Phase equilibrium modeling, fluid inclusions and origin of charnockites in the Datian region of the northeastern Cathaysia Block, South China

Charnockites in the Datian region of the northeastern Cathaysia Block, South China have an assemblage of garnet, clinopyroxene, orthopyroxene, plagioclase, anti-perthite, K-feldspar, biotite, quartz and ilmenite. Phase equilibrium modeling indicates that the Datian charnockite was formed at T = 845–855 °C and P = 8.2–8.4 kbar with corresponding water activity lower than 0.50. Fluid inclusions in the Datian charnockite are dominated by N 2 and CO 2 with minor CH 4. The fluids homogenized to liquid at −153.0 to −138.8 °C and 18.3–21.6 °C, respectively, showing a low-density nature. The low-density fluids could be attributed to selective leakage of water due to the affinity of water to melt and decompression-dominated retrograde process. Combined with previous studies, a two-stage formation model is proposed to interpret the petrogenesis of the Datian charnockite, viz emplaced at the Paleoproterozoic and underwent the granulite-facies metamorphism during the Phanerozoic tectonic event.