The Genetic Type And Geological Significe Of Late Paleozoic Granites In Yakeshi Region,North Great Xing'an Range

The study area is located in the Yakeshi of Hulunbeir League which is in the east of Inner Mongolia autonomous region,the tectonic units belong to the boundary of Ergun and Xing'an block and its two side.The found from the system geological investigation is that diorite-quartz diorite-granodiorite-tonalite diorite-biotite monzogranite are distributed in the north west of the fracture zite like a ribbon,and the leucogranites and syenogranite are distributed on the both sides.The geochemical data analysis of the granitic rocks in the Toudaoqiao-Wunuer indicates that:(1)the rock of diorites-granodiorite generally as a set of calcium-alkaline series rocks,is the I-type granite,has the basic characteristics of the granite rocks in subduction zones,LA-ICP-MS zircon U-Pb isotopic dating revealed that the formation age is the Middle Carboniferous(315-324 Ma);the rock of leucogranites and syenogranite is the S-type of calcium-alkaline series,has the basic characteristics of the collision granite,the study of the isotope chronology of its zircon U-Pb shows that the emplacement era is the Middle Permian(275 Ma).All characteristics above reflect the continuous evolution trend from neutral to acid of the lithology of granite rock with the tectonic environment from the island arc to collision between the Middle Carboniferous and the Middle Permian.The study shows that the fault of Toudaoqiao-Wunuer in the Late Palaeozoic controls the geological development process of the both sides of study's area.The area of the Carboniferous in the Toudaoqiao-Wunuer has appeared subduction to the north west,in the north west of the fault zone formed the subduction-related granite,in the north west of Yakeshi region formed the back-arc basin of tensile properties and on the back-arc basin formed deep sea-half a deep sea spilite keratophyre and radiolarian cherts rocks;In the Permian tectonic the environment from the subduction to the collision and formed a set of light color of S-type peraluminous collision granite.And because of the influence of subduction and collision,the Devonian-Carboniferous of regular deposits near the fault zone appeared strong broken,presented fragments contact in the fault zone.In addition,the collision lead to the crust near the fault zone and its south suffered erosion,generally lack of the Devonian-Carboniferous in this region.