• The Journal of the Petrological Society of Korea
• /
• v.11 no.3_4
• /
• pp.157-168
• /
• 2002

In Gimcheon area of the central Yeongnam massif granite gneiss occurrs with intercalated biotite gneiss at xenolith or restite. In order to understand the evolution of the central Yeongnam massif, it is essential to have absolute age information, but not many age data are available yet. Furthermore the previous age determinations from the study area are not compatible with the outcrop relationship. In this study we determined chemical ages from the zircon grains. We obtained ages of $1970\pm$ 78(l$\sigma$)Ma from the granite gneiss, $1814\pm$77(l$\sigma$)Ma from the outer rim of a rounded zircon and 1973$\pm$97(l$\sigma$)Ma from a longish zircon, both from the biotite gneiss. These ages seem to indicate the timing of granitic magma intrusion and subsequent metamorphism. Ages of $2954\pm$ 158($l\sigma$)Ma, 2440$\pm$58(l$\sigma$)Ma, and 2219$\pm$36($l\sigma$)Ma obtained from zoned core of the rounded zircon grain from the biotite gneiss suggest various geological events before such metamorphism of the biotite gneiss. Ages in the range of 1450~1670 Ma observed in zircons of both gniesses suggest later metamorphism that the granite gneiss and the biotite gneiss experienced together. The chemical age determination by electron probe micro-analyzer of this study utilized 1$\mu\textrm{m}$ beam diameter and it seems to be a very useful age determination from the zircons with complex growth history because of superior spatial resolution.

• Journal of the Korean earth science society
• /
• v.34 no.6
• /
• pp.550-560
• /
• 2013

In this study, the variations of geoid measured by GRACE satellite are investigated in the 20 volcanic areas erupted since 2005, and it is recognized that a detailed geological study is necessary in using geoid data for a research of the magmatic activities under the volcano. Therefore, the relationship between the regional geoid variation obtained by GRACE satellite and the change of magma activity, is studied in Japan's Shinmoedake volcano in the Kirishima volcanic complex whose eruption in 2011 was studied in detail geologically. Throughout this study the increase of geoid from 2002 in the Shinmoedake volcanic area is confirmed to be caused by the increase of gravity under the volcano, which is well matched with geological interpretation of the continuous intrusion of basaltic magma into magma chamber during several years before the 2011 eruption. The result indicates that information of the geoid variation measured by GRACE satellite is useful for monitoring the possibility of volcanic eruption although there is a need to more study to be able to confirm the possibility.

• Economic and Environmental Geology
• /
• v.50 no.4
• /
• pp.313-324
• /
• 2017

Tsogttsetsii area, an intrusive complex associated with Cu mineralization, is located in the South Gobi, Mongolia. We performed the cross geochemical and extended exploration survey in Tsogttsetsii area. Cu mineralization in Tsogttsetsii area is porphyry Cu type related with alkali granite intruded in Late Carboniferous to Early Permian. In the concentrated occurring to malachite appears extensively prophylitic alteration zone having a chlorite and epidote. As results of the survey, Cu contents of potable XRF and of chemical composition for altered rocks ranges 1.08 to 18.3% in the 30 points and 1.08 to 32.9% in the 13 points, respectively. Ore minerals identified in XRD analysis and polarizing microscope that samples of copper oxides were composed mainly of malachite, azurite, permingeatite and cuprite and the other minerals are pyrite, chalcopyrite, pyrargyrite, dickite, calcite, chlorite and epidote. Mineralization can be considered occurring to selectively some granite of the surrounding aplite and faults in the only upper part coming up the hydrothermal solution of the remaining residual magma after the aplite intrusion.

