In un paese come l`Italia, caratterizzato da una forte densità abitativa

Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
TITOLO TESI:
Silicic and basaltic Large Igneous Provinces: Examples of the Magmatic Province of Patagonia and
sills from Mauritania and Mali
Ph.D. candidate: Lina Serrano Durán, I course
Tutor: Prof. Andrea Marzoli
Co-tutor: Prof. Vadim Kamenetsky (University of Tasmania)
Cycle: XXVI
Abstract
Large Igneous Provinces are one of the most significant accumulations of mafic material on earth. Some continental provinces
have associated a silicic magmatic component that in cases can be also dominant. The relative role of different petrogenetical
processes as well as the tectonic settings in their origin is still unclear. During Jurassic time two continental provinces were
raised in Pangea, one of them (Central Atlantic Magmatic Province) with a dominant mafic composition and a mass extinction
event related at c. 200Ma, and a second one, (The Magmatic Province of Patagonia) composed by silicic rocks formed during
a longer period of volcanism (188 Ma-153Ma)and with no mass extinction event associated. Both of them are related to break
up processes but each case has a different length, dominant composition and grade of impact in the paleo-ecology. The study
of these Provinces allow to access to a better knowledge of the Large Igneous Provinces and the mechanisms that determine
its features. The scope of this project is an integrative geochronological and geochemical study employing melt inclusion
analysis. The results obtained from this research will contribute to identify the primordial processes involved and decipher its
role in the origin of the LIPs.
1. Introduction
“Large Igneous Provinces are magmatic provinces with areal extents >0.1 Mkm2 , igneous volumes >0.1
Mkm3 and maximum lifespans of ~50 Ma that have intraplate tectonic settings or geochemical affinities,
and are characterised by igneous pulse(s) of short duration (~1–5 Ma), during which a large proportion
(>75%) of the total igneous volume has been emplaced” (Bryan and Ernst, 2008). During Late Triassic–
Early Jurassic three major continental LIPs were formed (Marzoli et al. 1999; Riley & Knight 2001; Riley
et al. 2001; Vaughan and Storey, 2007) (fig1) (1) tholeiitic basaltic magmatism of the Central Magmatic
Atlantic Province (CAMP), outcrop over more than 7 x 106km2 and formed in a few million years, with
peak activity at 200 Ma (Marzoli et al, 1999). (2) Southern African Karoo basalts (2.5 x 106km3),
Antarctic Ferrar gabbro and Kirkpatrick basalts (0.5 x 106km3) that were emplaced c. 180 Ma ago
(Storey & Kyle 1997; Riley & Knight 2001; Jourdan et al., 2004); (3) the silicic magmatic province (2.35
x 105 km3) of South America and the Antarctic Peninsula, which formed between 188 and 153 Ma ago
(Feraud et al., 1999.; Riley et al., 2001; Vaughan and Storey, 2007). Outburst of the CAMP and the
Gondwana Large Igneous Provinces (2,3) occurred during break-up of the Pangea supercontinent and
coincide with two major mass extinction events at 200Ma (Tanner et al., 2004; Marzoli et al., 2004) and c
183Ma (Aberhan & Fursich 2000).
The present research project is based on a petrological study of two cases representative of continental
LIPs: 1) Mafic sills part of the CAMP from Hodd, Hank and Kaarta regions, in Mauritania and Mali, and
2) Silicic magmatism from Chon Aike, Marifil and Bajo Pobre Formations of the Silicic Magmatic
Province of Patagonia, Argentina. Both cases are related to extensional events, however it has been also
suggested that the origin of the Patagonian Province was influenced by the subduction of the Paleo
Pacific plate at the western margin. An integrative geochronological and geochemical study using melt
inclusions analysis will provide a reliable record of the evolving magmas, as well as the possibility to
recognize and estimate primordial characteristics of the source and large scale processes involved in the
origin of the rocks from both cases of study. The significance of the results would contribute to a better
comprehension of the magmatic processes and tectonic settings involved, as well as to clarify its relation
and influence to trigger the production of the large volumes of magma recorded by LIPs.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
Fig 1. Plate reconstruction for Pangea in Early Jurassic times. In highlights the Central Atlantic Magmatic Province
(CAMP) and Gondwana Large Igneous Province (GLIP). Figure from Vaughan and Storey (2007).
