| 摘要: | 本計劃係中央大學與Alberta大學(加拿大)合作TAIGER國際研究計畫，從事台灣深部電性構造研究，利用深部電磁波測勘方法:大地電磁波法(Magnetotellurics, MT)，來了解台灣深部的電性構造，尤其是資料缺乏之中央山脈深部構造，將可解答大陸如何增積及有關台灣造山之關鍵問題。中央大學負責寬頻MT 儀器，測深約20 km；而 Alberta大學提供超低頻MT儀器，測深可達50 km。第一年完成北中南三條東西向MT剖面(Fig 11-1a)，初步結果(Fig.11-1b) 顯示，台灣造山系統從地表至地函主要呈現東西兩高阻區(R1與R2) ，經與地震或重力觀測比對，可能解答大陸如何增積及有關台灣造山之關鍵問題包括: 1. 菲律賓海板塊斜向碰撞歐亞大陸板塊，台灣居間提供了獨一無二的觀察造山演化的連續過程的機會: 由南向北之三條電組率剖面顯示，台灣之造山活動系統可分為:發展階段，碰撞階段以及塌陷階段，因此島弧增積是台灣陸地生長之基本模式。 2. 從地質上約制，解釋大地電磁法模擬來追蹤從地殼和上部地函深部的構造，確定地殼在不同深度之變形模式。因為造山過程一直延伸到地函，而非薄皮變形。 3. 菲律賓海板塊碰撞歐亞大陸板塊邊緣中，菲律賓海板塊猶如一具推土機，是重要之推手，推向大陸邊緣之弱帶。 4. 造山是經由沉積物深埋後再迅速擠推至地表之作用。 5. 弧陸碰撞發展出寬廣之剪切帶而非挾窄板塊邊界，此寬廣之剪切帶向西遷移。第二年之重點為補足各剖之MT測點，尤其是一些中央山脈關鍵地區之深部電性構造。此外各測區之工作項目尚包括改進MT資料處理、分析深部電性構造、解釋深部地下水之分佈，再與TAIGER計畫中之震測或重力觀測比對，與加拿大方面共同討論，將可解答大陸如何增積及有關台灣造山之關鍵問題。 ; TAIGER- MT has been carried out for almost one fiscal year and we have collected MT data of three profiles covering the whole island of Taiwan (Fig. 11-1a). Based on 2-D resistivity inversion (Fig. 11-1b), where static shift and coastal effect are also a model parameter, each profile model is characterized by two main resistive blocks (R1 and R2) in the mid-crust to account for the response of Taiwan tectonics; the oceanic Philippine Sea plate (R1) to the east, while Eurasia continental plate (R2)to the west. The preliminary interpretations indicated that: 1. By looking at resistivity sections from south to north, we can trace the mass transfer of these volumes through the orogenic system of Taiwan: developing orogen, collision-orogen, and collapse-orogen. Arc accretion seemed to be the fundamental mode by which continental grow. 2. The oceanic Philippine Sea plate (R1) act as an indenter to the generally weaker continental margin. 3. The foreland deformation is basement deformation passive throughout the orogenic system, rather thin-skinned deformation. 4. The mountains formed through a corner flow process that rapidly exhumes materials previously buried to great depth. 5. A broad distributed shear system may have developed the arc-continent collision rather than a discrete plate boundary in Taiwan. This shear motion apparently moved westward. However, each profile is still lack of enough MT controls, especially the key area of the Central Range. Therefore, the coming fiscal year will concentrate on the imaged of the detailed Central Range of Taiwan with the MT in joint research by National Central University and the University of Alberta, Canada. Phoenix V5-2000 system will be used to measures electric and magnetic fields at frequencies from 1000-0.001 Hz. The crust and upper mantle structures in the survey area may be evaluated in details based on the geoelectric data collected by MT observations incorporated with known geologic, seismic, and co-projects data under the umbrella TAIGER. Academically, the first model of the deep electrical model and crustal deformation in the survey area will be proposed. This proposed model might provide one of the evidences for the dynamics and evolution of plate boundary deformation, as well as the physics of earthquakes. Practically, MT data will also provide geoelectric information in the assessment of the natural resources of geothermal, groundwater and mineral deposits in the Central Range. ; 研究期間 9708 ~ 9807 |
