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This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/authorsrights Author's personal copy Journal of Asian Earth Sciences 86 (2014) 1–11 Contents lists available at ScienceDirect Journal of Asian Earth Sciences journal homepage: www.elsevier.com/locate/jseaes Strain modes within the forearc, arc and back-arc domains in the Izu (Japan) and Taiwan arc-continent collisional settings Serge Lallemand ⇑ Géosciences Montpellier Laboratory, CNRS, Montpellier 2 University, CC.60, Place E. Bataillon, 34095 Montpellier, France Associated International Laboratory LIA ADEPT between NSC (Taiwan) and CNRS, France a r t i c l e i n f o Article history: Available online 20 August 2013 Keywords: Arc-continent collision Middle crust Intra-oceanic slivering Mantle decoupling Forearc subduction Luzon arc IBM arc a b s t r a c t In this study, I examine the strain modes of the forearc, arc and back-arc domains in arc-continent collisional settings leading to arc material subduction, delamination and/or accretion. The study focusses on two well-documented colliding island arcs: the Izu–Bonin–Mariana (IBM) arc in Japan and the Luzon arc in Taiwan, both carried by the Philippine Sea plate. Firstly, there is a body of evidence that both the IBM and the Luzon arcs were built on the same Late Jurassic to Early Cretaceous ‘‘proto-Philippine Sea Plate’’ crust. Their internal structure is thus more heterogeneous than expected from Paleogene or Neogene supposedly ‘‘intra-oceanic’’ island arcs. Secondly, those arc systems and proximal ‘‘back-arcs’’ have similar seismic characteristics attesting either for the presence of a middle crust with continental velocities and/or serpentinized uppermost mantle that facilitate crustal shortening/slivering and subsequent decoupling from the rest of the subducting plate. It is shown that the proximal back-arc domain (called ‘‘rear-arc’’ in case of paleoarc activity), overlying the mantle wedge and the subducting slab, may lose its strength if slab-derived hydration occur. Decoupling then occurs below the Moho. Arc delamination likely occurs in mid-crustal levels because middle-crust, heated by nearby magmatism, becomes weak. Accretion of arc material onto the upper plate depends on the characteristics of the arc itself and the geodynamic configuration. Most of the accreted material is probably underplated rather than frontally accreted. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Modern collisions between a volcanic arc and a continent are common in southeast Asia: Luzon arc in Taiwan, Izu–Bonin and Kurile arcs in Japan, Sulu and Halmahera arcs in the Philippines, Sunda arc in Indonesia or Melanesian arc in Papua – New Guinea (Lallemand et al., 2001a). Many authors have examined the ‘‘land’’ expression of such collisions by studying the associated orogens (e.g., Brown and Huang, 2009; Brown et al., 2011; Mann et al., 2011), the arc being often considered as a (semi-)rigid indenter pushing forward the continental upper crustal layers (e.g., Suppe, 1981; Wu et al., 1997; Malavieille and Trullenque, 2009). Some proportion of arc material may be scraped off the subducting plate and add to the growing orogen (e.g., Taira et al., 1998; Arai et al., 2009). In this study, I focus on the deformation of the subducting or colliding island arc from their initiation to the ultimate delamination/peeling or subduction. I do not describe onland outcrops of island arc slivers accreted to the overriding plate but rather examine the timing of the various deformation phases and the ingredients that control the localization of the arc deformation. E-mail address: [email protected] 1367-9120/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jseaes.2013.07.043 Well-constrained examples of such processes are found on both eastern and western borders of the Philippine Sea Plate (PSP). The collision of the Izu–Bonin–Mariana (IBM) Arc with central Japan has been carefully studied since the early eighties (e.g., Ogawa, 1983; Huchon and Kitazato, 1984; Soh et al., 1991; Taira et al., 1998; Mazzotti et al., 1999) but a new set of studies these last years has provided determining constraints on ongoing deep processes (e.g., Arai et al., 2009; Tamura et al., 2010; Tani et al., 2011). On the other side of the PSP, the Luzon Arc collides with Taiwan. Studies there were achieved later but again, efforts have been done these last two decades to better characterize the collision process, especially offshore (e.g., Wu et al., 1997; Teng et al., 2000; Lallemand et al., 2001b; Malavieille et al., 2002; Theunissen et al., 2012). Even if the geodynamic context differs from that in Japan, many similarities exist in these two situations and one may use the better knowledge of the IBM – Honshu collision to address questions in Taiwan, and vice versa. The two cartoons in Fig. 1 illustrate the common points and main differences between the geodynamic contexts in Taiwan and in Japan. In Taiwan, the Miocene to present Luzon volcanic arc results from the subduction of the South China Sea (SCS) oceanic lithosphere, which belongs to the Eurasia plate (EP), beneath the PSP. That subduction system ends at the latitude of (northern) Author's personal copy 2 S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 Taiwan and is relayed by an orthogonal subduction of the PSP beneath EP, so that the Luzon arc that overrides the EP in the southern part of Taiwan, subducts beneath the same EP east of northern Taiwan. To summarize the tectonic situation, one may say that the Luzon arc first collides with the Taiwan orogen as a result of the continental nature of the subducting EP at the latitude of Taiwan north of the SCS, and then collides with and subducts beneath the EP east of northern Taiwan. The convergence rate between both plates averages 8 to 9 cm/yr in the collision area and the convergence azimuth is oblique to both plate boundaries (Seno et al., 1993). The emerging part of the deformed Luzon arc forms the Coastal Range east of Taiwan (about 150 10 km). In Japan, the Eocene to present IBM arc results from the subduction of the Pacific plate (PAC) oceanic lithosphere beneath the PSP. The IBM arc is carried down the Nankai subduction zone at a rate of about 4 cm/yr as it is part of the subducting PSP. The emerging part of the deformed IBM arc forms the Izu Peninsula and collision zone (ICZ) along the southern coast of central Honshu. It covers an area of about 100 40 km. Despite variations in maturity, convergence rates and geometry of plate boundaries of both arc collision zones, we will see that their behavior is often similar in terms of deformation modes. 2. Recent advances in understanding the IBM arc and the ICZ in Japan 2.1. IBM arc origin and age Based on studies of forearc oceanic rocks, supposed to have formed as a result of subduction initiation stage along a former fracture zone (Stern and Bloomer, 1992), the inception of the IBM arc has been dated at 51–52 Ma (Ishizuka et al., 2011). Lallemand (1998) argued that an Early Eocene age is a minimum since the forearc rocks that have been sampled might have formed after subduction began, particularly if they did not formed in the former forearc (Deschamps and Lallemand, 2003). Indeed, IBM is an erosional margin with rates of forearc consumption of several kilometers per million years (von Huene and Scholl, 1991; Lallemand, 1995), and it may be that the oldest arc rocks have been consumed by subduction. Furthermore, the presence of Mesozoic continental crust in the Mariana forearc basement was suspected by Azéma and Blanchet (1982) after leg DSDP 60 when they discovered Late Jurassic–Early Cretaceous reworked pebbles in a volcanic matrix. More recently, Ishizuka et al. (2012) have described Jurassic basaltic pillow lavas with Indian Ocean MORB affinities in the Bonin forearc suggesting that Mesozoic crust constitutes the basement of the IBM arc. To summarize, most of the arc consists in a volcanic ridge that began to form in Early Eocene or earlier but there are striking evidences that part of the arc basement is inherited from a ‘‘proto-PSP’’ that is composed of older (Jurassic to Cretaceous detrital zircons), non-oceanic, possibly continental crust (Tani et al., 2012). 