middle miocene deduction and late miocene beginning of collision registered in the hengchun peninsula geodynamic implications for the evolution of taiwan abstract taiwan is located in the axis of the manila trench it results from an oblique collision between the northernmost part of the luzon arc and the chinese passive margin this active collision follows the subduction of the oligocene miocene oceanic crust of the south china sea along the manila trench the tectonized chinese margin emerged in the hengchun peninsula south taiwan gentle folds which are delineated by the quaternary reefal limestones demonstrate recent deformations these folds deformed a thick detrital sequence of miocene age ssuchung chi series which was previously strongly folded and thrust westward axis ns n20 upon the renting melange of latest miocene age these main deformations sealed by the middle pliocene are the evidence for the onset of collision in this part of taiwan at the end of the miocene because of its obliquity the collision started already in the northern part of taiwan during the late miocene 6 7 8 ma the ssuchung chi series a sequence of proximal turbidites has contained since the middle miocene nn 6 13 ma fragments of an oligocene to lower miocene oceanic crust this ophiolitic material is very similar to the east taiwan ophiolite of the coastal range it originated most probably from a slice of south china sea crust obducted in middle miocene times 13 14 ma upon the chinese margin north of the hengchun peninsula this obduction occurred 7 to 8 ma before the beginning of collision these results make it possible to propose an evolutionary model for taiwan from the oligocene to the recent with the different phases of a collision between a volcanic arc and a passive margin

present day interseismic surface deformation along the longitudinal valley eastern taiwan from a ps insar analysis of the ers satellite archives 1 in taiwan about one third of the lithospheric plate convergence between eurasia and the philippine sea plate is accommodated on the eastern coast across the narrow longitudinal valley lv the longitudinal valley fault lvf is the main seismically active fault zone in this region however the spatial distribution of ground deformation due to interseismic loading on locked fault segments remains widely unknown to address this problem we use a permanent scatterer ps interferometric synthetic aperture radar insar approach for processing the ers satellite archives the ps mean velocity maps allow accurately mapping and quantifying the ground deformation all along the lv assuming that close to the surface the fault plane along the central lvf creeping segment dips 55 to the east we derive a slip vector at the surface of 25 mm yr with a mean rake of 70 in agreement with our ps observations shallow seismicity indicates a clear change in the fault mechanical behavior of the creeping segment around fuli town finally we propose a combination of the ps velocity fields for estimating a 3 d map of ground deformation in the southern part of the lv the vertical component reveals an uplift of the coastal range with respect to the lv of 10 mm yr moreover between taitung and luyeh the vertical deformation is essentially accommodated along the luyeh strand finally north of rueisuei the coastal range uniformly subsides at 15 mm yr relative to the western side of the lv however a local uplift pattern is detected around latitude 23 42

numerical modelling of arc continent collision application to taiwan two dimensional finite element numerical modelling is applied to study the deformation and failure of the overriding plate during arc continent collision continental margin subduction this plate has elasto plastic rheology with strain weakening and contains a volcanic arc with thinned and weakened lithosphere the overriding plate deforms due to the normal and tangential stresses applied along the interplate surface these boundary conditions represent the friction and pressure between the plates the latter is due to the flexural rigidity of the subducting lithosphere and the buoyancy force generated by the subducting continental crust the modelling shows that continental margin subduction results in increasing compression and failure of the overriding plate which occurs along the surface dipping under the arc in either of two possible directions the failure mode is largely controlled by the two competitive factors the rigidity of the subducting plate and thickness gradient of the subducted continental crust a high rigidity favors failure along an ocean vergent fault which is followed by a subduction reversal while a high thickness gradient favors failure in the opposite direction which is followed by a fore arc block underthrusting beneath the arc both scenarios seem to have natural analogs we consider one of them the ongoing arc continent collision in taiwan and argue that this process occurs according to the second scenario corresponding to the fore arc underthrusting wavelet statistical analysis of the seismicity distribution to the south of taiwan has clearly displayed a shallow 0 40 km zone of high density coherently distributed seismicity beneath the luzon arc this zone interpreted as a lithospheric scale fault dips from the forearc basin to the east and corresponds to the initiation of the forearc block subduction a self consistent combined mechanical gravity topography model is used to see whether failure of the overriding plate to the south of taiwan can be captured by this model by tuning diverent controlling parameters we did not succeed in obtaining realistic topography and gravity field in a model where failure of the overriding plate was not allowed introduction of this failure and underthrusting of the forearc block under the luzon arc allowed us to fit both topography and gravity data 2000 elsevier science b v all rights reserved

