Goldschmidt Abstracts 2010 – M

Abstract

Much is made these days of compositional models for the Earth, its mantle and core, particularly in the light of 142 Nd isotopic studies and the nature of chondrites as a reference frame for planetary models. It is my assertion that, in the absence of a highly contrived differentiation condition, the composition of the primitive mantle can be reasonably assessed at better than the ±10% level (1σ) for elements at concentration levels of about 1000 μg/g using available mantle samples. A principle finding of the McDonough and Sun 1995 study [1] was that mantle peridotites showed differentiation trends that intersected uniquely chondritic compositions when ploting multiple, independent ratios of refractory lithophile elements. These plots used only the measured abundance data of a suite of peridotites, filtered to avoid (as much as possible) products of melt metasomatized material. That these data arrays cross chondritic space provides evidence that primtive mantle initially started from a chondritic precursor. Increasingly, studies of chondritic meteorites are providing insights into their compositional diversity and, to some extent, the radial distribution of material heterogeneities in the early solar system. Likewise, remote sensing studies of accreting nvebular disks are also yielding evidence of the radial distribution of material heterogeneities in other earlyforming solar systems. The importance of compositional variance in chondrites is underappreciated.