O - Università degli Studi Roma Tre
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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