Geochrononlogy and thermal history of the Chuncheon granite in the Gyeonggi massif, South Korea

We report Rb-Sr whole rock, K-Ar and fission track mineral ages for the Chuncheon granite in the Precambrian Gyeonggi massif. The Rb-Sr whole rock define an age of Ma with an initial ratio of , suggesting that the granitic magma might have been generated from crustal sources (S-type), or probably mixed mantle and crustal materials, and emplaced into the massif in the late Triassic or the early Jurassic. K-Ar mineral ages of hornblende, muscovite and biotite are ~210 Ma, ~180 Ma and 166-170 Ma respectively, and fission track zircon and apatite ages are 65-70 Ma, ~35 Ma respectively. These ages indicate that the granitic magma might have been emplaced at about 7 to 9 km from the paleosurface, and rapidly cooled down up to until middle Jurassic (~170 Ma) with a rate of about /Ma, due to thermal difference between the magma and the wall rock. During middle Jurassic to late Cretaceous (about 170-70 Ma), the granite pluton is assumed to have uplifted to 4 to 6 km level under the paleosurface with a rate of 30 m/Ma and slowly cooled down with a rate of about /Ma owing to relatively slow denudation of the massif. In late Cretaceous to the present, the pluton might have more rapidly uplifted to the present level with a rate of 85 m/Ma and rapidly cooled down with a rate of about /Ma compared to those of middle Jurassic to late Cretaceous time because of extensive igneous activities accompanied by tectonism in the Gyeonggi massif.