SIGRMET05: A SILICATE-GRAPHITE-METAL INCLUSION FROM THE CAMPO DEL CIELO (IAB) IRON.

KURAT G,; ZINNER ERNST; VARELA, M.E; NTAFLOS T,

Tucson

Congreso; Lunar and Planetary Science Conference; 2009

The Campo del Cielo (CC) IAB iron contains inclusions ("nodules") of a variety of mineralogical compositions ranging from graphite + metal or metal + graphite + silicates to silicates + graphite + metal [1 - 3]. The silicate-dominated inclusions have bulk chemical composi-tions and mineral abundances similar to those of chondrites ? with some exceptions. They all have silicates with low and variable Fe/(Fe+Mg) ratios, which indicate low and variable O fugacity. The variable abundances of Ca, Al and the alka-lis are believed to be due to removal of small amounts of partial melts [1]. All rocks appear to be strongly reduced, carry beside graphite and metal also minor amounts or traces of sulfides, schreibersite, cohenite, and lawrencite. The latter is highly unstable in the terrestrial environment and quickly produces rust. One metal-rich metal-graphite-silicate rock recently described [e.g., 3] is rich in clinopyroxene and albite, which seem to be missing from some of the silicate-rich inclusions. However, it is also rich in volatile elements such as S, alkalis and halogens, and in lawrencite. Clinopy-roxene and albite carry large amounts of radiogenic 129Xe of great antiquity [4]. Clearly, the commonly offered formation model for such rocks [e.g., 5] - heterogeneous partial melting of a chondritic parent - is not applicable and needs to be revised. In order to collect more data and gain insight into the genesis of silicate inclusions in meteoritic irons, we investigate a variety of inclusion types. Here we present a preliminary report on our study of a Campo del Cielo graph-ite-metal peridotite inclusion (SiGrMet05) of the common chondritic type [1], which, however, at close look turns out to carry memories of a complex history. 129Xe of great antiquity [4]. Clearly, the commonly offered formation model for such rocks [e.g., 5] - heterogeneous partial melting of a chondritic parent - is not applicable and needs to be revised. In order to collect more data and gain insight into the genesis of silicate inclusions in meteoritic irons, we investigate a variety of inclusion types. Here we present a preliminary report on our study of a Campo del Cielo graph-ite-metal peridotite inclusion (SiGrMet05) of the common chondritic type [1], which, however, at close look turns out to carry memories of a complex history.