• Journal of Integrative Natural Science
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• v.4 no.1
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• pp.58-71
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• 2011

The precambrian gneisses are widely distributed in the Jangsu area. This study focuses on the metamorphic mineral assemblages and metamorphic P-T conditions of the gneiss. We have analyzed garnet, biotite and plagioclase among the gneiss through the EPMA analysis, and calculated the metamorphic temperature and pressure accordingly. The metamorphic temperature was estimated by the average of values from the garnet and biotite formulas, and the metamorphic pressure by value of the Hoisch(1990) geopressured on garnet-biotite-plagioclase. The mineral sample we examined shows garnet-biotite-plagioclase-quartz composite and garnet-plagioclase-orthoclase-quartz composite. Garnet shows almandine-pyrope solid solution in general, while porphyroblastic gneiss shows almandine-grossluar solid solution. The fact that the abundances, observed by garnet profile, are almost identical in both the central region and the outer egion indicates that the crystal was developed uniformly. There is almost negligible variance in biotite on metamorphic grade, and andesine is observed in plagioclase. The metamorphic temperature and pressure from EPMA analysis and its indications are as follows: the middle-temperature, high-pressure metamorphism ($500-650^{\circ}C$, 6.9-10 kbar) ensued in the beginning, and then was followed by the high-temperature, middle-pressure($600-740^{\circ}C$, 2.7-5.9 kbar) to ($500-540^{\circ}C$, 3.1 kbar) retrograde metamorphism.

• 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.3 no.1
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• pp.94-108
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• 1994

The Precambrian granite, and the Yuli group and the Hyeondong gneisss complex are studied to unravel the metamorphic history of the northeastern Sobaeksan massif. The Hongjesa granite, emplaced at 650-$700^{\circ}C$ and $3{\pm}1$ kbar, has been altered at 310-$568^{\circ}C$. Not only the chloritization of biotite but also the sericitization and saussuritization of plagioclase occur at the subsolidus stage. Biotites of the Hongjesa granite vary in their Al, Fe and Mg contents through dioctahedral and tschermakitic substitutions during the subsolidus stage. Secondary muscovites from biotite and feldspars are enriched in their Si and Mg+Fe contents through tschermakitic and trictahedral substitutuions. The metamorphic pressures and temperatures estimated from the Hyeondong gneiss complex are 3.6-6.6 kbar and 593-$718^{\circ}C$, respectively. Local migmatization producing the cordierite-bearing assemblage occurs in the Hyeondong gneiss complex. The Gibbs' method applied to the assemblage of garnet+biotite+plagioclase+quartz in banded gneiss suggests a complex P-T history of the Hyeondong gneiss complex.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.138-156
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• 2002

Precambrian metamorphic rocks of southwest Sobaeksan massif consist of mainly granitic gneiss, porphyroblastic gneiss and quartzofeldspathic gneiss. The orthopyroxene-bearing rocks(charnockites) are found in the west of Hadong-Sancheong anorthosite complex. The charnockites are 3km wide, 12km long and divided into massive and foliated types based on their texture. The compositions of charnockites are comparable to granodiorite to adamellite and subalkaline. Variations in major and trace elemental abundances show typical magmatic differentiation trends. The geochemical data plotted on tectonic discrimination diagrams reveal that these charnockites were formed in the active tectonic environment. The massive and folidated charnockites are mainly composed of plagioclase, orthopyroxene, microcline, quartz and disseminated garnet. Camels generally show characteristic zonal textures with decreasing $X_{alm}$(0.74~0.83), $X_{Py}$ (0.07~0.12) and $X_{Mg}$ (0.12~0.08) and increasing $X_{grs}$(0.03~0.15) from core to rim. Metamorphic temperature and pressure of the charnockites estimated from orthopyroxene-garnet-plagioclase-quartz assemblages show wide range of variation of $600~900^{\circ}C$ and 2.5~7.5 kbar respectively. The results of P-T estimates indicate an anticlockwise P-T evolution path.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.623-633
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• 1995

The Beonam deposits which is located in south-western part of Sobaeksan massif are emplaced along $N20{\sim}30^{\circ}E$ trending fissures in Precambrian Sobaeksan gneiss complex. Surrounding granites are inferred to be differentiated and formed from calc-alkaline magma which was generated from remelting or partial melting of the crustral material having igneous composition. The Sr isotope data of ore minerals showing significantly low initial Sr value relative to those of surrounding granite batholiths suggest that the ore-bearing fluid formed the Beonam Au-Ag mine are isotopically distinct from those of the wall rocks, and it indicates that there is no evidence of genetic relationship between ore-bearing fluids and surrounding granites, although further study should be needed. The results of paragenetic studies suggest three stages of hydrothermal mineralization; stage I: base-metal sulfides stage, stage II: late base-metal sulfides, electrum and silver-bearing sulfosalts stage, stage III: minor silverbearing minerals, barren quartz and carbonates stage. The temperature, salinity and pressure of the Beonam deposits estimated from mineral assemblage, chemical composition, fluid inclusion and sulfur isotope geothermometry are as follows; stage I: $200{\sim}315^{\circ}C$, 3.5~6.5 NaCl eq. wt%, 0.28~0.61 Kbar, stage II: $150{\sim}235^{\circ}C$, 4.5~7.4 NaCl eq. wt%, 0.11~0.15 Kbar. The estimated oxygen and sulfur fugacity during first stage mineralization, based on phase relation of associated minerals, range from $10^{35.1}{\sim}10^{-39.7}$ atm. and $10^{-11.0}{\sim}10^{-13.4}$ atm., respectively. All these evidences suggest that the Beonam deposits are polymetallic meso-epithermal ore deposits.

