sources are represented with yellow rectangles,
Composite Seismogenic Sources with red ribbons. The cyan
polygon highlights the studied area.
The Adriatic domain is surrounded by active fold-andthrust belts that developed within the regional convergence, ca.
N-S oriented, between the African and European plates.
However, the distribution of seismicity reveals that active
deformation follows not only the Adria margins but it is
present also in its inner sector.
Along the western side of Adria, active deformation is
testified by faulting along the NE-verging shallow thrust fronts
of the Central and Northern Apennine belt. This process occurs
along the on-shore and off-shore areas of northern Abruzzo,
Marche and Emilia-Romagna (LAVECCHIA et alii, 2007;
SCROCCA et alii, 2007; VANNOLI et alii, 2004), as well as
along the thrust fronts buried underneath the Po Plain
(BURRATO et alii, 2003). Toward the inner sector of the
chain, active thrusting is being released by deeper portions of
the same SW-dipping thrust system. More to the South, the
western Adria margin is deformed by E-W trending strike-slip
regional faults, deep-seated in the crust (DI BUCCI et alii,
2006; FRACASSI & VALENSISE, 2007).
At the northern boundary zone, indentation of Adria in
Veneto and Friuli results in thrusting on generally E-W striking
thrusts of the Eastern Southalpine Chain (BURRATO et alii,
2008). Moving to Western Slovenia, active deformation is
taken up by dextral strike-slip faulting along steep NE dipping
fault planes (KASTELIC et alii, 2008; BURRATO et alii,
2008). Along the eastern side of Adria thrusting occurs along
the shallow SW-verging thrust fronts of the external Dinarides
in the coastal as well as off-shore areas (PRELOGOVIC et alii,
2003; HERAK et alii, 2005; KUK et alii, 2000).
The outermost thrust fronts of the Apennine and Dinaric
belts reach the central portion of the Adriatic Sea, showing that
Adria deforms also within its interior and not only along its
boundaries.
New feature included in DISS 3.1.0 are the composite
seismogenic sources covering areas of the external part of the
Dinaric belt.
The sources included in DISS were constrained taking into
consideration all available geological and geophysical data
both original and from the literature (i.e. traces of active faults,
drainage anomalies, studies of coastal geomorphology, data on
historic and instrumental seismicity, geodetic data).
Such approach will also be used to characterise and
parameterise active sources across Europe for the E.U. Project
Seismic Hazard Harmonization in Europe (SHARE), within
which DISS has been chosen as the template for constructing
and populating the regional databases of seismogenic sources.
This paper cannot substitute a complete in-depth visit of the
DISS web site (http://diss.rm.ingv.it/diss).
REFERENCES
AKINCI A., PERKINS D., LOMBARDI A. M. & BASILI R. (2008) Uncertainties in probability of occurrence of strong
earthquakes for fault sources in the Apennines, Italy.
Journal of Seismology. doi: 10.1007/s10950-008-9142-y.
BARBA S., CARAFA M.M.C. & BOSCHI E. (2008) - Experimental
evidence for mantle drag in the Mediterranean. Geophys.
Res. Lett., 35, L06302, doi:10.1029/2008GL033281.
BASILI R., VALENSISE G., VANNOLI P., BURRATO P., FRACASSI
U., MARIANO S., TIBERTI M.M. & BOSCHI E. (2008) - The
Database of Individual Seismogenic Sources (DISS),
version 3: summarizing 20 years of research on Italy's
earthquake geology. Tectonophysics, 453, 20–43,
doi:10.1016/j.tecto.2007.04.014.
BURRATO P., CIUCCI F. & VALENSISE G. (2003) - An inventory
of river anomalies in the Po Plain, Northern Italy: evidence
for active blind thrust faulting. Annals Geophys., 46, 5,
865-882.
BURRATO P., POLI M.E., VANNOLI P., ZANFERRARI A., BASILI
R. & GALADINI F. (2008) - Sources of Mw 5+ earthquakes
in northeastern Italy and western Slovenia: An updated
view based on geological and seismological evidence.
Tectonophysics, 453, 157-176, doi: 10.1016/j.tecto.
2007.07.009.
99
SEISMOGENIC SOURCES OF ADRIA MICROPLATE: AN OVERVIEW FROM THE DATABASE OF INDIVIDUAL SEISMOGENIC SOURCES
BURRATO P. & VALENSISE G. (2008) - Rise and fall of a
hypothesized seismic gap: source complexity in the 16
December 1857, Southern Italy earthquake (Mw 7.0). Bull.
Seism.
Soc.
Am.,
98
(1),
139-148,
doi:
10.1785/0120070094.
DI BUCCI D., RAVAGLIA, A., SENO, S., TOSCANI, G., FRACASSI,
U. & VALENSISE G. (2006) - Seismotectonics of the
Southern Apennines and Adriatic foreland: Insights on
active regional E-W shear zones from analogue modeling.
Tectonics, 25, TC4015, 10.1029/2005TC001898.
DISS WORKING GROUP (2009) - Database of Individual
Seismogenic Sources (version 3.1.0): A compilation of
potential sources for earthquakes larger than M 5.5 in Italy
and
surrounding
areas.
Available
at:
http://diss.rm.ingv.it/diss.
FRACASSI, U. & VALENSISE, G. (2007) - Unveiling the sources
of the catastrophic 1456 multiple earthquake: Hints to an
unexplored tectonic mechanism in Southern Italy. Bull.
Seismol. Soc. Am., 97, 3, 725-748, 10.1785/0120050250.
HERAK, D., HERAK, M., PRELOGOVIC, E., MARKUSIC, S. &
MARKULIN, Z. (2005) - Jabuka island (Central Adriatic
Sea) earthquakes of 2003. Tectonophysics, 398, 167-180.
KASTELIC, V., VRABEC, M., CUNNINGHAM, D. &. GOSAR, A.
(2008) - Neo-Alpine structural evolution and present-day
tectonic activity of the eastern Southern Alps: The case of
the Ravne Fault, NW Slovenia. J. Struct. Geol., 30, 963–
975. doi:10.1016/j.jsg.2008.03.009
KUK, V., PRELOGOVIC, E. & DRAGICEVIC, I. (2000)
Seismotectonically active zones in the Dinarides. Geologia
Croatica, 53, 2, 295-303.
LAVECCHIA, G., DE NARDIS, R., VISINI, F., FERRARINI, F., &
BARBANO S.M. (2007)- Seismogenic evidence of ongoing
compression in eastern-central Italy and mainland Sicily: a
comparison. Boll. Soc. Geol. It., 126, 209-222.
LORITO S., TIBERTI M.M., BASILI R., PIATANESI A. &
VALENSISE G. (2008) - Earthquake-generated tsunamis in
the Mediterranean Sea: scenarios of potential threats to
Southern Italy. Journal of Geophysical Research, 113,
B01301, doi:10.1029/2007JB004943.
