Metamorphic P-T paths and zircon U-Pb ages of the intermediate to felsic granulites from the Jianping Complex, the North China Craton:Implications for the Neoarchean tectonic regime

The Jianping Complex (JPC), located at the northwestern margin of the Eastern Block in the North China Craton (NCC), is one of the high-grade complexes that subjected to granulite facies metamorphism. It has been suggested that the JPC at least experienced two phases of Precambrian metamorphism. This study focuses on the late Neoarchean to early Paleoproterozoic metamorphic evolution of the felsic and intermediate granulites with 'redeye socket' texture. Typical peak stage minerals including plagioclase, orthopyroxene, clinopyroxene and quartz, as well as post-peak growth of garnet, clinopyroxene, plagioclase, amphibole and quartz were identified. Phase equilibria modelling for two selected samples was performed using THERMOCALC 3.45. Based on the petrographic observations and the modelling results, anticlockwise P-T paths are recovered for the granulites. Peak stage metamorphic P-T conditions are constrained to be 940-1000 degrees C/8.0-8.5 kbar, and the post-peak final solidus assemblages were stable at the conditions of 880-900 degrees C/9.5-10.5 kbar. U-Pb dating of three granulites yields magmatic ages of -2.50-2.53 Ga and metamorphic ages of -2.49 Ga, suggesting the short interval between the emplacement and the granulite facies metamorphism. Anticlockwise P-T paths can result from intrusion and underplating of mantle-derived magmas in several potential tectonic settings, among which scenarios of magmatic arc and mantle plume are both possible for the NCC at -2.5 Ga. Comprehensively considering the lithological, metamorphic, geochronological, and structural characteristics of the Neoarchean basement rocks in the NCC, we favor the mantle plume model in this study.

Automated summary

This study investigates the metamorphic evolution of the Jianping Complex in the North China Craton, using petrographic observations, phase equilibria modelling, and U-Pb dating. The results indicate an anticlockwise P-T path for the granulites, with peak stage conditions of 940-1000°C/8.0-8.5 kbar. U-Pb dating suggests a short interval between emplacement and metamorphism. Considering the lithological, metamorphic, geochronological, and structural characteristics, the mantle plume model is favored.