• Economic and Environmental Geology
• /
• v.26 no.2
• /
• pp.145-154
• /
• 1993

Gold-silver deposits in the Kwangyang-Seungju area are emplaced along $N4^{\circ}{\sim}10^{\circ}W$ to $N40^{\circ}{\sim}60^{\circ}W$ trending fissures and fault in Pre-cambrian Jirisan gneiss complex or Cretaceous diorite. Mineral constituents of the ore from above deposits are composed mainly of pyrite, arsenopyrite, pyrrhotite, magnetite, sphalerite, chalcopyrite, galena and minor amount of electrum, tetrahedrite, miargyrite, stannite, covellite and goethite. The gangue minerals are predominantly quartz and calcite. Gold minerals consist mostly of electrum with a 56.19~79.24 wt% Au and closely associated with pyrite, chalcopyrite, miargyrite and galena. K-Ar analysis of the altered sericite from the Beonjeong mine yielded a date of $94.2{\pm}2.4\;Ma$ (Lee, 1992). This indicates a likely genetic tie between ore mineralization and intrusion of the middle Cretaceous diorite ($108{\pm}4\;Ma$). The ${\delta}^{34}S$ values ranged from +1.0 to 8.3‰ with an average of +4.4‰ suggest that the sulfur in the sulfides may be magmatic origin. The temperatures of mineralization by the sulfur isotopic composition with coexisting pyrite-galena and pyrite-chalcopyrite from Beonjeong and Jeungheung mines were $343^{\circ}C$ and $375^{\circ}C$ respectively. This temperature is in reasonable agreement with the homogenization temperature of primary fluid inclusion quartz ($330^{\circ}C$ to $390^{\circ}C$; Park.1989). Four samples of quartz from ore veins have ${\delta}^{18}O$ values of +6.9~+10.6‰ (mean=8.9‰) and three whole rock samples have ${\delta}^{18}O$ values of +7.4~+10.2‰ with an average of 7.4‰. These values are similar with those of the Cretaceous Bulgugsa granite in South Korea (mean=8.3‰; Kim et al. 1991). The calculated ${\delta}^{18}O_{water}$ in the ore-forming fluid using fractionation factors of Bulgugsa et al. (1973) range from -1.3 to -2.3‰. These values suggest that the fluid was dominated by progressive meteoric water inundation through mineralization.

• The Journal of the Petrological Society of Korea
• /
• v.23 no.3
• /
• pp.209-220
• /
• 2014

SHRIMP zircon U-Pb age dating is carried out for the Yeongju and Andong granite batholiths intruding the Precambrian metamorphic complex and Paleozoic sedimentary formations within the NE Yeongnam Massif, Korea. Dating of zircons from a hornblende-biotite tonalite and an equigranular biotite granodiorite in the Yeongju granite has yielded ages of ca. 187 Ma and ca. 186 Ma, respectively. Also, dating of zircons from a biotite granodiorite and a very coarse-grained biotite granite in the Andong granite has yielded ages of ca. 182Ma and ca. 186Ma, respectively. These data indicate that the main intrusions of the Yeongju and Andong granite batholiths occur almost at the same age. The oldest age of ca. 194 Ma has been determined on zircons from a hornblende gabbro in the Andong granite, and the youngest age of 175 Ma is obtained from the Chunyang granite pluton, mainly consisting of fine-grained two-mica granite, of the Yeongju batholith. These results indicate that Jurassic Daebo magmatism in the Yeongju-Andong area, NE Yeongnam massif, started early at the Early Jurassic with an intrusion of mafic magma, and followed by an emplacement voluminous granite magma during the middle of the Early Jurassic, and was finalized with the emplacement of relatively small amount of much evolved granite magma at the end of Early Jurassic.

• The Journal of the Petrological Society of Korea
• /
• v.21 no.3
• /
• pp.287-307
• /
• 2012

The study area, which is located in the southeastern part of the Jirisan province of the Yeongnam massif, Korea, consists mainly of the Precambrian Hadong northern anorthosite complex (HNAC) and the Jirisan metamorphic rock complex (JMRC) and the Mesozoic granitoids which intrude them. Its tectonic frame is built into NS trend, unlike the general NE-trending tectonic frame of Korean Peninsula. This paper researched the structural characteristics at each deformation phase to clarify the geological structures associated with the NS-trending tectonic frame which was built in the HNAC and JMRC. The result indicates that the geological structures of this area were formed at least through three phases of deformation. (1) The $D_1$ deformation formed the $F_1$ sheath or "A"-type folds in the HNAC and JMRC, and the $S_{0-1}$ composite foliation and the $S_1$ foliation and the $D_1$ ductile shear zone which are (sub)parallel to the axial plane of $F_1$ fold, and the $L_1$ stretching lineation which is parallel to the $F_1$ fold axis owing to the large-scale top-to-the SE shearing on the $S_0$ foliation. (2) The $D_2$ deformation (re)folded the $D_1$ structural elements under the EW-trending tectonic compression environment, and formed the NS-trending $F_2$ open, tight, isoclinal, intrafolial folds with the $S_{0-1-2}$ composite foliation and the $S_2$ foliation and the $D_2$ ductile shear zone with S-C-C' structure and the $L_2$ stretching lineation which is (sub)parallel to the axial plane of $F_2$ fold. The extensive $D_2$ ductile shear zone (Hadong shear zone) of NS trend was persistently developed along the eastern boundary of HNAC and JMRC which would be to the limb of $F_2$ fold on a geological map scale. The Hadong shear zone is no less than 1.4 km width, and was formed in the mylonitization process which produced the mylonitic structure and the stretching lineation with the reduction of grain size during the $F_2$ passive folding. (3) The $D_3$ deformation formed the EW-trending $F_3$ kink or open fold under the NS-trending tectonic compression environment and partially rearranged the NS-trending pre-$D_3$ structural elements into (E)NE or (W)NW direction. The regional trend of $D_1$ tectonic frame before the $D_2$ deformation would be NE-SW unlike the present, and the NS-trending tectonic frame in the HNAC and JMRC like the present was formed by the rearrangement of the $D_1$ tectonic frame owing to the $F_2$ active and passive folding. Based on the main intrusion age of (N)NE-trending basic dyke in the study area, these three deformation events are interpreted to have occurred before the Late Paleozoic.

