The Significance Of Hf Isotope Characteristics Of Paleozoic Granitic Intrusive Rocks In Kuruktag Region,Xinjiang To The Provenance Identification And Crustal Growth

Tianshan orogenic belt is a part of the giant composite orogenic belt in Central Asia.Different types of palaeozoic granites are exposed in the Tarim basin on the South side,and the granites which is an ideal place to explore the composition and evolution of deep crust record the history of tectonic evolution.However,the lack of isotope data that can trace the material composition and evolution process in the source region of magma seriously limits the understanding of the crustal evolution in Tianshan orogenic belt.In this paper,four granite rocks(454.6~340.6Ma)without the trace of magmaof Kuruktag West at the north edge of Tarim were studied,their chronology and petrogeochemistry were collected,and their characteristics of Lu-Hf isotope were studied systematically.Finally,the crustal growth patterns of the Palaeozoic period and the tectonic background of the Palaeozoic period in the Southern Tianshan orogenic belt and the northern edge of Tarim are explored.The results of Lu-Hf isotope show that the granite rocks(454.6~340.6Ma)(-11.60~-26.71)and the age of the old Hf model(2.2~3.1Ga)have negative ?Hf(t)(11.60 ~-26.71)which shows the material in the source region is dominated by the crustal material of Paleoproterozoic--Neo-Archean.In the granite rocks of 419.2Ma and400.6 Ma,the values of ?Hf(t)are both in the negative(-6.59~0.82),and the age of the Hf model is between 1.3 and 1.8 Ga,which shows that the source region has not only late Mesozoic crustal material,but also mixed with mantle magma.In the granite rocks of 340.6Ma,The negative value of ?Hf(t)(-40.79 ~-17.28)and the age of the old Hf model(2.5 ~ 3.9 Ga)indicate that the source region is dominated by the crustal material of the late-early Proterozoic.Combined with regional geological data and geochemical characteristics,we think that 454.6 Ma ~ South Tianshan subducted towards south and the active continental marginwas generated.Subsequently,419.2 ~400.6 Ma,during the continuous oceanic-continental subduction,the mantle-bearing magma partially melted with the induced crustal material form the felsic magmawhich mixed in the deep crust to form the crust-mantle mixed magma.This reflects the vertical growth of the continental crust in this period.Finally,a large number of S-type granites which were formed on the edge of the active continent in ~340.6Ma suggests that the Southern Tianshan Ocean was in the late subduction stage and gradually closed in the collision environment.