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Reclassification and thermal history of Trenzano chondrite
Author(s) -
FIORETTI A. M.,
DOMENEGHETTI M. C.,
MOLIN G.,
CÁMARA F.,
ALVARO M.,
AGOSTINI L.
Publication year - 2007
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/j.1945-5100.2007.tb01007.x
Subject(s) - chondrite , meteorite , pyroxene , petrography , ordinary chondrite , geology , carbonaceous chondrite , closure temperature , parent body , mineralogy , geochemistry , olivine , physics , metamorphic rock , astrobiology
— We present a new single‐crystal X‐ray diffraction (XRD) study performed on a suite of six orthopyroxene grains from the low‐shocked H6 Trenzano meteorite. The quenched intracrystalline Fe 2+ ‐Mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature T c , thus yielding useful constraints on the last thermal event undergone by the host rock. The orthopyroxene T c of 522 ± 13 °C, calculated using a new calibration equation obtained by Stimpfl (2005b), is higher than in previously published H chondrite data. The orthopyroxene cooling rate at this T c is about 100 °C/kyr. This fast rate is inconsistent with the much slower cooling rate expected for H6 in the onion shell structural and thermal model of chondrite parent bodies. A petrographic study carried out at the same time indicated that the Trenzano meteorite is an H5 chondrite and not an H6 chondrite, as it is officially classified. Furthermore, the two‐pyroxene equilibrium temperature of Trenzano (824 ± 24 °C), calculated with QUILF95, is similar to the two‐pyroxene temperature of 750–840 °C obtained for the Carcote (H5) chondrite (Kleinschrot and Okrusch 1999).