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Two populations of carbonate in ALH84001: geochemical evidence for discrimination and genesis

Eiler, John M. and Valley, John W. and Graham, Colin M. and Fournelle, John (2002) Two populations of carbonate in ALH84001: geochemical evidence for discrimination and genesis. Geochimica et Cosmochimica Acta, 66 (7). pp. 1285-1303. ISSN 0016-7037. https://resolver.caltech.edu/CaltechAUTHORS:20121025-111250950

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Abstract

We present major and trace-element, oxygen isotope, textural, and structural data for carbonates and related phases in the SNC meteorite ALH84001. These data document the existence of at least two distinct carbonate populations: one composed of finely zoned, chemically and isotopically heterogeneous concretions of magnesio-siderite with distinct white magnesite rims, and a second composed of relatively homogeneous, isotopically and compositionally simple domains of ankeritic carbonate and intimately intergrown glass and fine-grained pyroxene. We suggest on the basis of textural evidence and geochemical systematics that the first population consists of low-temperature aqueous precipitates, and the second is produced by shock melting of the first. Values of δ^(18)O and Sr/Ca ratios are correlated with one another in magnesio-siderite concretions; the trend formed by these data is consistent with the predicted relationship for inorganic precipitation of carbonate from a solution of constant composition between temperatures of ∼190°C (for concretion cores) to 20°C (for magnesite-rich concretion rims). Given the assumptions inherent in this temperature estimate, the aqueous fluid parental to carbonate concretions is constrained to have a δ^(18)O of −5‰ VSMOW (significantly mass fractionated compared with expected juvenile martian volatiles) and minor-element abundances broadly similar to terrestrial seawater.


Item Type:Article
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http://dx.doi.org/10.1016/S0016-7037(01)00847-XDOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/S001670370100847XPublisherUNSPECIFIED
Additional Information:© 2002 Elsevier Science Ltd. Received 2 May 2001; Revised 10 October 2001; Accepted 10 October 2001; Available online 19 March 2002. This research was supported by NSF, DOE, and NERC. We thank Ronit Kessel for her helpful comments on an early draft of the manuscript. We thank Ed Scott and David Mittlefehldt for thorough and helpful reviews and Horton Newsom for editorial handling of the manuscript. We also thank John Craven for his support in use of the University of Edinburgh ion microprobe laboratory, Richard Hinton for his advice on trace-element analyses, and George Rossman for his assistance and advice with FTIR and X-ray diffraction analyses. Associate editor: H. E. Newsom
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Department of Energy (DOE)UNSPECIFIED
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Issue or Number:7
Record Number:CaltechAUTHORS:20121025-111250950
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20121025-111250950
Official Citation:John M. Eiler, John W. Valley, Colin M. Graham, John Fournelle, Two populations of carbonate in ALH84001: geochemical evidence for discrimination and genesis, Geochimica et Cosmochimica Acta, Volume 66, Issue 7, 1 April 2002, Pages 1285-1303, ISSN 0016-7037, 10.1016/S0016-7037(01)00847-X. (http://www.sciencedirect.com/science/article/pii/S001670370100847X)
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ID Code:35096
Collection:CaltechAUTHORS
Deposited By: Aucoeur Ngo
Deposited On:25 Oct 2012 20:34
Last Modified:03 Oct 2019 04:25

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