2.2. IBM arc seismic and petrological structure The oldest arc sequences mostly consist of tholeiitic basalts (Tamura et al., 2010). These Eo-Oligocene basaltic and rhyolitic rocks are exposed both in the forearc of the main actual IBM arc (sometimes in association with boninites) and along the PalauKyushu Ridge (Figs. 1 and 2) which is the remnant part of the pre-Miocene IBM arc rifted during the Miocene spreading of the Shikoku and Parece-Vela basins (e.g., Karig, 1971). This Eo-Oligocene arc was emplaced over a zone about 200 km wide across the present IBM arc (Suyehiro et al., 1996) to which the PalauKyushu Ridge must be added to restore the original arc. Based on seismic velocities, the crustal thickness varies from 20 to 30 km beneath the arc showing undulations with wavelengths of about Fig. 1. Map showing the northern part of the Philippine Sea Plate with main features and location of the two perspective views of the Luzon and Izu–Bonin arc collision zones. Note that the scales of each diagram is different even if horizontal and vertical proportions are similar. EP = Eurasia Plate; PSP = Philippine Sea Plate; PAC = Pacific Plate; Ky. = Kyushu; Sh. = Shikoku; and Hok. = Hokkaido. Author's personal copy S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 3 2.3. IBM ‘‘rear-arc’’ – transition between arc and back-arc The Izu–Bonin arc presents a singularity with respect to ‘‘classical’’ arcs. Mio-Pliocene volcanism occurred at distances up to 150 km back of the present volcanic front along en-échelon northeast-southwest trending ridges called ‘‘across-arc seamount chains’’ (Ishizuka et al., 2003; Fig. 2). These volcanoes first erupted contemporaneously with the last spreading episodes of the Shikoku Basin. Ishizuka et al. (2003) have demonstrated that the volcanism has migrated from west to east between 17 and 3 Ma. This migration coincides with the increasing dip of the Pacific slab caused by the motion change from trench rollback to advance around 8–5 Ma (Faccenna et al., 2009). The internal seismic structure of that region, called ‘‘rear-arc’’ by the authors, is similar to that of the main arc (Fig. 2). Indeed, it has been considered by Kodaira et al. (2008) as a paleoarc. Crustal thickness can reach 25–30 km beneath the rear-arc (Kodaira et al., 2007) but the thickest crust is not observed beneath volcanoes. For Kodaira et al. (2008), this finding suggests that the Mio-Pliocene volcanism may have been superimposed onto a crust formed before the opening of the Shikoku Basin. Rear-arc volcanic products are exposed in the Izu Peninsula. They consist of upper Miocene to Plio-Quaternary andesites and dacites (Tani et al., 2011). The most-striking across-arc seamount chain is the Zenisu Ridge which aligns parallel to the Nankai Trough south of the Izu Peninsula (Fig. 2; Lallemant et al., 1989). A small part of the ridge is subaerial (Zenisu Rocks outcrop of andesitic lava flows dated 2–3 Ma) but most of the ridge is submarine and older (Tani et al., 2011). A 6.4 Ma andesite was sampled in its central section and pillow basalts were collected along a fresh scarp at its southwest termination (Henry et al., 1997). A B Fig. 2. Top: Northern part of the IBM arc and collision area with central Japan (DEM and active volcanoes were extracted using SubMap tool http://submap.fr/) Dark triangles represent active volcanoes. The A–B profile of the bottom section and those of Figs. 3 and 4 are shown on the map. Bottom: Interpreted wide-angle velocity profile A–B after Takahashi et al. (2009). MC = Middle-crust. 100 km (Kodaira et al., 2007). Variations in crustal thickness mainly come from variations in thickness of the middle crust and, in a lesser extent, the lower crust (Takahashi et al., 2009). Middle-crust exhibits typically ‘‘continental crust’’ P-waves velocities VP between 5.7 and 6.8 km at depths ranging from 5 to 12 km (see section on Fig. 2; Kodaira et al., 2007). Such velocities commonly correspond to granites, diorites or tonalites (Tamura et al., 2010). Some authors like Tatsumi et al. (2008) considered that layer as an unsubductable nucleus of ‘‘continental’’ crust. The lower crust (6.7 < VP < 7.4 km/s at depths generally ranging from 10 to 20 km) is more mafic. It is likely composed of hornblende gabbros (Kitamura et al., 2003) or granulites derived from the melting and differentiation of underplated gabbros by comparison with the fossil Kohistan arc rocks sequence (Dhuime et al., 2009). Crustal materials are generally denser in the oldest Eocene arc than in the current volcanic arc (Takahashi et al., 2009). The upper crust (4.5 < VP < 6.0 km/s) consists of basalts, andesites and intrusives (Taira et al., 1998; Takahashi et al., 2007). 2.4. Focus on the Zenisu Ridge Before being described as an ‘‘across-arc seamount chain’’, the Zenisu Ridge was interpreted as an intra-oceanic sliver (Le Pichon et al., 1987b). The pillow basalts sampled at its southwestern edge thus represent the top layer of an uplifted oceanic crust sequence of the Shikoku Basin (Lallemant et al., 1989). Chamot-Rooke and Le Pichon (1989) have proposed a model of plate buckling and failure along a lithospheric thrust localized along the magmatic ridge, propagating further southwest into the oceanic crust, and caused by the compressive stress generated by the arc-continent collision. Nakanishi et al. (1998, 2002) found a 5 km vertical offset in the Moho beneath the south flank of the ridge supporting the lithospheric fault hypothesis. Given the dip angle of the thrusts imaged in reflection seismics, such offset should result in a 10 km throw along the main thrust which is not observed at the surface. Mazzotti et al. (2002) thus proposed a model of conjugated lowangle thrusts within the crust distributing the slip over a wide area. They also proposed that the serpentinized mantle–crust transition acts as a decoupling level above which distributed shortening may occur. Based on the deformation observed in the accretionary wedge landward of the ridge, Lallemand et al. (1992) have suggested that earlier oceanic slivers were formed, subducted and then potentially accreted to the margin. Le Pichon et al. (1996), Park et al. (2003) or Kimura et al. (2011) have confirmed, after a magnetic and a detailed seismic surveys, the presence in the subducting oceanic crust of two ridges, called ‘‘paleo-Zenisu’’ and ‘‘deeper paleo-Zenisu’’, elongated parallel to the Zenisu ridge (Fig. 3). Based on pre-stack MCS depth migration and full waveform inversion from dense OBS data, Kodaira et al. (2004) and Dessa et al. (2004) have proposed a tectonic interpretation of the thrusts that affect the ‘‘paleo-Zenisu’’ ridge. Knowing today that most of the Zenisu ridge has a magmatic origin with middle crust velocities, we have adapted the tectonic model of the Author's personal copy 4 S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 Fig. 3. Free tectonic interpretation of the section TKY1 (see Fig. 2 for location of the profile) superimposed on the velocity profile derived from a wide-angle dense OBS survey published by Park et al. (2003). The top of the subducting basement is those proposed by Park et al., whereas the major thrusts are inspired by the line drawings of Mazzotti et al. (2002), Kodaira et al. (2004) and Dessa et al. (2004). The presence of middle crust is inspired by Takahashi et al. (2009). UC = Upper crust; MC = Middle crust; and LC = Lower crust. previous authors onto the velocity profile of Park et al. (2003) assuming that most of the low-angle thrusts localize within the crust, and that the uppermost mantle, or the mantle–crust transition, acts as a decoupling layer (Fig. 3). 