Geochemical Features of Chondrules from Orlovka Meteorite (H5): Evidence of Melting Precursors.

The results of studies of the trace-element contents in olivine and plagioclase of chondrules from equilibrated ordinary chondrite Orlovka (H5) are reported. Olivine is represented by forsterite (Fo 79–80) and plagioclase is a mixture of oligoclase–andesine (An 19–49, Or 2–9) and pyroxene. The content of Y, Ti, Nb, and Ni in olivine from different chondrules ranges by factors of 12–20, while Sr, Ba, Al, and Zr range by factors of 5–6. The Y, Ti, Nb, and REE contents in plagioclase range by factors of 5–6. Such broad variations in the trace element concentrations in silicate minerals from porphyritic chondrules in the Orlovka meteorite do not provide evidence for equilibration due to thermal metamorphism or other secondary processes. Porphyritic olivine chondrule PO-1 are enriched in refractory (Zr, Hf, Nb) and rare-earth elements in relation to chondrules from unequilibrated ordinary and carbonaceous chondrites. The data obtained are consistent with the precursor melting hypothesis as a major chondrule-forming process. [ABSTRACT FROM AUTHOR]