• Journal of the Mineralogical Society of Korea
• /
• v.22 no.1
• /
• pp.13-22
• /
• 2009

The study area is a tunnelling section passing through the Yangsan Fault zone. Kyungbu express highway and national road 35 are located above the tunnel. Previous study showed that fault gouge and fault breccia were widely distributed in the tunnelling section with a maximum width of 100 m. From the present study, it is found that sedimentary rocks consisting mainly of shale are distributed at the eastern block of the Yangsan Fault and these rocks are not subject to mechanical fracturing and hydrothermal alteration. On the other hand, dacitic tuff distributed at the western block of the Yangsan Fault is largely affected by mechanical fracturing and hydrothermal alteration. The large fault zone of $50{\sim}130m$ width was formed by complex processes of mechanical fracturing and hydrothermal alterations such as chloritization, sericitization, and kaolinization. Based on the characteristics of mechanical fracturing and hydrothermal alterations, the Yangsan fault zone in the study area is geotechnically classified as four zones: unaltered zone, altered zone, altered fractured zone, and fault gouge zone. These zones show different degrees and aspects in mechanical fracturing and hydrothermal alterations, resulting in different engineering properties.

• The Journal of Engineering Geology
• /
• v.8 no.2
• /
• pp.175-188
• /
• 1998

This paper describes the internal structures and K-Ar ages of fault gouges collected from the Dongnae fault zone. This fault zone is internally zoned and occurs in the multiple fault cores. A fault core consists of thin gouge and narrow cataclastic zones that are bounded by a much thicker damage zone. Intensity of deformation and alteration increases from damage zone through cataclastic zone to gouge zone. It is thought that cataclasis of brittle deformation was the dominant strain-accomodation mechanism in the early stage of deformation to form the gouge zone and that crushed materials in the regions of maximum localization of fault slip subsequently moved by cataclastic flow. Deformation mechanism drastically changed from brittle processes to fluid-assisted flow along the gouge zone as the high porosity and permeability of pulverzied materials during faulting facilitated the influx of the hydrothermal fluids. Subsequently, the fluids reacted with gouge materials to form clay minerals. Fracturing and alteration could have repeatedly taken place in the gouge zone by elevated fluid pressures generated from the reduction of pore volume due to the formation of clay minerals and precipitation of other materials. XRD analysis revealed that the most common clay minerals of the gouge zones are illite and smectite with minor zeolite and kaolinite. Most of illites are composed of 1Md polytype, indicating the products of hydrothermal alteration. The major activities of the Dongnae fault can be divided into two periods based upon K-Ar age data of the fault gouges : 51.4∼57.5Ma and 40.3∼43.6Ma. Judging from the enviromental condition of clay mineral formation, it is inferred that the hydrothermal alteration of older period occured at higher temperature than that of younger period.

• Journal of the Mineralogical Society of Korea
• /
• v.18 no.3 s.45
• /
• pp.205-214
• /
• 2005

Some Quaternary faults developed in the eastern block of the Ulsan fault are Gaegok 1, Gaegok 2, Singye, Madong, Wonwonsa and Jinhyeon faults, which are characterized by thin gouge and narrow cataclasitic tones. This study was performed to emphasize the role of mineral alteration and microtexture in response to hydrothermal alteration of fault gouges during fault activity, using XRD, EPMA, BSE (backscattered electron image), and K-Ar age dating methods. Alteration minerals in fault gouges were formed in the age range of $44.3\~28.9Ma$ by hydrothermal alteration attributed to fault activity. XRD results show that fault gouges consist predominantly of clay minerals, quartz and feldspars. Clay minerals formed in the gouge zones are mainly composed of smectite with trace chlorite, illite and kaolinite. The evidence to support the hydrothermal alteration of preexisting minerals due to fault activity are easily recognized at the host rocks in contact with gouges zones. Injected gouge and calcite veins indicate that they were originated from multiple deformation by repeated fault activity. Gouge with green or greenish grey color, for example Jinhyeon fault, contains higher $Al_2O_3$ and lower MgO and CaO compared to those with reddish color. Various colors of fault gouge are intimately related to the chemical compositions of main constituent mineral as well as mineral assemblage.

