Characteristics And Tectonic Significance Of Late Paleozoic Intrusive Rocks Along The Yabrai-Bay An Noel Of Alxa,Inner Mongolia

The magmatic activity along the northern edge of "Alxa block" is very strong inEarly Permian Epoch. The genesis of the North China plate and Tarim plate collisionevolution is of great significance. This paper selects the Late Palaeozoic monzogranite,granodiorite and enclaves in both lithology as the main object of study.On the basis offield observations,author studied its geological features,geochemical characteristicsand geological ages,integrated to investigate the magma source,the age and tectonicenvironment by using the previous studies as well as magmatic activity of adjacentareasEarly Permian the Bayan Noel monzogranite characterized by weaklyperaluminous alkali rich high-K calc-alkaline series, poor Nb-Ta-Ti, high-fieldstrength elements.Sr average is of94.44×10^-6,and Yb3.10×10^-6—a characteristicof very low Sr and high of Yb (Sr=400×10^-6, and Yb=2×10^-6). The rock contains alarge number of MME. Completely the boundaries of the enclaves and hostrocks.enclaves belong to alkaline series,and Th element contents is significantlyhigher relatived to the host rocks.Two LA-ICP-MS zircon U-Pb dating ofmonzogranite samples, weighted average ages are of277.84±0.99Ma and285.52±0.78Ma, indicating that the rock formed in the Early Permian.Early Permian yabrai to-Bayan Noel granodiorite characterized by weaklyperaluminous calc-alkaline-high K calc-alkaline series of the same poor Nb-Ta-Tihigh field strength elements, Sr. average326.82×10^-6, Yb1.86×10^-6, with thecharacteristics of low-Sr and low Yb. Enclave is of calc-alkaline seriesand has verysimilar trace element and rare-earth element characteristics with thegranodiorite.Granodiorite samples for LA-ICP-MS zircon U-Pb dating, the weightedaverage age of265.0±1.3Ma, show that the rock formed in The Middle Permian.Engel Usu ophiolitic melange rocks on behalf of the ocean basin closed, thepost-collisional extensional-shear movement launched this large-scale magmatism,and of the same time with thetectonic activity of the Central Asian OrogenicBelt(CAOB).Early Permian, Bayan Noel monzogranite intruded along the north edge of yabraimountain shear zone at the same time with the activity of shear zone, represents theearlier stages of post-collision.Yabrai-Bayan Noel granodiorite intruded with thethrust activity,represents a later stage of post-collision. Overall, the conversion period the Alxa represent the northern margin of NorthChina, and Tarim plate to the south edge of the collision has been completed as earlyas two superimposed before collision in the Early Permian to enter the environmentconstructor.