HR: 09:45h
AN: T41D-08    [Abstracts]
TI: Magnetotelluric Imaging of an Arc-Continent Collision Beneath Central Taiwan
AU: * Bertrand, E A
EM: bertrand@phys.ualberta.ca
AF: University of Alberta, Department of Physics, Edmonton, AB T6G 2G7, Canada
AU: Unsworth, M J
AF: University of Alberta, Department of Physics, Edmonton, AB T6G 2G7, Canada
AU: Chiang, C
AF: National Central University, Institute of Geophysics, Chung-Li, 320, Taiwan
AU: Chen, C
AF: National Central University, Institute of Geophysics, Chung-Li, 320, Taiwan
AU: Turkoglu, E
AF: University of Alberta, Department of Physics, Edmonton, AB T6G 2G7, Canada
AU: Hsu, H
AF: National Central University, Institute of Geophysics, Chung-Li, 320, Taiwan
AU: Hill, G J
AF: Monash University, Australian Crustal Research Centre, Victoria, 3800, Australia
AB: Arc-continent collisions are a fundamental part of the plate tectonic cycle and play an important role in mountain building and the growth of continents. Studying this process in ancient orogens is often hindered by tectonic overprinting and poorly resolved synorogenic plate kinematics and tectonic settings. The Taiwan arc-continent collision between the Luzon arc and the Eurasian continental margin is one of the most active arc-continent collisions in the world. The current plate motions and surface geology are well understood, making Taiwan an ideal location for geophysical investigations of this important tectonic process. The Taiwan Integrated Geodynamical Research (TAIGER) project was initiated in 2004 to image the lithospheric structure beneath Taiwan. The project includes the acquisition of both active and passive seismic data plus detailed magnetotellurics (MT) surveys. MT is a passive geophysical technique which records time variations of natural electromagnetic fields at the surface of the Earth and can determine the subsurface resistivity. This parameter can be used to constrain lithospheric composition and strength. Over the fall of 2006 and spring of 2007, 82 long-period MT soundings were acquired in Taiwan. The fieldwork was accomplished by collaboration between the University of Alberta and National Central University of Taiwan. In fall 2007, collection of additional broadband MT will complement these data. The long-period data were processed using robust techniques and remotely referenced with a station on the PengHu islands (~100km from the nearest site) to reduce the influence of cultural noise. The conductive Taiwan strait separating PengHu from the mainland acts as an effective attenuator of cultural EM fields. Two closely spaced parallel transects across central Taiwan are formed by 46 of these stations with a nominal spacing of 5km. Dimensionality analysis of these transects using the McNeice-Jones tensor decomposition algorithm reveal local 3-D effects in some data. However, an overall regional 2-D strike direction is defined that is parallel to the coastline of Taiwan. Regularized 2-D inversions of these transects image conductive sedimentary rocks in the western foreland basin and an east dipping mid-crustal conductor beneath the fold-and-thrust belt. A sharp boundary is observed between the western sedimentary rocks and the more resistive slates and metamorphic rocks to the east in the Central Range. This boundary coincides with a conductor rising from the mid-crust that may be related to interconnected fluids.
DE: 8104 Continental margins: convergent
DE: 8108 Continental tectonics: compressional
DE: 9320 Asia
DE: 9605 Neogene
SC: Tectonophysics [T]
MN: 2007 Fall Meeting