• The Journal of the Petrological Society of Korea
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• v.14 no.4 s.42
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• pp.226-236
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• 2005

Using the concept of granite suite/supersuite we hierarchically divided the Triassic granites in South Korea which have spatio-temporally close relationships each other. Among the Triassic granites in the Okcheon belt (western Yeongnam massif), the Baegrok granite and the Jeomchon granite can be grouped into one suite, the Baegrok suite, whereas the Cheongsan granite into the Cheongsan suite. These two suites can be grouped again into a larger supersuite, the Baegrok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Three Triassic granites in the Gyeongsang basin - the Yeongdeok granite, the Yeonghae granite, and the Cheongsong granite - can be grouped into the Yeongdeok suite, Yeonghae suite and Cheongsong suite, respectively. These three suites can be grouped again into a larger supersuite, the Yeongdeok supersuite, on the basis of the similarity in the source rocks and the contrasts in the petrographic and geochemical characteristics. Nd-Sr isotopic signatures for the Baegrok supersuite are quite distinct from those for the Yeongdeok supersuite, indicating that the source materials of each granitic magma were not identical. The source rocks for the Baegrok supersuite are thought to be a mixture of two crustal components of the Yeongnam massif, whereas those for the Yeongdeok supersuite to be a mixture of the depleted mantle with the crustal components of the Yeongnam massif. The fact that the two contemporaneous granite supersuites were derived from the different sources can be explained by the difference of the tectonic environments where the granitic magmas were produced.

• The Journal of the Petrological Society of Korea
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• v.9 no.1
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• pp.40-50
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• 2000

This study is aimed at elucidating the source rocks of the Hayang strata in the northeastern part of the Gyeongsang Basin. Zircon morphology was analyzed for sandstones from the Iljig, Hupyeongdong, and Jeomgog formations of the Hayang Group and Precambrian gneisses and Jurassic granites. Generally, the composite zircon crystals extracted from the basement rocks and the Hayang Group sandstones show short prismatic to middle prismatic shapes. {110)={100) prism type is dominant and (101) pyramid is the average of the zircon morphology data. Zircon index@) and the shape trend characteristics clearly show that the zircon crystal forms of the Iljig and Hupyeongdong sandstones are dominantly similar to those of the biotite banded gneiss and granite gneiss of Precambrian age. Zircon morphology of the Jeomgog sandstones is dominantly similar to those of the Jurassic granites. Referring to the reported paleocurrent result, the source rocks of the Iljig and Hupyeongdong formations are mainly the Precambrian gneisses distributed in the southeastern and northeastern parts, respectively. And Jeomgog sandstones were mainly derived from Cheongsong granite at Cheongsong uplift region in the eastern part. At the time of completion of the Hupyeongdong sedimentation, the Precambrian basement rocks were severely eroded and formed low topography. During the Jeomgog period, the Jurassic granites which intruded the Precambrian basement began to crop out on the surface. The basin widely extended toward the east and the exposed Jurassic granite of Cheongsong uplift region actively supplied the sediments to the basin.

• The Journal of the Petrological Society of Korea
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• v.15 no.4 s.46
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• pp.180-193
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• 2006

