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. Structur ally it is divisible into three massifs, separated by two fold belts. The N angrim massif of North Korea is a high grade metamorphic terrain overlain b y Palaeozoic sedimentary rocks. In South Korea the Gyeonggi massif is predo minantly a metasedimentary gneiss terrain and in the Ryeongnam massif the o rthogneisses are dominant. These Precambrian rocks are overlain by Paleozoi c 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 Seongn am 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 t he Sachangri porphyritic granite at 164.7 +/- 2.4 Ma. Comparison of U-Pb ag es of Precambrian and Mesozoic rocks in the Gyeonggi massif with those in t he Ryeongnam massif ages reveals a different age pattern, which suggests a different evolutionary history of these two cratonic blocks. The Precambria n rocks of Gyeonggi massif are more similar in age to those of southeast Ch ina than to those of the Ryeongnam massif. The Mesozoic plutonism in both t he Gyeonggi and the Ryeongnam massifs is comparable to that of southeast Ch ina.