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천영범,손문,송철우,김종선,손영관 한국지질과학협의회 2012 Geosciences Journal Vol.16 No.3
Detailed geological mapping and observations of various structural elements were made in order to determine the geometry and kinematics of the Ocheon Fault System (OFS) along the boundary between the Early Miocene Janggi and the Middle Miocene Pohang basins, SE Korea, and to reveal its roles on the basin evolutions. The OFS is a NE-trending relayed fault system composed of a number of NE or NNE-trending normal-slip and sinistral-normal oblique-slip faults, and has a scissor fault geometry decreasing in vertical offset southwestward. The constituent faults created independent grabens or half-grabens on the hanging-walls for the deposition of the Early or Middle Miocene strata. The OFS was initially the northwestern border fault of the Janggi Basin which acted as normal faults by the WNW-ESE tensional stress associated with the NNW-directed dextral simple shear caused by the East Sea opening. Afterwards, it experienced clockwise rotation with change of slip sense from normal-slip to sinistral-normal oblique-slip in response to the progressive dextral simple shear. At about 17 Ma, the shear stress propagating westward was released rapidly by the dextral strike-slip faulting of the NNW-trending Yeonil Tectonic Line (YTL) and the normal faulting of the NNE-trending western border faults of the Pohang Basin. At that time, the depocenter suddenly migrated northward and the depositional environment also changed rapidly from terrestrial to marine due to dramatic subsidence of the Pohang Basin. The Pohang Basin is interpreted to be a pull-apart basin extended at releasing bend/overstep between two PDZs (Principal Displacement Zones), i.e., the YTL and probably the East Korea Fault. The OFS was also reactivated as the eastern border faults of the Pohang Basin. In contrast to the western border faults, the OFS was rotated clockwise and could not be linked with the YTL because of its scissor fault geometry. Our results suggest that the NNW-trending regional dextral shear stress persisted for a considerable period of time in SE Korea during the East Sea opening, supporting the pull-apart opening of the East Sea rather than the fan-shaped opening. Most of the previous studies advocating the pull-apart opening emphasize the role of the NNE-trending strike-slip faults, like the Yangsan fault and OFS, as PDZs. In contrast, this study suggests that the NNE-trending faults in SE Korea acted as major normal faults at releasing bends or stepovers in the NNW-trending dextral fault system during the East Sea opening
천영범,조형성,송철우,손문 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.1
The WNW-ESE-striking Sinnyeong Fault, the most conspicuous fault of the Gaeum Fault System in the Cretaceous Gyeongsang Basin of Korea, provides an opportunity to understand the architectures and evolution of an intracontinental transpressional fault zone. We focus on the structural characteristics of the Sinnyeong Fault based on detailed field observations and magnetic fabric analysis. Its main movement is interpreted as sinistral slip with a small reverse component, although it could also have been active before the main movement. The deformation zone is asymmetric about the fault core. Sedimentary strata of the southern deformation zone are more extensively folded and deformed than those of the northern part, and the southern zone is much wider than the northern zone. NW-SE-trending en-echelon folds are limited to the southern periphery of the fault zone, where it is narrow, and underwent rotation toward the fault surface. These contractional deformations along the entire length of the fault are interpreted to have formed approximately coevally with the sinistral faulting. Newly observed WNW-ESE-striking mappable faults show a similar structural feature. Our results suggest that the damage asymmetry resulted from the eastward transport direction and relative uplift of south blocks of the faults under NE-SW compressive stress, which oriented at high angle (60–70°) to pre-existing strike of the faults. During progressive deformation, continuing slip accumulation along vertically tilted and fault-parallel sedimentary strata located directly south of the fault cores was responsible for the larger motions of the southern blocks of the faults rather than the relatively fixed northern blocks. We highlight that the sinistral reactivation of the Sinnyeong Fault formed a continuous, narrow transpressional zone during its long-term evolution.
천영범(Youngbeom Cheon),강희철(Hee-Cheol Kang),하상민(Sangmin Ha),이선갑(Sun-Kap Lee),손문(Moon Son),류충렬(Chung-Ryul Ryoo) 한국암석학회 2019 암석학회지 Vol.28 No.3
강원도 평창군 뱃재터널의 북쪽 입구 사면에서 대규모 횡와습곡이 확인되어 이를 기재하고 형성기작에 관해 해석하였다. 이 습곡은 고생대 조선누층군 정선석회암층 내에 수백 m 규모로 발달하고 있다. 습곡의 머리는 북쪽을 향하며, 층리와 축면엽리의 복합엽리면상에 발달하는 신장선구조(L1)는 남쪽으로 약 10° 침강하고 있다. 습곡 날개부에는 S-형 비대칭 습곡과 함께 A-형 또는 안상 칼집습곡들이 흔히 관찰되며 이들 습곡의 축은 습곡의 중앙부와 후면부에서 확인된 신장선구조(L1) 방향과 거의 평행하다. 따라서 이곳 대규모 횡와습곡은 상부가 북쪽으로 향하는 강한 연성전단작용에 의해 생성된 칼집습곡으로 고생대말-트라이아스기 송림조산운동의 결과로 해석된다. This study describes a large recumbent fold, which occurs at the north entrance slope of the Batjae tunnel, Pyeongchang-gun, Gangwon-do, and interprets its formation mechanism. The several-hundred- meter scale fold, developed in the Jeongseon Limestone of the Paleozoic Joseon Supergroup, has a nearly horizontal axial plane and its head is facing north. Stretching lineations (L1) observed on the composite foliations of bedding and axial plane cleavage plunge southward at about 10°. Small A-type or eye-shaped sheath folds together with S-shaped asymmetrical folds are often observed in the fold limbs and their axes are nearly parallel to the lineations (L1) within center and rear parts of the fold. It is thus interpreted that the recumbent fold is a large sheath fold produced by the top-to-the-north ductile shearing due to the Songrim orogeny during the late Paleozoic to Triassic.