In situ zircon U-Pb dating of Jurassic granitoids in North Korea and its tectonic implications

Jurassic granitoids formed during the Daebo period of magmatism are common throughout the northern Korean Peninsula, but precise geochronological and geochemical data for these granitoids are lacking. In this study, 16 granitic rocks from 10 Jurassic plutons in the Rangrim Massif and Imjingang Belt, including diorite, biotite granite, two-mica granite, granodiorite, porphyry granite, and leucogranite, were subjected to in situ zircon U-Pb dating. The ages range from 197 +/- 3 to 164 +/- 4 Ma. Combined with previously published age data for the Jurassic granites, it is apparent that the Daebo period magmatism occurred mainly in the Early and Middle Jurassic (199-163 Ma). Early Jurassic granites are mostly exposed in the northern and southern Korean Peninsula (i.e., the Tumangang Belt and Kwanmo sub-massif in the north and Yeongnam Massif in the south). Middle Jurassic granites are mainly distributed in the central Korean Peninsula. These granites are peraluminous, high-K calc-alkaline or shoshonitic, and I- and highly fractionated I-type granites. The similar timing of magmatism and large-scale strike-slip shear structure demonstrates that the Daebo movement in the Korean Peninsula can be correlated with the early Yanshanian movement (the A episode) in eastern China, although the Daebo movement was slightly older than the early Yanshanian movement. This study considers that the Jurassic granitoids and the Honam shear zone are possibly products of the Paleo-Pacific subduction during Jurassic period. However, the Jurassic granitoids in the Korean Peninsula and east China have different spatial-temporal zonation features from the Paleo-Pacific subdution model, which provides a sample for further understanding the tectonics of ocean-land and deep shallow interactions of the Earth. We shall keep reporting our new study results.