Zircon and monazite petrochronology studies reveal Mesozoic amphibolite-facies metamorphism overprinting Paleoproterozoic granulite-facies metamorphism: A case study from Rangnim Massif, North Korea

Recent studies have shown similar geological evolution processes between the Precambrian basements in North Korea and North China Craton (collectively called the Sino-Korea Craton). However, the detailed metamorphic evolution of supracrustal rocks in North Korea is still poorly understood. In this study, we investigated the petrology, mineralogy, zircon, and monazite U-Pb geochronology of five metapelite samples from the Jungsan Group in the Rangnim massif, North Korea, with the aim of better documenting the geodynamic evolution. The mineral assemblages and microtextures recorded two distinct metamorphic events, 1 and 2. Event 1 is characterized by a low-Ca garnet main domain, their abundant sillimanite inclusions, and equilibrium assemblages of sillimanite and biotite in the matrix, with minimum peak P-T conditions estimated at - 820 degrees C and - 8 kbar (with a geothermal gradient of - 100 degrees C/kbar). The timing of Event 1 was constrained to ca. 1855 Ma by zircon U-Pbdating. Event 2 is characterized by a high-Ca garnet narrow chemical band, staurolite, kyanite, biotite, and muscovite in the matrix, with near peak P-T conditions estimated at - 610 degrees C and - 7.9 kbar (with a geothermal gradient of - 75 degrees C/kbar). The timing of Event 2 was constrained to ca. 155-110 Ma based on a previous study of titanite and rutile U-Pb ages, but a subsequent fluid infiltration event at ca. 106 Ma by monazite U-Pb dating in this study. Our study indicates that supracrustal rocks in North Korea have experienced the same Paleoproterozoic high-grade metamorphism as that in the Jiao-Liao-Ji mobile belt in the North China Craton related to the Columbia Supercontinent; however, there has also been overprinting of a thermal event with mineral assemblages of amphibolite-facies related to extensive Late Jurassic-Cretaceous granitoids intrusion in the region.

Automated summary

Recent studies have revealed that the supracrustal rocks in North Korea have undergone a similar Paleoproterozoic high-grade metamorphism as those in the Jiao-Liao-Ji mobile belt in the North China Craton, related to the Columbia Supercontinent. Additionally, there has been overprinting of a thermal event with mineral assemblages of amphibolite-facies due to extensive Late Jurassic-Cretaceous granitoids intrusion in the region.