Reconstruction of the Ogcheon Rift Basin and Pre-Cenozoic Tectonic Evolution of the Central Ogcheon Belt, Korea

Abstract:

The pre-Cenozoic tectonic structures of the Central Ogcheon Belt, Korea, were formed at least through five times of tectonic phases [D* Gyemyeongsan phase of Neoproterozoic∼Middle Permian, D1 Ogcheon-Cheongsan phase (Songnim orogeny) of Late Permian∼Middle Triassic, D2 Honam phase (Daebo orogeny) of Early∼Late Jurassic, D3 Cheongmari phase of Early Cretaceous, D4 Geumgang phase before Late Cretaceous] and three times of metamorphism [M1 medium-pressure type metamorphism of Late Permian, M2 contact metamorphism of Middle Jurassic, M3 retrograde metamorphism of Early Cretaceous]. The D* tectonic phase is marked by the rifting of the original Gyeonggi Massif into North Gyeonggi Massif (NGM: present Gyeonggi Massif) and South Gyeonggi Massif (SGM: Bakdallyeong and Busan gneiss complexes). Its associated bimodal type volcano-plutonism occurred at least four times, two times at Neoproterozoic, a Early Paleozoic, a Late Paleozoic ages. The lower (quartzose psammitic, pelitic, calcareous and basic rocks) and upper (conglomerate and pelitic rocks and acidic rocks) units of Ogcheon Supergroup (OSG) were deposited in the Ogcheon rift basin (ORB) during Early and Late Paleozoic times, respectively. The D1 phase is characterized by the coupling of NGM and SGM with closing of ORB and the M1 metamorphism of OSG at its earlier phase, and by the coupling of South China block (Gyeonggi Massif and Ogcheon Zone) and North China block (Yeongnam Massif and Taebaksan Zone) and Cheongsan dextral strike-slip shearing and formation of Middle Triassic Dadong basin in its later phase. The D2 is marked by Honam dextral strike-slip shearing and the M2 metamorphism of OSG by the intrusion of Daebo granitoids at the inter-tectonic phase. The D3 is by NNE-trending sinistral strike-slip shearing and the M3 retrograde metamorphism of OSG. The D4 occurred along Geumgang fault, and formed a giant-scale Geumgang drag fold intruded by Late Cretaceous acidic dykes.