The CK group of chondritic meteorites is of particular concern, because there is evidence for their very early generation and the primitive character of their material. Our study focused on the Dhofar 015 carbonaceous chondrite, 184 g in weight, which was found in Oman in 2001. Based on petrological and mineralogical observations and trace element analysis, Dhofar 015 can be reliably classified as a CK chondrite and regarded as a unique meteorite bearing indications for the occurrence of nebular processes in an oxidizing environment. The goal of this study was to distinguish such elemental ratios and noble gas isotope parameters that could support or reject the suggested very early genesis of the material of the Dhofar 015 chondrite and the nebular nature of these volatile components in CK meteorites. All the noble gases of the meteorite contain a considerable fraction of radiogenic components. There is evidence for a considerable loss of cosmogenic 3He. The cosmic ray exposure age calculated from 3He data is therefore strongly underestimated, ≈4 Ma. The exposure age estimated using 21Ne and 38Ar is typical of CK chondrites, 22.9 ± 5.2 Ma, but calculations from the concentrations of 83Kr and 126Xe and the shielding factor (22Ne/21Ne)cosm yielded a value of 46 ± 5 Ma. Cosmogenic 21Ne and 38Ar were probably lost and the age obtained from heavy noble gases is more plausible. The investigation of trapped noble gases revealed a very strong depletion of the Dhofar 015 chondrite in light noble gases relative to 132Xe, which is typical of all other CK meteorites. The observed effect is probably related to the characteristic features of initial trapped gases in the CK meteorites. It can be explained in terms of the M. Ozima hypothesis on the possible xenon enrichment relative to lighter helium, neon, and argon by several orders of magnitude under the influence of the gravitational field of porous planetesimals with a radius of about ≈5 km during the earliest stages of evolution of the solar system. This supports the previous suggestions on the nebular processes in the history of the Dhofar 015 CK chondrite.
|Number of pages||23|
|Publication status||Published - Jan 1 2005|
ASJC Scopus subject areas
- Geochemistry and Petrology