Phase Equilibria Modeling and Zircon Dating for Precambrian Metapelites from the Xinghuadukou Complex in the Lulin Forest of the Erguna Massif, Northeast China

Abstract

The nature and formation time of the Xinghuadukou complex in Northeast China are important for determining the tectonic evolution of the Precambrian geological evolution of the Erguna massif. In this study, we present the results of zircon U-Pb dating of two metapelites from the complex. Detrital and metamorphic zircons from the metapelites yield a depositional age of ~601 Ma and a metamorphic age of 496–509 Ma, indicating that the supracrustal rocks formed during the Neoproterozoic and recorded pan-African metamorphic events in the Erguna massif. Garnet porphyroblasts in Sil-Grt-Bt-Ms paragneiss show diffusion zoning, implying a decreasing P-T trend. Based on mineral transformation and P-T estimates using conventional geothermobarometers and phase equilibria modeling, three metamorphic stages were determined, including an early prograde metamorphic stage, a near peak upper amphibolite facies metamorphic stage, and a near-isobaric cooling stage with P-T conditions of 6.1 kb, 645 °C, 5–6 kb, 710–740 °C, and 4.4 kb, 625 °C, respectively. The metamorphic history of the Xinghuadukou complex is thus defined by a clockwise P-T trajectory, which implies that the metamorphism of the metapelites documented the subduction, subsequent uplift and post collision process.