Sapphirine-Bearing Pelitic Granulite from Ailaoshan Orogen,West Yunnan,China: Metamorphic Conditions and Tectonic Setting  

作　　者：Cheng Wei Yuhao Zhao Luhua Zhu Xuexiang Qi Zhihui Cai Xufeng Liu Guangfei Ma 

机构地区：[1]Key Laboratory for Continental Dynamics of Ministry of Land and Resources,Institute of Geology,Chinese Academy of Geological Sciences, Beijing 100037, China [2]School of Earth and Space Sciences, Peking University, Beijing 100871, China [3]Nanjing Institute of Geology and Mineral Resources, Chinese Academy of Geological Sciences, Nanjing 210016, China [4]Geology Bureau for Nonferrous Metals of Guangdong Province, Guangzhou 510080, China [5]Hangzhou Mechanical Design Research Institute of Ministry of Water Resources, Standard & Quality Control Research Institute of Ministry of Water Resources, Hangzhou 310012, China

出　　处：《Journal of Earth Science》2019年第3期621-635,共15页地球科学学刊（英文版）

基　　金：supported by the National Natural Science Foundation of China (Nos. 91755101, 41272219);the Chinese Ministry of Science and Technology (No. Sinoprobe-05-03);the China Geological Survey (No. DD20160022-07)

摘　　要：To reveal the petrological characteristics, metamorphic evolution histon and tectonic setting of the pelitic granulites from Ailaoshan Orogen, Uest Yunnan, China, a comprehensive study in mineral chemistry, petrogeochemistry and geochronology studies is presented in this paper. Two metamorphic stages of the granulites can be established:(1) the peak metamorphism recorded by the mineral assemblage of garnet, kyanite, K-feidspar and rutile, and the initial retrograde metamorphism shown by the mineral assemblage of garnet, sillimanite, sapphirine, spinel, K-feldspar, plagioclase and biotite;(2) the superim-posed metamorphism recorded by the mineral assemblage of biotite, muscovite, plagioclase, quartz and ilmenite. Zircon LA-ICP-MS U-Pb dating indicates that the protolith of the granulite was deposited after 337 Ma. The initial retrograde metamorphism occurred at P-T conditions of 8.6-12 kbar at 850-920℃ estimated by mineral assemblages, the low pressure limit of kyanite stability and GBPQ geothermobarometer in Indosinian (about 235 Ma), and the late superimposed metamorphism occurred at the P-T condition of 3.5-3.9 kbar at 572-576℃ estimated by GBPQ geothermobarometer since 33Ma. The first stage was related to the amalgamation of the South China and Indochina blocks during the Triassic, and the second stage was possibly related with the large scale sinistral slip-shearing since the Oligocene. It is inferred that the upper continental crust was suhducted/underthrusted to the lower continental crust (deeper than 30 km) and underwent granulite-facies metamorphism and then quickly exhumed to the middle-upper crust (10-12 km) and initial retrograde metamorphism occurred due to the collision of the Indochina and South China blocks during Indosinian, which was followed by superimposition of the second stage of metamorphism since the Oligocene.To reveal the petrological characteristics, metamorphic evolution history and tectonic setting of the pelitic granulites from Ailaoshan Orogen, West Yunnan, China, a comprehensive study in mineral chemistry, petrogeochemistry and geochronology studies is presented in this paper. Two metamorphic stages of the granulites can be established:(1) the peak metamorphism recorded by the mineral assemblage of garnet, kyanite, K-feldspar and rutile, and the initial retrograde metamorphism shown by the mineral assemblage of garnet, sillimanite, sapphirine, spinel, K-feldspar, plagioclase and biotite;(2) the superimposed metamorphism recorded by the mineral assemblage of biotite, muscovite, plagioclase, quartz and ilmenite. Zircon LA-ICP-MS U-Pb dating indicates that the protolith of the granulite was deposited after 337 Ma. The initial retrograde metamorphism occurred at P-T conditions of 8.6–12 kbar at 850–920 oC estimated by mineral assemblages, the low pressure limit of kyanite stability and GBPQ geothermobarometer in Indosinian(about 235 Ma), and the late superimposed metamorphism occurred at the P-T condition of 3.5–3.9 kbar at 572–576 oC estimated by GBPQ geothermobarometer since 33 Ma. The first stage was related to the amalgamation of the South China and Indochina blocks during the Triassic, and the second stage was possibly related with the large scale sinistral slip-shearing since the Oligocene. It is inferred that the upper continental crust was subducted/underthrusted to the lower continental crust(deeper than 30 km) and underwent granulite-facies metamorphism and then quickly exhumed to the middle-upper crust(10–12 km) and initial retrograde metamorphism occurred due to the collision of the Indochina and South China blocks during Indosinian, which was followed by superimposition of the second stage of metamorphism since the Oligocene.

关 键 词：high-pressure pelitic GRANULITE SAPPHIRINE zircon LA-ICP-MS U-PB dating METAMORPHIC rocks Ailaoshan OROGEN 

分 类 号：P[天文地球]