Petrology and geochemistry of ultrahigh‐temperature granulites from the South Altay orogenic belt,northwestern China: Implications for metamorphic evolution and protolith composition |
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| Authors: | Xiaoqiang Yang Zilong Li Huihui Wang Hanlin Chen Yinqi Li Wenjiao Xiao |
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| Institution: | 1. Department of Earth Sciences, Zhejiang University, Hangzhou, China;2. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China |
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| Abstract: | Ultrahigh‐temperature (UHT) granulites in the South Altay orogenic belt of Northwestern China provide important clues for the lower crustal components and tectonic evolution of the Central Asian Orogenic Belt during the Paleozoic. In this paper, we studied whole‐rock geochemistry and mineral characteristics to understand the protolith and metamorphic evolution of the Altay UHT granulite. The Altay granulite shows negative discriminant function values (DF) of ?9.27 to ?3.95, indicating a sedimentary origin, probably an argillaceous rock. The peak metamorphic temperature–pressure conditions of 920–1010 °C and > 9 kbar were estimated from the geothermobarometry, together with the stability of spinel (low ZnO) + quartz and orthopyroxene (Al2O3 up to 9.2 wt.%) + sillimanite + quartz in the Altay UHT rock, indicate a UHT metamorphic condition has been achieved. Two stages of retrograde conditions are recognized in these rocks; the first is an isothermal decompression to approx. 750 °C at 5.2–5.8 kbar at the early stage, and the second is the cooling down to 520–550 °C at 4.8–5.2 kbar. Combined with previous study, the formation of the Altay UHT pelitic granulite with a clockwise retrograde P–T path is inferred to be related with collisional and accretional orogenic process between the Siberian and Kazakhstan–Junggar plates. |
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| Keywords: | geochemistry mineral characteristics provenance reconstruction P– T estimate South Altay orogenic belt ultrahigh‐temperature granulite |
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