O - Università degli Studi Roma Tre

SYNCHROTRON RADIATION
IN THE EARTH SCIENCES
Simona Quartieri
Dipartimento di Scienze della Terra
Università di Messina
“The changes that have taken place in
mineralogy in the last decade can be
summarized as a shift in emphasis
towards understanding the behaviour of
minerals, that is, how they respond to
the chemical and physical changes during
the geological processes.”
A. Putnis
“.... Earth scientists should be able to explain the
few meter slip of San Andreas Fault during an
earthquake on the basis of the breaking of chemical
bonds in silicate minerals. The excitement of modern
Earth Sciences comes from this interplay of
microscopic and macroscopic phenomena.”
A. Navrotsky
In the Earth Sciences SR can be used
through two different approaches:
for applications of conventional techniques, already
widely used in mineralogical investigations, but by which we
intend, for instance, to study extremely small volumes, or
to obtain better resolution, signal-to-noise ratio and
detectability limits with respect to conventional sources;
as a unique radiation source, necessary for more
innovative techniques such as XAFS spectroscopy on trace
elements, DAFS spectroscopy, XAFS and X-ray
diffraction under extreme P and T conditions, anomalous
scattering, in-situ kinetic studies of phase transitions and
synthesis reactions, X-ray fluorescence microanalysis with
high spatial resolution and low detectability limits, X-ray
topography and tomography
Campo energetico più utilizzato:
–
4-70 KeV
Campo energetico interessante per
gli elementi leggeri:
–
1-3 KeV
Principali tecniche basate sulla LdS in uso in SdT
Diffrazione
—
a cristallo singolo
studi strutturali su cristalli estremamente piccoli
studi strutturali in condizioni estreme
—
su polveri “statica”
caratterizzazione strutturale
analisi qualitativa e quantitativa
—
su polveri “in situ”
cinetiche di sintesi
cinetiche di disidratazione
transizioni di fase in alta P e/o T
XAFS
Fluorescenza X; Spettroscopia IR
Zeolites are both very common minerals at the Earth
surface and important synthetic materials.
Much of
industrial
sorbers.
interest in zeolites comes from their
application as catalysts and selective
These properties are related to the typical structure
of zeolites, which consists of an aluminosilicate
framework with cavities and channels of various size,
which host cations and water molecules.
Terra Nova Bay Base
Na2.76K0.11Mg0.21Ca3.78Al11.20Si84.91O192 60H2O
Si/Al ratio = 7.6, the highest up to now found in natural
zeolites
new pentasil zeolite with ZSM-5 topology
MUTINAITE
Crystal dimensions:
0.03 x 0.03 x 0.01 mm3
Single-crystal synchrotron
X-ray diffraction
Crystal structure of the zeolite mutinaite, the natural analog of ZSM-5
Vezzalini et al. Zeolites, 19:323
MUTINAITE
ID11 (ESRF), detector: CCD camera
Intensities collected: 11548
Unique reflections: 5913
Reflections with I>5 σ (I): 3054
Rw: 8.86%
s.g. = Pnma
The
Thethermal
thermalbehaviour
behaviourof
of
zeolites
zeolitesis
iswidely
widelyinvestigated
investigatedbecause
becauseof
oftheir
their
potential
potentialuse
useas
asmolecular
molecularsieves
sievesand
andcatalysts.
catalysts.
The high-temperature structures of zeolites are often studied
by conventional single-crystal diffraction performed at room T
on crystals previously dehydrated in vacuum at selected
temperatures and subsequently sealed in glass capillaries.
This technique gives very detailed information on the
structure of the dehydrated phases, but not on the dynamics
and kinetics of the process.
Alternatively, in-situ synchrotron X-ray powder diffraction is
used for studying T-induced transformations and the
outstanding quality of the powder data collected in this way
can be used for full-profile Rietveld structural analysis.