2.5. Deformation mode in the Izu Collision Zone (ICZ) According to Taira et al. (1989) or Soh et al. (1991), collision between the IBM arc and Honshu arc might have begun as early as 15 Ma ago. Plates reconstructions (Sdrolias and Müller, 2006) rather predict a collision further west around 15 Ma near the Shikoku island and a beginning of collision with central Honshu around 10 Ma in better agreement with the end of Japan Sea opening. During its subduction, the IBM arc is supposed to have crept eastward along the Nankai Trough until about 5–8 Ma and then westward until present (Faccenna et al., 2009) so that the ICZ was confined to central Honshu, with some sinistral and dextral motion component, probably during the last 10 million years. Successive slivers of IBM arc material accreted onto Honshu since the beginning of the collision. The Tonoki–Aikawa Tectonic Line (TATL) is considered as the tectonic boundary between the original Honshu crust (Kanto Mountains) to the north and the accreted slivers (Tanzawa mountains, Izu Peninsula, Zenisu Ridge) to the south (e.g., Arai et al., 2009). Some other authors include another unit to the north delimited by the Mineoka Tectonic Line (Taira et al., 1998; Soh et al., 1998). Fig. 4 shows a simplified along-strike section across – from south to north – the undeformed IBM arc, the ICZ including the accreted IBM-derived units and the shortened crust of Honshu (Tamura et al., 2010). Two main Miocene batholiths are observed in the ICZ: the Tanzawa tonalites and the Kofu Granitic Complex. Based on their composition, Tamura et al. (2010) consider that they are derived from syn-collisional partially melted Oligocene middle crust. Based on an intensive seismic experiment, it has been possible to trace the TATL down to about 18 km beneath the Kanto mountains (Arai et al., 2009). From the geometry of reflectors and the seismic activity, the Tanzawa block, with VP typical of upper to middle crust of the IBM arc, appears delaminated from the subducting slab forming a wedge-like body which is inserted, through low-angle thrusts, between the upper and lower crust of Honshu. These results strongly suggest that the middle crust of the IBM arc is weak and localizes the intraarc deformation, allowing the lower crust and the mantle part of the arc to subduct with the rest of the PSP. Such process is in agreement with observations of arc-continent or continent–continent collisions in other contexts like the fossil Kohistan arc in eastern Himalaya (Burg et al., 2005) or the Alps (Schmid et al., 1996). Fig. 4. Schematic cross-section of the Izu–Bonin arc and the Honshu arc along a profile located on Fig. 2 after Tamura et al. (2010). The Kofu Granitic Complex and the Tanzawa tonalites were emplaced during the Miocene within the ICZ. TATL = Tonoki–Aikawa Tectonic Line. Closed and open-triangles show respectively basalt-dominant and rhyolite-dominant volcanoes. Author's personal copy S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 3. Recent advances in understanding the Taiwan collision zone (TCZ) 3.1. Luzon arc origin and age The Luzon volcanic arc results from the subduction of the South China Sea oceanic lithosphere beneath the PSP since mid-Miocene right after the cessation of back-arc spreading of the South China Sea (Defant et al., 1989; Briais et al., 1993). Late Oligocene to Early Miocene calc-alkaline volcanism is only found in northwest Luzon island and Dalupiri island (Yang et al., 1996) but these occurrences have been attributed by Polvé et al. (2007) to a short-lived episode of westward subduction of the PSP lithosphere beneath Luzon. After a quiescent period, magmatic activity resumed around 15 Ma in relation with the start of eastward subduction of the SCS off Luzon island. Geochemical patterns observed in these calc-alkaline lavas from 15 to 1 Ma reflect the progressive addition to the Luzon arc mantle wedge of SCS sediment (Polvé et al., 2007). Manila Trench extends from west of Luzon to the latitude of Taiwan, which probably did not exist yet in Miocene. Indeed, many authors consider that the orogen of Taiwan results from an arccontinent collision starting between 6.5 Ma (Huang et al., 1997) and 3 or even 2 Ma (Malavieille et al., 2002). However, Lu and Hsu (1992) have proposed a two-stage collision at 12 Ma and 3 Ma. Most absolute ages obtained on lavas from volcanoes situated north of Luzon Island are younger than 10 Ma (Defant et al., 1989; Yang et al., 1996). Closer to Taiwan, ages obtained on Lutao and Lanyu andesites cover a period between 3.9 and 5.5 Ma (McDermott et al., 1993). There is still an isolated oldest age around 16 Ma obtained on lavas from the Chimei complex which outcrops in the northern part of the Coastal Range of Taiwan (Juang and Bellon, 1984; Lo et al., 1994) that led Yang et al. (1995) to conclude that the volcanic activity of the arc segment forming the present Coastal Range of Taiwan extended from 16 to 2 Ma. The cessation of magmatism in the northern part of the Luzon arc coincides with the start of the collision between the arc and the Chinese continental platform. An interesting point is that recent radiolarian biostratigraphic results provide evidence for the existence of a Mesozoic substratum upon which Luzon and the neighboring regions within the Philippine archipelago were built (Queano et al., 2013). Similar ages were found by Deschamps et al. (2000) on gabbros dredged in the Huatung Basin east of the Taiwan, from radiolarian assemblages collected on Lanyu island (Yeh and Cheng, 2001), in eastern Indonesia (Ali et al., 2001) as well as in the basement of the IBM ridge (Ishizuka et al., 2012) or the Amami Plateau (Hickey-Vargas, 2005) and Oki-Daito ridges (Ishizuka et al., 2011) suggesting a common provenance. 5 trapped piece of an old oceanic basin (Deschamps et al., 2000), a composite back-arc basin with an old (Mesozoic ?) part in the south and an Eocene part in the north (Sibuet et al., 2002) or an Oligo-Miocene oceanic basin (Kuo et al., 2009). Since Hickey-Vargas et al. (2008) found an Indian MORB-OIB Hf–Nd isotopic signature and Pb isotope ratios intermediate between Indian and Pacific MORB in the mantle source of the gabbros dredged in the Huatung Basin, it likely corresponds to a trapped piece of early Cretaceous oceanic crust produced at a ridge overlying an Indian-type mantle as proposed by Deschamps et al. (2000). This old oceanic lithosphere might have been rejuvenated later in order to reconcile its geochronological and ‘‘isotopic’’ age with its ‘‘seismic’’ and ‘‘gravity’’ age (Kuo et al., 2009). Indeed, the basement of the basin is 400 m shallower than the theoretical depth according to normal thermal subsidence (Deschamps et al., 2000). Furthermore, the crust of the Huatung Basin is abnormally thick in some locations: up to 10 km (Yang and Wang, 1998) or even up to 16 km (McIntosh and Nakamura, 1998). Various scenarii can be proposed including the influence of a plume that would have thickened the crust or a rejuvenation caused by convective cells activated from the Manila subduction ‘‘back-arc’’ mantle dynamics, but since the subducting crust and the subduction itself are both young, it seems unlikely (Arcay, personal communication). Based on two onlandoffshore integrated seismic experiments (TAICRUST and TAIGER projects), McIntosh et al. (2005) and Kuo-Chen et al. (2012) have built velocity models across southern Taiwan (see location on Fig. 5). Despite some global agreement between the two models, they obtain quite different pictures along sections distant by only 50 km. Along the TAICRUST lines 29–33 at the latitude of Lanyu, McIntosh et al. (2005) have imaged a 30 km thick crust below the forearc region which was supposed to underthrust the 6 km crustal layer of the arc as a result of the collision with the Chinese platform. Further north at the latitude of Lutao (Fig. 5), Kuo-Chen 3.2. Luzon arc and ‘‘back-arc*’’ seismic and petrological structure The seismic structure of the Luzon arc is less known than that of the IBM arc except in its northern part near Taiwan where the Luzon arc collides with the Chinese margin. The width of the arc drastically reduces between northern Luzon island and southern Taiwan from 200 to 50 km even if, as mentioned above, early Cretaceous radiolarian cherts were sampled in both places (Luzon and Lanyu) indicating that the same Mesozoic substratum probably lies underneath the entire volcanic arc. Regarding the origin of the Huatung Basin situated in the backside of the arc, many interpretations have been given including an Eocene part of the West Philippine Basin (Hilde and Lee, 1984), an Early Cretaceous ⁄ The term ‘‘back-arc’’ here refers to the Huatung Basin which is today located back of the Luzon arc. It does not mean that the basin opened in a ‘‘back-arc’’ position as the result of a trench rollback. Fig. 5. Map of the Luzon arc (dark triangles = active volcanoes) with location of seismic profiles discussed in the text. S.O.T. = Southern Okinawa Trough; SRA = Southern Ryukyu Arc; PSP = Philippine Sea Plate; and EP = Eurasian Plate. Author's personal copy 6 S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 Fig. 6. Free tectonic interpretation of a velocity section obtained by Kuo-Chen et al. (2012) as a result of the TAIGER experiment. EP = Eurasia Plate; PSP = Philippine Sea Plate; HVZ = High Velocity Zone; LVZ = Low Velocity Zone; and MC = Middle Crust. See Fig. 5 for profile location. et al. (2012) found a Moho beneath the PSP at variable depths (Fig. 6): 27 km beneath the Coastal Range and the arc (Lutao), 40 km in between and 12 km beneath the Huatung Basin. Three points merit attention along this section. First, the rise of high velocities (HVZ) beneath the Longitudinal Valley (noted ‘‘suture’’ on Fig. 6) and the deepening of the Moho between the orogen and the arc support the ‘‘forearc subduction’’ model of Chemenda et al. (1997). Second, as in the IBM arc, a thick (10 km) sequence with ‘‘middle-crust’’ velocities is observed right beneath the extinct Lutao volcano (see MC on Fig. 6). Third, well-resolved low velocities (LVZ) are observed in the Huatung Basin, presumably within the uppermost mantle, down to 25 km (Fig. 6; Kuo-Chen et al., 2012). 