Tectonic evolution of the Central Ogcheon Belt, Korea

Abstract

The tectonic evolution of the Central Ogcheon Belt has been newly analyzed in this paper from the detailed geological maps by lithofacies classification, the development processes of geological structures, microstructures, and the time-relationship between deformation and metamorphism in the Ogcheon, Cheongsan, Mungyeong Buunnyeong, Busan areas, Korea and the fossil and radiometric age data of the Ogcheon Supergroup(OSG). The 1st tectonic phase(D*) is marked by the rifting of the original Gyeonggi Massif into North Gyeonggi Massif(present Gyeonggi Massif) and South Gyeonggi Massif (Bakdallyeong and Busan gneiss complexes). The Joseon Supergroup(JSG) and the lower unit(quartzose psammitic, pelitic, calcareous and basic rocks) of OSG were deposited in the Ogcheon rift basin during Early Paleozoic time, and the Pyeongan Supergroup(PSG) and its upper unit(conglomerate and pelitic rocks and acidic rocks) appeared in Late Paleozoic time. The 2nd tectonic phase(Ogcheon-Cheongsan phase/Songnim orogeny: D1), which occurred during Late Permian-Middle Triassic age, is characterized by the closing of Ogcheon rift basin(= the coupling of the North and South Gyeonggi Massifs) in the earlier phase(Ogcheon subphase: D1a), and by the coupling of South China block(Gyeonggi Massif and Ogcheon Zone) and North China block(Yeongnam Massif and Taebaksan Zone) in the later phase(Cheongsan subphase: D1b). At the earlier stage of D1a occurred the M1 medium-pressure type metamorphism of OSG related to the growth of coarse biotites, garnets, staurolites. At its later stage, the medium-pressure type metamorphic rocks were exhumed as some nappes with SE-vergence, and the giant-scale sheath fold, regional foliation, stretching lineation were formed in the OSG. At the D1b subphase which occurs under (N)NE-(S)SW compression, the thrusts with NNE-or/and SSW-vergence were formed in the front and rear parts of couple, and the NNE-trending Cheongsan shear zone of dextral strike-slip and the NNE-trending upright folds of the JSG and PSG were also formed in its flank part, and Daedong basin was built in Korean Peninsula. After that, Daedong Group(DG) of the Late Triassic-Early Jurassic was depoisited. The 3rd tectonic phase(Honam phase/Daebo orogeny: D2) occurred by the transpression tectonics of NNEtrending Honam dextral strike-slip shearing in Early~Late Jurassic time, and formed the asymmetric crenulated fold in the OSG and the NNE-trending recumbent folds in the JSG and PSG and the thrust faults with ESE-vergence in which pre-Late Triassic Supergroups override DG. The M2 contact metamorphism of andalusite-sillimanite type by the intrusion of Daebo granitoids occurred at the D2 intertectonic phase of Middle Jurassic age. The 4th tectonic phase(Cheongmari phase: D3) occurred under the N-S compression at Early Cretaceous time, and formed the pull-apart Cretaceous sedimentary basins accompanying the NNE-trending sinistral strike-slip shearing. The M3 retrograde metamorphism of OSG associated with the crystallization of chlorite porphyroblasts mainly o...

Deformation Microstructures of Phyllite in Gunsan, Korea, and Implications for Seismic Anisotropy in Continental Crust

“…Cluzel et al [64,65] divided the Ogcheon Metamorphic Belt into five main tectonic units bounded by thrusts: Iwharyeong, Poeun, Turungsan, Chungju, and Pibanryeong units. Although there has been some controversy regarding deformation stages and the exact timing of metamorphism, it has been suggested that bimodal volcanisms and sedimentation in the rift setting occurred from the Neoproterozoic [67,[74][75][76][77] to late Paleozoic [78,79], followed by the subsequent Permian to Triassic tectonic event that extensively affected the Ogcheon Metamorphic Belt, forming the southeastward stacking of the nappes [64,65,67,72,79,80]. [67,84].…”

Jurassic (~170Ma) Zircon U-Pb Age of a "Granite Boulder" in the Geumgang Limestone, Ogcheon Metamorphic Belt, Korea: Reinterpretation of its Origin

“…더 나아가 금강 석회암이 신원생대의 눈덩어리 지구(Snowball Earth) 에 수반된 빙하 기원의 덮개 탄산염암(cap carbonate) 으로 해석된 바 있다 (Choi et al, 2012). 금강휴게소 부근에는 1:5만 옥천도폭 (Kim et al, 1978)에 잘 기술된 바와 같이 금강석회암이 함력천매 암으로 구성된 황강리층과 암회색-흑색의 점판암과 천 매암으로 주로 구성된 변성이질암층[명오리층 (Lee et al, 1998b;Choi et al, 2012;Choi, 2014) 또는 창리층 (Kim et al, 1978;Kang et al, 2012)으로 불림] 사이에 존재한다 (Fig. 1c) (Fig.…”

Geological Structures and Mineralization in the Yeongam Mineralized Zone, Korea

“…영암의 은적-상은 광화대 지역은 지구조적으로 옥 천대의 남서단부에 위치하며 (Kang and Lee, 2002;Kang et al, 2012), 백악기의 화산활동에 의한 목포-해남-영암 환상구조대의 북동부에 위치하고 있다( (Kim, 1991;Kim and Nagao, 1992), 환상구조의 내부에 존재하는 화강암이 백악기가 아닌 쥐라기로 알려져, 콜드론 내 관입한 것이 아니라 쥐라기 산이 화 강암의 돔이 이들 연변에 퇴적한 백악기 지층의 기반 암으로 제시한 바 있다 (Koh, 1996;Koh and Chang, 1996). 조사지역인 상은-은적 광화대 일대의 지질은 유문 암질 응회암, 안산암질 응회암, 각력질 응회암, 유문 암 및 석영반암 등으로 구분한 경우 (Choi, 1987;Kim, 1989;Yun, 1989;Kim et al, 1990Kim et al, , 1991와 함화산력유문암질 응회암, 석영안산반암, 안산암, 석 영반암 등으로 구분한 경우 (Lee et al, 1996)와 함께 백악기 유천층군 화원층 내의 서호 응회암으로 기재 된 바 있다 (Koh, 1996;Koh and Chang, 1996).…”