Geochemical Characteristics And Tectonic Significance Of The Early Devonian Intermediate-acid Intrusive Rocks In The Xingxingxia Area,Eastern Tianshan Mountains,Xinjiang

Xingxing Gorge area is located in the intersection area of Xinjiang Uygur Autonomous Region and Gansu Province.It is located in the southern part of the Middle Tianshan Block in the East Tianshan Mountains.It is an important intersection zone between the Kazakhstan-Junggar Plate and the Tarim Plate.The rock types in the study area are complex,magmatic activities are frequent,evolution time is long,and geological history has experienced many tectonic events.The geochemical characteristics and tectonic significance of intermediate-acid intrusive rocks in Xingxing Gorge area are discussed on the basis of previous research results by means of field geological survey,chronological analysis and principal microanalysis.The intermediate-acid intrusive rocks in the Xingxing Gorge area are mainly distributed in the north-central part of the study area,and are distributed in an irregular pattern.Based on the field geological characteristics and Microscopic slice analysis,the rocks can be divided into three types: monzonitic granite,granodiorite and quartz diorite.According to LA-ICP-MS zircon U-Pb isotope dating,the age of monzonite granite is 411.5±3.2 Ma,granodiorite 409.3±3.1 Ma and quartz diorite 405.0±3.6 Ma.The ages of the three types of intermediate-acid intrusive rocks are between 400 and 420 Ma,all of which belong to the Early Devonian.Geochemical analysis shows that the main body of the early Devonian intermediate-acid intrusive rocks shows the characteristics of high-K calc-alkali-calc-alkaline quasi-aluminous rocks,which are based to type I granite.At the same time,it has negative anomaly of Nb and loss of P and Ti.REE content shows slight negative Eu anomaly,Ce anomaly is not obvious.It has obvious right-leaning light rare earth enrichment and heavy rare earth loss.The tectonic environment is volcanic arc,showing the characteristics of active continental margin.It is a volcanic arc,showing the characteristics of active continental margin.Comprehensive analysis shows that the early Devonian intermediate-acid intrusive rocks in Xingxing Gorge area were formed in volcanic arc tectonic environment.The spatial distribution of the three lithologic rocks is distributed from the southeast to the northwest,followed by the monzonitic granite,the granodiorite,and the quartz diorite.At the same time,the three rock masses are in order from old to new,forming order and south.The subduction direction of the Tianshan Ocean is nearly identical In the early Devonian study area,the tectonic activity was that the South Tianshan Ocean continued to subduct northward to the Middle Tianshan Block,and a large number of intermediate-acid intrusive rocks were formed by magmatic activity on the active continental margin.Subduction lasted until the late Devonian South Tianshan Ocean closed gradually.