a Scuola Nazionale Luce di Sincrotrone S. Margherita di...

SYNCHROTRON RADIATION IN THE EARTH SCIENCES

VIIa Scuola Nazionale Luce di Sincrotrone S. Margherita di Pula, Settembre 2003

Simona QuartieriDipartimento 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 behaviourof minerals, that is, how they respond to the chemical and physical changes during the geological processes.”

A. Putnis

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

F Vantaggi sincrotrone/tubo:– risoluzione– rapporto segnale/rumore– limiti di rivelabilita`

F Campo energetico più utilizzato:

– 4-70 KeV

F Campo energetico interessante per gli elementi leggeri:

– 1-3 KeV

Principali tecniche basate sulla Principali tecniche basate sulla LdSLdS in uso in in uso in SdTSdTF Diffrazione

— a cristallo singolou studi strutturali su cristalli estremamente piccoliu studi strutturali in condizioni estreme

F XAFSF Spettrosc. fluorescenza X; Spettrosc. IR

— su polveri “ statica”u caratterizzazione strutturale

u analisi qualitativa e quantitativa— su polveri “ in situ”

u cinetiche di sintesi

u cinetiche di disidratazione

u alta P e/o T

— scattering anomalo

Zeolites are both very common minerals at the Earth surface and important synthetic materials.

Much of interest in zeolites comes from their industrial application as catalysts and selective sorbers.

These properties are related to the typical structure ofzeolites, which consists of an aluminosilicate framework with cavities and channels of various size, which host cations and water molecules.

Terra Nova Bay Base

F Na2.76K0.11Mg0.21Ca3.78Al11.20Si84.91O192 60H2O

F Si/Al ratio = 7.6, the highest up to now found in natural zeolites

F new pentasil zeolite with ZSM-5 topology

Crystal structure of the zeolite mutinaite, the natural analog of ZSM-5

Vezzalini et al. (1997) Zeolites, 19:323

Crystal dimensions: 0.03 x 0.03 x 0.01 mm3

Single-crystal synchrotron X-ray diffraction

MUTINAITEID11 (ESRF), detector: CCD camera

Intensities collected: 11548

Unique reflections: 5913

Reflections with I>5 σσσσ (I): 3054

Rw: 8.86%

s.g. = Pnma

Ł The high-temperature structures of zeolites are often studied by conventional single-crystal diffractionperformed at room T on crystals previously dehydratedin 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 theprocess.

Ł Alternatively, in-situ synchrotron X-ray powder diffraction is used for studying T-induced transformations and the outstanding quality of thepowder data collected in this way can be used for full-profile Rietveld structural analysis.

The thermal behaviour of zeolites is widely investigated because of their potential use as molecular sieves and catalysts.

The thermal behaviour of zeolites is widely investigated because of their potential use as molecular sieves and catalysts.

Dehydration dynamics of zeolites using synchrotron X-ray powder diffraction

Dehydration dynamics of zeolites using synchrotron X-ray powder diffraction

Diffrazione da polveri in Diffrazione da polveri in LdSLdS• 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

• ottimo rapporto segnale/rumore• alta risoluzione dei picchi di diffrazione (FWHM<0.01°2θθθθ)• ampia flessibilita’ sperimentale

• 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

Beamline GILDA CRG (ESRF)

Sample heating: hot stream gas flowT range: 30 - 800°C, Heating rate: 4.7°/minPowder samples in quartz capillary, sample spinning Detector: translating imaging plate

Capillary

HeaterGoniometric head

Experimental set up

heating gun

sample

lead screen

image plate

Esempio di

immagine raccolta

suImage Plate

Aumento della temperatura Traslazione dell’ImagePlate

FASE 1 FASE 2

FASE 3

Data analysis of the powder patterns

FIT2D softwareRietveld method GSAS package

Dehydration dynamics of stilbite using synchrotron X-ray powder diffraction.