Dehydration
Dehydrationdynamics
dynamicsof
ofzeolites
zeolites
using
usingsynchrotron
synchrotronX-ray
X-raypowder
powderdiffraction
diffraction
Diffrazione da polveri in LdS
• Sviluppo parallelo di stazioni sperimentali ad alta
risoluzione e di metodi di analisi degli spettri di
diffrazione a profilo completo (es. metodo Rietveld)
larga diffusione della diffrattometria per polveri
• Caratteristiche della LdS che la rendono particolarmente
adatta per la diffrattometria per polveri:
— alta brillanza in un’ampia banda spettrale
— elevata collimazione (bassa divergenza del fascio)
— possibilita’ di selezione continua della λ
• ottimo rapporto segnale/rumore
• alta risoluzione dei picchi di diffrazione (FWHM<0.01°2θ)
• ampia flessibilita’ sperimentale
Beamline GILDA CRG (ESRF)
Sample heating: hot stream gas flow
T range: 30 - 800°C, heating rate: 4-5°/min
Powder samples in quartz capillary, sample spinning
Detector: translating imaging plate
Capillary
Goniometric head
Heater
Experimental set up
lead screen
image plate
sample
heating gun
Aumento della temperatura
FASE 1
Traslazione dell’Image
Plate
FASE 2
FASE 3
Esempio
di
immagine
raccolta
su
Image
Plate
Data analysis of the powder patterns
FIT2D software
Rietveld method GSAS package
Dehydration
Dehydration of
of stellerite
stellerite
Ca
·58H O
Ca88Al
Al1616Si
Si5656OO144
144·58H22O
Arletti
Arletti et
et al.
al. (2005)
(2005) Amer.
Amer. Mineral.
Mineral.
Experimental
•
•
•
•
Powder spectra collected at Gilda beamline (ESRF)
Detector: translating image plate
Powder sample packed in a rotating capillary
T range = rT- 976 K (4K/min)
Results
•Phase transition from Fmmm to Ammm
•Statistical breaking of T-O-T bridges
in the 4-rings
and the migration of tetrahedral atoms to new “facesharing” tetrahedra, which partially occlude the
channels
Stellerite
Stilbite
Grossular schematic formula:
Ca3 Al2 Si3 O12
Example of a real garnet formula:
(Ca2.9 Mg0.06 Mn0.02 Na0.02.....) (Mg0.08 Ti0.89 Zr0.04
Al0.71 Fe3+0.28......) (Si2.33Fe3+0.62......) O12
Most minerals are solid solutions
Main crystal-chemical problems of
SOLID SOLUTIONS
• The structural relaxations associated with the element
substitution, which affect the stability of the solid
solution;
• the relationship between local structural deformation
and the deviation from the ideal behaviour of the solid
solution;
• the location of minor and trace elements, which can
explain
• a) the element partitioning between cohexisting phases,
• b) the modification of the technological properties of the
material.
• the detection of order versus random distribution of
specific elements or clustering effects.
Mineralogical applications of XAFS
• determination of cation local environment, oxidation
state, site distribution and short-range order;
•
study of the distribution of major and minor elements
in glasses, silicatic melts and other disordered
systems;
•
determination of the local environment of minor and
trace elements in complex matrices;
• high pressure and/or temperature investigations;
•
time resolved studies of transient phenomena by
dispersive EXAFS;
•
study of the static and dynamic disorder in geological
materials.
GARNETS
Garnets are a critical mineral phase
for the Earth upper mantle studies,
but are also synthetic materials of
technological interest
Most garnet solid-solutions are not
ideal, and long-range data on pyropegrossular join indicate the presence
of two structure types, with an
inversion point at 50:50
Y
Z
X
Pyrope Mg3Al2(SiO4)3
Grossular Ca3Al2(SiO4)3
Almandine Fe3Al2(SiO4)3
Spessartine Mn3Al2(SiO4)3
Andradite Ca3Fe3+2(SiO4)3
Two possible approaches in the
study of a solid solution of
geological interest:
Natural samples: already available in nature,
but complex crystal-chemistry
Synthetic samples: simple crystal-chemistry
but need for synthesis work
Incorporation of Sc in garnets
Sc is generally treated as an octahedral cation, but
in garnets it might partition itself among sites with
different coordination.
Syntheses performed in a piston cylinder apparatus,
adding 5 wt% of Sc2O3 to the nominal mixtures, so
that the incorporation site was not determined a
priori.
Synthetic join: pyrope-grossular
Mg3Al2(SiO4)3: prp,
prp60grs40,
prp20grs80,
Ca3Al2(SiO4)3: grs
Oberti, Quartieri, Dalconi, Iezzi, et al. (2005) American Mineralogist, submitted
Open questions:
Does the site preference of dopant Sc
YES
change from pyrope to grossular?
