Neoproterozoic tectonic evolution of the Hongseong area, southwestern Gyeonggi Massif, South Korea; implication for the tectonic evolution of Northeast Asia

The Hongseong area is the south-western part of the Gyeonggi Massif in South Korea and is regarded as the eastward extension of the Dabie-Sulu collision belt in China due to the occurrence of Triassic (~230 Ma) eclogites. Two types of Neoproterozoic metabasites occur together with regionally intruded arc-related Neoproterozoic granitoids (ca. 850-830 Ma) in the Hongseong area. The first type of metabasite (the Bibong and Baekdong metabasites) is a MORB-like back-arc basin basalt or gabbro formed at ca. 890-860 Ma. The Bibong metabasites show light rare earth element (LREE) enriched patterns with LaN = 77.6-255.3 and (La/Yb) N = 2.8-10.7 and the Baekdong metabasite also show light rare earth element (LREE) enriched patterns with LaN = 3.5-5.9 and (La/Yb)N = 0.3-0.4. They may have formed during back-arc opening by diapiric upwelling of deep asthenospheric mantle which was metasomatized by large ion lithophile element (LILE) enriched melt or fluid derived from the subducted slab and/or subducted sediment beneath the arc axis. The second type of metabasite (the Gwangcheon metabasite) formed in a plume-related intra-continental rift setting at 763.5±18.3 Ma and is geochemically similar to oceanic island basalt (OIB) with La N = 197.7-523.2 and (La/Yb)N = 6.6-22.9. The Gwangcheon metabasites show strongly enriched LREE patterns with minor or absent negative Eu anomalies and are slightly depleted in Nb, Ta, Sr, P and Ti reflecting the mixing of upwelling mantle plume with subcontinental lithospheric mantle (SCLM) which is depleted in Ti during subduction stage prior to within-plate rifting . These data indicate a transition in tectonic setting in the Hongseong area from arc to intra-continental rift between ca. 830 and 760 Ma. This transition is well correlated to the Neoproterozoic transition from arc to intra-continental rift tectonic setting at the margin of the Yangtze Craton and corresponds to the amalgamation and breakup of Rodinia Supercontinent. The younger arc ages in the Hongseong area suggest that the amalgamation of Yangtze block started from west and propagated towards east.