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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 X_Mg and Al₂O₃ contents (up to 9.23 wt%). Biotites are enriched in TiO₂ and X_Mg 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 densities of the order of 0.86–0.88 g/cm³. Based on preliminary mineral 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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