Phanerozoic high-pressure eclogite and intermediate-pressure granulite facies metamorphism in the Gyeonggi Massif, South Korea: Implications for the eastward extension of the Dabie-Sulu continental collision zone

Petrological analysis, zircon trace element analysis and SHRIMP zircon U-Pb dating of retrogressed eclogite and garnet granulite from Bibong, Hongseong area, SW Gyeonggi Massif, South Korea provide compelling evidence for Triassic (231.4 +/- 3.3 Ma) high-pressure (HP) eclogite facies (Mll) metamorphisms at a peak pressure-temperature (P-T) of ca. 16.5-20.0 kb and 775-850 degrees C. This was followed by isothermal decompression (ITD), with a sharp decrease in pressure from 20 to 10 kb and a slight temperature rise from eclogite facies (M I) to granulite facies (M2), followed by uplift and cooling. Granitic orthogneiss surrounding the Backdong garnet granulite and the ophiolite-related ultramafic lenticular body near Bibong records evidence for a later Silurian (418 +/- 8Ma) intermediate high-pressure (IHP) granulite facies metamorphism and a prograde P-T path with peak P-T conditions of ca. 13.5 kb and 800 degrees C. K-Ar ages of biotite from garnet granulites, amphibolites, and granitic orthogneisses in and around the Bibong metabasite lenticular body are 208-219 Ma, recording cooling to about 310 degrees C after the Early Triassic metamorphic peak. Neoproterozoic zircon cores in the retrogressed eclogite and granitic orthogneiss provide evidence that the protoliths of these rocks were similar to 800 and similar to 900 Ma old, respectively, similar to the ages of tectonic episodes in the Central Orogenic Belt of China. This, and the evidence for Triassic HP/UEP metamorphism in both China and Korea, is consistent with a regional tectonic link within Northeast Asia from the time of Rodinia amalgamation to Triassic continent-continent collision between the North and South China Blocks, and with an eastward extension of the Dabic-Sulu suture zone into the Hongseong area of South Korea. (c) 2006 Elsevier B.V. All rights reserved.