New insights into accretionary prism development and deformation
in the pre-arc-continent-collision transition zone offshore Taiwan
By Eakin, D h, McIntosh, K D, Van Avendonk, HJ, Hsu, S, and Liu, C
Presented at the 2009 Fall AGU Meeting
San Francisco, CA
Abstract:
In April - July 2009 we conducted a seismic experiment with the R/V Marcus G. Langseth in as part of the Taiwan Integrated Geodynamic Research (TAIGER) project in the deep water Luzon Strait offshore Taiwan. The program acquired 12 high-quality MCS and OBS profiles across the Manila subduction zone in an effort to gain a further understanding of the evolution from a pure subduction regime south of ~20.5°N to initial-stage arc-continent collision north of ~21.3°N. This data combined with that from the 1995 TAICRUST project should provide new insights into the velocity structure of the region and levels of deformation and composition of the crust, whether oceanic, continental, or more likely transitional, in an area believed to be the pre-collision transition zone. Two of the main MCS transects are oriented E-W perpendicular to the strike of the Manila trench at approximately 21.3° N and 20.3° N. Here Eurasian oceanic crust subducts beneath oceanic crust of the Philippine Sea plate. These transects extend across the entire subduction zone so that it should be possible to track and correlate the structure and geometry of the subducting Eurasian slab from the near surface at the trench to well below the developing accretionary prism and forearc region of the Philippine Sea plate as well as the structure and deformation of the accretionary prisms in both transects. Initial processing shows the east dipping Eurasian slab reflector beneath the growing accretionary prism at the western margin of the Philippine Sea plate. Additional processing will allow us to better resolve this boundary as well as to determine the composition of the crust being accreted vs. subducted in both transects. Ongoing research will combine MCS and OBS data to address several topics related to the composition of both the subducting and overlying crust. First, to determine the dimensions and velocity structure of the developing accretionary prism in both transects to assess any similarities and differences. If differences do exist between regions it will also be important to analyze and constrain the geometry and position of the forearc basement and its effect on the deformation within the accretionary prism. Is the forearc basement being used as an abrupt backstop for accretionary prism development and deformation? Is there evidence of underplating? Finally it will be important to use these results in a regional analysis and comparison of the south to north evolution of the convergent margin from pure subduction to the incipient collision zone onshore Taiwan.
