Archean basement components and metamorphic overprints of the Rangnim Massif in the northern part of the Korean Peninsula and tectonic implications for the Sino-Korean Craton

摘要

The geology of the Korean Peninsula's northern part is little known to the international community. Even though this area is a critical link between various eastern Asia terranes, its tectonic architecture and geochronological framework are still gaps in knowledge. This study reports integrated field, geochemical and geochronological characteristics of the Precambrian gneissic rocks from this region, focusing on the Rangnim Massif. The studied samples are divisible into three groups according to their field occurrence as granitic gneiss, fine-grained biotite gneiss and leuco-veins. The essential mineralogy of all these rocks is biotite (Bt), muscovite (Mu), plagioclase (P1), K-feldspar (Kf) and quartz. The analyzed samples show high SiO2 (65.92-77.63 wt%) and Al2O3 (10.23 to 17.56 wt%) contents, low MgO and CaO. Their K2O contents is mostly higher than Na2O. SIMS (Secondary Ion Mass Spectrometry) zircon U-Pb dating of the eleven samples yields magmatic protolith ages of 2454-2567 Ma and multiple metamorphic overprintings during the earliest Paleoproterozoic (similar to 2.45 Ga), Paleoproterozoic (1.87-1.93 Ga) and Jurassic (160 Ma). The presence of these potassic granitoids in different locations indicate the high extent maturation of Neoarchean continental crust in the Rangnim Massif. Zircon Lu-Hf isotopic results of these samples show large variations, mostly plotting between the Depleted mantle linear model line and Chondritic Uniform Reservoir (CHUR) line, but some have negative epsilon(Hf)(t) values. Considering that their protoliths are all crust melting products, it can be concluded that the Neoarchean magmatism incorporated both juvenile crustal components as well as a reworking of older crust. This is supported by the detection of rare early Archean xenocrysts. Based on Juvenile crust having epsilon(Hf) values of similar to 0 before 3500-3600 Ma, it is concluded that the reworked components were Eoarchean in age, not Hadean. Magmatic as well as Precambrian metamorphic pulses of the Rangnim Massif show broad similarities with the eastern North China Craton, Gyeonggi and Yeongnam Massifs and southwest Japan, which seem to suggest that they might share a coherent Precambrian basement and evolutionary history, at least before the end of late Paleoproterozoic.