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摘要
Peridotite xenoliths hosted by Cenozoic basanite lava flows (21 center dot 2-23 center dot 5 Ma) occur at several localities in the western continuation of the Ohre/Eger rift (Central European Volcanic Province) in NE Bavaria, Bohemian Massif. Detailed petrography, major and trace element compositions of whole-rock samples and selected mineral phases as well as Sr-Nd-Li isotopic compositions for a suite of mantle xenoliths from Zinst, Hirschentanz and Teichelberg document variable degrees of partial melting and metasomatism. Melting models based on whole-rock major element composition and Cr# of spinel indicate similar to 6-30% melting in the spinel stability field. Subsequent metasomatism by alkaline and carbonate-rich melts resulted in modal and cryptic metasomatism, expressed by the presence of carbonate-bearing silicate melt pockets with complex secondary mineral assemblages and by enrichment in light rare earth elements, Li, Rb, U, Pb, high field strength elements and P. The carbonate is most probably associated with fractionation of the Na-rich silicate melt. High P contents, variable but low to negative delta Li-7 values from +2 center dot 5 to -9 center dot 7 parts per thousand, coupled with Sr-87/Sr-86 ratios between similar to 0 center dot 7032 and similar to 0 center dot 7041 may reflect a significant contribution of recycled crustal material such as eclogite in the infiltrating melts responsible for metasomatism, although the Li isotope compositions may reflect kinetic modifications through diffusion. The trace element geochemistry of clinopyroxene, carbonate and melt pockets suggests that clinopyroxene plays a very important role in fractionation of the rare earth elements, high field strength elements and Sr, whereas carbonate does not host large quantities of incompatible trace elements except for Sr, Ba and, to a lesser extent, Th and U.
- 出版日期2013-12
