Abstract
We first report discovery of the spinel-garnet-orthopyroxene granulite with pure CO2 fluid inclusions from the Fuyun region of the late Paleozoic Altay orogenic belt in Central Asia, NW China. The rock is characterized by an assemblage of garnet, orthopyroxene spinel, cordierite, biotite, plagioclase and quartz. Symplectites of orthopyroxene and spinel, and orthopyroxene and cordierite indicate decompression under UHT conditions. Mineral chemistry shows that the orthopyroxenes have high XMg and Al2O3 contents (up to 9.23 wt%). Biotites are enriched in TiO2 and XMg and are stable under granulite facies conditions. The garnet and quartz from the rock carry monophase fluid inclusions which show peak melting temperatures of around-56.7°C, indicating a pure CO2 species being presented during the ultrahigh-T metamorphism in the Altay orogenic belt. The inclusions homogenize into a liquid phase at temperatures around 15.3–23.8°C translating into CO2 of the order of 0.86–0.88 g/cm3. Based on preliminary minerals paragenesis, reaction textures and petrogenetic grid considerations, we infer that the rock was subjected to UHT conditions. The CO2-rich fluids were trapped during exhumation along a clockwise P-T path following isothermal decompression under UHT conditions.
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Project supported by the National Basic Research Program (973) of China (No. 2001CB409801), the Exemplary Young Teacher Education and Scientific Research Award Plan of China University, and Postdoctoral Fund of China (No. 2003033033), Postdoctoral Fund of Zhejiang Province, and Starting Fund of Education Ministry, China
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Li, Zl., Chen, Hl., Santosh, M. et al. Discovery of ultrahigh-T spinel-garnet granulite with pure CO2 fluid inclusions from the Altay orogenic belt, NW China. J. Zheijang Univ.-Sci. 5, 1180–1182 (2004). https://doi.org/10.1631/jzus.2004.1180
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DOI: https://doi.org/10.1631/jzus.2004.1180