Cruciani et al. (1997) Amer. Mineral. 82:729-739



• Powder spectra collected at beamline X7B at NSLS,Brookhaven; λ = 1.488 λ = 1.488 λ = 1.488 λ = 1.488 Å

• Curved position-sensitive detector covering a range of 120° 2θθθθ

• Powder sample packed in a 0.3 mm diameter capillary• Debye-Scherrer geometry• T range = 315-723 K; different heating rates• Two isothermal experiments at 423 and 450 K

Experimental





• At about 420 K a first-order transition occurs changing thesymmetry from the monoclinic F2/m to an orthorhombic Amma phase, whose framework is collapsible and show a large cell-volume contraction with T.

• The cell contraction is related to the process of T-O-T bond breaking and leads to a high-T stilbite phase (stilbite B) with thesame Amma s.g. and a collapsed structure similar to that of thedescribed B phase of stellerite and barrerite.

• The dynamics of bond breaking is related to the shift of the Cacations in the channels to achieve optimal coordination after therelease of the H2O molecules.

Results

Grossular schematic formula:

Ca3Al2 Si3O12

(Ca2.9 Mg0.06 Mn0.02 Na0.02.....) (Mg0.08 Ti0.89 Zr0.04

Al0.28 Fe3+0.71......) (Si2.33Fe3+

0.62......) O12

Example of a real formula:

Most mineralsMost mineralsMost minerals areareare solid solutionssolid solutionssolid solutions

Main crystalMain crystal--chemical problemschemical problems of of SOLID SOLUTIONSSOLID SOLUTIONS

• The structural relaxations associated with the element substitution, which affect the stability of the solid solution;

• the relationship between local structural deformationand the deviation from the ideal behaviour of the solid solution;

• the location of minor and trace elements, which canexplain• a) the element partitioning between cohexisting phases,• b) the modification of the technological properties of the

material.

• the detection of order versus random distribution ofspecific elements or clustering effects.

Mineralogical applicationsMineralogical applications of XAFSof XAFS

• determination of cation local environment, oxidationstate, site distribution and short-range order;

• study of the distribution of major and minor elementsin glasses, silicatic melts and other disordered systems;

• determination of the local environment of minor andtrace elements in complex matrices;

• high pressure and/or temperature investigations;

• time resolved studies of transient phenomena bydispersive EXAFS;

• study of the static and dynamic disorder in geological materials.

XAFS characterization of the structural site of Yb in garnets

Quartieri et al. Phys. Chem. Minerals (1999a,b)


Quartieri et al. Phys. Chem. Minerals (1999a,b)

•• EXAMPLE OF SITE LOCATION OF MINOR AND TRACE EXAMPLE OF SITE LOCATION OF MINOR AND TRACE ELEMENTS IN MINERALSELEMENTS IN MINERALS

•• COMBINED APPROACH BASED ON THE FOLLOWING COMBINED APPROACH BASED ON THE FOLLOWING TECHNIQUES:TECHNIQUES:

u Synthesis and electron microprobe analysis u X-ray powder diffraction and Rietveld refinementu XAFS spectroscopy (L-edge)u Full multiple scattering calculations

Electron micropobe analysis:

Grossular: [ Ca2.94(4)Yb0.03(1)]Al1.97(2)Si3.02(2)O12 ]

Pyrope: [ Mg2.92(4)Yb0.03(1)]Al2.02(6)Si3.00(4)O12 ]

Rietveld refinement of cell parameter a:

Pure pyrope at 23°C: 11.4555(1)Å

Yb-Py 11.4617(1)

Pure grossular at 23°C 11.8516(1)

Yb-Gr 11.8504(2)

XAFS experiments:

The Yb LI- and LIII-edge XAFS spectra were collected influorescence mode at different temperatures at the GILDA beamline (ESRF, Grenoble).



Conclusions• Both experimental and theoretical results indicate that Yb at low

concentration levels enters the garnet structure in thedodecahedral X site.

• The low DW factors and the values of the FWHM in the RDF indicate that the local Yb3+ environment has a regularity comparable with that of Fe in the end-member almandine andsuggest that Yb at about 1 wt% systematically enters lattice sitesand not extended structural defects or interstitial sites.

