TY - JOUR
T1 - Evidence for aqueous activity on comet 81P/Wild 2 from sulfide mineral assemblages in Stardust samples and CI chondrites
AU - Berger, Eve L.
AU - Zega, Thomas J.
AU - Keller, Lindsay P.
AU - Lauretta, Dante S.
N1 - Funding Information:
Special thanks to G. Consolmagno and the Vatican Observatory for providing samples of Orgueil. We thank D. Brownlee, D. Joswiak and G. Matrajt, at the University of Washington; K. Nakamura-Messenger for assistance in Stardust sample selection; and CAPTEM for providing Stardust samples; Emma Bullock, Hughes Leroux, and an anonymous referee for constructive reviews; and Associate Editor, Sara Russell, for helpful comments. This work was supported by NASA grants: NNX08AW48H (ELB), NNH08AH58I (Rhonda Stroud PI, TJZ Co-I), 06-SSAP06-0026 (Scott Messenger PI, LPK Co-I), and NNX09AC60G (DSL PI).
PY - 2011/6/15
Y1 - 2011/6/15
N2 - The discovery of nickel-, copper-, and zinc-bearing iron sulfides from comet 81P/Wild 2 (Wild 2) represents the strongest evidence, in the Stardust collection, of grains that formed in an aqueous environment. We investigated three microtomed TEM sections which contain crystalline sulfide assemblages from Wild 2 and twelve thin sections of the hydrothermally altered CI chondrite Orgueil. Detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities. The Stardust samples include a cubanite (CuFe2S3) grain, a pyrrhotite [(Fe,Ni)1-xS]/pentlandite [(Fe,Ni)9S8] assemblage, and a pyrrhotite/sphalerite [(Fe,Zn)S] assemblage. Similarly, the CI-chondrite sulfides include individual cubanite and pyrrhotite grains, cubanite/pyrrhotite assemblages, pyrrhotite/pentlandite assemblages, as well as possible sphalerite inclusions within pyrrhotite grains. The cubanite is the low temperature orthorhombic form, which constrains temperature to a maximum of 210°C. The Stardust and Orgueil pyrrhotites are the 4C monoclinic polytype, which is not stable above ~250°C. The combinations of cubanite and pyrrhotite, as well as pyrrhotite and pentlandite signify even lower temperatures. The crystal structures, compositions, and petrographic relationships of these sulfides constrain formation and alteration conditions. Taken together, these constraints attest to low-temperature hydrothermal processing.Our analyses of these minerals provide constraints on large scale issues such as: heat sources in the comet-forming region; aqueous activity on cometary bodies; and the extent and mechanisms of radial mixing of material in the early nebula. The sulfides in the Wild 2 collection are most likely the products of low-temperature aqueous alteration. They provide evidence of radial mixing of material (e.g. cubanite, troilite) from the inner solar system to the comet-forming region and possible secondary aqueous processing on the cometary body.
AB - The discovery of nickel-, copper-, and zinc-bearing iron sulfides from comet 81P/Wild 2 (Wild 2) represents the strongest evidence, in the Stardust collection, of grains that formed in an aqueous environment. We investigated three microtomed TEM sections which contain crystalline sulfide assemblages from Wild 2 and twelve thin sections of the hydrothermally altered CI chondrite Orgueil. Detailed structural and compositional characterizations of the sulfide grains from both collections reveal striking similarities. The Stardust samples include a cubanite (CuFe2S3) grain, a pyrrhotite [(Fe,Ni)1-xS]/pentlandite [(Fe,Ni)9S8] assemblage, and a pyrrhotite/sphalerite [(Fe,Zn)S] assemblage. Similarly, the CI-chondrite sulfides include individual cubanite and pyrrhotite grains, cubanite/pyrrhotite assemblages, pyrrhotite/pentlandite assemblages, as well as possible sphalerite inclusions within pyrrhotite grains. The cubanite is the low temperature orthorhombic form, which constrains temperature to a maximum of 210°C. The Stardust and Orgueil pyrrhotites are the 4C monoclinic polytype, which is not stable above ~250°C. The combinations of cubanite and pyrrhotite, as well as pyrrhotite and pentlandite signify even lower temperatures. The crystal structures, compositions, and petrographic relationships of these sulfides constrain formation and alteration conditions. Taken together, these constraints attest to low-temperature hydrothermal processing.Our analyses of these minerals provide constraints on large scale issues such as: heat sources in the comet-forming region; aqueous activity on cometary bodies; and the extent and mechanisms of radial mixing of material in the early nebula. The sulfides in the Wild 2 collection are most likely the products of low-temperature aqueous alteration. They provide evidence of radial mixing of material (e.g. cubanite, troilite) from the inner solar system to the comet-forming region and possible secondary aqueous processing on the cometary body.
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U2 - 10.1016/j.gca.2011.03.026
DO - 10.1016/j.gca.2011.03.026
M3 - Article
AN - SCOPUS:79955951012
SN - 0016-7037
VL - 75
SP - 3501
EP - 3513
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 12
ER -