• Economic and Environmental Geology
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• v.26 no.3
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• pp.349-361
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• 1993

The granitic rocks in the study area are divided into the schist and gneiss complex, Yongdok pluton, Yonghae pluton and Onjong pluton by their texture, fabric and relationship to the adjacent rocks in the field, Schist and gneiss complex occurs as xenolith or roof pendant in the Yongdok, Yonghae and Onjong plutons. The Yongdok pluton occurs in association with pegmatite and aplite in many places of its pluton. In the field it is obviously clarified that the Yongdok pluton is unconformably overlay by the Cretaceous sedimentary rocks. The Yonghae and Onjong plutons are gradationally changed each other, and these plutons truncate both the Yongdok pluton and the Cretaceous sedimentary rocks. Petrographically, the Yongdok pluton consists of granodiorite and granite with minor quartz monzonite. The Yonghae pluton is composed of diorite, quartz diorite, tonalite, and granodiorite. The Onjong pluton also ranges granodiorite to granite. Both the Yongdok and Yonghae-Onjong plutons are different in the constituent minerals, such as alkali feld~par, myrmekite, mica, sphene and mafic minerals. This suggests that each pluton might have been different crystallization sequence and characteristically different gological history during the crystallization period. Iron/magnesium ratio in biotite and hornblende from both the Yongdok and Yonghae-Onjong plutons gradually decrease as the differentiation index increasing in the whole rock. The decrease of this ratio strongly depend on the increase of opaque mineral contents. From the results of chemistry in the whole rocks and some mafic minerals, it is suggest that the granite plutons of the two different geological ages would have been suffered the environment of high oxygen fugacity in the process of magmatic emplacement and during the crystallization period.

• Economic and Environmental Geology
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• v.17 no.3
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• pp.197-214
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• 1984

This studg is to clarify intrusion sequence and petrogenetic processes of the so-called schistose granites in the northeastheastern part of the Kwangju, Chonnam Province. The study area is composed of the Pre-cambrian and Unknown age metasediments, the Unknown age schistose granites and basic plutons, the Cretaceous sedimentary and volcanic rocks, and the Cretaceous Ogang-ri granite and dykes. The schistose granites of the study area is divided into three rock units based on relative intrusion age, mineralogical constituent and texture;SoonChang schistose granite, two mica granite and Sam-o-ri schistose granite. The schistose granites intruded into metasediments, are intruded by Ogang-ri granite and dikes, and overlain by the Cretaceous sedimentary and volcanic rocks. The schistose granites vary widely in composition (granite-granodiorite-tonalite) and content of porphyroblastic feldspar Caugen and rectangular shaped). The foliation of schistose granites shows similar trend to the Shinian direction. In especially, strong foliation reflects dynamic metamorphism by mortar texture and much content of well oriented biotite. These schistose granites are characterized by its gray feldspar porphyroblasts. This feldspar is considered to be formed by potassic metasomatism and assimilation of pelitic metasediments of unexposed highly metamorphosed rocks deeply buried under the level of the schistose granites emplacement. Variation of silica versus oxides of major elements shows that the schistose granites are similar to the trend of Daly's average basalt-andesite-dacite-rhyolite which shows the trend of the fractional crystallization of magma. AMF diagram shows that the schistose granite is corresponded to contaminated differentiation products such as Lower California batholith and Cascade lava. These evidence suggest that the schistose granite is a series of differentiation products formed by fractional crystallization that associated with srtongly contamination and potassic metasomatism.

• Economic and Environmental Geology
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• v.51 no.5
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• pp.409-428
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• 2018

Yeongdong area is located on the border zone between Precambrian Yeongnam massif and central southeastern Ogcheon metamorphic belt, in which Cretaceous Yeongdong sedimentary basin exists. Main geology in this area consists of Precambrian Sobaeksan gneiss complex, Mesozoic igneous and sedimentary rocks and Quaternary alluvial deposits. Above this, age-unknown Ogcheon Supergroup, Paleozoic sedimentary rocks and Tertiary granites also occur in small scale in the northwestern part. This study focuses on the link between the various geology and Rn concentrations in groundwater. For this, twenty wells in alluvial/weathered zone and sixty bedrock aquifer wells were used. Groundwater sampling campaigns were twice run at wet season in August 2015 and dry season in March 2016. Some wells placed in alluvial/weathered part of Precambrian metamorphic rocks and Jurassic granite terrains, as well as Cretaceous porphyry, showed elevated Rn concentrations in groundwater. However, detailed geology showed the distinct feature that these high-Rn groundwaters in metamorphic and granitic terrains are definitely related to proximity of aquifer rocks to Cretaceous porphyry in the study area. The deeper wells placed in bedrock aquifer showed that almost the whole groundwaters in biotite gneiss and schist of Sobaeksan gneiss complex and in Cretaceous sedimentary rocks of Yeongdong basin have low level of Rn concentrations. On the other hand, groundwaters occurring in rock types of granitic gneiss or granite gneiss among Sobaeksan gneiss complex have relatively high Rn concentrations. And also, groundwaters occurring in the border zone between Triassic Cheongsan granites and two-mica granites, and in Jurassic granites neighboring Cretaceous porphyry have relatively high Rn concentrations. Therefore, to get probable and meaningful results for the link between Rn concentrations in groundwater and surrounding geology, quite detailed geology including small-scaled dykes or vein zones should be considered. Furthermore, it is necessary to take account of the spatial proximity of well location to igneous rocks associated with some mineralization/hydrothermal alteration zone rather than in-situ geology itself.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.108-120
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• 1996

