Petrogenesis Of The Palaeoproterozoic Granodiorite In Kuruktag,Xinjiang: Implications For The Differentiation Of The Old Basement Of The Northern Tarim

Recognizing the melting differentiation of TTG is the key to the evolution of the continental crust,which is essentially the improvement of the maturity of the continental crust.Because of its long and complex evolution history,the Tarim craton has become an important window to study the early crustal evolution.In order to study the evolution of the Tarim crust in Proterozoic,this paper mainly studies the U-Pb and Lu-Hf isotopes of zircons and rock geochemistry of the Paleoproterozoic granodiorites exposed in Kuruktag area,northern margin of Tarim.Achievements and understandings:?1?LA-ICP-MS zircon U-Pb dating of granodiorites from the Xishankou Blue Quartz granite body in Kurutag area,Tarim shows that the granodiorite was formed at 1945±7 Ma,which is a magmatic activity of late Paleoproterozoic.?2?The granodiorites have high SiO₂?62.69%⁶5.29%?,K₂O?5.01%⁶.25%?,K₂O/Na₂O?2.02².57?and low TiO₂?0.34%⁰.42%?,MgO?1.30%¹.48%?,Fe₂O₃^T?4.52%⁵.00%?,Na₂O?2.43%².58%?and Al saturation index ASI=1.01¹.11,which belong to weak peraluminous granites.The total amount of rare earth elements is high(540.78×10^-66.9.01×10^-6)with a wide range of variation.HREE?Gd,Tb,Dy,Ho,Er?and HISF?Nb,Ta,Zr,Hf?are deficient in trace element partition diagram,and LREE?La,Ce,Pr,Nd,Pm?and LILE?Rb,Sr,Ba,Na?are enriched.There are obvious Eu anomalies?delta Eu=0.50-0.77?.The saturation temperature of zircon ranges from 889.48?to 895.17?,with an average of 891?.The formation pressure of rock should be about 10 kbar.?3?Lu-Hf isotope analysis shows that zircon 176Hf/177Hf ranges from 0.281378 to0.281419,epsilon Hf?t?ranges from-4.7 to-6.9,T_DM¹=2513²574,and T_DM²=2875²976 Ma.This indicates that granodiorite originated from the old basement rock series in the northern margin of Tarim,which was partially melted under the high temperature and pressure of TTGs in the late Neoarchean.?4?By comparing the contents of geochemical elements in TTG whole rocks at the end of Neoarchaean in the study area,it is considered that there was a differential reconstruction of the old crust in the late Paleoproterozoic in the northern margin of Tarim,and the formation of this meta-potassium crust marked the further maturation and stability of the Tarim craton.?5?The formation of granodiorite by partial melting of TTG requires the convergence of lithospheric plates.The northern margin of Tarim is in the compressive environment of plate collision during the period of¹.95 Ga.Combining with previous research data,the Tarim craton belongs to a part of Columbia Supercontinent.