Characteristics And Tectonic Significance Of Granites In Sonid Youqi,inner Mongolia

The central Asian orogenic belt is the largest orogenic belt on earth since phanerozoic eon.There are also different opinions on the time of collision closure of the central Asian orogenic belt.More and more scholars believe that the closure time of different tectonic sections in the central Asian orogenic belt is different.Granite of different origins provides evidence for the closure of the central Asian orogenic belt.In the contact area between the Bainaimiao island arc and the north China craton,the Triassic monzogranite and miarolitic granite developed,showing the characteristics of high potassium calcium alkaline-potassium series,the enrichment of large-ion lithophilic elements,the depletion of high-field strength elements,the strong loss of Nb,Ta,P,Ti,owing the characteristics of high-differentiation type I granite.This provides evidence for collision closure in the eastern-middle part of the central Asian orogenic belt.This paper argues that in the middle Triassic period(230 ? 245Ma),the Bainaimiao island arc and the north China craton have evolved into the transition period of co-collision and post-collision.In this paper,the Triassic granite in the study area will be comprehensively analyzed based on the analysis of main trace elements of the whole rock,zircon LA-ICP-MS zircon U-pb dating,combined with microscopic observation and field investigation.In the contact area between the Bainaimiao Island Arc and the North China Craton,the Triassic monzogranites and miarolitic granite are developed,showing the characteristics of high K calc-alkaline-K series,enrichment of large ion lithophile elements,depletion of high field strength elements,and strong depletion of Nb,Ta,P,Ti,showing the characteristics of high differentiation type I granites.This provides evidence for collisional closure in the east-central Central Asian orogenic belt.In the Middle Triassic(230?245Ma),the Bainaimiao Island Arc and the North China Craton evolved into a transitional period of syn-collision and post-collision.In this paper,a comprehensive analysis of Triassic granites in the study area will be made based on whole-rock analysis of major and trace elements,zircon LA-ICP-MS zircon U-Pb dating,combined with microscopic observation and field investigation.Based on the field research,starting from the monzogranite and miarolitic granite in Sunite Youqi and Xianghuang Banner in the central part of Inner Mongolia Autonomous Region,this paper carried out LA-ICP-MS zircon U-Pb dating and whole-rock main and trace elements analysis on the collected rock samples through field geological survey and field sampling.According to LA-ICP-MS zircon U-Pb dating analysis of monzogranite and miarolitic granite,the formation age of monzogranite is 239.3±2.2Ma,and the age of miarolitic granite is not well obtained.The age distribution of its zircons is relatively dispersed between 1809-236 Ma.Combined with the whole rock analysis,The zircon ages of the granites are relatively dispersed.It is concluded that more traps were mixed in the formation process of the granites.It is considered that the monzogranite and miarolitic granite belong to the high-K calc-alkaline-K series,which are enriched in large ion lithophile elements,depleted in high field-strength elements,and strongly depleted in Nb,Ta,Pt,showing the characteristics of post-collision granite.The conclusion is drawn through graphical analysis.Triassic monzonite and miarolitic granite,transitional period of formation,syncollision and post-collision.In the early Triassic(230?245Ma),the central and eastern part of the Paleo-Asian Ocean had completed the collage with the North China Craton.The intrusive rocks developed in the early Triassic have highly differentiated geochemical characteristics.Therefore infer that in the early Triassic,Sauron suture zone in the transition period with the collision and after collision,then still happening at a certain degree of block together,As a result,the crust was remelted,and during the process of formation,the magma was mixed,and the crystallization and differentiation were stronger,and the intrusive rocks in the middle to late Triassic were formed eventually.