Structural Kinematics of Two Regional Transects Across the Manila Trench Offshore Southern Taiwan: Untangling Thick from Thin Skin Deformation
Abstract
Recent research offshore Southern Taiwan has proposed that a hyper-extended continental crust is involved in the convergent margin of the Manila trench as far south as 20。N (Lester et al., 2013; McIntosh et al., 2013; and Eakin et al., 2014). If and how such pre-existing structures affect modern deformation styles is still unclear. Here, we combine large offset seismic reflection profiles, gravity anomaly, and seismicity data to study two transects. Preliminary analyses of Bouguer gravity data and focal mechanisms are consistent with the proposed hyper-extended model. Observations suggest two major crustal lineament trends: 1. A NE-SW steep gravity gradient trend west of Taiwan that correlates with the passive margin normal faults as defined by Lin et al., 2003; 2. A NW-SE regional lineament that correlates with deep seismicity (>30km) offshore SW Taiwan (Wu et al., 2009) and is orthogonal to the normal fault trend. Preliminary gravity analyses also suggest southward deepening of the top of the basement from the Central Range, to the Hengchun Peninsula, to its offshore continuation. By integrating gravity and earthquake data with the structural interpretation of two 2D EW-trending regional seismic sections at 20oN and 22oN, we describe the geometry, and propose a kinematic history of the prowedge. Results display contrasting widths and taper angles between both sections. To the north, the wedge is wide ( 95km) and less steep (α+β= 6ͦ) than to the south. In contrast, the wedge to the south is narrower ( 65km) and steeper (α+β= 13ͦ). We interpret that differences in coulomb wedge behavior from north to south are due to the presence of inherited crustal structures and to the effect of the initial stages of collision. Inherited structures accommodate very thick sedimentary deposition and also accommodate deformation by buttressing younger structures. These characteristics make the Manila accretionary prism a unique example of ongoing basement-involved-deformation in an overriding plate.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T14A..08B
- Keywords:
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- 7221 Paleoseismology;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8107 Continental neotectonics;
- TECTONOPHYSICSDE: 8175 Tectonics and landscape evolution;
- TECTONOPHYSICS