262 D30. Planetary Geology (Posters)

Wednesday, 7 November 2018
9:00 AM - 6:30 PM
Halls J-K

INVESTIGATION OF AUBRITES THROUGH INTEGRATION OF 3D MODAL MINERALOGY WITH X-RAY MICRO-COMPUTED TOMOGRAPHY AND GEOCHEMISTRY

Paper number: 262-6
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

The aubrites (~30 known meteorites) are a unique group of differentiated meteorites that formed on parent bodies with oxygen fugacities (ƒO2) ~2 to ~6 log units below the iron-wüstite buffer. At these highly reduced conditions, elements deviate from the geochemical behavior exhibited at terrestrial fO2, including the formation of FeO-poor silicates and exotic sulfides. Geochemical examinations of aubrites, such as mineral major-element compositions, bulk-rock compositions, O isotopes, and crystallization ages, are crucial to understand their formation and evolution at extreme ƒO2 conditions. While previous studies have described the petrology and 2D modal abundances of aubrites, this work investigates the 3D modal mineralogies of silicate, metal, and sulfide phases in aubrite samples, which are compared to the available 2D data. We utilize X-ray computed tomography (XCT) to non-destructively analyze the distribution and abundances of mineral phases in aubrites and locate composite clasts of metal and sulfide grains for future analytical study. This study offers the first 3D modal mineralogical data for a representative suite of aubrites.

Currently, we have produced 3D scans of the Norton County aubrite. We have scanned 8- and 17-gram samples at 165 keV and 90 µA as well as 180 keV and 115 µA, respectively. The results of the XCT data have allowed for the determination of the abundances of silicate groundmass (i.e., enstatite, forsterite, albite, and diopside), light (based on electron density) sulfides (i.e., alabandite [MnS], and daubréelite [FeCr2S4]), heavy sulfides (i.e., troilite [FeS]), and Fe,Ni metal by segmenting a density histogram in Volume Graphics Studio software. XCT scans of the Peña Blanca Spring aubrite are currently underway. By combining the 3D representation of the exotic phases found in aubrites with existing 2D characterizations, we are able to better determine modal abundances. By integrating 3D and 2D modal abundances and geochemistry, we can ultimately better constrain aubrite petrogenesis and elemental partitioning. Furthermore, application of this new 3D approach offers the opportunity to identify and select clasts for future study prior to cutting the sample, which will minimize sample loss of this precious material.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-317290

© Copyright 2018 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.