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

active continental subduction and crustal exhumation the taiwan orogeny a tectonic model of active continental subduction followed by crustal exhumation is proposed to explain the orogeny in taiwan the subducted crust is represented by a low velocity zone dipping eastwards beneath the major part of taiwan while the exhumed crust is marked by a high velocity bulge high heat flow and absence of seismicity beneath the eastern central range the boundary between the subducted and exhumed crust has been identified from surface geology and analyses of thermal history across the central range the dynamic force that has been driving the exhumed crust is identified by results from focal mechanisms structural geology and geodetic survey in the eastern central range such a tectonic model may provide a good explanation for the evolution of the taiwan orogeny as well as an active case for studying other long extinct systems of continental subduction and exhumation

effect of unbalanced topography and overloading on coulomb wedge kinematics insights from sandbox modeling 1 this study addresses the effect of variable unbalanced topography and overload on the kinematics of a fold and thrust belt developed within a collisional belt that underwent a subduction polarity reversal event this was done by physical modeling of doubly vergent coulomb wedges using sand as an analogue material during the experimental procedure a preexisting topography was generated by a first phase of subduction in one direction a second phase of subduction was then initiated in the opposite direction simulating a subduction flip an anomalous strong frontal growth for the wedge during the second phase was experimentally shown to be dependent upon surface slope breaks and the critical asymmetrical architecture achieved by the wedge at mature stages of deformation the latter is suggested to be the rule for doubly vergent orogens at steady state even after a subduction flip during the experiments surface processes like syntectonic erosion and sedimentation markedly altered mass transfer within the wedge in particular lowering the surface slope by syntectonic erosion favored cycling between accretion and underthrusting modes by contrast a sudden syntectonic sediment load in the prowedge region promoted prolonged phases of underthrusting retarding accretion of new imbricates at the prowedge toe however at later stages of deformation the prowedge was forced to regain its characteristic minimum critical taper as predicted by theory and did so by the sudden nucleation of long flat thrust units rapidly rebalancing the asymmetry between prowedge and retrowedge regions the experiments suggest that given a fixed critical taper related to time invariant frictional properties along the wedge bounding surfaces deformation does vary within the wedge according to time varying location of normal stress surpluses and unbalanced topography acting on potential failure surfaces these in turn alter the equilibrium between prowedge and retrowedge basal detachments that is here considered to be a major factor controlling the self regulating dynamics of collisional orogens

sedimentology of early pliocene sandstones in the south western taiwan foreland implications for basin physiography in the early stages of collision abstract this work presents sedimentological observations and interpretations on three detailed sections of the pliocene yutengping ailiaochiao formations deposited in the early stages of collision in taiwan seven facies associations record paleoenvironments of deposition ranging from nearshore to lower offshore with a strong influence of tidal reworking even in shelfal sub tidal environments and a pro delta setting characterized by mass flows the association of shallow facies of the upper offshore to lower shoreface with pro delta turbidite facies sourced in the orogen to the east suggests a peculiar setting in which turbidite deposition occurred below wave base but on the shelf in water depths of probably less than 100 m this adds to the examples of shallow turbidites increasingly commonly found in foreland basins and challenges the classical view of a deep early underfilled foreland basin time series analysis on tidal rhythmites allow us to identify a yearly signal in the form of periodic changes of sand supply energy and bioturbation that suggests a marked seasonality possibly affecting precipitation and sediment delivery as well as temperature the taiwan foreland basin may also present a potentially high resolution record in shallow sediments of the early installation of monsoonal circulation patterns in east asia we confirm partly the paleogeography during the early stages of collision in taiwan the chinese margin displayed a pronounced non cylindrical geometry with a large basement promontory to the west in place of the modern taiwan mountain range collision in taiwan may have happened at once along the whole length of the modern mountain range instead of progressively from north to south as classically considered

from passive continental margin to mountain belt insights from analytical and numerical models and application to taiwan abstract the physics of deformation at plate boundaries is insufficiently understood taiwan is particularly interesting in this context since geological and geophysical arguments indicate that passive margin sediments were exhumed into an active mountain belt over a relatively short period of time classically taiwan has been described as a critical wedge orogeny in which deformation is entirely restricted to the crust more recent data however indicate that deeper parts of the lithosphere also participate in deformation in order to study the physical feasibility of various endmember hypothesis we have performed two dimensional 2 d thermo mechanical numerical experiments in which both mantle lithospheric and surface processes are taken into account and in which crustal deformation evolves as a function of mantle flow our setup consists of ocean ocean subduction followed by passive continental margin deformation results indicate that in most cases the subducting slab becomes close to vertical upon arrival of continental material to the trench whereas crustal rheology deformation and surface processes do not modify mantle flow significantly they are important for crustal scale processes relatively little crustal exhumation occurs if the crust is homogeneous and erosion rates are small significant exhumation in a dome like structure is obtained if a weak lower crust and large erosion rates are present the presence of an oceanic arc in the overriding oceanic lithosphere modifies but does not control crustal deformation synthetic metamorphic facies maps and thermochronological data computed from the numerical models are in reasonable agreement with observations in southern taiwan if exhumation occurs in a dome like structure further physical insight in the doming mechanisms is obtained by a combination of analytical techniques and crustal scale numerical models this analysis indicates that the dome like exhumation mechanism can be attributed to a compressional mechanical instability facilitated by both a weak lower crust and large rates of erosion both conditions are likely to be satisfied in taiwan

