TY - JOUR
T1 - A unique omphacite, amphibole, and graphite-bearing clast in Queen Alexandra Range (QUE) 99177
T2 - A metamorphosed xenolith in a pristine CR3 chondrite
AU - Abreu, Neyda M.
N1 - Funding Information:
A.J. Brearley is thanked for contributive discussions and insightful comments on N.M.A.’s dissertation and prior versions of this manuscript. H. Nagahara, M. Weisberg, T. Nakamura, and an anonymous reviewer are thanked for many helpful reviews that have improved the quality of this paper. Z. Sharp is thanked for helpful conversations regarding thermodynamics calculations. A. Rubin and R.H. Jones are thanked for insightful comments that have improved the quality of this manuscript. E.W. Schienke is thanked for manuscript editing. This work was supported by NNX11AH10G grant to N.M. Abreu and NAG5-13444 and NAG5-9798 grants to A.J. Brearley.
PY - 2013/3/5
Y1 - 2013/3/5
N2 - A metamorphosed, unshocked, chondritic clast, containing approximately equal volumes of matrix and chondrules, has been identified in the primitive CR3 chondrite QUE 99177. The most striking features of this clast are the presence of ferroan omphacitic pyroxenes, amphiboles (pargasite and pargasitic hornblende) and coarse-grained (up to 70. μm) graphite laths. The clast also contains relatively equilibrated FeO-rich olivine, low-Ca pyroxene, and sulfides (pentlandite and troilite). The clast's matrix contains coarse, interlocking crystals. The chondrules are extensively recrystallized, contain no mesostasis or metal, and present poorly-defined boundaries. Based on its compositional and crystallographic features, omphacite appears to have formed at high pressures (>6. GPa). Amphibole formation probably postdated graphite formation and occurred by reaction of olivine, clinopyroxene, and omphacite in the presence of an oxidizing, Na-rich fluid at high temperatures (>700. °C). The absence of metal suggests that this fluid was also rich in S.
AB - A metamorphosed, unshocked, chondritic clast, containing approximately equal volumes of matrix and chondrules, has been identified in the primitive CR3 chondrite QUE 99177. The most striking features of this clast are the presence of ferroan omphacitic pyroxenes, amphiboles (pargasite and pargasitic hornblende) and coarse-grained (up to 70. μm) graphite laths. The clast also contains relatively equilibrated FeO-rich olivine, low-Ca pyroxene, and sulfides (pentlandite and troilite). The clast's matrix contains coarse, interlocking crystals. The chondrules are extensively recrystallized, contain no mesostasis or metal, and present poorly-defined boundaries. Based on its compositional and crystallographic features, omphacite appears to have formed at high pressures (>6. GPa). Amphibole formation probably postdated graphite formation and occurred by reaction of olivine, clinopyroxene, and omphacite in the presence of an oxidizing, Na-rich fluid at high temperatures (>700. °C). The absence of metal suggests that this fluid was also rich in S.
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U2 - 10.1016/j.gca.2012.11.041
DO - 10.1016/j.gca.2012.11.041
M3 - Article
AN - SCOPUS:84872326786
SN - 0016-7037
VL - 105
SP - 56
EP - 72
JO - Geochimica et Cosmochimica Acta
JF - Geochimica et Cosmochimica Acta
ER -