The Journal of the Petrological Society of Korea (암석학회지)

The Petrological Society of Korea (한국암석학회)
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Petrological Evolution of the Saryangdo Tuff in Western Tongyeong

통영 서부 사량도응회암의 암석학적 진화

  • Lee, So Jin (Institute of Basic Science, Andong National University) ;
  • Hwang, Sang Koo (Institute of Basic Science, Andong National University) ;
  • Song, Kyo-Young (Korea Institute of Korea Institute of Geoscience and Mineral Resources)
  • 이소진 (안동대학교 기초과학연구소) ;
  • 황상구 (안동대학교 기초과학연구소) ;
  • 송교영 (한국지질자원연구원 국토지질연구부)
  • Received : 2019.03.18
  • Accepted : 2019.05.15
  • Published : 2019.06.30
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Abstract

The volcanic rocks in Saryangdo area are composed of Witseom Andesite, Punghwari Tuff, Araetseom Andesite, Obido Formation, Namsan Rhyolite and Saryangdo Tuff in ascending order. The volcanic rocks has a range of andesite-rhyodacite-rhyolite, which indicates calc-alkaline series and volcanic arc of orogenic belt. In Harker diagrams for trace element and REE pattern, these are also distinguished into so three groups(Witseom Andesite, Araetseom Andesite and Saryangdo Tuff) that each unit is interpreted to have originated in different magma chamber. The Saryangdo Tuff exhibits systematically(chemical zonations that gradually change) from lower dacite to upper rhyolite in section. The systematic sequence of compositional variations suggests that the tuffs were formed by successive eruptions of upper to lower part of a zoned magma chamber in which relatively dacitic magma is surrounded around rhyolitic magma of the central part. The zoned magma chamber was formed from marginal accretion and crystal settling that resulted form magmatic differentiations by fractional crystallization.

사량도 지역의 화산암류는 하부로부터 윗섬안산암, 풍화리응회암, 아랫섬안산암, 오비도층, 남산유문암 그리고 사량도응회암으로 구성된다. 이 화산암류는 안산암-유문데사이트-유문암의 범위를 가지며 칼크알칼리 계열이고 조산대의 화산호환경을 지시한다. 또한 이 화산암류는 미량원소 변화도와 REE 패턴에서 각기 다른 마그마챔버에서 유래된 것으로 해석되는 세 그룹(윗섬안산암, 아랫섬안산암, 사량도응회암)으로 나뉜다. 사량도응회암은 수직 변화도에서 하부에서 상부로 갈수록 데사이트에서 유문암까지 순차적으로 보여준다(점진적으로 변화하는 화학적 조성누대). 순차적인 일련의 조성 변화는 응회암이 중심부의 유문암질 마그마를 둘러싼 상대적으로 데사이트질인 마그마로 누대된 마그마챔버의 상부에서 하부의 연속적인 분출에 의해 형성되었음을 시사한다. 누대된 마그마챔버는 분별결정작용에 의한 마그마 분화과정으로 일어난 연변 누적 및 결정 퇴적으로부터 형성되었다.

Keywords

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Fig. 1. Geological map of the study area, showing sample locations of the whole rock chemical analysis (●) and the SHRIMP zircon U-Pb age dating (■).

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Fig. 2. Outcrop photographs and photomicrographs of the Saryangdo Tuff.

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Fig. 4. Harker variation diagram of the major and trace elements vs. SiO2 for the volcanic rocks of Saryangdo area. Symbols are the same as in Fig. 3.

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Fig. 5. Haker variation diagrams of some rare earth elements vs. Zr for the volcanic rocks of the Saryangdo area. Symbols are the same as in Fig. 3.

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Fig. 6. Chondrite nomalized REE patterns for the volcanic rocks of the Saryangdo area. Symbols are the same as in Fig. 3.

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Fig. 10. Schematic diagram showing compositional zonation (a, b) and eruption process (c, d) of Saryangdo Tuff (Rh, rhyolite; Da, dacite; An, andesite).

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Fig. 3. (a) Total alkalis vs. SiO2 (wt%) plotting for the volcanic rocks in the Saryangdo area. A curve diving between alkali (A) and sub-alkalic (SA) magma seriesis from Irvine and Baragar (1971), Kuno (1966); (b) Zr/TiO2-Nb/Y diagram for the volcanic rocks of the Saryangdo area(after Winchester and Floyd, 1976).

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Fig. 7. (a) Discriminant diagram of Rb as. Y+Nb showing the aparrent affinity of volcanic arc for the volcanic rocks of the Saryangdo area (after Pearce et al., 1984); (b) La/Yb vs. Th/Yb variation diagram for volcanic rocks of the Saryangdo area (after Condie, 1989). Symbols are the same as in Fig. 3.

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Fig. 8. (a) (Ce/Yb)N-CeN variation diagram distinguising between general petrogenetic processes by Gill (1981)(1; Effects of fractional crystallization, 2; Compositions of partial melts of peridotite, 3; Compositions of partial melts of eclogite, 4; Compositions of partial melts of average continental crust). (b) La/Yb-La diagram showing two different lines of both partial melting trend and differentiation trend(after Martin, 1987).

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Fig. 9. (a) Vertical spatial diagrams for major element from of Saryangdo Tuff; (b) Vertical spatial diagrams for trace element from of Saryangdo Tuff.

Table 1. Major element(wt%), trace element(ppm) and rare element(ppm) compositions for the Cretaceous volcanic rocks in Saryangdo area

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