Do the intermediate compositions behave:
(i) like the prevalent end-member (i.e.,
two different structures along the join)
(ii) like the weighted sum of the end-members
(i.e., “mechanical mixing”)?
Is there any clustering yielding domains of
pyrope-like and grossular-like structures?
NO
XANES ANALYSIS
Experiments at the Sc Kedge done at the ondulator
beamline ID26 at ESFR
The spectral features of
pyrope and grossular are
very different, suggesting
different environments
The solid-solution terms are
more similar to the prevalent
end-member, but show both
behaviours
EXAFS ANALYSIS
Sc-pyrope - multiple shells fit:
1.2
Sc-O
1
Sc-Si
Sc-Mg
pyr
fit
FT
0.8
Sc
0.6
0.4
0.2
0
0
1
2
3
R (Å)
4
5
6
Pyrope:
Sc at the X site
Sc1-O = 2.17(2)
Sc2-O = 2.31(2)
Sc-grossular: crystal-chemical indications
for a complex Sc distribution
Ca3 Al2Si3O12 : pure grossular end-member
Ca2.86 Al1.83 Si2.86 O12 : the composition of the
major elements at the X, Y and Z sites in Sc-Grs
Ca2.86Sc0.14Al1.83Sc0.17Si2.86Sc0.14O12:
final crystal-chemical formula, with the total Sc
content distributed to complete the three sites.
Confirmed by SC-XRD analysis
EXAFS ANALYSIS
Sc-grossular: a much more complex situation !
Multi-shell fit based on the Sc distribution
Simulated signal based on
suggested by crystal-chemical data
Sc occurring only at the Y site
EXAFS RESULTS
Sc-grossular
Sc distributed over all garnet
matrix sites
Y
40% in Y
30% in X
30% in Z
X
Z
K-edge XAFS characterization of the structural
site of Nd, Ce and Dy in natural garnets
Example of direct crystallographic site
assignment of trace elements
in few hundreds of ppm
A COMBINED APPROACH BASED ON THE
FOLLOWING TECHNIQUES:
SIMS and electron microprobe analysis
single-crystal X-ray diffraction
high-energy XAFS spectroscopy
full multiple scattering calculations
Quartieri et al. (2002) Phys. Chem. Minerals 29, 495
Quartieri et al. (2004) Phys.Chem. Minerals 31, 162
Sample compositions
Natural melanite garnets occurring in carbonatitic rocks:
A204: (Ca2.9Mg0.06Mn0.02Na0.02) (Mg0.08Ti0.89Zr0.04Al0.28Fe3+0.71) (Si2.33Fe3+0.62)
Nd =1125 ppm,
Ce = 830 ppm,
Dy = 299 ppm
V19: (Ca2.87Mg0.024Mn0.07Na0.04) (Mg0.06Ti0.82Zr0.03Al0.20Fe3+0.89) (Si2.45Fe3+0.49)
Nd = 349 ppm,
Ce = 260 ppm
89/35: Ca3,01(Mg0.08 Mn0.03Ti0.44Zr0.01Al0.26Fe3+1.18)(Si2.70Fe3+0.29)
Nd = 176 ppm,
Ce = 159 ppm
Nd (43569 eV), Ce (40443 eV) and Dy (53789 eV) K-edge spectra
collected at 77K in fluorescence mode at the GILDA beamline
Neodimium
0.2
176 ppm
0.15
Κχ(Κ)
89/35
0.1
349 ppm
0.05
1125 ppm
V19
A204
0
Nd(OH)
3
-0.05
2
4
6
8
Κ (Å-1 )
10
12
14
Neodimium: at the X site
Dysprosium (299 ppm): at the X site
REE-O bond distances derived by XAFS,
compared to those of Ca (by single-crystal XRD)
Ionic radii : Dy = 1.03, Nd = 1.109, Ce = 1.143, Ca = 1.12 Å
Garnet
A204
rX-O(1)
(Å)
σ2X-O(1)
(Å2)
rX-O(2)
(Å)
σ2X-O(2)
(Å2)
Nd
2.38(3)
0.006
2.47(3)
0.004
Ce
2.39(4)
0.004
2.51(4)
0.004
Dy
2.31(1)
0.003
2.41(3)
0.005
Ca
2.374(1)
2.523(1)
REE-O bond distances consistent with the i.r. of the trace elements
strong crystal-chemical control on the partitioning of these elements
among melt and coexisting mineralogical phases
XAFS STUDIES OF LIGHT ELEMENTS
TECHNICAL PROBLEMS:
• In the range between 100 and 1500 eV the
number of available beamlines which allow
good XAFS measurements is limited (ELETTRA,
Stanford, Lure, Wisconsin...)