• The Journal of the Petrological Society of Korea
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• v.16 no.3
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• pp.162-179
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• 2007

Macheon Layered Intrusion (MLI) which intruded into Precambrian gneiss complex of the northern Jirisan area, southeastern part of Youngnam (or Sobaeksan) Massif, is a layered mafic-ultramafic complex of Triassic age (ca. 223 Ma). The MLI is divided into Layered Series and Laminated Series. Layered Series is subdivided into Central Zone (Lower Zone) consisting of olivine gabbros and Peripheral Zone (Middle or Upper Zone) consisting of hornblende gabbros based on the type of cumulus texture and the main mafic phase. The Central Zone of Layered Series comprises thinly laminated olivine gabbros and uniform or thickly laminated coarse olivine gabbros which consist of mela-gabbro, troctolite, leuco-troctolite, and anorthositic rocks. Laminated Series is also subdivided into quartz-bearing biotite-pyroxene gabbros and homblende diorite and both have variable amount of interstitial quartz and microcline. Laminated series display moderately to slightly developed igneous lamination which is defined by the planar alignment of lath-shape plagioclases. Chilled margin of quartz-bearing biotite-pyroxene gabbro with surrounding Precambrian gneisses insists shallower intrusion of more felsic cognate magma evolved in the deep a little later. Rocks of Layered Series have orthocumulus to adcumulus olivine, adcumulus to intercumulus plagioclase, and intercumulus to heteradcumulus pyroxene and hornblende. Magmatic modally grading, folding, and cross-lamination are not rarely occurred in thinly layered rocks. These textural characteristics define main mechanisms of the formation of layered and laminated structure in mafic-ultramafic rocks of Macheon Layered Intrusion are gravity settling and in-situ crystallization associated with slumping and density current.

• Journal of the Korean association of regional geographers
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• v.4 no.2
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• pp.15-30
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• 1998

Physical geography is the discipline which deals with the relationship between man and natural environment. Therefore, it should be studied as the organized unity. In this paper I recognize the drainage basin as a framework outlining physical geography, describe the difference of inhabitant's life style due to the difference of natural environment in the drainage basin, and consider the meaning of drainage basin as a unit of life(and unit of regional geography). Munkyung is divided into three regions(intermontane basin region, middle mountainous region, marginal hilly region of the great basin) owing to the topographic characteristics. Subdivision in these regions is related closely to drainage network distribution, specially in intermontane basin region. And small regions have developed with the confluence point of $3{\sim}4$ order streams as the central figure. Intermontane basin region is the valley floor of Sinbuk-Soya-Kauun-Nongam stream located in the limestone region which is exposed according to Munkyung fault at its northern part. Small streams are affected strongly by the influence of the NNE-SSE or WNW-ESE tectolineament. Thus Kaeripryungro(鷄立嶺路), Saejaegil(새재길), Ewharyungro(伊火嶺路) and so on are constructed through the tectolineament. In the valley floors of small streams which flow into the intermontane basin, there are large floodplains. Floodplain in Sinbuk, Joryung, and Yangsan stream is used to paddy field or orchard, and in Nongam stream is used to paddy field or vegetable field. Hills are distributed largely in the periphery of intermontane basin. Limestone hills in Kauun and Masung basin are not continuous to the present low and flat floodplain, and most of those are used to forest land and field. On the other side. granite hills in Koyori are continuous to be used to the present floodplain, and they are used to residential area and field. In the middle mountainous region are there hilly mountains constructed in the geology of Palaeozoic Pyeongan System in northern area and Chosun System's Limestone Series in southern area, and banded gneiss and schist among Sobaeksan Gneiss Complex. In Palaeozoic Pyeongan System region are there relatively rugged mountains and ingrown meanders developed along tectolineaments. Chosun System's Limestone Series region builds up a geomorphic surface, develops various karst landforms. Mountainous area is used to field. On the other hand, especially in case of Hogye, valley bottom is wide, long, and discontinuous to slope, is used to paddy field dominantly. And schist region in Youngnam Block of Pre-Cambrian is rugged mountainous. Marginal hilly region of the great basin is hilly zone located in the margin of erosional basin(Bonghwa-Youngju-Yechon-Hamchang-Sangju). This region is lower geomorphic surface which is consisted of hills of $50{\sim}100$m height. Hills are used to field or orchard, and dissected gentle depression is used to paddy field.