The Gilan area in the central-northern part of Uiseong Block of Cretaceous Gyeongsang Basin is composed of Precambrian metamorphic rocks, Triassic Cheongsong granite, Early Cretaceous Hayans Group, and Late Cretaceous-Paleocene igneous rocks. In this area, the faults of various directions are developed: Oksan fault of $NS{\sim}NNW$ trend, Gilan fault of NW trend, Hwanghaksan fault of WNW trend, and Imbongsan fault of EW trend. Several fracture sets with various geometric indicators, which determine their relative timing (sequence and coexistence relationships) and shear sense, we well observed in the Cheongsong granite, the basement of Gyeongsang Basin. The aim of this study is to determine the development sequence of extension fractures and the movement sense of shear fractures in the Gitan area on the basis of detailed analysis of their geometric indicators (connection, termination, intersection patterns, and cross-cutting relations). This study suggests that the fracture system of the Gilan area was formed at least through seven different fracturing events, named as Pre-Dn to Dn +5 phases. The orientations of fracture sets show (W) NW, NNW, NNE, EW, NE in descending order of frequency. The orientation and frequency patterns are concordant with those of faults around and in the Gilan area on a geological map scale. The development sequence and movement sense of fracture sets are summarized as follows. (1) Pre-Dn phase: extension fracturing event of $NS{\sim}NNW$ and/or $WNW{\sim}ENE$ trend. The joint sets of $NS{\sim}NNW$ trend and of $WNW{\sim}ENE$ trend underwent the reactivation histories of sinistral ${\rightarrow}$dextral${\rightarrow}$sinistral shearing and of (dextral${\rightarrow}$) sinistral shearing with the change of stress field afterward, respectively. (2) Dn phase: that of NW trend. The joint set experienced the reactivations of sinistral${\rightarrow}$dextral shearing. (3) Dn + 1 phase: that of $NNE{\sim}NE$ trend. The joint set was reactivated as a sinistral shear fracture afterward. (4) Dn +2 phase: that of $ENE{\sim}EW$ trend. (5) Dn +3 phase: that of $WNW{\sim}NW$ trend. (6) Dn+4 phase: that of NNW trend. The joint set underwent a dextral shearing after this. (7) The last Dn +5 phase: that of NNE trend.

• 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.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2003.05a
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• pp.53-53
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• 2003

남한에 분포하는 현생 화강암류는 트라이아스기-쥬라기의 소위 대보화강암과 백악기-제3기의 불국사화강암으로 분류되어 왔다. 대보조산운동은 대동누층군의 퇴적이후에 일어난 조구조운동을 지칭하므로 트라이아스기의 화강암을 포함하는 대보화강암이라는 명칭은 그와 사실상 직접적인 관계는 없다. 트라이아스기-쥬라기의 화강암은 영덕, 청송 암체 외에는 경상분지 밖에 위치하고 백악기-제3기의 화강암은 속리산, 월악산 암체 외에는 경상분지 안쪽에 주로 분포한다. 트라이아스기-쥬라기의 화강암 중 영광-대전-청주-충주-원주-강릉 방면에 걸쳐 북동-남서 방향으로 분포하는 화강암질 저반은 남한에서 가장 넓은 면적을 차지하는 화강암체지만 신뢰할만한 연대측정 자료가 매우 부족한 실정이다. 이 화강암질 저반에 대해서는 Rb-Sr, K-Ar법이 해답을 주기 어렵다. 예를 들어 청주-음성-증평 지역의 화강암류에 대한 Rb-Sr 전암 자료는 분산이 심하며 약 380 Ma에 해당되는 초시선을 보여 기원물질의 불균질성 내지 불완전한 혼합 효과를 반영하고 있다. 옥천대와 영남육괴에 분포하는 일부 화강암체에 대해 잘못 보고된 Rb-Sr 전암연대 역시 모두 중광물의 U-Pb 연대보다 오래된 값을 보이는 것으로 보아 이들은 생성 당시부터 일정한 $^{87}$ Sr/$^{86}$Sr 초기치를 가지지 않고 Rb/Sr 비에 따른 양(+)의 기울기를 가졌음이 확실하다. 과잉의 방사기원 Ar을 가지거나 폐쇄온도가 낮은 광물들을 대상으로 한 K-Ar 자료 역시 화강암체의 관입편대를 정확하게 지시할 수는 없다. 우리는 이에 대한 연구의 일환으로 충청남도 청원군의 물류센터에서 채취한 중립질의 흑운모화강암 한 시료에 대한 U-Pb 스핀연대측정 결과를 다음과 같이 보고한다. $^{206}$ Pb$^{*}$ /$^{238}$ U age = 174.6$\pm$2.7 Ma $^{207}$ Pb$^{*}$ /$^{235}$ U age = 170.3$\pm$14.6 Ma $^{207}$ Pb$^{*}$ /$^{206}$ Pb sup */ age = 111$\pm$187 Ma 위에서 볼 수 있듯이 청주화강암의 스핀에 대해 콘코던트(concordant)한 연대가 얻어졌으며 자료의 오차, 스핀의 U-Pb계에 대한 폐쇄온도 및 화강암의 솔리더스(solidus)를 고려할 때 $^{206}$ Pb$^{*}$ /$^{238}$ U 연대인 174.6$\pm$2.7 Ma를 관입정치시기로 해석한다. 동일 시료의 흑운모에 대해서는 145 Ma의 Rb-Sr 연대가 얻어졌으며 따라서 관입이후 약 35$0^{\circ}C$까지 대략 1$0^{\circ}C$/Ma의 냉각속도를 구할 수 있었다. 청주화강암의 쥬라기 중기 연대는 영광-대전-청주-충주-원주-강릉 지역의 화강암질 저반이 대동누층군 퇴적 이후에 일어난 지구조 사건과 연관되었을 가능성을 지시하지만 이를 확인하기 위해서는 더 많은 자료가 요구된다. 우리는 현재 충주, 괴산 지역의 화강암체에 대해서도 스핀 연대측정을 수행중에 있으며 이들 자료를 암상을 구분하여 해석한다면 우리나라 중생대 지구조운동에 대한 새로운 사실이 밝혀질 수 있을 것으로 믿는다.

