Zircons LA-ICP-MS U-Pb Dating on the Baluntai Deformed Granitoids, Central Tianshan Block, Northwest China, and Its Tectonic Implications

Zircons LA-ICP-MS U-Pb dating was performed systematically on deformed granitoids in the Baluntai area of Central Tianshan Mountains. The gneissic granite occurring along the northern margin of the Central Tianshan block was formed during the Neoproterozoic, based on the magmatic zircons age of 630.0±5.0 Ma. The metamorphic zircon rims was dated at 440.9±3.3 Ma, which probably was related to the deformation process in the studied Neoproterozoic granite during the collision between the Central Tianshan block and the North Tianshan block in Early Silurian. The mylonitized granodiorite occurring along the southern margin the Central Tianshan block was formed during the Middle Devonian, based on the magmatic zircons age of 389.5±3.2 Ma, which indicate that the oceanic crust subducted northward under the Central Tianshan block at that time. The metamorphic zircon rims was dated at 362.1±4.3 Ma, which probably was related to the deformation process in the studied granodiorite during the collision between the Central Tianshan block and the South Tianshan block at the end of Late Devonian. Our dataset also shows that the zircon cores have apparent U-Pb ages of 2.5 Ga and 1.8 Ga, which was believed to be components of the Precambrian basement of the Central Tianshan Block.