Tectonophysics 333 02001) 1±7 www.elsevier.com/locate/tecto Active subduction and collision in Southeast Asiaq S. Lallemanda,*, C.-S. Liub, J. Angelierc, Y.-B. Tsaid aUMR CNRS-UM2 5573, Laboratoire de GeÂophysique, Tectonique et SeÂdimentologie, ISTEEM, Case 60, place E. Bataillon, 34095 Montpellier, France bInstitute of Oceanography, National Taiwan University, P.O. Box 23-13, Taipei, Taiwan cESA 7072, Laboratoire de Tectonique, UPMC, T.26-25, E1, BoõÃte 129, 4 place Jussieu, 75252 Paris ceÂdex 05, France dSchool of Earth Sciences, National Central University, 38 Wu-Chuan Li, 32054, Chung-Li, Tao-Yuan, Taiwan Keywords: Subduction; Collision; Southeast Asia; Taiwan 1. Introduction orogenic forelands; 04) active tectonics in mountain belts; 05) GPS and kinematics; 06) variations in subduc- This volume contains a collection of 18 papers on tion parameters and their implications; 07) newdata in `Active subduction and collision in Southeast Asia' and around the Taiwan arc-continent collision; 08) presented at the SEASIA International Conference recent geochemical and geophysical advances on arcs and Fourth Sino-French symposium in Montpellier, and back-arcs; 09) complex evolution of arcs and back- France, May 9±12, 1999. Previous Sino-French arcs; and 010) seismicity and tectonics in Taiwan and symposia on Earth Sciences have been held in Taipei models of arc-continent collision. The meeting was 01984 and 1995) and Paris 01988). Proceedings have followed by a four-day ®eld trip in Corsica. been published in Angelier et al. 01986), Angelier Arc-continent collision0s) usually occur before the 01990) and Lallemand and Tsien 01997). main continent±continent collision0s). Ophiolitic More than one hundred scientists have attended this rocks providing evidence for the early stages of moun- fourth meeting, about one half coming from abroad tain building are observed in and around the suture zones 0Fig. 1). The previous Sino-French symposia mainly of most collisional mountain belts. Southeast Asia offers dealt with onland geology. During this meeting, the a wide range of both active and ancient convergent results of both marine research carried out offshore domains, where collisions between arcs and continents Taiwan and in the surrounding seas, and onland played an important role. Black stars in Fig. 2 showsuch studies were presented. active collision zones between the Luzon Arc and the Sixty oral presentations and forty posters were Chinese margin in Taiwan, the Izu-Bonin Arc and presented in ten sessions including 01) SE Asian Central Japan, the Kurile Arc and Hokkaido, the Halma- tectonics and kinematic reconstructions; 02) tectonic hera and Sulu Arcs against the Philippine mobile belt, processes at the Taiwan±Ryukyu junction area; 03) the Timor Arc and the Australian margin, and the Mela- interaction between tectonics and sedimentation in nesian Arc against NewGuinea. The white star marks the area of the collisions between two arc terranes and the Kamtchatka Peninsula during the Early Tertiary and q A preface to the special issue of Tectonophysics. Active subduc- at the end of the Miocene. tion and collision in Southeast Asia 0SEASIA), edited by S. Lalle- Despite its relatively small size, the Taiwan arc- mand, C.-S. Liu, J. Angelier and Y.-B. Tsai. * Corresponding author. continent collision is probably one of the most E-mail address: [email protected] 0S. Lallemand). actively studied in the world. This interest is raised 0040-1951/00/$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. PII: S0040-1951000)00263-8 2 S. Lallemand et al. / Tectonophysics 333 >2001) 1±7 Fig. 1. Group photo of the participants of the SEASIA Meeting in front of the Corum Building of Montpellier 0France). From back left to front right: Robert Hall, Rinus Wortel, Claude Rangin, Jacques Malod, SteÂphane Dominguez, Florent Hinschberger, Philippe Schnurle, Fred Wang, BenoõÃt Deffontaines, Jean-Claude Sibuet, Anne Replumaz, Jonathan Aitchison, Eileen Davis, Kensaku Tamaki, Chao-Shing Lee, Shu-Kun Hsu, Hung-Ming Kao, Siegfried Lallemant, Herman Munsch, Jinder Chow, Martin Block, Chung-Pai Chang, Honn Kao, FreÂdeÂric Mouthereau, Tim Byrne, Laurent Jolivet, Hao-Tsu Chu, Olivier Lacombe, Wim Spakman, Rene Maury, Anne Deschamps, Alexandra Martinez, Dany Hurpin, Edith Hafkenscheid, Heidrun Legelmann, Elena Konstantinovskaya, Francis Wu, Ching-Hui Tsai, Chang Chi-Fong, Xavier Le Pichon, Alexandre Chemenda, Maurice Brunel, Jean-Francois SteÂphan, Marc-Andre Gutscher, Kirk McIntosh, Teh-Quei Lee, Jih-Chuan Tang, Win- Bin Cheng, Jian-Cheng Lee, Jacques Angelier, Shui-Beih Yu, Serge Lallemand, Jean-Paul Cadet, Roland von Huene, Yvonne Font, Mireille PolveÂ, Jacques Malavieille, Yi-Ben Tsai, Chi-Yue Huang, Char-Shine Liu, Bee-Deh Yuan, Ho-Shing Yu, Chia-Yu Lu, Jyr-Shing Lee, Jiun- Chuan Lin, and Wen-Chen Jou. because the collision zone is young 0a fewmillion that elastic energy could be released near the deforma- years), extremely active, easily accessible and well tion front of the orogen with surface displacements up to monitored through