• The Journal of the Petrological Society of Korea
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• v.18 no.4
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• pp.293-305
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• 2009

The Gilan-Cheongsong area, which is in contact with Yeongyang and Uiseong Blocks of Gyeongsang Basin, Korea, consists of Precambrian metamorphic rocks, Triassic Cheongsong granite, Cretaceous sedimentary rocks(Iljik, Hupyeongdong, Jeomgok Formations), and Cretaceous igneous rocks(andesite, quartz porphyry, felsite). In this area are developed faults trending in (W)NW, NNW, ENE, NS, (N)NE directions which are representative in the Gyeongsang Basin. We analyzed the geometric and kinematic characteristics of fracture systems to inquire into movement history and sense of these faults in this area. This study suggests that these faults were mainly strike-slip movement. The orientations of fracture sets show ENE, NNW, (W)NW, (N)NE, NS in descending order of frequency. Their prolongation presents (W)NW, NNW, ENE, (N)NE, NS in descending order of predominance, and also agrees with that of faults in this area. The development sequence and movement sense of fracture sets are summarized as follows; (1) (W)NW: dextral shearing $\rightarrow$ (2) (W)NW and NNW: conjugate shearing(the former: dextral, the latter: sinistral) $\rightarrow$ (3) NNW: dextral shearing $\rightarrow$ (4) (W)NW: sinistral shearing $\rightarrow$ (5) ENE: dextral shearing $\rightarrow$ (6) ENE and NS: conjugate shearing(the former: sinistral, the latter: dextral) $\rightarrow$ (7) (N)NE: sinistral shearing, and this result is closely associated with the development sequence and movement sense of faults developed in this area.

• 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.

• Journal of the Korean association of regional geographers
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• v.15 no.3
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• pp.328-336
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• 2009

This study aims to figure out the first-class geomorphic resources included in Yeongyang map sheet. The fieldwork shows that the first-class geomorphic resources are found mainly along the Banbyeoncheon(incised meander) and The Soojungsa(temple) valley that retain beautiful landscapes such as river cliff(including river bluff), water fall, pot hole. tafoni, canyon Such geomorphic resources are highly concerned with Bulguksa intrusive rocks (Cretaceous). Especially The Seonbawi and The Namipo(Yeongyang county), The Punghojung and its vicinities (Cheongsong county), and The Soojungsa(temple) valley are important in viewpoint of story telling tour marketing.

