Late Paleoproterozoic ( 1.7 Ga) granites and granitic gneisses at Garorim Bay, South Korea: Implications for tectonic setting

The Gyeonggi Massif , located in the central part of the Korean peninsula, is considered to be one of potential eastward extension of the Triassic Qingling-Dabie-Sulu collision belt between the North and South China cratons. Understanding the crustal evolution of the Gyeonggi Massif can thus provide important information on the tectonic history of the Korean Peninsula. The Precambrian basement of the Gyeonggi Massif is mainly composed of Paleoproterozoic (ca. 1.8 -1.9 Ga) gneisses, possibly associated with assembly of the supercontinent Columbia. In this study, we newly report late Paleoproterozoic granitic intrusions at Garorim Bay (Daewoodo, B oonjumdo, Gopado) in the southwestern part of the Gyeonggi Massif. We determined whole-rock major- and trace-element concentrations and sensitive high-resolution ion microprobe (SHRIMP) zircon U-Pb ages for four granites and two granitic gneisses. The granites and granitic gneisses yields ages of 1706 ± 17 Ma, 1690 ± 5 Ma and 1683 ± 18 Ma, and 1692 ± 9 Ma and 1679 ± 13 Ma, respectively. They are weakly peraluminous, and belong to the high-K calc-alkaline to shoshonite series. The samples show LREE-enriched patterns with/without Eu anomalies. They are characterized by high (K₂O+Na₂O)/CaO, K₂O/MgO and Ga/A l ratios, high contents of HFSE, showing the A-type granite affinity. Compared with the typical anorogenic intra-continental rift-related granites (A₁-type), the Yb/Ta, Y/Nb and Ce/Nb ratios of the samples studied are, however, much higher, and similar to the post-collisional/post-orogenic extension-related granites (A₂-type). They also plot within the field for post-collisional granitoids in the Rb vs. (Y+Nb) tectonic discrimination diagram. These geochemical characteristics indicate a post-collisional tectonic setting of the western part of the Gyeonggi Massif during the Paleoproterozoic, postdating continental collisions and final amalgamation of the Columbia supercontinent (ca. 2.1-1.8 Ga). The late Paleoproterozoic (ca. 1.75-1.65 Ga) extension-related igneous rock suites are widespread in the North China Craton (NCC), but rarely in the southwestern Yangtze Block. This observation combined with the geochemical systematics indicate tectonic affinity of the western part of the Gyeonggi Massif to the NCC.