• In the low energy region the absorption by air is
an important effect, hence ultrahigh vacuum
conditions are necessary
• Detection
modes:
fluorescence
total
electron
yield,
Some HP mineral phases
Mg2SiO4 Beta-Phase
Mg2SiO4 Ringwoodite
MgSiO3 Majorite
MgSiO3 Perovskite
Cationsites
sitesin
inAl-rich
Al-richMgSiO
MgSiO33perovskite
perovskite
Cation
Andrault etetal.
al. Amer.
Amer.Mineral.
Mineral.83:1045
83:1045
Andrault
MgSiO3 perovskite can accomodate significant amount of Al3+:
Al3+ can enter only one of the
perovskite sites and the charge
balance can be maintained via
vacancies;
or Al3+ cations can substitute for
a pair of Mg on the dodecahedral
site and Si on the octahedral site,
maintaining the electroneutrality
without vacancies.
Cation sites
sites in
in Al-rich
Al-rich MgSiO
MgSiO33 perovskite
perovskite
Cation
The local structure analysis of Al-containing silicate
perovskite synthesized at 26 GPa and 1973 K in a multi-anvil
apparatus has been performed by XAFS spectra recorded at
Mg, Al and Si K-edges at SA32 beam-line of Super Aco (extrasitu study)
Comparisons were made with spectra of standard
compounds and with theoretical multiple-scattering XAFS
spectra calculated with FEFF 6.0.1 package.
Conclusions
Al appears to be partitioned between both octahedral
and dodecahedral perovskite sites.
Fe2+ and Mg show a similar structural environment, i.e.
Fe2+ enters the dodecahedra of silicate perovskite.
Extreme conditions
Indagini con LdS in condizioni estreme
Gli esperimenti in altissime P e/o T
permettono di studiare in situ le proprietà
fisiche e strutturali delle fasi che si suppone
siano presenti nel mantello inferiore e nel
nucleo della Terra.
In questi studi si cerca di definire quali
materiali abbiano le proprietà fisicostrutturali
consistenti
con
osservazioni
indipendenti di tipo geofisico e geochimico.
Diamond anvil cell
The diamond-anvil cell has emerged as the dominant and most
versatile tool for achieving ultra-HP.
It uses two diamond anvils, which exert pressure and serve as
windows on the sample. A metal gasket confines the sample and
supports the anvils.
Pressures higher than 100 GPa can be obtained only
on micro-volumes of sample and hence synchrotron
radiation is mandatory.
Birch F. (1952) “Elasticity and constitution of the
Earth’s interior.” J. Geophys. Res. 57:227-286
“Unwary readers should take warning that ordinary language
undergoes modifications to a high-pressure form when applied to the
interior of the Earth; a few examples of equivalents follows:
High-Pressure:
certain
undoubtedly
positive proof
pure iron
Ordinary meaning:
dubious
perhaps
vague suggestion
uncertain mixture of
elements
Theories and models of the Earth’s interior
are only as good as the HP data behind them.
“Ultrahigh-pressure mineralogy.” (1998)
Reviews in Mineralogy Vol 37; R.J. Hemley Ed.
“High-T and high-P crystal chemistry”
chemistry (2000)
Reviews in Mineralogy Vol 41; Hazen and Downs Eds.
Acquisition of definitive high-pressure data depends
upon three basic pre-requisites:
• reaching P-T conditions to study the stable phases
• measuring material properties in situ at high P-T
• achieving necessary accuracy
Synchrotron radiation is a perfect match for the study of
the materials under extreme P and T: problems in HP
mineralogy that were previously considered completely
unapproachable can now being addressed.
In
In situ
situ structure
structure determination
determination
of
of the
the high-P
high-P phase
phase of
of Fe
Fe33O
O44
•
•
•
•
•
•
•
•
The high-P behaviour of Fe3O4 is studied because of its geophysical
importance and interesting magnetic properties at high pressure.