tectonic stresses seaward of an aseismic ridge trench collision zone a remote sensing approach on the loyalty islands sw pacific abstract the loyalty islands are a series of limestone karstified islands on the australian plate that are presently approaching the vanuatu subduction zone sw pacific they are deformed due to the combined effects of the bulging of the subducting lithosphere and the beginning collision between the loyalty ridge and the vanuatu subduction zone therefore they constitute a series of markers for early phases of ridge arc collision lineaments deduced from remote sensing images aerial photos spot3 spot4 and envisat data termed here as fractures are analyzed by comparison with planar structures measured during field studies and termed as geological data fracture data indicate a stable main n110 direction with a large variance of nearly 15 in rms and two minor directions 45 apart which may constitute shear directions associated to the major one a scale dependent analysis shows that fractures longer than 2000 m are close to the n110 direction and that their orientation shifts progressively to reach the n125 direction for l

shallow frontal deformation related to active continental subduction structure and recent stresses in the westernmost betic cordillera the westernmost betic cordillera front is located along the arcuate alpine belt formed by the interaction of the eurasian african plate boundary and the alboran continental domain in between although classical geological data suggest that the western cordillera front is inactive recent gps data show a westward north westward motion of up to 3 4 mm a 1 with respect to the foreland in addition the increasing thickness of guadalquivir sedimentary infill towards the cordillera and the rectilinear character of the front formed by soft sediments suggest that the cordillera is still active large ene wsw oriented open folds detected in the field seismic reflection profiles and new audiomagnetotellurics data are consistent with active deformation fracture analysis in quaternary deposits evidences recent nw se horizontal compression the gps motion and maximum stress orientation may be due to north westward tectonic collision of the westernmost betic cordillera accommodated at depth by active continental subduction of the iberian lithosphere

development of three dimensional basement structure in taiwan deduced from past plate motion consistency with the present seismicity 1 using colored clay we examined geometrical evolution of the three dimensional basement structure in taiwan due to relative plate motion under the following assumptions the motion of the philippine sea plate relative to the eurasian plate has been constant during the last 15 myr the ryukyu and manila trenches had been connected by a transform fault before the collision between the luzon arc and eurasian continental margin and the collision started at 5 ma the basement structure obtained from the clay model was fully consistent with observed deep seismicity which led us to the following conclusions there are no oceanic slabs beneath central taiwan instead the eurasian continental margin is underthrusting beneath it the philippine sea slab extends northwestward from the ryukyu trench while the south china sea slab extends southeastward from the manila trench the downdip length of the south china sea slab becomes shorter from south to north

synorogenic extension and exhumation of the taiwan hinterland structural data from two transects across the active taiwan arc continent collision indicate that normal faulting is an important mechanism in the exhumation of the hinterland the normal faulting extends to at least the brittle ductile transition records extension at a high angle to the topographic grain of the orogenic belt and is responsible for the regional scale rotation of ductile fabrics these results are supported by a recent gps survey of southern taiwan that reveals extension in the hinterland contemporaneous with shortening in the foreland and collided arc

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

subduction zone interaction controls on arcuate belts the interaction of neighboring subducting lithospheres is a characteristic feature of many tectonically complex areas here we use numerical modeling to study the interactions between two oppositely dipping adjacent subducting lithospheres and to understand their impact on the subduction evolution mantle flow and stress propagation through the mantle as slabs subduct rollback and approach they strongly affect each other if plate edges are at distances 600 km in this case the mantle flow around slabs combines into a single large convective cell trench migration is delayed and stress increases progressively with decreasing slabs distance the stress increases at depth as the slabs approach each other and it shallows up to the near surface as the slabs diverge a similar setting with two neighboring slabs migrating and passing each other is found in areas such as the alps apennines europe and the ryukyu manila subduction zones around taiwan where the arcuate trenches suggest the controls of deep slab interactions

