滇西哀牢山深变质杂岩新生代多期变质、剪切变形及地质意义

造山带内大型走滑断层带的运动、变形及变质事件的精细厘定，对研究造山带演化具有重要意义。沿着红河-哀牢山走滑断裂带出露大量深变质杂岩体，这些深变质杂岩保存了极其丰富的变形-变质以及热-构造演化信息。本文重点以红河-哀牢山走滑断层带中的变基性岩和变泥质岩为研究对象，开展了详细的宏观和显微构造、岩相矿物组合、变形温压条件及年代学的综合分析。所有的结果表明哀牢山深变质杂岩经历了至少三个阶段的变质以及依次的变形，即早期进变质阶段（M1）、峰期麻粒岩相变质阶段（M2）（T=780~840℃，P=~0.95GPa）以及峰后近等温减压阶段（M3），具有明显的顺时针P-T演化轨迹。获得片麻岩中的锆石边的变质或熔融年龄为35.2±0.9Ma~33.9±0.8Ma。同时结合EBSD变形矿物晶格优选定向分析，可以确定峰后近等温减压阶段（M3）与区域左行剪切变形阶段相一致。

Cenozoic multi-metamorphism, shear deformation and geological significance of Ailaoshan high-grade metamorphic complex, western Yunnan, China

Precise determination of deformation and metamorphic events of the continental-scale strike-slip fault zone in the orogenic belt is of great significance for the study of the evolution of the orogenic belt. Ailaoshan-Red River (ASRR) strike-slip fault is an important tectonic belt located on the western margin of the South China block and the southeastern margin of the Tibet Plateau, which has been widely advocated to be the result of the long-term interaction between the Indochina block and the South China block. There are four isolated narrow massifs exposed along the ASRR strike-slip fault, which recorded the Mesozoic collision-subduction event between the Indochina block and the South China block and deformation-metamorphism evolution of the Indian-Eurasian plate collision-subduction-exhumation since Cenozoic. Garnet gneisses widely exposed in the Ailaoshan high-grade metamorphic complex are studied, combined with microstructural observations, cathodoluminescence, petrographic analysis, geothermobarometer, thermodynamic phase equilibrium calculations and zircon LA-ICP-MS U-Pb dating. The results show that the Ailaoshan metamorphic complex has undergone at least three stages of deformation-metamorphism evolution, which are the early prograde metamorphic stage (M1), peak granulite facies metamorphic stage (M2) and post-peak near isothermal decompression stage (M3) with strong plastic left-lateral shear. The relic mineral assemblage preserved as inclusions in garnet porphyroblasts belongs to prograde stage (M1) and records P-T conditions of low amphibolite facies. Dehydration reactions of muscovite, biotite and mineral assemblages of sillimanite+K-feldspar formed at the peak granulite facies metamorphic stage (M2) yield P-T conditions of 780~840℃, ~0.95GPa. Post-peak near isothermal decompression stage (M3) is characterized by the white-eye fabric which shows P-T conditions of low-amphibolite facies. The lattice preffered orientation analysis of the deformed minerals by EBSD suggests that the post-peak near-isothermal decompression stage (M3) is consistent with the left-lateral shear deformation stage. The zircon rims of gneisses were dated indicating metamorphic age at 35.2±0.9Ma~33.87±0.8Ma. All these data also argue that the Ailaoshan high-grade metamorphic complex has undergone at least three stages of continuous metamorphism and sequential deformation through a clockwise P-T-t path.