Metamorphic and magmatic evolution of the Paleoproterozoic gneisses in the Sancheong area, Yeongnam Massif, South Korea, and their implications to the tectonics in the Northeast Asia

The Sancheong area in the southwestern Yeongnam Massif mainly consists of Precambrian paragneisses (quartz-feldspathic and garnet gneiss), orthogneiss (porphyritic gneiss) and anorthosite and is important for an understanding the tectonic evolution of the southern part of the Korean Peninsula and Northeast Asia. The Precambrian paragneisses in the Sancheong area underwent intermediate-PST metamorphism (quartz-feldspathic gneiss; 730 degrees C and 12.2 kbar). The intermediate-P/T metamorphism was overprinted by regional low-PST metamorphism (750-820 degrees C and 7.0-9.0 kbar) which was followed by amphibolite-fades retrograde metamorphism. In contrast, the orthogneiss only experienced the low-PST (750-800 degrees C and 8.0-8.7 kbar) metamorphism followed by the amphibolite-facies retrograde metamorphism. Zircon U-Pb dating indicates that the intermediate-PST metamorphism likely occurred at ca. 1880-1920 Ma and that the low-P/T metamorphism occurred at ca. 1855-1859 Ma. The whole-rock geochemical data and zircon U-Pb ages indicate that the protolith of the porphyritic gneiss and the anorthosite were emplaced in a post-collisional tectonic setting during ca. 1872-1880 Ma and ca. 1860 Ma, respectively. These data suggest that the Sancheong area underwent continental collision associated with the intermediate-PST metamorphism (ca. 1920-1880 Ma) and post-collisional igneous activity associated with the low-PST metamorphism during the Paleoproterozoic (ca. 1856-1880 Ma). Similar Paleoproterozoic tectonic events were recently reported from the eastern Cathaysia Block, suggesting that the Yeongnam Massif may have a close affinity to the eastern Cathaysia Block. (C) 2017 Elsevier B.V. All rights reserved.