rapid quaternary emergence uplift and denudation of the coastal range eastern taiwan a thick sequence of orogenic strata exposed in the coastal range of eastern taiwan documents uplift of at least 7 5 and 5 9 km at two anticlinal crests following marine deposition of the uppermost preserved beds at 1 0 ma the resulting mean uplift rates of 7 5 and 5 9 mm yr are minimum values for localities that represent relative maxima in total uplift and are consistent with previous studies that document general uplift of about 5 mm yr in taiwan despite rapid uplift the coastal range is transected by the antecedent course of the hsiukuluan river maintenance of this transverse drainage rather than defeat and diversion to a ready alternate course to the sea provided by the range bounding longitudinal valley suggests that uplift has been steady over time and exemplifies a general balance between uplift and denudation rates in taiwan denudation in the coastal range approximates the rapid present day denudation documented in the much higher central range due at least in part to less resistant rock types in the coastal range uplift of the coastal range is driven by the tectonic incorporation of the luzon island arc into the taiwan mountain belt and thus into the asian continental margin probably over a west dipping decollement hypothesized to have formed during eastward propagation of the eastern deformation front of the dominantly west vergent orogen

kinematic analysis of the taiwan slate belt the taiwan slate belt can be subdivided into two structural domains based on fold and cleavage geometries and finite and incremental strain histories the two belts correspond generally to two topographic ranges in taiwan the hsuehshan range and the backbone range rocks in the hsuehshan range are characterized by upright symmetric folds and a steeply se dipping axial planar pressure solution cleavage synkinematic fibers in pressure shadows are typically straight parallel to cleavage and plunge downdip indicating that the rocks experienced a coaxial strain history in contrast rocks in the backbone range are characterized by inclined asymmetric folds that verge toward the foreland and display a moderately se dipping axial planar pressure solution cleavage synkinematic fibers are straight and parallel to the downdip stretching lineation in xy sections in xz sections however the fibers typically display a clockwise curvature viewed to the ne indicating a noncoaxial strain history we propose that the different strain histories are due at least in part to differences in the original tectonostratigraphic settings of the strata in the two ranges strata in the hsuehshan range are interpreted to have been deposited in a half graben associated with an east dipping normal fault the strata of the backbone range in contrast are considered to have been deposited on the unfaulted chinese continental margin we suggest that the basement horst on the east side of the half graben functioned as a steep faced rigid backstop that concentrated pure shear deformation throughout most of the hsuehshan range shear strains were apparently limited to zones near the base of the sedimentary sequence and adjacent to the backstop the noncoaxial strains characteristic of the backbone range are interpreted to be the result of a regional scale shear zone that formed as chinese basement and its sedimentary cover were underthrust southeastward beneath the luzon arc

crust mantle boundaries in the taiwan luzon arc continent collision system determined from local earthquake tomography and 1d models implications for the mode of subduction polarity reversal abstract in order to better understand the mode of subduction polarity reversal in the taiwan luzon arc continent collision zone we mapped its crust mantle boundaries using local earthquake tomography by contouring surfaces of constant vp 7 5 km s 1 we identified three moho discontinuities and the plate interface that juxtaposes eurasian lower crust against mantle lithosphere of the philippine sea plate the plate interface dips to the east under southeastern taiwan and steepens progressively towards north until it becomes vertical at 23 7 n from there it continues northward in a vertical orientation until the limit of the tomographic model inhibited further mapping for the moho additional depth constraints were derived from 1d models using p wave arrivals of local earthquakes the mohos of the eurasian and philippine sea plates are disconnected across the plate interface beneath southern taiwan the eurasian moho dips to the east at 50 60 following the orientation of the plate boundary and continuous with the benioff zone towards north the eurasian moho steepens into subvertical again together with the plate boundary the philippine sea plate moho exhibits a synform like crustal root interpreted as the base of the magmatic luzon arc towards the north this root deepens from 30 to 70 km underneath the ryukyu trench in northernmost taiwan the hinge of the vertically subducting eurasian slab steps westward out of the thrust belt leaving the deformation front to the east inactive and giving way to the north dipping philippine sea plate a subhorizontal moho at 30 35 km depth overlies the north dipping philippine sea slab and is interpreted as a newly formed moho established after westward rollback and delamination of the subducting eurasian slab in combination these data support a model of progressive subduction polarity reversal in which a tear within the eurasian lithosphere propagated southwestward deactivating the deformation front