• The local geometry around Yb3+ is significantly different from thatof Mg and Ca in pyrope and grossular. These data demonstrate that strong structural relaxation effects occur around minor Yb3+

cations in both garnet structures.

K-edge XAFS characterizationof the structural site of Nd and Ce

in natural garnets.Quartieri et al. 2002 PCM

K-edge XAFS characterizationof the structural site of Nd and Ce

in natural garnets .Quartieri et al. 2002 PCM

First example of direct investigationon the site location and local environment

of trace-level REE in natural garnetsby means of

HIGH-ENERGY XAFS SPECTROSCOPY

Garnet compositionThe samples are melanite garnets occurring in carbonatitic rocks. A204 occurs in an alkaline pegmatite from Afrikanda (Kola-Karelia), V19 in a jiolite from Vuorijarvi (Kola-Karelia) and 89/35 in a jiolite from Potash Sulfur Spring (Arkansas)

A204

(Ca2.9Mg0.06Mn0.02Na0.02) (Mg0.08Ti0.89Zr0.04Al0.28Fe3+0.71) (Si2.33Fe3+

0.62)

Nd =1125 ppm, Ce = 830 ppm

V19

(Ca2.87Mg0.024Mn0.07Na0.04) (Mg0.06Ti0.82Zr0.03Al0.20Fe3+0.89) (Si2.45Fe3+

0.49)

Nd = 349 ppm, Ce = 260 ppm

89/35Ca3.01(Mg0.08 Mn0.03Ti0.44Zr0.01Al0.26Fe3+

1.18)(Si2.70Fe3+0.29)

Nd = 176 ppm, Ce = 159 ppm

The Nd K-edge (43569 eV) and Ce K-edge (40443 eV) spectra were collected at 77K in transmission mode on the reference compound and in fluorescence mode on the natural garnets

-0.05

0

0.05

0.1

0.15

0.2

2 4 6 8 10 12 14

Κχ(

Κ)

Κ ( )

Nd(OH)3

A204

V19

89/35

Å-1

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

2 4 6 8 10 12 14Κ

χ(Κ

)Κ

χ(Κ

)Κ

χ(Κ

)Κ

χ(Κ

)

CeO2

A204

K ( ) Å-1

A204 garnet (Nd)

V19 garnet

k0 3 6 9 12

-0.12

-0.08

-0.04

0

0.04

0.08

0.12A204_Ndfit

k0 3 6 9 12

-0.12

-0.08

-0.04

0

0.04

0.08

0.12

A204_Cefit

A204 garnet (Ce)

k0 3 6 9 12

-0.12

-0.08

-0.04

0

0.04

0.08

0.12

8935fit

8935 garnet

k0 3 6 9 12

-0.12

-0.08

-0.04

0

0.04

0.08

0.12V19_Ndfit

Results of the Nd and Ce K-edge XAFS analysis.REE-O bond distances are compared to those of Ca,

(the dominant cation in the X-site of these natural garnets)obtained by single-crystal X-ray diffraction

The coordination numbers of the two nearest oxygen shells were kept fixed tothe crystallographic value of 4.

Garnet Rx-O(1) σσσσ2x-O(1) Rx-O(2) σσσσ2x-O(2)(Å) (Å2) (Å) (Å2)

Nd 2.38(3) 0.006 2.47(3) 0.004A204 Ce 2.39(4) 0.004 2.51(4) 0.004

Ca 2.378(1) 2.515(1)

Nd 2.38(1) 0.004 2.49(2) 0.004V19 Ca 2.369(1) 2.519(1)

Nd 2.35(3) 0.004 2.47(3) 0.00489/35 Ca 2.359(1) 2.503(1)

0 50 100 150

1,0

Ab-initio Y-site (Al)

Experimental

Nor

mal

ised

Abs

orpt

ion

E - E0 (eV)

