Carbon in olivines of chondritic meteorites

Carbon concentrations have been measured, using the C-12(d,p)C-13 nuclear r eaction, in olivines from different chondritic meteorites: CV3 (Allende and Ningqiang), CH (Acfer214), CM (Mighei and Murchison), LL3.1 (Bishunpur) an d from a dark inclusion of the Allende CV3 meteorite. Their chemical compos itions vary from Mg-rich (primitive olivines grown under reducing condition s) to FeO-rich (olivines that have been affected by elemental exchange reac tions in a more oxygen-rich environment), with variable contents of MnO and Cr2O3. The ways these olivines occur in the chondrites (e.g., as isolated olivines or olivines in aggregates or in a ban ed chondrule) have also been considered as they can indicate different processes involved in their gene sis. Nevertheless, no correlation can be established between the chemical c omposition of olivines, their possible genesis and their carbon contents. C ontrary to previous measurements of carbon contents in chondrules, Nuclear Reaction Analyses (NRA) show that olivines have carbon contents of less tha n 120 ppm. Notwithstanding the different physico-chemical conditions under which olivines could have been formed or been altered in meteorites (from h ighly reducing to oxidising conditions) carbon does not enter the structure of olivine. This widespread feature appears as an intrinsic characteristic of olivines regardless of their origin. either on Earth or in the Solar Ne bula. Copyright (C) 2000 Elsevier Science Ltd.