The Journal of the Petrological Society of Korea (암석학회지)

The Petrological Society of Korea (한국암석학회)
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$^{230}$ Th/$^{234}$ U disequilibrium dating of fracture-filling carbonate veins from the Ipsil and Janghangri fault zones, Gyeongju, Korea by multiple collector inductively coupled plasma mass spectrometry

다검출기 유도결합 플라즈마 질량분석기를 이용한 경주 입실, 장항리 단층 파쇄대 충진 탄산염암 맥의 $^{230}Th/^{234}U$ 비평형 연대측정

  • 정창식 (한국기초과학지원연구원 동위원소분석팀) ;
  • 최만식 (한국기초과학지원연구원 동위원소분석팀) ;
  • 김현철 (한국기초과학지원연구원 동위원소분석팀) ;
  • 임상복 (한국원자력안전기술원 규제기술연구부)
  • Published : 2001.12.01
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Abstract

We report $^{230}Th/^{234}U$ disequilibrium ages of fracture-filling carbonate veins from the Ipsil and Janghangri fault zones, Gyeongju, Korea by multiple collector inductively coupled plasma mass spectrometry. The U and Th fraction was extracted from totally dissolved samples by rapid and convenient coprecipitation and ion exchange chemistry. The recovery was around 80% for Th and 70% for U. The $^{234}U/^{238}U,\;^{230}Th/^{232}Th$ ratios were analysed for this preconcentrated fraction and the U/Th ratio was directly analysed for untreated sample solution. The $^{234}U-^{230}Th$ system is in secular equilibrium for the Ipsil carbonate samples, supporting previously reported ESR ages. The detrital-corrected $^{230}Th/^{234}U$ age of the Janghangri carbonate samples is $48\pm$41 ka, which constrains the minimum age of the fracture zone.

경북 경주시 인근의 제4기 추정단층 중 입실단층과 장항리단층의 파쇄대를 충진하고 있는 탄산염암맥을 대상으로 다검출기 유도결합 플라즈마 질량분석기를 이용한 $^{230}$ $Th^{234}$ U 비평형 연대를 측정하였다. 완전히 녹인 시료로부터 공침과 이온교환화학을 통해 간편하게 U, Th을 단체분리하였는데 회수율은 Th 80%, U 70% 정도였다. 이 부분으로부터 기기 조건이 최적화된 다검출기 유도결합 플라즈마 질량분석기를 이용하여 $^{234}$ $U^{238}$ $U^{230}$ $Th^{232}$ Th비를 분석하였고 U/Th비는 처리하지 않은 시료로부터 직접 분석하였다. 분석 결과 입실 단층의 탄산염암 맥은 $^{234}$ U-$^{230}$ Th 시차평형에 도달하여 기존의 ESR 연대측정 결과를 지지하였으며 쇄설성 부분이 보정된 장항리단층 탄산염암 맥의 $^{230}$$Th^{234}$ /U 비평형 연대는$ 48\pm$41 ka로서 파쇄대의 최소 형성시기를 지시한다.

Keywords

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