Crustal structure and deformation associated with seamount subduction at the north Manila Trench represented by analog a
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ORIGINAL RESEARCH PAPER
Crustal structure and deformation associated with seamount subduction at the north Manila Trench represented by analog and gravity modeling Fucheng Li • Zhen Sun • Dengke Hu Zhangwen Wang
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Received: 8 April 2013 / Accepted: 3 September 2013 / Published online: 29 September 2013 Ó Springer Science+Business Media Dordrecht 2013
Abstract We investigated the deformation in the accretionary wedge associated with subducted seamounts in the northern Manila Trench by combining observations from seismic profiles and results from laboratory sandbox experiments. From three seismic reflection profiles oriented approximately perpendicular to the trench, we observed apparent variations in structural deformation along the trench. A number of back-thrust faults were formed in the accretionary wedge where subducted seamounts were identified. In contrast, observable back-thrusts were quite rare along the profile without seamounts, indicating that seamount subduction played an important role in deformation of the accretionary wedge. We then conducted laboratory sandbox experiments to investigate the effects of subducted seamounts on the structural deformation of the accretionary wedge. From the analog modeling results we found that seamount subduction could cause welldeveloped back-thrusts, gravitational collapse, and microfractures in the wedge. We also found that a seamount may induce normal faults in the wedge and that normal faults may be eroded by subsequent seamount subduction. In addition, we constrained the crustal structure of the South China Sea plate from modeling free-air gravity data. The
F. Li Z. Sun (&) Z. Wang Key Laboratory of Marginal Sea Geology, Chinese Academy of Sciences, Guangzhou 510301, China e-mail: [email protected] F. Li Z. Wang University of Chinese Academy of Sciences, Beijing 100049, China D. Hu School of Geosciences, University of Aberdeen, Aberdeen AB243UE, UK
dip angle of the subducting plate, which was constrained by hypocenters of available earthquakes, increased from south to north in the northern Manila Trench. We found a laterally heterogeneous density distribution of the oceanic crust according to the gravity data. The density of subducted crust is *2.92 g/cm3, larger than that of the South China Sea crust (2.88 g/cm3). Keywords Manila Trench Structural interpretation Deformation of upper plate Crustal structure Analog modeling Gravity inversion
Introduction The Manila Trench is an active convergent zone formed by the subduction of the South China Sea plate beneath the Philippine plate since the Middle Miocene (Taylor and Hayes 1983). It extends from the volcanic zone of Mindoro in the south to the Taiwan collision zone in the north (Sibuet and Hsu 1997). The Kaoping Slope and the Hengchun Ridge are recognized as the accretionary wedges formed by subduction in Neogene and Miocene, respectively (Fig. 1). The North Luzon Trough is viewed as the fore-arc basin, while the Luzon Arc is the volcanic arc (Huang et al. 2006). From south to north, the Mani
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