Geochemistry,Geochronology And Its Geological Significances Of Magmatic Rocks Of Chaiwa District In Tibet

In recent years,many scholars have been concerned about the cretaceous volcanic rocks in the Tethys-Himalayan region.The area is located in the eastern part of the Tethys-Himalayan region,which is the northern border of great India also in the remnants of Cuomei large igneous province.This paper researches the magmatic rock geochemistry and chronology,analysis of its causes,tectonic environment,provede evidence for east extension of the new Tethys ocean and the Cuomei great igneous,pointout directions of furtherprospecting.The rock types of the volcanic rocks in the Chaiwa area of Tibet are mainly the amphibolite,the basaltic basaltic and the arctic basalts.The zircon U-Pb age is 142 ± 1.0Ma,and its formation is Early Cretaceous.Elemental geochemical studies have shown that diabases are rich in total alkali,Ti,Fe,P,Mg,similar to OIB;rare earth elements' s ?REE = 270.01-311.19 ppm,LREE is slightly enriched,in large ion lithophile relatively enrichment of Ba,poor K,Sr;In the high field strength relatively rich of Th,U,Zr,Hf and depleted Nb,Eu is not obvious.The dacite is alkaline acidic rocks whch is rich of Si,Al,K,Ca,poor of Mg,Fe.rare earth elements ?REE =266.20-555.8ppm,enrichment of LREE,in the large ion lithophile elements,and the concentration of rare earth elements is rich of Rb,Ba,loss of Sr,K,Eu;in the high field strength relative enrichment of Th,U,loss of Nb,Ti,Zr,Hf;has a significant Sr negative anomalies,may be with low pressure conditions plagioclase(average of 40.1 ppm),and an average Nb/La of 0.29,suggesting that it is related to the deep melting effect of the silica-alumina crust.The rock types of the basic veins in the Chaiwa area of Tibet are mainly gabbro,diabase,and near east-west trending.The U-Pb ages of the two gabbro zircons are 145.99 ± 0.98 Ma and 146.12 ± 0.72 Ma,and their ages are Early Cretaceous.Elemental geochemical studies have shown that gabbro and diabase are enriched in all alkali,Ti,Fe,P and Mg,and are calciferous.They are similar to OIB.The total amount of rare earth elements ?REE = 897-1121 ppm,the relative enrichment of Ba in large ion lithophile elements poor K,Pb,Sr;in the high field strength element is relatively enrichment of Nb,Ta,Zr,Hf,Th,poor of U,Ti;Eu is not obvious.The magmatic rocks are formed in the background of the initial rift of the continental margin.The diabase,gabbro and basalts may be the product of the interaction between the Kerguelen mantle plume and the lithospheric mantle.The formation of the amphibolite and the resorption of the crust related.The Early Cretaceous magmatic rocks provide the source of ore-forming material for the enrichment of the initial source layer in the study area.The Paleogene and Neogene's acid intrusive rocks provide material source and thermodynamic power for the mineralization of the study area.The area and the acid rock surrounding tectonic development area are favorable locations for ore prospecting.