Taiwan is the result of the most active arc-continent collision in the world (uplift of 3cm/yr and convergence of up to 8 cm/yr). The Eurasian plate and the South China Sea have been moving to the SE wrt the Philippine Sea plate, with oceanic lithosphere of the southeast China continental margin subducting beneath the Luzon arc, which sits atop the Philippine Sea plate. Around 4 Ma ago, the margin of Eurasia entered the subduction zone, resulting in collisional orogeny that formed Taiwan. Taiwan consists of parallel belts representing 7 different tectonostratigraphic provinces. The collision is occurring at an oblique angle, with the northern margin colliding first, so that mountains are forming in the North and propagating south. This oblique collision allows spatial changes to be viewed as temporal evolution.
Arc accretion is arguably the most important mode of continent formation throughout the post-Archean Earth (perhaps even before). Taiwan offers the possibility of studying these processes in the world's most active arc collision zone with a temporal view of how such collisions progress, due to the oblique nature of the collision as mentioned above. The PIs put forward two end member hypotheses to be tested concerning what is happening to continental lithosphere during the collision: 1) It is subducted, with crust-mantle detachment causing crust to accrete while deeper lithosphere is subducted; 2) It doesn't subduct, but jams up in the subduction zone, leading to continuous deformation resulting in thickening of the lithosphere.
The two end-member scenarios for what is happening to continental lithosphere during the collision provide special opportunities to investigate some of the most fundamental questions of mountain building:
- Does continental subduction play a controlling role in arc-continent collision? Is the Eurasian continental lithosphere subducting beneath Taiwan? - One of the fundamental issues in orogeny is mass balance. How do factors such as erosion, crustal thickening, mantle flux, etc. interact quantitatively? - How did the orogen evolve through time? - How does surface kinematics relate to deep structure? - How does anisotropy vary in space, laterally and vertically? Do the S-splitting directions change with depth? Is the deformation of the orogen vertically coherent from surface to upper mantle?
To answer these questions the PIs will carry out an integrated geophysical imaging, earthquake recording and geodynamic research program to study the Taiwan orogeny. By combining detailed 2-D studies along transects and 3-D images for the whole region, the orogen and its evolution can be characterized. The data acquisition program includes broadband regional seismic and teleseismic recording, onshore-offshore and land refraction-reflection seismic transects, magnetotelluric sounding, petrophysics and gravity modeling. The geometry of the plate interactions, the mode of crustal deformation, and the material properties will provide a new quantitative basis for geodynamic modeling. The various datasets will be integrated into a geodynamic model which can be used to test conceptual models for mountain building.
The project will involve collaboration from six US institutions as well as collaboration and support from Taiwanese and Japanese groups. There is also the distinct possibility of the participation of scientists from mainland China. The educational impact of this project will be large, with more than 25 students from the participating institutions, US and foreign. In addition, the "Texas Teacher in the Field" program would involve one high school teacher in recording earthquakes offshore Taiwan, developing related teaching modules for Texas high school teachers.
