• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.311-324
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• 2014

The Hongjeom formation of the Pyeongan Supergroup in the Munkyeong coalfield mainly consists of metapsammite and metapelites. Metampelites occur as slate preserving chloritoid+chlorite+muscovite and andalusite+biotite+chlorite+muscovite mineral assemblages. Chloritoid and andalusite occur as porphyroblast, and the matrix composed of fine-grained micas. Metamorphic P-T conditions for these mineral assemblages are $510-520^{\circ}C$ and 3.0-3.5kbar based on P-T pseudosection in $MnO-K_2O-FeO-MgO-Al_2O_3-SiO_2-H_2O(MnKFMASH)$ system and isopleth intersections of Fe/(Fe+Mg) ratios in chloritoid and chlorite. The medium temperature and low pressure metamorphism resulted from a higher geothermal gradient ($40-45^{\circ}C/km$) condition than that of burial metamorphism. The youngest (SHRIMP U-Pb age; ca. 327-310 Ma) detrital zircon grains from the Hongjeom formation display oscillatory zoning and relatively high Th/U ratio (0.60-1.12). Based on the previous sedimentary, paleontological, and geochronological studies in the Taebaeksan basin together with results of this study, we suggest that (1) initial deposition of the Hongjeom formation was contemporaneous with a magmatic activity in the provenance, (2) the Pyeongan Supergroup was deposited in an arc-related basin at an active continental margin during the Carboniferous to Permain, and (3) magmatic activities occurred repetitively in relatively short interval in the active continental margin had continuously supplied sediments to the basin.

• The Journal of Engineering Research
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• v.2 no.1
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• pp.175-182
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• 1997

Field relationships indicate that the Jumchon granite intruded the Pyungan Supergroup but the Daedong Supergroup overlies Jumchon granite nonconformably. This relationship suggests that the Jumchon granite intruded after the sedimentation of the Pyungan Supergroup (at Late Permian or younger), but before the sedimentation of the Daedong Supergroup (at Early Triassic). The Jumchon granite intruded thrusts within Pyungan Supergroup indicating that the thrust event occurred after the sedimentation of the Pyungan Supergroup but before the intrusion of Jumchon granite. This justifies a narrow age bracket of the first thrusting event of the Mungyeong area, from Late Permian to Early Triassic. In other localities, rocks of the Daedong Supergroup override the rocks of Pyungan Supergroup by thrusts, indicating that another thrust event occurred after sedimentation of the Daedong Supergroup (after Early Devonian).

• The Journal of Engineering Geology
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• v.13 no.2
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• pp.207-225
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• 2003

According to the data analysis of the regional fracture systems in southern Korea, the fracture orientations show three dominant sets : NNE, NW and WNW. A NNE set is the most abundant and includes most of the largest fractures. The highest fracture density is shown in the Taebaegsan mineralized area corresponding to Ogchon nonmetamorphic belt and the lowest one in the southwestern area of southern Korea. In addition, the density is higher in nonmetamorphic sedimentary rocks such as Choseon Supergroup. Pyeongan Supergroup, Daedong Supergroup and Kyeongsang Supergroup than in Precambrian basements and Jurassic granites. The regional fractures in southern Korea can be classified into four orders designated $F_1,{\;}F_2,{\;}F_3{\;}and{\;}F_4${\;}and{\;}F_4$ on the basis of their trace length. It is quite significant that fractures of each order are self-similar with respect to orientation and the combined fracture length distribution indicates a power-law distribution with an exponent of -2.04. As fractures were analyzed based on the tectonic provinces, Gyeonggj Massif and Kyeongsang Basin have all orders of fractures from $F_1$ to $F_4$. Most of the large scale faults may be ascribed to the products of slip accumulation through multiple deformation. Others besides $F_1$ fractures are thought to be evenly distributed through the whole area of southern Korea.