• Economic and Environmental Geology
• /
• v.37 no.5
• /
• pp.437-457
• /
• 2004

The geology of the Kualakulun in the Middle Kalimantan, Indonesia comprises Permian to Carboniferous Pinoh Metamorphic Rocks and Cretaceous Sepauk Plutonics of the Sunda Shield, late Eocene Tanjung Formation, Oligocene Malasan Volcanics, Oligocene to early Miocene Sintang Intrusives and Quaternary alluvium. Tanjung Formation was deposited in low-and high-sinuosity channel networks developed on the proximal to distal delta plain and delta front forming southward paleoflow system, which, in turn, gradually change into shallow marine environment. Four main deformational phases are recognized: D1, folding of metamorphic rocks accompanied by development of S1 schistosity under regional metamorphic condition; D2, ductile shearing in Cretaceous granitoids; D3, folding of metamorphic rocks accompanied by S2 crenulation cleavage; D4, faulting under N-S compressional regime during Tertiary times, producing NE-trending sinistral and NW-trending dextral strike-slip faults and N-S to NNE-trending normal faults.

• The Journal of Engineering Geology
• /
• v.18 no.2
• /
• pp.145-152
• /
• 2008

A fault gouge zone which is about 25cm thick crops out along a small valley in Yangbuk-myeon, Gyeongju city. It is divided into greenish brown gouge and bluish gray gouge by color. Under the microscope, the gouges have a lot of porphyroclasts composed of old gouge fragments, quartz, feldspar and iron minerals. Clay minerals are abundant in matrix, defining strikingly P foliation by preferred orientation. Microstructural differences between bluish pay gouge and greenish brown gouge are as follows: greenish brown gouge compared to bluish gray gouge is (1) rich in clay minerals, (2) small in size and number of porphyroclasts, and (3) plentiful in iron minerals which are mostly hematites, while chiefly pyrites in bluish gray gouge. Hematites are considered to be altered from pyrites in the early-formed greenish brown gouge under the influence of hydrothermal fluids accompanied during the formation of bluish gray gouge that also precipitated pyrites. It is believed that the fault core including bluish gray gouge zone and greenish brown gouge zone was formed by progressive cataclastic flow. In the first stage the fault core initiates from damage zone of early faulting. In the second stage damage zone actively transforms into breccia zone by repeated fracturing. The third stage includes greenish brown (old) gouge formation in the center of the fault core mainly by particle grinding. In the third stage further deformation leads to the formation of new (bluish gray) gouge zone while old gouge zone undergoes strain hardening. Consequently, the whole gouge zone in the core widens.

• Economic and Environmental Geology
• /
• v.37 no.5
• /
• pp.543-554
• /
• 2004

Analysis of multi-channel seismic reflection and well data serves to detail the structural evolution of the northern Okinawa Trough, southern offshore Korea. The overall structural style of the area is characterized by a series of half grabens and tilted fault blocks bounded by basement-involved listric normal faults. Most half grabens and tilted fault blocks developed in the direction of NNE-SSW, parallel to the axis of the Okinawa Trough. Orientation and distribution of the listric faults also suggest the development of transfer faults in NW-SE direction. The rifting phase of the northern Okinawa Trough have been established on the basis of structural and stratigraphic analyses of depositional sequences and their seismic expressions. Major phase of rifting probably started in the Late Miocene and the most active rifting occurred during the Early Pliocene. The rifting produced a series of half grabens and tilted fault blocks bounded by listric normal faults. It appears that the rifting activity has become weaker since the Late Pliocene, but the Pleistocene sediments faulted by listric faults bounding tilted fault blocks suggest that the rifting activity is probably still in progress.

• Economic and Environmental Geology
• /
• v.34 no.6
• /
• pp.583-593
• /
• 2001

Clay minerals are common component of fault gouge and have been used to determine the fault activity age using K-Ar dating technique. We carried out XRD and K-Ar analyses of the mica clay minerals from the fault gouge along the Ulsan Fault Zone, southeastern Korea to estimate the timing of the major fault activity. Mica clay minerals for four grain size fractions of 5-2 Um, 2-1 $\mu$m, 1-0.35$\mu$m, and 0.35-0.05 $\mu$m were separated from the gouge samples in the three locations by the hydraulic elutriation and contrifugal separator. Fault gouges are composed of smectite, mica clay minerals, kaolinite, chlorite, quartz, and feldspar. The illite crystallinity of mica clay minerals is the highest in the finest grained fraction with lM polytype, indicating that the aulhigenic mica clay minerals have been concentrated in the fraction. K-Ar ages give some variation from 46 to 35 Ma (330-2), 45 to 39 Ma (16Ww), and 32 to 15 Ma (102Ws) and are the youngest in the finest grained fraction. These results suggest that the hydrothermal alteration associated with the major fault activities along the Ulsan fault Zone took place twice at 39-35 Ma and 15 Ma.

