Geological Characteristics And Tectonic Significance Of Late Paleozoic Intrusive Rocks In Xibodu Area,Altay,Xinjiang

The study area is located in the southern part of the Altai Orogen Belt,the Xibodu area,which is the junction of the Siberian plate and the Kazakhstan-Junggar plate.An important part of the Central Asian Orogenic Belt(CAOB).The area involves the interaction between the two major plates and the ancient Asian Ocean,which restricts the structural evolution of the study area and controls the geological characteristics of strata,magmatic rocks and deposits in the area.In recent years,there has been considerable controversy regarding the time limit for the transformation of the ocean and land in the southern margin of Altai and complicated orogeny.At the same time,the study area is located at the intersection of two large plates.The magmatic activity and evolution in this area represent the activity records of some plate tectonics on the southern margin of Altai.The study of geology,rock geochemistry,and chronology also provides new evidence for the evolution of tectonic magma in the southern margin of Altai,with a view to supporting the tectonic evolution of the ancient Asian ocean basin in the study area.Intrusive rocks in the Xibodu area include Devonian and Permian intrusive rocks:the Devonian intrusive rocks are medium-fine and coarse-grained monzonite granites,and the LA-ICP-MS method is used for zircon U-Pb In dating,the age of Devonian monzonite granite was identified as 391.4 ± 4.0Ma,indicating that the formation time of this rock mass is Middle Devonian.The Permian intrusive rock types are diorite,quartz diorite,granodiorite and monzonite granite.The age of the Permian diorite was identified as 280.7 ± 2.4 Ma,indicating that the formation time of this rock mass was Early Permian,and the age of the Permian granodiorite was 269.1 ± 2.2 Ma,indicating that the formation time of this rock mass For the late Permian.Based on the rock geochemical characteristics and regional data,it is believed that Devonian intrusive rocks are type I to A transitional high-calcium-calcium alkaline series rocks of crust-mantle mixed origin,formed in the plate subduction-convergent tectonic environment.Permian diorite and quartz diorite basically belong to the calcareous-alkaline series transitioning from type I to type A of crust-mantle mixed source.Geochemical characteristics of Permian granodiorite and monzonite granite show that they belong to type I.The high-calcium-calcium-alkaline series rocks have a tectonic environment that belongs to the post-collision extension environment.In general,the Late Paleozoic intrusive rocks discovered in the Devonian in the Xibodu area on the southern margin of Altai were the product of the magmatic arc formed by the subduction of the Kazakhstan-Junggar plate to the northern Siberian plate,which was active in the tectonic plate.period.From the Carboniferous to the plate subductionmarginal orogenic development stage.The intrusive rocks discovered in the Permian were formed in the post-collision extension environment,that is,the study area entered the inland evolution stage.