• The Journal of Engineering Geology
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• v.10 no.3
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• pp.237-245
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• 2000

This study was for characterizing the engineering geological properties of Moryang Fault, and providing the basic data for tunnel design. Land-sat image analysis, geologic surveys, resistivity prospecting and 3-dimensional analysis for results of resistivity prospecting, core boring, mineralogical identification and chemical analysis for the bedrock, and K-Ar age dating for fault clay were carried out for the study of Moryang Fault which is located at Duckhyunri Sangbukmyun Uljinkun Ulsan metropolis. As a result of the study, it was shown that strike/dip was N20-3$0^{\circ}C$E/70-9$0^{\circ}C$NW, width of fault ranged from 20 to 60m(maximum 80m), and depth was more than 50m. K-Ar age dating results of fault clay were 5,700$\pm$1.129Ma and 1,900$\pm$0.380Ma. Hydraulic fracturing test results showed the principal stress direction similar to the strike of Moryang Fault.

• The Journal of the Petrological Society of Korea
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• v.12 no.2
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• pp.70-78
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• 2003

Sado, Chudo, Mokdo, Nangdo, and Jeokgeumdo are the islands which belong to Hwajeong-myeon, Yeosu-si, Jeollanam-do and there are various kinds of volcanic rocks, volcaniclastic sedimentary rocks, and dinosaur-fossil bearing sedimentary rocks on these islands. This study is designed to constrain geologic ages of these volcanic and sedimentary rocks. K-Ar ages of these rocks indicate that the volcanism of this area occurred mainly during the period of 91.8 ${\pm}$ 3.5∼65.5 ${\pm}$ 1.3(l$\sigma$) Ma. Deposition ages of the sedimentary rocks were bracketed based on the ages of the volcanic rocks and observed field relationship between sedimentary and volcanic rocks. The oldest sedimentary deposit of the area is the volcanic pebble bearing conglomerate of the Jeokgeumdo and its deposition age is ca. 81 Ma or less. The deposition age of the Chudo shale, which belongs to stratigraphically upper sequence and bears many dinosaur footprints, is at least ca. 77 Ma. Conglomerate of the Mokdo was deposited at ca. 72∼70 Ma. The deposition age of the dinosaur fossil deposit of the Sado is at least ca. 65 Ma. All the investigated volcanic and sedimentary rocks of the Yeosu islands were formed during the late Cretaceous and dinosaurs lived until the latest Cretaceous in this area.

• Economic and Environmental Geology
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• v.25 no.3
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• pp.337-349
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• 1992

