Trace element studies of silicate-rich inclusion in the Guin (UNGR) and Kodaikanal (IIE) iron meteorites.

KURAT GERO,; ZINNER ERNST,; MARIA EUGENIA VARELA

METEORITICS & PLANETARY SCIENCE

METEORITICAL SOC

Año: 2007 vol. 42 p. 1441 - 1463

1086-9379

A total of 56 non-porphyritic pyroxene and pyroxene/olivine micro-objects from different unequilibrated ordinary chondrites were selected for detailed studies to test the existing formation models. Our studies imply that the non-porphyritic objects represent quickly quenched liquids with each object reflecting a very complex and unique evolutionary history. Bulk major element analyses, obtained with EMPA and ASEM, as well as bulk lithophile trace element analyses, determined by LA-ICP-MS, resulted in unfractionated (solar-like) ratios of CaO/Al, Yb/Ce as well as Sc/Yb in many of the studied objects and mostly unfractionated refractory lithophile trace element (RLTE) abundance patterns. These features support an origin by direct condensation from a gas of solar nebula composition. Full equilibrium condensation calculations show that it is theoretically possible that pyroxene-dominated non-porphyritic chondrules with flat REE patterns could have been formed as droplet liquid condensates directly from a nebular gas strongly depleted in olivine. Thus, it is possible to have enstatite as the stable liquidus phase in a 800 x CI dust-enriched nebular gas at a ptot of 10-3 atm., if about 72 % of the original Mg is removed (as forsterite?) from the system. Condensation of liquids from vapor (Primary Liquid Condensation) could be considered as a possible formation process of the pyroxene-dominated non-porphyritic objects