경상분지 북동부 선백악기 기반암류와 백악기 하양층군 사암의 저어콘 결정 형태학 및 사암의 기원암

Zircon morphology of the Pre-Cretaceous basement rocks and Cretaceous Hayang Group sandstones in the northeastern part of Gyeongsang Basin and its implication to provenance of the sandstones

  • 발행 : 2000.03.01

초록

경상분지 북동부에 분포하는, 하양층군 사암의 기원암을 규명하기 위하여 일직층, 후평동층 및 점곡층의 층위별 사암과, 그 기반암인 선캠브리아기 편마암류와 쥬라기 화강암류에 대해 저어콘 지수값과 저어콘 결정의 형태학적 특징을 비교분석하였다. 저어콘 지수값과 형태학적 특징의 유사성에 바탕하여 하양층군 퇴적암의 기원암을 해석하면 일직층과 후평동층의 사암은 선캠브리아기의 화강편마암과 흑운모 호상편미암, 그리고 점곡층의 사람은 쥬라기 안동화감암과 청송화감암에서 각각 기원하였을 것으로 판단된다. 기존 연구자료에서 일직층 퇴적기에는 본역의 남동부에 위치하였던 편마암류가, 후평동층 퇴적기에는 본역 북동부의 편마암류가, 그리고 점곡층 퇴적기에는 본역 동부에 위치한 청송 융기부의 청송화강암이 퇴적물의 주 공급원이었음이 밝혀졌다. 후평동층이 퇴적을 완료할 쯤에는, 선캠브리아기 편마암류로된 기원지는 상당히 삭박당하여, 평탄화되면서 그 분포 면적이 협소해졌으며, 점곡층 퇴적기에는 편마암류를 관입한 쥬라기 화강암류가 본격적으로 침식을 당하기 시작하였고, 퇴적분지는 동쪽으로 확장하였던 것으로 해석된다.

This study is aimed at elucidating the source rocks of the Hayang strata in the northeastern part of the Gyeongsang Basin. Zircon morphology was analyzed for sandstones from the Iljig, Hupyeongdong, and Jeomgog formations of the Hayang Group and Precambrian gneisses and Jurassic granites. Generally, the composite zircon crystals extracted from the basement rocks and the Hayang Group sandstones show short prismatic to middle prismatic shapes. {110)={100) prism type is dominant and (101) pyramid is the average of the zircon morphology data. Zircon index@) and the shape trend characteristics clearly show that the zircon crystal forms of the Iljig and Hupyeongdong sandstones are dominantly similar to those of the biotite banded gneiss and granite gneiss of Precambrian age. Zircon morphology of the Jeomgog sandstones is dominantly similar to those of the Jurassic granites. Referring to the reported paleocurrent result, the source rocks of the Iljig and Hupyeongdong formations are mainly the Precambrian gneisses distributed in the southeastern and northeastern parts, respectively. And Jeomgog sandstones were mainly derived from Cheongsong granite at Cheongsong uplift region in the eastern part. At the time of completion of the Hupyeongdong sedimentation, the Precambrian basement rocks were severely eroded and formed low topography. During the Jeomgog period, the Jurassic granites which intruded the Precambrian basement began to crop out on the surface. The basin widely extended toward the east and the exposed Jurassic granite of Cheongsong uplift region actively supplied the sediments to the basin.

키워드

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