Cosmochemical and isotopic study of the origin and evolution of chondrites and achondrites, their genetic relationship and timescales.

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In order to obtain new evidences constraining the timing, origin and evolution of primitive and differentiated meteorites and their genetic relationships, we have carried out chemical, petrological and isotopic analyses for chondrites and achondrites. Results are summarized bellow :(1)Under international consortium for the Kobe (CK) meteorite, we obtained a unique REE pattern and detailed chemical and petrological features, which constrains nebular fractionations and meteorite parent body processes of CK chondrites yielding silicate-darkening of the meteorites. The age determination by U-Pb and Rb-Sr methods were carried out for the meteorite, indicating complicated thermal histories of CK chondrite parent body.(2)REE and Rb-Sr isotopes were analyzed for the most pure matrix materials or chondrules from the Allende (CV) meteorite, respectively. REE results suggest that the precursor of matrix formed by nebular processes. The 4.4Ga alteration event was newly discovered from Rb-Sr system of Allende.(3)The precise Sm-Nd isotopic analyses were carried out for 5 acapulcoites : We obtained a significantly young age (4.13±0.10Ga) for one acapulcoite, indicating young thermal event on the parent body.(4)The low Pb blank technique for U-Pb dating was established and precise U-Pb ages as well as Sm-Nd and Rb-Sr ages and REE patterns were obtained for three newly found Antarctic Martian meteorites.(5)The Mo isotopic anomalies derived from stellar processes were discovered in primitive meteorites. Precise Cr and Ba isotopic analysis techniques were established and new isotopic anomalies were found for primitive and differentiated meteorites.(6)Precise chlorine isotopic analyses were carried out for Allende and 9 standard rocks using thermal ionization mass spectrometry (TIMS). We also established a high sensitivity negative TIMS for Cl.