tectonic wedging along the rear of the offshore taiwan accretionary prism abstract the structural geometry kinematics and density structure along the rear of the offshore taiwan accretionary prism were studied using seismic reflection profiling and gravity modeling deformation between the offshore prism and forearc basin at the point of incipient collision and southward into the region of subduction has been interpreted as a tectonic wedge similar to those observed along the front of mountain ranges this tectonic wedge is bounded by an east dipping roof thrust and a blind west dipping floor thrust an east dipping sequence of forearc basin strata in the hanging wall of the roof thrust reaches a thickness in excess of 4 km near the tip of the interpreted tectonic wedge section restoration of the roof sequence yields an estimate of 4 km of shortening which is small compared with that inferred in the collision area to the north based on the variation in distance between the apex of the prism and the island arc previous studies propose that either high angle normal faulting or backfolding has exhumed the metamorphic rocks along the eastern flank of the central range in the collision zone on land to better constrain the initial crustal configuration we tested 350 crustal models to fit the free air gravity anomaly data in the offshore region to study the density structure along the rear of the accretionary prism in the subduction and initial collision zones before the structures become more complex in the collision zone on land the gravity anomaly observed in the region of subduction 20 2 n can be modeled with the arc basement forming a trenchward dipping backstop that is overlain by materials with densities in the range of sedimentary rocks near the point of incipient collision 20 9 n however the free air gravity anomaly over the rear of the prism is approximately 40 mgal higher compared with the region of subduction and requires a significant component of high density crustal rocks within the tectonic wedge these results suggest that the forearc basement may be deformed along the rear of the prism associated with the onset of collision but not in the subduction region further to the south

mountain building in taiwan insights from 3 d geodynamic models taiwan is widely considered to be a typical example of an arc continent collision surrounded by two opposite dipping subduction zones the manner by which the interaction of the two neighboring slabs caused plate collision and mountain building is insufficiently understood various hypotheses have been proposed but the geodynamic feasibility of those remains to be tested here we present 3 d thermomechanical models to study the geodynamic evolution process of a taiwan like setting after an initial transform fault was consumed in our model setup the boundary between the eurasian plate and the south china sea is northeast trending the results show that all simulations result in toroidal mantle flow around the slab edges and that slab breakoff as well as a small scale mountain belt with high topography and crustal exhumation occurs in most cases the eurasian continental crust is exhumed in a dome like manner exposing higher grade metamorphic rocks facilitated by high erosion rates and a weak continental lower crust rheology but inhibited by the presence of a weak arc a high topography within the orogen as well as continental slab detachment can develop for the convergence direction of n307 degrees and large convergence rates our modeling results are thus generally consistent with the eurasian slab tearing model proposed for taiwan based on seismic tomographic studies and we suggest that the main characteristic features in taiwan can be explained by the combined effects of fast erosion a weak lower crust fast convergence and a small convergence azimuth

new results from physical modelling of arc continent collision in taiwan evolutionary model abstract both the analysis of the geological data and the results from 2d and 3d experimental modelling of arc continent collision in taiwan reveal the following major stages in this process 1 failure and thickening of the subducting crust of the chinese continental margin under the frontal part accretionary prism of the philippine sea plate psp since ca 6 7 ma 2 uplift squeezing and exhumation of the subducted crustal slice of the chinese margin and initiation of the central range about 5 ma ago 3 flexural buckling subsidence of the luzon arc fore arc under strong horizontal compression and sedimentary infilling of this area by the material shed from the growing and exhuming central range 4 failure of the psp along the west vergent longitudinal valley fault dipping beneath the arc and closure of the fore arc 5 subduction reversal and stoppage of continental subduction which has already occurred in northern taiwan and propagates to the south the southward propagation of the collision is not stationary currently occurring initial collision in southern taiwan and offshore to the south does not follow the same described above evolution as in central and northern taiwan the evolution of the collision in time and space should be considered in the framework of a 3d model where the psp rupture is preparing in the central and northern taiwan during a long time passing through a number of evolutionary stages once it has occurred the rupture longitudinal valley fault rapidly propagates to the south into the domain which did not undergo the pre rupture evolution the rupture front is currently located near 21 30 n

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

suspended particulate matter on the laptev sea shelf siberian arctic during ice free conditions optical turbidity surveys combined with pigment plankton and current measurements were used to investigate the vertical and horizontal dynamics of suspended particulate matter spm in the laptev sea one of the largest siberian shelf seas during the ice free period optical measuring devices prove to be an excellent tool to measure spm distribution in real time spm concentrations were quantified owing to the high correlation of water samples and optical backscatter thus the formation and distribution of the bottom nepheloid layer a layer of increased spm concentration and its significance for the sediment transport on the laptev sea shelf can be described two nepheloid layers exist in the eastern and central laptev sea formation and concentration of the surface layer are mainly related to the amount of phytoplankton and zooplankton occurrence however in the vicinity of the lena delta the concentration is strongly dependent on riverine discharge the bottom nepheloid layer is suggested to develop during and briefly after the spring breakup when about 60 of the mean annual sediment input is discharged onto the shelf spm spreads over the shelf and is kept in suspension within the bottom layer especially during the ice free period almost no sedimentation takes place however bottom material is resuspended due to wind induced increased bottom currents mainly in paleo river valleys and on shoals valleys act as transport conduits during the ice free period and spm is shifted within them an intermediate layer near stolbovoy bank is probably caused by the displacement of the bottom layer from the topographic highs into the valleys the combined turbidity and current measurements indicate that most of the sediment transport on the laptev sea shelf takes place in the bottom nepheloid layer

