• The Journal of Engineering Geology
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• v.19 no.3
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• pp.331-344
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• 2009

Large landslides occurred since 1990 on natural terrain, Korea were reviewed with the existing data to characterize them in terms of the condition of rainfall, geology and geometry. Ten landslide areas over the nationwide are selected for this study. Among them, five areas consist of granite basement, four areas of granite and metamorphic rocks and the remaining an area of gabbro. The basement lithology on which landslides most dominantly occurred is granite, on which 58% of landslides among the total 3,435 are taken place, the next dominant one is metamorphic rocks where 24% of landslides are occurred, and the remaining 18% are on the areas of volcanic and sedimentary rocks which are partly distributed in some areas. The landslide occurrences may depend on the rainfall intensities rather than durations. We applied the theories of Caine's threshold and Olivier's final response coefficient to the Korean cases. The rainfall conditions at the landslide areas were all satisfied enough with the landslide triggering conditions suggested by Caine and Olivier. The triggering mechanism and type of landslides may largely depend on the weathering and geomorphic characteristics of basement lithology. The granite areas are characterized by being relatively shallow but consistent weathering profiles and almost no outcrop, and therefore, shallow translational slides are dominant. Whereas metamorphic areas are characterized by consisting of steep slope, weathered outcrops on ridges and partly on flanks and irregular weathering profiles, and relatively large debris flows are dominant.

• Economic and Environmental Geology
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• v.46 no.2
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• pp.141-151
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• 2013

This study examines the mineralogy of sepiolites occurred within the carbonaceous rocks of Songak schist and Pyeongtaek migmatitic gneiss of Precambrian Seosan group, in the western part of Chungnam. Host rocks of the sepiolite were dolomitic rocks and have experienced hydrothermal alteration and metamorphism. Mesozoic granite is assumed as a main source of hydrothermal alteration for the dolomitic rocks. Some of the tremolite asbestos coexist with the sepiolites. Representative sepiolite and tremolite samples were collected from the layers cracks or fractures of the dolomitic rocks and/or examined with microscope with microscope, XRD, SEM and TEM. Sepiolites are mainly recognized along the cracks assumed as pathways of hydrothermal solution. Tremolites are mainly found at layers or cracks of the dolomitic rocks and occur as asbestos as well as non-asbestos forms. It was confirmed that some of the tremolite asbestos were coexisted with the sepiolites. Overall results suggest that the occurrences of sepiolites within the dolomitic rocks mainly result in the hydrothermal alteration and the fluid from the acidic rocks, possibly granites. It also suggests that coexisting tremolite asbestos were formed by similar geological environment.

• Journal of the Korean Geographical Society
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• v.28 no.2
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• pp.99-111
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• 1993

The transformation of rocks into unconsoli-dated debris is the prime geomorphic processes including weathering and soil forming process. In these processes, rocks tend to be unconsol-idated debris with small particles. Particularly, typical granite is more likely affected by weathering, since the rock consists of quartz, feldspar and mica that can be easily coarse-grained and well jointed without bedding. The purposes of this study are to clarify the index and properties of mechanical weathering that contributed to transformation of granite distributed in Korea. A total of seventy-three samples of weathering products of granite in Korea were collected during the three-year period, March 30, 1989 to February 21, 1992. The prticle analysis was performed for clay, silt and sand using Sieve and Hydrometer. The results of the analysis are as the followings: First, soil textures in the study area are included seven categories of textures as C, CL, SCL, Sil, SL, LS, and S. Among these textures, the most frequent soil texture were SL, S and SCL in order. Second, the weathering products of granite are crumbled by weathering and hydrothermal. Clay texture consisted of fine materials seems to be influenced by hydrothermal, while Sand texture composed of coarse materials, seems to be significantly influenced by weathering. Third, the index of mechanical weathering by region indicates that Hawngdeung(1) is the lowest as 2.37 and the index by soil texture shows that Clay texture is the lowest as 2.46. Forth, the regression analysis of MW showes that sand/clay variable is the most significant variable. Finally, pedochemical weathering is prevailed on the clayey gruss and geochemical weathering is on the gruss and shattering is on the weathered rock, strongly, but the fine materials in some sites were formed by argillation of hydrothermal.

• The Journal of the Petrological Society of Korea
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• v.13 no.1
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• pp.1-15
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• 2004

