The signature of a prolonged subduction-accretion history from Paleozoic to Early Mesozoic is preserved within the dismembered serpentinite mélanges within the Hongseong suture. Here we present major and trace element data from the mafic fragments/blocks within the Baekdong serpentinite mélange 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 (17-25wt.%) 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 ~310Ma and ~228Ma, respectively. Zircons from an associated orthogneiss block within the mélange yield a Neoproterozoic crystallization age of ~748Ma. These results, together with the recent SHRIMP zircon ages from other dismembered serpentinite mélanges 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.
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We thank Drs. Sung-Tack Kwon, Wenjiao Xiao and an anonymous reviewer for constructive reviews and Dr. Damian Nance for valuable comments and editorial handling. We also thank Dr. Ngo Thanh for chromian spinels. This work was supported by the Basic Research Project ( GP2009-012 ; “Tectonic Evolution of Major Crustal Units in the Midwestern Part of the Korean Peninsula”) of the Korea Institute of Geoscience and Mineral Resources, funded by the Ministry of Knowledge and Economy of Korea to S.W. Kim. This paper represents part of N. Park's M.Sc. research performed at Yonsei University. This work was supported by Grant in-Aid NRF 2010-0011102 to S. Kwon.
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