Kaarta, Hodh and Hank sills from Maurtiania and Mali
The Central Atlantic Magmatic Province (CAMP) is defined by tholeiitic basalts that crop out in oncecontiguous parts of North America, Europe, Africa, and South America and is associated with the
breakup of Pangea (Marzoli et al., 1999). Extensive dyke swarms and hypabyssal sills partly distributed
in the western margin of Africa are described as part of this Province (Bertrand, 1991; Marzoli et al.,
1999; Marzoli et al., 2004; Verati et al., 2005; Chabou et al., 2010). Sills were formed as large
accumulations of tubular lava piles of fisural origin intruding different levels of sedimentary rocks of
Paleozoic age (Bertrand, 1991). A few major dikes of more than 100km of length are present in the
northern part of the margin. Instead, Southward several swarms of generally shorter dykes form dense
networks dominating the area. Sills are highly variable in thickness and extension. The most important
are tabular and are widespread in Guinea, Southwest Mali (Diallo et al. 1976; Dars 1961 in Bertrand
1991) or in South East Mauritania (Hodh area). The Kaarta sill, at the south west of Mali, is one of the
best exposed (over 7000 km2 ; Rossi 1982; Bertrand and Coffrant 1986 in Bertrand, 1991). Some others
exhibit numerous secondary ramifications (Lajoinie and Bonifas 1961 in Bertrand, 1991), or are cut by
associated dyke swarms. Others are dyke-like elongated, such as Touirist and Azlaf sills in the Hank
region in Mauritania (Villemur, 1967 in Bertrand, 1991). Petrographically and mineralogically sills and
dykes from the North West of Africa have been described as dolerites and microdolerites by Bertrand
(1991). A relative age was stablished based on the correlation of the extension structures with the tectonomagmatic events related to the progressive continental fragmentation at 200 Ma Some Ar-Ar, K-Ar and
U-Pb analysis in the Taoudeni region, exhibit ages between 190 Ma and 198Ma. These that are supported
by some other Ar-Ar radiometric ages on mafic intrusive rocks from Mauritania that also reflect CAMP
magmatism (Usui et al., 2010).
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
Fig 2. Geographic distribution of dykes, sills and lavas in Nort West of Africa. Continents are reassembled
according to their predrift position from Bullard et al (1965) (Modified from Bertrand, 1986 in Bertrand, 1991).
Silicic Magmatic Province of Patagonia
The Silicic Magmatic Province of Patagonia extends from the Atlantic Coast to the Chilean Andes
(Pankhurst et al., 1998) and is correlated with the Jurassic volcanic rocks of the Antarctic Peninsula
(Riley and Leat, 1999 in Bryan et al., 2002). It covers an area of about 1x 106 km2 and in many places it
has a minimun thickness of 500m (Panhkurst et al., 1995). It is composed by a thick sequence of
magmatic rocks of predominant felsic composition mainly recorded by Chon Aike and Marifil (or Grupo
Bahia Laura) Formations in the eastern margin. In the Andean region, the magmatism is represented by
deformed, tilted and altered rocks of the Ibañez, Tobífera and El Quemado Formations (Pankhrust et al.,
1995; Bryan et al., 2002) The lithology is dominated by ignimbrites, rhyolites, debris flow, fallout and
epiclastic deposits. Chemically, the province exhibit a bimodal composition with a clear predominance of
the felsic events. The -intermidiate magmatism is represented by the Bajo Pobre Formation, underlying e
Marifil and Chon Aike Formations (Guido et al., 2006). Most of the magmatism is related to graben and
hemigraben structures distributed along the Province and related with the extension event of the
Gondwana break up (Feraud et al., 1999). Available K-Ar ages from, Ar-Ar, Rb-Sr and U-Pb ages
evidence a period of magmatic activity that ranges between c. 184Ma and c. 154Ma (Uliana et al., 1985;
Varela et al., 1991; Panhkurst et al., 2000, Feraud t al., 1999).
2. Methodology
The methodology that has been followed during the first year and is proposed for the second and third
years of this PhD is based on the next “outline”
1.Bibliographic review
2.Field work: Patagonia, Argentina
3.Analitical procedures: Ar-Ar, trace elements and isotopic (Sr, Nd, Pb) and melt inclusion analysis
on both cases of study.
4.Analysis of the results
5.Thesis writing
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
The study of Kaarta, Hodh and Hank sills is based on a collection of samples previously collected by
Prof. Hervé Bertrand from University of Lyon. No further field work has been planned to develop the
research on this subject. The study is focused on petrological work based on detailed petrography, major
and trace element analysis together with Sr, Nd, Pb isotopic data. Some Ar-Ar radioisotopic ages will be
also obtained on the best preserved samples. The preparation of samples for isotopic analysis has been
made using the available laboratories of the Dipartimento di Geoscienze della Università di Padova. The
research on the Silicic Magmatic Province of Patagonia is part of a collaboration started with Prof. Hervé
Bertrand, Prof. Giuliano Bellieni from Dipartimento di Geoscenze, Universitá di Padova, Prof. Marcelo
Marquez from Universidad Nacional de Patagonia, and Prof. Dima Kamenetsky from University of
Tasmania. Some samples and previous data obtained by Prof. Bertrand and Prof Bellieni during past
works contribute to the development of this research. A new field work to have a better control of the
regional geology as well as to get new samples will be done during the next months. One of the main
scopes of this research is related with the study of melt inclusions. The analysis will be done in the
University of Tasmania with the advice of Prof. Kamenetsky. The data provided by the implementation of
this technique for the first time in these rocks will contribute to the comprehension of the
tectonomagmatic processes involved in the origin of the cases to the study in this project.
