Éditeur(s) : HAL CCSD Elsevier
Résumé : 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.
ISSN: 0743-9547

hal-01243080
https://hal.archives-ouvertes.fr/hal-01243080
DOI : 10.1016/j.jseaes.2013.07.043

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The active collision zone around Taiwan orogen receives a variety of sedimentary inputs, including terrigenous flux from Taiwan and Chinese rivers, oceanic currents and atmospheric dust. In order to determine the present-day respective contributions of these different sources, we analysed the Pb and Sr isotopic compositions of late Quaternary sediments accumulated offshore east Taiwan. Samples from the Taiwan Coastal Range (andesites, sandstones, conglomerate and Peinan River terraces and suspended loads) have also been analysed to constrain the mean Taiwan isotopic signature. Mixing lines between the different sources of material indicate that the core located in the Okinawa Trough represents a mixture of about 60% of Taiwan, 30% of Chinese Loess and 10% of Yangtze River contributions. The southernmost core, located close to Luzon Are, is influenced by Taiwan (60%) and volcanic material (40%). The Sr and Pb isotopic compositions of samples cored in the Manila Trench and in the Huatung Basin are strongly influenced by the Taiwan signature, while the Ryukyu Trench core samples point to significant but variable contributions of Chinese Loess and Yangtze River. This work also reports Zn isotopic variations in the silicate fraction of these marine core samples. The overall variation in Zn isotopic compositions (expressed as 666 Zn) is greater than 0.3 per mil (parts per thousand) for an analytical precision of +/- 0.05 parts per thousand. The Zn isotopic signal for most of the marine core samples is similar to the literature data measured on sedimentary material, except for the Manila Trench core samples and the older sample from the Huatung Basin: they present values heavier by 0.2-0.3 parts per thousand, close to those obtained on all Taiwan rocks and Peinan River particulates. These results show: 1- the particular characteristics of Taiwan Zn isotopic compositions on a large scale; and: 2- the possible use of Zn isotopes as a tracer of material sources.
ISSN: 0009-2541

hal-00412214
https://hal.archives-ouvertes.fr/hal-00412214
DOI : 10.1016/j.chemgeo.2007.10.024

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In southeastern Taiwan a slice of forearc basement belonging to the Philippine Sea Plate upper-plate is suspected to subduct under the Luzon arc as a consequence of the transition from oceanic to incipient continental subduction. Effects on the morphology, deformation, geometry of structures and tectonic evolution of the orogenic wedge in the collision area are numerous. This study examines the impact of foreare lithosphere subduction on forearc basin and accretionary wedge deformation. A morpho-structural analysis of the geological features observed onland and offshore allows describing in detail the complex deformation suffered by the area. A combined approach by analogue modeling is applied to better understand the phenomenon. Comparison between nature and experimental results shows that subduction of a forearc basement slice induces intense shortening and concomitant deformation in the foreare domain. Such process involves deformation of the foreare basin previously developed in a setting of oceanic subduction. Sediments of the forearc basin are involved in the growth of a new thrust ridge backthrusted against the basement slope of the volcanic arc edifice. Sediments coming from the growing orogenic wedge are trapped in the trough developed between its backpart and the topographic high of the new rising ridge. A syn-collisional orogenic basin develops which structural evolution characterizes the progressive shortening of the forearc domain. Most of the deformation and tectonic events recorded offshore or onland in the complex area south of Taiwan can be explained using results of our specific modeling which well describe the tectonic processes associated with continental subduction under a volcanic are.
ISSN: 0040-1951

hal-00420080
https://hal.archives-ouvertes.fr/hal-00420080
DOI : 10.1016/j.tecto.2007.11.016

Éditeur(s) : HAL CCSD
Résumé : In Taiwan , the subduction of the Chinese continental margin under the Luzon arc results in the progressive growth of an active orogenic wedge. It is one of the best places to study the complex relationships that occurs between the tectonic processes controlling deformation (plate rheology and kinematics, metamorphism and magmatism) and surface processes (erosion and sedimentation). In order to study the kinematics of the present day convergence of Philippine Sea plate to the Asian continent around Taiwan, we perform 2D and 3D sandbox modeling and we analyzed the models with PIV (Particle Image Velocimetry) software. In 2D experiments, a model Coulomb wedge is submitted to erosion and sedimentation under topography and flux steady state conditions. The 3D experiments are mainly used to study the escape tectonics occurring in the middle west and southwest Taiwan. A wedge shaped indenter and a basement relief were used to simulate the mechanical plate boundary between Philippine Sea plate and Eurasia plate and the basement topography to the west of Taiwan respectively. We examine the exhumation patterns, the mode of fault propagation and displacement patterns by strain partitioning of vertical vs. horizontal displacement and convergent parallel vs. orogen parallel components. The preliminary conclusions are: 1. The interactions between tectonics, erosion and sedimentation control geometry and kinematics of the doubly vergent transpressional orogen. 2. Exhumation processes are controlled by the balance between erosion, frontal accretion and underplating in different structural domains of the wedge. 3. Retrowedge erosion favorites backfolding and backthrusting, induces flower structures and fan shaped cleavage distribution. 4. Sedimentation promotes underplating and out-of sequences thrusting. 5. Continental subduction or subduction of topographic highs will enhance underthrusting/underplating, thick-skin tectonics and inversion of sedimentary basin.
Bolletino di Geofisica teorica ed applicata

