Research On Jiageda Formation Geological Characteristics And Zircon U-Pb Age In Taerqi,Inner Mongolia

The authors studied the characteristics including petrology, structure, geochemistry and zircon U-Pb age, and discussed deformation features, regional tectonic background and formation age for the Jiageda Formation in Tarqiareas. The results show that the Jiageda Formation is mainly composed of mica quartz schist, chlorite schist and, quartzite. The metamorphic mineral assemblage is Quartz+amphibole+biotite+plagioclase, The metamorphic grade is equivalent to high green-schist facies—low amphibolite: The LA-ICP-MS zircon U-Pb dating results of the sample is 440 Ma,which indicates that it is not traditional sense of the Precambrian metamorphic rock series but the product of magmatism and the metamorphism and deformation effect. The geochemical study shows that the A/CNK are greater than 1.6, which belongs to high-K calc-alkaline series rocks. The samples are characterized by relatively high content of REE. The REE patterns decline to right and Eu negative slightly. They are also enriched in LILE and LREE, and depletion of HFSE. The above show its magma experienced varying degrees of continental crust contamination or partial remelting crustal material. In trace element tectonic discrimination diagrams, samples all fall into arc granite and continental collision zone. Therefore, Jiageda Formation might be formed in the magma arc environment of Paleo-Asian Ocean northward subduction.Jiageda Formation underwent two-phases deformations: The first phase of the stress field direction of NW se trending extrusion, forming ne structure in the direction of distribution line, which might be occurred beforeCarboniferous; The second phase of stress field direction of NS se trending extrusion, forming ew structure in the direction of distribution line. which might be occurred in Carboniferous or after Carboniferous.