Chronology,Geochemistry And Petrogenesis Of Granites In The Badaguan Area,Northern Hailaer

Badaguan Area in the northern of Hailaer locates between China and Russia as well as in Derbugan tectonic belt,belonging to the erguna massif.In the north of erguna massif is Mongolia-okhotsk belt while in the south is coveraged by the ancient marine sediment of late palezozic.Where the Paleo-Asian Ocean,Pacific Ocean and Mongolia-okhotsk Ocean strong superposition,compound and transform,tectonic evolution is extremely complex,which played an important role in the tectonic evolution of the NE Asia.In recent years,Many scholars have carried out a detailed of researches about Formation time,geochemistry and petrogehesis of granites in northern erguna block.Accumulate a large number of U-Pb and 40Ar/ 39 Ar isotope chronology and geochemistry.But in contrast,chronology and geochemistry in west erguna block,especially in Hf isotope research is very sharp shortage.Predecessors were mainly based on the contact relationship of between granite and strata,degree of metamorphism,deformation characteristics and the K-Ar dating results.But due to the complexity of badaguan regional structural feature,mostly through reformation in granite,destroy the isotope system from their samples,so the age of granites in badaguan can't response of magmatic emplacement age.while missing of the geochemica restricted the deep understanding of its causes.On this condition,this paper does some researches for the granite on the respect of chronology,geochemistry and zircon Hf isotopic chronology,in order to define the specific formation of granite accurely,discuss the geodynamics backdrop of its factors and formation,as well as provide new evidence for regional tectonic evolution in NE China.1.Rock association and the ageThe granites in Badaguan area is composed of syenogranite and monzonitic granite,Zircon U-Pb dating indicates that the ages of syenogranite are216²26Ma and the monzonitic granites are 212²20Ma.Overall,the granites in Badaguan area is very similar,all belong to Late Triassic.2.Geochemical characteristics of the granitePetrogeochemistry characteristics of the granitic rocks show that syenogranites are in Late Triassic period.w?SiO₂?=71.34%⁷6.41%,w?Al₂O₃?=10.86%¹5.61%,w?MgO?=0.08% ⁰.31%,w?CaO?=0.33%⁰.44%,They are metaluminous with A/CNK ratios of 1.02¹.10?molecule?and low magnesium and calcium,and the content of alkli is higher and differentiation index?DI?of 92.48⁹5.80,w?K₂O?+w?N₂O?=7.37%¹0.00%,K₂O/Na₂O =1.12¹.35,rich kalium.Syenogranite rare earth element REE pattern shows that europium has middle negative anomalies??Eu=0.51⁰.71?for the right type,The total amount of rareearth elements is 112.37×10^-6193.13×10^-6,with rich light rare earth elements and depleted heavy ones,which are enriched in Zr,Hf,Rb,Th,K and depleted HFSE?e.g.,Nb,Ta,P and Ti?.Monzonitic granite has75.86%⁷7.75%SiO₂,10.99%¹1.78% Al₂O₃,0.27%⁰.31% MgO,0.33%⁰.62%CaO,and rich the content of alkli?w?K₂O?+w?N₂O?=6.59%⁸.01%?.They are metaluminous with A/CNK ratios of 1.01¹.10?molecule?and low magnesium and calcium,with differentiation index?DI?of 93.35⁹4.14.Monzonitic granite rare earth element REE pattern also shows that europium has middle negative anomalies??Eu=0.56⁰.65?for the right type and with rich light rare earth elements and depleted heavy ones,The total amount of rareearth elements is 141.66×10^-6164.75×10^-6,which are enriched in LILE,such as Rb,Th,K,etc.,depleted in Ba,Sr and HFSE such as Nb,Ta,P,Ti,etc.As a conclusion,The granites in Badaguan area have similar characteristics and change rules,such as rich silicon and alkli,low magnesium and calcium,all weakly peraluminous,right type and with rich light rare earth elements and depleted heavy ones and high differentiation index?DI>90?and so on.According to total amount of rare earth elements,Identifying the syenogranite and monzonitic granite in Badaguan are all highly fractionated I-type granites.3.Petrogenesis of the graniteThe Zircon Hf isotope data of granites in Badaguan area shows that ?Hf?t?of both syenogranite and monzonitic granites were positive?4.50¹0.45?with two-stage Hf model ages1 of 0.59-0.97 Ga,suggesting that they are derived from the newly formed young crust which separated from NeoProterozoic depleted mantle.Combined with the U-Pb ages and other geochemical features,we propose that the granite of Late Triassic formed in an active continental margin setting of the Mongol-Okhotsk ocean.