Middle Jurassic tectono-magmatic evolution in the southwestern margin of the Gyeonggi Massif, South Korea

Abstract

Sensitive high-resolution ion microprobe (SHRIMP) U-Pb zircon dates and geochemical and isotopic (Sr and Nd) data were obtained for Middle Jurassic granitoids from the Buyeo area along the southwestern margin of the Gyeonggi Massif, South Korea. Foliated 179 Ma granitoids are dominated by granite and diorite, non-foliated 167 Ma granitoids include granite to alkalifeldspar granite, and the youngest, non-foliated 165 Ma granitoids consist of alkali-feldspar granite. The 179 Ma and 167 Ma rocks are geochemically typical of I-type granitoids, and their LILE enrichment and negative Nb-Ta-Ti-P anomalies are common features of subduction-related granitoids. In contrast, 165 Ma rocks are A-type granitoids that show HREE-enriched patterns with significant depletions of Sr, P, Eu, and Ti. I-type granitoids dated at 179 Ma and 167 Ma have I Sr = 0.7092-0.7158, 0.7206-0.7263 and ε Nd (T) = -13.96 to -13.55, -21.47 to -19.51, respectively. A-type, 165 Ma granitoids have relatively lower I Sr (0.7052) and strongly negative ε Nd (T) (-20.47), reflecting melt derivation from the lower crust. These results suggest that the formation of granitoids along the southwestern boundary between the Gyeonggi Massif and the Okcheon Belt took place at ca. 179-167 Ma by the subduction of the paleo-Pacific plate. The 165 Ma post-orogenic A-type granites intruded in an extensional setting, providing a critical time constraint on the termination of Jurassic plutonism in South Korea. The 179 Ma foliated granitoids are similar to syn-kinematic granitoids in and around the Honam shear zone, indicating that ductile shear movement may have occurred at ca. 179 Ma. Biotite K-Ar ages of deformed Precambrian rocks and Middle Jurassic granitoids from the Buyeo area generally yield ages of 144-152 Ma and 124-135 Ma. These results probably reflect pervasive reactivation during Latest Jurassic to Early Cretaceous deformation that postdated the main ductile shearing event along the southern boundary of the Gyeonggi Massif.

Temperature and Timing of the Mylonitization of the Leucocratic Granite in the Northeastern Flank of the Taebaeksan Basin

“…Cluzel et al (1991) suggested that the shear zones are amalgamated during the Triassic associated with the Chinese continental collision. However, as mentioned before, geochronologic data for the shearing indicate that the Honam shear zone dominantly initiated during the Middle to Late Jurassic and then reactivated during the Early Cretaceous (Cho et al, 1999;Cheong et al, 2006;Kim et al, 2009;Park et al, 2009).…”

“…1a) is recognized by mylonitized granitoid rocks. The Honamshear zone mainly developed around the tectonic boundaries between the Yeongnam massif and the Okcheon Basin (e.g., Sunchang, Cheongsan, and Yecheon shear zones; Cho et al, 1999;Cheong et al, 2006;Cho et al, 2007) and within the Okcheon Basin (Jeonju-Muan shear zones; Lee et al, 2001;Lee et al, 2003;Kim et al, 2003;Park et al, 2009). These shear zones are dominantly characterized by right lateral strike-slip movement of ductile or brittle-ductile shearing (Kim and Kee, 1994;Lee, 1996a, 1996b;Chough et al, 2000;Ree et al, 2001).…”

“…1). The Honam shear zone is characterized by a dextral strike-slip shear zone and mainly developed around the Okcheon belt and the Yeongnam massif (Kim and Kee, 1994;Lee 1996a, 1996b;Cho et al, 1999;Ree et al, 2001Ree et al, , 2005Cheong et al, 2006;Kim et al, 2009;Park et al, 2009). Yin and Nie (1993) suggested that the dextral strike-slip shear zone developed during the middle-late Triassic Songrim orogeny associated with collision between the North and South China Blocks (e.g., Yanai et al, 1985).…”

Geochemical Composition of the Continental Crust in Korean Peninsula

“…(g) Koh et al, 1996Kim, et al, 2005;Kim et al, 2009;Kim et al, 1995;Kim and Park, 1996;Kim et al, 1997;Min and Kim, 1996;Park et al, 1997;Wee et al, 2007;Wee and Kim, 2009;Wee et al, 2005;Wee et al, 2006;Youn and Park, 1995;Yun andHong, 2004, Yun et al, 2006;Lee et al, 2008;Cheong et al, 1998;Jwa et al, 1998;Yun, 2003. (h) Min andKim, 1996;Park, 2009;Park et al, 1997;Lee et al, 2008. (i) Lee et al, 1997a.…”

In-situ analyses of zircon and other minerals: Contributions to the Asian geology and tectonics

“…The authors further suggest that the Busan complex is possibly linked with the Hida-Oki terrane in Japan. Park et al (2009) report the SHRIMP U-Pb zircon ages, together with geochemical and Sr-Nd isotopic data, for Jurassic granitoids from the southwestern Gyeonggi massif, Korea. Foliated and non-foliated I-type granitoids are dated at ca.…”