Paleoproterozoic amphibolite to ultrahigh temperature granulite facies metamorphism of the Rangnim massif in the Northern Korean Peninsula and tectonic implications

Three Paleoproterozoic orogenic/mobile belts were suggested for the North China Craton (NCC), which were further suggested to represent global networks of narrow plate boundaries and argue for the operation of plate tectonics during the Paleoproterozoic. However, recent studies raised serious challenges to such advocates in that the seemingly belt-like occurrences of the Paleoproterozoic high-grade terranes are related to Phanerozoic tectonic processes. The basement components and metamorphic features of the Rangnim Massif in North Korea can provide critical evidence for a thorough understanding of the tectonic implications of these high-grade terranes, because it was assumed to be an Archean microcontinent that accreted to the NCC during the Paleoproterozoic through one of the three orogenic bents. This massif was assumed to be linked to the NCC through the Jiao-Liao-Ji orogenic belt in the traditional tectonic models. In this paper, we present both new study results and a summarization of previously published data on the Rangnim Massif. The Paleoproterozoic metamorphic rocks collected from the Rangnim Massif show amphibolite to UHT granulite facies metamorphism at ∼ 1.90 Ga, with peak metamorphic conditions reaching up to 940 – 980 ℃ at 7 – 9 kbar. The Paleoproterozoic metamorphism, the widespread Paleoproterozoic sedimentary and magmatic rocks of this massif, are identical with those of the Paleoproterozoic “orogenic belts” of the NCC. Therefore, the Jiao-Liao-Ji “orogenic belt” is extendable to the Rangnim Massif, or even to the whole Korean Peninsula. The newly established spatial occurrences and the metamorphic features of these metamorphic rocks of the eastern NCC are different from those of plate margin orogenic belts. Therefore, the exact geological implications should be reconsidered and that these high-grade terranes might represent the NCC’s uplifted Paleoproterozoic lower crustal components.