臺灣深部電性構造及其板塊構造意義

Deep electrical structure of Taiwan and its tectonic implications

姜智文(Chih-wen Chiang)

指導教授 ： 陳洲生 ； 陳建志 ； 謝秋雰

國立中央大學/地球科學學院/地球物理研究所/博士(2010年)

摘要

歐亞大陸與島弧相互碰撞機制形成臺灣造山帶，是稀有的斜向弧-陸碰撞系統。菲律賓海板塊與歐亞大陸板塊之間複雜的碰撞機制，形成許多的研究議題，尤其是島內深部構造。因此，本研究分別收集長周期與寬頻大地電磁資料，包含遠端參考點，總計84個測點，分別橫跨臺灣北、中、南部，探討臺灣地區之深部電性構造與板塊碰撞間之關聯性。大地電磁資料處理應用張量分解技術、三維順推模擬以及二維逆推，作為本研究資料分析之工具。
電性剖面發現一系列的導體異常分佈於淺部與中深部地殼，位於海岸平原及縱谷平原帶的淺部導體異常是屬於多孔隙沉積岩構造，結果與地質、震波低速帶和低密度構造相吻合；中央山脈區下方深部普遍存在導體異常，研判與地殼內孔隙流體及熱流有關聯，導體異常主要受控於增厚地殼深部強烈的變質作用所釋放出之流體。中部中央山脈區深部的地殼含水率較高; 中央山脈區南部含水率略低於中部。
歸納臺灣地體構造模型可簡化為兩大假說：1. 薄皮構造模型，2. 岩石圈碰撞模型，兩模型間最大的差異在於臺灣內陸深部構造之解釋。根據臺灣中、南部資料發現，中央山脈區深部普遍存在導體異常現象，研判為山根存在之重要證據。電性構造與岩石圈構造模型相吻合，較適合解釋目前臺灣的地體構造機制。經由分析北、中、南三條電性剖面，位於中央山脈區之孔隙含水率與地熱資料等顯示，臺灣北部區域之板塊活動屬於已碰撞狀態、中部正處於碰撞時期，以及南部屬於碰撞前期的三種不同的碰撞機制，提供造山臺灣機制重要的新證據。

關鍵字

大地電磁法 ； 電性構造 ； 電阻率

並列摘要

The Taiwan orogen has formed as a result of the arc-continent collision between the Eurasian continental margin and the Luzon volcanic arc and is the type example of an arc-continent collision. The tectonic processes at work beneath Taiwan are still debated; the available data have been interpreted with both or thin-skinned and lithospheric collision models. In 2004, the magnetotellurics (MT) study began a systematic investigation of the crustal and upper mantle structure beneath Taiwan. The data from central and southern Taiwan favour a lithospheric collision model for that region. The Taiwan orogen becomes younger to the south, so the early stage of collision were investigated in southern Taiwan. Data were recorded at 84 MT sites included one of remote station at Penghu island. Tensor decomposition, three-dimensinoal forward and two-dimensional inversion were applied to the MT data.
The shallow electrical resistivity structure is in good agreement with surface geology. The deeper structure shows a major conductor in the mid-crust that can be explained by fluid content. The conductor in central Taiwan is likely caused by fluids generated by metamorphic reactions in a thickened crust. A similar feature was observed in southern Taiwan, but with a lower fluid content. Together the central and southern Taiwan profiles show a crustal root beneath Central Range. Three stages of tectonics collision process has respectively revealed post-collision, collision and early stage from the northern to the southern profiles in terms of the porosity and the heat flow analyses.

並列關鍵字

Resistivity ； Magnetotelluric ； Electrical structure

參考文獻

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