• Title/Summary/Keyword: 소백산육괴

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Granulite xenoliths in porphyroblastic gneiss from Mt. Jiri area, SW Sobaegsan massif, Korea (소백산육괴 서남부 지리산지역의 반상변정질 편마암에서 산출되는 백립암질 포획암)

    • The Journal of the Petrological Society of Korea
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    • v.8 no.1
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    • pp.34-45
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    • 1999

  • Mafic granulite xenoliths are found in precambrian porphyroblastic gneiss of the Mt. Jiri area, SW Sobaegsan massif, Korea. The xenoliths are rounded to ellipsoidal in shape, 50-100 cm in length and coarse-grained with granoblastic and foliated texture. The xenoliths consist of orthopyroxene, garnet, biotite, plagioclase, quartz, ilmenite and secondary orthoamphibole. Orthopyroxene is mostly resorbed and rimmed by coronitic orthoamphiboles. Garnets occur as porphyblasts and are zoned with higher pyrope content in cores than in rims. Geothermo-barometry results yield conditions of about $800-850^{\circ}C$, 6 kb and $500^{\circ}C$, 4 kb for early and retrograde stages of equilibration, respectively. According to available geochronological data, it is suggested that the granulite facies metamorphism occurred prior to 2.1-1.9Ga and that the area was superimposed by the high-grade (over $600-700^{\circ}C$) metamorphism between 1.9-1.7Ga, followed by cooling during uplift.

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Geochemistry of Orthogneisses in the Seungju-Suncheon Area, Korea (승주-순천 지역에 분포하는 정편마암류의 지구화학적 특성)

  • Ahn, Kun-Sang;Oh, Chang-Whan;Park, Bae-Young
    • Journal of the Korean earth science society
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    • v.22 no.3
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    • pp.163-178
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    • 2001

  • Granite gneiss, pophyroblastic gneiss and leucocratic gneiss are widely distributed in the Seungju-Suncheon area, the southwestern part of the Sobacksan Massif, Korea. These orthogneisses show intrusive relationships in outcrops of the study area. This study focuses on the geochemical properties and the tectonic environments for the original rocks of these orthogneisses. The pophyroblastic gneiss is plotted in diorite and granodiorite domain, and granite gneiss and leucocratic gneiss are plotted in both of granodiorite and granite domains on lUGS silica-alkali diagram. Geochemical properies of major elements suggest that these rocks are sub-alkali rock series, and were formed from S-type magma which generated in syn-collision tectonic environment. Discrimination diagrams using HFS elements suggest that original rocks of the three orthogneisses were granitoid of calc-alkali rock series, and were formed in syn-collision environment.

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Pb-Pb Age of Marble from Muju, Korea (무주지역 대리암의 Pb-Pb 연대)

  • Park, Kye-Hun
    • The Journal of the Petrological Society of Korea
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    • v.5 no.1
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    • pp.84-88
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    • 1996

  • Pb isotope composition is analyzed from the rock chips of marbles intercalated between gneisses of Muju area and it shows very large variation ($^{206}Pb/^{204}Pb$=23.74~4142, $^{207}Pb/^{204}Pb$=16.32~18.43, $^{208}Pb/^{204}Pb$=36.42~39.75). The data points form well defined positive relationship on $^{206}Pb/^{204}Pb$ vs $^{207}Pb/^{204}Pb$ plot, which corresponds to $1.99{\pm}0.10$($2{\sigma}$) Ga. This age is very similar to the formation ages of the granitic gneisses from Buncheon and Cheondongri (Tanyang), and suggests that the fairly large volume of Sobaeksan Massif suffered regional metamorphism at this time. It is suggested that the most parts of Korean peninsula including Kyeonggi and Sobaeksan Massifs were very close each other and experienced a regional metamorphism together about 2.0 Ga ago from the fact that galenas from whole Korean Peninsula except Kyeongsang Basin and metamorphic rocks from Kyeonggi Massif also reveal a similar slope corresponding 2.0 Ga on Pb-Pb isotope plot.