0 50 100 150

0,00

0,01

0,02

0,03

0,04

0,05

0,06

0,07

0 50 100 1500,8

1,0

Ab-initio X-site (Ca)

Experimental

Nor

mal

ised

Ab

E - E0 (e

0 50 100 150

0,00

0,01

0,02

0,03

0,04

0,05

XANES Full multiple scattering calculations at Nd K-edge

Conclusions

• USE OF FLUORESCENCE XAFS AT HIGH ENERGY IS OF GREAT INTEREST FOR EARTH SCIENCES. THIS CORRESPONDS TO ONE OF THE AREAS OF DEVELOPMENT OF XAFS AT THIRD GENERATION SOURCES

• Both experimental and theoretical results indicate that Nd and Ceat trace levels enter the garnet structure in the dodecahedral X site and not in extended structural defects or interstitial sites. This conclusion is completely in agreement with the XAFS results obtained at Yb L I ,I I I edges for a synthetic Yb-bearing grossular.

• The REE-O bond distances determined by XAFS are consistent with the ionic radius of the trace element, confirming the strong crystallochemical control on the partitioning of these elements among the magma and the cohexisting mineralogical phases

K-edge XAFS characterization of the structural site of Nd and Ce

in natural garnets.Quartieri et al. Phys. Chem. Minerals (2002)

K-edge XAFS characterization of the structural site of Nd and Ce

in natural garnets.Quartieri et al. Phys. Chem. Minerals (2002)

XAFS STUDIES OF LIGHT ELEMENTSXAFS STUDIES OF LIGHT ELEMENTSXAFS STUDIES OF LIGHT ELEMENTS

TECHNICAL PROBLEMS:

• In the range between 100 and 1500 eV thenumber 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: total electron yield, fluorescence

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 cationspresent 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.

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 albitespectrum). These data indicate that Al is fourfold-coordinated in all the six tektites studied.

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 wasmonochromatized by two YB66 (400) crystals (2d = 5.88 Å)

Mg2SiO4 Ringwoodite

Mg2SiO4 Beta-Phase MgSiO3 Major ite

MgSiO3 Perovskite

Some HP Some HP Some HP mineral phasesmineral phasesmineral phases

Cation sites in Al-rich MgSiO3 perovskiteAndrault, Neuville, Flank, Wang (1998) Amer. Mineral. 83:1045-1053

Cation sites in Al-rich MgSiO3 perovskiteAndrault, Neuville, Flank, Wang (1998) Amer. Mineral. 83:1045-1053

MgSiO3 perovskite can acco-modate significant amount of Al3+:

˚ Al3+ can enter only one of theperovskite sites (more likely theoctahedral site) and the charge balance can be maintained viavacancies;

¸ or Al3+ cations can substitute fora pair of Mg on the dodecahedralsite and Si on the octahedral site,maintaining the electroneutrality without vacancies.

Cation sites in Al-r ich MgSiO3 perovskiteAndrault, Neuville, Flank, Wang. Amer. Mineral. (1998) 83:1045-1053

Cation sites in Al-r ich MgSiO3 perovskiteAndrault, Neuville, Flank, Wang. Amer. Mineral. (1998) 83:1045-1053

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.

Comparisons were made with spectra of standardcompounds and with theoretical multiple-scattering XAFSspectra calculated with FEFF 6.0.1 package.

Conclusions ¶ Al appears to be partitioned between both octahedraland dodecahedral perovskite sites.¸ Fe2+ and Mg show e similar structural environment, i.e. Fe2+ enters the dodecahedra of silicate perovskite.

The following criteria are assumed as sufficient for two spectra to be considered distinguishable:

1) there must be a peak of 5 data points or more that does not appear in one spectrum, or is shifted by > 1.0 eV

2) the two spectra contain a peak at the same energy but which differ in normalised intensity, or width, by > 50%

Analysis of a 100 µµµµm zircon, in which a pure quartz inclusion, approximately 7 µµµµm x 3.5 µµµµm in size, is identified and mapped with sub-micrometer resolution, at the SiL2,3 edge. (Gilbert et al. (2003) Amer. Mineral.)

