• 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.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.

• The Journal of the Petrological Society of Korea
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• v.27 no.2
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• pp.97-104
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• 2018

The U-Pb isotopic and rare earth element compositions of zircon were measured using a SHRIMP from a tonalitic gneiss sample DE43 in Daeijak Island, central Korea. Zircon crystals, up to ${\sim}300{\mu}m$ in diameter, rarely contain thin overgrowth rims. In contrast to Paleoproterozoic cores, the $^{206}Pb/^{238}U$ ages of $256{\pm}23Ma(1{\sigma})$, and $221{\pm}7Ma(1{\sigma})$ were yielded from two spot analyses on the overgrowth rims of zircon. The rims are geochemically characterized by low Th/U ratios (<0.01) and strongly depleted light rare earth elements. The Permian-Triassic apparent ages of zircon are consistent with the $^{208}Pb/^{232}Th$ ages dated from allanite ($227{\pm}7Ma(t{\sigma})$) in the same sample within uncertainties, indicating an equilibrium growth of allanite and zircon at ~227 Ma. On the other hand, the younger $^{208}Pb/^{232}Th$ and $^{206}Pb/^{238}U$ ages ($213{\pm}4Ma(t{\sigma})$ and $186{\pm}9Ma(t{\sigma})$, respectively) of allanite may result from Pb loss due to the infiltration of alkali fluids from Late Triassic and Jurassic granitoids nearby.

• The Journal of the Petrological Society of Korea
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• v.19 no.1
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• pp.89-101
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• 2010

To constrain the depositional ages of the Gyeongsang sedimeantary formations, SHRIMP U-Pb ages were determined from detrital zircons in three samples: (1) a pebble-bearing sandstone from the lowermost Jinju Formation of the Sindong Group and (2) two conglomerates from the Silla Conglomerate of the Hayang Group. Their concordia ages are $112.4{\pm}1.3(2{\sigma})$ Ma and $110.4{\pm}2.0(2{\sigma})$ Ma respectively. Such ages represent the maximum deposition ages for the lowermost Jinju Formation and Silla Conglomerate, indicating the deposition of the Jinju Formation started from late Aptian and lasted to early Albian, then deposition of the rather thin Chilgok Formation and Silla Conglomerate was followed during the Albian. The age distribution of the analyzed detrital zircons indicates the presence of protoliths, or zircons derived from them, regarding a wide span of igneous activities from Mesozoic to Archean. Among such ages, there are Mesoproterozoic, Neoproterozoic and Paleozoic igneous activities, which have not been known or seldom reported from Korean peninsula. These ages further suggest the possible presence of rocks with such ages during the deposition periods or their derivation through a long river system developed into the continents at the time of deposition.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.4
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• pp.339-347
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• 2020

We carried out the U-Pb age dating of zircon from basement rocks in the southern part of the Danyang National Geopark. Two migmatitic gneisses composed of biotite±sillimanite±garnet+feldspar+quartz were dated. Leucosomes in the samples were clearly distinguished from their melanosomes. The U-Pb isotopic compositions of zircon from sillimanite- and garnet-bearing migmatitic samples were measured using a secondary ion microprobe, yielding metamorphic ages, 1870±10 Ma (2σ)와 1863±6 Ma (2σ), respectively. 1.87~1.86 Ga metamorphic ages are consistent with those of the Paleoproterozoic low-P and high-T regional metamorphism (1.87~1.85 Ga) in the Yeongnam Massif. The maximum depositional age based upon the apparent 207Pb/206Pb ages of detrital zircon in the samples was estimated as 2.06 Ga, and thus sedimentation age of the protolith of the migmatitic gneisses ranges between 2.06 and 1.87 Ga.

• 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.21 no.1
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• pp.31-45
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• 2012

We investigated the various lithologies and zircon U-Pb ages of metasedimentary rocks from the Yeongheung-Seonjae-Daebu Islands, western Gyeonggi Massif, whose geologic and geochronologic features are poorly constrained in spite of their significance for tectonic interpretation. Major lithology consists of quartzites or meta-sandstones commonly alternating with semi-pelitic schists, together with lesser amounts of calcareous sandstones with matrix-supported quartzite clasts, calcareous schists, and pelitic schists. Pelitic schists uncommonly contain large porphyroblasts of garnet as well as quartz veins with large crystals of muscovite and andalusite or kyanite. SHRIMP U-Pb ages of detrital zircons from two analyzed metasandstones define four age populations: Neoarchean (~2.5 Ga), Paleoproterozoic (~2.0-1.5 Ga), Neoproterozoic (~1.1-0.7 Ga), and Early Paleozoic (~560-400 Ma). The youngest zircon ages are clustered at ~420 Ma. These results suggest that the deposition of meta-sandstones took place after the Silurian, possibly during the Devonian, and are analogous to those of the Taean Formation reported from the western part of the Gyeonggi Massif. Moreover, The age distribution patterns of detrital zircons and the Barrovian-type metamorphic facies of pelitic schists are similar to those reported from the Imjingang belt, suggesting that the Taean Formation likely corresponds to southwestward extension of the Imjingang Belt.

