The growth history of meteoritic minerals as recorded by mineral and glass inclusions

Research project P 13975 Inclusions in meteoritic minerals Gero KURAT 24.01.2000 Solid, liquid, and gaseous inclusions in meteorite minerals record details on the environment and the conditions of growth of the host mineral. We, the Argentine partner and I propose to utilize this fact for constraining the genesis of meteoritic minerals. The focus of this study will be some chondritic meteorites as well as some achondritic ones. For the chondritic meteorites we want to investigate the genesis of the chondrite components (chondrules and others) which are geochernically fractionated but isotopically inhomogeneous. Consequently, fractionation could not have been achieved by conventional geochemical processing. Inclusions in the major minerals of these components shall allow us to constrain the formation conditions. Pilot studies of glass inclusions in olivines from carbonaceous chondrites make it likely that these olivines grew from the vapor phase by a process known (and industrially utilized) as vaporliquid-solid (VLS) growth. High contents of C and N of the glass indicate trapping of refractory C and N species during growth. We would also like to eventually identify these species. As for the achondritic meteorites we would like to study in particular two groups for which we have performed some pilot studies with unexpected results. One group is the enstatite achondrites (aubrites), meteorites of an extreme mineralogical composition. The mainly consist of large, pure enstatite and a variety of exotic phases (sulfides of Ca, Mg, Ti and others). Our pilot studies revealed that many enstatites are very rich in gaseous inclusions indicating growth in a gas-rich environment. We would like to characterize that environment properly and define the growth mechanism. The second group of interest are the SNC achondrites, rocks widely believed to originate on Mars. These rocks (basalts, peridotites, pyroxenites) are believed to be of igneous origin. However, our pilot study of Chassigny, a dunite, revealed that the abundant glass-bearing inclusions in the olivine of that rock were formed by heterogeneous trapping and cannot be of igneous origin. This iconoclastic result urgently needs follow-up studies of other rocks from the SNC clan. Samples are available from the Vienna collection and collections in Argentina. The techniques to be applied are optical microscopy, SEM, EMPA, SIMS, nuclear reaction micro-analysis, PIXE, synchrontron X-ray analysis, laser ablation microprobe ICP-MS IR and RAMAN spectroscopy. Research will jointly be conducted with Dr. M.E. Varela, Bahia Blanca, Argentina (CONICET) and in co-operation with laboratories in France, Germany, Canada, and the USA.