Deformation Patterns of an Accretionary Wedge in the Transition Zone from Subduction to Collision Offshore Southwestern
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Springer 2005
Deformation patterns of an accretionary wedge in the transition zone from subduction to collision offshore southwestern Taiwan Char-Shine Liu1,*, Benoit Deffontaines2, Chia-Yu Lu3 and Serge Lallemand4 1
Institute of Oceanography, National Taiwan University, Taipei, Taiwan, ROC Laboratoire de Geomateriaux, Universite de Marne-la-Vallee, Institut Francilien des Geosciences, France 3 Department of Geosciences, National Taiwan University, Taipei, Taiwan, ROC 4 Laboratoire Dynamique de la Lithosphere, Universite Montpellier 2, France *Corresponding author (Fax: +886-2-23660881; E-mail: csliu@ntu. edu.tw) 2
Received 16 May 2004; accepted 8 October 2004
Key words: accretionary wedge, deformation front, morphotectonics, seismic reflection, southwestern Taiwan, swath bathymetry
Abstract Swath bathymetry data and seismic reflection profiles have been used to investigate details of the deformation pattern in the area offshore southwestern Taiwan where the Luzon subduction complex encroaches on the passive Chinese continental margin. Distinctive fold-and-thrust structures of the convergent zone and horst-and-graben structures of the passive margin are separated by a deformation front that extends NNW-ward from the eastern edge of the Manila Trench to the foot of the continental slope. This deformation front gradually turns into a NNE–SSW trending direction across the continental slope and the Kaoping Shelf, and connects to the frontal thrusts of the mountain belt on land Taiwan. However, the complex Penghu submarine canyon system blurs the exact location of the deformation front and nature of many morphotectonic features offshore SW Taiwan. We suggest that the deformation front offshore SW Taiwan does not appear as a simple structural line, but is characterized by a series of N–S trending folds and thrusts that terminate sequentially in an en-echelon pattern across the passive Chinese continental slope. A number of NE–SW trending lineaments cut across the fold-and-thrust structures of the frontal accretionary wedge and exhibit prominent dextral displacement indicative of the lateral expulsion of SW Taiwan. One of the prominent lineaments, named the Yung-An lineament, forms the southeastern boundary of the upper part of the Penghu submarine canyon, and has conspicuous influence over the drainage pattern of the canyon.
Introduction Located at the western corner of the Philippine Sea plate, Taiwan is an active mountain belt formed by the collision of the Luzon volcanic arc with the passive Chinese continental margin (Biq, 1972; Bowin et al., 1978; Ho, 1986; Teng, 1990; Huang et al., 2000). Due to the obliquity of the passive continental margin with the impinging volcanic arc, this collision is propagating southward (Suppe, 1984; Byrne and Liu, 2002). At present, the most active deformation occurs in eastern and central Taiwan as revealed by GPS observations (Yu et al., 1997), whereas the offshore area south of Taiwan represents the incipient arc-continent collision zone (Huang et al., 1992; Lundberg et al., 1992, Reed
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