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Valence determinations and oxybarometry on FIB‐sectioned olivine and pyroxene using correlated Ti, V, and Cr micro‐XAFS spectroscopy: Evaluation of ion‐milling effects and application to Antarctic micrometeorite grains

Year: 2020
Type: article
DOI: 10.1111/maps.13603
Authors: S. R. Sutton, A. J. Brearley, E. DobricĂ, A. Lanzirotti, M. Newville, O. Tschauner
Language: English
Subfield: Radiation
Open Access status: closed
Award: THE OXIDATION STATE AND MINERALOGY OF EXTRATERRESTRIAL MATERIALS ARE CRUCIAL PROPERTIES FOR CONSTRAINING THE CONDITIONS UNDER WHICH PRIMITIVE SOLAR SYSTEM OBJECTS ORIGINATED AND EVOLVED. SYNCHROTRON-BASED X-RAY ABSORPTION FINE STRUCTURE (XAFS) TECHNIQUES HAVE PROVEN TO BE VALUABLE IN DEFINING OXIDATION STATE WHERE THE VALENCES OF MULTIVALENT ELEMENTS (TI V CR AND FE) ARE USED AS PROXIES. COUPLED WITH HIGH-SPEED SYNCHROTRON X-RAY MICRODIFFRACTION (MICRO-XRD) MAPPING NEW OPPORTUNITIES ARE AVAILABLE TO CORRELATE CHEMICAL STATE AND MINERALOGY (INCLUDING ORIENTATION AND STRAIN) AT MICROMETER SCALES. THESE METHODS HAVE BEEN APPLIED TO RELATIVELY LARGE (>TENS OF M) MINERAL GRAINS AND GLASSES IN THIN SECTIONS. HOWEVER SAMPLES RETURNED BY NASA SPACECRAFT ARE TYPICALLY CHARACTERIZED BY MINERAL GRAINS OF MUCH SMALLER DIMENSIONS (<10 M). THE PROPOSED WORK WILL DEVELOP AND TEST TECHNIQUES FOR APPLYING MICRO-XAFS AND MICRO XRD METHODS TO PICOGRAM MINERAL GRAINS FOCUSING ON FIB METHODS FOR PRODUCING MONO-MINERALIC SAMPLES. TOMOGRAPHIC TECHNIQUES WILL BE DEVELOPED TO ALLOW THE MINERALOGIC INFORMATION TO BE VISUALIZED IN 3D PROVIDING THE SPATIAL DISTRIBUTION OF A SELECTED CRYSTALLINE OR AMORPHOUS PHASE INSIDE THESE ISOLATED PICOGRAM SAMPLES IDEALLY WITHIN SEALED CONTAINERS AND CAPTURE MEDIA WITHOUT THE NEED FOR EXTRACTION. THE METHODS WILL BE APPLIED TO STARDUST GRAINS FROM COMET WILD-2 AND HAYABUSA1 GRAINS FROM ASTEROID ITOKAWA AND WILL BE APPLICABLE TO RETURNED REGOLITH SAMPLES FROM THE HAYABUSA-2 AND OSIRIS-REX MISSIONS. WE WILL DEVELOP AND TEST MICRO-XAFS AND XRD TECHNIQUES APPLICABLE TO PICOGRAM EXTRATERRESTRIAL SAMPLES USING THE GSECARS X-RAY MICROPROBE AT THE ADVANCED PHOTON SOURCE. FOR FOCUS OF MICRO-XAFS STUDIES WILL BE USING FIB METHODS TO PRODUCE MONOMINERALIC SAMPLES. DEVELOPMENT WILL BE ACCOMPLISHED USING VALENCE STATE STANDARDS (BOTH MINERALS AND GLASSES). FIB SECTIONS WILL ALSO BE MADE OF LARGER MINERAL GRAINS FROM METEORITIC THIN SECTIONS WHERE XAFS SPECTRA FOR THE FIB SAMPLE AND PARENT GRAIN IN THIN SECTION CAN BE USED TO TEST FOR VALENCE ALTERATIONS DUE TO SAMPLE PREPARATION. MICRO-XRD STUDIES WILL ALSO UTILIZE THESE FIB SECTIONS BUT THE ULTIMATE GOAL WILL BE TO DEVELOP METHODOLOGIES FOR SAMPLES THAT ARE MINERALOGICALLY HETEROGENEOUS AT THE MICROMETER SCALE. A NEW GENERATION OF HIGH SPEED AREA DETECTORS WILL BE USED TO COLLECT THE DIFFRACTION DATA IN MAPPING MODE WITH ACCUMULATION TIMES<100 MSEC PER PIXEL. INTERPRETABLE DIFFRACTION PATTERNS WILL BE COLLECTABLE FROM PICOGRAM SAMPLES/VOXELS. WE WILL DEVELOP METHODS TO COLLECT THE DATA TOMOGRAPHICALLY AND RECONSTRUCTION ALGORITHMS TO VISUALIZE THE DIFFRACTION PATTERN WITHIN RECONSTRUCTED SLICES OF THE ANALYZED MATERIALS. THESE METHODS WILL THEN BE APPLIED TO STARDUST MINERAL GRAINS NOTABLY FROM OLIVINE- AND PYROXENE-BEARING TRACKS. THE COUPLED XAFS/XRD DATA MAY ALSO BE USEFUL IN IDENTIFYING MATERIALS PRODUCED/MODIFIED DURING CAPTURE. THIS WORK WILL DEVELOP COORDINATED VALENCE/OXIDATION STATE AND MINERAL PHASE DETERMINATION METHODS APPLICABLE TO PICOGRAM SAMPLES RETURNED BY NASA MISSIONS AND WILL PROVIDE INSIGHTS INTO THE ORIGINS OF SAMPLED SOLAR SYSTEM BODIES. THE RESULTS WILL ALSO LIKELY PROVIDE INSIGHTS INTO THE REDOX EFFECTS AND MINERAL MODIFICATIONS OF SECONDARY PROCESSES SUCH AS RE-MELTING SHOCK AND CAPTURE. THUS THIS STUDY IS RELEVANT TO THE CALL OF THE LABORATORY ANALYSIS OF RETURNED SAMPLES (LARS) PROGRAM ELEMENT.
OpenAlex ID: W3110936953
FWCI: 0.178
Cites: 36
Cited by: 1
Related to: 10