Fe2+-Mg ORDER-DISORDER PROCESSES IN ORTHOPYROXENES FROM SÃO JOÃO NEPOMUCENO (IVA) IRON METEORITE: 57Fe MÖSSBAUER SPECTROSCOPY AND SINGLE-CRYSTAL X-RAY DIFFRACTION STUDIES

DOS SANTOS E.; SCORZELLI R,; ABDU Y; VARELA M.E.; MUNAYCO P.

Edmonton

Congreso; Annual Meeting of the Meteoritical Soc; 2013

NASA

São João Nepomuceno (SJN) is an iron meteorite belonging to the IVA chemical group. It consists of Fe-Ni metal matrix and silicate inclusions, mainly orthopyroxene (Opx). Notwithstanding the ex-tensive work that has been done on IVA iron meteorites, there is still no consensus about their origin. On the one hand, the large spread of metallographic cooling-rate data argues against an origin from a single asteroidal core. On the other hand, the chemical char-acteristics of IVA metal phases are consistent with this model [1].