In this study we propose that the ‘enclaves’ which occur in the granites should be translated into ‘Po-yu-am’in Korean. Also we suggest some criteria to discriminate the mafic microgranular enclaves (MME) of igneous origin from the xenoliths, which possibly come from the plutonic, volcanic and sedimentary country rocks. The color of the MME is gray green∼dark gray and the mineral grains are fine and equigranular. The MME are generally of ellipsoidal shape and can be easily found within the granites. They do not show any evidence of contact metamorphism by granite host. On the other hand. the xenoliths are generally of angular shape and are of the same mineral assemblage and texture as the country rocks around the granites. The distribution of the xenoliths is mostly concentrated along the intruding plane of the granites near the country rocks. The xenoliths were partly metamorphosed by the granite intrusion. The xenoliths from the plutonic rocks are easily distinguished from the MME in terms of their angular shape and coarser grain size, but they do not have any metamorphic mineral assemblage and texture. The xenoliths from the tuffaceous rocks show angular shape and porphyritic and pyroclastic textures. Large size xenoliths from the sedimentary rocks specifically preserve bedding structure which are indicative of the sedimentary strata. However, the sedimentary xenoliths of small size are often difficult to distinguish from the MME. Metamorphic minerals and texture are a useful key to discriminate the small-sized sedimentary xenoliths from the MME. In summary the xenoliths in the granites can be megascopic ally distinguished from the MME by comparing their color, shape, grain size and remnant original structure like bedding. Additionally the metamorphic mineral assemblage and texture are microscopic discriminators between the xenoliths and the MME in the granites.

• The Journal of the Petrological Society of Korea
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• v.24 no.3
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• pp.193-207
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• 2015

This study analyzed ancient documents and established petrological database through extensive field investigation of provenance sites to presume stone source areas of the Seoul City Wall. By summarizing the ancient documents, the rampart stone was mostly supplied from a stony mountain adjacent to the City Wall in the early Joseon period, whereas the stone was provided from fixed quarry outside the City Wall in the late Joseon period. As a result of the petrological investigation based on quarries recorded in the ancient documents, pinkish granite and leucogranite were distributed as a whole, and the granitoid rocks are similar in mineralogical compositions and geochemical behavior characteristics. However, the pinkish granite with magnetic-series show that the magnetic susceptibility increased from the north slope of Namsan Mountain to Bulamsan Mountain. The leucogranite with ilmenite-series mainly occurred along the boundary between granite and gneiss from Yongmasan Mountain to Inwangsan Mountain. Consequently, the important petrological indicators for presumption of stone source areas are the rock color and the magnetic susceptibility. In addition to the petrological features, the reliability for provenance interpretation should improve considering stone quantities in the quarries, transportation distance and technical skills.

• Journal of The Geomorphological Association of Korea
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• v.18 no.4
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• pp.1-15
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• 2011

This work is to review the granite landforms studies by Korean geographers. It is verified that geomorphlogical characteristics of granite present landscapes characterized by 1) in case of mountains, are difficultly or irregularly weathered, so as to develop rocky forms such as domes, cliffs, and tors ; 2) in case of stream valley that is inter-massif lowland, low relief hills and flood plains with alluvium. All these facts owe to the difference of weathering mode granite properties. The granite hills and alluvial plains of southwestern coastal parts in Korean peninsula is low undulatory and large owing not only to the existence of highly weathered granitic regolith, but also to frequent flooding. Cultivated brownish field, orchard, meadow and forest are located at granite hills. On the other hand paddy rice field at granite alluvial plains. Korean peninsula have endured erodible geomorphlogical processes since Miocene when warping it up. Therefore many intermontane basins are located on the weathered granite areas which are surrounded by mountains composed of much less Precambrian gneiss complex. In fact, intermontane basin is mainly linear fault-line valley. The landforms of the intermontane basins are characterized by gentle piedmont slopes, alluvial fans, fluvial terraces and alluvial plains.

• Economic and Environmental Geology
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• v.22 no.4
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• pp.381-393
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• 1989

Hydrogeological modelling was performed to evaluate groundwater flow system in Igsan Area. The study area extends over $790km^2$. The geology consists of Jurassic Daebo granite and gneissose granite and Precambrian metamorphic rocks. The capability of pumping yield is the highest in gneissose granite region among them due to comparatively thick weathered zone with thickness ranging from 10m to 25m. The Colorado State University Finite Difference Model was used for the model simulation. The model was divided into 28 rows and 31 columns with variable grid spacing. The model was calibrated under steady-state and unsteady-state conditions. In the steady-state simulation, the model results were compared with measured water table contours in September 1985 with determining hydraulic conductivities and net recharge rates during rainy season. Unsteady state simulation was done to know the aquifer response due to groundwater abstraction. The non- steady state calibration was conducted to determine the distribution and magnitudes of specific yields and discharge/recharge rates during dry season as matching water level altitudes in May 1986. The calibrated model was used to simulate water level vaiation caused by groundwater withdrawal and natural recharge from 1 October, 1985 until 30 September, 1995. The calibrated model can be used to groundwater development schemes on regional groundwater levels, but it cannot be used to simulate local groundwater level change at a specific site.