This study reports petrography and geochemical characteristics of the Cretaceous volcanic rocks that are distributed in the vicinity of the Cheonsungsan area, Yangsan-Gun, Gyeongsangnam-Do. The Cretaceous volcanic rocks composed of andesitic rocks, Wonhyosan tuff, Cheonsungsan tuff in ascending order. Sedimentary rock is the basement in the study area cofered with volcanic rocks. These volcanic rocks are Wonhyosan tuff and Cheonsungsan tuff that represented the early phase of the Bulgugsa igneous activity. Wonhyosan tuff are classified into dacite tuff and dacite welded tuff based on the rock texture and their mineral composition. They are covered with Cheonsungsan tuff. Dacite tuff composed of lithic lapilli ash-flow tuff and vitric ash-flow tuff. Most dacite welded tuff are lapilli ash-flow tuff. Cheonsungsan tuff overlying the Wonhyosan tuff consists of rhyolite tuff and rhyolite welded tuff. Rhyolite tuff are lithic crystal ash-flow tuff and crystal vitric ash-flow tuff with somewhat accidental fragments of andesitic and sedimentary rocks. Rhyolite welded tuff is distinguishe from rhyolite tuff by is typical eelded fabrics and its rock color. According to petrochemical data, the volcanic rocks in study area belong to high-K orogenic suties. On the discriminant diagrams such as La/Yb versus Th/Yb, these rocks falls into the discriminant fields for the normal continental margin arc.

• The Korean Journal of Petroleum Geology
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• v.7 no.1_2 s.8
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• pp.28-34
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• 1999

The Cretaceous Poongam sedimentary Basin in Kangwon-do, Korea consists alluvial deposits of conglomerates, sandstones, mudstones or siltstones, and volcaniclastics. The Poongam Basin was formed as a fault margin sag or a transpressional basin developed along a strike-slip fault zone, and received huge amount of clastic sediments from the adjacent fault-scaip. It formed an aggrading alluvial fan system and a volcaniclast-supplied marginal lake environment, while tectonic activity and volcanism attenuated toward the end of basin formation. Following the Folk's classification, the sandstones of the Poongam Basin are identified as lithic wackes or feldspathic wackes. The areal and sequential variation of the mineral composition in the sandstones is not distinct. The results of K-Ar age dating from the intruding andesites, volcaniclastics and volcanic fragments in sedimentary rocks show a range of 70 Ma to 84 Ma. It suggests that volcarism occurred sequentially within a relatively short period as the pre-, syn-, and post-depositional events. It was the short period in the late Cretaceous that the basin had evolved i.e., the basin formation, the sediment input and fill, and the , intrusion and extrusion of volcanic rocks occurred. The Poongam sedimentary sequence is a typical tectonic-controlled coarse sedimentary facies which is texturally immature.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.463-478
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• 2021

The subjects of the study are the sedimentary rock slope of the Mesozoic Gyeongsang Supergroup, which has a high risk of failure. The orientation of the slope-face represents a variety of changing characteristics. The rocks of the slope shall be sandstone, siltstone and dacite, and discontinuities shall develop beddings, shear joints, extension joints, and dacite dyke boundary planes. The type and scale of failure varies depending on the type of rock and the strike/dip of the discontinuities, but the toppling failure prevails. Based on the face-mapping data, SMR, physical and mechanical testing of rocks, analysis and review of the stereonet projections and the critical equilibrium analysis, all four representative sections required a countermeasure method because the acceptable safety factor during dry and rainy seasons were far below Fs = 1.5 and Fs = 1.2. After applying the countermeasure method, both the dry and wet conditions of the slope exceeded the allowable safety factor. In particular, the face-mapping data of the slope-face, the geological cross-sections of several representative sections perpendicular to the slope-face, and the critical equilibrium analysis and the presentation of countermeasure methods that have been reviewed based on them are expected to be reasonable tools for the slope stability. In addition, it will be possible to use it as basic data for performance evaluation for slope maintenance.

