Metamorphic evolution of high-pressure felsic and pelitic granulites from the Qianlishan Complex and tectonic implications for the Khondalite Belt, North China Craton

Abstract

Abstract High-pressure felsic granulites in association with pelitic granulites are widely distributed in the Qianlishan Complex of the Khondalite Belt, North China Craton. A link between “inter-layered” felsic and pelitic granulites was established based on comprehensive metamorphic analysis, revealing that they record similar metamorphic stages: peak pressure (M1), post-peak decompression (M2), and late retrograde cooling (M3) stages. Felsic granulites experienced high-pressure metamorphism up to ∼12 kbar, while pelitic granulites estimated peak pressure is 11–15 kbar. The decompression stage (M2) is indicated by cordierite + sillimanite symplectite and/or cordierite coronae with conditions of 5.7–6.5 kbar/800–835 °C in pelitic granulites, and by garnet-sillimanite assemblages with conditions of >6.5 kbar/810–865 °C in felsic granulites. The later cooling stage (M3) is marked by sub-solidus biotite-quartz-plagioclase symplectite and later melt crystallization. These mineral assemblages and pressure-temperature (P-T) conditions define clockwise P-T paths involving near-isothermal decompression and near-isobaric cooling, suggesting a continent-continent collisional event. Secondary ion mass spectrometry zircon U-Pb dating yields a consistent metamorphic age of ca. 1.95 Ga, interpreted as peak metamorphism. The results, combined with available data, suggest that the Khondalite Belt formed by collision between the Yinshan and Ordos blocks at ca. 1.95 Ga.