• Economic and Environmental Geology
• /
• v.53 no.4
• /
• pp.397-411
• /
• 2020

The Cretaceous Yucheon Group is volcano-sedimentary successions that are formed by volcanic activities of the Gyeongsang Volcanic Arc. Lack of the detailed field researches on the Yucheon Group results in poor understanding of the formation time and the tempo-spatial development of the volcanic arc. Also, this causes difficulties to reconstruct the depositional history from the Sindong and Hayang groups to the Yucheon Group. In this study, we conducted field research targeting to the interface between topmost part of the Hayang Group and the lowermost part of the Yucheon Group from Hyeonpoong to Bugok areas. We also identified depositional timing of the lowermost part of the Yucheon Group using SHRIMP U-Pb zircon age dating. This Yucheon Group is composed of tuff and lapilli tuff, conformably overlying the Jindong Formation. The results of SHRIMP U-Pb zircon age are 97 to 96 Ma, indicating cessation of deposition of the Hayang Group at 97 to 96 Ma by input of pyroclastic materials into the Jinju Subbasin during the explosive volcanic eruptions from the Gyeongsang Volcanic Arc. In comparison with field researches and results of LA-ICP-MS zircon U-Pb age dating (88-85 Ma) of the lowermost part of the Yucheon Group in Gyeongju areas, the volcanic activities that formed Yucheon Group and their influence ranges varied tempo-spatially. This is probably due to distance difference from the volcanic arc or establishment of the paleo-drainage system from the Gyeongsang Volcanic Arc to nearby lowlands.