U-Pb zircon ages for Precambrian and Mesozoic plutonic rocks in the Seoul-Cheongju-Chooncheon area, Gyeonggi massif, Korea.

The Korean peninsula is composed of Precambrian to Holocene rocks. Structurally it is divisible into three massifs, separated by two fold belts. The Nangrim massif of North Korea is a high grade metamorphic terrain overlain by Palaeozoic sedimentary rocks. In South Korea the Gyeonggi massif is predominantly a metasedimentary gneiss terrain and in the Ryeongnam massif the orthogneisses are dominant. These Precambrian rocks are overlain by Paleozoic and Mesozoic sedimentary rocks and are intruded by Mesozoic plutons. In the Gyeonggi massif the oldest rocks dated here are the Gongju migmatite 2417 ± 39 Ma, and the Inje crystalline schist 2413 ± 21 Ma. The Seongnam migmatite has a younger age of 1868 ± 9 Ma. The Hwacheon banded gneiss has an age of 2164 ± 18 Ma, the Hongcheon porphyroblastic gneiss has an age of 1952 ± 13 Ma, and the Kanghwa granite gneiss has an age of 1673 ± 10 Ma. The Mesozoic Otanri gabbro was emplaced at 166.2 ± 1.2 Ma, and the Sachangri porphyritic granite at 164.7 ± 2.4 Ma. Comparison of U-Pb ages of Precambrian and Mesozoic rocks in the Gyeonggi massif with those in the Ryeongnam massif ages reveals a different age pattern, which suggests a different evolutionary history of these two cratonic blocks. The Precambrian rocks of Gyeonggi massif are more similar in age to those of southeast China than to those of the Ryeongnam massif. The Mesozoic plutonism in both the Gyeonggi and the Ryeongnam massifs is comparable to that of southeast China.