MELETTI C., GALADINI F., VALENSISE G., STUCCHI M., BASILI
R., BARBA S., VANNUCCI G. & BOSCHI E. (2008) - A seismic
source zone model for the seismic hazard assessment of the
Italian territory, Tectonophysics, 450 (1-4), 85-108,
doi:10.1016/j.tecto.2008.01.003.
PRELOGOVIC, E., PRIBICEVIC, B., IVKOVIC, Z., DRAGICEVIC, I.,
BULJAN, R. & TOMLJENOVIC, B. (2003) - Recent structural
fabric of the Dinarides and tectonically active zones
important for petroleum-geological exploration in Croatia.
Nafta, 55, 155-161.
SCROCCA, D., CARMINATI, E., DOGLIONI, C., & MARCANTONI,
D. (2007) - Slab retreat and active shortening along the
Central-Northern Apennines. O. Lacombe, J. Lavé, F.
Roure and J. Verges (Eds): Thrust belts and Foreland
Basins. From Fold Kinematics to Hydrocarbon Systems,
Frontiers in Earth Sciences, Springer, 471-487.
TIBERTI M.M., LORITO S., BASILI R., KASTELIC V., PIATANESI
A. & VALENSISE G. (2008) - Scenarios of earthquakegenerated tsunamis in the Adriatic Sea. P. Cummins, L.
Kong and K. Satake (Eds): Topical Issue on Tsunamis.
Pure and Applied Geophysics, doi: 10.1007/s00024-0080417-6.
Detrital garnet in SE Alps and Outer Dinarides flysch basins:
EPMA and PIXE analyses to discriminate different source areas
DAVIDE LENAZ (*), CLAUDIO MAZZOLI (**)
RIASSUNTO
Granati detritici nei bacini flyschoidi delle Alpi Sudorientali e delle
Dinaridi Esterne: Analisi EPMA e PIXE per discriminare le aree sorgenti
Lo studio dei granati detritici presenti nei flysch del Bacino Giulio, di
Brkini e Istriano è stato effettuato tramite analisi in microsonda elettronica
(EPMA) e analisi in raggi-X indotti da protoni (PIXE). Tali metodologie hanno
permesso di determinare le composizioni chimiche degli elementi maggiori e in
traccia allo scopo di determinare le aree sorgenti. Le analisi EPMA hanno
permesso di distinguere due gruppi principali. Il primo gruppo presente in tutti
i campioni ha un chimismo compreso tra Alm+Sp60-100, Py0-20, Gr0-30, mentre il
secondo gruppo presente solo in alcuni campioni (quasi totalmente assente nel
Brkini) ha composizioni più alte in Py e Gr. Tali composizioni sono
riconducibili rispettivamente a possibili rocce sorgenti come metapeliti e
anfiboliti. Analisi PIXE preliminari hanno mostrato come l’Y sia sempre
presente con valori talvolta molto elevati (4100 ppm). Sono anche presenti Zn,
Zr, Yb e Ga.
glaucophane) associated with pyroxenes (omphacite) found in
Lower Eocene (about 52 Ma) deep-sea turbidite of the Julian
Basin (JB) suggesting these detrital minerals belong to limited
metamorphic bodies exhumed at about 56Ma during a phase of
Dinarides uplift.
Lenaz (2008) studied few detrital augites and pigeonites
from the flysch of the Istrian basin (IB). Their chemistry
suggests that they are related to subalkaline rocks (within-plate
tholeiites) crystallized at a pressure between 0 and 5 kbar. The
Key words: Analisi EPMA e PIXE, detrital garnet, flysch,
Outer Dinarides, SE ALps.
INTRODUCTION
In the Late Cretaceous, subduction of oceanic crust
occurred to the north of the Adria plate and was followed by
the formation of ophiolitic complexes. Continental collision in
Alpine orogenic belts lasts from the Late Cretaceous to Early
Tertiary. The progressive contraction of oceanic crust caused
the uplift of previously rifted continental margin and platforms
and the formation of foredeep flysch basins.
Detrital garnets are widespread in all the studied flysch
basins. Previous studies, focused on Cr-spinels present in the
same flysch basins, outlined on the basis of their TiO2 content
and FeO/Fe2O3 ratio they derived from peridotites and mantlederived magmatic rocks (LENAZ et alii, 2000; 2003). The first
are statistically more abundant and are considered to have been
derived from type I and II peridotites. The second appear to be
mainly related to back-arc basin products. These results
suggest that Cr-spinels derived from the erosion of the Internal
Dinarides, where type II and III peridotites are present, and
also from the Outer Dinarides, where type I peridotites outcrop.
Lenaz & Princivalle (2002) studied the occurrences of
detrital amphiboles (actinolite, Mg-hornblende, barroisite and
_________________________
(*) Dipartimento di Scienze della Terra, Via Weiss 8, Trieste
(**) Dipartimento di Geoscienze, Via Giotto 1, Padova
Fig. 1 – Sketch map of the studied flysch basins
aim of this study is the chemistry (major and trace elements) of
garnets in these flysch basins to improve the knowledge of
possible source areas.
RESULTS AND DISCUSSIONS
About 300 detrital garnet have been handpicked and
mounted for chemical analyses. Apart from scattered garnets
from the JB with high Gr and And content, the majority of the
garnets plot into two groups (Fig. 2). The group with low-Py
content (Group I) is present in all the analysed samples and the
Sp-content ranges from 0 to 45 mol %. It corresponds to the
Type B garnet according to Morton et al. (2004). Type B
garnets are derived from amphibolite-facies metasediments.
DETRITAL GARNETS IN SE ALPS AND OUTER DINARIDES FLYSCH BASINS: EPMA AND PIXE ANALYSES TO DISCRIMINATE
DIFFERENT SOURCES
101
Fig. 2 – From left to right, compositions of detrital garnets in Julian, Brkini and Istrian flysch basins according to their Almandine + Spessartine (Alm+Sp),
Grossular (Gr) and Pyrope (Py) contents.
Subdivision of Type B garnets into Bi (XCa<10%) and Bii
(XCa>10%) suggests a possible supplying of sediments from
granitoids and sediment derived from metasediments, which
tend to have a wider range of compositions within the overall
Type B spectrum. In our sediments both types seem to be
present. It is to notice that in Brkini Basin (BK) and IB about
55-70% of the garnets fall in the Bi field while in JB the
majority of garnet population (about 35%) plot in the Bii field.
The other group, with higher Py content (Group II, hereafter)
corresponds to Type C garnets sensu Morton et al. (2004).
