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Title: Sulfide isotopic compositions in shergottites and ALH84001, and possible implications for life on Mars

Abstract

The shergottite and ALH84001 meteorites hold keys for understanding geologic and possibly biologic processes on Mars. Recently, it has been proposed that carbonates in ALH84001, and the Fe-sulfides they contain, are products of extraterrestrial biogenic activity. Here we report ion microprobe analyses of sulfides in shergottites and ALH84001. The sulfur isotope ratios of igneous pyrrhotites in shergottites (mean {delta}{sup 34}S{sub CDT}: Shergotty = -0.4{per_thousand}, Zagami = +2.7{per_thousand}, EETA79001A = 1.9{per_thousand}, EETA79001B = -1.7{per_thousand}, LEW88516 = -1.9{per_thousand}, QUE94201 = +0.8{per_thousand}) are similar to those of terrestrial ocean-floor basalts, suggesting that the sulfur isotopic composition of the Martian mantle may be similar to that of the mantle of the Earth. The sulfur isotopic systematics of ALH84001 sulfides are distinct from the shergottites. Measured sulfur isotope ratios of eight pyrite grains ({delta}{sup 34}S{sub CDT} = +2.0 to +7.3{per_thousand}) in crushed zones confirm previously reported analyses of isotopically heavy sulfides and are indistinguishable from an Fe-sulfide zone within a carbonate globule ({delta}{sup 34}S{sub CDT} = +6.0{per_thousand}). Analyses of synthesized, fine-grained mixtures of sulfide, carbonate, and magnetite indicate than the measured sulfur isotope ratio is independent of the presence of carbonate and magnetite in the sputtered volume, confirming the accuracy of the analysis of themore » fine-grained sulfide in the carbonate globule. Terrestrial biogenic sulfate reduction typically results in light isotopic enrichments. The similarity of {delta}{sup 34}S values of the sulfides in ALH84001 imply that the Fe-sulfide zones within ALH84001 carbonates are probably not the result of bacterial reduction of sulfate. 38 refs., 3 figs., 1 tab.« less

Authors:
;  [1];  [2]
  1. Univ. of Tennessee, Knoxville, TN (United States)
  2. Oak Ridge National Lab., TN (United States)
Publication Date:
OSTI Identifier:
618157
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta
Additional Journal Information:
Journal Volume: 61; Journal Issue: 20; Other Information: PBD: Oct 1997
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 58 GEOSCIENCES; MARS PLANET; ORNL; RESEARCH PROGRAMS; ISOTOPE RATIO; SULFIDES; ORIGIN; METEORITES; CHEMICAL COMPOSITION; ION MICROPROBE ANALYSIS

Citation Formats

Greenwood, J P, McSween, Jr, H Y, and Riciputi, L R. Sulfide isotopic compositions in shergottites and ALH84001, and possible implications for life on Mars. United States: N. p., 1997. Web. doi:10.1016/S0016-7037(97)00246-9.
Greenwood, J P, McSween, Jr, H Y, & Riciputi, L R. Sulfide isotopic compositions in shergottites and ALH84001, and possible implications for life on Mars. United States. https://doi.org/10.1016/S0016-7037(97)00246-9
Greenwood, J P, McSween, Jr, H Y, and Riciputi, L R. 1997. "Sulfide isotopic compositions in shergottites and ALH84001, and possible implications for life on Mars". United States. https://doi.org/10.1016/S0016-7037(97)00246-9.
@article{osti_618157,
title = {Sulfide isotopic compositions in shergottites and ALH84001, and possible implications for life on Mars},
author = {Greenwood, J P and McSween, Jr, H Y and Riciputi, L R},
abstractNote = {The shergottite and ALH84001 meteorites hold keys for understanding geologic and possibly biologic processes on Mars. Recently, it has been proposed that carbonates in ALH84001, and the Fe-sulfides they contain, are products of extraterrestrial biogenic activity. Here we report ion microprobe analyses of sulfides in shergottites and ALH84001. The sulfur isotope ratios of igneous pyrrhotites in shergottites (mean {delta}{sup 34}S{sub CDT}: Shergotty = -0.4{per_thousand}, Zagami = +2.7{per_thousand}, EETA79001A = 1.9{per_thousand}, EETA79001B = -1.7{per_thousand}, LEW88516 = -1.9{per_thousand}, QUE94201 = +0.8{per_thousand}) are similar to those of terrestrial ocean-floor basalts, suggesting that the sulfur isotopic composition of the Martian mantle may be similar to that of the mantle of the Earth. The sulfur isotopic systematics of ALH84001 sulfides are distinct from the shergottites. Measured sulfur isotope ratios of eight pyrite grains ({delta}{sup 34}S{sub CDT} = +2.0 to +7.3{per_thousand}) in crushed zones confirm previously reported analyses of isotopically heavy sulfides and are indistinguishable from an Fe-sulfide zone within a carbonate globule ({delta}{sup 34}S{sub CDT} = +6.0{per_thousand}). Analyses of synthesized, fine-grained mixtures of sulfide, carbonate, and magnetite indicate than the measured sulfur isotope ratio is independent of the presence of carbonate and magnetite in the sputtered volume, confirming the accuracy of the analysis of the fine-grained sulfide in the carbonate globule. Terrestrial biogenic sulfate reduction typically results in light isotopic enrichments. The similarity of {delta}{sup 34}S values of the sulfides in ALH84001 imply that the Fe-sulfide zones within ALH84001 carbonates are probably not the result of bacterial reduction of sulfate. 38 refs., 3 figs., 1 tab.},
doi = {10.1016/S0016-7037(97)00246-9},
url = {https://www.osti.gov/biblio/618157}, journal = {Geochimica et Cosmochimica Acta},
number = 20,
volume = 61,
place = {United States},
year = {Wed Oct 01 00:00:00 EDT 1997},
month = {Wed Oct 01 00:00:00 EDT 1997}
}