利用三維光達地形解析葉理分佈：對臺灣南部造山帶變形過程的啟示

Abstract

在造山帶中，與大地構造與地體動力學相關的地殼變形常透過變質組構揭露。然而，在露頭有限的區域，傳統構造調查的解析度經常受到限制。過去研究指出，空載光達生成的數值高程模型能透過地形線型揭示區域性的葉理軌跡，即使在出露受限的區域中亦然。本研究聚焦於臺灣造山帶中央山脈南段，此區域的變形歷程仍不清楚。本研究以三維視角分析光達數值地形中的葉理線型，並結合野外構造調查，重新檢視該區域的構造樣貌。基於地形分析與野外觀察，本研究定義兩組與葉理相關的線型（層理與變質葉理）與兩種變形模式（DA與DB）。根據線型與葉理間的空間關係，本研究揭露過去未被描繪的巨觀構造，並重建葉理在三維空間中的分布樣態。結果顯示，光達地形的三維製圖提供的宏觀視野能有效精進構造調查的解析度與廣度；新的葉理分布模式則指出，中央山脈南段主要受到前衝與左剪構造所控制，局部地區則可觀察到背衝與伸張構造。這些變形構造的空間分布與年代關係揭示了臺灣造山帶南部在底部加積、應變分配與同造山伸張之間的複雜交互作用。

Metamorphic fabrics can reveal deformation patterns associated with the tectonic and geodynamic conditions of orogenic belts. However, in terrains with poor exposure, the accuracy of structural mapping is often limited. Previous studies have demonstrated that Digital Elevation Models (DEMs) generated by airborne LiDAR (Light Detection and Ranging) can display regional foliation trajectories through geomorphic lineaments in poorly exposed regions. Therefore, we conducted LiDAR-based 3D mapping of foliation lineaments, along with field-based structural investigations, to reappraise the structural patterns of the southern Central Range in the Taiwan orogen, where the deformational processes remain unclear. Based on geomorphic analysis and field investigations, we defined two suites of foliation lineaments (bedding and metamorphic foliations) and two deformation patterns (DA and DB), respectively. By interrelating lineaments and foliations, a previously unmapped macroscale structure was revealed, and foliation patterns were refined. This indicates that the macroscopic perspective provided by LiDAR-based 3D mapping enhances structural investigations in poorly exposed, intensely deformed metamorphic terrains. Moreover, the 3D foliation patterns indicate that forethrusting and left-lateral shearing dominate the southern Central Range, while backthrusting and extensional deformations are also observed locally. Based on the spatial distribution and chronological relationships of deformation patterns, we highlight the complex interplay among tectonic underplating, strain partitioning, and synorogenic extension within the southern Taiwan orogen.