The Tertiary basins in Korea have widely been studied by numerous researchers producing individual results in sedimentology, paleontology, stratigraphy, volcanic petrology and structural geology, but interdisciplinary studies, inter-basin analysis and basin-forming process have not been carried out yet. Major work of this study is to elucidate evidences obtained from different parts of a basin as well as different Tertiary basins (Pohang, Changgi, Eoil, Haseo and Ulsan basins) in order to build up the correlation between the basins, and an overall picture of the basin architecture and evolution in Korea. According to the paleontologic evidences the geologic age of the Pohang marine basin is dated to be late Lower Miocence to Middle Miocene, whereas other non-marine basins are older as being either Early Miocene or Oligocene(Lee, 1975, 1978: Bong, 1984: Chun, 1982: Choi et al., 1984: Yun et al., 1990: Yoon, 1982). However, detailed ages of the Tertiary sediments, and their correlations in a basin and between basins are still controversial, since the basins are separated from each other, sedimentary sequence is disturbed and intruded by voncanic rocks, and non-marine sediments are not fossiliferous to be correlated. Therefore, in this work radiometric, magnetostratigraphic, and biostratigraphic data was integrated for the refinement of chronostratigraphy and synopsis of stratigraphy of Tertiary basins of Korea. A total of 21 samples including 10 basaltic, 2 porphyritic, and 9 andesitic rocks from 4 basins were collected for the K-Ar dating of whole rock method. The obtained age can be grouped as follows: $14.8{\pm}0.4{\sim}15.2{\pm}0.4Ma$, $19.9{\pm}0.5{\sim}22.1{\pm}0.7Ma$, $18.0{\pm}1.1{\sim}20.4+0.5Ma$, and $14.6{\pm}0.7{\sim}21.1{\pm}0.5Ma$. Stratigraphically they mostly fall into the range of Lower Miocene to Mid Miocene. The oldest volcanic rock recorded is a basalt (911213-6) with the age of $22.05{\pm}0.67Ma$ near Sangjeong-ri in the Changgi (or Janggi) basin and presumed to be formed in the Early Miocene, when Changgi Conglomerate began to deposit. The youngest one (911214-9) is a basalt of $14.64{\pm}0.66Ma$ in the Haseo basin. This means the intrusive and extrusive rocks are not a product of sudden voncanic activity of short duration as previously accepted but of successive processes lasting relatively long period of 8 or 9 Ma. The radiometric age of the volcanic rocks is not randomly distributed but varies systematically with basins and localities. It becomes generlly younger to the south, namely from the Changgi basin to the Haseo basin. The rocks in the Changgi basin are dated to be from $19.92{\pm}0.47$ to $22.05{\pm}0.67Ma$. With exception of only one locality in the Geumgwangdong they all formed before 20 Ma B.P. The Eoil basalt by Tateiwa in the Eoil basin are dated to be from $20.44{\pm}0.47$ to $18.35{\pm}0.62Ma$ and they are younger than those in the Changgi basin by 2~4 Ma. Specifically, basaltic rocks in the sedimentary and voncanic sequences of the Eoil basin can be well compared to the sequence of associated sedimentary rocks. Generally they become younger to the stratigraphically upper part. Among the basin, the Haseo basin is characterized by the youngest volcanic rocks. The basalt (911214-7) which crops out in Jeongja-ri, Gangdong-myon, Ulsan-gun is $16.22{\pm}0.75Ma$ and the other one (911214-9) in coastal area, Jujon-dong, Ulsan is $14.64{\pm}0.66Ma$ old. The radiometric data are positively collaborated with the results of paleomagnetic study, pull-apart basin model and East Sea spreading theory. Especially, the successively changing age of Eoil basalts are in accordance with successively changing degree of rotation. In detail, following results are discussed. Firstly, the porphyritic rocks previously known as Cretaceous basement (911213-2, 911214-1) show the age of $43.73{\pm}1.05$ 및 $49.58{\pm}1.13Ma$(Eocene) confirms the results of Jin et al. (1988). This means sequential volcanic activity from Cretaceous up to Lower Tertiary. Secondly, intrusive andesitic rocks in the Pohang basin, which are dated to be $21.8{\pm}2.8Ma$ (Jin et al., 1988) are found out to be 15 Ma old in coincindence with the age of host strata of 16.5 Ma. Thirdly, The Quaternary basalt (911213-5 and 911213-6) of Tateiwa(1924) is not homogeneous regarding formation age and petrological characteristics. The basalt in the Changgi basin show the age of $19.92{\pm}0.47$ and $22.05{\pm}0.67$ (Miocene). The basalt (911213-8) in Sangjond-ri, which intruded Nultaeri Trachytic Tuff is dated to be $20.55{\pm}0.50Ma$, which means Changgi Group is older than this age. The Yeonil Basalt, which Tateiwa described as Quaternary one shows different age ranging from Lower Miocene to Upper Miocene(cf. Jin et al., 1988: sample no. 93-33: $10.20{\pm}0.30Ma$). Therefore, the Yeonil Quarterary basalt should be revised and divided into different geologic epochs. Fourthly, Yeonil basalt of Tateiwa (1926) in the Eoil basin is correlated to the Yeonil basalt in the Changgi basin. Yoon (1989) intergrated both basalts as Eoil basaltic andesitic volcanic rocks or Eoil basalt (Yoon et al., 1991), and placed uppermost unit of the Changgi Group. As mentioned above the so-called Quarternary basalt in the Eoil basin are not extruded or intruaed simultaneously, but differentiatedly (14 Ma~25 Ma) so that they can not be classified as one unit. Fifthly, the Yongdong-ri formation of the Pomgogri Group is intruded by the Eoil basalt (911214-3) of 18.35~0.62 Ma age. Therefore, the deposition of the Pomgogri Group is completed before this age. Referring petrological characteristics, occurences, paleomagnetic data, and relationship to other Eoil basalts, it is most provable that this basalt is younger than two others. That means the Pomgogri Group is underlain by the Changgi Group. Sixthly, mineral composition of the basalts and andesitic rocks from the 4 basins show different ground mass and phenocryst. In volcanic rocks in the Pohang basin, phenocrysts are pyroxene and a small amount of biotite. Those of the Changgi basin is predominant by Labradorite, in the Eoil by bytownite-anorthite and a small amount pyroxene.

