Late Paleozoic Tectonic Framework And Evolution Of The Southern Central Tianshan: Constraints From The Granites In Caixiashan, Xinjiang, China

The Tianshan orogenic belt is located in the southwestern part of the Central Asian orogenic belt.It through the Xinjiang,China and extend eastward to the Beishan,Gansu.The Central Tianshan plays a major role of Central Asian orogenic belt.And then it play a significant role in tectonic-magmatic evolution.Late Paleozoic is a key period which an active continental margin arc setting caused by the northward subduction from the South Tianshan Ocean.In the past,a number of various researches in the South Tianshan Ocean which locate in the eastern part of the Xingxia fault are and the western part of the Baluntai area.However the research in the central Kawabulak area is rare.So we choose the Caixiashan area as us research area.The Caixiashan granitic pluton,which consists of mylonitized monzonitic granite and porphyritic moyite,is located in the Kawabulake area of the southern Central Tianshan.The LA-ICP-MS zircon U-Pb dating results show that those granitoids were formed at 330.0±3.6 Ma and 333.3±3.6 Ma respectively.The?_Hf?t?values of mylonitized monzonitic granite vary from+5.23 to+0.87 with the t _DM2M2 values of1.28-1.00 Ga,while the?_Hf?t?values of porphyritic moyite vary from 10.85 to-5.81with t_DM2M2 values of 1.7-0.65 Ga.Geochemical analyses indicate that the A/CNK,Na₂O+K₂O ratios are 6.40 and 45.91 for the mylonitized monzonitic granite and 4.17and 33.19 for the porphyritic moyite,and respectively.Both of them belong to the high-K calc-alkaline peraluminous I-type granite.They have relatively enriched in LREE with obviously negative Eu anomalies??Eu=2.76-4.14?.Microstructural features of syntectonic emplacement for themylonitized monzonitic granite indicate that the Kawabulake ductile shear zone was in an active state at least during the late agee of Early Carboniferous.Integrating with the regional geological data,It is believed that the Caixiashan pluton was formed in an active continental margin arc setting caused by the norward subduction of the South Tianshan Ocean and it represents a part of the Late Paleozoic magmatic arc in southern margin of the Central Tianshan.