TY - JOUR
T1 - Early solar system processes recorded in the matrices of two highly pristine CR3 carbonaceous chondrites, MET 00426 and QUE 99177
AU - Abreu, Neyda M.
AU - Brearley, Adrian J.
N1 - Funding Information:
We are grateful to Dr. Rhian Jones and Jana Berlin for many useful discussions and suggestions during the course of this research. We also thank Mike Spilde, Dr. Ying-Bing Jiang, and Dr. Peng Li for their invaluable help with the SEM, microprobe, and TEM analysis. We are extremely appreciative of the thoughtful and comprehensive reviews by Dr. Lindsay Keller, Dr. Mike Weisberg, and Dr. Mike Zolensky which contributed significantly to improving the manuscript. Electron microscopy and electron microprobe analyses were carried out in the Electron Microbeam Analysis Facility in the Department of Earth and Planetary Sciences, University of New Mexico, USA, a facility that is supported by funds from the State of New Mexico, NSF, and NASA. This work was supported by NASA Cosmochemistry Grants NAG5-13444 and NAG5-9798 to A.J. Brearley.
PY - 2010/2/1
Y1 - 2010/2/1
N2 - The mineralogy and bulk compositions of the matrices of the CR chondrites MET 00426 and QUE 99177 have been studied using a combination of SEM, EPMA, and TEM techniques. The matrices of these two chondrites are texturally, chemically, and mineralogically similar and are characterized by significant FeO-enrichments with respect to other CR chondrite matrices, nearly flat refractory lithophile patterns, variable volatile element patterns, and a simple mineral assemblage dominated by amorphous silicate material and Fe,Ni sulfides. Fine-grained, crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites. Instead, the mineralogy of matrices and fine-grained rims of both meteorites consists of abundant amorphous FeO-rich silicate material, containing nanoparticles of Fe,Ni sulfides (troilite, pyrrhotite, and pentlandite). Secondary alteration minerals that are characteristic of other CR chondrites (e.g., Renazzo and Al Rais), such as phyllosilicates, magnetite, and calcite are also rare. The texture and mineralogy of the matrices of MET 00426 and QUE 99177 share many features with matrices in the primitive carbonaceous chondrites ALH A77307 (CO3.0) and Acfer 094 (unique). These observations show that MET 00426 and QUE 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration, unlike other CR chondrites, which are typically classified as petrologic type 2. We suggest that these meteorites represent additional samples of highly primitive, but extremely rare carbonaceous chondrites of petrologic type 3.00, according to the classification scheme of Grossman and Brearley (2005). The highly pristine nature of MET 00426 and QUE 99177 provides important additional insights into the origins of fine-grained materials in carbonaceous chondrites. Based on our new observations, we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high-temperature events, such as those that formed chondrules.
AB - The mineralogy and bulk compositions of the matrices of the CR chondrites MET 00426 and QUE 99177 have been studied using a combination of SEM, EPMA, and TEM techniques. The matrices of these two chondrites are texturally, chemically, and mineralogically similar and are characterized by significant FeO-enrichments with respect to other CR chondrite matrices, nearly flat refractory lithophile patterns, variable volatile element patterns, and a simple mineral assemblage dominated by amorphous silicate material and Fe,Ni sulfides. Fine-grained, crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites. Instead, the mineralogy of matrices and fine-grained rims of both meteorites consists of abundant amorphous FeO-rich silicate material, containing nanoparticles of Fe,Ni sulfides (troilite, pyrrhotite, and pentlandite). Secondary alteration minerals that are characteristic of other CR chondrites (e.g., Renazzo and Al Rais), such as phyllosilicates, magnetite, and calcite are also rare. The texture and mineralogy of the matrices of MET 00426 and QUE 99177 share many features with matrices in the primitive carbonaceous chondrites ALH A77307 (CO3.0) and Acfer 094 (unique). These observations show that MET 00426 and QUE 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration, unlike other CR chondrites, which are typically classified as petrologic type 2. We suggest that these meteorites represent additional samples of highly primitive, but extremely rare carbonaceous chondrites of petrologic type 3.00, according to the classification scheme of Grossman and Brearley (2005). The highly pristine nature of MET 00426 and QUE 99177 provides important additional insights into the origins of fine-grained materials in carbonaceous chondrites. Based on our new observations, we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high-temperature events, such as those that formed chondrules.
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U2 - 10.1016/j.gca.2009.11.009
DO - 10.1016/j.gca.2009.11.009
M3 - Article
AN - SCOPUS:72149120849
SN - 0016-7037
VL - 74
SP - 1146
EP - 1171
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
IS - 3
ER -