Experiments performed at ESRF, beamline ID30
powdered sample
Image plate detector
monochromatic (0.4253 Å ) synchrotron X-radiation
room s.g.: Fd3m
P/T conditions:
— 34.45 GPa, 300 K
— 26.42 GPa, 723 K
— 23.96 GPa, 823 K
— 9.04 GPa, 923 K
23.96 GPa, 823K -phase structure
— s.g. Pbcm (CaMn2O4-type structure)
Fei, Frost, Mao, Prewitt, Hausermann; Amer. Mineral. (1999) 84:203-206
High-P
High-P phase
phase of
of Fe
Fe33O
O44
Magnetite structure
Part of Fe3+ cations occupy
the tetrahedral sites;
the Fe2+ and the remaining
Fe3+ occupy the octahedral
sites of the spinel structure
23.96 GPa and 823K phase
s.g. Pbcm (CaMn2O4-type structure)
The trivalent cations occupy the
octahedral sites;
the divalent
cations occupy the 8-fold sites.
This is one of the densest AB2O4
structures.
The observed two quadrupole
doublets for the high-P Fe3O4 phase
by Mossbauer data are consistent
with Fe3+ and Fe2+ occupying two
different crystallographic sites.
While magnetite is the best known
example of ferrimagnetic material,
the orthorhombic high-P phase is
not magnetically ordered on the
basis of the Mossbauer results.
Then, the magnetic transition in
corresponding
to
the
Fe3O4,
structural transformation, is best
described by the change from the
ferrimagnetic to the paramagnetic
state.
Synchrotron Infrared Microspectroscopy
∗
∗
∗
∗
Vibrational IR spectra are particularly useful to:
elucidate changes in bonding properties;
allow identification of phase transitions;
provide information on crystal symmetry;
reveal directly lattice dynamical variables important
for calculating thermodynamic properties.
In particular, synchrotron IR microspectroscopy has
emerged as an important technique to study
microscopic samples and is ideally suited to study
geological materials under extreme pressures, where
sample sizes are necessarily small.
Some applications of synchrotron
IR spectroscopy to geological materials
⇒In situ studies of phase transitions
⇒OH content in microscopic inclusions in
diamond
⇒trace hydrogen in nominally anhydrous
mantle phases
⇒hydrogen at ultrahigh pressure
⇒mineralogical composition of interplanetary
dust particles
Ruolo dell’ acqua nel mantello
L’interesse per la definizione del contenuto di idrogeno nel
mantello e nel core terrestri è dovuto alle importanti
implicazioni che esso ha su:
a) proprietà di trasporto nei minerali
b) sui processi di formazione dei fusi
c) sulla evoluzione dell’atmosfera e degli oceani
omphacite
zircone
enstatite
olivine
kyanite
garnet
Trace hydrogen
in nominally anhydrous mantle phases
The
trace
hydrous
species
can
have
a
disproportionately large influence on the chemical,
mechanical, electronic and physical properties of the
mineral.
The uptake of hydrogen in MgSiO3 perovskite, the
most abundant mineral in the planet, was examined.
Although nominally anhydrous, the synchrotron
measurements revealed that the material can
accommodate a surprising amount of hydrogen such
that a significant fraction of the water in the current
oceans could be stored in the lower mantle.
Synchrotron Infrared Absorbance Measurements
of hydrogen in MgSiO3 Perovskite
Micro-IR
measurements show
two hydroxyl
absorbance peaks at
3483 and 3423 cm-1
Meade et al. (1994) Science, 264:1558
The frequency of the absorption
peak indicates that there is a weak
hydrogen bonding in the perovskite
crystals and that the proton is
positioned between two oxygen
atoms that are spaced about 2.75 Å
apart, that is between oxygens on
adjacent octahedrons that are tilted
toward each other in the 001, 110
and -110 planes.
The estimated trace hydrogen content, when integrated
over the lower mantle volume, corresponds to a
concentration comparable to 12% of the mass of
hydrogen in the Earth’s hydrosphere.
Future studies to determine the maximum hydrogen
concentrations in perovskites synthesized over a
range of compositions are needed for assessing the
importance of nominally anhydrous phases as
repositories of the Earth’s hydrogen.
If the hydrogen content of perovskite is as
variable as that of low-pressure silicates, the
hydrogen content of the lower mantle
perovskite could exceed that of the
hydrosphere.