geological, geophysical, geodetic 10 m both in the horizontal and vertical directions 0Ma and remote sensing approaches. et al., 1999). Hypocentral and focal determinations of The main plate boundaries in and around Taiwan the mainshock and aftershocks 0Kao and Chen, 2000) are shown in Fig. 3. Major collision occurred in are in agreement with the existence of a seismogenic Taiwan because the continental part of the Eurasia zone dipping 25 to 308 east beneath the central foothills 0EUR) plate 0including the Chinese continental area as expected from a `subduction' earthquake shelf) entered into subduction beneath the Luzon 0Lallemand, 2000; see BB0 on Fig. 3). There exists volcanic arc a fewmillions years ago. A simpli®ed another active fault: the Longitudinal Valley Fault section across the Manila Trench 0AA0 in Fig. 3) 0LVF) that has long been considered as `the' plate shows a typical oceanic subduction, whereas another boundary by many authors. The kinematic role of the section to the north across Taiwan 0BB0 in Fig. 3) LVF as an `eastern Taiwan plate boundary' is high- shows a less typical continental subduction beneath lighted by the occurrence of continuous creep, with an oceanic plate 0i.e. the Philippine Sea Plate, PSP). about 3 cm/year shortening. However, the kinematic The September 21, 1999 Mw7.6 Chi-Chi earthquake, contribution of the thrust zone at the belt front as which occurred in Central Taiwan, clearly demonstrated a `western Taiwan plate boundary' is similar in S. Lallemand et al. / Tectonophysics 333 >2001) 1±7 3 importance. As a rough preliminary estimate, assuming Lallemand and Angelier 02000a,b) have thus that the Chi-Chi earthquake represents about 3 m of proposed that the present-day plate boundary in average shortening and follows a period of about 100 Taiwan is essentially a twin-fault system 0Fig. 3) years of compressive stress accumulation, one obtains with contrasting mechanical behaviors in the upper the same average velocity of 3 cm/year as for the crust 0creep and periodical large earthquakes), at Longitudinal Valley. least for the present. 4 S. Lallemand et al. / Tectonophysics 333 >2001) 1±7 Fig. 3. Location of major plate boundaries in and around Taiwan. The two schematic sections AA0 and BB0 are located on the map. This ®gure is modi®ed from Lallemand and Angelier 02000b) and Lallemand 02000). The papers in this special issue are arranged on the the kinematic reconstructions. Hinschberger et al. basis of the investigation area, starting with Southeast 0this issue) provide additional constraints based on Asia including Indonesia, then moving along the magnetic anomalies interpretation for the Late Paci®c rim from the Kamtchatka to Taiwan. Miocene±Early Pliocene back-arc opening of the South Banda Basin that supports recent geochronolo- gical studies on dredge samples. Their results con®rm 2. The origin of back-arc basins in Southeast Asia the extreme youth of the basin despite its great depth. The paper by Milsom et al. 0this issue) aims at demon- The ®rst paper by Flower et al. 0this issue) presents strating that gravity variations and ophiolite distribu- an extensive reviewof isotopic data supporting a tion around the Banda Sea are consistent with model in which the openings of the Western Paci®c extension in the Sulawesi region following, and as a back-arc basins are linked with the extrusion of East result of Oligo±Miocene collision with an Australian- Asia in response to the `hard' collision between India derived microcontinent. and Eurasia. The link can be obtained by the singu- larity of the asthenosphere that has contaminated the basement of the Western Paci®c arcs, including the 3. Subduction and collision from the Kamtchatka Izu-Bonin±Mariana Arc. The next three papers to the Ryukyus concern the history of subduction, back-arc opening and post-orogenic `collapse' in the Indonesian region. A set of ®ve papers present detailed studies on Hafkenscheid et al. 0this issue) have computed seis- various subduction zones of the northwest Paci®c rim mic velocity models from kinematic reconstructions starting in Kamtchatka 0NE Russia). Konstantinovskaya and compared them to a recent tomographic model. 0this issue) proposes a model of arc-continent collision This technique allows them to discuss the validity of that evolved into a reversal of subduction, based on S. Lallemand et al. / Tectonophysics 333 >2001) 1±7 5 detailed ®eld studies in Kamtchatka. Gutscher 0this subduction are described as a logical suite of events issue) has applied a model of interplate coupling that occur during oblique arc-continent collision. Kao and strain partitioning that was developed for the and Jian 0this issue) provide the global seismogenic northern Andes 0Gutscher et al., 1999), to the `¯at' patterns in Taiwan based on a source parameter subduction of Nankai 0Southwest Japan). The model inversion of 96 earthquakes recorded by the newly infers that a newtranscurrent shear zone is developing established Broadband Array in Taiwan for Seis- along the northern rim of SW Japan, that should mology 0BATS).