• Economic and Environmental Geology
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• v.19 no.3
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• pp.179-192
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• 1986

In the Bupyeong district, Mesozoic pyroclastic rocks, intrusive breccia, granites and felsic porphyries comprise a volcano-plutonic complex, overlying and intruding the Precambrian Gyeonggi gneiss complex. pyroclastic rocks, consisted mainly of rhyolitic welded tuffs, form a topographic circular structure about 10 kilometers in diameter. Granites and felsic porphyries which intruded the pyroclastic rocks are distributed in the inner side and also along the outer margin of the circular structure. K-Ar ages of two granite bodies(biotite), 162 and $148{\pm}7$ Ma, and that of the intrusive rhyolite (whole rock), $121{\pm}6$ Ma indicate that a series of volcano-plutonic igneous activity occurred between Jurassic and early Cretaceous age. Petrochemical characteristics suggest that the pyroclastic rocks, granites and felsic porphyries were originated from the comagmatic source. From the evidences of field occurrence, petrochemical and geochronological characteristics of igneous rocks and the geologic structures, it is believed that the igneous rocks in the Bupyeong district were formed during a Jurassic to early Cretaceous resurgent caldera evolution.

• The Journal of the Petrological Society of Korea
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• v.17 no.1
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• pp.36-43
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• 2008

Many plutonic rock fragments of granitic composition were collected from the Deception Island. We obtained K-Ar ages of $62.5{\pm}1.2\;Ma$ and $140.7{\pm}2.7\;Ma$ from the two samples. Such result contradicts the general belief that most of the volcanic rocks of Deception Island are products of very recent activities and their maximum age does not exceed 200 ka. On the other hand, Mesozoic to Cenozoic rocks produced by subduction-related active magmatism have been reported from both South Shetland Islands and Antarctic Peninsula, located to the north and south of the Deception Island respectively. Also, various kinds of plutonic rocks with granitic composition are distributed widely. Therefore, plutonic rock fragments with granitic composition discovered from the Deception Island seem to indicate their derivation by capturing granitic crustal material underlying volcanic edifice during the volcanic activities, instead of differentiation from magmas related with recent volcanism. Ages and rock types of the plutonic rock fragments suggest arc-related origin just as adjacent South Shetland Islands and Antarctic Peninasula.

• Economic and Environmental Geology
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• v.33 no.5
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• pp.367-377
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• 2000

The purpose of this study is to elucidate the source of U anomaly formed in stream water of the drainage system around the Shinbo talc mine area based on the O, H, S and Sr isotopic characteristics of water masses and wall rocks. The ${\delta}$D and ${\delta}^{18}O$ of surface and ground waters show highly restricted range and plotted on the same meteoric water line, indicating that they are all originated from the meteoric water. The ${\delta}^{34}S$value of the ground water containing high U shows slightly negative (-0.2${\textperthousand}$) and quite distinct from those of the other surface and ground waters that are similar to those of wall rocks (>5.8${\textperthousand}$), indicating that they have a different S isotopic fractionation or less probably, source. The $^{87}Sr/^{86}{Sr}$ratios of water masses around the Shinbo talc mine area show a variable range from 0.724325 to 0.744928, but tend to increase with increasing U concentration of water mass. Although it is not possible to determine precisely the source rock of U anomaly formed in the hydrologic system around the Shinbo talc mine, the evidence obtained from the Sr isotopic compositions strongly suggests that coal schist and/or pegmatite vein could be the most likely candidate for the source rock.

