Trace element composition of silicate minerals from Kunashak Meteorite (L6)

Major (EPMA) and trace (SIMS) element geochemistry in the silicate minerals (olivine, pyroxene and plagioclase) of Kunashak equilibrated ordinary chondrite (L6) is described. No variations in the major element concentrations of the silicate minerals have been found, which is characteristic of equilibrated chondrites of petrological type VI. Low-Са pyroxene and plagioclase from the radiated olivine-pyroxene chondrule of Kunashak Meteorite contain an abundance of trace elements (Yb, Cr, Nb and Ti – pyroxene; Sr, Y, Ti and Zr – plagioclase), which is not characteristic of minerals from the porphyritic olivine and olivine-pyroxene chondrules of the meteorite. The porphyritic olivine-pyroxene chondrule of the Kunashak Meteorite has high trace element concentrations in olivine, in particular, the highest Yb concentration (0.12 ppm on the average) relative to porphyritic and radiated olivine-pyroxene chondrules (0.02 ppm). High trace element concentrations indicate rapid crystallization of a radiated chondrule in a nebula and show no traces of trace element homogenization upon thermal metamorphism. The trace element composition of silicate minerals from Kunashak Meteorite has retained the individual melting pattern of the chondrules and remained unaffected by thermal metamorphism on the parent bodies of the chondrules. Similar results, obtained in the study of Bushkhov Meteorite (L6), indicate that trace elements in olivine and low-Са pyroxene are resistant to thermal metamorphism. The persistence of the individual pattern of the chondrules enables us to use equilibrated ordinary chondrites for the study of processes at early stages in the formation of the Solar System and to better understand chondrule and planet formation mechanisms.