These garnets are derived mainly from high-grade metabasic
rocks. A further subdivision of type C garnets into Ci
(XMg<40%) and Cii (XMg>40%) may be useful in assessing the
relative contributions from mafic and ultramafic (pyroxenites
and peridotites) metamorphic sources. In the studied basins,
Group II garnets are very few in the BK, while they are present
in both JB and IB. Only few crystals in IB and one crystal in
BG show Py content higher than 40 mol % and can be
considered as derive from peridotites. There are few garnets
plotting out of these two large groups. There are few garnets
(less than 2% in IB) with high-Py and low-Gr content similar
to Type A garnets of Morton et al. (2004). These garnets
derived from high-grade granulite-facies metasediments or
charnockites, but can also be supplied from intermediate-acidic
igneous rocks sourced from deep in the crust. The last group
corrsponds to few garnets from JB and IB with very high- Gr
and/or -And content generally derived from metasomatic rocks
such as skarns, from very low-grade metabasic rocks, or from
ultra-high temperature metamorphosed calc-silicate granulites
(Type D; Morton et alii, 2004). It is to notice that in the JB
garnets are more or less equally distributed (30% Bi, 35% Bii,
30% Ci), while for the other two basins there is a clear
decrease from Bi to Bii and Ci suggesting a change in the
supplies. Preliminary PIXE analyses show that Y is present in
almost all of the analysed garnets sometimes reaching high
content (4100 ppm). Zr, Zn, Yb and Ga have been also
detected.
References
LENAZ D. (2000) - Detrital pyroxenes in the Eocene flysch of
the Istrian basin (Slovenia, Croatia). Geologica Acta, 6,
259-266.
LENAZ D., KAMENETSKY V.S., CRAWFORD, A. & PRINCIVALLE
F. (2000) - Melt inclusions in detrital spinels from the SE
Alps (Italy-Slovenia): A new approach to provenance
studies of sedimentary basins. Contrib. Mineral. Petrol.,
139, 748-758.
LENAZ D., KAMENETSKY V.S. & PRINCIVALLE F. (2003) - Crspinel supply in the Brkini, Istrian and Krk Island flysch
basins (Slovenia, Italy and Croatia). Geol. Mag., 140, 335372.
LENAZ D. & PRINCIVALLE F. (2002) - Detrital high pressure –
low temperature minerals in Lower Eocene deep-sea
turbidites of the Julian Alps (NE Italy). Per. Mineral., 71,
127-135.
MORTON A.C., HALLSWORTH C.R. & CHALTON B. (2004) Garnet composition in Scottish and Norwegian basement
terrains: a framework for interpretation of North Sea
sandstone provenance. Mar. Petrol. Geosci., 21, 393-410.
Subsidence pattern in the Central Adriatic and its influence on
sediment architecture during the last 364 kyr
VITTORIO MASELLI (*), FABIO TRINCARDI (**), ANTONIO CATTANEO (***), DOMENICO RIDENTE (****),
ALESSANDRA ASIOLI (*****) & ANDREA PIVA (******)
RIASSUNTO
Subsidenza nell’ Adriatico centrale e la sua relazione con l’architettura
dei corpi sedimentari durante gli ultimi 364 ka.
Il margine occidentale del bacino Adriatico presenta stili tettonici
contrapposti: l’area settentrionale è caratterizzata da una forte subsidenza di
origine tettonica, accentuata durante il ‘900 da cause antropiche, mentre la
regione Apula è in sollevamento a partire dal Pleistocene Medio. Investigare la
subsidenza dell’Adriatico centrale è di fondamentale importanza perché l’area
rappresenta un raccordo da un punto di vista strutturale tra l’Adriatico
settentrionale e la Puglia, e perché permette di indagare con maggior dettaglio
la relazione tra la messa in posto dei corpi deposizionali tardo Quaternari e le
variazioni eustatiche e di apporto di sedimenti. I tassi di subsidenza in
Adriatico centrale sono stati calcolati sia mediante semplici modelli isostatici
seguendo la teoria di Airy, sia calcolando la profondità attuale di quattro paleo
linee di riva riferibili ai massimi glaciali stadio degli stadi isotopici dal 2 al
10, analizzando profili sismici ad alta risoluzione. I valori ottenuti sono stati
utilizzati per calcolare le paleo-profondità di sedimentazione del pozzo
PRAD1.2, il primo record sedimentario continuo per gli ultimi 364 ka presente
in Adriatico centrale, e per eseguire un confronto con le paleo profondità
ottenute analizzando le associazioni di foraminiferi campionate nel pozzo.
The Central Adriatic can be considered as a transitional zone
between the Northern and Southern extremes in the Adriatic
sea.
The stratigraphy of the Central Adriatic has been
investigated during the European Project PROMESS1 through
the borehole PRAD1.2 (71.2 m long), the first continuous
marine record in the Adriatic basin encompassing the slope
correlative of the last four Quaternary depositional sequences,
reaching the top of Marine Isotope Stage 11 (MIS11), in order
to quantify the subsidence values in this crucial area (Piva et
al., 2008; Ridente et al., 2008; Fig. 1).
Key words: Adriatic Sea, borehole PRAD1.2, decompaction,
late Quaternary, lowstand shoreline, subsidence, sediment
supply.
The Western Adriatic margin, part of the Appenine
foredeep, is characterized by a differentiated tectonic setting,
that likely reflect variations in the thicknesses of the subducting
lithosphere (Doglioni et al., 1994). A high subsidence rate, up
to 1 mm/yr, characterizes the northernmost part of the basin, in
marked contrast with the uplift of the Southern area (Apulia
region) in the order of 0.3 – 0.5 mm/yr (Doglioni et al., 1994;
Amorosi et al., 1999; Massari et al., 2004; Tosi et al., 2007).
_________________________
(*) Università di Bologna, Dipartimento di Scienze della Terra e GeologicoAmbientali.
(**) ISMAR – CNR, Istituto di Scienze Marine.
(***) Ifremer, Département Géosciences Marines.
(****) IGAG – CNR, Istituto d Geologia Ambientale e Geoingegneria.
(*****) IGG – CNR, Istituto di Geoscienze e Georisorse.
(******) ENI – Agip SpA.
Fig. 1 – Central Adriatic Sea bathymetry with the location of PRAD1.2
borehole. Track line refers to the seismic profile shown in Fig. 2.
Subsidence calculations were performed by applying a 2D
simplified model of the Adriatic margin, also taking into
103
MASELLI ET ALII
account an Airy correction for the sediment load. In the first
case, the subsidence rates obtained are equal to that of the
sediment accumulation rate, in the order of 0.2 mm/yr; in the
Using the calculated subsidence rate and taking into account
sediment supply fluctuations and sea level falls during glacial
lowstands (Bard et al., 1990; Chappell and Shackleton, 1986;
Fig. 2 – High resolution seismic profile AMC-179 and corresponding line drowing of major stratigraphic surfaces. Circles represent the position of the
lowstand shorelines, showing a backstepping configuration indicating Subsidence Rate > Sediment Supply.
second case, an Airy compensated model, the margin shows a
net shoaling, in contrast with the observed overall deepening of
the area where the borehole was retrieved, as indicated by the
trends in its foraminifera content (Piva et al., 2008).
A more accurate subsidence rate of 0.3 mm/yr is obtained
by correlating the present-day burial depth of past shorelines
deposited during the main glacial lowstands, from MIS 2 to
MIS 10 (Fig. 2).
