Syn-tectonic extension and lateral extrusion in Taiwan: The tectonic response to a basement high promontory

Syn-tectonic extension is a process that has been observed by previous workers in the eastern Central Range of Taiwan, using geodetic, geologic and seismic data. The details of the location, direction and magnitude of the extension, as well as the mechanism by which extension occurs, has not been adequately explained in a comprehensive tectonic model of the Taiwan arc-continent collision. This study correlates multiple sets of data to constrain the location of active block bounding structures that accommodate extension and interprets extension in both northern and southern Taiwan to be associated with the lateral extrusion of the crust, parallel to the Taiwan orogen. The extent of lateral extrusion is interpreted to be controlled by the location of a basement high indenter below the topographic low of the Puli basin. ^ The first chapter examines the distribution of low to intermediate magnitude (ML1-4) earthquakes, available focal mechanisms and GPS data across north-central Taiwan. These data suggest the presence of two shear zones that accommodate exhumation and lateral extrusion of the metamorphic basement: the western and eastern metamorphic shear zones. ^ The second chapter presents the results from a three-year GPS campaign across the northern Hengchun Peninsula. Velocity vectors are used in a strain analysis across the region by interpolating between the irregularly spaced data. Extension is generally constrained to the central and eastern portions of the Central Range and is oriented northeast/southwest. The magnitude of extension is higher than the magnitude of compression and is interpreted to be the result of transtension between two range bounding oblique faults. ^ The third chapter compares the irregular strain pattern of the fold-and-thrust belt of south-central Taiwan to the strain pattern of the Zagros fold-and-thrust belt of Iran and identifies the boundaries of lateral extrusion in southern Taiwan from the systematic changes in GPS velocity vectors. The western boundary is interpreted to be approximately coincident with the Kouhsiaoli/Lunhou fault system and the eastern boundary is interpreted to be approximately coincident with the metamorphic and slate belt boundary. In addition, lateral extrusion is interpreted to extend as far north as the southern edge of the Puli basement high indenter.