The Taiwan orogen, situated on a portion of the Eurasian (EUP) and the Philippine Sea (PSP) plates, is young (∼6.5 Ma) and active with frequent earthquakes. It is called a natural laboratory because it is an environment in which detailed ongoing tectonic processes of mountain building can be investigated. A large number of geologic studies have led to a number of models regarding the mechanics of mountain building. As with all scientific models further testing to verify or disprove them is needed. Two methodologies, teleseismic shear wave splitting and travel-time tomography, are applied to obtain the bulk intensity of orogenic deformation and the velocity structures of the crust and the upper mantle, respectively. The results from teleseismic shear wave splitting measurements imply that the crust and the upper mantle are highly anisotropic as a result of coherent shear deformation or collision induced mantle flow in the upper 200 km. The velocity structures indicate crustal thickening in both of the EUP and PSP during the collision. Furthermore, the velocity structures of the upper mantle reveal in the 3D geometry a high-velocity anomaly. There are two possible reasons for this high-velocity anomaly, the ancient subducted EUP slab and a mantle drip formed from both the EUP and PSP, and either mechanism shows that tectonic processes clearly involve the upper 200 km of the mantle, and that the high-velocity structure changes from shallow dipping to nearly vertical. Although a significant crustal root is observed at present, the tectonic evolution of Taiwan in the future depends on whether or not this crustal root delaminates. This will lead to different destinies of the mountain belts, namely collapsing if it delaminates or building up if it does not. If, for example, a small amount of fluid is present in the lower crust, this will aid the formation of dense eclogite and cause the root to delaminate and eventually result in collapsed mountain ranges. To accompany the improved subsurface tomography reported in this dissertation, the physical properties in the lower crust deserve to be investigated in greater detail to better foresee the tectonic evolution of Taiwan.
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|Advisor:||Wu, Francis T.|
|Commitee:||Barker, Jeffrey S., Dickman, Steven R., Jenkins, David M., Roecker, Steven W.|
|School:||State University of New York at Binghamton|
|Department:||Geological Sciences and Environmental Studies|
|School Location:||United States -- New York|
|Source:||DAI-B 72/10, Dissertation Abstracts International|
|Keywords:||Mountain building, Shear wave splitting, Subduction system, Taiwan orogeny, Tectonic evolution, Travel time tomography|
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