Triassic mafic and intermediate magmatism associated with continental collision between the North and South China Cratons in the Korean Peninsula

Triassic coeval mafic and intermediate magmatism occurred in the area suggested to be the southern margin of the North China Craton (NCC) in the Gyeonggi Massif (GM) of the Korean Peninsula. This study investigates aspects of the mafic and intermediate magmatism using SHRIMP zircon ages and whole-rock chemical and isotopic Sr-Nd data. The mafic and intermediate rocks intruded into a basement paragneiss in three areas (Yangpyeong, Odesan and Yangyang) within the GM at ca. 230Ma. The paragneiss was metamorphosed in both the Paleoproterozoic and Triassic. Gabbros (hornblende gabbro and pyroxene-mica gabbro) from the study areas exhibit strong light REE (LREE) enrichment relative to chondrite (La_N/Yb_N=11.1-30.6) and a high LILE/HFSE pattern, Ta-Nb-P-Ti troughs and positive Ba-K-Pb-Sr spikes on the N-MORB-normalized multi-element variation diagram. These features are typical characteristics of arc-related gabbros. The gabbros also show strongly enriched initial isotopic compositions (⁸⁷Sr/⁸⁶Sr_(i)=0.7100-0.7137; ε_Nd(t)=-13.1 to -19.7). The coeval intermediate intrusive rocks also exhibit whole-rock chemical and isotopic features (⁸⁷Sr/⁸⁶Sr_(i)=0.7099-0.7143; ε_Nd(t)=-10.8 to -18.6) similar to those of the gabbros. The mafic and intermediate intrusive rocks plot in the within-plate and/or post-collisional fields on tectonic discrimination diagrams. These data indicate that the mafic and intermediate magmatism in the study areas occurred during the Triassic post-collisional relaxation period via partial melting of sub-continental lithospheric mantle (SCLM) that was enriched in a subduction environment prior to (or during) the Permo-Triassic continental collision between the NCC and the South China Craton (SCC). The highly enriched mantle signatures revealed by the gabbros from the study areas are matched to the enriched features identified in Cretaceous mafic igneous rocks (ca. 130Ma) on the southern margin of the NCC. Thus, this study suggests that the lithospheric mantle beneath the Yangpyeong, Odesan and Yangyang areas are comparable to the SCLM of the NCC southern margin. The highly enriched nature of mafic and intermediate rocks from the study areas indicates that their source is the SCLM that was metasomatized by Permian to early Triassic subduction-continental collision processes.