Conclusions

By combining the XANES spectra at SiK, SiL2,3 and OK edges and their first energy derivative collected for 11 silicate and aluminosilicate minerals and two glasses, every mineral studied is distinguishable.

This background work, combined with X-ray PhotoElectron Emission spectroMicroscopy(X-PEEM), allows non-destructive in situ, sub-micrometric X-ray analysis of geological materials and silicate inclusions.

Indagini con Indagini con LdSLdS in condizioni estremein condizioni estreme

• Gli esperimenti in altissime P e/o T permettono di studiare in situ le proprieta’ 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 proprieta’fisico-strutturali consistenti con osservazioni indi-pendenti di tipo geofisico e geochimico.

• Pressioni superiori ai 100 GPa possono essere raggiunte solo su piccolissimi volumi di materiale, e quindi l’utilizzo della LdS e’ assolutamente necessario.

Diamond anvil cellDiamond anvil cellDiamond 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.

BirchBirch F. (1952) “F. (1952) “ ElasticityElasticity andand constitutionconstitution of theof theEarth’sEarth’s interior.” J.interior.” J. GeophysGeophys. Res. 57:227. Res. 57:227--286 286

High-Pressure: Ordinary meaning: certain dubious undoubtedly perhaps positive proof vague suggestion pure iron uncertain mixture of

elements

TheoriesTheoriesTheories andandand modelsmodelsmodels of theof theof the Earth’sEarth’sEarth’s interior interior interior areareare only as good asonly as good asonly as good as the HP data behindthe HP data behindthe HP data behind themthemthem...

“ 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:

““ UltrahighUltrahigh--pressure mineralogypressure mineralogy.”.” (1998) Reviews in Mineralogy Vol 37; R.J. Hemley Ed. “ HighHigh--T and highT and high--P P crystal chemistrycrystal 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 studyof the materials under extreme P and T: problems in HP mineralogy that were previously considered completely unapproachable can now being addressed.

In situ structure determination of the high-P phase of Fe3O4

Fei, Frost, Mao, Prewitt, Hausermann; Amer. Mineral. (1999) 84:203-206

In situ structure determination of the high-P phase of Fe3O4

Fei, Frost, Mao, Prewitt, Hausermann; Amer. Mineral. (1999) 84:203-206

F The high-P behaviour of Fe3O4 is studied because of its geophysical importance and interesting magnetic properties at high pressure.

F Experiments performed at ESRF, beamline ID30F powdered sampleF Image plate detectorF monochromatic (0.4253 Å ) synchrotron X-radiationF room s.g.: Fd3mF P/T conditions:

— 34.45 GPa, 300 K— 26.42 GPa, 723 K— 23.96 GPa, 823 K— 9.04 GPa, 923 K

F 23.96 GPa, 823K -phase structure— s.g. Pbcm (CaMn2O4-type structure)

High-P phase of Fe3O4 High-P phase of Fe3O4

Magnetite structure Part of Fe3+ cations occupy

the tetrahedral sites; the Fe2+

and the remaining Fe3+

occupy the octahedral sitesof the spinel structure

23.96 GPa and 823K phases.g. Pbcm (CaMn2O4-type structure)

The trivalent cations occupy theoctahedral sites; the divalent cations occupy the 8-fold sites.This is one of the densest AB2O4structures.

YThe observed two quadrupole doublets for the high-P Fe3O4 phase by Mossbauer data are consistent with Fe3+ and Fe2+ occupying two different crystallographic sites.

YWhile magnetite is the best known example of ferrimagnetic material, the orthorhombic high-P phase is not magnetically ordered on thebasis of the Mossbauer results.

YThen, the magnetic transition in Fe3O4, corresponding with thestructural transformation, is bestdescribed by the change from theferrimagnetic to the paramagneticstate.

Synchrotron Infrared MicrospectroscopySynchrotron 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.

