Magmatic Process And Source For The Permian Basic Rocks In The Northeast Of Tarim Plate

Beishan region in Xinjiang has focused attention on extremely geoscience,because it distributes extensively magmatite of Late Paleozoic. The studying degree of the predecessor is low to the Permian mafic-ultramafic rock. The representative Gubaoquan rock body, dikes from the 1:200000 geological map in north of Baiyushan region and Liuyuan basalt are selected and studied on petrology,crystal chemistry, rare-earth elements, trace elements and Nd, Sr, Pb isotopes in detail, which analysis the magmatic processing, magmatic character, mantle source character and probably formation mechanism. The following conculsions have been drawn:1. Gubaoquan rock body mainly is composed of the gabbros, it also contains a few olivine pyroxenites and the pyroxene troctolite. The characteristics of petrography, petrochemistry, crystal chemistry of petrogenetic minerals and REEs geochemistry all display plagioclase and clinopyroxenite fractional crystallization greatly developed. Nd, Sr, Pb isotopic compositions and lithogeochemical characteristics fully evidence the exchange of material between magma and country rock. TiO₂, Na₂O, K₂O contents are very low in all kind of rocks, the eNd_t value is + 6.89, + 8.09, + 6.94 in gabbros, olivine gabbro and the pyroxene troctolite respectively, which indicate they source from in highly the depleted lithosphere mantle. Its primary magma is high MgO tholeiite. The FeO^*and SiO₂ contents evidence that source rock was lherzolite when melting began, and the soure rock type has changed into harzburgite when melting persisted to a certain extent. REEs geochemical Characteristics evidence that melting occurred in the stable domain of spinel.2. In meymechite dike and phogopite-plagioclase peridotite dike, MgO content respectively is 28.86% ～ 32.78% and 27.28% ～ 34.99%., they belong to the ferrguinous ultrabasic rock . The dikes all include the considerable amount the early olivine.crystallization phase and undergo the strong assimilate-contamination, the meymechite is stronger . Especially, the meymechite is relatively depleted in...