Lea et al., 2002) it is possible to estimate the paleo-water depth
of the conformity surface ES1-ES3 and erosional surface ES4
in PRAD1.2.
The results obtained document a progressive deepening of
the Central Adriatic margin at the site of the borehole from one
lowstand to the next. This trend is confirmed by foraminifera
assemblages showing an evolution of the depositional
environment from inner shelf to mid-outer shelf conditions,
Fig. 3 – Left: Schematic representation of the stratigraphic relationship between progradational units on the shelf and onlapping units on the upper slope
(modified from Ridente et al., 2008). Red dashed lines are the major unconformities (Sequence Boundaries). Right: sediment supply fluctuation obtained from
borehole PRAD1.2 and global sea level oscillations. The two peaks in sediment supply corresponding to sea level falls during MIS 2 and MIS 10 are correlated
to the most important progrations of the Late Quaternary units.
SUBSIDENCE PATTERN IN THE CENTRAL ADRIATIC AND ITS INFLUENCE ON SEDIMENT ARCHITECTURE DURING THE LAST 364 KYR
since the glacial lowstand of MIS 10 followed by a progressive
shoaling, during MIS 2, caused by increased sediment flux
from the Po lowstand drainage system.
The subsidence rate obtained, even if reflecting a relatively
high sediment flux from the catchment, is insufficient to
compensate the subsidence rate and this fact explains the
overall backstepping arrangement of the four 100-kyr
regressive sequences along the western margin of the Central
Adriatic, mimicking the typical stratigraphic pattern of a young
passive continental margin (Fig. 3).
REFERENCES
AMOROSI A., COLALONGO M.L., FUSCO F., PASINI, G. & FIORINI
F. (1999) - Glacio-eustatic Control of Continental–Shallow
Marine Cyclicity from Late Quaternary Deposits of the
Southeastern Po Plain, Northern Ital. Quaternary Research,
52, 1-13.
BARD E., HAMELIN B. & FAIRBANKS R.G. (1990) - U–Th ages
obtained by mass spectrometry in corals from Barbados:
sea level during the past 130,000 years. Nature, 346, 456458.
CHAPPELL J. & SHACKLETON N.J. (1986) - Oxygen isotopes and
sea level. Nature, 324, 137-140.
104
DOGLIONI C., MONGELLI F. & PIERI P. (1994) - The Puglia
uplift (SE Italy): An anomaly in the foreland of the
Apenninic subduction due to buckling of a thick continental
lithosphere. Tectonics, 13, 1309-1321.
LEA D. W., MARTIN P. A., PAK D. K., & SPERO H. J. (2002) Reconstructing a 350 ky history of sea level using
planktonic Mg/Ca and oxygen isotopic records from a
Cocos Ridge core. Quaternary Science Reviews, 21(1-3),
283-293.
MASSARI F., RIO D., SERANDREI BARBERO R., ASIOLI A.,
CAPRARO L., FORNACIARI E. & VERGERIO P.P. (2004) - The
environment of Venice area in the past two million years.
Palaeogeography, Palaeoclimatology, Palaeoecology, 202,
273-308.
PIVA A., ASIOLI A., SCHNEIDER R. R., TRINCARDI F., ANDERSEN
N., COLMENERO-HIDALGO E., DENNIELOU B., FLORES J.-A.
& VIGLIOTTI L. (2008) - Climatic cycles as expressed in
sediments of the PROMESS1 borehole PRAD1–2, Central
Adriatic, for the last 370 ka: 1. Integrated stratigraphy.
Geochem.
Geophys.
Geosyst.,
9,
Q01R01,
doi:10.1029/2007GC001713.
RIDENTE D., TRINCARDI F., PIVA A., ASIOLI A. & CATTANEO A.
(2008) - Sedimentary response to climate and sea level
changes during the past ∼ 400 ka from borehole PRAD1.2
(Adriatic margin). Geochem. Geophys. Geosyst., 9, 1-20.
Crystal-chemistry of diopsides from mantle xenoliths in the Becco di
Filadonna area: equilibration pressure and petrological
implications.
F. NARDUZZI (*), A. DE MIN (*), D. LENAZ (*) & F. PRINCIVALLE (*)
RIASSUNTO
Cristallochimica di diopsidi in xenoliti di mantello dell’area del Becco di
Filadonna: pressioni di equilibratura ed implicazioni petrologiche
Alcuni Cr-diopsidi inclusi in xenoliti di mantello presenti in alcuni blocchi
basaltici rinvenuti nell’area del Becco di Filadonna (TN) sono stati studiati dal
punto di vista strutturale e chimico e i dati sono stati comparati con quelli di
analoghi Cr-diopsidi presenti in xenoliti ultrafemici provenienti da Predazzo
(TN) e dall’area di San Giovanni Ilarione. Particolare attenzione è stata rivolta
alle stime della pressione di equilibratura dei clinopirosseni studiati. I dati
hanno evidenziato come gli xenoliti di mantello del Becco di Filadonna siano
stati campionati da magmi ad una profondità comparabile a quella degli
xenoliti dei basalti Terziari di San Giovanni Ilarione e a profondità maggiori
rispetto agli xenoliti inclusi nei basalti Triassici di Predazzo.
area (Dolomites, Trento province) and in lherzolite xenoliths
included in Paleogenic basalts present in the San Giovanni
Ilarione area (Verona province). Their equilibration pressure
was evaluated and the results were compared with data of
clinopyroxene from worldwide mantle xenoliths (DAL NEGRO
et alii, 1984; CUNDARI et alii, 1986; SECCO, 1988; PRINCIVALLE
et alii, 1989, 1994, 1998, 1999, 2000a, 2000b; SALVIULO et alii,
1992; NIMIS, 1995).
2. GEOLOGICAL SETTINGS AND PETROGRAPHIC
NOTES OF BECCO DI FILADONNA MANTLE
XENOLITHS
Key words: Crystal-chemistry, diopside, mantle xenoliths,
Trento province, Veneto Volcanic Province.
INTRODUZIONE
Clinopyroxene is one of the most important mineralogical
phase present in the mantle xenoliths. Its crystal chemistry and
structure give important information to understand the
evolution of the host rock. The crystal chemical variations in
the pyroxene structure are sensible to the genetic environment
and reflect the pressure and temperature of crystallization
and/or equilibration. Therefore, the inter- and intra-crystalline
relations in these minerals are useful for geo-thermobarometric evaluations and allow petrological considerations
(DAL NEGRO et alii., 1989; BERTOLO & NIMIS 1993; SAXENA &
DAL NEGRO, 1983).
