Petrogenesis and tectonic implication of Paleoproterozoic granites and granulites in the Fengzhen area of North China craton

The North China Craton (NCC) is one of the oldest cratons in the world that preserves the records of many important geological events in the early evolution of the Earth. However, the early Precambrian tectonic evolution history of the NCC is still controversial. Here we report Paleoproterozoic leucogranites, garnet granites and granulites in the Fengzhen area that constitutes a junction between the Khondalite Belt and the Trans-North China Orogen (TNCO). The leucogranites have high SiO2 content (75-85 wt%), and magmatic zircon U-Pb age of 2199 ± 3 Ma. Their zircons have slightly various εHf(t) values (−0.45 to 1.41) with TDM model ages of 2.5-2.6 Ga. The granites show strong LREE enrichment with La/Ybcn ratio of 12-176, and have high initial Nd isotope (εNd(t) = 3.5-4.5). Most of them display positive Eu anomaly, excluding fractional crystallization contribution on the high Si feature. The leucogranite was produced by melting of Late Archean felsic TTGs (tonalite-trondhjemite-granodiorite) and addition of juvenile crust. Magmatic zircons yield the garnet granite age of 2002 ± 3 Ma. The zircons show various εHf(t) values (−5.8 to 7.1) and TDM model ages (2.1-2.6 Ga). Low initial εNd(t) isotope value (−4.2 to −8.3) was determined in the granites. The granulites are high pressure metamorphic rocks with a peak pressure of 12.0 ± 0.8 kbar, and have similar metamorphic age of 1967 ± 10 Ma to the garnet granites. This indicates that the Fengzhen area underwent 2-Ga inter-continental orogeny, in which the melting of sedimentary rock formed the garnet granites. Similarly, sodic TTG melting to form K-rich leucogranites also needs high pressure. However, the leucogranite age is obviously older than the peak metamorphic timing of continent-continent collision. This implies that the Fengzhen area may have underwent arc-continental collision at 2.2 Ga.