Petrological Investigations and Zircon U‐Pb Dating of High Pressure Felsic Granulites from the Yushugou Complex,South Tianshan,China |
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| Authors: | Lu ZHANG Lifei ZHANG Jianjiang ZHU Bin XIA Zeng LÜ Thomas BADER |
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| Institution: | 1 The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking
University, Beijing 100871, China,1 The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking
University, Beijing 100871, China,1 The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking
University, Beijing 100871, China,2 State Key Laboratory of Geological Processes and Mineral Resources, College of Earth Sciences, China
University of Geosciences, Wuhan 430074, China,1 The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking
University, Beijing 100871, China and 1 The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking
University, Beijing 100871, China |
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| Abstract: | As a window of insight into the lower crust, high pressure granulite has received much attention since last decade. Yushugou high pressure granulite‐peridotite Complex was located in the northeast margin of Southern Tianshan, NW China. Previous ideas agreed that the peridotite unit in Yushugou, combined with the ultramafic rocks in Tonghuashan and Liuhuangshan, represent an ophiolite belt. However, the metamorphic evolution and tectonic mechanism of the Yushugou high pressure (HP) granulite remain controversial. Petrological investigations and phase equilibrium modelling for two representative felsic granulite samples suggest two stages metamorphism of the rocks in Yushugou Complex. Granulite facies metamorphism (Stage I) with P‐T conditions of 9.8–10.4 kbar at 895–920°C was recorded by the porphyroblastic garnet core; HP granulite facies metamorphism (Stage II) shows P‐T conditions of 13.2–13.5 kbar at 845–860°C, based on the increasing grossular and decreasing pyrope contents of garnet rims. The Yushugou HP felsic granulites have recorded an anticlockwise P‐T path, characterized by the temperature decreasing and pressure increasing simultaneously. The LA‐ICP‐MS isotopic investigations on zircons from the felsic granulite show that the protolith ages of the granlulites are ～430 Ma, with two age groups of ～390 Ma and 340–350 Ma from the metamorphic rims of zircon, indicating the Stage I and II metamorphic events, respectively. A tectonic model was proposed to interpret the processes. The investigated felsic granulite was derived from deep rooted hanging wall, with Stage I granulite facies metamorphism of ～390 Ma, which may be related to the Devonian arc magmatic intrusion; Stage II HP granulite facies metamorphism (340–350 Ma) may due to the involvement of being captured into the subducting slab and experienced the high pressure metamorphism. |
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| Keywords: | Anticlockwise P-T path HP felsic granulites P-T pseudosection U-Pb zircon dating South
Tianshan |
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