Organic thermometry for chondritic parent bodies

A unique spectroscopic feature has been identified in a Study of twenty-five different samples of meteoritic insoluble organic matter (IOM) spanning multiple chemical classes, groups, and petrologic types, using carbon X-ray Absorption Near Edge Structure (XANES) spectroscopy. The intensity of this feature, a 1s-sigma* exciton, appears to provide a precise measure of parent body metamorphism. The intensity of this exciton is also shown to correlate well with a large negative paramagnetic shift observed through solid state C-13 NMR. Experiments reveal that upon heating primitive IOM is transformed into material that is indistinguishable from that in thermally processed chondrites, including the development of the 1s-sigma* exciton. A thermo-kinetic expression is derived front the experimental data that allows the intensity of the 1s-sigma* exciton to be used to estimated the effective temperature integrated over time. A good correlation is observed between the intensity of the 1s-sigma* exciton and previously published microRaman spectral data. These data provide a self-consistent organic derived temperature scale for the purpose of calibrating Raman based thermometric expressions. (C) 2008 Elsevier B.V. All rights reserved.