Metamorphic P-T Path of the Southern Jilin Complex: Implications for Tectonic Evolution of the Eastern Block of the North China Craton

摘要

The Southern Jilin complex represents the northeasternmost exposure of the basement rocks in the Eastern block of the North China craton and consists of intensely foliated tonalitic-trondhjemitic-granodioritic (TTG) gneisses, weakly foliated syn-tectonic potassium granites, post-tectonic hypersthene-quartz diorite and clinopyroxene granodiorite and a minor amount of supracrustal rocks, The supracrustal rocks include ultramafic to felsic volcanic rocks, BIF, felsic paragneisses, pelitic gneisses, calc-silicates, and marbles metamorphosed from amphibolite to granulite facies. The petrological evidence from the mafic granulites and pelitic gneisses indicates three metamorphic mineral assemblages (M 1 to M 3). The early prograde assemblage (M1) is preserved as mineral inclusions within minerals of the peak assemblages, represented by hornblende + plagioclase + quartz +- biotite in the mafic granulites and biotite + plagioclase + quartz in the pelitic gneisses, with P-T conditions estimated at ~0.6 GPa and 750 deg C. The peak assemblage is represented by orthopyroxene + clinopyroxene + garnet + plagioclase + quartz in the mafic granulites and garnet + sillimanite + plagioclase + quartz + biotite in pelitic gneisses, with P-T conditions estimated at 0.84-0.87 GPa and 800-850 deg C. The post-peak assemblage is characterized by garnet + quartz symplectic coronas in mafic granulites and kyanite replacing sillimanite in the pelitic gneisses, which probably occurred at ~0.85 GPa and 760 deg C. These mineral assemblages and their P-T estimates define an anticlockwise P-T path involving nearly isobaric cooling, reflecting an origin related to the intrusion and underplating of large amounts of mantle-derived magmas, which are considered to have been related to the interaction of upwelling mantle plumes wish the lithosphere in the Eastern block of the North China craton in the Late Archean.