台灣南部恆春半島的地體動力模擬

Geodynamic Modeling Of The Hengchun Peninsula In Southern Taiwan

李沅(Li Yuan)

指導教授 ： 王維豪

國立中正大學/理學院/地球與環境科學系地震研究所/碩士(2014年)

摘要

本研究修改Gerya所設計的地體動力模擬程式，模擬台灣恆春半島的地體構造演化。根據地質資料顯示，在形成恆春半島與墾丁混同層時可能封閉了一個古南中國海洋盆，本研究依據此假設建立大陸板塊隱沒模型，根據初步的研究結果顯示，恆春半島的隆起可能與歐亞大陸地殼沿花東縱谷向東隱沒有關，而非弧陸碰撞所致。當歐亞大陸地殼隱沒時，菲律賓海板塊碰撞刮起部分大陸地殼而形成新的山脈。在陸塊與洋盆相繼隱沒後，相同的機制刮起海盆內的沉積物質及少量海洋地殼與地函而形成墾丁混同層。本研究的最佳模擬結果與地震層析成像類似，並暗示地殼應變弱化是控制此處構造演化與的最主要因素；當考慮應變弱化效應時，我們發現一個沿上部大陸地殼底部的剪切帶會逐漸形成，造成板塊聚合帶由原本的花東縱谷逐漸轉移至馬尼拉海溝，並減緩恆春半島的造山作用。

關鍵字

地體動力 ； 恆春半島

並列摘要

We employed a geodynamic program modified from Gerya to explore the tectonic evolution in Taiwan Hengchun Peninsula. According to the geological records, it is likely that an ancient South China Sea was closed during the formation of the Hengchun Peninsula and the Kenting mélange. Based on this hypothesis, we set up a numerical model to test how it may evolve. Our simulation results show that the Hengchun Peninsula may most likely result from eastward subduction of the Eurasian continental crust along the Longitudinal Valley rather than arc-continent collision. While the Eurasia continental crust was colliding with the Philippine Sea Plate, the compression force scraped off part of the continental crust and created a new mountain. Subsequently, the ocean basin also went below the Philippine Sea plate, and similar mechanism resulted in piling up the sediments in the oceanic basin and some debris form oceanic crust and mantle, which formed the Kenting Mélange. Our optimal model implies that the crustal strain softening is essential to reproduce the tectonic structures observed by seismic tomography. When strain softening was taking into account, a shear zone would gradually develop along the base of the upper continental crust, which allowed the plate boundary to transfer from the Longitudinal Valley to the Manila Trench. As a result, the orogeny in the Hengchun Peninsula has been slowing down ever since.

並列關鍵字

Hengchun Peninsula ； Geodynamic

參考文獻

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