• The Journal of the Petrological Society of Korea
• /
• v.17 no.2
• /
• pp.83-94
• /
• 2008

The Pungcheon-myeon, Andong, consists mainly of Precambrian metamorphic rocks, Jurassic igneous rocks, Cretaceous sedimentary rocks (Hasandong, Jinju and Iljik Formations) and Cretaceous igneous rocks (gabbroic rocks, dykes), in which several major faults are developed; Andong fault of ENE trend, which is the boundary fault of the Cretaceous Gyeongsang Basin and the Precambrian-Jurassic basement (Yeongnam Massif), Namhu fault parallel to it, Maebong fault of NNW direction, bow-shaped Gwangdeok fault of ENE direction which is convex toward SSE direction, and Hahoe fault of NNE direction. This paper is researched the geological structures around these major faults by means of the detailed geometric analysis on beddings, joints, faults and drag folds. As a result, a reverse slip faulting of top-to-the SSE movement accompanied with a regional drag folding is recognized from the arrangement of bedding poles measured around the Gwangdeok and Hahoe faults at its northeastern extension, and a zone of Gwangdeok drag fold of 150-300 m width, which is wider at the central and eastern parts of Gwangdeok fault and narrower at its western part and Hahoe fault, is also defined. It indicates that the Hahoe and Gwangdeok faults are a single fault and their movements are coeval unlike the results of earlier reasearchers. And, In this area are recognized two types of faults [(E)NE${\sim}$EW(fault I), WNW${\sim}$NNW (fault II), trending faults] and four types of joints [EW (I), (N)NW (II), NNE (III), NE (IV) trending joints]. These fractures were formed at least through four different events, named as Dn to Dn+3 phases. (1) Dn phase; the formation of joint (I) (Gwangdeok joint) and the intrusion of acidic dykes of EW trend under the compression of EW direction. (2) Dn+1 phase; the formations of joint (II) (Maebong joint), lens-shaped boudinage of acidic dykes, oblique-slip reverse fault (Fault I-Gwangdeok fault) under the compression of (N)NW direction, and the formation of regional zone of Gwangdeok drag fold accompanying the Gwangdeok faulting. (3) Dn+2 phase; those of joint (III), Fault II (Maebong fault) by dextral strike-slip movement of Maebong joint under the compression of NNE direction, and the extension cutting of Dn+1 structures due to the Maebong faulting. (4) Dn+3 phase; the jointing (IV) and the reactivation of Fault II as oblique-slip type with predominant dextral motion which took place under the compression of NE direction. It also suggests that the Maebong fault is not a tear fault deveolped during thrust tectonics of the Andong and Gwangdeok faults but is a post-fault during different tectonic event.

• Economic and Environmental Geology
• /
• v.43 no.6
• /
• pp.637-648
• /
• 2010

The Songbong Formation (so-called Bangrim Group), correated to the lower part of Choseon Supergroup, unconformably overlies the Precambrian Gyeonggi massif at northeastem tip of the Ogcheon belt The contact relationship between the Choseon Supergroup and the Yeongnam massif is also known as an unconformity at northeastem part of the Ogcheon belt. lt implies that the Gyeonggi and Yeongnam massifs were probably connected each other before the Early Paleozoic. Three deformational phases are recognized in the study area, The first phase is the north-northeastward ductile thrusting, which places Precambrian granite of the Gyeonggi massif over the Paleozoic rocks of the Ogcheon belt. The second phase is characterized by the southeastward thrusting and deformation partitioning along the Nuruhaji compartment fault. The third phase is the reactivation of the Nuruhaji Fault into dextral strike-slip fault with over a few kilometers displacement.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2007.09a
• /
• pp.170-181
• /
• 2007

암반내 존재하는 단층은 암반거동에 중대한 영향을 미치게 되며, 특히 단층내에 충전물이 협재되어 있거나, 파쇄대가 넓게 발달한 경우에는 암반구조물의 안정성에 보다 심각한 문제를 가져오는 경우가 많다. 이는 단층의 불연속적인 거동과 충전물의 거동이 복합적으로 작용하게 되며, 장기적인 시간을 두고 나타나기 때문이다. 본 검토에서는 단층의 공학적 특성을 분석하고, 단층대 구간에서는 보강설계 사례 및 단층대 구간에서의 붕락사고로 인하여 문제가 발생한 현장사례분석을 통하여 단층이 암반사면이나 터널과 같은 암반 구조물에 미치는 영향을 검토하였다. 이를 통하여 단층과 점토 그리고 지하수 등의 복합거동에 의한 장기적이고 잠재적인 거동을 수반할 수 있는 단층의 공학적 문제점을 고찰하였다.