The Characteristics Of The YingFeng Rapakivi Granite And Petrologic Significance

According to field examination,the Yingfeng rapakivi granite which is mid-Proterozoic body occur in the structural belt of north Qaidam basin,which located between shear belt as a lentiform.Meanwhile the diabase dyke and quartz diorite digoclase-trondhjemite dyke vein were formed,which show a character of bimodal magmatic association.The magmatic body has pyterlitic rapakivi texture,and each main mineral is polygenetic.K-feldspar mainly shows the form of oval phenocryst,and exsolved albite stripe is well-developed.Plagioclase of magmatic crystallization mainly is oligoclase,owing to the alteration of different degree,then causing the drop of An and emerging many albite.Most biotite have separated magnetite and ilmenite as the result of alteration in different degree.The diabase has the characteristic of low alkali and high∑FeO,which belongs to tholeiitic rock,compared with the Ocean ridge tholeiite,it has high incompatible elements such as K₂O,which possessed the character of continental tholeiite.The geochemistry of rapakivi granite has the features of high value of alkali(Na₂O+K₂O=8.49%～9.39%),enrichment of K(K₂O/Na₂O=1.12～1.43),being closing to Al-saturation,high ratio of Fe and Mg(∑FeO/MgO=4.91～7.19);The enrichment of Rb,Ba,Ga,Th,Zr,Nb,Ta and the dilution of Cr,Ni,V;High value of∑REE (392.24x 10-6-594.76 x 10-6),strongly differentiation of REE((La/Lu)N =12.67-17.09) and weakly negative Eu anomaly(δEu=0.58～0.78),showing the features of A-type granite,which are similarto Miyun rapakivi granite.Yingfeng magrnatic body is similar to typical rapakivi granite,but they also have some defferent stage,some different reflected characteristics of magmatic body's forming environment and process.The matrix texture is eroded,because of deformation and metamorphism.The typical texture may be caused by reforming in Caledonian period.Also can be caused by the magrnatic effect of medium-Proterozoic in this area.The synthesize analysis shows that these intrusion formed in extension background and it's one member of anorogenic rapakivi granite of the North Hemisphere in Proterozoic,these intrusion were involved in ancient crust of North Qaidam basin orogenic belt in Caledonian period.