• Economic and Environmental Geology
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• v.30 no.6
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• pp.603-612
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• 1997

Cretaceous sedimentary-volcanoclastic formations of the Kyeongsang Supergroup were intruded by granitic rocks in the late Cretaceous and early Tertiary. In the Euiseong and Shinryeong area, these intrusives have various compositions including gabbro, diorite，biotite granite and feldspar porphyry. Associated volcanic rocks consist of two chemically distinct types: the bimodal suite of basalt and rhyolite in the Keumseongsan caldera, and the felsic suite of andesite and rhyolite in the Sunamsan-Hwasan calderas. Most rocks are subalkaline, and follow a typical differentiation path of the calc-alkaline magma. The granitic rocks can be distinguished chemically from the volcanics by high Zr/Y ratios. Differences in Zr/Y and K/Y ratios between the two volcanic suites can be accounted for by mantle source and fractionation. Chondrite-normalized trace element abundances of granitic rocks are depleted in Th and K, whereas those of the Keumseongsan rhyolites are depleted in Sr and Ti. Rb, La and Ce is enriched in rhyolites of the Sunamsan-Hwasan calderas. $Rb-SiO_2$ and Rb-Y+Nb discrimination diagrams suggest that the intrusives and volcanics have a volcanic arc setting. K-Ar ages indicate four plutonic episodes : diorite (89 Ma), granite (66~62 Ma), granite and porphyry (55~52 Ma) and gabbro (52~45 Ma), and two volcanisms : bimodal basaltic and rhyolitic volcanism (71~66 Ma) in the Keumseongsan caldera, and felsic andesitic and rhyolitic volcanism (61~54 Ma) in the Sunamsan-Hwasan calderas. Geochemical and age data thus suggest that the igneous rocks are related to several geologic episodes during the late Cretaceous to early Tertiary.

• Geosciences Journal
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• v.22 no.6
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• pp.1001-1013
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• 2018

A new type of uranium occurrence in Korea was identified in pegmatitic and hydrothermally altered granite in the Daejeon area. The U-bearing parts typically include muscovite, pink-feldspar and sericite as alteration minerals. In this study, the geochemical characteristics and alteration age of the granitic rocks were examined to provide evidence for hydrothermally-enriched uranium. The K-Ar ages of muscovite coexisting with U-bearing minerals were determined as 123 and 128 Ma. The U-bearing rocks have relatively low ($CaO+Na_2O$), high $K_2O$ contents, and high alteration index values by major element geochemistry. The trace element geochemistry shows that the uraniferous rocks have significantly low Th/U ratios and strongly differentiated features. The rare earth element patterns indicate that the uraniferous rocks have a low total REE and LREE contents with depletion of Eu. Considering the geochemical variation of the granitic rock major, trace and rare earth elements, it can be concluded that uranium enrichment in pegmatites and altered granite should be genetically related to post-magmatic hydrothermal alteration of K-metasomatism after emplacement of the two-mica granite. This is the first report for geochemical characteristics of Mesozoic granite-related U-occurrences in South Korea. This study will help further research for uranium deposits with similarities in geological setting, mineralogy and age data between South China and Korea, and can also be expected to help solve the source problems related to high uranium concentrations in some groundwater occurring in the granitic terrane.

