TY - JOUR
T1 - Opaque phases in type-II chondrules from CR2 chondrites
T2 - Implications for CR parent body formation
AU - Schrader, Devin L.
AU - Connolly, Harold C.
AU - Lauretta, Dante S.
N1 - Funding Information:
The authors thank K. Domanik for assistance with the EMP, and J. Mey for assistance with the FEG-SEM. M.K. Weisberg and D.S. Ebel are thanked for their helpful discussions. We also thank the MWG and NMNH for the samples used in this study, as well as Sara Russell, Brigitte Zanda, and others for helpful reviews. This research was funded in part by the Carson Fellowship, NASA Grant NNG05GF39G (HCCJr, PI), NNX07AF96G (DSL, PI), and NSF-REU # AST-055258, CUNY and AMNH.
PY - 2008/12/15
Y1 - 2008/12/15
N2 - We report the results of a detailed study of sulfide-bearing opaque assemblages from the MAC 87320, EET 92011, and Renazzo CR carbonaceous chondrites. The objectives of this study are to (1) characterize sulfide and associated phases within CR2 chondrites; (2) determine the petrographic relationship between sulfides, metals, and chondrules; (3) constrain the history of type-II chondrules; (4) ascertain the environments in which type-II chondrules formed and were altered; and (5) unravel the formation and alteration history of the CR parent body as recorded in sulfide-bearing assemblages. Sulfide-bearing opaque assemblages occur primarily within type-II (FeO-rich) chondrules. The sulfide assemblages are concentrated near the chondrule edges. Assemblages in MAC 87320 are composed of troilite, phosphate, and Ni-rich metal. EET 92011 contains assemblages composed of pentlandite, troilite, and Ni-rich metal. The assemblages in Renazzo contain tochilinite, magnetite, troilite, pentlandite, and phosphate. In all of the assemblages in Renazzo the tochilinite is fine grained and intimately mixed with troilite, pentlandite, or magnetite. Opaque assemblages in CR chondrites record a complex history that includes both high- and low-temperature processes. The morphology and composition of sulfides in CR2 chondrites suggests that the sulfide-bearing assemblages originally formed in gas-solid reactions in the nebula at temperatures above the Fe-FeS eutectic (988 °C). Many of the assemblages were subsequently aqueously altered on the CR-chondrite parent body to various degrees at temperatures from ∼50 to 200 °C. We combine these observations and interpretations to provide a detailed model of the history of the CR parent body.
AB - We report the results of a detailed study of sulfide-bearing opaque assemblages from the MAC 87320, EET 92011, and Renazzo CR carbonaceous chondrites. The objectives of this study are to (1) characterize sulfide and associated phases within CR2 chondrites; (2) determine the petrographic relationship between sulfides, metals, and chondrules; (3) constrain the history of type-II chondrules; (4) ascertain the environments in which type-II chondrules formed and were altered; and (5) unravel the formation and alteration history of the CR parent body as recorded in sulfide-bearing assemblages. Sulfide-bearing opaque assemblages occur primarily within type-II (FeO-rich) chondrules. The sulfide assemblages are concentrated near the chondrule edges. Assemblages in MAC 87320 are composed of troilite, phosphate, and Ni-rich metal. EET 92011 contains assemblages composed of pentlandite, troilite, and Ni-rich metal. The assemblages in Renazzo contain tochilinite, magnetite, troilite, pentlandite, and phosphate. In all of the assemblages in Renazzo the tochilinite is fine grained and intimately mixed with troilite, pentlandite, or magnetite. Opaque assemblages in CR chondrites record a complex history that includes both high- and low-temperature processes. The morphology and composition of sulfides in CR2 chondrites suggests that the sulfide-bearing assemblages originally formed in gas-solid reactions in the nebula at temperatures above the Fe-FeS eutectic (988 °C). Many of the assemblages were subsequently aqueously altered on the CR-chondrite parent body to various degrees at temperatures from ∼50 to 200 °C. We combine these observations and interpretations to provide a detailed model of the history of the CR parent body.
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U2 - 10.1016/j.gca.2008.09.011
DO - 10.1016/j.gca.2008.09.011
M3 - Article
AN - SCOPUS:56549098552
SN - 0016-7037
VL - 72
SP - 6124
EP - 6140
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 24
ER -