Architecture and fluid-assisted evolution of a basin-forming normal fault zone: Insight from a drillcore in Miocene Waup Basin, SE Korea

초록

The evolution of basin-forming faults involves long-term brittle deformation coupled with fluid-rock interactions. We investigated a basin-bounding normal fault zone along the margin of the Miocene Waup Basin, southeastern Korea, using a vertical drillcore (812 m deep) that penetrates the fault zone between the Miocene basin fill and Late Cretaceous basement rocks. The similar to 150 m-thick fault zone, developed within Late Cretaceous felsic volcanic basement, consists of an anastomosing network of fault-related hydrothermal breccias with locally developed gouge strands. Deformation is spatially heterogeneous: localized slip zones and injected fine-grained materials are concentrated at the basin fill-basement contact, whereas deeper, widespread hydrothermal breccia domains exhibit variable deformation intensity and pervasive calcite cement. Diverse vein assemblages, authigenic metallic minerals, zircon U-Pb discordia, and fractured and altered zircon textures indicate that the fault zone acted as a conduit for episodic fluid flow. Zircon U-Pb ages record multiple episodes of fluid infiltration, including an event at ca. 21 Ma that was broadly coeval with the eruption of Miocene pyroclastic rocks, suggesting a temporal association between fault activity, fluid migration, and volcanism. Our observations indicate that the fault zone evolved at shallow crustal levels (<2 km) under persistent extension, where repeated brittle deformation and fluid-assisted processes contributed to shaping fault-zone architecture and influenced basin development over several million years.

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