Geochronology and Petrogenesis of Mylonitized Granite from Wulonggou Area in East Kunlun and Its Tectonic Significance

The mylonited granite is located at Shenshuitan mining setion of Wulonggou area in the middle part of the East Kunlun, with a yielded LA-ICP-MS zircon U-Pb age of 389.7±3.9Ma. This granite has high SiO₂ (74.86%~76.64%), K₂O (5.20%~6.06%) and total alkali content (K₂O + Na₂O=8.05%~8. 83%) values. The samples are characterized by strong loss in Ba, Nb-Ta, Sr, P and Ti, as well as strong negative Eu anomaly (δ Eu=0.07~0.12), which shows characteristics of A type granite. Combined with the studies of Silurian-Devonian magmatic rocks in this studying area, it's proposed that the East Kunlun Orogenic belt has entered the post-collision stage in early Devonian, and the most intense of extension was happened in the conversion period of from early Devonian to middle Devonian, forming A type granite with considerable size, and standing for the end of the Caledonian orogenic cycle.