| Summary: | 碩士 === 國立臺灣大學 === 地質科學研究所 === 107 === Geologic map and regional geologic cross-section are the important base map to understand the local geologic conditions. In the past, however, geologists could collect very limited field data due to the heavy vegetation, steep terrain, human activity, etc. The previous studies used LiDAR-based high-resolution DEM to interpret geomorphic features and improved the geologic map in the fold and thrust belts in northern Taiwan. In this study, we focus on the low-grade metamorphism area in Toucheng, northern Taiwan. The age of the formations is from Oligocene to Miocene and lithology contains quartzite, argillite, shale, sandstone and their alternations. We overlay the pseudocolored DEM, hillshade and slope layers in the 3D GIS environment, where we can not only adjust view angle and illumination but also mark geomorphic features directly. In the mapping stage, a custom-built human interface device, Liandianjun, can improve the mapping efficiency. We first identify the regional structure reference lines and then map the feature lines of bedding carefully. Finally, fault lineaments are determined based on the different attitudes between the two walls. With 2600 feature lines of bedding and field verification, we finish the 1:50000 Toucheng geologic map. One fold and five major faults are in the study area. Yingzilai syncline is an asymmetric fold where beddings in the north are steeper than the south ones. The location of Jingualiao fault and Sanchakeng are modified based on geomorphic evidence. Fangjiao fault is reinterpreted as a back-thrust fault that cut the north limb of Yingzilai syncline. The Dajinmianshan normal fault system is introduced for the first time in the southern study area. It can be further divided into three regions: Fanshuliao region, Wai’ao-Fudekeng region and Sidu-Shipai- Jinmianshan region. We have successfully concurred the difficulties of the traditional geologic mapping work and provided detailed geologic information in the metamorphic area. The map can be used as the base map of future research in this area.
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