Zircon U-Pb Dating And Geological Significance Of The Biotite Monzonitic Granite From Yimin Area In Inner Mongolia

Yimin area is located in the western slope of the northern part of Great Xing,an Range.During the Paleozoic,it was influenced by the Paleozoic Asian tectonic domain,the Mesozoic and Cenozoic experienced by the coastal Pacific tectonic domain and the Mongolian-Huocikeyang oceanic tectonic domain.There are some granitic rocks in the Yimin area.However,due to the large area covered by Quaternary Period,the vegetation development and the low degree of rock outcrop,the lack of granite chronology and rock geochemical data in this area that restricts the research work on the tectonic evolution and geodynamic background in different geological periods in this area.In view of this,this paper selects the biotite monzonitic granite in this area as the research object,conduts systematic studies on the petiology,zircon LA-ICP-MS U-Pb geochronology,whole-rock geochemistry,and zircon in-situ Lu-Hf isotope test and analysis of biotite monzonitic granite in Yimin area,in order to find out the formation era of biotite monzonitic granite,rock formation,the nature of the source area etc.To provide evidences for the study of magmatic activity and geodynamic background in the study area.Biotite monzonitic granite in Yimin area are gray,with medium fine unequal grain structure and massive structure,containing diorite inclusion.The main mineral composition is plagioclase,potassium feldspar,quartz,biotite,and the accessory mineral is zircon,titanite,magnetite and so on.Analytical results show that Yimin biotite monzonitic granite has the geochemical characteristics of high silica?68.32%⁷0.62%?,alkalirich?Na₂O+K₂O=7.79%⁹.01%?,and poor in CaO?0.89%².51%?,MgO?0.80%¹.30%?and P₂O₅?0.16%⁰.23%?.The values of A/CNK and A/NK are between 0.99¹.08 and1.22¹.42 respectively,which belong to metaluminous-peraluminouscalc-alkaline series.The contents of total rare earth elements in biotite monzonitic granite are low,with remarkable fractionation between light rare earth elements and heavy rare earth elements,but without obvious Eu and Ce anomalies.The trace element contents display enrichment in K?Rb?Th?Ba?Sr and LREE,relatively depletedin U?Ti?La?Ce.Combined with all above mentioned geological features,the biotite monzonitic granitehas the characteristics of I-type granite.Zircon LA-ICP-MS U-Pb dating results suggest that the granite was formed at 303±2Ma,which was a product of late Carboniferous magmatism.Hf isotopic data show that it has high?Hf?t?values?+9.20⁺15.89?,the corresponding two stage model ages(T_DM2)clustered in 500⁷00Ma.It reflects the origin of the biotite monzonitic granite magma was derived from thecrustal growth in Neoproterozoicand.Based on the study of biotite monzonitic granite in Yimin area combined with the regional geological data and previous research results,it is believed that the extension background of the collision of biotite monzonitic granite in Yimin area.The collision collage between Xing,an Range and Songnen Range occurred before the late carboniferous period.