• The Journal of the Petrological Society of Korea
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• v.25 no.4
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• pp.349-360
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• 2016

The Bunam Stock ($29.5km^2$ area) is an outcrop of plutonic complex classified four facies: coarse-grained granite, quartz monzodiorite, granodiorite and fine-grained granite. Three facies except the last one exhibit very irregular boundaries with gradational compositional variations between both facies and show concentric zoning from the central quartz monzodiorite through granodiorite to outer coarse-grained granite. Mafic microgranular enclaves (MME) commonly occur in granodiorite. Some MMEs, have very fine-grained chilled margins and indentedly crenulate contacts, and display horizontally circular and vertically elongate shapes. Their shape and granularity indicate coeval flow and mingling of partly crystalline felsic and mafic magmas. MMEs exhibit dark fine-grained margins giving them a ellipsoidal form that has been attributed to undercooling of a mafic magma as blobs intruded into a felsic magma. The observed relations in the Bunam Stock identify that two endmembers are coarse-grained granite from a felsic magma and quartz monzodiorite from a mafic magma, and hybrid is granodiorite including MMEs. So they exhibit concentric zoning that lays the center on the mafic endmember due to magma mixing at the contacts of two magmas, when mafic magma injected into felsic magma. Thus the quartz monzodiorite may probably represent an ancient conduit of mafic magma transport through a granitic magma chamber. Mafic magma would rise through the conduit in which favorable conditions for magma mixing occurred. All these features suggest that they formed from mixing processes of calc-alkaline magma in the Bunam Stock.

• The Journal of the Petrological Society of Korea
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• v.26 no.3
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• pp.235-254
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• 2017

We investigate the geological history that formed geology and landscapes of the Juwangsan National Park and its surrounding areas. The Juwangsan area is composed of Precambrian gneisses, Paleozoic metasedimentary rocks, Permian to Triassic plutonic rocks, Early Mesozoic sedimentary rocks, Late Mesozoic plutonic and volcanic rocks, Cenozoic Tertiary rhyolites and Quaternary taluses. The Precambrian gneisses and Paleozoic metasedimentary rocks of the Ryeongnam massif occurs as xenolithes and roof-pendents in the Permian to Triassic Yeongdeok and Cheongsong plutonic rocks, which were formed as the Songrim orogeny by magmatic intrusions occurring in a subduction environment under the northeastern and western parts of the area before a continental collision between Sino-Korean and South China lands. The Cheongsong plutonic rocks were intruded by the Late Triassic granodiorite, which include to be metamorphosed as an orthogneiss. The granodiorite includes geosites of orbicular structure and mineral spring. During the Cretaceous, the Gyeongsang Basin and Gyeongsang arc were formed by a subduction of the Izanagi plate below East Asia continent in the southeastern Korean Peninsula. The Gyeongsang Basin was developed to separate into Yeongyang and Cheongsong subbasins, in which deposited Dongwach/Hupyeongdong Formation, Gasongdong/Jeomgok Formation, and Dogyedong/Sagok Formation in turn. There was intercalated by the Daejeonsa Basalt in the upper part of Dogyedong Formation in Juwangsan entrance. During the Late Cretaceous 75~77 Ma, the Bunam granitoid stock, which consists of various lithofacies in southwestern part, was made by a plutonism that was mixing to have an injection of mafic magma into felsic magma. During the latest Cretaceous, the volcanic rocks were made by several volcanisms from ubiquitous andesitic and rhyolitic magmas, and stratigraphically consist of Ipbong Andesite derived from Dalsan, Jipum Volcanics from Jipum, Naeyeonsan Tuff from Cheongha, Juwangsan Tuff from Dalsan, Neogudong Formation and Muposan Tuff. Especially the Juwangsan Tuff includes many beautiful cliffs, cayon, caves and falls because of vertical columnar joints by cooling in the dense welding zone. During the Cenozoic Tertiary, rhyolite intrusions formed lacolith, stocks and dykes in many sites. Especially many rhyolite dykes make a radial Cheongsong dyke swarm, of which spherulitic rhyolite dykes have various floral patterns. During the Quaternary, some taluses have been developed down the cliffs of Jungtaesan lacolith and Muposan Tuff.