Clockwise P-T-t path of Paleoproterozoic metamorphism from the Dengfeng Complex, southern North China Craton

Abstract

Garnet-bearing metapelites are widely distributed in the Dengfeng Complex situated in the southern segment of the North China Carton (NCC). Petrological studies indicate that garnet-bearing metapelites mainly comprise quartz, muscovite, chlorite, plagioclase, garnet and biotite, with minor ilmenite, zircon, and apatite. Garnet porphyroblasts show obvious growth zoning from the core to inner rim and they are separated by a prominent chemical discontinuity narrow edge. By pseudosection modeling calculations, the P-T conditions of sample 20DF17-C determined by the isopleths of XGrs and XPrp of the garnet core and inner rim are ∼ 530 °C/6.7 kbar and ∼ 560 °C/5.1 kbar, respectively; while the P-T conditions of sample 20DF24 determined by the isopleths of the garnet core and inner rim are ∼ 530 °C/5.2 kbar and ∼ 550 °C/4.5 kbar, respectively. LA-ICP-MS zircon U-Pb dating from the Dengfeng metapelites suggest that the maximum depositional age of their protoliths was ∼ 2.52 Ga. These metapelites were affected by the hydrothermal event immediately after diagenesis. The age of ∼ 1.92 Ga contributed to clockwise P-T paths containing decompression with slight heating segments, which occurred at the Paleoproterozoic and likely were related to a subduction-collision event in the NCC. Combined with the occurrence features of the amphibolites, TTG gneisses, metapelites and quartzites, we inferred that all the Dengfeng metapelites and Songshan Group involved a Paleoproterozoic orogenic event along the Trans-North China Orogen (TNCO)/Jinyu Mobile Belt (JMB).