title: Isotopic links between atmospheric chemistry and the deep sulphur cycle on Mars.
abstract: The geochemistry of Martian meteorites provides a wealth of information about the solid planet and the surface and atmospheric processes that occurred on Mars. The degree to which Martian magmas may have assimilated crustal material, thus altering the geochemical signatures acquired from their mantle sources, is unclear. This issue features prominently in efforts to understand whether the source of light rare-earth elements in enriched shergottites lies in crustal material incorporated into melts or in mixing between enriched and depleted mantle reservoirs. Sulphur isotope systematics offer insight into some aspects of crustal assimilation. The presence of igneous sulphides in Martian meteorites with sulphur isotope signatures indicative of mass-independent fractionation suggests the assimilation of sulphur both during passage of magmas through the crust of Mars and at sites of emplacement. Here we report isotopic analyses of 40 Martian meteorites that represent more than half of the distinct known Martian meteorites, including 30 shergottites (28 plus 2 pairs, where pairs are separate fragments of a single meteorite), 8 nakhlites (5 plus 3 pairs), Allan Hills 84001 and Chassigny. Our data provide strong evidence that assimilation of sulphur into Martian magmas was a common occurrence throughout much of the planet's history. The signature of mass-independent fractionation observed also indicates that the atmospheric imprint of photochemical processing preserved in Martian meteoritic sulphide and sulphate is distinct from that observed in terrestrial analogues, suggesting fundamental differences between the dominant sulphur chemistry in the atmosphere of Mars and that in the atmosphere of Earth.
authors.affiliation: 1] Center for Research and Exploration in Space Science and Technology, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA [2] Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Heather B
authors.initials: HB
authors.lastname: Franz
authors.affiliation: School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario L8S 4K1, Canada.
authors.forename: Sang-Tae
authors.initials: ST
authors.lastname: Kim
authors.affiliation: Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: James
authors.initials: J
authors.lastname: Farquhar
authors.affiliation: Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093, USA.
authors.forename: James M D
authors.initials: JM
authors.lastname: Day
authors.affiliation: Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: Rita C
authors.initials: RC
authors.lastname: Economos
authors.affiliation: Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: Kevin D
authors.initials: KD
authors.lastname: McKeegan
authors.affiliation: Department of Earth and Space Sciences, University of California, Los Angeles, California 90095, USA.
authors.forename: Axel K
authors.initials: AK
authors.lastname: Schmitt
authors.affiliation: Department of Earth and Space Sciences, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Irving
authors.affiliation: Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Joost
authors.initials: J
authors.lastname: Hoek
authors.affiliation: Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: James
authors.initials: J
authors.lastname: Dottin
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