Evolution Pattern Of Continental Crust During Paleozoic Accretionary Orogeny: Evidence From Detrital Zircon Geochronology And Hf Isotopic Characteristics Of South Tianshan

The south Tianshan orogenic belt belongs to the southwest margin of the Central Asia orogenic belt,is located between the central Tianshan block and Tarim craton.The orogenic belt has experienced a series of multi-stage tectonic movements,including the breakup and expansion of the South Tianshan paleo ocean basin,the subduction and closure of the South Tianshan ocean,and the continental collision and post collision extension,Strong magmatic activity.It is great significance to understand the structural evolution of Tianshan structural belt.At present,there is a great controversy about the Paleozoic accretive orogenic process of the South Tianshan orogenic belt.In order to clarify the Paleozoic tectonic evolution process of the South Tianshan orogenic belt further,this paper selected the Weigan river sediments as the research object,based on the systematic field geological investigation and the comprehensive collection of indoor data,study on the U-Pb geochronology,Hf isotope and trace isotopic characteristics of detrital zircon from the Weigan River sediments,determine to the formation time,magmatic properties and provenance of detrital zircon,discussion on the tectonic evolution of the South Tianshan orogenic belt combined with previous research results,it provides a basis for the evolution of continental crust in the Paleozoic accretive orogenic process of the South Tianshan orogenic belt.The mainly achievements are as follows:1.Based on the age results of the predecessors in the study area and the U-Pb isotope age results in this paper,the age of detrital zircons of the South Tianshan area is from Archean to early Mesozoic,mainly Paleozoic zircons,it accounting for 74.7%of the total samples,followed by Precambrian,it accounting for 22.4% of the total sample.The ages of Paleozoic zircons are mainly 460-400Ma(late Ordovician to early Devonian)and 310-260 Ma(from late Carboniferous to early Permian).It shows that the orogenic belt of south Tianshan had intense magmatic activity in Paleozoic.Potential provenance analysis suggests that these detrital zircon grains were predominately derived from the magmatic rocks in the Tarim Craton and south Tianshan orogenic belt.2.By comparing and analyzing the U-Pb ages of detrastic zircons in the southern and northern fluvial sediments of the southern Tianshan orogenic belt and combining with other geological evidence,this paper supports the tectonic model of simultaneous north-southsubduction in the southern Tianshan ocean during the 460-400 Ma(late Ordovician to middle Devonian).The southern Tianshan ocean finally closed in the late Carboniferous and had a continental collision,while the late carboniferous to early Permian(310-260 Ma)formed a large number of syn-collision or post-collision magmatic rock.3.Zircon Hf isotopic data analysis of magmatic and clastic rocks in the South Tianshan orogenic belt shows that the continental crust evolution of the South Tianshan orogenic belt in the early Paleozoic(late Silurian to early Devonian)is dominated by the reconstruction of the old crust and the addition of some new mantle materials,and the continental crust evolution of the South Tianshan orogenic belt in the late Paleozoic(Late Carboniferous Permian)may be based on the old base of Tarim craton The bottom rocks are mainly transformed,and the limited new components are added to the formation of magma.Compared with other tectonic units in the Central Asia orogenic belt(such as Junggar and Altay area),the recycling of ancient lithosphere materials in the South Tianshan orogenic belt is still the main form of Paleozoic continental crust evolution.