Sr And Nd Isotopic Characteristics Of Paleozoic Granitic Intrusive Rocks In Kuruktag Region,Xinjiang,Constraints On Crustal Growth And Tectonic Evolution

Kuruktag is located at the junction between the southern Tianshan and the Tarim Craton.it is a key area to the study of the northern Tarim tectonic setting,So its crustal evolution is very important to understand the evolution process of the Southern Tianshan Ocean.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,the Rb-Sr and Sm-Nd isotope measurements of East of ustengoller,Western ustengaele,Tiemenguan Southeast,Bosten lake country,Tiemenguan east,ustengaele,Ahongkailide rocks,seven granite are studied and analyzed,and their chronological,geochemical and isotopic data are collected.The geotectonic and evolution of Paleozoic granites in the depth of 455-341 Ma in the Kuruktag area are discussed,and the crustal evolution in the Kuruktag area in the Paleozoic is discussed,which provides a new reference for the crustal growth and tectonic evolution of the Kuruktag area in the Paleozoic.The main understandings are as follows:?1?There are a large number of Paleozoic granitic intrusive rocks along the Singer fault.The I_Srr of Early Paleozoic rock mass belongs to medium I_Sr.It has low value of?_Nd?t??average-18.18?and high value of t²_DM?average 2.70Ga?.The values of zircon Hf isotopes of 455 Intrusive rock are-19.15 and 2.65Ga,respectively.The lower value of?_Hf?t?represents the magmatic composition formed by early melting of the basic crust.Its rock mass is not affected by mantle-derived components during its formation,but is related to partial melting of the crust.The Sr-Nd isotope data of middle paleozoic intrusion are between 0.70658 and 0.71206,belonging to medium I_Sr.During this period,the?_Nd?t?=-11.82-6.81 of the rock mass was 10?units higher than that of the Ordovician period,indicating that the Mantle-Derived magmatism increased significantly and the genesis and tectonic dynamics of the rock changed.419Ma intrusive rock?_Hf?t?=-6.59⁰.82,t²_DM=1.36¹.66Ga.During this period,Hf was located between the evolution of Hf isotopes of upper and lower crustal melts.The parent magma came from partial melting of crustal materials in Kuruktag area,and?_Hf?t?floated between positive and negative values.Compared with the Ordovician period,mantle-derived materials were obviously added in this period.Before middle paleozoic,?_Nd?t?and?_Hf?t?increased steadily with the decrease of age.At 341 Ma,the value of Hf isotope shows that the intrusion originated from partial melting of the ancient crust,and the Mantle-Derived material decreased significantly.?2?There is short-term mantle-derived magmatic activity at 420±20Ma,and high magmatic differentiation occurs in the continental crust.Mantle-derived magmatism resulted in the growth of new crust,which was the main reason for the growth of subduction zone crust.The invasion of mantle-derived magma at middle paleozoic resulted in the formation of new crust,which resulted in the increase of crustal thickness during this period,reflecting the existence of vertical growth of the continental crust during this period.The growth of 341Ma juvenile crust and subduction and accretion are the main causes of crustal thickening in Kuruktag area.?3?During the Early Carboniferous?341Ma?,the Kuruktag area on the northern margin of Tarim belonged to the active continental margin arc environment.The extensive development of granites indicates that the Southern Tianshan Ocean did not die out and was still subducted under the Tarim plate.The 341Ma pluton probably formed in the later stage of oceanic crust subduction.Since the Ordovician?458 Ma?,the South Tianshan Ocean lithosphere began to subduct,the Silurian?419 Ma-418Ma?to Devonian?401Ma-400Ma?period continued to deepen,the Early Carboniferous?341 Ma?reached the end of subduction,and the Late Carboniferous entered the collision stage.