• 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.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.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.

• 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.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.23 no.4
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• pp.393-403
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• 2014

U-Pb ages were determined from the Yongyudo biotite granites from western parts of Gyeonggi massif. The results show that the emplacement age of the Yongyudo biotite granite is ca. 227-230 Ma. Such age result that is somewhat older than previous reported ages, suggesting further investigations for the timing and evolution of the Jurassic granites of the western Gyeonggi massif.

• 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.28 no.4
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• pp.237-249
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• 2019

The volcanic rocks around the Jayang caldera are classified in an order such as Jukjang Volcanics, Doil Rhyolite, Unjusan Tuff and Rhyolite intrusions. By the SHRIMP U-Pb zircon datings from zircons, eruption ages of the Unjusan Tuff are constrained as 66.65±0.96 Ma in the intracaldera, and 66.08±0.62 Ma in the extracaldera outflow, and intrusion age of the ring dike is investigated as 60.74±0.66 Ma. The age data indicate that the caldera was collapsed between 66.08 Ma and 60.74 Ma, just before the dike intruded after the explosive eruption of the Unjusan Tuff. The Jayang caldera shows the composite igneous process of a perfect volcanic cycle passing from ash-flow tuffs through caldera collapse into ring dikes in the Jayang area.

• Journal of the Korean earth science society
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• v.38 no.2
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• pp.141-149
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• 2017

The geology of Saok island area in Jeollanam-do can be divided into 4 lithologic types: Jurassic granite, Cretaceous sedimentary rocks, acidic tuff and acidic dikes. In the Saok island area, dinosaur and web-footed bird footprints, arthropod trackway and silicified wood were found recently in the Cretaceous sedimentary rocks which composed of alternating light grey sandstone, shale and mudrock. The fossil-bearing sedimentary rock is overlain by an acidic tuff, and the sedimentary rock and acidic tuff are cut by acidic dykes. In order to constrain the depositional age of the Cretaceous sedimentary rocks in Saok island area, SHRIMP U-Pb zircon ages were determined in the tuffaceous sandstone and overlying acidic tuff. Zircon U-Pb ages of the sandstone and tuff are $83.58{\pm}0.86$ and $79.80{\pm}0.75Ma$, respectively, which belong to the Campanian of the Late Cretaceous. The U-Pb age of the acidic tuff indicates the eruption time of acidic tuff and thus the minimum age of the fossil-bearing sedimentary rocks in this area. Therefore, the formation age of the dinosaur and web-footed bird footprints can be constrained between 83.6 and 79.8 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.