Isotopically heavy and heterogeneous C in graphite of the Vaca Muerta mesosiderite

MARUOKA T,; MARIA EUGENIA VARELA; KURAT G,; ZINNER ERNST,

Houston, Texas

Congreso; Lunar and Planetary Sciences Conference; 2006

The genetic models for mesosiderites are still highly controversial. The most popular model sees mesosiderites as to represent a mixture of crustal and core material from a differentiated asteroidal body. Several mechanisms for the silicate-metal mixing – a non-trivial task - have been proposed [1-4] but all are incapable to fully explain mesosiderite petrographic, geochemical and isotopic features. Consequently, complex scenarios had to be designed to explain some of these intriguing features - like the proposal that mesosiderites formed by fragmentation and re-accretion of a large (~ 200-400 km diameter) differentiated asteroid [3]. Common to all complex and diverse genetic models propose is the need that the Fe-Ni metal was in a molten state during mixing with the silicate phases [3-5]. Here we report on FeNi metal and the carbon isotopic composition of graphite associated with the metal that severely constrains the conditions prevailing during formation of the Vaca Muerta mesosiderite.