• Economic and Environmental Geology
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• v.31 no.2
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• pp.149-158
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• 1998

Volcanic rocks including rhyolitic tuff, rhyolite and welded tuff in the Bupyeong silver mine area form a topographic circular structure known as a resurgent caldera. Granitic rocks are emplaced inside and outside area of the circular structure. K-Ar dating and Nd-Sr isotope studies were carried out to invesitigate the origin and petrogenetic evolution of the rhyolitic and granitic magma in the Bupeong silver mine area. Whole rock K-Ar age ranges from 208 to 131 Ma for rhyolitic rocks. Radiometric ages for the granitic rocks are 167.6 Ma for pink feldspar biotite granite from inside granitic pluton of the circular volcanic body, 178.8 Ma for the Kimpo hornblende biotite granite and 111.8 Ma for the Songdo foliated granite from outside granitic plutons of the volcanic body. The radiometric age data indicates that the volcanic activities which are partly overlapped by granite plutonic activities in the Bupyeong mine area had recorded early Jurassic and early Cretaceous in age. Initial Sr and Nd isotopic ratios of the rhyolitic rocks ($^{87}Sr/^{86}Sr$=0.710~0.719 and $^{143}Nd/^{144}Nd$=0.5115~0.5118) are similar to those of granitic rocks ($^{87}Sr/^{86}Sr$=0.709~0.716 and $^{143}Nd/^{144}Nd$=0.5115~0.5116) from inside granite stock. This means that similar source materials of felsic magma responsibles for the Bupyeong volcanic rocks and inside plutonic rocks. Based on the Nd and Sr isotopic compositions, rhyolitic and granitic magmas in the Bupyeong area originated from the partial melting of the old continental crust which has Nd model age ranging from 1500 to 2900 Ma. This is analogous to those of the other Jurassic granitoids in South Korea.

• Journal of Chest Surgery
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• v.37 no.6
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• pp.492-498
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• 2004

Background: In this study, we investigated the risk factors for the development or progression of aortic regurgitation(AR) in patients with type I ventricular septal defect (VSD) to determine the optimal surgical timing and strategy. Material and Method: Three-hundred and ten patients with type I VSD with or without AR were included. The mean of age was 73.7$\pm$114.7 (1-737) months. One hundred and eighty six patients (60%) had no AR, 83 (27%) had mild AR, 25 (8%) had moderate AR and 16 (5%) had severe AR. Aortic valve was repaired in 5 patients and replaced in 11 patients with closure of VSD in the first operation. Four patients required redo aortic valve repair and 11 patients required redo aortic valve replacement. Age at operation, association with aortic valve prolapse, Qp/Qs, systolic pulmonary arterial pressure, VSD size and systolic pulmonary artery to aortic pressure ratio(s[PAP/AP］) were included as risk factors analysis for the development of AR. The long-term result of aortic valve repair and aortic valve replacement were compared. Result: Older age at operation, association with aortic valve prolapse, high Qp/Qs, and s[PAP/AP] were identified as risk factors for the development of AR (p<0.05, Table 2). The older the patient at the time of operation, the higher the severity of preoperative AR and the incidence of postoperative AR (p<0.05, Table 1, Fig. 1). For the older patients at operation, aortic valve repair had higher occurrence of AR compared to those who had aortic valve replacement (p<0.05, Fig. 2). Conclusion: From the result of this study, we can concluded that early primary repair is recommended to decrease the progression of AR. Aortic valve repair is not always a satisfactory option to correct the aortic valve pathology, which may suggest that aortic valve replacement should be considered when indicated.

• Economic and Environmental Geology
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• v.34 no.6
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• pp.583-593
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• 2001

Clay minerals are common component of fault gouge and have been used to determine the fault activity age using K-Ar dating technique. We carried out XRD and K-Ar analyses of the mica clay minerals from the fault gouge along the Ulsan Fault Zone, southeastern Korea to estimate the timing of the major fault activity. Mica clay minerals for four grain size fractions of 5-2 Um, 2-1 $\mu$m, 1-0.35$\mu$m, and 0.35-0.05 $\mu$m were separated from the gouge samples in the three locations by the hydraulic elutriation and contrifugal separator. Fault gouges are composed of smectite, mica clay minerals, kaolinite, chlorite, quartz, and feldspar. The illite crystallinity of mica clay minerals is the highest in the finest grained fraction with lM polytype, indicating that the aulhigenic mica clay minerals have been concentrated in the fraction. K-Ar ages give some variation from 46 to 35 Ma (330-2), 45 to 39 Ma (16Ww), and 32 to 15 Ma (102Ws) and are the youngest in the finest grained fraction. These results suggest that the hydrothermal alteration associated with the major fault activities along the Ulsan fault Zone took place twice at 39-35 Ma and 15 Ma.

