Late Cretaceous-early Paleogene magmatism in the Gyeongsang basin, southeast Korea and its implications for middle Paleogene climate change

Abstract

• The youngest volcanic rocks in the Gyeongsang basin were formed at ∼ 56 Ma. • Paleogene magmatic activities indicate a transformation in tectonic regime. • Magmatic lull along east Asian and global cooling start from Cenozoic. The Gyeongsang basin is the largest volcanic-sedimentary basin in Korean Peninsula. It is characterized by widespread late Cretaceous-early Paleogene plutonic and volcanic rocks called Gyeongsang Supergroup, with its uppermost part of Yucheon group consisting mainly of andesitic to rhyolitic lavas and their derivative pyroclastic rocks. However, the precise geochronological framework of this supergroup remains elusive. In this study, we present new SIMS zircon U-Pb and whole-rock 40 Ar/ 39 Ar ages for the volcanic rocks of the Yucheon group and associated Bunam granites in the Juwangsan area, north of the Gyeongsang basin. Seven volcanic samples range in age from 71 to 56 Ma, while a granite sample has an age of 74 Ma. Combined with literature data, the Yucheon volcanic activities can be divided into two stages: 94–78 Ma and 71–56 Ma, comparable to 91–48 Ma of the granites in the basin. Actually, a gigantic igneous belt developed along the continental margin of NE Asia during the Mesozoic-Cenozoic, with a length over 10000 km and a width ∼ 1500 km. Exhibiting an eastward migration trend during 145–48 Ma and a magmatic tempo from flare-up to lull, this magmatic belt experiences a transformation in tectonic regime from active continental margin to back-arc due to subduction retreating of the Pacific subduction. The continental arc magmatic flare-up and associated contact metamorphism during Jurassic-early Paleogene may provide a huge amount of CO 2 for the global warming. With the magmatic lull after about 50 Ma, the cool Earth may be caused by less CO 2 inputs.