• Economic and Environmental Geology
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• v.39 no.4 s.179
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• pp.353-368
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• 2006

The modem kinematic behaviors of the rigid block motions are well developed using synthetic analyses of paleomagnetic, petrologic, paleontologic and geophysical data which have been established in the last a quater of a century. Phanerozoic geodynamic evolution and tectonic episodes of the Korean Peninsula and East Asia region are discussed and summarized here.

• Proceedings of the KSEEG Conference
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• 1999.04a
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• pp.303-305
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• 1999

• Economic and Environmental Geology
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• v.53 no.5
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• pp.565-583
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• 2020

In recent years, various social issues related to the natural radioactive elements detected in household goods and building materials are addressed, and should be solved promptly. In Korea, for more than 20 years, the Ministry of Environment has investigated the natural radioactive materials such as heavy metals, uranium, and radon in soil or groundwater. The origins of natural radioactive materials in them may have a close correlation with the geological factors including classification of rocks, petrogenetic origins, and deformation characteristics, but the exact geological correlations are not clarified because of the absence of the government policy preserved in the basement rocks, soils as well as groundwater in fault-related reservoirs. This study aims to perform a research on the correlation between the petrogeneses of the Phanerozoic plutonic rocks and natural radioactive concentrations in rocks (radon, uranium, thorium, potassium etc.) in Korea. Among the Phanerozoic plutonic rocks, alkaline plutonic rocks (syenite, monzonite and monzodiorite and alkali granite) show high U and Th concentrations by high solubilities of U, Th, Zr, REE, and Nb until the most extreme stages of magmatic fractionation (viz. crystal fractionation) due to high magma temperature and high alkalinity tendency. The highly fractionated high-K calalkaline and peraluminous granitic rocks (leucogranite, two-mica granite and leucocratic pegmatite are also U and Th concentrations compared with other less or medium fractionated granitic rocks (diorite, granodiorite and granite). The alkaline plutonic rocks are associated with intracontinental rifting and extensional environment after crustal thickening by collisional and subductional processes. In contrast, the dominant calc-alkaline granitic rocks in Korea are related to the arc environment of the subduction zone. In summary, the trends of the U, Th and K concentration from the Phanerozoic plutonic rocks in Korea are closely linked to the petrogenesis of the rocks in tectonic environment. The preliminary data for gamma-spectrometric mesurments of natural radionuclide contents (²²⁶Ra, ²³²Th and ⁴⁰K) in the Phanerozoic plutonic rocks show high values in the alkaline and highly fractionated granitic rocks.

• The Journal of the Petrological Society of Korea
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• v.21 no.2
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• pp.173-192
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• 2012

Previous age data were reviewed for 98 sites of Phanerozoic granitoids in the southern part of the Korean Peninsula. Subduction-related granitic magmatism has occurred in southeastern Korea since Early Permian. In the middle part of the Yeongnam massif, arc-related tonalites, trondhjemites, granodiorites, and monzonites were emplaced during Early Triassic. After Middle Triassic continental collision in central Korean Peninsula, post-collisional shoshonitic and high-K series and A-type granitoids were emplaced in the southwestern Gyeonggi massif and central Okcheon belt during Late Triassic. Early Jurassic calc-alkaline granitoids are mostly distributed in the middle part of the Yeongnam massif and Mt. Seorak area, northeastern Gyeonggi massif. On the other hand, Middle Jurassic calc-alkaline granitoids pervasively occur in the Okcheon belt and central Gyeonggi massif. This selective distribution could be attributed to the change in the position of trench, subduction angle, or the direction of subduction. Most Cretaceous and Paleogene granitoids are distributed in the Gyeongsang basin, with the latter emplaced exclusively along the eastern coastline. Outside the Gyeongsang basin, Cretaceous granitoids emplaced in relatively shallow depth occur in the Gyeonggi massif and central Okcheon belt.

• The Journal of the Petrological Society of Korea
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• v.23 no.3
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• pp.279-292
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• 2014

Nd isotopic compositions analyzed from the Phanerozoic granitoids of Korea are integrated and discussed. Variations in Nd isotopic compositions can be explained either by temporal trend or by regional differences. Among the three active periods, first two periods during the Permian-Triassic and Jurassic seem to show variations from rather high ${\varepsilon}_{Nd}(t)$ values at the beginning to lower ${\varepsilon}_{Nd}(t)$ values during the later stages. Such trends probably reflect melting of the subducting oceanic crust and producing magma with higher proportion of depleted mantle derived materials during the early stage of subduction process, and subsequent magmas with greater proportion of old continental crust with progress of subduction. However, the Cretaceous-Paleogene period of active magmatism displays higher ${\varepsilon}_{Nd}(t)$ values during the advanced stage of the igneous activities, which is opposite to the previous active periods. The other explanation is that such differences in ${\varepsilon}_{Nd}(t)$ reflect regional differences, based on the observations that such high-${\varepsilon}_{Nd}(t)$ granitoids distribute in the northeastern Gyeongbuk Province and Gyeongsang Basin. If this is the case, the regions with highr ${\varepsilon}_{Nd}(t)$ values may have distinct crustal evolution histories, e.g. younger average age. The choice between the two hypothesis could be made through further studies.

