Defining the mechanism for compaction of the CV chondrite parent body

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Title: Defining the mechanism for compaction of the CV chondrite parent body
Author(s): Forman, LV
Bland, PA
Timms, NE
Daly, L
Benedix, GK
Trimby, PW
Collins, GS
Davison, TM
Item Type: Journal Article
Abstract: The Allende meteorite, a relatively unaltered member of the CV carbonaceous chondrite group, contains primitive crystallographic textures that can inform our understanding of early Solar System planetary compaction. To test between models of porosity reduction on the CV parent body, complex microstructures within ~0.5-mm-diameter chondrules and ~10-μm-long matrix olivine grains were analyzed by electron backscatter diffraction (EBSD) techniques. The large area map presented is one of the most extensive EBSD maps to have been collected in application to extraterrestrial materials. Chondrule margins preferentially exhibit limited intragrain crystallographic misorientation due to localized crystal-plastic deformation. Crystallographic preferred orientations (CPOs) preserved by matrix olivine grains are strongly coupled to grain shape, most pronounced in shortest dimension <a>, yet are locally variable in orientation and strength. Lithostatic pressure within plausible chondritic model asteroids is not sufficient to drive compaction or create the observed microstructures if the aggregate was cold. Significant local variability in the orientation and intensity of compaction is also inconsistent with a global process. Detailed microstructures indicative of crystal-plastic deformation are consistent with brief heating events that were small in magnitude. When combined with a lack of sintered grains and the spatially heterogeneous CPO, ubiquitous hot isostatic pressing is unlikely to be responsible. Furthermore, Allende is the most metamorphosed CV chondrite, so if sintering occurred at all on the CV parent body it would be evident here. We conclude that the crystallographic textures observed reflect impact compaction and indicate shock-wave directionality. We therefore present some of the first significant evidence for shock compaction of the CV parent body.
Publication Date: 11-Apr-2017
Date of Acceptance: 7-Mar-2017
URI: http://hdl.handle.net/10044/1/45489
DOI: https://dx.doi.org/10.1130/G38864.1
ISSN: 1943-2682
Publisher: Geological Society of America
Journal / Book Title: Geology
Copyright Statement: © Geological Society of America
Sponsor/Funder: Science and Technology Facilities Council (STFC)
Science and Technology Facilities Council (STFC)
Funder's Grant Number: ST/J001260/1
ST/N000803/1
Keywords: Geochemistry & Geophysics
04 Earth Sciences
Publication Status: Published
Embargo Date: 2018-04-11
Appears in Collections:Faculty of Engineering
Earth Science and Engineering



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