| Summary: | 博士 === 國立中央大學 === 地球物理研究所 === 99 === 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.
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