• Economic and Environmental Geology
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• v.54 no.2
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• pp.187-197
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• 2021

The Hyeongjeseom (Islet) is an erosional remnant of volcano which is located about 2 km northeast of sea shore of the Songaksan tuff ring, and is composed of volcaniclastic deposit, agglomerate and scoria deposit, ponded lava, aa lava flows, reworked deposit and beach deposit in ascending order from the base. The volcano is formed by volcaniclastic deposits and lava flows that recorded a transition from initial phreatomagmatic to magmatic explosions followed by lava effusion. It is interpreted that the outcropped volcaniclastic deposit may be a remaining portion of outer ring of a tuff cone. A bomb and a ponded lava yield geochemically basaltic trachyandesite compositions (SiO2 51.3 wt%, Na2O+K2O 6.0 wt%) and belong to olivine basalt with scarce (<5 %) phenocrysts of olivine, petrographically. By incremental heating Ar-Ar dating method, the plateau age of lava flow in the Heongjesom is 9.2±3.6(2σ) ka, implying that the volcanism of Heongjeseom may have occurred earlier than the Songaksan tuff ring which erupted ca. 3.7 ka. It still remains a task to find a volcano which matches with a historical record of volcanic activity that occurred a thousand years ago.

• The Journal of the Petrological Society of Korea
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• v.14 no.1
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• pp.73-81
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• 2005

K-Ar ages have been determined for the submarine basalts dredged from the P2 and P3 segments of the Phoenix Ridge, Drake Passage, Antarctica, for better understanding on the extinction of seafloor spreading. At the P3 segment, the K-Ar ages of the rifted ridge basalts are 3.5-6.4 Ma, and those for the axial seamount basalts are 1.5-3.1 Ma. The K-Ar ages for the basalts at the rifted ridge and axial central high in the P2 segment are 2.1 and 1.4-1.9 Ma, respectively. We suggest that the extinction of seafloor spreading at the P3 and P2 segments occurred at 3.3 and 2.0 Ma, respectively, on the basis of ridge structure and formation time of basalts. This result favors a stepwise extinction model rather than a simultaneous one on the extinction of the Phoenix Ridge.

• Economic and Environmental Geology
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• v.19 no.spc
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• pp.175-191
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• 1986

The Geodo granodiorite intruded into the Joseon Supergroup is fine-grained at the marginal part, and medium-grained and more leucocratic at the central part. The Quartz monzonite porphyry intruded inte Precambrian granite and Geodo granodiorite has abundant plagioclase phenocryst. The Imog granite intruded into the Yulri Group and the Joseon Supergroup is mediumgrained biotite granite with partly pinkish feldspar phenocryst. The K/Ar ages obtained from the biotite of the Geodo granodiorite and Imog granite are Early ($111{\pm}1{\sim}107{\pm}1$ Ma) and Late ($93{\pm}1{\sim}92{\pm}1$ Ma) Cretaceous, respectively. The K/Ar sericite age of the quartz-sericite zone of the lower Jangsan quartzite occuring in the western area gave much younger age (about 170 Ma) than that of the Jangsan quartzite, that might be reset due to the regional metamorphism of the Daebo orogeny. The granitic rocks of the area are felsic to mafic, metaluminous to peraluminous, calc-alkalic (alkali-lime index${\fallingdotseq}$ 57) and I-type (magnetite-series) based on the chemical data_ And they appear to have been fractionated at the order of Geodo granodiorite, Quartz monzonite porphyry and Imog granite. In terms of mineralogy, geochemistry and K/Ar biotite age, a rock suite of monzodiorite, quartz monzodiorite and quartz monzonite-granodiorite in the Geodo stock was fractionally differentiated from a magmatic body from its margin to inward.

• Journal of the Korean earth science society
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• v.36 no.1
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• pp.27-35
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• 2015

This study aims to establish the age of the Cretaceous Togeum Formation in Gurye that reported the discovery of dinosaur eggshells and bones. This study also investigates to determine the period of the dinosaurs' dominance in the region. K-Ar ages are measured on the whole volcanic rocks in the lower - and upper parts of the formation. The six samples dated are volcanic pebbles deposited in the Geumjeongri Conglomerate that is distributed underneath the Togeum Formation, and the ages dated as Aptian ($118.3{\pm}2.3Ma$) or Albian ($103.6{\pm}2.0$, $102.5{\pm}2.0$, $99.9{\pm}1.9Ma$), which all correspond to the Early Cretaceous. In addition, the ages of andesites and porphyritic andesites overlying the Togeum Formation are dated in a similar way. The result is that the ages are apparently corresponding to the Campanian ($83.9{\pm}1.6$, $74.2{\pm}1.5$Ma) of the Late Cretaceous. Field evidence and the age results indicate that the formation of the Togeum and the activities of dinosaurs dated back between 84 and 100Ma. It suggests that the Togeum Formation be somewhat older than the Boseong Seonso Formation (81Ma) which contains egg shells, the Haenam Uhangni Formation (79-81 Ma) that has dinosaur, pterosaur and webbed bird footprints, and also older than the theropod egg nests (77-83Ma) found in the Aphaedo area.