• The Korean Journal of Petroleum Geology
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• v.12 no.1
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• pp.1-8
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• 2006

Jiaolai Basin is the Cretaceous continental sedimentary basin developed in Shandong Province of China. It is interpreted as a pull-apart basin which is filled with fluvio-lacustrine sediments and volcanic rocks. The sedimentary strata are divided into three formations: Laiyang Formation, Qingshan Formation and Wangshi Formation in ascending order. Laiyang Formation of the early Cretaceous consists of conglomerate, sandstone and shale, which are grey, black or red in color, respectively. Qingshan Formation of early Cretaceous includes various kinds of volcanic rocks. Late Cretaceous Wangshi Formation consists of red conglomerate, sandstone and shale. Various types of oil shows are observed on many outcrops in the basin such as asphalt filing fissures, oil smelling, rocks wetted with oil. However, commercial oil discovery was not made. Laiyang Formation is the richest in terms of organic matter contents. Some grey or black shales of Laiyang Formation contain more than 1% of organic matter. Kerogens of some layers mainly consist of amorphous organic matter or pollen. Thermal maturity of the organic matter reached main oil generation zone and hydrocarbon genetic potential is fairly good. According to such geochemical data, some layers of Laiyang Formation can act as hydrocarbon source rocks.

• Economic and Environmental Geology
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• v.24 no.2
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• pp.167-176
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• 1991

The Yeongweol - Yemi area, in the area between the Kagdong thrust fault and Samcheog Coalfield, comprises Paleozoic and Mesozoic sedimentary and igneous rocks. Geologic structures related with thrust movements are dominant in the area. These are thrust faults, imbricate structures and hanging-wall anticline. Thrust sheets were transported from NW to SE and these differ from the Cretaceous Bulkuksa Orogeny of which thrust sheets were transported from N to S. NE - trending folds are dominant, but NW - trending folds and refolded folds are also found. NW - trending folds are only found in the Cambro-Ordovician sedimentary rocks. It might be an indication of the presence of late Paleozoic tectonism in the Korean Peninsula.

• Journal of the Korean Geophysical Society
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• v.3 no.1
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• pp.67-74
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• 2000

Subsurface structure of the Bomun basin was studied along three survey tracks of Line-1, Line-2, and Line-3 using geomagnetic, radioactive, and seismic refraction methods. Abrupt changes found at 2.55 km west and 1.6 km east in the profile of magnetic anomaly along Line-1 are correlated with geologic boundary of the basin. Profiles of radioactive intensity also represent abrupt changes at 2.55 km west of Line-1 and at 1.9 km of Line-2. Cretaceous basement rock has relatively high magnetic anomaly of $200\;{\sim}\;500\;nT$ while sedimentary rocks of the Bomun basin have relatively low magnetic anomaly of $-100\;{\sim}\;+100\;nT$. Radioactive intensity also represents charateristic differences between Cretaceous basement and sedimentary rocks of the Bomun basin. Rocks of Cretaceous basement have lower radioactive intensity than the rocks of the Bomun basin. Magnetic anomaly of of the Bomun basin represents lowest anomaly in western part and increases gradullay toward east. This phenomenon is interpreted as a half graben structure dipping westward. Black shale known by previous studies near the western boundary has high magnetic anomalies and low radioactive intensity. This phenomenon provide a possibility of volcanic rock rather than black shale near the western boundary of the basin along Line-1. Sedimentary layers having velocities of 455 m/s, 1904 m/s, and 2662 m/s are developed to have westward dipping of $2.3^{\circ}$ in the central area of the Bomun basin. The result is consistent with a half-graben model dipping westward which were derieved from magnetic anomaly data.

• Geotechnical Engineering
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• v.12 no.6
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• pp.37-50
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• 1996

In this study, we collected data through the investigation of rock slopes of highway. By analyzing the collected data, the main factors of rock slope failure were studied. We studied on the failure types and scales according to rock types and geological structures in many rock slopes of highway. As a result, it was shown that many failed slopes were distributed in the areas of Cretaceous sedimentary rocks of south-eastern part in the Korean Peninsula and the Gneiss Complex in both Kyonggi-Do and Kangwon-Do. According to rock types, the following slope failure types were shown : that igneous rocks had the types of rock fall, plane failure, soil erosion and circular failure but had low failure frequency, and sedimentary rocks had predominantly the type of plane failure. Metamorphic rock showed the types of circular failure, wedge failure and plane failure due to poor rock qualities . According to geological structures, the following slope failure types were shown slope failure in igneous rocks was caused by joints, and in sedimentary rocks by bedding plane, and in metamorphic rocks by faults and poor rock qualities.