由阿朗壹古道的區域地質展示中央山脈南段的構造

臺灣南部的恆春半島及臺東為初始碰撞演化至聚合的關鍵樞紐區。最初為菲律賓海板塊朝西北方斜向聚合歐亞板塊，隱沒作用造成呂宋島火山島弧及台灣島的增積岩體，後期發展出南北向的台灣造山帶，因此我們可由現今臺灣南部的野外構造研究可窺知臺灣造山初期的樣貌及演化關鍵。恆春半島保留了臺灣從隱沒帶到造山帶的增積楔形體構造演化證據，而該區的詳細研究卻十分有限。前人於太麻里—金崙海岸沿線進行研究，藉由從構造地形圖、野外地質調查等方法，分析類背斜褶皺以及剪切帶的構造，發現了中央山脈南段紀錄了臺灣島造山的豐富構造演變史，包含一系列的向東伸向構造並造成地層倒轉，以及橫移壓縮作用造成左移斷層。因此本研究欲延續前人研究近一步的詳細記錄整合野外構造特徵，以屏東縣牡丹鄉旭海村為中心，朝北以塔瓦溪為界，以台東縣南田—屏東縣旭海海岸的「旭海—觀音鼻自然保留區」中的阿朗壹古道為主，往南於旭海—大流海岸沿線進行野外考察，達旭海溪及省道台26線海岸處。阿朗壹古道中不僅保存了珍貴的生態環境與生物多樣性，也保存了豐富的地質活動紀錄。本研究除使用基礎野外地質量測方法，另採用了5m DTM數值地形模型圖，配合GPS定位標記位態資料，呈現觀察到的構造特徵，並結合地形資料來掌握構造分布。在野外繪製素描以及側視構造剖面圖後，更使用以UAV拍攝影像完成的三維真實模型，在室內觀察徒步不可及的地形高處。以FaultKin軟體整合斷層及褶皺所指示的應力方向之後，利用截切關係分期並與前人研究的結果比較，發現向東伸向的逆衝斷層和褶皺以及橫移壓縮構造為斜向聚合的關鍵證據，再藉由地理位置及構造延續性，發現與前人研究之中央山脈東南側有關。最後結合了應力分期資料，提出小區域的演化模型解釋本研究區的構造變形歷史。

關鍵字

野外地質調查；向東伸向構造；橫移壓縮作用；斷層及褶皺分析

並列摘要

Southern Taiwan, including Pingtung peninsula and Taitung, is the incipient oblique convergent zone of Eurasian plate and Philippine Sea plate. Subduction activity formed the Luzon volcanic arc and accretionary wedge offshore southern Taiwan. So that we can infer the incipient feature structure from the topography and outcrop study of southern Taiwan. Hengchun peninsula remained the structural evolution evidence about Taiwan as subduction zone to orogenic zone inside the accretionary wedge. Previous studies observed some mountain building history by analyzing the antiformal syncline and shear zone by the tomography and field survey along the Taimali to Jinlun coastline Such as east-vergent structures which formed the overturned formation and left lateral faults which caused by transpression process. In this study, we continued the former studies and integrate the records of the structure from the field survey to complete the structure evolution story. The field survey of this study is in the Reserve area from Nantien to Syuhai, Southeast coastline of Taiwan, also known as A-Lan-Yi Trail, which preserving the ecological environment and biodiversity with abundant geological activity record. Furthermore, to map the distribution of regional structures with topography in this accessible area, I applied the 5m DTM (Digital Terrian Model) to mark the bedding attitudes with GPS data, then I adopted the true 3D model based on unmanned aerial vehicle-derived images to observe the inaccessible high area. Afterword, I use FaultKin to calculate the striation data for paleo-stress direction and divide it to different stages by the crosscutting relationship then compare the result with former studies. This study provides a strong evidence of back-thrusting and back-folding deformation during the incipient oblique collision stage, and as well as the discovered structures in this area show the similar kinematic history as the eastern flank of Central Range. Finally, after concluding the paleo-stress stages to above-mentioned results, I propose a possible evolution model with deformation history of this study area.

並列關鍵字

field survey ； east vergent structure ； transpression ； faults and folds analysis

參考文獻

陳麗雯 (2006) 台灣東南海域弧前盆地之構造演化特徵。國立臺灣大學海洋研究所碩士論文，共100 頁。

Angelier, J. (1979) Determination of mean principal directions of stresses for a given fault population: Tectonophysics, v. 56, p. 17–26.

Chang, C. P., Angelier, J., and Huang, C. Y. (2000) Origin and evolution of a mélange: the active plate boundary and suture zone of the Longitudinal Valley, Taiwan: Tectonophysics, v. 325, no. 1-2, p. 43-62.

Chang, C. P., Angelier, J., and Lu, C. Y. (2009) Polyphase deformation in a newly emerged accretionary prism: Folding, faulting and rotation in the southern Taiwan mountain range: Tectonophysics, v.466, p. 395–408.

Chi, W. C., Reed D. L., Moore G., Nguyen, T., Liu, C. S., Lundberge, N. (2003) Tectonic wedging along the rear of the offshore Taiwan accretionary prism, Tectonophysics, v. 374, p. 199-217.

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由阿朗壹古道的區域地質展示中央山脈南段的構造

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