• The Journal of the Petrological Society of Korea
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• v.13 no.3
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• pp.119-125
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• 2004

Using a SHRIMP ion microprobe, we have dated zircon grains of a felsic meta-tuff from the so-cal1ed Munjuri Formation, Ogcheon metamorphic belt. The weighted mean $^{206}$ Pb/$^{238}$ U zircon ages obtained from 13 spot analyses of 10 grains provide an essentially concordant age of 747${\pm}$7Ma. This result corroborates the conventional U-Pb zircon age (756${\pm}$1Ma; Lee et al., 1998) for the Neoproterozoic bimodal volcanism in the Ogcheon belt. Thus, proto-basins associated with intracontinental, high-volcanicity rift in the Ogcheon belt are most likely to have formed at ca. 750 Ma.

• The Journal of the Petrological Society of Korea
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• v.25 no.4
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• pp.401-407
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• 2016

The SHRIMP zircon U-Pb age dating was carried out for the age-unknown Haeinsa Granite located in the middle Yeongnam Massif. SHRIMP zircon U-Pb age determinations of 7 samples from the Haeinsa Granite in Geochang area show two age groups. Ages from 5 samples (M-3-1, H-1, 3, 5, 10) are $192.4{\pm}1.4{\sim}195.5{\pm}1.9Ma$, whereas ages from 2 samples (H-11 and 12) are $187.7{\pm}3.3Ma$ and $188.2{\pm}3.6Ma$, respectively.

• The Journal of the Petrological Society of Korea
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• v.25 no.1
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• pp.29-37
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• 2016

A "granite boulder", ~70 cm in size, was reported from the Geumgang Limestone, and has been considered as a glaciogenic dropstone. Since this interpretation has enormous implications for unraveling the evolution history of the Ogcheon Metamorphic Belt, we re-examined the contact relationship and structure of the "granite boulder", and estimated its emplacement age based upon SHRIMP U-Pb zircon dating. The weighted mean $^{206}Pb/^{238}U$ age pooled from 6 spot analyses of two specimens is $170{\pm}2Ma$ ($2{\sigma}$, MSWD=2.2). This zircon age suggests that the "granite boulder" in the Geumgang Limestone is a part of Jurassic granite, rather than a glaciogenic dropstone.

• The Journal of the Petrological Society of Korea
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• v.26 no.1
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• pp.73-82
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• 2017

We determined SHRIMP U-Pb ages of the detrital zircons separated from the Bangnim Group of the Pyeongchang area to constrain its depositional age. As the result, the minimum age group yielded $^{206}Pb/^{238}U$ age of $450.3{\pm}4.2Ma$ (n=3), suggesting depositional age younger than Late Ordovician. Therefore, the Bangnim Group cannot be a Precambrian sedimentary formation but is younger than Myobong Formation of the Early Paleozoic Joseon Supergroup of the Taebaeksan basin. Such a depositional age implies that the Bangnim Group and structurally overlying Jangsan Quartzite should be in fault contact, suggesting that the Jangsan Quartzite, Myobong Formation and Pungchon Limestone thrusted over the Bangnim Group. The zircon U-Pb age distribution pattern of the Bangnim Group resembles those of the Early Paleozoic Myobong and Sambangsan Formations of the Taebaeksan basin and seemingly Middle Paleozoic Daehyangsan Quartzite and the Taean Formation. However, detrital zircon U-Pb age patterns of the Late Paleozoic Pyeongan Supergroup are quite distinct from them, suggesting drastic change in provenance of the detrital zircon supply. Therefore, we suggest that the Bangnim Group was deposited before the Pyeongan Supergroup.

