Geochronology,petrogenesis And Tectonic Setting Of Monzogranite In Suolun Area,Central-southern Great Xing'an Range

This thesis studies the monzogranite in Suolun area,central-southern Great Xing'an Range.Based on the results of geological survey in the field,we present petrological,geochronology,petrogeochemistry and Hf isotope characteristics of zircon for these monzogranite rocks,the geological characteristics of monzogranite in the region were identified,the formation age of monzogranite was determined,information on the petrogenesis and tectonic setting of monzogranite were analyzed.1.The monzogranite in Suolun area are mainly medium grain biotite monzogranite and fine grain biotite monzogranite.The rocks have a semi-automorphic granular structure,block structure.2.Two monzogranite samples of Suolun area were chosen for zircon U-Pb dating by LA-ICP-MS method.The U-Pb age data show that the weighted mean ²⁰⁶Pb/²³⁸U ages of these samples are 127.4Ma,and 125.6Ma,respectively,suggesting that the selected monzogranite were formed in the Early Cretaceous.3.The whole rock geochemical data show that the monzogranite in the research area have the characteristics of high Silicon and alkalis,and low Calcium,Iron and Magnesium,SiO₂=67.40%⁷6.85%,K₂O+Na₂O=7.82%⁹.35%,MgO=0.07%⁰.89%,CaO=0.15%².66%,TFeO=0.97%³.40%,A/CNK=0.97¹.19,indicating they are weakly peraluminous high-k calc-alkaline I-type granites.Besides,these monzogranite's light heavy rare earth fractionation is obvious,with moderate Eu negative anomaly,they are rich in LILEs?Rb,U and Th?and LREEs,and depleted in HFSEs?Ti,Nb and Ta?,Ba and Sr.4.The Nb/Ta and Zr/Hf mean values of monzogranite in Suolun area are 10.50 and26.15 respectively,which are relatively close to the corresponding values of the crust,11.4and 33.The mean value of Rb/Sr is 1.82,the mean value of Ti/Y is 75.20,and the mean value of Ti/Zr is 7.70,which have the properties of shell source magma.The sample's zircon Hf isotope data indicate that the monzogranite's?_Hf?t?values of+7.3 to+14.7,and the model ages(T_DM2)of two stages are from 511Ma to748Ma,which implies that the monzogranite's magma might be derived from the partial melting of the crustal substance from depleted mantle during Neoproterozoic-Early Palaeozoic.5.The monzogranite in Suolun area formed in the extensional tectonic system,the development of this extensive background may be related to the the lithosphere extension after the Mongol-okhotsk closure.