3. Results and advances
1. Review of previous works
During the development of the PhD project a detailed review of the previous works and available data has
been made, starting from the regional studies to the more local and specific obtained data of each case of
interest. A revision and digitalization of the available material provided by Prof. Bertrand and Prof.
Bellieni has been a fundamental part of the research.
2. Analitical Procedures
Petrography
Detailed petrographic analysis of samples from Kaarta, Hodh and Hank sills show that they are mostly
afanitic rocks with hypocristaline, subofitic and intersertal texture composed mainly by clinopiroxene and
plagioclase +/-olivine; opaques possibly as magnetite, are the most common accesories. Some unusual
faneritic samples are holocrystaline with the same mineral association.
Preparation of samples
All samples have been crashed, sieved and cleaned with distilled water using the ultrasound system. A
careful handpick of fractions smaller than 4mm and 2mm was made in order to select the best preserved
fragments and remove accidental materials. A quantity between 900mg and 2gr has been picked
considering to use part of it to pre-contaminate the instrument during the pulverized process. Major
elements concentrations were previously obtained by Prof. Bertrand using XRF analyses at ENS-Lyon.
Trace elements will be measured at University of Brest. Ar-Ar analysis will be made using plagioclases
fenocrystals of faneritic samples. The selections of these crystals will be made using Franz instrument
once it will be available at the Dipartimento di Geoscienze.
3. Logistic
Planning of a field work in febrary of 2012 to the Nord Patagonian Massif
After the compilation of the available cartography, location of previous sampling and analysis of the
logistic facilities, it has been defined to focus the campaign on a E-W transect that cut mafic and felsic
Jurassic units in the Nord Patagonian Massif to sampling the Marifil, Chon Aike and Bajo Pobre
Formations. The field work will be assisted by Prof Marcelo Marquez.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
4. References
Aberhan, M., Fursich, F.T., 1996. Diversity analysis of Lower Jurassic bivalves of the Andean Basin and
the Pliensbachian–Toarcian mass extinction. Lethaia 29, 181–195
Aberhan, M. & Fursich, F.T. 2000. Mass origination versus mass extinction: the biological contribution
to the Pliensbachian–Toarcian extinction event. Journal of the Geological Society, London, 157(1), 55–
60.
Bertrand, H., 1991, The Mesozoic tholeiitic province of northwest Africa: A volcano-tectonic record of
the early opening of the Central Atlantic, in Kampunzu, A.B., and Lubala, R.T., eds., Magmatism in
extensional structural setting (the Phanerozoic African plate): New York, Springer, p. 147–191.
Bryan, S. E. and Ernst, R.E. 2008. Revised definition of Large Igneous Provinces (LIPs). Earth-Science
Reviews 86, 175 – 202.
Bryan, S.E., Riley, T.R., Jerram, D.A., Leat, P.T., Stephens, C.J., 2002. Silicic volcanism: an undervalued component of large igneous provinces and volcanic rifted margins. In: Menzies, M.A., Klemperer,
S.L., Ebinger, C.J., Baker, J. (Eds.), Magmatic Rifted Margins. Geological Society of America Special
Paper, vol. 362, pp. 99–118.
Chabou, M.C., Bertrand, H., Sebai, S. 2010. Geochemistry of the Central Atlantic Magmatic Province
(CAMP). South western Algeria, African Earth Sciences. doi: 10.1016/j.jafrearsci.2010.02.009
Féraud, G., Alric, V., Fornari, M., Bertrand, H., and Haller M., 1999, 40Ar/39Ar dating of the Jurassic
volcanic province of Patagonia: Migrating magmatism related to Gondwana break-up and subduction:
Earth and Planetary Science Letters, v. 172, p. 83–96.
Guido, D., Escayola, M., De Barrio, R., Schalamuk, I., Franz, G. 2006. La Formación Bajo Pobre
(Jurásico) en el este del Macizo del Deseado, Patagonia: Vinculación con el Grupo Bahia Laura. Revista
de la Asociación Geológica Argentina 61 (2), 187-196.
