The Petrographic And Petrochemical Characteristics Of The Mantle Fluid Metasomatism

The mantle fluid metasomatism research is hot spot and the difficulty in the currentgeology study, and the research in alkali-rich porphyry and its xenoliths is one of themost important methods or ways to study it. The xenoliths, which derived fromdifferent depth, were found in the alkali-rich porphyries in western Yunnan. Thealteration features and petrochemistry data from the porphyries (host rocks) and itsxenoliths were studied in this paper. It showed that the metasomatic fluids, whichwere consanguineous with alkali-rich magma, were rich in volatile, silicon and alkaliand originated from enriched mantle. On the basis of the analysis of petrographycombining electron microprobe and SEM, black opaque matters, which compositionis mostly of microcrystalline silicate and magnetite, are widely found runningreticulately through mineral particles, crystal and cleavage crack followingmetasomatic alteration in the altered host rock and its xenoliths. Our research draw aconclusion: The microcrystalline silicate and magnetite showed character of liquationin back scattered electrons graph. And this microcrystalline solid, which resulted inmetasomatic alteration, is one of the direct microcosmic impressions of mantle fluidmetasomatism with characters of melted and supercritical fluid. Several specialxenoliths are discovered in the alkali-rich porphyry in Hedong village, Liuhe, westernYunnan. The primary research by petrography, petrochemistry, electron microprobeand SEM shows that the pure calcite peritecticum (xenolith) and bearing-quartz topazpegmatite xenolith resulted from the degasification in the migration process of mantlefluids. And the black microcrystalline iron-rich silicate-melting xenolith is theseparation product of degasification in the migration process of mantle fluids. Thecharacters of petrochemistry and mineral compositions and the analysis of crystallinestate, especially the existence of native iron further prove that the xenolith is mantlefluid matters of reduction or anoxic condition. The data of the metallogenic elementsin the deep-derived xenoliths were studied by contrast with the average of those of themantle. The study showed that mantle fluid hasten the concentration of metallogenicelements and primarily discussed the relationship between mantle fluid metasomatismand mineralization.