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Structural Analysis of the North Sobaegsan Massif in the Sangun-myeon area, Bonghwa-gun, Korea (봉화군 상운면지역에서 북부 소백산육괴의 지질구조 해석)

  • 강지훈;김형식
    • The Journal of the Petrological Society of Korea
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    • v.9 no.4
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    • pp.254-270
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    • 2000

  • To clarify the geological structure of North Sobaegsan Massif in the Sangunmyeon area, Bonghwagun, Korea, where the Yecheon Shear Zone passes and the NE-SW and E-W trending structural lineaments are developed, the rock-structures of its main constituent rocks(Precambrian Won-nam Formation and Mesozoic Hornblende Granite) were examined. In this area, the geological structure was formed at least by four phases of deformation after the formation of gneissosity or schistosity of the Wonnam Formation: one deformation before D2 ductile shearing related to the for-mation of the Yecheon Shear Zone and two deformations after that. The NE-SW and E-W trending structural lineaments were formed by a giant open or gentle type of F4 fold, and their trends before D4 deformation are interpreted to be parallel to the orientation(ENE-WSW trend) of folded surface in the F4 hinge zone. The structural features of Dl-D3 deformations and their relative occurrence times are as follows. Dl deformation is formative period of the boudin structures and ENE-WSW trending isoclinal folds with sub-horizontal hinge lines and steeply inclined axial surfaces. D2 deformation is that of the mylonite foliation, stretching lineation and Z-shaped asymmetric folds related to top-to-the ENE dextral strike-slip shearing on the distinct foliations of Wonnam Formation(after intrusion of Mesozoic Hornblende Granite). D3 deformation is that of the ENE trending S-shaped asymmetric folds with sub-horizontal hinge lines and axial surfaces related to normal-slip shearing on the distinct foliations. It is expected that the result will be contributed to as valuable data for interpreting the tectonic evolution of the North Sobaegsan Massif and the Northeast Ogcheon Belt whose tectonic lineaments are changed from NE-SW to E-W trends at the Sindong-Bonghwa line.

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Geological Structure of Precambrian to Paleozoic metasedimentary rocks in the Janggunbng area, Korea -Crustal evolution and environmental geology of the central part of the North Sobaegsan Massif, Korea- (장군봉지역 선캠브리아대-고생대 변성퇴적암류의 지질구조 -북부 소백산육괴의 중앙부지역의 지각진화와 환경지질)

  • Gang, Ji Hun;Kim, Hyeong Sik;O, Se Bong
    • The Journal of the Petrological Society of Korea
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    • v.6 no.3
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    • pp.244-244
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    • 1997

  • The Janggunbong area(this study area) at the central-south part in the North Sobaegsan Massif, Korea, consists mainly of Precambrian(Wonnam and Yulri Formations)-Paleozoic [Joseon Supergroup(Jangsan Quarzite, Dueumri Formation and Janggum Limestone) and Pyeongan Group(Jaesan and Dongsugok Formations)] metasedimentary rocks and Mesozoic granitoid(Chunyang granite.) This study is to interpret geological structure of the North Sobaegsan Massif in the Jang-gunbong area by analysing rock-structure and microstructure of the constituent rocks. It indicates that its geological structure was formed at least by four phases of deformation after the formation of gneissosity(S0) in the Wonnam Formation and bedding plane(S0) in the Paleozoic metasedimentary rocks. The first phase deformation(D1) formed tight isoclinal fold(F1). Its axial plane(S1) strikes east-west and steeply dips north. Its axis (L1) subhorizontally plunges east-west. The second phase deformation(D2), which was related to ductile shear deformation, formed stretching lineation(L2) and shear foliation(S2). The sense of the shear movement indicates dextral strike-slip shearing(top-to-the east shearing). The third phase deformation(D3) formed open inclined fold(F3). Its axial plane(S3) strikes east-west and moderately or gently dips north. Its axis(L3) subhorizontally plunges east-west. The F3 fold reoriented the original north-dipping S1 foliation and D2 shear sense into south-dipping S1 foliation(top-to-the west shear sense on this foliation) at its a limb. The four phase of deformation(D4) formed asymmetric-type open inclined fold(F4) of NE-vergence with NW striking axial plane(S4) and NW-NNW plunging axis(L4). The F4 fold partly reoriented pre-D4 structural elements with east-west trend into those with north-south trend. Such reorientation is recognized mainly in the Paleozoic metasedimentary rocks.