3.3. Deformation mode in the Luzon arc and ‘‘proximal back-arc ’’ In terms of deformation mode, the situation differs from the IBM case, not only because of the ‘‘maturity’’ of the island arc (Miocene vs Eocene), but also because of the nature of the indenter. Indeed on one hand, the Chinese platform acts as an indenter with respect to the PSP and more specifically with respect to the northern Luzon volcanic arc including the Coastal Range of Taiwan, north of 22°N (see Fig. 1). On another hand, the ‘‘indented’’ northern Luzon arc, acts itself as an indenter north of 23°N, with respect to the EP under which it subducts. Onshore and offshore geological and geophysical records and observations east of Taiwan show that the arc and ‘‘back-arc’’ strain is dominated by the collision with the Chinese platform. 3.3.1. Effects of the collision between the Luzon arc and the Chinese platform The main feature observed south of Taiwan is the underthrusting of the whole forearc basement beneath the arc within less than 200 km along strike (Fig. 6; Chemenda et al., 1997; Malavieille et al., 2002; Shyu et al., 2011). The width of the forearc basement does not exceed 60 km at the latitude of the Batan islands south of Taiwan so that, if we consider that the forearc block was fully locked with the subducting plate (extreme case) and a splay (out of sequence) fault accommodated its underthrusting, about 1 m.y. is enough for the forearc to totally disappear from the surface. If the convergence partitioned equally between frontal The ‘‘proximal back-arc’’ refers to the domain of a back-arc that is close to the arc. When it is associated with arc magmatism, it is called ‘‘rear-arc’’ like in IBM. subduction and the splay fault, then 2 m.y. are needed for full subduction of the forearc block which is still plausible with respect to convergence rates. The forearc block, about 45 km long and 25 km thick, is well identified on the velocity profile at the latitude of Lutao (Fig. 6). It appears tilted clockwise as it underthrusts the arc. The narrow Coastal Range is mostly made of forearc and intra-arc sedimentary material including an ophiolitic mélange (Lichi), detrital and volcanoclastic series and limited volcanic rocks (Chimei complex) in the northern part (Huang et al., 1995). Based on the Moho depth extracted from two different 3D-tomographic models, Kuo-Chen et al. (2012) and Theunissen et al. (2012) have shown that the root axis of the volcanic arc aligns about 10 ± 5 km offshore the east coast. They also noticed that the Coastal Range was underlain by a narrow (10 km wide) high-velocity zone (HVZ) that could be interpreted as relics of the forearc basement squeezed in the suture zone (Figs. 6 and 7a). Moreover, there are seismic evidences that the arc itself is decoupled from the PSP all along the Coastal Range along west-dipping thrusts (Lallemand et al., 1999; Malavieille et al., 2002). Both tomography and seismicity confirm the previous hypothesis of Chemenda et al. (1997) that incipient subduction of the PSP occurs off the east coast of Taiwan north of 23°300 N. Despite the fact that part of the arc overthrusts the Taiwan orogen along the Longitudinal Valley separating the Coastal from the Central ranges, the arc is shortened and underthrust beneath the Central Range north of the Coastal Range (Fig. 7a; Lallemand et al., 2013). Upper crustal slices may ultimately be accreted to EP, thanks to decoupling levels allowing the Huatung Basin lithosphere to subduct beneath the arc. Only relics of the forearc are detected between the orogen and the arc up to the section illustrated on Fig. 7a (see HVZ), suggesting that the main part of the forearc has been subducted to larger depths. 3.3.2. Effects of the collision between the Luzon arc and the South Ryukyu margin Active and passive seismic experiments were conducted in 2008 and 2009 (RATS-TAIGER project) with a dense OBS network in the southern Ryukyu forearc area where the arc-continent collision culminates as attested by the seismic deformation (Klingelhoefer et al., 2012; Theunissen et al., 2012). The new 3-D velocity model, as well as the improved resolution of earthquakes distribution, allowed Lallemand et al. (2013) to revisit the PSP deformation in its subducted part below the Southern Ryukyu arc (Fig. 7b). The two orthogonal velocity profiles shown on Fig. 7 (see location on Fig. 5) were interpreted using constraints Author's personal copy S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 7 Fig. 7. Two orthogonal velocity sections obtained after the RATS experiment in the southernmost Ryukyu forearc (Lallemand et al., 2013). Sections are located in Fig. 5. EP = Eurasia Plate; PSP = Philippine Sea Plate; SRA = Southern Ryukyu arc; MC = Middle crust; LVZ = Low velocity zone; HVZ = High velocity zone; A.W. = accretionary wedge; and S.O.T. = Southern Okinawa Trough. Grey dots are M > 3 relocated 1992–2008 earthquakes. from adjacent lines, seismicity distribution, focal mechanisms of earthquakes, upper plate deformation and any available data in the survey area. Thrusting mainly develops along NNE-SSW faults as a result of the collision between the arc and the Taiwan orogen even in the subducted part of the PSP (Fig. 7a). The thrusting is likely responsible for local thickening of the oceanic crust. The short wavelength of the oceanic slivers indicates a shortening mainly confined within crustal levels rather than lithospheric buckling. In a direction normal to the Ryukyu subduction zone (Fig. 7b), no compressional feature is observed within the subducting plate. On the contrary, the slab appears down-faulted along a major shear zone which has been interpreted by Lallemand et al. (2013) as an incipient sinistral tear accommodating the differential stress between E–W compression in the south and free subduction in the north (Lallemand et al., 1997). As observed by Kuo-Chen et al. (2012) and Klingelhoefer et al. (2012), velocities are rather low in the mantle beneath the Huatung Basin crust (see low velocity zones (LVZ) in Fig. 7). These low velocities were attributed by Klingelhoefer et al. to mantle serpentinization. On the contrary, some ‘‘relatively’’ high velocity regions were mapped in the basement of the Southern Ryukyu arc right above the ramp in the subducting PSP (Fig. 7b). These velocities are similar to those observed below the Coastal Range and Longitudinal Valley. It may thus represent relics of the subducting Luzon arc or forearc basement squeezed or accreted in the collision zone. This would be the only expression of a ‘‘collision’’ between the subducting Luzon arc and the Southern Ryukyu arc. 4. Comparison of the deformation styles and possible analogies 4.1. Crustal distinctive characteristics and rheology of an island arc and its proximal ‘‘back-arc’’ We have shown that based on seismic velocities, both arc and proximal ‘‘back-arc’’ (called ‘‘rear-arc’’ by Japanese authors) crusts show seismic and petrological characteristics contrasting from a regular oceanic crust. Thick sections characterized by intermediate velocities between 5.7 and 6.8 km/s are interpreted as the presence of middle crust in the IBM arc and rear-arc by analogy with the rocks exposed in the Izu Peninsula (Tani et al., 2011). Burg et al. (2005) have described in detail the processes of shear strain localization from uppermost mantle to middle-crust levels in the exceptional outcrops of the fossil Kohistan