ABSTRACT

The Yeongnam Massif represents a key Precambrian basement of the Korean Peninsula, and its northeastern part preserves important records of Paleoproterozoic magmatism. Although Orosirian magmatism is widely reported from this region, several magmatic bodies remain insufficiently identified, and no integrated interpretation combining both mafic and felsic magmatism has been conducted to evaluate mantle-crust differentiation processes in an arc environment. This study refines the temporal evolution of arc-related magmatism by integrating new lithological, geochronological, and geochemical data from amphibolite and granite suites. A newly defined Buncheon amphibolite intruded the Buncheon granite gneiss at ca. 1.99–1.96 Ga, followed by metamorphism at ca. 1.86 Ga. The Okbang amphibolite intruded the southern margin of the Buncheon granite gneiss at 1.86–1.84 Ga. At a similar time, a newly defined Seokpo granite intruded the Hongjesa granite gneiss at 1.87 Ga. The Buncheon and Okbang amphibolites have slightly enriched LREEs and high Th/Yb and Nb/La ratios with mostly positive zircon εHf(t) values, suggesting derivation from a fluid-metasomatized mantle source in an arc setting. The Seokpo granite has various εHf(t) values, implying a heterogeneous crustal source, and exhibits A2-type granite signature which is associated with extensional regime within the arc environment. Integrating this and previous studies, the Orosirian magmatism in the northeastern Yeongnam Massif is divided into early (2.0–1.94 Ga) and late (1.87–1.82 Ga) episodes. In the early Orosirian episode, north-to-southward subduction occurred and induced arc magmatism forming the Buncheon amphibolite, Imgye gabbroic diorite, and the Buncheon and Hongjesa granite gneisses. During the late Orosirian episode, slab roll-back triggered renewed arc magmatism under extensional conditions and asthenospheric mantle upwelling, leading to the formation of the Okbang amphibolite and A2-type Jungbongsan and Seokpo granites. This study enhances our understanding of the arc-related magmatism and the tectonic evolution of the northeastern Yeongnam Massif during the Orosirian.