• Proceedings of the Petrological Society of Korea Conference
• /
• 2009.05a
• /
• pp.74-74
• /
• 2009

• Proceedings of the Mineralogical Society of Korea Conference
• /
• 2005.05a
• /
• pp.63-63
• /
• 2005

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

• The Journal of the Petrological Society of Korea
• /
• v.24 no.3
• /
• pp.273-289
• /
• 2015

This study used the petrological features and the whole rock susceptibility characteristics suggest ways to determine the domestic dimension stones and Chinese similar dimension stones. In addition, this study compare the intrusive period by measuring the zircon U-Pb age of these stones. Result of comparing the petrological feature, with the exception of Macheon stone and Boryeong stone to show the differences in mineral composition and texture under a microscope, the domestic dimension stones and Chinese similar dimension stones exhibit substantially the same petrological feature. According to the measurement results for the whole rock magnetic susceptibility, Goheong, Iksan, Pocheon stones are the similar as Chinese dimension stones, and other stones are easily distinguished. The zircon U-Pb age results for Geochang, Iksan, and Pocheon stones are equivalent to the Jurassic Daebo granites and G603, G633, G655 are the Cretaceous granites. Therefore, the domestic dimension stones and Chinese similar dimension stones can be clearly determined by the zircon U-Pb age results.

• The Journal of the Petrological Society of Korea
• /
• v.15 no.3 s.45
• /
• pp.119-127
• /
• 2006

Detrital zircons in iron-bearing quartzite of the Seosan Croup from southeastern part of the Cyeonggi Hassif were analysed for SHRIHP U-Pb ages. Among 42 analyses, 38 data yield concordant ages (less tan 10 % discordancy), and they concentrated at 1781~1898 Ma (n=19), $1781{\sim}1898\;Ma(n=19),\;1935{\sim}1941\;Ma(n=4),\;1996\;Ma,\;2120\;Ma\;2403{\sim}2459\;Ma(n=5)$, 2661 Ma and 3198 Ma. The data indicate that sedimentation of iron-bearing quartzite should be after ca 1.78 Ga (the youngest detrital zircon age), and argue against some of conventional idea that iron-bearing quartzite of the Seosan Group might be correlated with the Archean iron-bearing quartzite in the North China Craton.

• The Journal of the Petrological Society of Korea
• /
• v.27 no.4
• /
• pp.223-233
• /
• 2018

In this study, SHRIMP zircon U-Pb dating was performed on deformed granitic rocks in the Sancheong area in the northeastern part of the Jirisan area, southwest of Yeongnam Massif. Until now, these have been known as Precambrian or age-unknown old igneous rocks, but the U-Pb concordant ages obtained from two samples are $237.8{\pm}4.0Ma$ and $230.2{\pm}3.4Ma$, respectively, showing their emplacements in Early to Middle Triassic. These results indicate that the deformed granite was emplaced at about 238~230 Ma. The study area shows the characteristics of ductile deformation with prominent development of foliation, augen structure, and lineation. It is observed that the deformed granites occur as xenoliths within the syenite, indicating that the time of deformation is earlier than the intrusion of the syenite of about 220 Ma. The emplacement and deformation periods of the deformed granite is similar to that of Permo-Triassic granite gneisses distributed in the Gimcheon and Andong areas of the Yeongnam Massif. Taken together, the eastern part of the Yeongnam Massif, extending from the central part to the southwestern part, granite intrusions occurred at about 260-230 Ma, followed by metamorphism-deformation of about 230-220 Ma.

• The Journal of the Petrological Society of Korea
• /
• v.14 no.1
• /
• pp.1-11
• /
• 2005

Sphene U-Pb ages were determined for the granodiorites from Gimcheon, Seongju and Anui areas of the middle Yeongnam massif. The determined ages were in the narrow range of 195.7±2.4∼200.8±1.9(2σ) Ma that are approximately coincident with the boundary between Triassic and Jurassic. Even though the studed plutons are aerially separated, they reveal quite similar major element compositions and almost identical ages, suggesting that they were generated from the similar source materials under the identical tectonic environment and thus they can be considered to form a single suite. Considering the age and spatial distribution of the Triassic to Lower Jurassic plutons of the Yeongnam Massif and Okcheon Belt, it seems that there were episodic changes in tectonic environment in both areas with relatively short intervals. In general, the compressive environment of active continental margin was prevailed. However, the tensional environment of within-plate was also appeared several times intermittently. In conclusion, Yeongnam Massif and Okcheon Belt experienced distinct tectonic environments during Triassic to Lower Jurassic, providing important clue to reveal the crustal evolution of the Korean Peninsula.

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

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

• The Journal of the Petrological Society of Korea
• /
• v.23 no.3
• /
• pp.167-185
• /
• 2014

SHRIMP zircon U-Pb ages and major element and Sr-Nd isotopic compositions were determined for drill cores (374-3390 m in depth) recovered from three boreholes in the Pohonag basin, southeastern Korea. Shallow-seated volcanic rocks and underlain plutonic rocks were geochemically classified as rhyolite and gabbro-granite, respectively. They showed high-K calc-alkaline trends on the $K_2O-SiO_2$ and AFM diagrams. Zircons from volcanic rocks of borehole PB-1 yielded concordia ages of $66.84{\pm}0.66Ma$ (n=12, MSWD=0.02) and $66.52{\pm}0.55Ma$ (n=12, MSWD=0.46). Zircons from volcanic rocks of borehole PB-2 gave a concordia age of $71.34{\pm}0.85Ma$ (n=11, MSWD=0.79) and a weighted mean $^{206}Pb/^{238}U$ ages of $49.40{\pm}0.37Ma$ (n=11, MSWD=1.9). On the other hand, zircons from plutonic rocks of borehole PB-3 yielded weighted mean $^{206}Pb/^{238}U$ ages of $262.4{\pm}3.6Ma$ (n=21, MSWD=4.5), $252.4{\pm}3.6Ma$ (n=8, MSWD=1.9) and $261.8{\pm}1.5Ma$ (n=31, MSWD=1.3). Detrital zircons from the sedimentary strata overlain the volcanic rocks showed a wide age span from Neoproterozoic to Cenozoic, with the youngest population corresponding to $21.89{\pm}1.1Ma$ (n=15, MSWD=0.04) and $21.68{\pm}1.2Ma$ (n=10, MSWD=19). These dating results indicate that the basement of the Pohang basin is composed of Late Permian plutonic rocks and overlain Late Cretaceous to Eocene volcanic sequences. Miocene sediments were deposited in the uppermost part of the basin, possibly associated with the opening of the East Sea. The Sr-Nd isotopic compositions of the Permian plutonic rocks were comparable with those reported from Permian-Triassic granitoids in the Yeongdeok area, northern Gyeongsang basin. They may have been recycled into parts of the Cretaceous-Paleogene magmatic rocks within the Gyeongsang basin.