Geochronology And Geochemistry Features Of Early Permian Magmatite From Xiwuzhumuqin Hanwula Area Of Inner Mongolia

Xing-Meng orogenic belt has experienced frequent magmatic activity. This article selects Bayan Prague compound rock mass of early Permian in Xiwuqi Hanwula area of Inner Mongolia as the research object, its field distribution, scale, occurrence, rock assemblages and petro-graphic features have been studied in detail through the detailed field route survey, our key profile, and indoor microscopic thin section analysis.At the same time, this article preliminary limits the set of rock geochemical properties and formation age, briefly analyzes the origin and formation of rock mass structure environment. The purpose is providing basis to find out tectonic evolution history of central Xing-Meng orogenic belt in early Permian. The paper mainly made the following preliminary understanding:1.Bayan Prague compound rock mass consists of gabbro, pyroxene diorite, long alkali granite.LA-ICP-MS zircon U-Pb isotope dating shows,gabbro and alkali-feldspar granite emplacement age is 280.1± 1.3Ma and 279.8±1.2Ma?279.9±1.6Ma,in early Permian,formed in the same tectonic magmatism event?Petrological and geochemical characteristics show that they are closely related causes,which SiO2 content of 44.01%-77.60%, with a obvious gap between 55.91%-75.97%.This shows bimodal type characteristic of magmatic rocks.2.Gabbro is a set of low potassium series- calcium alkaline porphyry rock series,which SiO2 content of 44.01%-52.63%,Na2O+K2O content of 2.78%-5.33%(Na2O>K2O),Al2O3 content of 15.11%-24.43%, TiO2 content of 0.55%-3.59%, Mg content of 23%-60%.The content of rare earth elements is low,with a consistent flat type partition type and Eu positive anomaly. Rock relative enrichment of Ba, K, Sr, Eu and other large ion lithophile elements,losses of Nb, Zr and Hf high field strength elements,which reflects the subduction zone tectonic background characteristics.Alkali-feldspar granite relative enrichment of SiO2, K2O+Na2O, FeOT/MgO, losses of Al2O3,CaO, MgO. The content of rare earth elements is low,with a consistent seagulls type distribution curve. Trace elements content is higher as a whole,with a consistent distribution curve. Alkali-feldspar granite is obvious enrichment of Th, U K, Rb large ion lithophile elements,losses of Ba,Nb,Ta,Sr,P and Ti,with A type granite geochemical characteristics.3.Paleo-Asian Ocean mainly northward subduction between Carboniferous and Permian.Southern margin of the Siberia plate belongs to the active continental margin environment, oceanic plate subducted fast with high angle, induced convection upwelling mantle material to shunt after reach the bottom of the lithosphere,which offers both A type granite output back-arc tectonic environment and lower crust molten condition. Upwelling mantle material forms gabbro.Pyroxene diorite formed by crystallization differentiation,who contacts with the earth's crust to partial melting of crust formation of the alkali-feldspar granite.4.The presence of Bayan Prague bi-model intrusive rocks and A type granite means Xiwuqi Hanwulla region in stretch tectonic setting in the Permian period.Combined with regional geological background,the authors concluded that Bayan Prague compound rock mass is most likely formed in the back-arc spreading or interarc basin,which is the product of oceanic crust subduction to reduce function before Paleo-Asian Ocean closed in Early Permian.