• The Journal of the Petrological Society of Korea
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• v.22 no.2
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• pp.83-115
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• 2013

Erroneous fission-track (FT) ages caused by an inappropriate calibration in the initial stage of FT dating were redefined by re-experiments and zeta calibration using duplicate samples. Revised FT zircon ages newly define the formation ages of Yucheon Group rhyolitic-dacitic tuffs as Late Cretaceous to Early Paleocene ($78{\pm}4$ Ma to $65{\pm}2$ Ma) and Gokgangdong rhyolitic tuff as Early Eocene ($52.1{\pm}2.3$ Ma). In case of the Early Miocene volcanics, FT zircon ages from a dacitic tuff of the upper Hyodongri Volcanics ($21.6{\pm}1.4$ Ma) and a dacitic lava of the uppermost Beomgokri Volcanics ($21.3{\pm}2.0$ Ma) define chronostratigraphies of the upper Beomgokri Group, respectively in the southern Eoil Basin and in the Waeup Basin. A FT zircon age ($19.8{\pm}1.6$ Ma) from the Geumori dacitic tuff defines the time of later dacitic eruption in the Janggi Basin. Based on FT zircon ages for dacitic rocks and previous age data (mostly K-Ar whole-rock, partly Ar-Ar) for basaltic-andesitic rocks, reference ages are recommended as guides for stratigraphic correlations of the Miocene volcanics and basements in SE Korea. The times of accumulation of basin-fill sediments are also deduced from ages of related volcanics. Recommended reference ages are well matched to the whole stratigraphic sequences despite complicated basin structures and a relative short time-span. The Beomgokri Group evidently predates the Janggi Group in the Eoil-Waeup basins, while it is placed at an overlapped time-level along with the earlier Janggi Group in the Janggi Basin. Therefore, the two groups cannot be uniformly defined in a sequential order. The Janggi Group of the Janggi Basin can be evidently subdivided by ca. 20 Ma-basis into two parts, i.e., the earlier (23-20 Ma) andesitic-dacitic and later (20-18 Ma) basaltic strata.

• The Journal of the Petrological Society of Korea
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• v.15 no.4 s.46
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• pp.167-179
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• 2006

Division of granites in the Galmal-Yeonbug area, northern Gyeonggi, can be grey hornblende biotite granite (JHBG), biotite granite (JBG) and pink hornblende biotite granite (CHBG) by lithofacies. JHBG of small stock occurs as medium-grained with grey color and minute sphene. JBG occurs as medium-grained and light grey to grey in the north-east part of the area. The main study target CHBG covers in the north-southeast part of the area, and occurs medium-to coarse-grained with pink color. CHBG shows partly minute miaroles, and pegmatitic pocket with druse texture. From the mineral age data (K-Ar method). JHBG and JBG and CHBG are the igneous activity products of Daebo orogeny with different Jurassic and Bulgugsa disturbance of Cretaceous, respectively. And the age data also agree with geologic occurrences and interpretations of the granites in the field. CHBG consists of quartz, plagioclase, alkali-feldspar, biotite, hornblende, allanite, apatite, zircon, some calcite and opaques. Among them, alkalifeldspar and calcite occur characteristically in mostly perthitic othoclase and secondary filling of minutely miarolitic cavity, respectively. In modal analysis and QAP diagram, CHBG plots in granite field, and especially boundary of monzo-and syeno-granite fields. From the major oxide variations, molar A/CNK, $SiO_{2}\;vs\;K_{2}O$, AMF and so on, CHBG belongs to the acidic, peraluminous and high-K calc-alkaline, and was late differentiation product of single granitic magma. Barium and strontium have also dominantly differentiation trend, and in CaO vs Sr and $K_{2}O$ vs Sr, Sr was more participitated in the fractionation of plagioclase than that of alkali-feldspar. Normalized REE concentrations to chondrite value have parallel and gradual LREE enrichment and HREE depletion patterns, and weak Eu negative anomalies and narrow ranges of normalized Eu can suggest that plagioclase fractionations occurred mildly in the whole CHBG.