Synchrotron IR spectroscopy of synthetic
P21/m amphiboles at HP and HP
(Iezzi et al. 2005 a,b)
Taking into account the widespread presence of
amphiboles in subduction zone, it is important to
understand their behaviour at depths within the
Earth (HT and HP), as a function of their
compositions
How and which are
the structures of
amphiboles inside
the Earth?
Synchrotron IR spectroscopy of synthetic
P21/m amphiboles at HP
(Iezzi et al. 2005)
Na(Na0.6Li0.4Mg)Mg5Si8O22(OH)2 (sample 405) P21/m at room T
HIGH-P FTIR OH-stretching spectra
have
been
(3000-4000
cm-1)
collected at the U2A beamline, VUV
ring of the National Synchrotron
Light Source, Brookhaven NY, USA.
Optical Layout of the Infrared Synchrotron U2A Beamline
NSLS
VUV
FTIR Spectrometer
M2
The fine amphibole powder was
loaded into a symmetric diamond
anvil cells (DAC) together with some
ruby chips as pressure gauge.
A Bruker IFS 66v/S vacuum Fourier
transform interferometer, with a
Bruker IRscope II microscope
equipped with a HgCdTe type-A
detector was used.
Microscope 1
N2 purged
Bruker IRscope II
Vacuum
Bruker IFS66v/s pipe
Detector
M1
MCT Detector
Ø10mm
diamond
window
DAC
Vacuum box
Vacuum
Bench
KBr window
Visible
spectrograph
Ø10mm
diamond
window
eyepiece
FS
Laser
FS
Vacuum
Microscope
Microscope 2
CCD detector
MCT 1
Bolometer
Diamond cell
in the cryostat
Diamond lens
MCT 2
MCT Detector
Bolometer
FS
N2 purged Low-T
Far/Mid-IR MICROSCOPE
Microscope 3
notch filters
U2A beamline optical hutch
• Near IR through far IR spectral range
• Reflectivity and absorption
measurements
• Low-temperature measurements
• Mapping of the samples
• In situ Raman and fluorescence
measurements
• diamond lens
3900 3880 3860 3840 3820 3800 3780 3760 3740 3720 3700 3680 3660 3640
P
3600
3700
3800
3900
P
SAM PLE
405
3 1 .1 8 G P a
31.2
2 7 .7 3 G P a
27.7
25 G Pa b
23.2
2 3 .2 2 G P a
2 1 .7 9 G P a
21.8
18.6
1 8 .6 G p a
arbitrary units
15.1
1 5 .0 8 G P a
1 6 .4 8 G P a b
11.6
1 0 .8 1 G P a b
9.4
1 1 .5 9 G P a
9 .3 5 G P a
8
6.9
7 .9 7 G P a
6 .0 9 G P a b
4 .1 3 G P a
4.1
6 .9 4 G P a
1 .5 0 G P a b
1.4
1 .4 2 G P a
0 .6 6 G P a b
1 atm
1 a tm R o m e
3900 3880 3860 3840 3820 3800 3780 3760 3740 3720 3700 3680 3660 3640
wavwnumbers (cm-1)
The two main bands present in the
low-P spectra merge into a unique
symmetrical band at high pressure
3600
3700
3800
3900
Completely reversible
transformation
The appearance at high-P of a single IR OHsymmetric stretching band suggests the presence
of a unique O–H bond
Pnma and P21/m structures have two symmetrically
independent tetrahedral chains, determining also
two O-H bonds; C2/m amphiboles has a unique type
of tetrahedral chains and a unique O-H bond type
HP-induced phase transition
to C2/m s.g.
The same phase transition is observed at HT, at different temperatures
depending on the amphibole composition
+250°C
C2/m
-180°C
P21/m
Aim: to investigate the possible
existence of a low-T (rT-8K) phase
transition form P21/m to C2/m
both
neutron
diffraction
Results:
(presence of reflections with h+k= 2n+1)
and FTIR data confirm that the lattice
remains primitive
The OH and OD spectra obtained at 300 and
20 K are very similar, in agreement with the
fact that both samples have the same
symmetry
Angle-dispersive XRD spectra (SPring-8)
Pbnm perovskite
Cmcm post- perovskite
Layer-stacking
structure
CORE
iron
Since iron is the dominant component of Earth’s core, information on
its behavior at high-T and high-P is necessary to understand the
structure of the core, the chemical and dynamical coupling between
core and mantle, and Earth’s magnetic field.
