Paleoproterozoic Orosirian tectono-thermal events in the Nangrim Massif, North Korea: Cratonic and supercontinental connection

Abstract

The Paleoproterozoic Orosirian period of ca. 2.05–1.8 Ga saw unique magmatic manifestations of Andean-type arc to Caledonian-style post-collisional batholiths, anorthosite–mangerite–charnockite– granite suites and mafic dyke swarms. Chronicling their timeline in North Korea presents a pivotal task in the palinspatic reconstruction of the Korean Peninsula relative to the North China Craton (NCC) and the supercontinent Columbia. Here we document episodic late Orosirian tectono-thermal events from the northern Nangrim Massif, spanning from ca. 1871–1851 Ma tonalitic intrusions through ca. 1856 Ma granites and ca. 1839 Ma gabbroic diorites to ca. 1830 Ma mafic dykes and ca. 1828 Ma metamorphism. Meta-gabbroic/doleritic rocks range in SiO2 from 46.6 to 57.8 % and in MgO from 6.46 to 11.5 %, with moderately enriched light rare earth elements (LaN/YbN = 3.55–12.3) and depleted high field strength elements. Together with their variable zircon εHf(t) values from −10.0 to +5.2, these rocks tend to call for a heterogeneous lithospheric mantle that experienced prior melt depletion and subsequent fluid refertilization. Pyroxene-bearing tonalite–granite suite spans in SiO2 from 59.0 to 76.4 % and exhibits transitional character from magnesian and alkalic to ferroan and calc-alkalic. These elemental features and zircon εHf(t) values of −7.9 to −1.0 are consistent with partial melting of newly- underplated mafic middle crustal protoliths. By combining these newly identified tectono-thermal events with massif-scale coeval syenite-granite suites as well as anatexis-induced metamorphic pulses, we updated the profile of Orosirian tectono-thermal episodes in the Nangrim Massif, which present successive snapshots into post-collisional geodynamic processes from orogenic collapse to lithospheric delamination. This renewed profile not only provides convincing evidence for demarcating the influence scope of the giant Paleoproterozoic Jiao-Liao-Ji-Korean (JLJK) orogeny in the Korean Peninsula, but also offers key reference for applying analogous Phanerozoic accretionary to collisional orogenic processes to their ancient tectono-magmatic expressions. The JLJK case of Orosirian orogeny exemplifies the importance of Phanerozoic-style Wilson orogenic cycle in the amalgamation of the Sino-Korean craton and its incorporation into the Paleoproterozoic supercontinent Nuna–Columbia.