island arc in Pakistan. They observed that the plutonic lower crust of the arc is strongly affected by sub-horizontal, syn-magmatic shear zones, probably consistent with the bulk flow direction of the paleo-subduction zone. Whatever the origin of this middle crust is in the IBM arc: continental or differentiated from underplated gabbros, the rocks should be weak and prone to shear. One may notice that the same seismic structure in the IBM arc and rear-arc lead to different levels of decoupling. It either occurs within the weak middle crust in the arc probably because it is heated by the active volcanic activity, or below the Moho in the rear-arc. In the last case, the lithosphere is certainly colder because volcanism is no more active but the uppermost mantle might have been Author's personal copy 8 S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 serpentinized by dewatering from the subducting Pacific slab. Rocks of the middle and lower crust of the Luzon arc do not outcrop even though the crust exhibits similar seismic characteristics to that of the IBM arc. Along the velocity section shown in Fig. 7a, the Taiwan orogen is backthrust onto the Luzon arc but the arc itself decouples from the adjacent Huatung Basin and could still potentially be accreted to the orogen. The proximal Huatung Basin oceanic crust, although much older than the Shikoku Basin, shows anomalous low velocities (LVZ) down to a depth of about 25 km (Fig. 6) or even 50 km (Fig. 7). Three non-exclusive explanations can been proposed: – Since the Huatung Basin is sliced by numerous north–south trending fracture zones (Deschamps et al., 1998) and east–west trending neo-formed normal faults caused by plate bending before subduction (e.g., Schnürle et al., 1998), seawater can penetrate to great depths and serpentinize the oceanic crust and even the uppermost lithospheric mantle (e.g., Ranero et al., 2003). – The western part of the Huatung basin lies above the subducting EP slab at least south of 23°N today (see Fig. 6). Considering the thermal state of the subducting oceanic crust, slab dehydration can occur down to 150 km depth and cause serpentinization of the top lithospheric mantle (Arcay et al., 2005). – The crust has been thickened and rejuvenated when passing above a plume in Eo-Oligocene time (Deschamps and Lallemand, 2003). The first two processes produce serpentinites that favor shear strain localization and low-angle thrusting within the crust and the uppermost mantle if compression occurs. The last process rather produces OIB but differentiation may also occur in case of thick accumulation of oceanic material. 4.2. Crustal versus lithospheric deformation Based on seismic imagery, the ICZ appears to be mainly constructed by the stacking of upper and mid-crustal slivers scraped off the subducting IBM arc (Fig. 4; Arai et al., 2009; Tamura et al., 2010). First interpretations, which proposed that thrusting along the Zenisu Ridge might cut through the entire lithosphere, should result in successive seaward jumps of the subduction interface associated with duplication of the slab thickness in the subduction zone, which is not observed. Data re-examination and new data acquisition show that compressive features like the Zenisu Ridge or the accreted imbricates of the ICZ only affect the crustal levels. Decoupling occurs in the middle crust along the main ridge and beneath the Moho in the uppermost mantle in the ‘‘rear-arc’’ (Fig. 8). Because of the special configuration of the arc-continent collision in Taiwan, i.e., the main collision involves an arc system on the upper plate and a subducting ocean-continent transition zone, part of the deformation occurs at a lithospheric scale (forearc subduction) and part at a crustal scale (arc and proximal ‘‘back-arc’’ crustal shortening). Two mechanical explanations can be invoked for the subduction of the Luzon forearc: – forearc buckling and horizontal compression caused by the subducting buoyant Chinese continental platform (Chemenda et al., 2001; Tang et al., 2002) and/or – increasing friction between the two converging plates caused by the cooling of the forearc as a result of the decreasing convergence rate (Arcay et al., 2007). The high velocities observed at depth between the arc and the Taiwan orogen (HVZ in Figs. 6 and 7a) might attest for the presence of cool forearc basement material (Kuo-Chen et al., 2012; Lallemand et al., 2013). Moreover slab dehydration should be amplified Fig. 8. Simplified cartoons of Izu and Taiwan collision zones with three schematic sections illustrating the two main levels of decoupling during arc-continent collision. For Taiwan, only the collision between the Luzon arc and the Chinese continental platform has been sketched because the other arc collision with the overriding southern Ryukyu arc is probably much less important than the previous one. Section BB’ across the Nankai Trough might also illustrate the case of the Luzon arc subducting beneath the SRA except that the vergence of the thrusts in the Huatung Basin are orthogonal to the trench. COB = Continent-ocean boundary; PBA = Proximal back-arc; AW = accretionary wedge; CP = Chinese platform; ICZ = Izu collision zone; IBM = Izu–Bonin–Mariana arc; T.C. = Tenryu Canyon; and M = Moho. Author's personal copy S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 by the northward decrease in subduction rate as a result of continental subduction (Arcay et al., 2007). Lithospheric mantle weakening may thus occur right above the slab dehydration domain, i.e., in the arc and proximal ‘‘back-arc’’. One may also expect that water impregnation of the mantle favors melting, but no volcanic activity was mentioned in the Huatung Basin except one controversed report off the Coastal Range in 1853 (Chen and Shen, 2005). Such uppermost mantle weakening combined with crustal hydrothermalism and eventually the presence of ‘‘middle crust’’ in the arc favor the development of crustal and uppermost mantle shortening whereas the lower lithospheric PSP mantle subducts beneath the Taiwan orogen. 4.3. Arc (and ‘‘back-arc’’) accretion in the collision zone Arc and ‘‘rear-arc’’ crustal accretion has been demonstrated by many authors in the ICZ (e.g., Taira et al., 1998; Tani et al., 2011). Accretion is restricted to the upper crustal levels in the arc itself and may involve the uppermost lithospheric mantle in the ‘‘reararc’’ domain. Present observations in the Nankai margin do show deformation in the overriding wedge like ridges controlled by out-of-sequence thrusts (Lallemand et al., 1992; Lallemant et al., 1995; Dessa et al., 2004) or the presence of a transfer zone, which surface expression is the Tenryu Canyon in the prolongation of the Akaishi Tectonic Line, accommodating the differential motion between the normal subduction to the west and shortening above the rear-arc domain (Le Pichon et al., 1987a, 1996, see T.C. in Fig. 8). Despite no direct observations, Shikoku Basin crustal accretion beneath the accretionary wedge, thanks to a decoupling level located in the uppermost mantle, is suspected (Fig. 8). East of northern Taiwan, the slivering of the crustal part of the arc and proximal ‘‘back-arc’’ is reflected in the shallower bathymetry of the Southern Ryukyu forearc basement which is uplifted with respect of the rest of the forearc (Font et al., 2001; Lallemand et al., 2013). As a consequence, the crust is probably decoupled from the PSP lithospheric mantle. A décollement level in the uppermost mantle of the Huatung Basin is required to accommodate the shortening of the crust and the westward subduction of the lower part of the Huatung lithosphere (see LVZ in Figs. 7 and 8). The crustal wedge is underthrusted beneath the Central Range north of 24°N (Fig. 7a, Lallemand et al., 2013) and could potentially be accreted to the orogen. With respect to the northward subduction beneath the Southern Ryukyu arc, rather than massive accretion of the crustal wedge, little evidences of arc or forearc material were found in the deeper parts of the SRA basement based on seismic velocities (HVZ in Fig. 7b). 