SomeSome applicationsapplications ofof synchrotron synchrotron IRIR spectroscopy to geological materialsspectroscopy to geological materials

�trace hydrogen in nominally anhydrous mantle phases

�OH content in microscopic inclusions indiamond

�mineralogical composition of interplanetary dust particles

�hydrogen at ultrahigh pressure

garnetkyanite

olivine

enstatite

zircone

omphacite

Trace hydrogen Trace hydrogen inin nominally anhydrous mantle phasesnominally anhydrous mantle phases

The trace hydrous species can have a disproportionately large influence on the chemical, mechanical, electronic andphysical properties of the mineral.

They also may reflect the water activity in the environmentof formation, or hold a record of processes undergone by the mineral.

The uptake of hydrogen in MgSiO3 perovskite, the most abundant mineral in the planet, was examined. Although nominally anydrous, the synchrotron measurements revealed that the material can accomodate a surprising amount of hydrogen such that a significant fraction of the water in the current oceans could be stored in the lower mantle.

SynchrotronSynchrotron Infrared Absorbance Measurements of Infrared Absorbance Measurements of Hydrogen in MgSiOHydrogen in MgSiO33 PerovskitePerovskite

C. Meade, J. C. Meade, J. ReffnerReffner, E. Ito (1994) Science, 264:1558, E. Ito (1994) Science, 264:1558--15601560

Micro-IRmeasurements showtwo hydroxyl absorbance peaks at 3483 and 3423 cm-1

The frequency of the absorptionpeak 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 onadjacent octahedrons that are tilted toward each other in the 001, 110 and -110 planes.

The estimated trace hydrogen content, when integratedover the lower mantle volume, corresponds to aconcentration comparable to 12% of the mass ofhydrogen in the Earth’s hydrosphere.

FCC

HCP

BCC

Since iron is the dominant component of Earth’s core, information onits behavior at high-T and high-P is necessary to understand thestructure of the core, the chemical and dynamical coupling betweencore and mantle, and Earth’s magnetic field.

CORECORECORE ironironiron

The orthorhombic structure of iron: an in situ study at high-T and high-P

Andrault et al., Amer Mineral. (2000) 85:364

The orthorhombic structure of iron: an in situ study at high-T and high-P

Andrault et al., Amer Mineral. (2000) 85:364

• In situ angle-dispersive X-ray diffraction study in a laser-heated, diamond-anvil cell up to 2375 K andbetween 30 and 100 GPa.

• RESULTS: at high-T and P iron undergoes a phase transformation to an orthorhombic lattice with s.g. Pbcm

Quenched phase

ββββ-Fe

εεεε-Fe

εεεε-Fe

ββββ-Fe

γγγγ-Fe

ββββ-Fe Orthorhombic cell: a=2.346, b=4.144, c=4.063

XX--ray Fluorescence Microanalysisray Fluorescence Microanalysis

La microsonda a raggi X da luce di sincrotrone consente di coniugare la diffusissima tecnica di analisi per fluorescenza-X, divenuta tra lepiu’ 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.

XX--ray Fluorescence Microanalysisray Fluorescence Microanalysis

VANTAGGI:—e’ un metodo non distruttivo

—ha un limite di rivelabilita’ inferiore a 0.1-5 ppm per gli elementi con Z maggiore di quello del K, ed e’ molto inferiore a quello dellamicrosonda elettronica in virtu’ dell’elevatissimo rapporto segnale/rumore

—ha una risoluzione spaziale dell’ordine di 10µµµµm

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)

XX--ray Fluorescence Microanalysisray Fluorescence Microanalysis++

micromicro--XANESXANES

Un’ interessante combinazione sperimentale e’ rappresentata dall’utilizzo combinato di micro-fluorescenza a raggi X in LdS e micro-XANES, per esempio per avere 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 µµµµm zircon, in which a pure quartz inclusion, approximately 7 µµµµm x 3.5 µµµµm 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 generally consistent with the formation of these rocks in a very “ terrestrial” , i.e. oxidized, setting: the range of Fe3+/ΣΣΣΣFe 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 (NASAJohnson Space Center)

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