• Economic and Environmental Geology
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• v.48 no.4
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• pp.287-299
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• 2015

The metapsammite distributed in the Yeongam-Gangjin area had been classified into age-unknown Yongamsan Formation, Seologri Formation and age-unknown Seogisan Formation, and these formations are reported as each other different formations. These formations have been renamed Precambrian Galdu or Permian Songjong Formations. In this study, we present detrital zircon SHRIMP U-Pb age data from the metapsammite to examine deposition time and stratigraphy. The analyzed U-Pb zircon ages dominantly reveal Paleoproterozoic ages of ca. 1.87Ga and the youngest detrital grains are constrained by the age of 246-265 Ma. The youngest age indicates late Permian or early Triassic for the deposition time. Therefore, the metapsammite in the Yeongam-Gangjin area is considered to be the upper formation of the late Paleozoic Pyeongan Group which is correlated with the Gohan-Donggo Formations or Nokam Formation of the Samcheock coal field and the Cheonunsan Formation of the Hwasun coal field. The metapsammite of the study area is the late Paleozoic Pyeongan Group by the zircon age rather than Precambrian Galdu and Permian Songjeong Formations are no longer meaningful. Therefore, we propose the upper Paleozoic 'metapelite' and 'metaspammite', or original formation name defined by 1:50,000 geological maps, instead of Galdu and Songjeong Formations.

• The Journal of the Petrological Society of Korea
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• v.26 no.1
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• pp.63-72
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• 2017

We report an Early Cretaceous zircon U-Pb age ($113.9{\pm}1.2Ma$) for the Heuksan-do granite located about 90km from Mokpo offcoast of the southwestern Korean peninsula. At this Aptian/Albian boundary, widespread igneous activities occurred not only in the Korean peninsula but also in the eastern China and Japan. We raise the possibility that the flat-slab subduction and delamination triggered such an episodic igneous activity over the large areas of East Asia.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.197-208
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• 2014

Zircon separated from a biotite schist of the Guryong Group in Odesan area, eastern part of the Gyeonggi Massif in Korea were analysed for SHRIMP U-Pb ages. CL images display composite core-rim structures of the zircon, indicating an in-situ overgrowth of zircon through a high-grade metamorphism. The metamorphic zircon rims give a weighted mean age of $247{\pm}6Ma$. While the detrital zircon cores have zoning patterns and Th/U ratios indicative of a magmatic origin. Among 53 analyses from the cores, 46 data yield near concordant ages which are concentrated at $378{\pm}10Ma$ (n=9), $420{\pm}4Ma$ (n=6) and $1845{\pm}9Ma$ (n=18) with sporadic Neoproterozoic ($687{\pm}9Ma$) to late Archean ($2519{\pm}20Ma$) ages. The age data constraint sedimentation age of protolith of the Guryong Group, so far unknown, as late Paleozoic. The Guryong Group of this study is the first late Paleozoic strata reported from eastern Gyeonggi Massif, and its maximum depositional age (ca 378 Ma) is identical with those of the late Paleozoic strata in the southwestern Ogcheon Belt. The Triassic metamorphic age and abundant middle Paleozoic provenance (361~425 Ma) of the Guryong Group are similar with those reported from the Triassic collisional belt in central China. Thus this study indicates that the Odesan area would be an possible eastward extension of the Triassic collisional belt in central China.

• 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 Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.197-208
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• 2013

The Namwon and Sunchang granites are neighbouring plutons intruding the Yeongnam massif and the Okcheon metamorphic belt, respectively in the southwestern part of the Korean peninsula. In this study, SHRIMP zircon U-Pb ages are determined from these plutons. The results show that the emplacement age of the Namwon granite is $185.8{\pm}0.9(2{\sigma})$ Ma. We obtained $175.0{\pm}2.0(2{\sigma})$ Ma from the northern part and $179.8{\pm}0.9(2{\sigma})$ Ma from the central part of the Sunchang granite, yielding $177.4{\pm}1.3(2{\sigma})$ Ma as the average age of the pluton. Such age results confirm that the Honam shear zone, which cause marked deformation of the Sunchang granite, was active after ca. 175 Ma.

• The Journal of the Petrological Society of Korea
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• v.22 no.4
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• pp.299-305
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• 2013

It is well known that the Hongcheon iron-rare earth deposit is composed of carbonatite-phoscorite complex. We conducted zircon U-Pb age determination for the gneissic country rocks of this deposit. As the result we obtained ca. 1830 Ma, which is somewhat younger than igneous and metamorphic ages of ca. 1870 Ma generally reported from the Gyeonggi massif, suggesting further investigations for the timing and evolution of the Paleoproterozoic activities of the Gyeonggi massif.