Istituto di Geoscienze e Georisorse     
Fioretti A., Domeneghetti M., Molin G., Camara F., Alvaro M., Agostini L. Reclassification and thermal history of Trezano chondrite. In: Meteoritics & Planetary Science, vol. 42 (12) pp. 2055 - 2066. Meteoritical Society; University of Arizona. Dept. of Geosciences, 2007.
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 Fe2+-Mg ordering state in orthopyroxene preserves the memory of the cooling rate near closure temperature Tc, thus yielding useful constraints on the last thermal event undergone by the host rock. The orthopyroxene Tc of 522 13C, 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 Tc is about 100C/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 750-840C obtained for the Carcote (H5) chondrite (Kleinschrot and Okrusch 1999).
URL: http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1945-5100
Subject meteorites
thermal history
Trenzano chonodrite
X-ray diffraction

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