In this work are compared data of diopsides from mantle
xenoliths hosted in basalts boulders found near Becco di
Filadonna in Trento province, from xenoliths of cumulitic
clinopyroxenites hosted in Triassic basalt dykes outcropping in
Latemar Group (Dolomites, Trento province), from lherzolite
xenoltihs in Triassic camptonite dykes in Predazzo magmatic
_________________________
(*) Dipartimento di Scienze della Terra Università degli Studi di Trieste,
Via Weiss 8, 34127 Trieste
Notably, in NE Italy two main volcanic episodes are
characterized by the presence of xenoliths-bearing alkaline
rocks types: a) the Cainozoic Veneto Volcanic Province
(VVP), in which Na- and K-alkaline basalts are often
associated or interbounded with tholeiitic flows (DE VECCHI et
alii, 1976; DE VECCHI & SEDEA, 1995; SAVELLI & LIPPARINI,
1979; MACERA et alii, 2003; b) the Triassic (Ladinian) calcalkaline magmatism in which shoshonitics, K-alkaline basalts
and lamprophyres are presents (GALITELLI & SIMBOLI, 1970;
BOSELLINI et alii, 1982; DOGLIONI, 1987; VISONÀ, 1997).
The magmatic products of the two provinces are
characterized by different chemical behaviours as La/NbPM
ratio (< 1 in the first case and > 1 in the second one).
In the VVP (Adige Valley, San Giovanni Ilarione, Lessini
Mts.) several xenoliths hosted by Na-alkaline extensionalrelated magmas outcrop, usually being spinel lherzolites and
spinel harzburgites. The second type of occurrence is related to
the Triassic volcanics (Predazzo area) and includes spinel
lherzolite, cumulitic pyroxenite and olivine pyroxenite
xenoliths. They are included in K-alkaline dykes of varying
chemical composition and thickness. The age of the rocks from
Becco di Filadonna area is unknown.
The Becco di Filadonna xenoliths, included in K-alkaline
basalts, range from harzburgite-lherzolite to dunite and always
show eterogranular porphyroclastic textures partially altered in
iddingsitic products. These xenoliths differ in texture with
respect to the other ones taken here for comparison because
they display evident melt structures (i.e. ortopyroxene with
clinopyroxene exsolution lamellae replaced by oxides,
F. NARDUZZI, A. DE MIN, D. LENAZ, F. PRINCIVALLE
106
Fig. 1 -
Vcell vs VM1 variations
presence of clinopyroxene partially melted and glass with
newly-formed clinopyroxenes). Finally we report the presence
of primary carbonate.
3. CLASSIFICATION OF PYROXENE AND
CRYSTAL-CHEMISTRY
Studied clinopyroxenes fall in the diopside field. The
Becco di Filadonna (FDCPX) and San Giovanni Ilarione
(SGICPX) diopsides are Cr-diopsides, while the
clinopyroxenes from cumulitic clinopyroxenites (Cpxte Prdz)
are diopside s.s. (Fig. 1). Cristal-chemistry of pyroxene and in
particular the relationships between cell and M1 site volumes
allowed to estimate the equilibration pressure of these minerals
within the lithospheric mantle. Data for Becco di Filadonna
diopsides shows Vcell ranging from about 430 to 434 Å3 while
VM1 show values from 11.29 to 11.53 Å3. These values
plotted in the diagram by NIMIS & ULMER (1998) suggested an
equilibration pressure between 15 and more than 20 Kbars
(Fig. 1). In comparison clinopyroxene from two localities of
Predazzo magmatic area, show Vcell and VM1 larger than
those of the Becco di Filadonna clinopyroxene suggesting
lower pressure. In fact, the clinopyroxene from xenoliths
hosted in camptonite dykes (Cpx Car Prdz) (Vcell between
437 and 440 Å3) show lower equilibration pressure (9-14
Kbars; CARRARO & SALVIULO, 1998) and the other ones from
cumulitic pyroxenites included in basalt dykes in Latemar
Group show an equilibration pressure close to 6-7 Kbar (these
data are not derived from clinopyroxene crystalchemistry;
FERRARA et alii, 1974). The clinopyroxene from San Giovanni
Ilarione shows a pressure comparable to those of Becco di
Filadonna (>20 Kbar) and in agreement with SIENA &
COLTORTI (1989). This study shows how during the Triassic,
basalts sampled mantle xenoliths at different depths. In the
Becco di Filadonna (here supposed as Triassic according to its
chemical signature) they are sampled in the spinel + garnet
peridotite stability field. In the Predazzo area they are sampled
within the crust and in the spinel peridotite field within the
litospheric mantle. The same depths of the Becco di Filadonna
xenoliths have been recorded also for those of the San
Giovanni Ilarione magmatic area (SIENA & COLTORTI, 1989).
4. FINAL REMARKS
Crystal chemical studies allowed the reconstruction of the
equilibration pressure of different mantle xenoliths from the
VVP and Predazzo magmatic area. But further steps are
necessary. In the near future the petrography and the
geochemistry of the Becco di Filadonna mantle xenoliths will
be studied, as well as the petrography and the geochemistry of
the host rocks. The mineralogy of other phases will be further
evaluated. Moreover, geochronological studies will be
performed to understand if they are Triassic or Paleogenic in
age.
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The Ivrea-Verbano Zone as an analogue for the crustal section
beneath the Athesian District
GABRIELLA PERESSINI (*), SILVANO SINIGOI (*), JAMES E. QUICK (**)
RIASSUNTO
La Zona Ivrea-Verbano come modello della sezione crostale al di sotto del
distretto Atesino
Datazioni SHRIMP su zirconi di vulcaniti e graniti del distretto della Val
Sesia danno età sostanzialmente coeve con quelle del Complesso Basico della
Zona Ivrea-Verbano, dimostrando una relazione di causa-effetto tra l’intrusione
di grossi volumi di magma mantellico nella crosta inferiore e la produzione di
grandi quantità di magmi acidi, in un processo che può perdurare anche oltre 10
milioni di anni. L’analogia nel chimismo e nell’età tra le vulcaniti del Sesia e
quelle del distretto Atesino suggeriscono che anche quest’ultimo sia il prodotto
di un processo simile a quello che aveva interessato la zona Ivrea-Verbano. Se
così, profili sismici profondi dovrebbero evidenziare la presenza di un livello
simile al Complesso Basico al di sotto del distretto Atesino.
ABSTRACT
The Ivrea-Verbano Zone as an analogue for the crustal section beneath the
Athesian District
Magmatic intrusives and volcanics of the Sesia Valley district, dated by
Quick et alii (2009) through U/Pb SHRIMP on zircons, indicate that volcanism
and granitic plutonism were coincident with intrusion of mantle-derived mafic
melt in the deep crust as dated by Peressini et alii (2007) with the same
method. Age-correlation of volcanic and middle to deep crustal plutonic rocks
points to a cause-effect link between intrusion of mantle-derived basalt in the
deep crust, and large-scale, silicic volcanism. The Sesia Valley district
constitutes an unprece-dented exposure of a subcaldera magmatic plumbing
system to a depth of 25 km, based on which a restoration of the Permian lowercrustal section of NW-Italy has been proposed.
Volcanism and formation of granitic plutons in the Sesia Valley district
occurred within a ~10 Ma interval, an age span identical to that found with the
same isotopic system in the Athesian Volcanic District.
