Study On The Petrography And Geochemistry Characteristics Of Volcanic Rocks In The Northern Part Of The Tarim Basin

It has great theoretical and practical significance that study Permian volcanic rocks of Tarim.Permian volcanic rocks in the Northern Tarim Basin have been studied and gained some achievements in this paper.The Permian volcanic rocks in the north of Tarim basin can be divided into tuffs,basalts,dacites and andesites.The lithofacies can be divided into effusion facies,fallout facies or volcanic eruptive sedimentary facies and pyroclastics flow facies.The major stages of Permian volcanic activity in the study area can be divided into three according to the research of petrology and logging curves.The explosive eruption is the main mode and the main product is intermediate acid volcanic tuffs,sedimentary tuffs or tuffaceous sedimentary rock of the first stage.The effusion eruption is the main mode and the main product is basalt of the second stage.The effusion eruption combine with intensity explosive eruption is the main mode and the main product is dacitic lava or(melting)tuff of the third stage.The volcanic rock of each stage is controlled by foundational fault.The geochemistry characteristics indicate that the influence of differentiation is little on the magma evolution in this area.The volcanic rocks are enriched in incompatible element and there is a separation and crystallization of plagioclase during the process of magma rising.The volcanic rocks are enriched in LREE.The basaltic magma is formed by partial melting of the enriched mantle.There is contamination of lithospheric mantle material and crustal material in the process of magmatism.The separation and crystallization of olivine may exist in the process of basaltic magma evolution.The acidic magma is formed by partial melting of the crust without mantle material.The volcanic rocks of the study area are developed in intraplate setting.The Permian volcanic activities in the study area is related to the mantle plumes.The Permian volcanic rocks in this area are part of the Tarim Igneous Province.The basaltic magma is formed by melting of the mantle plumes.The acid magma is formed by the partial melting of cruatal material under the action of the mantle plumes.The basaltic magmatic activities of the second stage have created conditions for the acid magmatic activities of the third stage.The evolution of the Permian magmatic activities in this area: Low degree partial melting of the lithosphere mantle caused by continuous high heat roasting.With the increase ofmagma and then it is erupted to the surface,forms flood basalt of central Tarim area.The magma which formed by mantle plume melting,it converts into flood basalt of the north Tarim area.Partial melting of crustal material caused by continuous rising,heating and self melting of the mantle plume.The magma formed by partial melting of crustal material is the thick dacite of the third stage in the North Tarim.