repeating earthquakes and seismic potential along the northern longitudinal valley fault of eastern taiwan 1 the northern longitudinal valley fault in eastern taiwan creeps at the surface with a small rate of 1 cm yr but slips in large earthquakes to improve seismic hazard assessment it is important to comprehend the slip deficit rate distribution at depth we discovered 25 ml 2 1 4 6 repeating earthquakes in this area and inverted gps measurements for producing an image of the along strike spatial distribution of deep fault slip rates the repeating events are located at the depths of 10 22 km with 24 9 77 5 mm yr slip rates which are comparable with the gps derived slip rates of 47 5 5 8 mm yr at similar depth ranges based on distribution of gps derived slip deficits since 1951 the northern longitudinal valley fault has become capable of releasing stored strain in a future mw 7 3 earthquake

displacement field and fault model for the september 7 1999 athens earthquake inferred from ers2 satellite radar interferometry on september 7 1999 a moderate mw 5 9 normal faulting earthquake occurred in the northwest of athens hellas causing heavy damages and casualties using interferometric combinations of ers2 sar images we analyzed the coseismic deformation field two fringes are observed south of the fill mountain up to the coastline of the elefsis gulf they correspond to 56 mm increase in slant range modeling the earthquake as a dislocation in an elastic half space we inverted the interferometric data to assess the fault location and geometry and the amplitude of the coseismic slip the model suggests 300 mm slip on an 18 km long blind fault composed of two pieces the intersection of the fault plane with the earth surface is located in the fill mountain with a n 120 o orientation

provenance evolution and unroofing history of a modern arc continent collision evidence from petrography of plio pleistocene sandstones eastern taiwan abstract plio pleistocene sandstones from the coastal range of eastern taiwan provide a record of shifting source areas and unroofing events in adjacent arc and accretionary wedge terranes during the early stages of are continent collision in latest miocene and early pliocene time arc derived sediments were deposited in a precollisional forearc basin between the luzon volcanic arc and the manila trench sandstones of this age are rich in zoned plagioclase volcanic lithic fragments and pelagic foraminifera and contain only minor quartz and sedimentary metasedimentary lithic fragments in contrast lower pliocene to lower pleistocene sandstones are poor in feldspar and volcanic fragments and contain abundant sedimentary and metasedimentary lithic fragments this reflects a provenance shift f om the volcanic arc to the uplifted meta sedimentary accretionary wedge of proto taiwan which resulted from the early pliocene onset of arc continent collision a refined classification of sedimentary and metasedimentary lithic fragments is introduced here and used to interpret the early evolution of the collisional orogen lithic fragments are rich in pelitic minerals and are divided into 1 sedimentary ls mudstone shale siltstone chert and argillite 2 low grade metamorphic lm1 slate slatey siltstone and quartzite and 3 medium grade metamorphic lm2 phyllite schist phyllitic quartzite and quartz mica albite aggregate a good correlation is observed between these lithic fragment types and bedrock lithologies exposed in the present day central range of taiwan based on this correlation the change in relative abundance of sedimentary and metasedimentary lithic fragments through time has been used to interpret an unroofing sequence for the collisional fold and thrust belt lower pliocene taiwan derived sandstones are rich in sedimentary lithic fragments ls which were shed from the accretionary wedge during the earliest stages of arc continent collision from early pliocene to early pleistocene time sandstones became progressively depleted in ls lithic fragments and enriched first in lm1 and later in lm2 fragments as deeper levels in the metamorphic complex were uplifted and exposed to erosion regional metamorphism of biotite grade rocks lm2 occurred at about 4 5 ma at depths of 12 15 km ernst 1983 and were uplifted to the surface by about 1 4 ma this study these ages give an uplift rate of 4 to 5 km m y which is in good agreement with independent estimates based on fission track studies raised coral reefs quaternary elevation changes and present day denudation rates thus it appears that sandstone detrital modes of clastic orogenic sequences can be used to interpret specific aspects of unroofing and tectonic evolution in nearby active mountain belts