hal-00411133
https://hal.archives-ouvertes.fr/hal-00411133

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The Ryukyu subduction is known to generate very few earthquakes in its central segment contrarily to its two extremities. We focus in this study on the southernmost part of the Ryukyu subduction zone offshore east Taiwan. Our first task was to build a homogeneous earthquake catalogue for the period 1900–2007. The new catalogue provides homogenized M′W magnitudes and shows that several M′W≥ 7.0 earthquakes occurred offshore Hualien and Suao cities. We then focused on the 1920 June 5 earthquake (reported surface wave magnitude 8.1) previously located beneath the accretionary prism. The revised moment magnitude has been estimated in our catalogue at 7.7 ± 0.2. It is the biggest earthquake ever recorded in the Taiwan area but the fault that has produced this earthquake has not yet been identified with confidence. We relocated this event using regional phases (seismological bulletins archived at the Central Weather Bureau of Taiwan) about 50 km NNE and shallower of its former location, that is, within the Ryukyu Arc basement. According to earthquake bulletin information, revised magnitude, new hypocentral determination and known regional faults, we propose four potential active faults as candidates for the slip associated to this event: (1) the interplate seismogenic zone (ISZ), (2) an out-of-sequence thrust cutting through the forearc and branching on the ISZ, (3) a NS strike-slip fault cutting through the Ryukyu arc and (4) a N–S, westward dipping thrust fault, affecting the Philippine Sea Plate east of the Luzon Arc. The best compromise is to consider a rupture along the ISZ with a shallow nucleation possibly along a splay-fault followed by a downward and lateral propagation of the rupture that would explain the lack of significant seafloor motion and subsequent tsunami. We also estimate the maximum seismic coupling of the ISZ in the region east of Taiwan to about 0.4. In parallel, the evidences of aseismic slip occurring along the ISZ allow us to conclude that this region should only be affected by M < 8 earthquakes.
ISSN: 0956-540X

hal-00545459
https://hal.archives-ouvertes.fr/hal-00545459
https://hal.archives-ouvertes.fr/hal-00545459/document
https://hal.archives-ouvertes.fr/hal-00545459/file/theunisseGJI2010.pdf
DOI : 10.1111/j.1365-246X.2010.04813.x

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We analyze in this study a new set of marine data including 3D local tomography, 1992-2008 relocated earthquakes and two recent multichannel seismic lines to characterize the deformation style in the collision area offshore east Taiwan. We have mapped in detail the Mohos of the converging plates as well as the subduction interface with a resolution never reached before. We show that the sharp continental subduction of the Eurasia plate, beneath the middle part of the Central Range, indents the Philippine Sea plate (PSP) as attested by intra-oceanic slicing and incipient subduction of the PSP beneath the east coast of Taiwan. The westernmost part of the PSP slab is probably experiencing a beginning of break-off as attested by NW-trending en-échelon shear zones beneath the southern slope of the southern Ryukyu arc (SRA). These en-échelon shear zones have a sinistral component favored by the "collision-free" subduction of the PSP north of 24°30′N. The down-faulting of the subduction interface forms ramps along which earthquakes clusterize. Three M7 subduction earthquakes occurred offshore Suao city along these ramps with a recurrence interval of about 40 years: 1920 Mw7.7, 1963 Mw7.2 and 2002 Mw7.1 events. The 1966 Mw6.0-7.5 earthquakes sequence likely outlines a WNW-ESE left-lateral intra-slab shear zone. The SRA upper plate accommodates the complex geometry and deformation of the subducting PSP through seismic deformation. Shallow high velocities fringing the Luzon volcanic arc (LVA) beneath the Longitudinal Valley and north of the southernmost Ryukyu forearc basins are interpreted as relics of the LVA forearc basement squeezed in the collision zone. Based on the accommodation of a large part of the convergence through shortening within the PSP and the subsequent segmentation of the shallow subduction interface, we consider that the nucleation of a Mw ≥ 8 earthquake along the southernmost Ryukyu megathrust is unlikely.
ISSN: 0040-1951

hal-00853365
https://hal.archives-ouvertes.fr/hal-00853365
https://hal.archives-ouvertes.fr/hal-00853365/document
https://hal.archives-ouvertes.fr/hal-00853365/file/publallemandifremer.pdf
DOI : 10.1016/j.tecto.2013.03.020

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
[1] Based on geological and geophysical data collected from the West Philippine Basin and its boundaries, we propose a comprehensive Cenozoic history of the basin. Our model shows that it is a back arc basin that developed between two opposed subduction zones. Rifting started around 55 Ma and spreading ended at 33/30 Ma. The initial spreading axis was parallel to the paleo-Philippine Arc but became inactive when a new spreading ridge propagated from the eastern part of the basin, reaching the former one at an R-R-R triple junction. Spreading occurred mainly from this second axis, with a quasi-continuous counterclockwise rotation of the spreading direction. The Gagua and Palau-Kyushu ridges acted as transform margins accommodating the opening. Arc volcanism occurred along the Palau-Kyushu Ridge (eastern margin) during the whole opening of the basin, whereas the paleo-Philippine Arc decreased its activity between 43 and 36 Ma. The western margin underwent a compressive event in late Eocene-early Oligocene time, leading to the rising of the Gagua Ridge and to a short subduction episode along Eastern Luzon. In the western part of the basin, the spreading system was highly disorganized due to the presence of a mantle plume. Overlapping spreading centers and ridge jumps occurred toward the hot region and a microplate developed. Shortly after the end of the spreading, a late stage of amagmatic extension occurred between 30 and 26 Ma in the central part of the basin, being responsible for the deep rift valley that cut across the older spreading fabric. Citation: Deschamps, A., and S. Lallemand, The West Philippine Basin: An Eocene to early Oligocene back arc basin opened between two opposed subduction zones,
ISSN: 2169-9313

hal-01261388
https://hal.archives-ouvertes.fr/hal-01261388
https://hal.archives-ouvertes.fr/hal-01261388/document
https://hal.archives-ouvertes.fr/hal-01261388/file/DeschampsJGR2002.pdf
DOI : 10.1029/2001JB001706