Chronology, Geochemistry And Petrogenesis Of The Mesozoic Granites From Southern Khanka Block

Khanka block mostly Located in Russia, In the North-West, Khanka block andJiamusi block are bounded by Dunmi fracture, in the North, it adjacentNadanhada-BijinTerrane, and It′s in superimposition section Paleo-Asian Oceantectonic domain and Pacific tectonic domain, experienced a very complex tectonicevolution. Khanka block have experienced Series tectonic evolution such as thecollage process with Songnen-Zhangguangcailing plots, Western Pacific′ssubduction, and the Sinistral strike-slip of Dunmi fracture. So the South Khanka blockhave provided a platform for the regional tectonic evolution study of NortheasternChina. There′s a large area of granites exposed in the Southern Khanka block,Heilongjiang Bureau of Geology divided them into INDOSINIAN and channeledthem to the east granites, but it′s lack of precise isotopic dating data. In the same time,there is no system Information about the causes and tectonic settings of the granits.We choose Balengshan rock mass, Jinchanggou rock mass, Tianqiaoling rockmass and Fengyueqiao forest rock mass as our objects of study. Carried out a study ofpetrology, geochronology, geochemistry and zircon Hf isotope. We find the granitesmoustly were monzogranite and some were granodiorite, The LA-ICPMS U-Pbisotopic dating results shows that the monzogranite′ages respectively were204±2Ma,203±2Ma and205±2.4Ma.(the Balengshan rock mass′s age was204±2Ma, theJinchanggou rock mass′s age was203±2Ma, the Tianqiaoling rock mass′s age was 205±2.4Ma) and the Fengyueqiao forest rock mass whose age was202±2.5Ma isgranodiorite. Overall, these granites from Southern Khanka block crystallized in closeage. Considering that the age201.3Ma was the boundary of Triassic and Jurassic inthe international stratigraphic table and some other error factors, we draw them to theend of the Late Triassic-Early Jurassic early.These granites geochemical composition is relatively rich in silicon, SiO2contentof69.61%-77.27%, SiO2content which granodiorite of69.61%-69.98%, SiO2contentmonzogranite74.24%~77.27%; Weakly peraluminous, the aluminum saturationindex A/CNK was1~1.1; The monzogranite was K-rich, K2O/Na2O=1.08~1.33,w(K2O)+w（Na2O）=8.02%~8.39%, the granodiorite was relatively rich in sodium,K2O/Na2O=0.58~0.65, w(K2O)+w（Na2O）=6.71%~7.83%；The two have largedifferences in total REE, LREE enriched and loss of HREE; Large LILE such as Rb,Th,U, K enriched and loss of HFSEs such as Sr, P, Ti. The monzogranite has aModerate-strong negative Eu anomaly(δEu=0.19~0.43), and the granodiorite has aModerate-weak negative Eu anomaly(δEu=0.57~0.82). Overall, all of the graniteshave the characteristics of silicon-rich, richer aluminum and weak peraluminous, Themonzogranites were high-K calc-alkaline highly fractionated I-type granites and thegranodiorite was calc-alkaline I-type granites.The Zircon Hf isotope data of granites in Southern Khanka block shows that εHf（t）of both monzogranite and granodiorite were positive,4.39~9.32; the Hf modelages is relatively young(0.65~0.96Ga), which was Neoproterozoic. Considering thestudy of Major elements and trace element characteristics, Regional tectonicevolution, we believe the source magma derived from partial melting of theNeoproterozoic crust in the context of Pacific plate subducting to the west.