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

kinematic analyses of the hsuehshan range taiwan a large scale pop up structure the hsuehshan range exposed in the northern and central taiwan slate belt is a fault bounded structural high cored by biotite grade slates and metasandstones syntectonic overgrowths in pyrite pressure shadows indicate that much of the eastern hsuehshan range experienced coaxial strain histories and that finite strain magnitudes generally increase toward the hinterland near the eastern boundary of the hsuehshan range however pressure shadows record noncoaxial strain histories consistent with a top to the east sense of shear along a steep nw dipping shear zone this noncoaxiality is attributed to se directed backthrusting on the lishan fault which separates the higher grade eo oligocene rocks of the hsuehshan range from the lower grade miocene rocks of the backbone range because it is bounded to the east by the se vergent lishan fault and to the west by a series of nw vergent thrusts e g the chuchih fault the hsuehshan range is envisaged as a pop up structure strain magnitudes measured from pressure shadows in the coaxial part of the range are consistently lower than those predicted by steady state wedge models that assume all deformation is accommodated by penetrative strain departure from the model predictions is attributed primarily to strain localization along discrete fault surfaces e g the lishan fault the hsuehshan range tapers in width to the south thus the pop up may be buried or die out to the south where the collision is younger

evolutionary model for the taiwan collision based on physical modelling abstract 2 d and 3 d physical modelling of lithospheric convergence in the luzon taiwan ryukyu region is performed with properly scaled laboratory models the lithospheric model consists of two parts continental the asian plate ap and oceanic the philippine sea plate psp the oceanic lithosphere has one layer while the continental lithosphere includes both mantle and crustal layers the continental margin is covered by sediments a low viscosity asthenosphere underlies the lithosphere the opposing luzon and ryukyu subduction zones are initiated by inclined cuts made within the psp the subduction collision is driven by a piston pre collisional intraoceanic subduction along the luzon and ryukyu boundaries results in the formation of a transform zone between them with two tear faults at the ends the psp undergoes strong compression along this zone subduction of the chinese margin under the luzon boundary further increases the compression compressive stresses reach the yield limit of the psp in the arc area which is a weak zone in the experiments the plate fails at the western side of the arc along an eastward dipping fault the longitudinal valley fault underthrusting of the frontal wedge of the psp along this fault results in the closure of the fore arc basin and is then blocked the psp fails at the opposite side of the luzon arc along the westward dipping fault the failure releases lithospheric compression in this region and results in the initiation of southward propagating subduction of the psp under northeastern taiwan the incipient subduction zone becomes part of the southeastward retreating ryukyu subduction zone which allows the okinawa back arc rift to propagate into taiwan the taiwan collision thus includes the following succession of major processes over time or from south to north 1 an e w shortening of the psp in the luzon arc 2 a failure of this plate at the western side of the arc and the formation of the eastward dipping longitudinal valley fault the transient plate boundary 3 a closure of the fore arc basin and a rapid uplift of the orogen 4 a failure of the psp at the eastern side of the luzon arc partly overthrusting the orogen and the initiation of westward wn ward subduction of the psp 5 and finally back arc rifting in the rear of this incipient subduction zone i e in northern taiwan all these processes commence with some delay with respect to the preceding ones and propagate southwards

miocene to recent calc alkalic volcanism in eastern taiwan k ar ages and petrography abstract k ar radiometric datings are presented for volcanic rocks from the coastal range of taiwan and from lanhsu and lutao islands the samples involved are basalts andesites and dacites which show the main petrological and geochemical characteristics of island arc magmas the k ar data show that volcanic activity occurred from early miocene to early pliocene times in the coastal range and in lanhsu island and during pliocene times ca 1 3 4 3 ma in lutao island the geological significance of early and middle miocene ages is discussed with respect to hydrothermal metasomatic alterations which have affected most of the samples a significant increase in incompatible elements e g k and sr is shown to have occurred during pliocene to recent times and is exemplified by the compositions of the lanhsu and lutao volcanic rocks the origin of these chemical variations is related to the magmatic effects of crustal thickening linked to the transition from subduction to collision regimes

polyphase history and kinematics of a complex major fault zone in the northern taiwan mountain belt the lishan fault abstract the lishan fault is a major fault zone in the taiwan collision belt it separates two major units the hsuehshan range and the backbone range which differ in lithology ages of sediments metamorphic grades and deformation styles despite the importance of the lishan fault its evolution and tectonic behaviour remained poorly known and controversial we therefore carried out a tectonic study which includes both the identification of structures in and along the fault zone and the palaeostress analysis aiming at reconstructing the succession of fault mechanisms the lishan fault zone underwent polyphase evolution with reactivations under different tectonic regimes consistent with the cenozoic history of taiwan 1 1 on the hsuehshan range the earliest events reflect the palaeogene miocene extension of the chinese continental margin 2 2 serial cross sections and observation of ductile brittle structures show east vergent folding indicating that for the most recent compressional evolution related to late cenozoic taiwan collision the lishan fault was a steeply dipping east vergent back thrust the compression occurred along nw se trends inducing thrusting but also along n s ones inducing transpression with reverse sinistral slip the lishan fault thus underwent contraction as well as strike slip during the mountain building of the taiwan orogeny reverse and strike slip fault systems alternated because of permutations 2 3 under the same compressional stress regime of nw se 1 minor compressional events also occurred 3 3 a late extension accommodated by normal faulting reveals the influence of both the n s extension in the okinawa trough northeast off taiwan