FCC
HCP
BCC
The orthorhombic
orthorhombic structure
structure of
of iron:
iron:
The
an in
in situ
situ study
study at
at high-T
high-T and
and high-P
high-P
an
Andraultet
etal.,
al.,Amer
AmerMineral.
Mineral.(2000)
(2000)85:364
85:364
Andrault
•
•
In situ angle-dispersive X-ray diffraction study in a
laser-heated, diamond-anvil cell up to 2375 K and
between 30 and 100 GPa.
RESULTS: at high-T and P iron undergoes a phase
transformation to an orthorhombic lattice with s.g.
Pbcm
β-Fe
Quenched
phase
γ-Fe
β-Fe
ε-Fe
ε-Fe
X-ray Fluorescence Microanalysis
La microsonda a raggi X da luce di sincrotrone
consente di coniugare la diffusissima tecnica di
analisi per fluorescenza-X, divenuta tra le piu’
comuni tecniche di quantificazione chimica
elementare nelle scienze geologiche, con la
possibilita’ di mantenere un’elevata risoluzione
spaziale nel volume di campione analizzato, tipica
della microsonda elettronica.
X-ray Fluorescence Microanalysis
VANTAGGI:
— e’ un metodo non distruttivo
— ha un limite di rivelabilità inferiore a 0.1-5 ppm per gli elementi con
Z maggiore di quello del K, ed è molto inferiore a quello della
microsonda elettronica in virtù dell’elevatissimo rapporto
segnale/rumore
— ha una risoluzione spaziale dell’ordine di 10µm
ESEMPI DI APPLICAZIONI:
— analisi dei componenti in traccia in minerali, anche su piccoli
volumi (<1ng) quali microparticelle, micrometeoriti e inclusioni
fluide
— valutazione delle distribuzioni spaziali degli elementi a scala
micrometrica (es. distribuzione di impurezze, zonature chimiche,
profili di diffusione)
X-ray Fluorescence Microanalysis
+
micro-XANES
Un’ interessante combinazione sperimentale
è
rappresentata dall’utilizzo combinato di microfluorescenza a raggi X in LdS e micro-XANES, per
esempio per ricavare mappe bidimensionali dei
gradienti di ossidazione sul campione o per vedere la
variazione spaziale della concentrazione degli
elementi di interesse nel composto in funzione dello
stato di ossidazione.
Analysis of a 100 µm zircon, in which a pure quartz
inclusion, approximately 7 µm x 3.5 µm in size, is
identified and mapped with sub-micrometer resolution,
at the SiL2,3 edge.
(Gilbert et al. (2003) Amer. Mineral.)
Iron in Martian Meteorites: Microanalyses of
Fe3+/ΣFe by Synchrotron MicroXANES
as Indicators of Variable Oxygen Fugacity
J.S. Delaney, S.R. Sutton and M.D. Dyar
The results for the Martian suite are consistent with
the formation of these rocks in a very “terrestrial”,
i.e. oxidized, setting: the range of Fe3+/ΣFe seen is
comparable to that found in many mantle and
eruptive rocks on Earth.
Martian samples are much more oxidized than
lunar, basaltic achondrite and most chondritic
meteorites.
Chemical Analysis of Impact Material on a Dust
Collector Flown on the MIR Space Station
G. J. Flynn (SUNY-Plattsburgh) S. R. Sutton (The University of Chicago)
F. Horz (NASA Johnson Space Center)
Sub-micrometer scale minor element mapping
in interplanetary dust particle:
a test for stratospheric contamination
Flynn et al. Lunar and Planetary Science XXXV (2004)
S
Ca
Fe
Ni
Cr
Zn
Applications of
Synchrotron Radiation in
Low-Temperature Geochemistry
and Environmental Science
Review in Mineralogy and Geochemistry, Vol. 49 (2002)
Editors: P. Fenter, M. Rivers, N. Sturchio, S. Sutton.
Changes in the <X-O> bond distances for different
X-site cations in different garnet compositions
The
observed
different
show
the = Euler
structural
Squares
= Quartieri
et al (PCM slopes
2002; PCM
2004);that
diamonds
and
relaxation
around
the= Quartieri
dopant strongly
on the overall
Bruce (1965);
triangles
et al (PCM depends
1999).
garnet composition and that the X site has a different
compliance for solid solution in the various garnet compositions
Tektites are naturally occurring glasses which are found, after
an impact event, scattered over wide areas called strewn
fields.
