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Appears in Collections:Biological and Environmental Sciences Journal Articles
Peer Review Status: Refereed
Title: Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum
Author(s): Ashley, James W
Golombek, Matthew
Christensen, Philip R
Squyres, Steven W
McCoy, Timothy J
Schröder, Christian
Fleischer, Iris
Johnson, Jeffrey R
Herkenhoff, Kenneth E
Parker, Timothy J
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Keywords: meteorite
Issue Date: Jul-2011
Date Deposited: 24-Oct-2013
Citation: Ashley JW, Golombek M, Christensen PR, Squyres SW, McCoy TJ, Schröder C, Fleischer I, Johnson JR, Herkenhoff KE & Parker TJ (2011) Evidence for mechanical and chemical alteration of iron‐nickel meteorites on Mars: Process insights for Meridiani Planum. Journal of Geophysical Research: Planets, 116 (E7), Art. No.: E00F20.
Abstract: The weathering of meteorites found on Mars involves chemical and physical processes that can provide clues to climate conditions at the location of their discovery. Beginning on sol 1961, the Opportunity rover encountered three large iron meteorites within a few hundred meters of each other. In order of discovery, these rocks have been assigned the unofficial names Block Island, Shelter Island, and Mackinac Island. Each rock presents a unique but complimentary set of features that increase our understanding of weathering processes at Meridiani Planum. Significant morphologic characteristics interpretable as weathering features include (1) a large pit in Block Island, lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction; (2) differentially eroded kamacite and taenite lamellae in Block Island and Shelter Island, providing relative timing through crosscutting relationships with deposition of (3) an iron oxide–rich dark coating; (4) regmaglypted surfaces testifying to regions of minimal surface modification, with other regions in the same meteorites exhibiting (5) large‐scale, cavernous weathering (in Shelter Island and Mackinac Island). We conclude that the current size of the rocks is approximate to their original postfall contours. Their morphology thus likely results from a combination of atmospheric interaction and postfall weathering effects. Among our specific findings is evidence supporting (1) at least one possible episode of aqueous acidic exposure for Block Island; (2) ripple migration over portions of the meteorites; (3) a minimum of two separate episodes of wind abrasion; alternating with (4) at least one episode of coating‐forming chemical alteration, most likely at subzero temperatures.
DOI Link: 10.1029/2010JE003672
Rights: Copyright 2011 by the American Geophysical Union. AGU allows authors to deposit their journal articles if the version is the final published citable version of record, the AGU copyright statement is clearly visible on the posting, and the posting is made 6 months after official publication by the AGU.

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