5. Conclusions The comparative examination of the deformation modes within two colliding island arcs of the PSP lead us to a series of observations that illustrate original mechanical processes of arc-continent interaction in collision zones. The Luzon and IBM arcs were both emplaced on the same Late Jurassic–Early Cretaceous ‘‘proto-PSP’’ crust. The studied island arcs have distinctive petrological and rheological characteristics that facilitate strain localization. Forearc lithospheric subduction is favored when a continent subducts beneath a volcanic arc because of the combination of increasing compression due to continental crust buoyancy and increasing friction due to forearc cooling as a result of subduction slowing. The oceanic crust and uppermost mantle adjacent with the arc on the back-arc side is still under the influence of the 9 subducting slab as attested either by ancient magmatism (northern IBM rear-arc) or by a higher hydration (Huatung Basin). Slab hydration is amplified if subduction slows and slab dip increases. Accretion of arc material onto the upper plate is not systematic. It strongly depends on the characteristics of the arc itself and the geodynamic configuration. When accretion occurs, like in the Izu collision zone, only upper crustal levels are involved. The main part of the lithosphere still subducts. In Taiwan, similar conclusions may be reached except that no surface outcrop attests yet for arc crustal accretion. Only seismic evidences might indicate that arc and/or forearc material may be underplated beneath the upper plate. In both cases, decoupling levels allow the delamination between upper and lower lithospheric levels. Such decoupling levels can be either facilitated by the presence of ‘‘weak and hot middle crust’’ or serpentinized uppermost mantle. Acknowledgements I acknowledge Michel Faure and Yan Chen who invited me to present a keynote at the International Conference ‘‘Tectonics of Asia’’ hold in Orléans in November 2012 in honour of Jacques Charvet, with whom I shared memorable discussions about the IBM subduction in Japan at the end of the eighties and early nineties. It was a unique opportunity for me to reconcile some early work in Japan with present studies in Taiwan. Anne Delplanque has done a tremendous work in drawing most of the illustrations. I have tested some suggested processes of lithospheric weakening through ‘‘recurrent’’ discussions with Diane Arcay. I also deeply thank Ken Tani, Jin-Oh Park, Hao Kuo-Chen, Stéphane Mazzotti, Stéphane Dominguez, Y. Font, Thomas Theunissen, Jacques Malavieille, René Maury, Hervé Bellon, Jean-Louis Bodinier, Fleurice Parat, Adolphe Nicolas, Françoise Boudier and Fred Gueydan for the scientific discussions or help. The revised manuscript has benefited from two anomymous reviews. References Ali, J.R., Hall, R., Baker, S.J., 2001. Paleomagnetic data from a Mesozoic Philippine Sea Plate ophiolite on Obi Island, Eastern Indonesia. Journal of Asian Earth Sciences 19, 537–548. Arai, R., Iwasaki, T., Sato, H., Abe, S., Hirata, N., 2009. Collision and subduction structure of the Izu–Bonin arc, central Japan, revealed by refraction/wide-angle reflection analysis. Tectonophysics 475, 438–453. Arcay, D., Tric, E., Doin, M.-P., 2005. Numerical simulations of subduction zones: effect of slab dehydration on the mantle wedge dynamics. Physics of the Earth and Planetary Interiors 149, 133–153. Arcay, D., Doin, M.-P., Tric, E., Bousquet, R., 2007. Influence of the precollisional stage on the subduction dynamics and the buried crust thermal state: insights from numerical simulations. Tectonophysics 441, 27–45. Azéma, J., Blanchet, R., 1982. The late-jurassic-early cretaceous genus Calpionella in reworked pebbles from deep-sea drilling project site 460, Mariana transect. In: Hussong, D.M., Uyeda, S., et al., Initial Reports of the DSDP, vol. 60, U.S. Govt. Printing Office, Washington, pp. 575–576. Briais, A., Patriat, P., Tapponnier, P., 1993. Updated interpretation of magnetic anomalies and seafloor spreading stages in the South China Sea: implications for the Tertiary tectonics of Southeast Asia. Journal of Geophysical Research 98, 6299–6328. Brown, D., Huang, C.-Y., 2009. An introduction to the Tectonophysics special issue on arc-continent collision processes. Tectonophysics 479, 1–3. Brown, D., Ryan, P.D., Afonso, J.C., Boutelier, D., Burg, J.P., Byrne, T., Calvert, A., Cook, F., DeBari, S., Dewey, J.F., Gerya, T.V., Harris, R., Herrington, R., Konstantinovskaya, E., Reston, T., Zagorevski, A., 2011. Arc-continent collision: the making of an orogen. In: Brown, D., Ryan, P.D. (Eds.), Arc-Continent Collision, Frontiers in Earth Sciences. ÓSpringer-Verlag, Berlin, Heidelberg. http://dx.doi.org/10.1007/978-3-540-88558-0_17. Burg, J.P., Arbaret, L., Chaudhry, M., Dawood, H., Hussain, S., Zeilinger, G., 2005. Shear strain localization from the upper mantle to the middle crust of the Kohistan Arc (Pakistan). In: Bruhn, D., Burlini, L. (Eds.), High-Strain Zones: Structure and Physical Properties, vol. 245. Geological Society, Special Publications, London, pp. 25–38. Author's personal copy 10 S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 Chamot-Rooke, N., Le Pichon, X., 1989. Zenisu ridge – mechanical model of formation. Tectonophysics 160, 175–193. Chemenda, A., Yang, R.K., Hsieh, C.H., Groholsky, A.L., 1997. Evolutionary model for the Taiwan collision based on physical modelling. Tectonophysics 1–3, 253– 274. Chemenda, A.I., Yang, R.K., Stéphan, J.F., Konstantinovskaya, E.A., Ivanov, G.M., 2001. New results from physical modelling of arc-continent collision in Taiwan: evolutionary model. Tectonophysics 33 (1–2), 159–178. Chen, C.-H., Shen, J.J.-S., 2005. A refined historical record of volcanic eruptions around Taiwan: tectonic implications in the arc-continent collision area. Terrestrial, Atmospheric and Oceanic Sciences 16 (2), 331–343. Defant, M.J., Jacques, D., Maury, R.C., De Boer, J.Z., Joron, J.L., 1989. Geochemistry of the Luzon arc, Philippines. Geological Society of America Bulletin 101, 663–672. Deschamps, A., Lallemand, S., 2003. Geodynamic setting of Izu–Bonin–Mariana boninites. In: Larter, R.D., Leat, P.T. (Eds.), Intra-oceanic Subduction Systems: Tectonic and Magmatic Processes, vol. 219. Geological Society, Special Publications, London, pp. 163–185. Deschamps, A.E., Lallemand, S.E., Collot, J.Y., 1998. A detailed study of the Gagua Ridge: a fracture zone uplifted during a plate reorganization in the Mid-Eocene. Marine Geophysical Researches 20, 403–423. Deschamps, A., Monié, P., Lallemand, S., Hsu, S.-K., Yeh, K.-Y., 2000. Evidence for Early Cretaceous crust trapped in the Philippine Sea Plate. Earth and Planetary Science Letters 179, 503–516. Dessa, J.X., Operto, S., Kodaira, S., Nakanishi, A., Pascal, G., Uhira, K., Kaneda, Y., 2004. Deep seismic imaging of the eastern Nankai trough, Japan, from multifold ocean bottom seismometer data by combined travel time tomography and prestack depth migration. Journal of Geophysical Research 109, B02111. http:// dx.doi.org/10.1029/2003JB002689. Dhuime, B., Bosch, D., Garrido, C.J., Bodinier, J.-L., Bruguier, O., Husain, S.S., Dawood, H., 2009. Geochemical Architecture of the Lower- to Middle-crustal Section of a Paleo-island Arc (Kohistan Complex, Jijal-Kamila Area, Northern Pakistan): implications for the evolution of an oceanic subduction zone. Journal of Petrology 50 (3), 531–569. Faccenna, C., Di Giuseppe, E., Funiciello, F., Lallemand, S., van Hunen, J., 2009. Control of seafloor ageing on the migration of the Izu–Bonin–Mariana trench. Earth and Planetary Science Letters. http://dx.doi.org/10.1016/ j.epsl.2009.09.042. Font, Y., Liu, C.-S., Schnürle, P., Lallemand, S., 2001. Constraints on backstop geometry from the southwest Ryukyu Subduction based on reflection seismic data. Tectonophysics 333 (1–2), 135–158. Henry, P., Mazzotti, S., Maury, R., Robert, C., Lallemant, S.J., 1997. Uplifted oceanic crust outcrops on Zenisu Ridge. JAMSTEC Journal of Deep Sea Research 13, 509– 520. Hickey-Vargas, R., 2005. Basalt and tonalite from the Amami Plateau, northern West Philippine Basin: new Early Cretaceous ages and geochemical results, and their petrologic and tectonic implications. The Island Arc 14, 653–665. Hickey-Vargas, R., Bizimis, M., Deschamps, A., 2008. Onset of the Indian Ocean isotopic signature in the Philippine Sea Plate: Hf and Pb isotope evidence from Early Cretaceous terranes. Earth and Planetary Science Letters 268, 255–267. Hilde, T.W.C., Lee, C.-S., 1984. Origin and evolution of the West Philippine Basin: a new interpretation. Tectonophysics 102, 85–104. Huang, C.-Y., Yuan, P.B., Song, S.-R., Lin, C.-W., Wang, C., Chen, M.