• Economic and Environmental Geology
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• v.19 no.3
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• pp.231-237
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• 1986

Samples of porphyries, andesites, decites and sandstones were collected from 14 sites in order to study paleomagnetism and to determine K-Ar age in Guryongpo area. K-Ar age dating indicates that porphyries and volcanic rocks formed 41.7 and 22.7~19.4Ma, respectively. The mean direction of remanent magnetization for each site was generally well grouped after alternating field demagnetization. Both normal and reversed directions are present. The mean magnetic direction of the porphyries of Late Eocene and that of the volcanic rocks of Late Oligocene to Early Miocene have similar, easterly declinations. Overall magnetic direction is $Dm=43.8^{\circ}$, $Im=53.5^{\circ}$, ${\alpha}95=12.2^{\circ}$. the reliability of the observed paleomagnetic directions is ascertained by the presence of normal and reversed polarities. This is also conformed by the similarity of the declinations of the normal and reversed polarities. Observed easterly declinations in this area are attributed to local clockwise rotation of the land mass by approximately 40~50 degrees since early Miocene.

• Journal of the Mineralogical Society of Korea
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• v.26 no.3
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• pp.161-174
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• 2013

The geology of the weondong deposit area consists mainly of Cambro-Ordovician and Carboniferous-Triassic formations, and intruded quartz porphyry and dyke. The skarn mineralized zone in the weondong deposit is the most prospective region for the useful W-mineral deposits. To determine the skarn-mineralization age, U-Pb SHRIMP and K-Ar age dating methods were employed. The U-Pb zircon ages of quartz porphyry intrusion (WD-A) and feldspar porphyry dyke (WD-B) are 79.37 Ma and 50.64 Ma. The K-Ar ages of coarse-grained crystalline phlogopite (WD-1), massive phlogopite (WDR-1), phlogopite coexisted with skarn minerals (WD-M), and vein type illite (WD-2) were determined as $49.1{\pm}1.1$ Ma, $49.2{\pm}1.2$ Ma, $49.9{\pm}3.6$ Ma, and $48.3{\pm}1.1$ Ma, respectively. And the ages of the high uranium zircon of hydrothermally altered quartz porphyry (WD-C) range from 59.7 to 38.7 Ma, which dependson zircon's textures affected by hydrothermal fluids. It is regarded as the effect of some hydrothermal events, which may precipitate and overgrow the high-U zircons, and happen the zircon's metamictization and dissolution-reprecipitation reactions. Based on the K-Ar age datings for the skarn minerals and field evidences, we suggest that the timing of W-skarn mineralization in weondong deposit may be about 50 Ma. However, for the accurate timing of skarn mineralization in this area, the additional researches about the sequence of superposition at the skarn minerals and geological relationship between skarn deposits and dyke should be needed in the future.

• The korean journal of orthodontics
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• v.25 no.5 s.52
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• pp.557-566
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• 1995

Postpubertal craniofacial growth changes were assessed from serial lateral cephalograms taken at which subjects were 16 and 18 years of age. The sample consisted of 19 male and 14 female subjects with no previous orthodontic treatment who had normal occlusion. The craniofacial growth changes of these samples during this study period might be summarized as follows 1. Significant increase in mean maxillary and mandibular length, cranial base length, posterior md anterior facial height were observed at the age period studied in male(P<0.05), however, in female significant increase was observed only mandibular length(Ar-Gn, Ar-Go) and anterior and posterior facial height(P<0.05). 2. Total growth increment of all measumenats were below 1mm in female, but in male, total mandibular(Ar-Gn) growth increment was 2.0mm and those of mandibular tody length, ram length, posterior facial height, and anteior facial height were 1 to 1.54mm and the others were below 1mm 3. A closing, forward rotation of the mandible occured with a significant decrease in mandibular plane angle of $0.61^{\circ}$ in male(P<0.01). 4. Summarized the findings, even though statistically significant growth changes in some dimensions of female were observed, the amount of growth change were very small, however, in male the growth changes of some dimensions associated with mandible were significant and considerable amount.