A Study On The Geochemistry Characeristics And The Genesis Of The Permian Typical Plutons In Xinhure Reigion,Urad Middle Banner,Inner Mongolia

The study area is located in the middle segment of the northern margin of the North China Craton?NCC?,about 100 km from the Solonker suture zone in the north,where the middle-late Paleozoic magmatism is strong,these magmatic activities can not only constrain the time of the regional tectonics evolution,but also are important means for the study of the interactions of crust and mantle.Therefore,this study selected typical Permian intrusive rock in this region as the research object.The age of the plutons,geochemistry characteristics and the genesis of these plutons were disscussed,through detailed research of petrology,geochemistry,isotope geology and chronology,etc.The main results are followed:A weighted mean ²⁰⁶Pb/²³⁸ U age of 265.9±2.4Ma was yielded for Wuhaolai gabbro diorite by LA-ICP-MS zircon U-Pb,which indicates the pluton emplaced in the late Permian.According to the available previous research in this area,the Permian magmatism sequence is Dawudian pluton,Zhaogentaola pluton,Wuhaolai pluton and Hanihe pluton.Dawudian and Zhaogentaola granites are similar in geochemistry characteristics,they both belong to metaluminous and weakly peraluminous series and can be attributed to the high-K calc-alkaline I-type granites.In term of REE and trace element,they are both characterized by sub-strong fraction between LREE and HREE,obvious enrichment of LILEs?K,Rb,Ba?and high loss of HFSEs?Nb,Ta,Ti?,which is shared by many arc magmatic rocks.Wuhaolai pluton is characterized by high Mg#?0.50⁰.72?,low REE content,enrichment of compatible element?V,Cr,Ni?and LILEs?K,Ba,Th,U?and high loss of HFSEs?Nb,Ta,Ti,P?,which indicate the pluton may be derived from enriched lithospheric mantle,which had been metasomated by the subduction-related fluid.Hanihe granite pluton is characterized by high silcon,potassium and aluminous,what's more,it has obvious fraction between LREE and HREE,and the rock are also enriched in LILEs and depleted in HFSEs,these characters indicate that the pluton can be attributed to the typical S-type granite,which derived from crust partial melting.The Nd-Sr isotopic data of Dawudian,Zhaogentaola and Wuhaolai plutons are similar,which are all ploted between the mantle array and lower crust in(⁸⁷Sr/⁸⁶Sr)_i-?_Nd?t?diagram,which means these plutons may be generated by mixture of mantle and lower crust magma.However,the Hanihe pluton has very high(⁸⁷Sr/⁸⁶Sr)i ratio?>0.732355?and very low ?Nd?t??-34.59^-36.60?,which is similar to the Nd-Sr content of lower to middle crust.Combine with previous research and the geochemistry characteristics of these plutons,the Dawudian pluton could be formed in the Andean-type active continental margin,which is related to the southern subduction of the Paleo-Asia Ocean beneath the North China Craton?NCC?.For the Zhaogentaola and Wuhaolai pluton,they were all formed in the transformation of sys-collision to post-collision tectonic environment,and the slab break-off could play an important role in the process of the magma formation.And the Hanihe pluton was formed in the post-collision tectonic environment,its magma could be derived from partial melt of the lower to middle crust,which was thickened by the collision of the North China Craton and South Mongolia microplate.Therefore,the Palo-Asia Ocean had not been closured before 290 Ma,but during 275²65Ma,the Palo-Asia Ocean had been closured yet,and the North China Craton and South Mongolia microplate were collisoned.