Study On Magma Mixing Of Early Permian Granites In Bailingshan Area,Xinjiang

Bailingshan Mountain composite pluton is located in the western of Aziz- Yamansu tectonic belt,East Tianshan Mountains, The study of the tectonic zone’s tectonic setting is the important part of restoring Northern Tianshan orogenic belt evolution. This dissertation is objecr on the early Permian host rocks and their enclaves.By the systematic overall study of field macroscopic outcrop characteristics, petrology characteristics, petrography characteristics, geochemistry characteristics of rocks and ore deposits,meanwhile,through the discussion on tectonic setting, source nature,and the mechanism of rock origin,we made the progresses as follows:1. Bailingshan Mountain composite pluton is the product of multi stage magmatic intrusions. The intrusive sequence of preliminary division from early to late is diabase, quartz diorite, granodiorite, monzogranite, syenogranite,granite-porphyry.2. The early Permian granodiorite as the representative of Bailingshan Mountain composite pluton widely expose mafic microgranular enclaves.By macroscopic geological characteristics from field observation, petrography characteristics from microscopic observation, and geochemical characteristics, mafic enclaves belongs to the mixing product of the felsic magmas and mafic magma from different source area.3. There are some amphiboles observed as the typical rock-forming mineral of I-type granite in host granodiorite,and not peraluminous mineral. A/CNK(aluminum saturation index) < 1.0, host granodiorite fall into calc-alkaline to high-k calc-alkaline regions.In a wor,the host granodiorite belongs to I-tyoe granite which is metaluminous, calc-alkaline to high-k calc-alkaline series.4. The source rocks of host granodiorite may be partial mafic andesite or basaltic andesite which is rich in amphibole. Residual mineral in source region are amphibole and plagioclase,The pressure of forming magma is less than 0.8 or 1.0GPa. The depth of forming magma is about 30 km.5. The host granodiorite is not subjected to metamorphism and deformation.Its mineral association show that it belongs to KCG,and indicate that it is formed in the tectonic regime conversion setting.Combination with the regional setting,we judge that the host granodiorite is formed in post-collision tectonic setting which may be associated with Kangguer remnant oceanic basin evolution.6. Bailingshan Mountain area has not the condition of lower crustal delamination. Therock-forming mechanism of host granodiorite may be associated with regional underplating,but don’t eliminate the influence of oceanic lithosphere delamination.7. The magmatic mixing processes in Bailingshan Mountain area may be a metallogenic factor of some iron ore-deposits.The data of isotopic and electron probe from Tieling iron ore-deposit show that both acidic and basic magma have some contribution during metallogenic process, and suggest that the magmatic mixing has great significance to the mineralization.