Zircon LA-ICP-MS U-Pb Dating for Mylonitized Granite from the Ailaoshan-Jinshajiang Tectonic Zone in the Eastern Qinghai-Tibetan Plateau and Its Tectonic Significance

• 责任者：Qi Xuexiang (Key Laboratory for Continental Dynamics of the Ministry of Land and Resources ; Institute of Geology ; Chinese Academy of Geological Sciences ; Beijing 100037 ; China) ; Zhu Luhua
• 刊名：Acta Geologica Sinica
• 出版年：2010
• 卷期：84(3)
• 关键词：花岗岩 ; granite ; 糜棱岩化 ; mylonitization ; 铀—铅计时 ; U-Pb dating ; 青藏高原 ; Qinghai-Tibetan Plateau
• 页码：p.357-369
• 图表：7 illus., 2 tables, 65 refs.
• 分类号：0802
• issnNo：ISSN0001-5717
• isbnNo：CN11-1951/P

Mylonitized granite in the Ailaoshan-Jinshajiang tectonic zone is hosted in the center of the Ailaoshan high grade metamorphic belt. LA-ICP-MS U-Pb dating of two zircon samples (08Q2-22 and 08Q2-15) shows the ages of the growth rims of zircon grains are 250.2+2.l Ma (MSWD= 2.5) and 247.2+2.3 Ma (MSWD=0.15), respectively.  The lattice preferred orientations by EBSD suggest that the c-axis fabrics of quartz are prism slip, and the ductile deformation formed under the condition of amphibolite facies(500~630℃). This temperature is far lower than the zircon crystallized temperature (675~864℃) in magmatism and the closed temperature (>800℃) of U-Pb system in zircon, so the deformation and metamorphism can not destroy the U-Th-Pb stabilization of zircon grains crystallized during magma intrusion. The features of zircon Cathodoluminescence images and the U-Pb concordia lines of zircon indicate that the LA-ICP-MS U-Pb dating (247~250 Ma) for zircon rims represents the emplacement age of granite.