Early proterozoic granulites in central Korea: Tectonic correlation with Chinese cratons

A coherent granulite complex has been discovered in the central part of the Korean Peninsula, formerly regarded as the eastern Imjingang belt. This gr anulite complex (Hwacheon granulite complex [HGC]) experienced two cycles o f tectonometamorphic events. The first event corresponded to crustal thicke ning, 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 m idcrustal levels prior to exhumation of the HGC. The timing of peak metamor phism was dated from the unzoned overgrowth rims on zircons in a migmatitic granulite at 1872 +/- 7 (2 sigma) Ma, using an ion microprobe. Detrital co res 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 Kore a. Sm-Nd model ages of migmatitic granulites (ca. 2.8-2.6 Ga) further sugge st that a significant addition of juvenile materials from the mantle took p lace prior to granulite-facies metamorphism. The second tectonometamorphic event may be responsible for the final exhumation of the HGC toward the sur face. The age of exhumation is interpreted to be Permo-Triassic on the basi s of available isotopic data. These results suggest correlation of the Gyeo nggi massif with the Yangtze craton, and as a corollary, that both this mas sif and the Imjingang belt correspond to the eastward continuation of the C hinese collisional belt.