• The Journal of the Petrological Society of Korea
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• v.2 no.1
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• pp.19-31
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• 1993

Oxygen isotope compositions of whole rock and/or mineral separates (quartz and feldspar) have been determined for the granitic and related rocks from the Wolf River Batholith, Wisconsin. Hydrothermal alteration resulting in the decrease of ${\Delta}_{Q-F}$/ values was obaserved locally throughout the batholith. Feldspars of different colors (pink, gray and red) were separated whenever feasible and analyzed. Most red feldspars (An$_{10-30}$/) show the highest and constant ${\delta}^18O$/ values (9.3~10.0 permil) suggesting nearly complete isotope exchange with hydrothermal fluid. Based on ${\delta}^18O$/ values and the alteration temperatures (260~$350^{\circ}C$) estimated from fluid inclusion study, ${\delta}^18O$/ of fluid is calculated to be $5.0{\pm}1.4$ permil. Phanerozoic sedimentary formation water in Wisconsin is most likely the source of the fluid.

• The Journal of the Petrological Society of Korea
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• v.24 no.4
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• pp.291-305
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• 2015

Microbialites are defined as rocks formed by microbial organisms. After their first appearance around 3.5 billion years ago, microbialites occur in various depositional environments throughout geological periods. Microbial organisms form microbialites by trapping and binding detrital sediments and/or precipitating carbonate cements, resulting in formation of various microstructures and mesostructures. Four major types of microbialites are distinguished based on their mesostructures: stromatolite, thrombolite, dendrolite, and leiolite. In the geological records, occurrences of microbialites are influenced by calcium carbonate saturation of seawater and interaction of microbialites with metazoans. Stromatolites mainly flourished during the Precambrian, and diminished as level of atmospheric carbon dioxide declined. On the other hand, thrombolites, mainly formed by calcified microbes, began to flourish from the Neoproterozoic. As metazoans diversified in the Phanerozoic, proportion of the microbialites within sedimentary record declined. Since then, microbialites only occasionally flourished during the Phanerozoic, such as shortly after mass-extinction events. In the Korean Peninsula, microbialites occur in the Neoproterozoic Sangwon System, the Early Paleozoic Joseon Supergroup, and the Cretaceous Gyeongsang Supergroup, which form different shapes according to their age and depositional environments. By performing detailed studies on these Korean microbialites, it is possible to understand how microbes affected geological records and sedimentary environments, as well as their interaction with other organisms.

• The Journal of the Petrological Society of Korea
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• v.12 no.4
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• pp.207-209
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• 2003

The Honam Shear Zone, an important feature in the Phanerozoic geologic history of Korea, has attracted much attention due to its potential tectonic significance. However, little has been known about the displacement amount of the shear zone. Here, we propose a possible displacement marker for the shear zone. The geographic position and peculiar lithology of the Sancheong and Gaya anorthosite bodies in the south-central part of Korea suggest a NE-trending dextral strike slip shear zone that has a displacement of ca. 50 km. This hypothetical shear zone is considered as a part of the Honam Shear Zone since the former has the same trend and shear sense as the latter.

• Economic and Environmental Geology
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• v.24 no.3
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• pp.277-285
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• 1991

We applied Sm-Nd isotopic system to so-called amphibolites occurring within the Ogcheon group to provide constraints on the age of the metasedimentary rocks and to characterize tectonic environment of basaltic magmatism. An internal mineral isochron age of $677{\pm}91Ma({\sigma})$ was obtained from a coarse-grained, intrusive, amphibolite near Mungyeong. Considering previous studies on the age of the Ogcheon group, we interpret that the isochron represents either early metamorphic or emplacement age. The depositional age of the metasedimentary rocks intruded by the amphibolite would be prior to late Proterozoic. The present study and Cambro-Ordovician fossil evidences of previous workers suggest that both Precambrian and Phanerozoic rocks are present in the Ogcheon group. Positive ${\varepsilon}$ Nd values(+2.4 to +3.5) of four whole rocks indicate mantle origin for the amphibolite. These isotopic data, along with published immobile trace element data of Cluzel et al.(1989), strongly suggest that parental rocks of the amphibolite formed in an intraplate environment rather than in island arc or midocean ridge. The age and tectonic environment of amphibolites in the Ogcheon belt suggest that the basaltic magmatism may be related to the late Proterozoic break-up of a presumed supercontinent, but not to the Triassic(?) collision between North and South China continents.

• The Journal of the Petrological Society of Korea
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• v.14 no.2 s.40
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• pp.83-92
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• 2005

It has recently been proposed that granites can be divided into hot and cold ones by absence and presence of inherited zircon, respectively, which is closely related to zircon saturation temperature. The Phanerozoic granites in South Korea are divided into high- and low-Zr groups in a $SiO_2-Zr$ diagram, which appears to be related to their intrusive age. Most Triassic-Jurassic granites belong to low-Zr group, whereas most Cretaceous-Early Tertiary granites belong to the high-Zr group with the exception of geographically distinct Masan and Jinhae granites that belong low-Zr group. Calculated zircon saturation temperatures using major elements and Zr contents indicate that the Cretaceous-Early Tertiary granites $(608-834^{\circ}C,\;average\; 782\pm31^{\circ}C)$ except for the Masan and Jinhae granites $(average\;759\pm16^{\circ}C)$ show higher temperature than the Triassic-Jurassic granites $(642-824^{\circ}C,\;average\;756\pm31^{\circ}C)$. U-Pb zircon isotope data of the Triassic-Jurassic granites reported so far define discordia in a concordia diagram, which indicates presence of inherited zircon and agrees with their low zircon saturation temperatures. So the Triassic-Jurassic granites appear to belong to cold granite. On the other hand, presence or absence of inherited zircon has not been known for the Cretaceous-Early Tertiary granites with relatively high zircon saturation temperature, so that their classification into hot or cold granite awaits further study. Nevertheless, the Creatceous-Early Tertiary granites may have formed at higher temperature than the Triassic-Jurassic granites, since zircon saturation temperature reflects formation temperature of magma to a certain degree.