From the Foreland and Retroarc Thrust Belts to the Mantle Transition Zone: First Multi-Scale Retrodeformable Transect of the Active 90 mm/yr Taiwan Arc-Continent Collision
This dissertation presents integrated multi-scale retrodeformable transects of the Taiwan arc-continent collision. Chapter 1 presents reprocessed marine seismic reflection profiles of the retroarc thrust belt near Chimei Canyon offshore eastern Taiwan, which is one of the largest submarine canyons around Taiwan and results from the <1 Ma uplift of the retroarc thrust belt and submarine erosion. Chapter 2 presents the precollisional architecture of the Luzon arc and the thin-skinned structure and stratigraphy of the deforming arc on land. We show that the Miocene and younger northern Luzon Arc is built on Early Cretaceous Huatung Basin oceanic lithosphere of the Philippine Sea plate, which underwent >100 Ma of pelagic sedimentation at abyssal depths prior to the onset of Eurasian subduction and arc volcanism at ~18-14 Ma. This onset is marked in the Huatung Basin by seismic facies that thicken arcward, including mass-transport deposits, in contrast with underlying 1-2 km thick pelagic facies. The contact between oceanic crust and the pelagic sequence provides a zone of detachment that is the locus of deep massive laccolithic intrusions at ~1 Ma imaged in our reprocessed seismic reflection profiles. The ~2-3 km thick roof stratigraphy has been flexed upward by 2-3.5 km laccolithic inflation. Chapter 3 presents progress towards a multi-scale retrodeformable transect across the entire orogen from the foreland and retroarc thrust belts to the mantle transition zone. Multiscale tomographies define two active east-dipping Eurasian and Luzon forearc subduction systems that detach from their upper crusts and form thin-skin foreland and retroarc thrust belts above fundamental detachments. A new retrodeformable cross-section that extends from the imbricated foreland to the metamorphic core defines the post 1 Ma structure of western Taiwan, which shows two detachment levels, imbricated fault-propagation folds and agrees with tomographic and resistivity images. The upper detachment is the Eurasian subduction interface, which is the roof thrust of a low velocity channel defining a mid-crustal duplex under Taiwan. The lower detachment defined by tremor seismicity and tomography is the floor thrust of the channel, which is currently active and probably results in uplift of the Taiwan mountain belt after 1 Ma.
Networked Digital Library of Theses and Dissertations