Geochemical Characteristics Of Volcanic Rocks In Late Jurassic Manitu Formation At Hao Qin Of West Ujimqin Banner,Inner Mongolia

This paper is supported by The project“Inner Mongolia 1:50000 of Haoqin etc four pieces of regional geological and mineral survey”.The study area is located in the eastern central Asia orogenic belt and within the Xingan-mongolia orogenic belt.The Paleozoic formation development in the studied area,magmatic activity is strong,has a long,complicated tectonic evolution history and metamorphism,deformation characteristics.Starting from the late Jurassic,a violent volcanic eruption occurred in the study area,formed a wide range of Mesozoic volcanic rocks,that become an important part of the Greater Xinggan mountains' Mesozoic volcanic rock belt.Manitu Formation volcanic rocks mainly are a suit of the intermediate volcanic rock?The rock types are basaltic trachyandesite,trachyandesite,latite,trachyte,and belong to high-k calc-alkaline-alkaline series.Standardized rare earth elements' distribution curve is the right type,light rare earth moderate concentration and does not have Eu negative anomaly.Manitu Formation volcanic rocks have the characteristic that enrichment of Rb,Ba,Th and K large ion lithophile elements,high field strength elements Nb,Ti,P elements relatively depleted,Cr,Ni strongly depleted.The span of Manitu Formation volcanic rocks' dating data is very big,between125.92±0.50~158.7±1.2Ma.In the area of Haoqin,this article,through the zircon U-Pb LA-ICP-MS testing,elicit that the age of the Manitu Formation is 163.8±1.9Ma,in the middle-late Jurassic,and this article will classify it as the late Jurassic.Manitu Formation volcanic rocks are not the products of crystallization differentiation,but directly formed in high pressure environment 1.5 Gpa,have high potassium and rich alkali features,from the petrology characteristics determine its form in the continental collision orogenic belt.The trachyandesite magma originated from the lower thickening crust.Its source area evolved from the upper mantle is similar to the basaltic composition and trachyandesite magma formed by partial melting.Some degree of magma mixing happened in the process of magma migration.There is not obvious that differentiation crystallization and assimilation-contamination.The tectonic setting of Manitu Formation volcanic rocks is the early of continental collision orogenic post-collisiona and display continental compression environment.The dynamic source is the closure of the Mongol-Okhotsk Ocean and subduction of the paleo-Pacific plate.