Key words: northern Italy, Permian magmatism, Sesia Valley
Caldera root-system
INTRODUCTION
The Ivrea-Verbano Zone and Serie dei Laghi constitute the
deep- and the middle-crustal components, respectively, of a
virtually complete cross section through the pre-Alpine
continental crust of northwest Italy (FOUNTAIN, 1976; RUTTER
et alii, 1999; for a dissenting view see BORIANI & GIOBBI,
2004). In the vicinity of the Sesia Valley (Fig. 1), this section
is juxtaposed against silicic volcanic rocks by Tertiary, strikeslip faults of the Cremosina Line (BORIANI, 1974). Rhyolite is
the dominant volcanic lithology, comprising lava flows,
massive porphyry, ignimbrites, pyroclastic rocks, and a
spectacular megabreccia with gigantic inclusions of volcanic
rock and schist encased in a matrix of welded tuff. Similar
megabreccias have been shown to be diagnostic of calderaforming eruptions, forming as the subsiding caldera fills with
volcanic ash mixed with landslide debris derived from the
caldera walls (LIPMAN, 1997). East of the Sesia Valley, a relic
of the caldera wall places the megabreccia in contact with twomica schist of the Serie dei Laghi. In the west, the volcanic
pile is intruded by granophyre that grades downward into
aplitic granite (the upper Valle Mosso granite, “u” in Figure 1),
a relationship typical of the “roots” of calderas. The
distribution of megabreccia indicates a minimum northeastsouthwest caldera dimension of 13 km.
Recently published SHRIMP U-Pb zircon ages (QUICK et
alii, 2009) demonstrate that eruption of the Sesia-Valley
volcanics overlapped in time with the dominant, deep-crustal
magmatic event in the Ivrea-Verbano Zone: volcanic rocks are
dated between 288±2 and 282±3 Ma, granites from 289±3 to
275±4 Ma, essentially coeval with or slightly younger than the
IVZ Mafic Complex, dated at about 288 Ma by PERESSINI et
alii (2007).
This magmatism is essentially coeval with that of the
Athesian Volcanic District, where similar silicic volcanic rocks
range 291±3 to 274±2 Ma, and granitic plutons were dated at
285±2 to 276±2 Ma (BARTH et alii, 1994; MAROCCHI et alii,
2008; VISONÀ et alii, 2007). These ages recall those from the
Collio Basin at 283±1 to 281±2 Ma (SCHALTEGGER & BRACK,
2007).
CONCLUSIONS
_________________________
(*) Dipartimento di Scienze della Terra, Università di Trieste, via Weiss 8,
34127 Trieste (Italy)
(**) Roy M. Huffington Department of Earth Sciences, Southern Methodist
University, Dallas, Texas 75275-0395, USA
[email protected]
Lavoro parzialmente eseguito nell’ambito del progetto PRIN 2007
QUICK et alii (2009) demonstrated that volcanism and
granitic plutonism were coincident with, and probably
triggered by, intrusion of mantle-derived mafic melt in the
deep crust, concluding that intrusion of the upper Mafic
Complex at depths ≥15 km induced anatexis in the continental
crust and generated
PERESSINI ET ALII
110
Fig. 1 – Geological sketch map of the Massiccio dei Laghi and neighbouring zones, comprised in between the Pennidic Unites and the Po plain (from W
eastward: Sesia-Lanzo zone, Canavese Zone, Scisti di Fobello and Rimella, Ivrea-Verbano zone, Serie dei Laghi, Strona-Ceneri zone). Compiled after: Quick et
al. (2003): Ivrea-Verbano Zone; Pezzotta & Pinarelli (1994): Ordovician metagranitoids; Giobbi Origoni et al. (1997): Strona-Ceneri Border Zone.
VILLAGES: Va: Varallo; Vb: Verbania
silicic melts that fed granites and erupted as rhyolites for
~10-15 Ma, from ca. 289 to ca. 275 Ma.
Figure 2 represents the crustal section obtained by QUICK et
alii (2009) after restoration of alpine fault displacements. The
authors concluded that a synthetic seismic profile across such a
crustal structure should produce two well-defined deep- and
middle- to upper-crustal low-velocity zones similar in scale
and
depth to those detected beneath active calderas such as Campi
Flegrei (GUIDARELLI et alii, 2006).
Age ranges found in the Sesia Valley district are very
similar to those determined for the Early Permian Athesian
District, where igneous activity also lasted ~10-15 Ma.
Based on this striking analogy, we suggest that also the
Permian Athesian igneous system should have been triggered
by a huge mafic intrusion in the lower crust. If so, the crustal
structure beneath the Athesian District should resemble closely
that represented in Figure 2 and relative to the Ivrea- Verbano
Zone.
Fig. 2–Palinspastic reconstruction by QUICK et alii (2009) of Early Permian
Ivrea Verbano–Serie dei Laghi crust shortly after caldera formation. Faults in
caldera floor are schematic. P wave and S wave velocities (Vp ,Vs) calculated
along profile A-A′ for subsolidus and hypersolidus conditions are compared to
S wave velocity profile beneath Campi Flegrei Caldera (GUIDARELLI et alii,
2006). CMB—Cossato-Mergozzo-Brissago Line.
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111
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Up-to-date geological cartography of the Venice Lagoon (Italy)
FEDERICA RIZZETTO (*), LUIGI TOSI (*), MASSIMO ZECCHIN (**) & GIULIANO BRANCOLINI (*)
RIASSUNTO
Cartografia geologica aggiornata della Laguna di Venezia
Negli ultimi anni numerose ricerche di carattere geologico hanno permesso
di aggiornare le conoscenze relative all’assetto ed all’evoluzione dell’area
lagunare veneziana. Fondamentale importanza hanno assunto soprattutto gli
studi condotti nell’ambito del Progetto di Cartografia Geologica CARG
finalizzati alla realizzazione dei Fogli Geologici 128 “Venezia” e 148-149
“Chioggia-Malamocco” alla scala 1:50.000, la cui pubblicazione è avvenuta nel
2007. Queste indagini hanno permesso di definire l’età, la distribuzione, i
reciproci rapporti e le caratteristiche litologiche e di facies dei sedimenti tardopleistocenici ed olocenici affioranti e sepolti in laguna, nell’adiacente fascia di
bacino scolante e presso il litorale. I depositi individuati sono stati classificati
utilizzando le Unconformity Bounded Stratigraphic Units: in particolare sono
stati definiti il Supersintema di Venezia, comprensivo delle unità postmessiniane deposte a partire dal Pliocene fino alla base del Pleistocene
superiore, il Supersintema di Mestre, rappresentativo dei depositi alluvionali
tardo-pleistocenici, ed il Sintema del Po, costituito dai depositi olocenici e
diviso in due unità, l’Unità di Malamocco e l’Unità di Torcello, distinte
esclusivamente su base cronologica.
