Petrogenesis Of Paleoproterozoic Granites In Quruqtagh,Xinjiang

The structure, composition and evolution of the continental crust is one of the most important scientific problems of earth science. As an important part of the continental crust,granites are the best objects to study the formation and evolution of the continental crust.Quruqtagh block is located in the northern margin of the Tarim block, and it has an old precambrian basemen with large scale and intact ancient tectonic magmatic evolution information, hence it’s amost important windows to research the precambrian geological evolution of Tarim block.This article systematically studied on the petrology,chronology,and geochemistry of the granits which exposed in the west of Quruqtagh.The main research results and cognition are as follows:(1)Quruqtagh region mainly exposed gneissic granite diorites, quartz diorites, granodiorites and quartz monzodiorites.LA-ICP-MS zircon U-Pb dating results give an emplacement age of 2405.8±5.2Ma for North Kawuliuke gneissic granite diorites and 2314.4±8.8Ma for Kawuliuke quartz diorites,they are the same products of magma in Early paleoproterozoic in Quruqtagh;Xishankou granodiorites and Aoyikuruke quartz monzodiorites formed in the late paleoproterozoic,the Zircon U-Pb dating results shows 2015±17Ma and 1922±16Ma.(2)The early paleoproterozoic granites are the calc-alkaline series and I-type granites,they have the same characteristics as TTG rocks.They are characterized by enrichment in SiO2,Na2 O and Al2O3,depletion in K2 O,MgO,CaO and Fe2O3, higher alkaline,A/CNK=0.90-1.05, belonging to metaluminous series rocks,and higher Sr/Y,La/Yb.Because of the rocks are enrichment light rare earth elements(LREEs),depletion in heavy rare earth elements(HREEs) and positive Eu anomaly,suggesting that the source area residual hornblendes or garnets.The late paleoproterozoic granites are Shoshonite series and I-type granites, depletion in SiO2 and Na2 O, enrichment in K2 O and Al2O3, A/CNK=0.92~1.01, belonging to metaluminous series rocks. The chondrite-normalized REE patterns show that the granites are enriched in LREEs but depleted in HREEs, with high fractionations between LREEs and HREEs and the chondrite-normalized REE patterns of the overall curve was rightist.In addition, the granites are relatively rich in such LILEs as K,Rb and Ba, but poor in such HFSEs as Nb,Ta,P and Ti in the primitive mantle-normalized trace elements patterns,and they are indicated the characteristics of volcanic arc granites.(3)Petrology, geochemistry and tectonic environment discrimination show that early paleoproterozoic TTG granites are the product of oceanic crust subduction; Late paleoproterozoic granites are continental arc melting granites, by the thickening of the lower crust. Combining with regional geologic data, we make a conclusion that late paleoproterozoic granites are the products of Columbia supercontinent convergence.