Geological And Geochemical Characteristics And Tectonic Significance Of Early Paleozoic Tonalite In Inner Mongolia

The Taigushengmiao area is located at the junction of the southern margin of the Xingmeng orogenic belt(Central Asian orogenic belt)and the northern margin of North China.The Xinmin-Zhangmao Wusu fault zone serves as the boundary of the primary structural unit and traverses the study area along the east-west trend.In order to help study the boundary between the Suniteyouqi-Xianghuangqi area and the Central Asian orogenic belt,it provides new constraints on Early Paleozoic magmatism and tectonic evolution in the Taigushengmiao area.This article is based on the study of the geological characteristics of the Early Paleozoic Late Silurian tonalite in the area,including petrographic characteristics,chronological characteristics,geochemical characteristics,isotope characteristics and tectonic studies.At the same time,we pay attention to the chronology and rock characteristics of other rocks of similar ages during the conversion of the Bai Naimiao Island Arc from the island arc to the mainland.So we can determine the formation time of the intrusive rocks and the magmatic evolution process in the Taigushengmiao area,and the regional structural background of the island arc magmatic rock zone.By observing the characteristics of tectonic deformation,the northern margin of North China was affected by two-stage tectonic events of the early Paleozoic arccontinent collision and the late Paleozoic ocean closure and orogeny,resulting in multistage deformation.The first stage is the shearing in the subduction stage.It developed in the Haerhada Formation of the Wenduermiao Group.The second stage is the extrusion process of arc-land collision.It developed in the Halhada Formation and the Bainaimiao Formation and Xuniwusu Formation in the island arc belt.The third period is the process of the final closure of the ocean basin at the end of the late Paleozoic.It reformed the Late Paleozoic and Early Paleozoic strata.The age of the volcanic rocks on the east side of the study area precisely controls the time limit of arc-continent collision events during the Silurian.The age of the quartz diorite in the north of Bainaimiao indicates the time of collision.Late Silurian tonalite is the largest unit of distribution area of Early Paleozoic magmatic rocks,accounting for about 50% of the exposed area of Early Paleozoic rocks.LA-ICP-MS zircon U-Pb age test shows that its weighted average age is 425.8 ± 1.6Ma.At the same time,geochemical experiment analysis shows that there are mantle or primary crust components involved in diagenesis.Comparing the experimental data with predecessor data,this paper believes that the late Silurian tonalite may indicate the beginning of the arc-continent collision.The subduction of the eastern section of the Bainaimiao Island arc belt ends later,and this age difference may indicate that the closure time of the early Paleozoic ocean basins in the two places is different.The ancient Asian Ocean gradually closed from west to east.