• Economic and Environmental Geology
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• v.9 no.2
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• pp.85-106
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• 1976

The Bulgugsa acidic igneous rocks of the late Cretaceous age are largely distributed in Busan area, which is located in the southeastern corner of the Korean Peninsula. These igneous rocks comprise in ascending order, felsite, dacitic-rhyolitic welded tuffs, granite porphyry and granitic rocks. The former three members represent the early phase of volcanic activities, so that they are named as Jangsan volcanic rocks. The granitic rocks consist of granodiorite, hornblende biotite granite, Kumjongsan granite, fine grained granite, and Daebyen granite, represent the late phase of igneous activities. The Kumjongsan grainte, the largest pluton of the granitic mass, emplaced between two great vertical faults trending NNE. New chemical analyses of 33 rock samples of these acidic rocks are given. Their chemical compositions are generally similar to those of the late Mesozoic acidic igneous rocks of the northern Ashio mountains, and C-Zone granite group of the Ogcheon geosyncline, with their characteristic variation trends of several oxides. Their chemical compositions also show that $Al_2O_3$ is high value, and differentiation index is high, too. Systematically developing joints in Kumjungsan granite are divisible into two types at least. One is the NS-N $20^{\circ}E$ trendirig, $85^{\circ}{\sim}90^{\circ}$ dipping type of joint system which coincides with the trends of distribution of the granite mass and the dikes intruding this granite. Joints of this type may be cooling joints generated as tension cracks. The other is the $N60^{\circ}{\sim}70^{\circ}W$ or $N40^{\circ}{\sim}60^{\circ}E$ trending type of joint systems. It is considered that. joints belonging to this type may be shear joint occurring under the state of south-north tectonic couple acting at the east and west side of the granite mass. Igneous activities of the the Bulgugsa acidic igneous rocks in Busan area was taken place as. follows, formation of the magma reservoir, eruption and intrusion of felsite, consolidation of vents. and increasing vapor pressure in magma reservoir, eruption of pyroclastic flows, caldera collapse, intrusion of granite porphyry, and intrusion of granitic rocks at the latest stage.

• Economic and Environmental Geology
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• v.23 no.2
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• pp.135-141
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• 1990

A number of alunite and pyrophyllite deposits occur around the Haenam area where Cretaceous volcanic and volcanogenic sediments are widely distributed. The K-Ar ages of alunite, sericite and whole rocks collected from alunite and pyrophyllite deposits and unaltered rocks representing various stratigraphic horizon of the area were determined and their formation stage was discussed. The ages of volcanic rocks range between $68.6{\pm}1.9$ and $94.1{\pm}2.0$ Ma corresponding to Cenomanian-Maastrichtian of upper Cretaceous. Andesitic rock gives $94.1{\pm}2.0$. Rhyolite and acidic tuffs give $79.47{\pm}1.7$ and $82.8{\pm}1.2$ Ma corresponding to Campanian. The later stage andesite gives $68.6{\pm}1.9$ Ma of Maastrichtian. The results suggest that volcanism of the area can be devided into three different stages. The ages of alunite and sericite range $71.8{\pm}2.8$ to $76.6{\pm}2.9$ Ma of late Campanian to early Maastrichtian which is rather earlier than the age of granite(67 Ma). It indicates that the alteration ages of these clay mineral deposits appeared to be related with its volcanism rather than the hydrothermal stage of granite of this area.

• Economic and Environmental Geology
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• v.12 no.4
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• pp.207-221
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• 1979

The studied area occupies the southern part of Haenam peninsula located in the southwestern corner of Korea. The stratigraphic sequences of the area are grouped into following three units in ascending order. (1) Late Cretaceous sedimentary rocks of Uhangri Formation which consist of the alternative beds of black shales and tuffaceous sediments, Hwangsan acidic fine grained tuffs and Jindo rhyolite flows. (2) Late Cretaceous biotite granite and acidic porphyries which intruded the Late Cretaceous sedimentary rocks. (3) Tertiary(?) pitchstone. The study purposes to delineate any of geochemical aspects on the deposition of the sequences, the average amounts of organic materials and the effect to the maturation of hydrocarbonization which has been occured by the intrusives. Sixty nine black shale samples were collected from Uhangri Formation in the northern and southern coasts of the peninsula. Organic carbons, total extracted organic matters and hydrocarbons were mainly determined by the Soxhlet extraction method, together with C-H-N elemental analyses. Based on the field and laboratory studies, the following interpretations have been obtained. (1) The paleohydrostatic condition of the sedimentation which took place was relatively calm and stable to delineate a lacustrine environment. (2) The amounts of organic material were more or less constant throughout the period of the deposition of the sediments. (3) The degree of hydrocarbonization of the Uhangri Formation in the northern coast was taken place higher than that in the southern coast due to the differences of thermal effect by the biotite granite which is assumed to be as a heat source in the area. Among the northern coast, some black shales in Uhangri and Mogsam areas which had been under the most moderate temperature environment snow symptomatic oily material, whereas, those in Sinseongri area do not, which were presumably to be intensive thermal alteration by the later acidic porphyries.

• Tunnel and Underground Space
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• v.10 no.4
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• pp.497-505
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• 2000

The surveyed area is mainly distributed by the sedimentary rocks, tuffs, and esites in Cretaceous age and acidic and basic dikes are intruded in these rocks. The principle discontinuities are represented by beddings, joints and faults. The trends of the beddings of sedimentary rocks develop as E-W direction in the start area. However, they are gradually bending and finally their trends are N-S direction in terminal area. In the sedimentary rocks the 3∼4 joint sets are distributed and in dikes joints are more scattered. The majority of joints are highly dipped. Sampo fault which has NE-SW trend makes a valley and NW trending normal faults are well developed at 50k+600 to 51k+000 area. During the construction of tunnel the orientation of discontinuities will not significantly influence on the stability of excavation. Since the rock mass is extensively jointed, the overbreak in tunnel wall may be placed.

