한국광물학회지 (Journal of the Mineralogical Society of Korea)

  • 제28권3호
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  • Pages.221-231
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  • 2015
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  • 1225-309X(pISSN)
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  • 2288-7172(eISSN)
한국광물학회 (The Mineralogical Society of Korea)
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각섬석류를 활용한 하동지역 회장암체의 변성작용에 관한 연구

Metamorphism of Anorthositic Rocks with Respect to Amphiboles in Hadong Area

  • 곽지영 (경상대학교 지질과학과 및 기초과학연구소) ;
  • 최진범 (경상대학교 지질과학과 및 기초과학연구소)
  • Kwak, Ji Young (Department of Geology Sciences and Research Institute of Natural Sciences, Gyeongsang National University) ;
  • Choi, Jin Beom (Department of Geology Sciences and Research Institute of Natural Sciences, Gyeongsang National University)
  • 투고 : 2015.05.21
  • 심사 : 2015.09.09
  • 발행 : 2015.09.30
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초록

선캠브리아기의 지리산 편마암 복합체는 초기의 백립암상에서 후기의 각섬암상 또는 녹색편암상까지 후퇴변성작용을 받았으며, 편마암 복합체 내 관입한 하동 회장암체는 이 중 후기 변성작용의 영향을 받았다. 회장암체 내 주요 유색광물은 각섬석으로 이를 통해 변성조건 및 변성상에 관한 추정이 가능하다. 회장암체 내 각섬석은 개방니콜 하에서 주로 청녹색 내지 녹색을 나타내고, 반자형 내지 타형의 형태를 보인다. 일부 갈색의 각섬석 주변부로 청록색으로 변하는 누대조직(zonal texture)이 존재하고, 사방휘석 내에는 각섬석으로 변하는 반응부가 존재해 후퇴변성 내지 변질 양상을 보인다. 회장암을 구성하는 각섬석은 크기 및 산상에 따라 기질을 이루는 미정질의 각섬석[I 그룹 : 페로혼블렌드(ferrohornblende)]과 1 mm 이상의 크기를 보이며, 주로 불투명광물 내지 사장석과의 경계에서 산출되는 각섬석[II 그룹 : 페로파가사이트(ferropargasite)]으로 구분된다. 화학분석결과, 각섬석 내 $Al^{vi}$의 함량을 통해 회장암체의 변성압력이 5 kbar 이하의 저압의 조건이었음이 인지되는 한편, 각섬석 내 Ti 함량범위 및 각섬석+사장석+석류석+흑운모+녹니석의 광물조합을 통해 회장암체의 변성상이 각섬암상에 속하는 것으로 판단된다.

Precambrian Jirisan gneiss complex suffered retrograde metamorphism ranging from granulite facies to the amphibolite facies and/or greenschist facies. Intrusive anorthositic rocks in gneiss complex are influenced by late metamorphism. Mafic mineral in anorthositic rock composed mainly of amphiboles, which can anticipate the information about metamorphic conditions and metamorphic facies. Amphiboles from anorthositic rock show subhedral to anhedral in shape and mostly blueish green and/or green in colour in plane polarized light. Some of brownish amphiboles show zonal texture with brownish to blueish green in color from core to rim. Reaction parts in clinopyroxene which exchange with amphibole. It suggests retrograde metamorphism and/or alteration. Amphiboles composing anorthositic rocks can be classified into two types depending on the size and occurrence of amphibole. The first type is microcrystalline amphibole occurring matrix [Group I: ferrohornblende]. The second type is amphibole with 1 mm or larger in size, which is usually occurred in the boundary between opaque mineral and plagioclase [Group II: ferropargasite]. Electron microscopic analyses base on the $Al^{vi}$ composition in amphiboles suggest that the metamorphic pressure of anorthositic rock was low with 5 kbar or less. Ti compositional range in amphibole and representing hornblende+ plagioclase+garnet+biotite+chlorite mineral assemblage suggest that metamorphic facies of anorthositic rock is in amphibolite facies.

키워드

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