Early Proterozoic Granulites in Central Korea: Tectonic Correlation with Chinese Cratons

Abstract

A coherent granulite complex has been discovered in the central part of the Korean Peninsula, formerly regarded as the eastern Imjingang belt. This granulite complex (Hwacheon granulite complex [HGC]) experienced two cycles of tectonometamorphic events. The first event corresponded to crustal thickening, followed by peak granulite‐facies metamorphism and associated partial melting. The quasi‐isobaric cooling path, suggested by the occurrences of secondary garnet mantling orthopyroxene and secondary kyanite in mafic and pelitic granulites, respectively, indicates substantial residence time at midcrustal levels prior to exhumation of the HGC. The timing of peak metamorphism was dated from the unzoned overgrowth rims on zircons in a migmatitic granulite at $$1872\pm 7$$ (2σ) Ma, using an ion microprobe. Detrital cores of zircon, however, give diachronous U‐Pb ages of ca. 2.30, 2.45, 2.65, and 2.90 Ga, attesting to the presence of Archean protoliths in South Korea. Sm‐Nd model ages of migmatitic granulites (ca. 2.8–2.6 Ga) further suggest that a significant addition of juvenile materials from the mantle took place prior to granulite‐facies metamorphism. The second tectonometamorphic event may be responsible for the final exhumation of the HGC toward the surface. The age of exhumation is interpreted to be Permo‐Triassic on the basis of available isotopic data. These results suggest correlation of the Gyeonggi massif with the Yangtze craton, and as a corollary, that both this massif and the Imjingang belt correspond to the eastward continuation of the Chinese collisional belt.