TY - JOUR
T1 - The formation and alteration of the Renazzo-like carbonaceous chondrites II
T2 - Linking O-isotope composition and oxidation state of chondrule olivine
AU - Schrader, Devin
AU - Connolly, Harold C.
AU - Lauretta, Dante S.
AU - Nagashima, Kazuhide
AU - Huss, Gary R.
AU - Davidson, Jemma
AU - Domanik, Kenneth J.
N1 - Funding Information:
The authors thank the ANSMET, JSC and MWG for samples. We would also like to thank Dolores Hill for assistance with sample curation, and Alexander Krot and Conel Alexander for helpful discussions. We thank Diane Johnson and Ian Franchi for the use of, and assistance with, the SEM at the Open University. We thank AE Sara Russell for editorial handling and helpful comments, Dominik Hezel, Richard Ash, and an anonymous reviewer for constructive reviews. This research was funded in part by the NASA Astrobiology Institute, NASA Grant NNX10AG46G (HCCJr, PI), and the Carson Fellowship at LPL (DLS).
PY - 2013/1/15
Y1 - 2013/1/15
N2 - To better understand the formation conditions of type-I and type-II chondrules in the Renazzo-like carbonaceous (CR) chondrites, an in situ major- and minor-element and O-isotope study was conducted. Twenty-one ferromagnesian chondrules from three CR chondrites (GRA 95229, GRA 06100, and QUE 99177) were analyzed to establish an internally-consistent data set. From this study we infer that type-II chondrule precursors contained enhanced S-bearing dust and ice abundances relative to type-I chondrules. There is a relationship between the O-isotope composition and oxidation state of olivine, which may be related to the amount of 16O-poor ice and reduced carbon accreted by chondrule precursors before melting. Type-II chondrules formed under H2O/H2 ratios of ∼230-740 times solar. In contrast, type-I chondrules formed under more reducing conditions with lower H2O/H2 ratios of ∼10-100 times solar. We find a relationship between type-II chondrule petrology (relict free vs. relict grain-bearing) and O-isotope composition, which is due to degree of melting and exchange with a 16O-poor gas reservoir. The 16O-poor gas that interacted with both type-I and type-II chondrules is estimated to have an isotopic composition between ∼δ18Og=13-27‰ and δ17Og=10-22‰, different from the O-isotope composition of the water accreted by the CR chondrite parent body. Due to partial melting, type-I chondrules and relict grain-bearing type-II chondrules exchanged with the 16O-poor gas to a lower degree than relict-free type-II chondrules.
AB - To better understand the formation conditions of type-I and type-II chondrules in the Renazzo-like carbonaceous (CR) chondrites, an in situ major- and minor-element and O-isotope study was conducted. Twenty-one ferromagnesian chondrules from three CR chondrites (GRA 95229, GRA 06100, and QUE 99177) were analyzed to establish an internally-consistent data set. From this study we infer that type-II chondrule precursors contained enhanced S-bearing dust and ice abundances relative to type-I chondrules. There is a relationship between the O-isotope composition and oxidation state of olivine, which may be related to the amount of 16O-poor ice and reduced carbon accreted by chondrule precursors before melting. Type-II chondrules formed under H2O/H2 ratios of ∼230-740 times solar. In contrast, type-I chondrules formed under more reducing conditions with lower H2O/H2 ratios of ∼10-100 times solar. We find a relationship between type-II chondrule petrology (relict free vs. relict grain-bearing) and O-isotope composition, which is due to degree of melting and exchange with a 16O-poor gas reservoir. The 16O-poor gas that interacted with both type-I and type-II chondrules is estimated to have an isotopic composition between ∼δ18Og=13-27‰ and δ17Og=10-22‰, different from the O-isotope composition of the water accreted by the CR chondrite parent body. Due to partial melting, type-I chondrules and relict grain-bearing type-II chondrules exchanged with the 16O-poor gas to a lower degree than relict-free type-II chondrules.
UR - http://www.scopus.com/inward/record.url?scp=84870276086&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84870276086&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2012.09.045
DO - 10.1016/j.gca.2012.09.045
M3 - Article
AN - SCOPUS:84870276086
SN - 0016-7037
VL - 101
SP - 302
EP - 327
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -