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The Korean Peninsula mainly comprises the Paleoproterozoic Gwanmo, Nangnim, Gyeonggi, and Yeongnam massifs from north to south. The Paleoproterozoic basement is rarely exposed in the Paleozoic Taebaeksan basin, which is located in the northeastern part of the Okcheon belt between the Gyeonggi and Yeongnam massifs. One of the most important issues in the tectonic interpretation of the Korean Peninsula is whether Paleoproterozoic rocks in the Taebaeksan basin have an affinity with those in the Gyeonggi or Yeongnam massifs. To solve this problem, we focused on the petrogenesis of the Imgye gabbroic diorite, Jungbongsan granite, and Jangsan quartzite in the Imgye area of the Taebaeksan basin. The Imgye gabbroic diorite shows mafic to intermediate compositions with slightly enriched LREEs compared to HREEs, slightly positive Rb, K, and Pb anomalies, and negative Ta, Nb, and P anomalies. The Imgye gabbroic diorite formed in a volcanic arc tectonic setting. The geochemical compositions of the Jungbongsan granite show enriched LREEs compared to HREEs with negative Eu anomalies, and reveal strong positive Rb, Th, K, and Pb anomalies with negative Ba, Ta, Nb, Sr, P, Eu, and Ti anomalies. This Jungbongsan granite also formed in an arc tectonic setting like the Imgye gabbroic diorite. LA-ICP-MS zircon age dating of the Imgye gabbroic diorite gives an intrusion age of 1948 ± 21 Ma, whereas SHRIMP U–Pb zircon age dating on the Jungbongsan granite yields an emplacement age of 1873 ± 14 Ma. The ε_Hf(t) values of the Imgye gabbroic diorite are from 3.5 to 9.7, whereas those of the Jungbongsan granite are from −2.9 to 0.6. These data imply that the Imgye gabbroic diorite formed from a depleted mantle in the arc tectonic environment, whereas the Jungbongsan granite formed by reworking pre-existing crust material in the arc environment. The detrital zircons in the Jangsan quartzite show ages ranging from 3.06 to 1.85 Ga, with a peak concentration of ca. 2.5 Ga. Previous studies have suggested that the northern Gyeonggi and Nangnim massifs underwent collision-related magmatism and metamorphism at ca. 1.93–1.90 Ga, and then post-collisional magmatism and metamorphism at ca. 1.89–1.83 Ga, whereas the southern Gyeonggi massif underwent subduction-related magmatism and metamorphism at ca. 1.94–1.92 Ga, and then post-collision-related magmatism and metamorphism at ca. 1.84–1.78 Ga. By contrast, subduction-related events were recognized in the northern Yeongnam massif at ca 2.02–1.96 Ga and 1.90–1.85 Ga. This work, combined with the previous studies, suggests that the Paleoproterozoic basement in the Imgye area of the Taebaeksan basin can be correlated with the Paleoproterozoic basement of the northern Yeongnam massif rather than with those of the Nangnim and Gyeonggi massifs. Full article

Jurassic dioritic to granitic igneous rocks extensively intrude into the southern Korean Peninsula, including the Yuseong area located at the boundary between the southern margin of the Gyeonggi Massif and the northern margin of the Okcheon Belt. In this study, the petrogenesis and sources of Jurassic igneous rocks in the Yuseong area were investigated. The U–Pb zircon age data from the Jurassic plutonic rocks in the Yuseong area give two igneous ages, ca. 178–177 Ma and 169–168 Ma, indicating that two stages of igneous activity occurred in the Yuseong area during the Jurassic. The geochemical characteristics of Jurassic diorites indicate that they originated from enriched mid-ocean ridge basalt (E-MORB; Nb/Yb = 5.63–7.27; Zr/Yb = 118–156). The enriched Th/Yb ratios (5.5–8.0) in the diorites imply that they experienced crustal contamination during magma ascent. The Jurassic granitoids in the Yuseong area are divided into I- and S-type granites. The Jurassic I-type granitoids may have formed via the partial melting of mafic rocks with mixtures of 10–40% pelite-derived melt, while the S-type granites originated from felsic pelite. The Jurassic diorites have low Nb/Th ratios with depletion of the Nb and Ta components, indicating that they formed in a volcanic arc tectonic environment. On the other hand, the Jurassic granitoids show two different tectonic environments: a volcanic arc, and a syncollisional environment. The granites with syncollisional character are S-type granites, and may give incorrect information about tectonic setting because of the changes in the trace elements of the S-type granite due to fractional crystallization. Early Jurassic (200–190 Ma) igneous rocks are distributed only in the southeastern Korean Peninsula, including the Yeongnam Massif; Jurassic igneous rocks formed at ca. 190–180 Ma occur mainly in the Okcheon Belt and southern Gyeonggi Massif, which includes the Yuseong area. Middle Jurassic igneous rocks widely intruded from the Okcheon Belt, through the Gyeonggi and Nangrim massifs in the Korean Peninsula, to the Liaoning area in the North China Craton at 180–160 Ma. This distribution pattern of the Jurassic granitoids suggests that flat subduction started after 180 Ma in Northeast Asia. Full article

To test the previous hypothesis that upper Paleozoic sediments in the eastern Sino-Korean Block were mostly derived from the paleo-orogen located to the east, we compared published and new U–Pb age data of detrital zircons from Pennsylvanian strata distributed in the Sino-Korean Block (SKB). The age distributions of detrital zircons from different localities of Pennsylvanian strata in North China reflect varying contributions from the Inner Mongolia Paleo-uplift in the north and the Central China Orogenic Belt in the south. The supply of detritus from the northern source to distant areas, however, appears to have been limited during the Pennsylvanian times. The age distributions of detrital zircons from Korean Pennsylvanian strata located in the east of the SKB are characterized by a dense cluster of 1.84–1.90 Ga and differ from those of North China. The Korean age characteristic is best explained by strong influences of the detritus derived from the Paleoproterozoic Yeongnam Massif in southeastern Korea. Along with the significant number of zircons that record syn- to near-depositional magmatic activities, this observation supports the hypothesis of the existence of an active continental margin setting in the east of the SKB. Full article