The Journal of the Petrological Society of Korea (암석학회지)

The Petrological Society of Korea (한국암석학회)
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CHIME Monazite Ages of Jurassic Foliated Granites in the Vicinity of the Gangjin Area, Korea

강진 인근 쥬라기 엽리상 화강암류의 CHIME 모나자이트 연대측정

  • Cho, Deung-Lyong (Division of Geology and Geoinformation, Korea Institute of Geoscience and Mineral Resources) ;
  • Kee, Weon-Seo (Division of Geology and Geoinformation, Korea Institute of Geoscience and Mineral Resources) ;
  • Suzuki, Kazuhiro (Center for Chronological Research, Nagoya University)
  • 조등룡 (한국지질자원연구원 지질기반정보연구부) ;
  • 기원서 (한국지질자원연구원 지질기반정보연구부) ;
  • Published : 2007.09.30
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Abstract

The CHIME (chemical Th-U-total Pb isochron method) dating on monazite was carried out for two foliated granites from a dextral ductile shear zone in the vicinity of Gangjin area, which is considered to be a southern extension of Sunchang shear zone. The result gives emplacement age of the medium-grained biotite granite and the coarse-grained biotite granite as $183.6{\pm}2.2Ma$(MSWD=0.21) and $171.7{\pm}4.0Ma$(MSWD=0.57), respectively. Microtextures of quartz and feldspar observed in the foliated granite are almost identical with those reported in Jurassic (ca 180 Ma) foliated granites from the Imsil-Namwon area of the Sunchang shear zone, and they constraint that the ductile deformation took place at temperature condition of $300{\sim}550^{\circ}C$. Assuming cooling curves of the foliated granites in this study are similar with those of Jurassic foliated granites from Imsil-Namwon area, dextral ductile shear in the Gangjin area would take place between 172 Ma and 150 Ma, about 10 Ma later than the previous estimation based on CHIME monazite ages.

순창전단대의 남쪽 연장이라 여겨지는 강진 인근에 분포하는 우수향 연성전단대의 엽리상 화강암류 2시료에 대한 CHIME 모나자이트 연대측정을 실시하여 중립질 흑운모 화강암과 조립질 흑운모 화강암의 관입시기에 해당하는 $183.6{\pm}2.2Ma$(MSWD=0.21)와 $171.7{\pm}4.0Ma$(MSWD=0.57)를 각각 얻었다. 이 연구의 엽리상 화강암에서 관찰되는 석영과 장석의 미구조적 특징은 순창전단대의 임실-남원 지역 쥬라기(약 180 Ma) 엽리상 화강암류에서 보고된 것과 대단히 흡사하며, 우수향의 연성전단작용이 $300{\sim}550^{\circ}C$의 온도조건에서 일어났음을 제한한다. 이 연구의 엽리상 화강암이 임실-남원 지역의 쥬라기 엽리상 화강암류와 유사한 냉각과정을 거쳤다고 가정하면 강진 지역의 우수향 전단작용의 시기는 172 Ma와 150 Ma사이에 일어났을 것이고, 이는 기존의 CHIME 모나자이트 연령에 근거한 추정보다 약 10 Ma 후기이다.

Keywords

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