TRACE ELEMENT GEOCHEMISTRY OF ACHONDRITIC METEORITES

Abstract

Geochemical modelling of major and trace element data (EMP and LA-ICPMS) from Achondritic meteorite samples (ureilites) for Ca, Mg, Al, Si, Fe with Sc, Cr, Mn, Fe, Co, Ni, Zn, Ga, REE, W, Re, Os, Ir, and Au is presented. Data for bulk samples as well as different phases present in the samples such as Olivine, Fe-Ni metal and sulphide phases were considered. In the bulk samples the refractory siderophile concentrations range from approximately 0.1 to 1.0 times CI chondrites while the volatile siderophiles range from about 0.07 to 0.3 times CI chondrites which indicates the separation/ loss of a metal phase enriched in those elements as well as loss due to early volatilization processes. For the Fe-S and Fe-Ni phases the siderophile elements are considerably high when compared to olivine and bulk sample analyses for those elements. However, normalized concentrations of several siderophile elements are still subchondritic which may indicate that these metallic and sulphide phases represent a second generation of metallic melt separation in the parent body. Rare earth elements (REEs) in bulk ureilites are quite depleted indicating a separate silicate melt phase