The Chemical Petrology Characteristics And Tectonic Evolution Of Renacuo Volcanics Of Gaize, Tibet

Volcanic rocks,can reflect the magma’s activity and the evolution of the tectonic of the plate clearly as the products of the magmatic activity of the deep level of the earth. The formation and evolution of the BN suture zone has always been the focus of research both at home and abroad. Especially in recent years the found of super large gold porphyry copper deposits in the BN suture zone makes the study of mineralization have great economic benefits. And the early cretaceous magmatic activity plays an important role for the analysis of metallogenic regularity as the source of the minera.The study area is located in the south of the south Qiangtang basin,between the BN suture zone and the LS suture zone. It is also located in the northern of Tibet alpine desert. The research Level of here is very low. Volcanic activity has been going on since the Mesozoic era. The characteristics of these volcanic rocks help usunderstand the region intracontinental subduction and collision orogenic belt thickening and the spread of late chasmic process. Series of calcium alkaline igneous rocks may form in the collision period or before the collision period. The causes may be related to the oceanic basin subduct to the bottom of qiangtang block in the Mesozoic. After the subduction, arc-land’s collision and land–land’s collision began. Southern qiangtang region rise for the first time and ocean basin closed gradually. Then the nature of magma converse to potassic-super potassic alkaline igneous rocks. The reason may be the uplift of qiangtang basin, the lithosphere delamination effect caused the upwelling of the asthenosphere material and the enrichment mantle’s melting.Through this survey and the experimental results of the analysis, it is concluded that the volcanic rocks of Renacuo region is consist of andesite, dacite and acidic volcanic clastic rock. They are potassium-high potassium calc-alkaline series. Light rare earth elements and large ion lithophile elements are enrich, high field strength elements are little. It also has a weak negative Eu anomaly. The age of them are about 111.7 Ma. In the early there are basaltic magma and in the late there are acid rhyolite and volcanic clastic rock. Volcanic rocks of research area show that ocean basin closed after the subduction, lead to the Lhasa collide to qiangtang block.Then the subduction plate dehydrate and break away. Then the mantle wedge partial melting. And mixed with crustal material. The Magma rocks formed through crystallization differentiation. The completely closed time of Tethys ocean should be the late of early cretaceous.