-T., Shyu, C.-T., Karp, B., 1995. Tectonics of short-lived intra-arc basins in the arc-continent collision terrane of the Coastal Range, eastern Taiwan. Tectonics 14 (1), 19–38. Huang, C.-Y., Wu, W.-Y., Chang, C.-P., Tsao, S., Yuan, P.B., Lin, C.-W., Kuan-Yuan, X., 1997. Tectonic evolution of accretionary prism in the arc-continent collision terrane of Taiwan. Tectonophysics 281, 31–51. Huchon, P., Kitazato, H., 1984. Collision of the Izu block with central Japan during the Quaternary and geologic evolution of the Ashigara area. Tectonophysics 110, 201–210. Ishizuka, O., Uto, K., Yuasa, M., 2003. Volcanic history of the back-arc region of the Izu–Bonin (Ogasawara) arc. In: Larter, R.D., Leat, P.T. (Eds.), Intra-oceanic Subduction Systems: Tectonic and Magmatic Processes, vol. 2. Geological Society, Special Publications, London, pp. 187–205. Ishizuka, O., Tani, K., Reagan, M.K., Kanayama, K., Umino, S., Harigane, Y., Sakamoto, I., Miyajima, Y., Yuasa, M., Dunkley, D.J., 2011. The timescales of subduction initiation and subsequent evolution of an island arc. Earth and Planetary Science Letters 306, 229–240. Ishizuka, O., Tani, K., Harigane, Y., Reagan, M.K., Stern, R.J., Taylor, R.N., Sakamoto, I., 2012. Evidence for Mesozoic basement in the Izu–Bonin–Mariana arc system. Abstract in: Japan Geoscience Union Meeting 2012, Makuhari, Chiba, Japan (May 20–25). Juang, W.S., Bellon, H., 1984. The potassium-argon dating of andesites from Taiwan. Proceedings of the Geological Society of China 27, 86–100. Karig, D.E., 1971. Origin and development of marginal basins in western Pacific. Journal of Geophysical Research 76 (11), 2542–2561. Kimura, G., Moore, G.F., Strasser, M., Screaton, E., Curewitz, D., Streiff, C., Tobin, H., 2011. Spatial and temporal evolution of the megasplay fault in the Nankai Trough. Geochemistry Geophysics Geosystem 12, Q0A008. http://dx.doi.org/ 10.1029/2010GC003335. Kitamura, K., Ishikawa, M., Arima, M., 2003. Petrological model of the northern Izu– Bonin–Mariana arc crust: constraints from high-pressure measurements of elastic waves velocities of the Tanzawa plutonic rocks, central Japan. Tectonophysics 371, 213–221. Klingelhoefer, F., Berthet, T., Lallemand, S., Schnürle, P., Lee, C.-S., Liu, C.-S., McIntosh, K., Theunissen, T., 2012. Velocity structure of the southern Ryukyu margin east of Taiwan: new results from ACTS wide-angle seismic experiment. Tectonophysics 578, 50–62. http://dx.doi.org/10.1016/j.tecto.2011.10.010. Kodaira, S., Iidaka, T., Kato, A., Park, J.-O., Iwasaki, T., Kaneda, Y., 2004. High pore fluid pressure may cause silent slip in the Nankai Trough. Science 304, 1295– 1298 (20 May 2004). Kodaira, S., Sato, T., Takahashi, N., Miura, S., Tamura, Y., Tatsumi, Y., Kaneda, Y., 2007. New seismological constraints on growth of continental crust in the Izu– Bonin intra-oceanic arc. Geology 35 (11), 1031–1034. Kodaira, S., Sato, T., Takahashi, N., Yamashita, M., No, T., Kaneda, Y., 2008. Seismic imaging of a possible paleoarc in the Izu intraoceanic arc and its implications for arc evolution processes. Geochemistry, Geophysics, Geosystems 9, 10. http://dx.doi.org/10.1029/2008GC002073. Kuo, B.-Y., Chi, W.-C., Lin, C.-R., Chang, T.-Y., Collins, J., Liu, C.-S., 2009. Two-station measurement of Rayleigh-wave velocities for the Huatung basin, the westernmost Philippine Sea, with OBS: implications for regional tectonics. Geophysical Journal International 179, 1859–1869. Kuo-Chen, H., Wu, F.T., Roecker, S.W., 2012. Three-dimensional P velocity structures of the lithosphere beneath Taiwan from the analysis of TAIGER and related seismic data sets. Journal of Geophysical Research 117, B06306. http:// dx.doi.org/10.1029/2011JB009108. Lallemand, S.E., 1995. High rates of arc consumption by subduction processes: some consequences. Geology 23 (6), 551–554. Lallemand, S.E., 1998. Possible interaction between mantle dynamics and high rates of arc consumption by subduction processes in circum-Pacific area. In: Flower, M.F.J., Chung Sun-Lin, Lo Ching-Hua, Lee Tung-Yi (Eds.), Mantle Dynamics and Plate Interactions in East Asia, Geodynamic Series AGU, vol. 27, pp. 1–10. Lallemand, S.E., Malavieille, J., Calassou, S., 1992. Effects of oceanic ridge subduction on accretionary wedges: experimental modeling and marine observations. Tectonics 11 (6), 1301–1313. Lallemand, S.E., Liu, C.-S., Font, Y., 1997. A tear fault boundary between the Taiwan orogen and the Ryukyu subduction zone. Tectonophysics 274 (1/3), 171–190. Lallemand, S., Liu, C.-S., Dominguez, S., Schnürle, P., Malavieille, J., The ACT Scientific Crew, 1999. Trench-parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern Ryukyus: a case of strain partition caused by oblique convergence. Tectonics 18 (2), 231–247. Lallemand, S., Liu, C.-S., Angelier, J., Tsai, Y.-B., 2001a. Active subduction and collision in Southeast Asia. Tectonophysics 333 (1–2), 1–7. Lallemand, S., Font, Y., Bijwaard, H., Kao, H., 2001b. New insights on 3-D plates interaction near Taiwan from tomography and tectonic implications. Tectonophysics 335 (3–4), 229–253. Lallemand, S., Theunissen, T., Schnürle, P., Lee, C.-S., Liu, C.-S., Font, Y., 2013. Indentation of the Philippine Sea Plate by the Eurasia Plate in Taiwan: details from recent marine seismological experiments. Tectonophysics 594, 60–79. Lallemant, S., Chamot-Rooke, N., Le Pichon, X., Rangin, C., 1989. Zenisu Ridge: a deep intraoceanic thrust related to subduction, off Southwest Japan. Tectonophysics 160 (1–4), 161–174. Lallemant, S.J., Lallemand, S.E., Cadet, J.-P., Chamot-Rooke, N., Iiyama, J., von Huene, R., Tokuyama, H., Glaçon, G., 1995. First in-situ observation at a major backthrust system of an active accretionary prism (eastern Nankai Trough – Japan). Bulletin de la Société Géologique de France 6 (166), 823– 834. Le Pichon, X., Iiyama, T., Chamley, H., Charvet, J., Faure, M., Fujimoto, H., Furuta, T., Ida, Y., Kagami, H., Lallemant, S., Leggett, J., Muruta, A., Okada, H., Rangin, C., Renard, V., Taira, A., Tokuyama, H., 1987a. The eastern and western ends of Nankai Trough: results of Box 5 and Box 7 Kaiko survey. Earth and Planetary Science Letters 83, 199–213. Le Pichon, X., Iiyama, T., Boulègue, J., Charvet, J., Faure, M., Kano, K., Lallemant, S., Okada, H., Rangin, C., Taira, A., Urabe, T., Uyeda, S., 1987b. Nankai Trough and Zenisu Ridge: a deep-sea submersible survey. Earth and Planetary Science Letters 83, 285–299. Le Pichon, X., Lallemant, S., Tokuyama, H., Thoué, F., Huchon, P., Henry, P., 1996. Structure and evolution of the backstop in the eastern Nankai Trough area (Japan): implications for the soon-to-come Tokai earthquake. The Island Arc 5, 440–454. Lo, C.H., Onstott, T.C., Chen, C.H., Lee, T., 1994. An assessment of 40Ar/39Ar dating for the whole-rock volcanic samples from the Luzon arc near Taiwan. Chemical Geology 114, 157–178. Lu, C.-Y., Hsu, K.J., 1992. Tectonic evolution of the Taiwan mountain belt. Petroleum Geology of Taiwan 27, 21–46. Malavieille, J., Trullenque, G., 2009. Consequences of continental subduction on forearc basin and accretionary wedge deformation in SE Taiwan: insights from analogue modeling. Tectonophysics 466, 377–394. Malavieille, J., Lallemand, S.E., Dominguez, S., Deschamps, A., Lu, C.-Y., Liu, C.-S., Schnürle, P., The ACT Scientific Crew, 2002. Arc-continent collision in Taiwan: New marine observations and tectonic evolution. Geological Society of America Special Paper, vol. 358, pp. 187–211. Mann, P., Vargas, C., Whitehill, C., 2011. Neotectonics of arc-continent collision. Geological Society of America Today (July 2011), 36–38. Mazzotti, S., Henry, P., Le Pichon, X., Sagiya, T., 1999. Strain partitioning in the zone of transition from Nankai subduction to Izu–Bonin collision (Central Japan): implications for an extensional tear within the subducting slab. Earth and Planetary Science Letters 172, 1–10. Mazzotti, S., Lallemant, S.J., Henry, P., Le Pichon, X., Tokuyama, H., Takahashi, N., 2002. Intraplate shortening and underthrusting of a large basement ridge in the eastern Nankai subduction zone. Marine Geology 187, 63–88. Author's personal copy S. Lallemand / Journal of Asian Earth Sciences 86 (2014) 1–11 McDermott, F., Defant, M.J., Hawkesworth, C.J., Maury, R.C., Joron, J.L., 1993. Isotope and trace element evidence for three component mixing in the genesis of the North Luzon lavas (Philippines). Contrib. Mineral. Petrol. 