Provenance and Diagenesis of the Miocene Pohang Basin, SE Korea

암석기재학;사암상;기원지;속성작용;포항분지;당겨열림형분지;petrography;detrital opaque Fe-Ti oxide mineral;petrofacies;eogenesis;Pohang Basin;pull-apart basin;550

자연과학대학 지구환경과학부 ;

University:서울대학교 대학원

关键词: 암석기재학;    사암상;    기원지;    속성작용;    포항분지;    당겨열림형분지;    petrography;    detrital opaque Fe-Ti oxide mineral;    petrofacies;    eogenesis;    Pohang Basin;    pull-apart basin;    550;   

Others  :  http://s-space.snu.ac.kr/bitstream/10371/131376/1/000000017166.pdf

美国|英语

来源: Seoul National University Open Repository

【 摘 要 】

PF2B – arkose and ilmenite with low MnO wt%. They reflect provenance change due to different lithologies of source rock by temporal variation.Previous study about Cretaceous to Tertiary granitoids in the Gyeongsang Basin, which is adjacent possible source area of the Pohang Basin, suggested that magnetite-series and ilmenite-series granitoids are observed. Considering the paragenesis of Fe-Ti oxide minerals and sandstone composition, petrofacies 1 sandstone was derived from margin of plutonic rocks in contact with felsic-intermediate volcanic rocks, and petrofacies 2A and 2B sandstones were derived from central part of plutonic rocks in contact with sedimentary rocks or marginal part of plutonic rocks in contact with sedimentary rock, respectively.Considering the regional geology and paleocurrent patterns, petrofacies1 sandstone was derived from northwestern side of the basin margin, and petrofacies2 sandstone was derived from southwestern side of the basin margin. Both petrography and detrital opaque Fe-Ti oxide minerals of the Doumsan Fan-delta indicate that the source area was changed by strike-slip movement during basin evolution. In the initial stage, sediments were derived from adjacent volcanic rocks and plutonic rocks. During the back-arc opening of the East Sea, basin had undergone clockwise rotation due to dextral shear stress. In response to tectonic event, source area change of the Doumsan Fan-delta system was occurred, and later stage sediments were derived from southwestern direction of the basin margin.Near-surface eogenetic diagenesis of the Pohang Basin sandstone was controlled by detrital composition and depositional environment. Chemically and mechanically unstable detrital grain, such as volcanic rock fragment, is related to diagenetic alteration. Formation of pore-lining chlorites occurs ubiquitous in the Pohang Basin sandstone, but authigenic zeolite occurs in the formation of sandstone having high volcanic rock fragments ratio (PF1, and some part in the PF2A and PF2B). Low degree of compaction and unconsolidated states enabled through the sandstone active water circulation, which led to chlorite precipitation. Stability fields of chlorite for pH, and ferromagnesian cations are consistent with sea-water characteristics, and depositional environment of the Pohang Basin. And then, high percentage of reactive materal led to authigenic zeolite cements in the formation of volcanic rock fragment rich sandstone.Combining the results of petrofacies, depositional environment, paletectonic, paleocurrents studies on the Pohang Basin, this research suggests that during deposition of the Pohang Basin, basin was produced as pull-apart. Thus, the methods of combining the results of petrography and single mineral analysis have allowed us to differentiate the source area.