• Korean Journal of Mineralogy and Petrology
• /
• v.34 no.2
• /
• pp.107-120
• /
• 2021

The Komdok Pb-Zn deposit, which is the largest Pb-Zn deposit in Korea, is located at the Hyesan-Riwon metallogenic zone in Jiao Liao Ji belt included Paleoproterozoic Macheolryeong group. The geology of this deposit consists of Paleoproterozoic metasedimentary rocks, Jurassic Mantapsan intrusive rocks and Cenozoic basalt. The Komdok deposit which is a SEDEX type deposit occurs as layer ore and vein ore in the Paleoproterozoic metasedimentary rocks. Based on mineral petrography and paragenesis, dolomites from this deposit are classified four types (1. dolomite (D₀) as hostrock, 2. early dolomite (D₁) associated with tremolite, actinolite, diopside, sphalerite and galena from amphibolite facies, 3. late dolomite (D₂) associated with talc, calcite, quartz, sphalerite and galena from amphibolite facies, 4. dolomite (D₃) associated with white mica, chlorite, sphalerite and galena from quartz vein). The structural formulars of dolomites are determined to be Ca_1.00-1.20Mg_0.80-0.99Fe_0.00-0.01Zn_0.00-0.02(CO₃)₂(D₀), Ca_1.00-1.02M_0.97-0.99Fe_0.00-0.01Zn_0.00-0.02(CO₃)₂(D₁), Ca_0.99-1.03Mg_0.93-0.98Fe_0.01-0.05Mn_0.00-0.01As_0.00-0.01(CO₃)₂(D₂) and Ca_0.95-1.04Mg_0.59-0.68Fe_0.30-0.36Mn_0.00-0.01 (CO₃)₂(D₃), respectively. It means that dolomites from Komdok deposit have higher content of trace elements (FeO, MnO, HfO₂, ZnO, PbO, Sb₂O₅ and As₂O₅) compared to the theoretical composition of dolomite. These trace elements (FeO, MnO, ZnO, Sb₂O₅ and As₂O₅) show increase and decrease trend according to paragenetic sequence, but HfO₂ and PbO elements no show increase and decrease trend according to paragenetic sequence. Dolomites correspond to Ferroan dolomite (D₀, D₁ and D₂), and Ferroan dolomite and ankerite (D₃), respectively. Therefore, 1) dolomite (D₀) as hostrock was formed by subsequent diagenesis after sedimentation of Paleoproterozoic (2012~1700 Ma) silica-bearing dolomite in the marine evaporative environment. 2) Early dolomite (D₁) was formed by hydrothermal metasomatism origined metamorphism (amphibolite facies) associated with intrusion (1890~1680 Ma) of Paleoproterozoic Riwon complex. 3) Late dolomte (D₂) was formed from residual fluid by a decrease of temperature and pressure. and dolomite (D₃) in quartz vein was formed by intrusion (213~181 Ma) of Jurassic Mantapsan intrusive rocks.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
• /
• v.18 no.1
• /
• pp.1-12
• /
• 2013