• The Journal of the Petrological Society of Korea
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• v.28 no.4
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• pp.237-249
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• 2019

The volcanic rocks around the Jayang caldera are classified in an order such as Jukjang Volcanics, Doil Rhyolite, Unjusan Tuff and Rhyolite intrusions. By the SHRIMP U-Pb zircon datings from zircons, eruption ages of the Unjusan Tuff are constrained as 66.65±0.96 Ma in the intracaldera, and 66.08±0.62 Ma in the extracaldera outflow, and intrusion age of the ring dike is investigated as 60.74±0.66 Ma. The age data indicate that the caldera was collapsed between 66.08 Ma and 60.74 Ma, just before the dike intruded after the explosive eruption of the Unjusan Tuff. The Jayang caldera shows the composite igneous process of a perfect volcanic cycle passing from ash-flow tuffs through caldera collapse into ring dikes in the Jayang area.

• The Journal of the Petrological Society of Korea
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• v.19 no.4
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• pp.293-301
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• 2010

The Ipbong Andesite is a stratigraphic unit which is lain in the lowermost part of the Yucheon Group in the southeastern Yeongyang sbbasin. The Ipbong Andesite is lain on the Sinyangdong Formation and under the dacitic tuff, and consists in its lower andesitic tuffs and upper lavas. The andesitic lavas show some alignments of elongate vesicles filling with calcite amygdules and plagioclase microphenocrysts, and show rare imbrication of the microphenocrysts in vertical sections parallel to them. The flow directions which is measured from the flow indicators are laid along NNW-SSE trend in the eastern part and NNESSW in the southwestern part of the study area. Movement pattern from the flow lineations suggests that the Ipbong Andesite had a fanlike pattern by flowing southwards from the mid-northern part. Accordingly a small diorite stock in the mid-northern part area may probably be a source area of the Ipbong Andesite.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.51-65
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• 2010

The Dongmakgol Tuff is a stratigraphic unit which is composed of voluminous ignimbrites in the Cheolwon basin. The ignimbrites belong to pumice-rich vitric tuffs that show eutaxitic to parataxitic fabrics from fiamme or pumice clasts. They are almost densely welded and strongly flattened, but often parallel aligned and stretched. Also they exhibit flow indicators such as flow lineations, imbrications, tensional cracks and boudins from their alignment and/or elongation, and lithic and pumice clasts show lateral grading in their average maximum diameter. Flow direction map from the lineations, asymmetric structures and lateral grading diagram indicate that the Dongmakgol Tuff has a source from its southwestern part near a boundary between southern Dongmakri and northern Gomunri, and is considered that the ignimbrites took emplacement processes of laminar flows during the final stage of flowage and the flow lineations are from the result of shear stress during that times.

• 한국지구물리탐사학회:학술대회논문집
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• 2008.10a
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• pp.125-130
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• 2008

Electrical resistivity and seismic refraction surveys were conducted to investigate geologic structures and geotechnical characteristics of the subsurface in Dok-do island, along with rock physical properties. The resistivity results in Seo-do island show that the fault adjacent to the fisherman's shelter is a normal fault and extended towards the NW direction. Bedded Rapilli Tuff in the downstream was more severely influenced in depth by weathering and erosion than Trachy Andesite II in the upstream area. The physical properties of the rocks illustrate that Trachyte and Trachy Andesite are hardest, Massive Tuff Breccia is next, and Tuffs are the most soft rocks in Dok-do island.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.325-336
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• 2014

Even though Mesozoic Mudeungsan tuff, located within Neungju Basin, has been named several rock names, it should be named as Mudeungsan tuff due to several evidences, such as fiamme, welded texture and rock fragments in the Mudeungsan tuff. Volcanic eruption boundary between the Cheonwangbong and Anyangsan areas is not clear, but petrochemical and mineral chemical evidences with different ages indicate clear petrological boundary between Cheonwangbong and Anyangsan. The Mudeungsan tuffs from Cheonwangbong and Anyangsan is welded crystal tuff with dacitic composition and were generated from cogenetic calc-alkaline magma in the volcanic arc environment. Geochemical events indicate that magma beneath Cheonwangbong was seems to have been evolved from the magma beneath Anyangsan due to fractional crystallization dominated by plagioclase.

• The Journal of the Petrological Society of Korea
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• v.26 no.2
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• pp.153-163
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• 2017

The Naeyeonsan Tuff is a stratigraphic unit which is distinguished as a cooling unit in the volcanic rocks of the northern Pohang. The Naeyeonsan Tuff, which is composed of crystals of plagioclase, quartz and hornblende, glasses of pumice and shard, and lithics of dacite, rhyolite, sandstone and shale, belongs to a lapilli tuff field according to the granulometric classification and to a vitric tuff field according to the constituent classification. The tuffs mostly develop welding foliations by dense welding and flatterning pumices and shards, and show several flow indicators by pyroclastic flowing. We can know a movement pattern from flow lineations and imbrications by pumices and lithics, and lateral gradings in isopleth map by average largest lithics and pumices in the Naeyeonsan Tuff, which indicate that the Naeyeonsan Tuff had a possible source area from the southeastern part.