Korean Journal of Mineralogy and Petrology (광물과 암석)

The Petrological Society of Korea & The Mineralogical Society of Korea (한국암석학회 & 한국광물학회)
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Geochemical Implication of Rare Earth Element pattern and Rb-Sr mineral isochron from consituent minerals in the Naedeokri-Nonggeori granite, Yeongnam Massif, Korea

영남육괴 북동부 내덕리-농거리 화강암내 구성광물의 희토류원소 분포도 및 Rb-Sr 광물연대의 지구화학적 의의

  • Seung-Gu Lee (Geology & Space Research Division, Korea Institute of Geoscience and Mineral Resources) ;
  • SeungRyeol Lee (Geologic Hazards Research Division, Korea Institute of Geoscience and Mineral Resources)
  • 이승구 (한국지질자원연구원 국토우주지질연구본부) ;
  • 이승렬 (한국지질자원연구원 지질재해연구본부)
  • Received : 2022.12.01
  • Accepted : 2023.06.13
  • Published : 2023.06.30
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Abstract

The Naedeokri and Nonggeori granites are early Proterozoic granites of the Taebaek-Sangdong area in the northeastern part of the Yeongnam Massif. In this paper, rare earth elements (REEs) concentrations of the minerals in Naedeokri and Nonggeori granites and Rb-Sr mineral isochron age are reported. Except zircon, the constituent minerals such as mica, feldspar, quartz, and tourmaline show LREE-enriched and HREE-depleted REE patterns with relatively large Eu negative anomaly. However, zircon has geochemical characteristic of LREE- and HREE-enriched REE pattern with large Eu positive anomaly. This pattern suggests that zircon should be hydrothermal zircon due to deuteric hydrothermal alteration. In addition, the Rb-Sr mineral age of Naedeokri granite indicates an age value of 1.814±142(2σ) Ma. The Rb-Sr whole rock age including pervious data of Naedeokri and Nogggeori granite indicates an age value of 1,707±74(2σ) Ma. This value is younger than the Sm-Nd isochron of 1.87 Ga, indicating that the Rb-Sr isotope system may be re-homogenized by hydrothermal alteration during the transition from a magmatic to a hydrothermal system.

내덕리 화강암과 농거리 화강암은 영남육괴 동북부의 태백-상동지역에서 분포하는 고원생대 화강암이다. 이 단보에서는 내덕리 화강암과 농거리 화강암에서 추출된 광물들에 대해 희토류원소의 함량측정 및 이들 광물들로 부터의 Rb-Sr 광물연대를 구함으로써 내덕리-농거리 화강암의 지구화학적 진화사를 재조명할 수 있는 틀을 마련하고자 하였다. 운석으로 규격화한 희토류원소 분포도에서는, 저어콘을 제외한 흑운모, 장석, 석영, 전기석 등 모든 주구성광물은 경희토류가 부화되어 있고, 중희토류가 결핍된 희토류원소 분포도를 보여주고 있다. 저어콘의 경우 Eu의 강한 부(-)의 이상과 더불어 경희토류와 중희토류 모두 부화된 특성을 보여주는데. 이는 열수기원임을 지시하는 증거라 할 수 있다. 그리고 Rb-Sr 광물연대에 있어서 광물분리한 시료만을 이용한 Rb-Sr 광물연대는 1.814±142(2σ) Ma의 연대치를 지시해주었고, 기존의 자료와 함께 통합하여 계산했을 때는 1,707±74(2σ) Ma의 연대치를 지시해주었다. 이 광물연대값은 겉보기에서는 기존의 1.72 Ga Rb-Sr 전암연대보다는 더 오래됐고, 1.87 Ga의 Sm-Nd 전암연대보다는 더 젊다. 이와 같이 광물연대와 전암연대가 다르게 나타나는 것은, 저어콘의 희토류원소 분포도가 지시해주는 바와 같이 Rb-Sr 동위원소계가 화강암의 정치 후 열수변질을 받았음을 지시해준다고 해석된다.

Keywords

Acknowledgement

본 연구는 한국지질자원연구원 주요사업인 국토 지질조사 및 지질도-지질주제도 발간(과제번호 23-3111-1, GP2020-003) 및 한국연구재단의 기본연구사업(화강암질 마그마의 분화과정이 희토류원소의 방사성 동위원소와 안정동위원소 조성변화에 미치는 영향(2020R1F1A1075924, NP2020-012) 과제의 지원 하에 수행되었다. 이 기술보고의 내용이 향상되도록 세밀하게 검토해주신 부경대학교의 박계헌 교수님과 익명의 심사위원께 깊은 감사드립니다.

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