Mar Geophys Res DOI 10.1007/s11001-013-9175-7 ORIGINAL RESEARCH PAPER Segmentation of the Manila subduction system from migrated multichannel seismics and wedge taper analysis Junjiang Zhu • Zongxun Sun • Heidrun Kopp • Xuelin Qiu • Huilong Xu • Sanzhong Li • Wenhuan Zhan Received: 12 December 2012 / Accepted: 25 April 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Based on bathymetric data and multichannel It suggests that subduction accretion dominates the north seismic data, the Manila subduction system is divided into Luzon and seamount chain segment, but the steep slope three segments, the North Luzon segment, the seamount indicates in the West Luzon segment and implies that chain segment and the West Luzon segment starts in tectonic erosion could dominate the West Luzon segment. Southwest Taiwan and runs as far as Mindoro. The volume variations of the accretionary prism, the forearc slope Keywords Manila subduction system Á Accretion and angle, taper angle variations support the segmentation of erosion Á Accretionary/frontal prism Á Forearc slope angle the Manila subduction system. The accretionary prism is and taper angle Á Tsunami earthquake Á Splay faults composed of the outer wedge and the inner wedge sepa- rated by the slope break. The backstop structure and a 0.5–1 km thick subduction channel are interpreted in the Introduction seismic Line 973 located in the northeastern South China Sea. The clear de´collement horizon reveals the oceanic Convergent margins are the site of subduction processes sediment has been subducted beneath the accretionary including accretion, tectonic underplating and subduction prism. A number of splay faults occur in the active outer erosion. Subduction accretion and subduction erosion wedge. Taper angles vary from 8.0° ± 1° in the North (tectonic erosion) have been observed and elucidated in the Luzon segment, 9.9° ± 1° in the seamount segment to past decades. The observations of the subduction system 11° ± 1° in the West Luzon segment. Based on variations can be explained by the above two end-member models. between the taper angle and orthogonal convergence rates Subduction accretion preferentially occurs in regions of in the world continental margins and comparison between slow convergence (\7.6 cm year-1) and/or trench sedi- our results and the global compilation, different segments ment thickness [1 km (Clift and Vannucchi 2004). The of the Manila subduction system fit well the global pattern. material within the wedge is shortened horizontally by folding and thrusting similar to analog models (Lallemand et al. 1994). A weaker base of the sediments enhances the & J. Zhu ( ) Á Z. Sun Á X. Qiu Á H. Xu Á W. Zhan growth of the wedge (Ellis et al. 1999; Beaumont et al. Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences (CAS), 1999). Accretionary wedge (prism) has been analyzed in 164 West Xingang Rd., Guangzhou 510301, People’s Republic terms of a static force balance using critical wedge theory of China (Davis et al. 1983; Dahlen 1990) and dynamic Coulomb e-mail: [email protected] wedge theory (Wang and Hu 2006). Accretionary prisms H. Kopp are formed by the external tectonic addition of sedimentary Helmeholtz Center for Ocean Research Kiel (GEOMAR), rocks through lithospheric convergence at a subduction Wischhofstrasse 1-3, 24148 Kiel, Germany zone (Moore and Silver 1987). Commonly between the accretionary prism and the underthrusting oceanic crust, a S. Li College of Marine Geosciences, Ocean University of China, de´collement zone is observed (Bangs and Westbrook 1991; Qingdao 266100, China Bangs et al. 1999; Park et al. 2002; Bangs et al. 2003) 123 Mar Geophys Res along the plate boundary. Megasplay faults are very long reflector (BSR) was imaged in the accretionary prism and thrust-type reverse-faults that rise from the subduction seismic attributes indicate that gas hydrate and free gas plate boundary megathrust and intersect the sea floor at the layers are present at the place of BSR (Deng et al. 2006). landward edge of the accretionary prism (Park et al. 2002; The integrated seismic interpretations were related to the Moore et al. 2007). Slip on the megasplay faults in the plate regional tectonic evolution of the northeastern South China boundary contributed to generating devastating historic Sea (Li et al. 2007) and tectonic features, such as frontal tsunami (Park et al. 2002; Moore et al. 2007). de´collement and out-of-sequence of thrusts in the accre- In the Manila subduction system, oceanic lithosphere of tionary wedge (Lin et al. 2009). The purpose of this paper the South China Sea subducts eastward beneath the Phil- is to present a new compilation and analysis of multi- ippine Sea plate along the Manila trench (Bowin et al. channel seismic and bathymetric data which have increased 1978; Taylor and Hayes 1980) (Fig. 1). Most recent our understanding the subduction accretion and erosion in researches focus on the region between Taiwan and Luzon. the convergent continental slope along the Manila trench. The Manila subduction zone includes a very well devel- The main aim is to establish the segmentation of the sub- oped fore arc basin system, the West Luzon Trough and the duction system and to determine which end-member model North Luzon Trough (Ludwig 1970; Pautot and Rangin or mixture model controls the individual segments. 