THE DETERMINATION AND GENESIS OF METAMORPHOSED A-TYPE GRANITESOF THE DABIE ULTRAHIGH PRESSURE BELT
Qian Cunchao,Lu Yulin(Anhui Academy of Geological Survey, Hefei 230001,China)
The metamorphosed granites of the Dabie UHPMB are characterized by:(1)single rock association dominated by adamellite(protolith)lacking intermediate-basic rock and syenite;(2)scale granoblastic texture, gneissic structure and the remains of igneous rock texture and structure; (3)evident intrusive contact relationship with eclogite and other ultrahigh pressure metamorphosed rocks and their xenoliths; (4)petrochemically rich silicon and alcali and poor calcium and magnesium with SiO276%, (Na2O+K2O)7%, CaO0.5%and MgO0.4%; (5)trace elements of high content of Zr, Y,Nb and REE and low content of Sr, Sc,V , Ni, etc.;(6)amphibolite facies of metamorphosed mineral association of plagioclase+quartz+potassium feldspar+mica+garnet+epidote. Based on the above characteristics of the metamorphosed granites in the Dabie ultrahigh pressure belt, they are thought to be A-type granites, close to A2 subtype, which provide important geological basis for further recognition of the tectonic evolution, the formation of eclogite and other ultrahigh pressure metamorphosed belts and exhumational mechanism of the Dabie Mts.
【CateGory Index】： P588.121