Forearc serpentinite melange from the Hongseong suture, South Korea

The signature of a prolonged subduction-accretion history from Paleozoic to Early Mesozoic is preserved within the dismembered serpentinite melanges within the Hongseong suture. Here we present major and trace element data from the mafic fragments/blocks within the Baekdong serpentinite melange revealing their arc-like tholeiite affinity within a suprasubduction zone tectonic setting. Chromian spinel compositions from the Baekdong hydrated mantle peridotite (serpentinite) are characterized by high Cr# (0.53-0.67) and Fe2+/Fe3+ ratio, medium Mg# (0.42-0.55), and Al2O3 contents (17-25 wt.%) indicating a forearc tectonic environment for the hydrated mantle peridotite. The estimated melting degree (>17.6%) and FeO/MgO of the parental melt (0.9-1.3) are consistent with that of forearc magmas. SHRIMP zircon U-Pb ages from a high-grade mafic rock and an anorthosite from the study area give protolith ages of similar to 310 Ma and similar to 228 Ma, respectively. Zircons from an associated orthogneiss block within the melange yield a Neoproterozoic crystallization age of similar to 748 Ma. These results, together with the recent SHRIMP zircon ages from other dismembered serpentinite m langes within the Wolhyeonri complex, suggest that Paleozoic to Early Mesozoic subduction and subsequent collision events led to the exhumation of the hydrated forearc mantle peridotites from a metasomatized mantle wedge. The Hongseong region preserves important clues to a long-lived subduction system related to global events associated with the final amalgamation of the Pangaea supercontinent. (C) 2011 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.