Paleoproterozoic (ca. 1.87–1.69 Ga) arc-related tectonothermal events on northcentral Yeongnam Massif, South Korea and its tectonic implications: Insights from metamorphism, geochemistry and geochronology

Abstract

The Paleoproterozoic basement of the Korean Peninsula consists of three massifs, the Nangrim, Gyeonggi and Yeongnam Massifs, from north to south. In the Muju area of the northcentral Yeongnam Massif, amphibolites intruded the Paleoproterozoic metasedimentary rocks and orthogneisses. The amphibolites can be divided into Type-I and Type-II amphibolites. The whole-rock geochemical data and zircon Lu–Hf composition of the amphibolites suggest that the Type-I and Type-II amphibolites formed in an island and continental arc tectonic setting, respectively, and both amphibolites were derived from enriched mantle sources. Zircon U–Pb dating reveals that the Type-I and Type-II amphibolites were emplaced at ca. 1.87 Ga and 1.69 Ga, respectively. The surrounding metasedimentary rock (migmatite) underwent upper amphibolite facies (720–730 °C and 7.3–7.4 kbar) metamorphism and then underwent amphibolite facies retrograde metamorphism (520–622 °C and 1.7–3.5 kbar). The zircon U–Pb dating reveals that the peak metamorphism occurred at ca. 1.87–1.86 Ga. The geothermal gradient (approximately 32 °C/km) during peak metamorphism correlates with that of the arc area, indicating that metamorphism occurred in an arc tectonic setting. These data suggest that the northcentral Yeongnam Massif underwent arc-related magmatic and metamorphic events during ca. 1.87–1.69 Ga. This finding indicates that the northcentral Yeongnam Massif does not correlate well with the Nangrim and northern Gyeonggi Massifs, which are correlated with the eastern North China Craton, because the Nangrim and Gyeonggi Massifs underwent postcollisional igneous activity during ca. 1.88–1.84 Ga.