Marzoli, A., Bertrand, H., Knight, K., Cirilli, S., Buratti, N., Verati, C., Nomade, S., Renne, P.R., Youbi,
N., Martini, R., Allenbach, K., Neuwerth, R., Rapaille, C., Zaninetti, L., Bellieni, G. Synchrony of the
Central Atlantic magmatic province and the Triassic–Jurassic boundary climatic and biotic crisis,
Geology, 32 (2004) 376 – 973.
Marzoli, A., Renne, P. R., Piccirillo, E. M., Ernesto, M., Bellieni, G., De Min, A. 1999. Extensive 200Million-Year-Old Continental Flood Basalts of the Central Atlantic Magmatic Province. Science 284,
616-618
Pankhurst, R.J., and Rapela, C.R., 1995. Production of Jurassic rhyolite by anatexis of the lower crust of
Patagonia: Earth and Planetary Science Letters, 134, 23–36.
Pankhurst, R.J., Leat, P.T., Sruoga, P., Rapela, C.W., Márquez, M., Storey, B.C., and Riley, T.R., 1998.
The Chon Aike silicic igneous province of Patagonia and related rocks in Antarctica: A silicic large
igneous province: Journal of Volcanology and Geothermal Research, 81, 113–136.
Pankhurst, R.J., Riley, T.R., Fanning, C.M., and Kelley, S.R., 2000. Episodic silicic volcanism along the
proto-Paciμc margin of Patagonia and the Antarctic Peninsula: Plume and subduction inÅ~uences
associated with the break-up of Gondwana: Journal of Petrology, 41, 605–625.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
Riley, T.R. & Knight, K.B. 2001. Age of pre-break-up Gondwana magmatism. Antarctic Science, 13(2),
99–110.
Riley, T.R., Leat, P.T., Pankhurst, R.J. & Harris, C. 2001. Origins of large volume rhyolitic volcanism in
the Antarctic Peninsula and Patagonia by crustal melting. Journal of Petrology, 42(6), 1043–1065.
Storey, B.C. & Kyle, P.R. 1997. An active mantle mechanism for Gondwana breakup. South African
Journal of Geology, 100(4), 283–290.
Tanner, L.H., Lucas, S.G., and Chapman, M.G., 2004. Assessing the record and causes of Late Triassic
extinctions: Earth-Science Reviews, 65, 103–139.
Usui, Y., Tarduno, J.A., Lô, K.,, Duncan, R.A., Mason, S.N., Cottrell1, R.D., Voronov, J. 2010. The
geodynamo at ~200 Ma: paleosecular variation and paleointensity recorded by Central Atlantic Magmatic
Province mafic rocks of Mauritania. American Geophysical Union, Fall Meeting 2010, abstract #GP33B0949.
Vaughan, A. P. and Storey, B.C. 2007. A new supercontinent self-destruct mechanism: evidence from the
Late Triassic–Early Jurassic. Journal of the Geological Society, 164, 383-392.
Verati, C., Bertrand, H., Féraud, G. 2005. The farthest record of the Central Atlantic Magmatic Province
into West Africa craton: Precise 40Ar/39Ar dating and geochemistry of Taoudenni basin intrusives
(northern Mali). Earth and Planetary Science Letters 235, 391– 407.
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Scuola di Dottorato in Scienze della Terra,
Dipartimento di Geoscienze, Università degli Studi di Padova – A.A. 2010-2011
SUMMARY LAST YEAR’S ACTIVITY
Courses:
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Diamond School. Bressanone, Feb 2011.
Statistica applicata alla sperimentazione scientifica: 24hrs. Feb 15, 2011.
Corso di Statistica aplicata alla scienza. 24 hrs. Feb 15, 2011.
Introduction to the investigation of fluid inclusions 12 hrs. May 13, 2011
Corso RefWorks Biblioteca: 4 hrs. Oct 18, 2011.
Corso di Comunicazione Scientifica: 12hrs. Oct 27, 2011.
Posters:
Serrano, L., Ferrari, L., López Martínez, M., Petrone, C.M. Petrogenesis of Gorgona Island and its
implications for the origin of the Caribbean Plateau. Congreso Latinoamericano de Geología. Medellín,
Sept. 2011.
Publications:
Serrano, L. Ferrari, L., López Martínez, M., Petrone. C.M., Jaramillo, C. 2001. An integrative geologic,
geochronologic and geochemical study of Gorgona Island, Colombia: Implications for the formation of
the Caribbean Large Igneous Province. Earth and Planetary Science Letters. 309, 324–336.
Other:
 XIV Congreso Latinoamericano de Geología. Medellín, Aug 31- Sept 2, 2011.
 IGCP field trip “Geological transect through the evolution of an accretionary margin, Western
Colombia” September 3-6, 2011.
 Goldschmidt Conference. Prague, Aug 14-19, 2011.
 Humboldt fellowship for an academic stage at the University of Bonn in 2012.
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