1989). The disappearance of the Manila trench to the west of Henchun ridge/peninsula seems to correlate with a sudden drop in the number of outer rise earthquakes there Tectonic setting of the Manila subduction system (Kao et al. 2000). The accurate northward extension of the Manila trench to southern Taiwan or as a buried feature is The onset of rifting of the proto-China margin occurred still debated (Bowin et al. 1978; Lewis and Hayes 1984; during the latest Cretaceous or Paleocene (65 ± 10 Ma) Liu et al. 1997; Hsiung and Yu 2011). In the east of the (Taylor and Hayes 1983) and is manifested as thereafter South China Sea, a historical M7.5 tsunami event on seafloor spreading evidenced by magnetic anomalies in the February 14, 1934 was reported (Heck 1947; Engdahl and South China Sea marginal basin (Taylor and Hayes 1980, Villasenor 2002; Duong et al. 2009). The generated loca- 1983; Briais et al. 1993; Hsu et al. 2004; Hsu and Sibuet tion of this event could be offshore in the South China Sea 2004; Barckhausen and Roeser 2004) in Middle Oligocene/ at 18°N, 118°E (Berninghausen 1969). The exact location early Middle Miocene time (32–17 Ma). The extinct of this event is the latitude 17°240N, the longitude spreading center has a complex configuration trending 119°11.40E and the focal depth of 35 km (see earthquake N60°E and is dissected by N50°W trending transform catalogues shown in Engdahl and Villasenor 2002) located faults (Pautot and Rangin 1989). The lithosphere of the between the Line 10 and Line 11 (Fig. 1) within the obli- South China Sea becomes older both to the north and to the que seamount subduction domain. Tsunami height may south away from the east–west trending relict spreading reach 14 m near the Philippines and southwest of Taiwan center now located between 15°N and 16°N (Fig. 1) (Bo- at the Manila trench (Ha et al. 2009). The Stewart Bank has win et al. 1978; Taylor and Hayes 1980, 1983). Based on been proposed as a seamount protruded through the forearc the reconstruction of the South China Sea region, the in the surface (Pautot and Rangin 1989), and it is not clear Manila trench was located at the eastern side of the South whether the seamount subduction is related to this event China Sea basin in the early Miocene when the seafloor although it is very close to this tsunami event (Fig. 1). The spreading has proceeded (Taylor and Hayes 1983) or at the subduction convergence rate decreases southwards from southern side in the middle Miocene when southward 98 mm year-1 to 52 mm year-1 as established by GPS subduction of proto-South China Sea initiated at 45 Ma measurements (Rangin et al. 1999) and no large difference (Hall 2002). The Manila subduction system progressively with other investigations (Seno et al. 1993; Kuo et al. evolves from normal subduction to initial arc-continent 1999). Subduction accretion clearly dominates the north collision of the Taiwan orogen (Suppe 1984; Kao et al. Manila subduction system, however, in the central and the 2000). Seismicity patterns indicate a clear subduction zone, southern portion it remains unclear which mechanism although the deepest seismic events occur only to about dominates which segment. 200 km (Kao et al. 2000; Zhu et al. 2005). Between about In 2001, a 240 multichannel seismic (MCS) section 116°E and 118°Eat15°N, many of the seamounts of the (Line 973, Fig. 2) was acquired by Guangzhou Marine Scarborough chain have formed along the axis of the Geological Survey (GMGS) of the Chinese Ministry of central segment (Pautot et al. 1986) (Fig. 1). The Scar- Land and Resources (Li 2005). Seismic interpretations of borough Seamount Chain is present near the axis of the this line were published and addressed questions in the seafloor spreading magnetic lineation (Taylor and Hayes different aspects (Deng et al. 2006; Ding et al. 2006;Li 1980; 1983; Briais et al. 1993; Hsu et al. 2004; Barck- et al. 2007; Lin et al. 2009). A clear bottom-simulating hausen and Roeser 2004). The Philippine Sea plate is 123 Mar Geophys Res Fig. 1 The bathymetric map along the Manila trench. Bathymetric of the Ms 7.5 tsunami earthquake on 14 February 1934 (location from data is from the GEBCO 1-min grid (http://www.gebco.net/data_ Engdahl and Villasenor 2002).