A morphologic and crystallographic comparison of CV chondrite matrices

1L. V. Forman,1N. E. Timms,1P. A. Bland,1,2L. Daly,1G. K. Benedix,3P. W. Trimby
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13380]
1Space Science & Technology Centre, School of Earth & Planetary Sciences, Curtin University, GPO Box U1987, Perth, WesternAustralia 6845, Australia
2School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
3Oxford Instruments Nanoanalysis, High Wycombe HP12 3SE, UK
Published by arrangement with John Wiley & Sons

Meteoritic matrices are commonly classified by their modal mineralogy, alteration,and shock levels. Other “textural” characteristics are not generally considered inclassification schemes, yet could carry important information about their genesis andevolution. Terrestrial rocks are routinely described by grain morphology, which has led tomorphology-driven classifications, and identification of controlling processes. This paperinvestigates three CV chondrites—Allende (CV3.2oxA), Kaba (CV3.0oxB), and Vigarano(CV3.3red)—to determine the morphologic signature of olivine matrix grains. 2D grain sizeand shape, and crystallographic preferred orientations (CPOs) are quantified via electronbackscatter diffraction mapping. Allende contains the largest and most elongate olivinegrains, while Vigarano contains the least elongate, and Kaba contains the smallest grains.Weak but notable CPOs exist in some regions proximal to chondrules and one region distalto chondrules, and CPO geometries reveal a weak flattening of the matrix grains against theedge of chondrules within Allende. Kaba contains the least plastically deformed grains, andAllende contains the most plastically deformed grains. We tentatively infer that morphologyis controlled by the characteristics of the available population of accreting grains, andaqueous and thermal alteration of the parent body. The extent of overall finite deformationis likely dictated by the location of the sample with respect to compression, the localizedenvironment of the matrix with respect to surrounding material, and the post deformationtemperature to induce grain annealing. Our systematic, quantitative process forcharacterizing meteorite matrices has the potential to provide a framework for comparisonwithin and across meteorite classes, to help resolve how parent body processing differedacross and between chondritic asteroids.

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