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.52-74
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• 2000

The basement rock of upper stream of Keum River Valley consists of Precambrian gneiss which is resistant to weathering. That of mid and lower stream valley, however, is mainly composed of Mesozoic granites which are vulnerable to weathering. The upstream part of Geum River Basin is typified by the deeply-incised and steep meandering streams, whereas mid and lower part is characterized by wide floodplain and gently dipping river bottom toward the Yellow Sea. In particular flooding deposits, in which are imprinted a number of repetitions of erosion and sedimentation during the Holocene, are widely distributed in the lower stream of Geum River Basin. For understanding of erosions in the mid and lower stream of Geum River Basin, the rate of erosion of each small basins were estimated by using the data of field survey, erosional experiments and GIS ananlysis. It was revealed that erosion rate appeared highest in granite areas, and overall areas, in this field survey were represented by relatively high erosion rates. By implemeatation of remote sensing and imagery data, the temporal changes of river bed sediments for about last 11 years were successfully monitored. Observed as an important phenomenon is that the river bed has been risen since 1994 when an embankment (Dyke) was constructed in the estuarine river mouth. From the results derived from the detailed river bed topographical map made in this investigation, the sedimentation of the lower river basin is considered to be deposited with about 5 cm/year for the last 11 years. Based on this river bed profile analysis by HEC-6 module, it is predicted that Geum River bed of Ganggyeong area is continuously rising up in general until 2004. Although extraction of a large amount of aggregates from Gongju to Ganggyung areas, the Ganggyung lower stream shows the distinct sedimentation. Therefore, it is interpreted that the active erosions of tributary basins Geum drainage basins can affect general river bed rising changes of Geum River.

• The Journal of the Petrological Society of Korea
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• v.28 no.2
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• pp.53-69
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• 2019

In the Jirisan area of the Yeongnam Massif, Korea, several ductile shear zones are developed within Precambrian gneiss complex (Jirisan metamorphic rock complex). The ductile shear zones have a general NS- and NNE-striking foliation with westward dipping directions. The foliation developed in the shear zones cut the foliation in gneiss complex. The stretching lineations are well developed in the foliated plane of the shear zone, showing ENE-trend with gentle plunging angle to the ESE direction. Within shear zone, several millimetric to centimetric size of porphyroclasts are deformed strongly as a sigmoid form by ductile shearing. The sigmoid patterns of porphyroclasts in the shear zones indicate the dextral shearing. The spatial distribution of ductile shear zone is characterized by the dominant NS- and NNE-striking dextral sense in the central and eastern regions respectively. In the western part, it develops in NE-striking dextral sense which is the general direction of the Honam shear zone. The U-Pb concordant ages obtained from the two samples, the strongly sheared leucocratic gneiss, are $1,868{\pm}3.8Ma$ and $1,867{\pm}4.0Ma$, respectively, which are consistent with the U-Pb ages reported around the study area. We supposed that the ductile shearing in the study area is occurred about 230~220 Ma during late stage of the continental collision around Korea and is preceded by granitic intrusion related to subduction during 260~230 Ma, which are supported by compiling the age data from sheared gneiss, deformed mafic dyke intruded gneiss complex, and non-deformed igneous rocks.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.167-185
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• 2014

SHRIMP zircon U-Pb ages and major element and Sr-Nd isotopic compositions were determined for drill cores (374-3390 m in depth) recovered from three boreholes in the Pohonag basin, southeastern Korea. Shallow-seated volcanic rocks and underlain plutonic rocks were geochemically classified as rhyolite and gabbro-granite, respectively. They showed high-K calc-alkaline trends on the $K_2O-SiO_2$ and AFM diagrams. Zircons from volcanic rocks of borehole PB-1 yielded concordia ages of $66.84{\pm}0.66Ma$ (n=12, MSWD=0.02) and $66.52{\pm}0.55Ma$ (n=12, MSWD=0.46). Zircons from volcanic rocks of borehole PB-2 gave a concordia age of $71.34{\pm}0.85Ma$ (n=11, MSWD=0.79) and a weighted mean $^{206}Pb/^{238}U$ ages of $49.40{\pm}0.37Ma$ (n=11, MSWD=1.9). On the other hand, zircons from plutonic rocks of borehole PB-3 yielded weighted mean $^{206}Pb/^{238}U$ ages of $262.4{\pm}3.6Ma$ (n=21, MSWD=4.5), $252.4{\pm}3.6Ma$ (n=8, MSWD=1.9) and $261.8{\pm}1.5Ma$ (n=31, MSWD=1.3). Detrital zircons from the sedimentary strata overlain the volcanic rocks showed a wide age span from Neoproterozoic to Cenozoic, with the youngest population corresponding to $21.89{\pm}1.1Ma$ (n=15, MSWD=0.04) and $21.68{\pm}1.2Ma$ (n=10, MSWD=19). These dating results indicate that the basement of the Pohang basin is composed of Late Permian plutonic rocks and overlain Late Cretaceous to Eocene volcanic sequences. Miocene sediments were deposited in the uppermost part of the basin, possibly associated with the opening of the East Sea. The Sr-Nd isotopic compositions of the Permian plutonic rocks were comparable with those reported from Permian-Triassic granitoids in the Yeongdeok area, northern Gyeongsang basin. They may have been recycled into parts of the Cretaceous-Paleogene magmatic rocks within the Gyeongsang basin.