Acoustic backscatter profiles were measured by Eco-sounder along an east-west section in the mid-eastern Yellow Sea and at an anchoring station in the low salinity region off the Keum River estuary in September 2012, with observing physical water property structure by CTD. Tidal front was established around the sand ridge developed in 50 m depth region. Internal waves measured by Eco-sounder during low tide period in the eastern side of the sand ridge were nonlinear depression waves with wave height of 15 m and mean wavelength of 500 m. These waves were interpreted into tidal internal waves that were produced by tidal current flowing over the sand ridge to the southeast. When weakly non-linear soliton model was applied, propagation speed and period of these internal depression wave were 50 m/s and 16~18 min. Red tides by Dinoflagelates Cochlodinium were observed in the sea surface where strong acoustic scattering layer was raised up to 7 m. Hourly CTD profiles taken at the anchoring station off the Keum River estuary showed the halocline depth change by tidal current and land-sea breeze. When tidal current flowed strongly to the northeast during flood period and land-breeze of 7 m/s blew to the west, the halocline was temporally raised up as much as 2 m and acoustic profile images showed a complex structure in the surface layer within 5-m depth: in tens of seconds the declined acoustic structure of strong and weak scattering signals alternatively appeared with entrainment and intrusion shape. These acoustic profile structures in the surface mixed layer were observed for the first time in the coastal sea of the mid-eastern Yellow Sea. The acoustic profile images and turbidity data suggest that relatively transparent low-layer water be intruded or entrained into the turbid upper-layer water by vertical shear between flood current and land breeze-induced surface current.

• The Journal of the Petrological Society of Korea
• /
• v.14 no.2 s.40
• /
• pp.108-115
• /
• 2005

Gyeonggi metamorphic complex in the Gwangju area include banded biotite gneiss and quartzofeldspathic gneiss. Detailed structural analysis suggests that structural elements in the study area were formed by at least five phase of deformations. Penetrative compositional foliations(S1) formed in the banded gneiss during the first metamorphism and deformation (D1). After intrusion of plutonic rocks, the second deformation (D2) produced S2 foliations in the banded gneiss and quartzofeldspathic gneiss during the second metamorphism. D3 structures are represented by isoclinal folds (F3) whose axial surfaces are parallel to S3 foliations. The N-S oriented shortening (D4) was accommodated by closed upright F4 fold with about 100m of axial surface separation. F4 fold is refolded by regional F5 folding resulting in different orientation and fold style of F4 fold according to the position of F5 fold. The F4 fold with tight interlimb angle is subparallel to the axial surface (north-south) of F5 fold in the core of the F5 fold. In contrast the F4 fold trends northeast in the western limb and northwest in the eastern limb of F5 fold. The interlimb angle is larger in the limbs than that in the core of F5 fold. The trace of foliations is constrained by mainly F4 and F5 folds. Joint fanning around fold is developed in the limbs of F5 fold and bc joints are dominant in the hinge area of F5 fold. A strike-slip fault had developed in tile central part of the study area after F5 folding. The orientation of joint and foliation is rotated anticlockwise about $15^{\circ}$ by the landslide occurred during the Quaternary.

• The Journal of the Petrological Society of Korea
• /
• v.2 no.2
• /
• pp.74-94
• /
• 1993

Metabasites and metapelites in the Mungyong area were intruded by Cretaceous granites with radius of 4-8 km. As the distance from granite body increases, the mineral assemblage of metabasite changes from amphibole + plagioclase through amphibole + plagioclase + epidote to amphibole + plagioclase + epidote + chlorite. The compositional variations of amphibole and plagioclase according to the change of metamorphic grade and bulk rock compositions are very complex. Towards the Mungyong Cretaceous granite body, the mineral assemblage of metapelite changes from chlorite+ muscovite(ch1orite zone) through biotite + chlorite + muscovite(biotite zone) to andalusite+biotite + muscovite${\pm}$chlorite or cordierite+ biotite+ muscovite${\pm}$chlorite(cordierite zone). The estimated metamorphic conditions of cordierite zone are 480~$580^{\circ}C$ 1.5-3.3 kb. The theoretical study on the thermal metamorphism caused by the Cretaceous granite with radius longer than 4 km in the Mungyong area suggests the followings: The degree of metamorphism is mainly determined not by the size of granite body but by the temperature of granite intrusion; The country rocks within 2 km from Cretaceous granite have undergone metamorphism with temperature higher than $500^{\circ}C$, which is consistent with the petrological study in the Mungyong area. Mungyong Cretaceous granite caused a low P/T thermal metamorphism to the country rocks; the amphibolite facies metamorphism to the country rocks within 1-2 km from the granite body and the epidote-amphibolite and greenschist facies metamorphism to the country rocks within 2-5 km.