Tektites are virtually crystal-free so that it is not possible to reconstruct their
T-P history directly from phase stability considerations.
However, glass structural properties, such as coordination number of its
constituting elements, depend on their composition and P-T history.
Pressure tends to increase the mean coordination number of the cations
present which, in turn, directly affects glass properties such as density and
viscosity. Thus, the knowledge of the glass structure of tektites could help to
constrain the P-T conditions of formation.
EXPERIMENTALS XANES spectra were collected at the beamline SB03-3 of the SPEAR storage ring
(SSRL, Stanford, U.S.A.) operating at 3 GeV with ring current ranging from 65 to 90 mA. Radiation was
monochromatized by two YB66 (400) crystals (2d = 5.88 Å)
Tektite spectra clearly resemble the spectrum of albite. Both display a
single and narrow peak A; the energies of the absorption edge are similar,
as are the energy positions of the features A, B and the large peak at the
high energy side (peak C of tektite spectra and peak D and E of the albite
spectrum). These data indicate that Al is fourfold-coordinated in all the six
tektites studied.
GARNET STRUCTURE
X site: [4+4]-fold coordination
[8]Mg =0.89 Å
prp: 2.270 Å, S<U [8]
Ca = 1.12 Å
grs: 2.405 Å, U<S
Y site: [6]-fold coordination
prp: 1.887 Å, S<U
grs: 1.925 Å, U<S
[6]Al
= 0.535 Å
Z site: [4]-fold coordination
prp: 1.633 Å, S<U
grs: 1.640 Å, S<U
[4]Si
= 0.26 Å
TWO STRUCTURES, RELAXATION
LONG-RANGE EVIDENCES FOR NON-IDEALITY
OF GARNET SOLID-SOLUTIONS
prp
grs adr
a vs. spigoli X
3,00
2,95
spigoli X (Å)
2,90
2,85
U(X)
2,80
rosso gar +Sc
blu gar + Ti
verde gar + Zr
+ rosso gar Na+Nb
2,75
S(X)
2,70
grs adr
a vs. delta X-O
0.175
2,65
rosso gar +Sc
blu gar + Ti
verde gar + Zr
+ rosso gar Na+Nb
0.170
0.165
0.160
0.155
0.150
0.145
0.140
0.135
a
Unit-cell edge (Å)
prp
grs adr
Unit-cell edge (Å)
prp
grs adr
a vs. S(Y)-U(Y)
a vs. rotaz T
rosso gar +Sc
blu gar + Ti
verde gar + Zr
+ rosso gar Na+Nb
0.11
28.5
0.10
27.5
0.07
0.06
26.5
26.0
25.5
25.0
rosso gar +Sc
24.5 blu gar + Ti
verde gar + Zr
24.0 + rosso gar Na+Nb
differenza spigolo Y (Å)
0.09
0.08
S(Y) - U(Y)
28.0
27.0
rotaz. T
Z rotation
12.20
12.15
12.10
12.05
12.00
11.95
11.90
11.85
a
11.80
11.75
11.70
11.65
11.60
11.55
11.50
11.45
11.40
12,20
12,15
12,10
12,05
12,00
11,95
11,90
11,85
11,80
11,75
11,70
11,65
11,60
11,55
11,50
11,45
11,40
(X1-O) - (X2-O)
3,05
delta X-O (Å)
prp
0.05
0.04
0.03
0.02
0.01
0.00
-0.01
-0.02
-0.03
-0.04
-0.05
-0.06
-0.07
-0.08
12.20
12.15
Crystallographic Data Base at
CNR, Istituto di Geoscienze e Georisorse, Pavia (I)
12.10
a
12.05
12.00
11.95
11.90
11.85
11.80
11.75
11.70
11.65
11.60
11.55
11.50
11.45
11.40
12.20
12.15
12.10
12.05
12.00
11.95
11.90
11.85
11.80
11.75
11.70
11.65
11.60
11.55
11.50
11.45
11.40
a
Mineral descriptions based on
averaged partial occupancies and
random distributions of different
species often fail spectacularly
Information on the local environment
and properties has proven to be crucial