Recentemente nuove ricerche, alcune delle quali tuttora in corso, hanno
fornito importanti risultati che hanno permesso di aggiornare ulteriormente le
conoscenze geologiche finora acquisite nel corso dei precedenti studi. In
particolare, l’analisi congiunta di carotaggi e di profili ottenuti mediante un
sistema di acquisizione sismica ad altissima risoluzione adatto per rilievi in
bassi fondali (profondità inferiore ad 1 m) si sta rivelando particolarmente utile
per migliorare la ricostruzione dell’assetto morfostratigrafico della laguna.
Questo sistema ha permesso di riconoscere anche lineamenti geomorfologici
finora sconosciuti sepolti in ambiente lagunare e di stabilire le relazioni tra
questi ultimi ed analoghe strutture presenti nell’adiacente terraferma.
realized within the framework of the CARG Project and
published in 2007 (TOSI et alii 2007a; TOSI et alii 2007b) (Fig.
1). They point out geological, geomorphological, and
lithostratigraphic settings of the Lagoon and Gulf of Venice
and nearby mainland, showing age, distribution,
sedimentological
characteristics,
and
depositional
environments of the exposed and buried stratigraphic units.
The results of these studies have been recently updated
through the analysis and interpretation of a number of data and
information derived from other research projects carried out in
the last years and aimed at studying geological and
geomorphological setting and evolution of the Venice coastal
area (ZECCHIN et alii, 2008; RIZZETTO et alii, 2009; TOSI et
alii, 2009; ZECCHIN et alii, 2009). In particular, new Very High
Resolution Seismic (VHRS) surveys realized in shallow water
and new geological data have allowed a more detailed
reconstruction and mapping of the Venice lagoon subsoil down
to about 30 m b.s.l., useful to better understand the Late
Pleistocene and Holocene evolution of the territory.
The aim of this paper is to present a brief description of the
geological maps of the Venice Lagoon and the first results
obtained from new researches, still in progress.
Key words: Geological Maps, stratigraphy, geomorphology,
Venice Lagoon.
INTRODUCTION
The Geological Sheets 128 “Venezia” and 148-149
“Chioggia-Malamocco” of the new 1:50,000 scale map series
of the Institute for Environmental Protection and Research
(ISPRA, formerly APAT and Italian Geological Survey) were
_________________________
(*) Istituto di Scienze Marine, CNR, Castello 1364/A, 30122, Venezia
(**) Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS,
Borgo Grotta Gigante 42/C, 34010, Sgonico (Trieste)
This study was performed within the framework of the following projects:
CARG; CORILA - R.L. 3.16; VECTOR, Action 3, R.L. 5 (CLIVEN); CNR
- RSTL 809.
Fig. 1 – Location of the Venice Lagoon and area covered by the Geological
Sheets 128 “Venezia” and 148-149 “Chioggia- Malamocco”.
MATERIALS AND METHODS
The Geological Maps of the Venice Lagoon are the result
of multidisciplinary investigations, i.e. photo-interpretation,
remote sensing, studies on historical cartographic documents,
topographic and bathymetric data processing, geological and
geomorphological in situ surveys (including hundreds of
drillings from 1 to 100 m deep), geophysical investigations (in
particular VHRS profiles), and laboratory analyses on the
collected samples (detailed stratigraphic descriptions,
paleontological,
mineralogical,
and
sedimentological
investigations, radiocarbon datings) (TOSI et alii 2007a; TOSI et
alii, 2007b).
The joint analysis of VHRS profiles and data from cores
allowed the identification of the stratigraphic units present in
the Venice lagoon subsoil and the reconstruction of its
geological setting. For the realization of the CARG Project
VHRS surveys were mainly carried out along lagoon channels
and canals; consequently, as the channels are cut into the
Holocene deposits (sometimes also reaching the Late
Pleistocene sediments) and are frequently dredged, many
information related to the Holocene sequence were lost.
To overcome this problem, in the last years a new VHRS
system, suitable for investigations in water depths less than 1
m, has been implemented and used in more recent researches.
The new seismic data obtained by this method, which allows
113
the acquisition of clear images of the subsurface also in the
lagoon shallows and with a resolution of about 10 cm, have
been used to improve and complete the reconstruction of the
morphostratigraphic framework of the Venice basin (RIZZETTO
et alii, 2009; TOSI et alii, 2009).
STRATIGRAPHIC UNITS
According to the guidelines for geological investigations of
the Quaternary continental deposits (SERVIZIO GEOLOGICO
NAZIONALE, 2001), in the Geological Maps the Unconformity
Bounded Stratigraphic Units were used to classify the different
kinds of deposits, buried and exposed in the investigated area
(TOSI et alii, 2007a; TOSI et alii, 2007b) (Fig. 2).
The Venice Supersynthem (Pliocene-110 kyr BP) is the
earliest stratigraphic unit identified in the subsoil of the Venice
Lagoon during the surveys, but not exposed. The lower
boundary coincides with the Messinian unconformity, whereas
the upper one marks the transition from the last lagoonal and
deltaic deposits (Correzzola Unit) of the Tyrrhenian marine
transgression to the fluvial sediments of the overlying Mestre
Supersynthem.
The Mestre Supersynthem (110-18 kyr BP) is composed of
Upper Pleistocene alluvial deposits. The boundary with the
overlying Holocene units is often representative of much
Fig. 2 – Stratigraphic relations within the Venice Supersynthem, the Mestre Supersynthem, and the Po Synthem in the Geological Sheet 128 “Venezia” (modified
from TOSI et alii, 2007a).
114
P. AUTORE ET ALII
reduced sedimentary supply or “non depositional” conditions.
The top layers are often characterized by the presence of a
paleosoil (caranto), developed in conditions of prolonged
subaerial exposure and sedimentation starving (GATTO and
PREVIATELLO, 1974; BONARDI and TOSI, 2000; MOZZI et alii,
2003; TOSI et alii, 2007a; TOSI et alii, 2007b). In the study area
the Mestre Supersynthem is exposed only in the coastal plain
close to the north-western lagoon margin and in the deeper
lagoon channels.
The Po Synthem, composed of alluvial, deltaic, littoral
(beach and lagoon), and shelf sediments, represents the
Holocene deposition, occurred during the marine transgressive
event that took place after the Last Glacial Maximum. It is
exposed both in the mainland and in the lagoon bottom. As in
the different parts of the Venice basin its lower boundary has
diverse ages, ranging from about 10 to 5 kyr BP, a stratigraphic
hiatus, varying from 8 to 13 kyr, is recorded between the Late
Pleistocene and the Holocene sedimentation.
The Torcello Unit and the Malamocco Unit, divided only
on a chronological basis, constitute the Po Synthem. The
Malamocco Unit represents the lower and most ancient part of
the Po Synthem. Its top layers, dating back to the Late Roman
Age, show evident signs of pedogenesis that indicate past
conditions of subaerial exposure. The Torcello Unit, the upper
and most recent part of the Po Synthem, refers to the postRoman sedimentation, occurred from V-VI century A.D. and
ended with the present. Its deposition started under worsen
climatic conditions that, from IV-VI century A.D., caused a
significant increase in rainfall, and consequently in flooding
(VEGGIANI, 1994), and probably also a sea level rise,
responsible for a partial submersion of the lagoon area.
setting of the Venice lagoon subsoil.