113, 9–23. McIntosh, K.D., Nakamura, Y., 1998. Crustal structure beneath the Nanao forearc basin from TAICRUST MCS/OBS Line 14. Terrestrial, Atmospheric and Oceanic Sciences 9 (3), 345–362. McIntosh, K., Nakamura, Y., Wang, T.-K., Shih, R.-C., Chen, A., Liu, C.-S., 2005. Crustal-scales seismic profiles across Taiwan and the western Philippine Sea. Tectonophysics 401, 23–54. Nakanishi, A., Shiobara, H., Hino, R., Kodaira, S., Kanazawa, T., Shimamura, H., 1998. Detailed subduction structure across the eastern Nankai Trough obtained from ocean bottom seismograph profiles. Journal of Geophysical Research 103, 27151–27168. Nakanishi, A., Shobara, H., Hino, R., Mochizuki, K., Sato, T., Kasahara, J., Takahashi, N., Suyehiro, K., Tokuyama, H., Segawa, J., Shinohara, M., Shimahura, H., 2002. Deep crustal structure of the eastern Nankai Trough and Zenisu Ridge by dense airgun-OBS seismic profiling. Marine Geology 187, 47–62. Ogawa, Y., 1983. Mineoka ophiolite belt in the Izu forearc area – Neogene accretion of oceanic and island arc assemblages on the northeastern corner of the Philippine Sea Plate. In: Hashimoto, M., Uyeda, S. (Eds.), Accretion Tectonics in the Circum-Pacific Regions, TERRAPUB, Tokyo, pp. 245–260. Park, J.-O., Moore, G.F., Tsuru, T., Kodaira, S., Kaneda, Y., 2003. A subducted oceanic ridge influencing the Nankai megathrust earthquake rupture. Earth and Planetary Science Letters 217, 77–84. Polvé, M., Maury, R.C., Jego, S., Bellon, H., Margoum, A., Yumul Jr, G.P., Payot, B.D., Tamayo Jr., R.A., Cotten, J., 2007. Temporal geochemical evolution of Neogene magmatism in the Baguio gold–copper mining district (northern Luzon, Philippines). Resource Geology 57 (2), 197–218. Queano, K.L., Marquez, E.J., Aitchison, J.C., Ali, J.R., 2013. Radiolarian biostratigraphic data from the Casiguran ophiolite, northern Sierra Madre, Luzon, Philippines: stratigraphic and tectonic implications. Journal of Asian Earth Sciences 65, 131–142. Ranero, C.R., Phipps-Morgan, J., McIntosh, K., Reichert, C., 2003. Bending-related faulting and mantle serpentinization at the Middle America trench. Nature 425, 367–373 (25 September 2003). Schmid, S.M., Pfiffner, O.A., Froitzheim, N., Schönborn, G., Kissling, E., 1996. Geophysical–geological transect and tectonic evolution of the Swiss-Italian Alps. Tectonics 15, 1036–1064. Schnürle, P., Liu, C.-S., Lallemand, S.E., Reed, D., 1998. Structural insight into the south Ryukyu margin: effects of the subducting Gagua Ridge. Tectonophysics 288, 237–250. Sdrolias, M., Müller, R.D., 2006. Controls on back-arc formation. Geochemistry, Geophysics, Geosystems 7 (4), Q04016. http://dx.doi.org/10.1029/ 2005GC001090. Seno, T., Stein, S., Gripp, A.E., 1993. A model for the motion of the Philippine Sea plate consistent with NUVEL-1 and geologic data. Journal of Geophysical Research 98, 17941–17948. Shyu, J.B.H., Wu, Y.-M., Chang, C.-H., Huang, H.-H., 2011. Tectonic erosion and the removal of forearc lithosphere during arc-continent collision: evidence from recent earthquake sequences and tomography results in eastern Taiwan. Journal of Asian Earth Sciences 42, 415–422. Sibuet, J.-C., Hsu, S.-K., Le Pichon, X., Le Formal, J.-P., Reed, D., Moore, G., Liu, C.-S., 2002. East Asia plate tectonics since 15 Ma: constraints from the Taiwan region. Tectonophysics 344, 103–134. Soh, W., Pickering, K.T., Taira, A., Tokuyama, H., 1991. Basin evolution in the arc–arc Izu collision zone, Mio-Pliocene Miura Group, central Japan. Journal of the Geological Society, London 148, 317–330. Soh, W., Nakayama, K., Kimura, T., 1998. Arc–arc collision in the Izu collision zone, central Japan, deduced from the Ashigara basin and adjacent Tanzawa Mountains. The Island Arc 7, 330–341. Stern, R.J., Bloomer, S.H., 1992. Subduction zone infancy: examples from the Eocene Izu–Bonin–Mariana and Jurassic California arcs. Geological Society of America Bulletin 104, 1621–1636. Suppe, J., 1981. Mechanics of mountain building and metamorphism in Taiwan. Memoirs of the Geological Society of China 4, 67–89. 11 Suyehiro, K., Takahashi, N., Ariie, Y., Yokoi, Y., Hino, R., Shinohara, M., Kanazawa, T., Hirata, N., Tokuyama, H., Taira, A., 1996. Continental crust, crustal underplating, and low-Q upper mantle beneath an island arc. Science 272, 390–392. Taira, A., Tokuyama, H., Soh, W., 1989. Accretion tectonics and evolution of Japan. In: Ben-Avraham, Z. (Ed.), The Evolution of the Pacific Ocean Margins. Oxford Univ. Press, New York, pp. 100–123. Taira, A., Saito, S., Aoike, K., Morita, S., Tokuyama, H., Suyehiro, K., Takahashi, N., Shinohara, M., Kiyokawa, S., Naka, J., Klaus, A., 1998. Nature and growth rate of the northern Izu–Bonin (Ogasawara) arc crust and their implications for continental crust formation. The Island Arc 7, 395–407. Takahashi, N., Kodaira, S., Klemperer, S.L., Tatsumi, Y., Kaneda, Y., Suyehiro, K., 2007. Crustal structure and evolution of the Mariana intra-oceanic island arc. Geology 35, 203–206. http://dx.doi.org/10.1130/G23212A.1. Takahashi, N., Kodaira, S., Tatsumi, Y., Yamashita, M., Sato, T., Kaiho, Y., Miura, S., No, T., Takizawa, K., Kaneda, Y., 2009. Structural variations of arc crusts and rifted margins in the southern Izu-Ogazawara arc–back arc system. Geochemistry, Geophysics, Geosystems 10 (9), Q09X08. http://dx.doi.org/10.1029/ 2008GC002146. Tamura, Y., Ishizuka, O., Aoike, K., Kawate, S., Kawabata, H., Chang, Q., Saito, S., Tatsumi, Y., Arima, M., Takahashi, M., Kanamaru, T., Kodaira, S., Fiske, R.S., 2010. Missing Oligocene crust of the Izu–Bonin arc: consumed or rejuvenated during collision ? Journal of Petrology, 1–24. Tang, J.-C., Chemenda, A.I., Chéry, J., Lallemand, S., Hassani, R., 2002. Compressional subduction regime and initial arc-continent collision: numerical modeling. Geological Society of America Special Paper 358, 177–186. Tani, K., Fiske, R.S., Dunkley, D.J., Ishizuka, O., Oikawa, T., Isobe, I., Tatsumi, Y., 2011. The Izu Peninsula, Japan: zircon geochronology reveals a record of intra-oceanic rear-arc magmatism in an accreted block of Izu–Bonin upper crust. Earth and Planetary Science Letters 303, 225–239. Tani, K., Ishizuka, O., Ueda, H., Shukuno, H., Hirahara, Y., Nichols, A.R.L., Dunkley, D.J., Horie, K., Ishikawa, A., Morishita, T., Tatsumi, Y., 2012. Izu-Bonin arc: Intraoceanic from the begining ? Unraveling the crustal structure of the Mesozoic proto-Philippine Sea Plate. Abstract in: AGU Fall Meeting, San Francisco (December 2012). Tatsumi, Y., Shukuno, H., Tani, K., Takahashi, N., Kodaira, S., Kogiso, T., 2008. Structure and growth of the Izu–Bonin–Mariana arc crust: 2. Role of the crustmantle transformation and the transparent Moho in arc crust evolution. Journal of Geophysical Research 113, B02203. http://dx.doi.org/10.1029/2007JB005121. Teng, L.S., Lee, C.T., Tsai, Y.B., Hsiao, L.Y., 2000. Slab breakoff as a mechanism for flipping of subduction polarity in Taiwan. Geology 28 (2), 155–158. Theunissen, T., Lallemand, S., Font, Y., Gautier, S., Lee, C.-S., Liang, W.-T., Wu, F., Berthet, T., 2012. Crustal deformation at the southernmost part of the Ryukyu subduction (East Taiwan) as revealed by new marine seismic experiments. Tectonophysics 578, 10–30. http://dx.doi.org/10.1016/ j.tecto.2012.04.011. von Huene, R., Scholl, D.W., 1991. Observations at convergent margins concerning sediment subduction, subduction erosion, and the growth of continental crust. Reviews of Geophysics 29 (3), 279–316. Wu, F.T., Rau, R.J., Salzberg, D., 1997. Taiwan orogeny: thin skinned or lithospheric collision. Tectonophysics 274, 191–220. http://dx.doi.org/10.1016/S00401951(96)00304-6. Yang, Y.-S., Wang, T.-K., 1998. Crustal velocity variation of the western Philippine Sea Plate from TAICRUST OBS/MCS Line 23. Terrestrial, Atmospheric and Oceanic Sciences 9 (3), 379–394. Yang, T.F., Tien, J.L., Chen, C.-H., Lee, T., Punongbayan, R.S., 1995. Fissiontrack dating of the Taiwan–Luzon arc: eruption ages and evidence for crustal contamination. Journal of Southeast Asian Earth Sciences 11, 81– 93. Yang, T.F., Lee, T., Chen, C.-H., Cheng, S.-N., Knittel, U., Punongbayan, R.S., Rasdas, A.R., 1996. A double island arc between Taiwan and Luzon: consequence of ridge subduction. Tectonophysics 258, 85–101. Yeh, K.-Y., Cheng, Y.-N., 2001. The first finding of Early Cretaceous radiolarians from Lanyu, the Philippine Sea Plate. Bulletin of the National Museum of Natural Sciences 13, 111–146.