Abstract:

Abstract:  We have systematically studied the shock melting and the fractional crystallization of minerals in the three Chinese fallen chondrites, the Suizhou, the Sixiangkou and the Yanzhuang chondrite, using modern micromineralogical techniques. It was revealed that there exist three types of shockinduced melts, namely, the monomineral silicatemelt, the mixed silicatemineralmelt, and the wholerock melt. The research results may be summed up as follows. (1)No obvious differences in major and trace element constituents between the melted and unmelted phases, implying that they are the products of insitu melting. However, the shock melting process did cause the differentiation of some siderophile elements, of light and heavy rare earth elements, and of the element Se in some large melt pockets. (2)Al2O3, Cr2O3, Na2O, and CaO preferentially entered into pyroxene or its highpressure polymorphic majorite (main mineral phase in Earths transition zone), both of which were crystallized from the shock induced silicate melts. (3)The element Al may enter into akimotoite, the ilmenitestructured polymorph of pyroxene and one of the mineral phases in lower mantle, and stabilized as the solid solution. The ELNES analyses revealed that the Fe3+/∑Fe ratio for akimotoite is as high as 067(3). (4)The complete immiscibility of silicate and metalsulfide phases is observed in the whole rock melt, and the latter occurs in the silicate melt as isolated eutectic nodules. No significant differences were found in the concentrations of elements in the melted and unmelted phases, except the Zn,Na,Cr,Co and Cu enrichment in molten sulfide phase and the Na enrichment in molten metal phase. (5)The presence of the FeNi metaltroilitemagnetite assemblage in a melt vein of Sixiangkou chondrite implies that the light elements of S and O may be involved in the Earths core in which FeNi metal is the main mineral composition. (6)Some spherules of Na, Mn and Fe phosphates were observed in the FeNiFeS eutectic nodules in the Yanzhuang chondrite, indicating that the elements of P, Na and Mn may be also involved in the Earths core. The above mentioned phenomena are of important significance in the study of planet evolution, in the Earths mantle mineralogy and geochemistry, as well as in meteoritics itself.

Key words:

Key words: meteorite mineral; high pressure and temperature; shock melting; fractional crystallization; element partitioning