In particular, the new VHRS profiles, combined with core
analysis, provided detailed information about depositional
geometries, internal bounding surfaces, and stratal
relationships, and, consequently, the identification of large- to
medium-scale sedimentary structures, the corresponding
sedimentary environment, and the retrogradational and
progradational trends (ZECCHIN et alii, 2008; ZECCHIN et alii,
2009).
As regards the southern Venice Lagoon, where part of the
results of the new surveys has been already interpreted, three
main seismic units (H1, H2, H3), separated by key stratal
surfaces (S1, S2, S3), have been recognized in the Holocene
succession.
Unit H1, the lower part of the Holocene sequence,
represents the Transgressive Systems Tract (TST). Its bottom
boundary (S1) coincides with the Pleistocene/Holocene
unconformity.
Unit H2 has been interpreted as the Highstand Systems
Tract (HST), composed of marine deposits in seaward
locations and lagoon sediments landwards.
TST and HST are separated by the maximum flooding
surface (S2), locally amalgamated with a wave ravinement
surface where transgressive marine deposits of Unit H1 are
absent.
Unit H3 consists of more recent lagoon sediments, whose
accumulation was mainly influenced by human interventions
(e.g. river diversion and consequent delta abandonment,
dredging of new canals) occurring during historical times.
S3 is the youngest surface, which bounds the base of the
channelized deposits, and coeval laminated sediments, of Unit
H3.
ARCHITECTURAL SCHEME OF THE HOLOCENE
SUBSOIL
GEOMORPHOLOGICAL FEATURES
The joint interpretation of data from deep cores and VHRS
surveys has allowed the reconstruction of the stratigraphic
In the Geological Maps the main geomorphological
features (i.e. traces of abandoned riverbeds, ancient fluvial and
Fig. 3 – (a) Simplified architectural scheme of the Holocene deposits in the southern Venice Lagoon. A-Active tidal channel; B-Lateral accretion; C-Buried tidal
channel; D-Channel-levee system; E-Clinoforms; F-Early Holocene estuarine and fluvial channels; G-Pleistocene fluvial channel; H-Pleistocene alluvial plain.
(b) Late Pleistocene and Holocene complex channelized sequences (modified from TOSI et alii, 2009).
beach ridges, old lagoon channels and inlets) were indicated to
favour the identification of the different processes responsible
for the evolution of the study area (TOSI et alii, 2007a; TOSI et
alii, 2007b). A detailed identification of these structures was
made possible in the mainland through the interpretation of
satellite images and aerial photographs, altimetry data, and
historical maps, integrated by field surveys and core analyses.
On the other hand, their recognition in the lagoon was more
difficult, as it is a submerged environment.
VHRS surveys recently carried out in very shallow waters
have allowed the identification of many geomorphological
features buried in lagoon subsoil or exposed on the lagoon
bottom (RIZZETTO et alii, 2009; TOSI et alii, 2009) (Fig. 3).
Consequently, they have provided an important support to the
knowledge of the genetic relationships between the
geomorphological structures recognized in the mainland and
the ones identified in the lagoon basin.
REFERENCES
BONARDI M. & TOSI L. (2000) - Studio sedimentologico di un
livello di argilla sovraconsolidata sottostante il litorale
veneziano. Ist. Ven. SS LL AA, La Ricerca Scientifica Per
Venezia, Il Progetto Sistema Lagunare Veneziano,
Modellistica del Sistema Lagunare, Studio di Impatto
Ambientale, 2 (2), 952-960.
GATTO P. & PREVIATELLO P. (1989) - Significato stratigrafico,
comportamento meccanico e distribuzione nella Laguna di
Venezia di un’argilla sovraconsolidata nota come
“Caranto”. C.N.R., Lab. per lo Studio della Dinamica delle
Grandi Masse, Venezia, Rapporto Tecnico 70, 45 pp.
MOZZI P., BINI C., ZILOCCHI L., BECATTINI R. & MARIOTTI
LIPPI M. (2003) - Stratigraphy, palaeopedology and
palinology of late Pleistocene and Holocene deposits in the
landward sector of the lagoon of Venice (Italy), in relation
to caranto level. Il Quaternario, 16 (1bis), 193-210.
RIZZETTO F., TOSI L., ZECCHIN M., BRANCOLINI G. &
BARADELLO L. (2009) - Ancient geomorphological features
115
in shallows of the Venice Lagoon (Italy). Journal of Coastal
Research, SI 56, ISSN 0749-0258, 752-756.
SERVIZIO GEOLOGICO NAZIONALE (2001) - Indicazioni per il
rilevamento del Quaternario continentale. Circolare
CARG: SGN/2155/U1CARG, 11 maggio 2001.
BARBERO R. & TOFFOLETTO F. (2007a) - Note illustrative
della Carta Geologica d’Italia alla scala 1:50.000. 128 Venezia. APAT, Dip. Difesa del Suolo, Servizio Geologico
d’Italia, Casa Editrice SystemCart, Roma, 164 pp., 2
allegati cartografici.
BARBERO R. & TOFFOLETTO F. (2007b) - Note illustrative
della Carta Geologica d’Italia alla scala 1:50.000. 148149 - Chioggia-Malamocco. APAT, Dip. Difesa del Suolo,
Servizio Geologico d’Italia, Casa Editrice SystemCart,
Roma, 164 pp., 2 allegati cartografici.
TOSI L., RIZZETTO F., ZECCHIN M., BRANCOLINI G. &
BARADELLO L. (2009) - Morphostratigraphic framework of
the Venice Lagoon (Italy) by very shallow water VHRS
surveys: Evidence of radical changes triggered by humaninduced river diversions. Geophysical Research Letter, 36,
L09406, doi:10.1029/2008GL037136.
VEGGIANI A. (1994) - I deterioramenti climatici dell’Età del
Ferro e dell’alto Medioevo. Bollettino della Società
Torricelliana di Scienze e Lettere, Faenza, 45, 3-80.
ZECCHIN M., BARADELLO L., BRANCOLINI G., DONDA F.,
RIZZETTO F. & TOSI L. (2008) - Sequence stratigraphy
based on high-resolution seismic profiles in the late
Pleistocene and Holocene deposits of the Venice area.
Marine
Geology,
253,
185-198,
doi:
10.1016/j.margeo.2008.05.010.
ZECCHIN M., BRANCOLINI G., TOSI L., RIZZETTO F., CAFFAU
M. & BARADELLO L. (2009) - Anatomy of the Holocene
succession of the southern Venice lagoon revealed by very
high-resolution seismic data. Continental Shelf Research,
29,
1343-1359,
doi:10.1016/j.csr.2009.03.006.

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