Establishment Of Intrusive Magmatic Stage In Lingbei Area Of East Tianshan And Its Constraints On Regional Structural Evolution

The juerotage orogenic belt is sandwiched between the quasi Turpan Hami block and the Precambrian block of the Middle Tianshan Mountains.It is divided into the great Nanhu tousuquan island arc belt in the north and the Aqishan Yamansu island arc belt in the south by the Kangur Huangshan ductile shear belt.The Lingbei area of the eastern Tianshan Mountains is located between the Siberian plate and the Tarim Sino Korean block,the South Turpan Hami marginal active belt of the Central Asia orogenic belt,which is characterized by Paleozoic accretion orogeny,and between the Yamansu fault and the aqikkuduk fault.In the study area,magmatic intrusive activity is relatively strong,intrusive rocks are relatively developed,widely distributed,and developed from basic to acid,mainly intrusive rocks in the middle stage of Variscan.According to lithology,it can be divided into two types: basic rock(No.1,No.4,No.5 and No.6),neutral rock(No.2,No.3 and No.7)and acid rock(No.8 and No.9).Zircon U-Pb dating results of three intrusive rocks from Lingbei area,Xinjiang indicate that the formation age of grayish white medium-fine-grained granodiorite is 309 ±3.1ma(mswd = 0.78),that of diorite is 304 ± 19ma(mswd = 49),and that of basic intrusive diabase is 302 ± 11ma(mswd = 0.32).In addition,it intrudes into the lower Carboniferous Yamansu formation,so the formation age of all intrusive rocks in this study is determined as the Late Carboniferous.Acid rock No.8(Yulin rock body)and No.9(Bailingshan rock body)have similar trace element characteristics.They are rich in high field strength elements(HFSE)such as th,u and HF,and relatively deficient in elements such as Ba,Nb,Sr,P and Ti.The No.8 rock mass has lower NB TA element than the No.9 rock mass.The content of trace elements in No.2 and No.7 rock masses of neutral rock is similar to that in acid rock,but the No.2 and No.7 rock masses are rich in SR,Ba,and other large ion lithophile elements,loss Nb,Ta,th and other high field strength elements.The characteristics of trace elements and rare earth elements are not consistent among various rock masses,which indicates that the intrusive rocks in the study area have multi-stage characteristics.The magma source of Lingbei intermediate acid rock body is crust mantle mixed source,and the formation process is that the lower crust is remelted and mixed with mantle source material in the subduction process,and the magma upwelling,finally forming the Late Carboniferous intermediate acid intrusive body in Lingbei area.The peridotdiabase of No.1 rock body is characterized by high Mg,Fe and low Al,and belongs to alkaline rock series.Large ion lithophile elements K,Ba and P are obviously enriched,and Rb,HF,TB,Nb and Ti are deficient.Lingbei olivine diabase is formed in the subduction tectonic environment of the same age as the intermediate acid rock body.The magma source is not only from the mantle,but also obviously influenced by the fluid metasomatism formed by the mixing of surrounding rock or the dehydration of subduction plate.It is formed by a large number of mixed crust source materials during the magma upwelling process.The results show that there was plate subduction in Lingbei area in Late Carboniferous,and the Kanggur ocean was completely closed in Permian.