Geochemical Characteristics Of The Yanshanian Intrusion From The Wangxiang Area In Northeast Hunan Province And Its Geodynamic Significance

The northeastern Hunan Province is located in Southern China plate and has undergone intense magmatic activities since Mesozoic time.The Yanshanian is the strongest period.The Wangxiang intrusion includes three kinds of rocks: two mica granite(5 to 50% of muscovite,0.2-5% of biotite,);garnet granite(Garnet 2-5%,muscovite 15-20%,biotite 0.2-5%);biotite granite Biotite 30-35%,muscovite 0.2-3%,free of garnet).Based on the major and trace elements,REE geochemical test,and the main trace element geochemical characteristics collected from the Yanshannian Wangxiang intrusion,these granite has high SiO2 and Al2O3,but low MgO content.The aluminum saturation index for(1.12-1.43)is a strong peraluminous granite.In the trace elements and rare earth elements Y and Yb were generally low,two mica granite and garnet granite trace elements Ba,Sr,Eu,Ti elements in losses,rare earth elements,two mica granite is right type with light rare earth enrichment pattern,the heavy rare earth is flat,light hree,in varying degrees,the samples showed negative Eu anomaly.But the total amount of rare earth garnet bearing granite samples not high REE fractionation is not obvious,a dish,which all samples showed negative Eu anomaly,showed four grouping effect of rare earth elements and geochemical characteristics of biotite granite is similar the adakite and adakite,discriminant in Sr/Y-Y diagram,biotite granite all fall on the adakite area in the partition map showed a significant enrichment of light rare earth elements,the reaction occurred obvious fractionation of rare earth elements,no obvious The initial Eu value of abnormal.Based on the analysis of the diagenetic source area,the tectonic setting and the magmatic evolution process of the Xiangxiang rock mass,it is speculated that the resorption of the mound sand,the metamorphic mudstone and the amphibolite is mainly from the ancient base.Yanshanian thickening of the thickness of the crust itself is not uniform,or the nature of the crust,or the different tensile strength caused by the depth of the granite source area,through the basaltic magma invasion of the impact of thickening crustal melting of the formation of biotite granite,The crust is about 40 Km in the crust to form two mica granite and garnet-bearing granite.For this kind of crustal thickness,this paper suggests that it may be caused by the difference of the early tensile strength of the lithosphere extensional thinning.Therefore,it is inferred that the northeastern part of Yanshanian is in tensile stress state.