Late Paleoproterozoic ultrahigh-temperature metamorphism in the Korean Peninsula

Abstract

The Paleoproterozoic rock record from the Sino-Korean Peninsula was fundamental to the models on evolution of the Asian continental collage and its relationship with the amalgamation and disruption of Proterozoic supercontinents such as Columbia and Rodinia. In this study, we present results from a comprehensive investigation on the khondalites in the Hongseong area, along the western part of the Gyeonggi massif within the central Korean Peninsula involving petrography, phase equilibria forward modeling, and zircon U-Pb geochronology, REE geochemistry and Lu – Hf isotopes. The P-T pseudosections show that the peak mineral assemblage of garnet + sillimanite + quartz + plagioclase + K-feldspar + ilmenite in the khondalite is stable at 7.5-9.6 kbar and 895-990 °C, corresponding to ultra-high temperature (UHT) metamorphism. We also report the first finding of corundum and quartz inclusions within sillimanite enclosed in garnet porphyroblast further confirming UHT metamorphism. The interpreted P-T path involves decompression and exhumation along a clockwise trajectory as suggested by the retrograde textures and mineral phase equilibria modeling. The detrital zircon U - Pb data from the khondalite show multiple age peaks for the magmatic population suggesting Neoarchean - Paleoproterozoic provenance. Metamorphic zircons from the khondalites yield ages of 1931 ± 33 Ma, 1871 ± 11 Ma and 1866 ± 10 Ma. The spot ages range from 1923 Ma to 1832 Ma suggesting either a long-lived metamorphic event or two distinct thermal events. The REE patterns of the zircon grains also clearly distinguish the magmatic and metamorphic populations. The garnet + sillimanite assemblage is considered to represent the peak UHT assemblage and the cordierite + biotite represents the post-peak retrograde assemblage. The ca. 1923-1832 Ma ages obtained in our study from metamorphic zircon domains correlate well with similar ages reported for metamorphism associated with the amalgamation of crustal blocks within the North China Craton. Our study suggests that the Late Paleoproterozoic UHT metamorphism in the central Korean Peninsula might be part of a common event within the Sino-Korean Craton related to the tectonics of final assembly of cratonic blocks within the Columbia supercontinent. Although a substantial volume of the Paleoproterozoic basement of the Korean Peninsula was destroyed and recycled during the Neoproterozoic and Phanerozoic tectonic events, the preserved remnants provide insights into the contiguity of the basements of the Korean Peninsula and the North China Craton.