• The Journal of the Petrological Society of Korea
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• v.20 no.4
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• pp.191-206
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• 2011

The emplacement ages, whole-rock geochemistry and Sr-Nd isotopic compositions of granitoid rocks from Cheongju area, South Korea, were investigated for delineating their petrogenetic link to the Jurassic Daebo granitoid rocks. Zircon crystals were collected from the diorite, biotite granite and acidic dyke samples in a single outcrop. Cross-cutting relationships show that the emplacement of diorite was postdated by the intrusion of biotite granite. Both rocks have been subsequently intruded by acidic dyke. The U-Pb isotopic compositions of zircon from the diorite, biotite granite, and acidic dyke were measured using a SHRIMP-II ion microprobe, yielding the crystallization ages of $174{\pm}2Ma$, $170{\pm}2Ma$, and $170{\pm}5Ma$, respectively, with 95% confidence limits ($t{\sigma}$). The emplacement ages are consistent with those determined from the above relative ages. The major and trace element patterns of the rocks are consistent with those of the Jurassic Daebo granitoid rocks, possibly suggesting a subduction-related I-type granite. The geochemical signature is, however, betrayed by the Sr and Nd isotopic compositions of these rocks. The isotopic signatures suggest that the rocks were produced either by the partial melting of lower-crust or by the mantle-derived magma contaminated by the basement rocks during its ascent and/or emplacement. In addition, the inherited ages of zircons of the rocks (ca. 2.1, 1.8, 0.8 and 0.4 Ga) suggest a possible assimilation with crustal rocks from the Gyeonggi massif and Ogcheon metamorphic belt.

• Journal of the Korean earth science society
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• v.29 no.7
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• pp.539-550
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• 2008

In this paper, we investigate the geochemical and isotope properties of the Jeongeup foliated granite (hereafter, the JFG) in the Jeongeup area, aiming at establishing the movement age of the Honam shear zone by U-Pb sphene geochronology. In the AMF diagram, the JFG corresponds to the calc alkalic rock series, and belongs to the magnesia region in the diagram of silica versus $FeO^{total}/(FeO^{total}+MgO)$. Additionally, in the Rb-Ba-Sr diagram, it is classified as granodiorite and anomalous granite with distinctive negative Eu-anomaly in the REE patterns. According to the silica and trace element contents, the JFG falls on the type VAG+syn-COLG, which implies that this was formed under the circumstance of compressional continental margin or volcanic arc. $^{143}Nd/^{144}Nd$ isotope ratios range from 0.511495 to 0.511783 and $T_{DM}$ are calculated to be about $1.68{\sim}2.36Ga$. U-Pb sphene ages of the JFG are $172.9{\pm}1.7Ma$ and $170.7{\pm}2.8Ma$, based on $^{238}U-^{206}Pb$ and $^{235}U-^{207}Pb$ ages, respectively. Presumably, the dextral ductile shearing in the Jeongeup area has occurred after 173 Ma.

• Journal of the Korean earth science society
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• v.43 no.3
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• pp.405-429
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• 2022

Detrital zircon LA-MC-ICP-MS U-Pb dating of the Cretaceous Gurye Group, Gurye Basin, was carried out. Gurye Group consists of Supyeongri, Geumjeongri, Togeum, and Obongsan formations in ascending order, and five samples were collected for age dating. Based on the dating results, the lowermost Supyeongri and the uppermost Obongsan formations show narrow age ranges. Only Precambrian and Late Cretaceous zircons were found in the Supyeongri and Obongsan formations, respectively. However, the upper and lower Geumjeongri, and Togeum formations show wide age ranges from the Precambrian to Cretaceous. The youngest detrital zircon U-Pb ages of each formation except the Supyeongri Formation, which lacks Cretaceous zircon, were calculated to be ca. 107.4 Ma in the lower Geumjeongri Formation, ca. 104.6 Ma in the upper Geumjeongri Formation, ca. 97.7 Ma in the Togeum Formation, and ca. 88.5 Ma in the Obongsan Formation. Such results indicate that the depositional age of the Gurye Group can be constrained from the Lower Cretaceous Albian to the Upper Cretaceous Coniacian. Based on the distribution of the detrital zircon ages from each formation, the source area of the Gurye Group is interpreted to have been extended from the adjacent Youngnam Massif to the Okcheon Belt throughout the basin evolution. The increase of the Cretaceous zircon with time is thought to reflect the slab roll-back of the proto-Pacific plate during the Cretaceous.