Late Cretaceous volcanic rocks and associated granites in Gyeongsang Basin, SE Korea: Their chronological ages and tectonic implications for cratonic destruction of the North China Craton

Abstract

The Gyeongsang Basin is the largest exclusively non-marine sedimentary basin in Korean Peninsula, located in southeastern part of the Peninsula. Its sedimentary setting, magma source, tectonic nature, and formation age are important to understand the Mesozoic tectonic evolution of not only the Sino-Korea Craton, but also the entire Northeast Asia. The Gyeongsang Supergroup, the basin fill, is divided into the Sindong, Hayang, and Yucheon Groups in ascending order. The Sindong and Hayang Groups are composed of sandstone, shale, minor amounts of conglomerate, and marl deposited in a non-marine environment, whereas the Yucheon Group is characterized by the dominance of volcanic rocks. Precise isotopic ages and geochemical analyses are scarce for the volcanic elements of this basin, restricting our understanding of its geodynamic setting and evolution. In this study, we present new U–Pb zircon ages from the volcanic rocks of the Yucheon Group and associated granites in the Gyeongsang Basin. Thirteen volcanic samples yielded ages ranging from 94.4 to 78.4Ma, and four granite samples give ages ∼72Ma. These data confirm that a major magmatic event occurred during Late Cretaceous, and the Gyeongsang volcano-sedimentary complex represents a rock association representing a Late Cretaceous island arc. In comparison with the Sambagawa metamorphic belt, the Jurassic Chichibu accretionary complex (AC) with Cretaceous strike-slip basin sediments, and the Cretaceous Shimanto mélange zone in southwest Japan, it is likely that above-motioned complexes constitute the trace of a continuous subduction-related island arc system in SE Korea extending from SW Japan. Although the peak ages of the magmatic rocks in the eastern part of the North China Craton (NCC) are 130±10Ma, indicating an important time of continental lithospheric thinning under the NCC, the ages of the Gyeongsang magmatic rocks are markedly younger. Late Cretaceous magmatism was very weak in the eastern NCC. Therefore, it is probable that Early–Middle Mesozoic lithospheric thinning beneath the eastern NCC is triggered by multiple tectonic factors, not only by the subduction of the Pacific plate suggested by some previous studies. In addition, 20 inherited/xenocrystic zircons from these volcanic rocks give Archean ages ranging from 2.5 to 2.6Ga, suggesting the existence of late Archean rocks in the Yeongnam Massif. The Yeongnam Massif is predominated by the latest Archean crustal growth at ∼2.50Ga, consistent with the characteristics of the North China Craton.