Abstract

옥천변성대 계명산층 변성화산암에서 분리한 저어콘의 일부 입자들 연변부에는 덧성장 누대가 잘 발달되어 있음이 발견되었다. 이러한 덧성장 누대들은 대체로 낮은 Th/U 비율을 갖는 것으로 확인되었으며, 계명산층 변성화산암이 변성작용을 받는 동안에 생성된 것으로 판단된다. 이 중에서 비교적 넓은 폭을 가진 구역들에 대하여 SHRIMP U-Pb 분석을 할 수 있었다. 분석결과 <TEX>$259.7{\pm}3.3Ma$</TEX> (n=8, <TEX>$2{\sigma}$</TEX>)의 일치곡선 연령을 구할 수 있었으며, 이 연령은 계명산층 변성화산암의 변성시기를 나타낸다. We identified well developed overgrowth rims from several zircon grains separated from the Gyemyeongsan metavolcanics of the Okcheon Metamorphic Belt. Such overgrowth rims reveal generally quite low Th/U ratios indicating formation during the metamorphism. We were able to conduct SHRIMP U-Pb spot analyses from the relatively wide overgrowth rims and determined a concordia age of <TEX>$259.7{\pm}3.3Ma$</TEX> (n=8, <TEX>$2{\sigma}$</TEX>), which indicates timing of the regional metamorphism occurred in the Gyemyeongsan Formation.

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