impact of arc continent collision on the conditions of burial and exhumation of uhp lt rocks experimental and numerical modelling abstract a 2 d physical and finite element numerical modelling of arc continent collision was performed to study the deformation and failure of the overriding lithosphere the experimental technique allowed us to model the whole subduction collision process from oceanic subduction to deep subduction of the continental crust with the numerical approach we have modelled the deformation of the overriding plate only through initial stages of its failure and studied the influence of different parameters on this process the results obtained by both techniques are coherent and mutually complementary they show that the failure of the overriding plate is physically quite plausible or even inevitable during subduction the conditions for such a failure the weakening of this plate are prepared during oceanic subduction the weakening occurs due to the interaction between the subducting lithosphere and the asthenosphere in the mantle corner between the two plates and due to back arc spreading in oceanic subduction zones with a compressional regime no back arc opening thick and strong back arc lithosphere the weakest zone is volcanic arc area when weakening becomes sufficient during subduction the lithosphere fails in this area the failure occurs along a fault dipping under the arc in either of two possible directions and results either in subduction reversal or subduction of the fore arc almost half of the presently active subduction zones are characterised by a tensional subduction regime with back arc spreading in such subduction zones the weakest place is not the volcanic arc but the back arc spreading centre when a subduction regime changes from tensional to compressional failure occurs in the vicinity of the extinct spreading centre this process can occur during oceanic subduction again along either a trench vergent or trenchward dipping fault but the formation of a trench verging fault is most likely in this latter case which is a principal subject of our study the failure is followed by partial subduction of the arc plate complete subduction occurs during arc continent collision subduction of the continental margin when tectonic compression of the lithosphere increases rapidly and becomes sufficient to push the arc plate into the mantle the arc itself can be subducted completely or be partially or completely scraped off and accreted a deeply subducted material including continental margin is preserved at relatively low temperatures between the lithospheric mantle and the cold subducted arc plate to about 150 km depth subduction of the arc plate is a major phenomenon which affects all processes associated with continental subduction from deep burial and hp lt metamorphism to exhumation of subducted material does this process occur in nature future investigations will allow us to answer this question in this paper we analyse the conditions of emplacement of a very young oceanic lithosphere samail ophiolite on the continental crust in oman in the late cretaceous and argue that this lithosphere formed in a back arc basin it reached and overthrust the arabian continent after complete subduction of the arc plate

taiwan mountain building insights from 2 d thermomechanical modelling of a rheologically stratified lithosphere summary the taiwan orogen has long been regarded as a case example for studying mountain building in association with subduction processes in this paper we present a fully coupled thermomechanical modelling of the taiwan collision based on a realistic viscous elastic plastic rheology it satisfactorily reproduces available thermochronometric data long short term deformation patterns heat flux and erosion sedimentation distribution across the taiwan orogeny we found that a deep seated flux of asian crustal material into the orogenic wedge should be invoked to counter balance observed exhumation and erosion in the central range however in contrast with recent thermokinematic models of exhumation and deformation suggesting that underplating plays a significant role we show that most constraints on exhumation and deformation can be more straightforwardly interpreted by the frontal accretion of the rheologically layered asian crust we finally infer that such a model is in better agreement with the basic expectation that the hot young and buoyant chinese continental margin should hardly be subducted beneath the cold old and dense oceanic plate of the philippines sea

destruction of luzon forearc basin from subduction to taiwan arc continent collision abstract along offshore to the east of southern taiwan different stages of subduction and collision occur simultaneously along strike of the convergent boundary as a result the evolution of the luzon arc and its forearc basin can be studied from the younger subduction zone to the south to the collision zone to the north examining more than 8000 km of seismic lines we analyzed the seismic stratigraphy of strata in a forearc basin and its successive basins in the collision zone to study the processes related to arc collapse and forearc basin closure the study area presents three evolutional stages intra oceanic subduction initial arc continent collision and arc continent collision we divided 9 seismic sequences in the forearc basin and found older sub parallel basin fill sequences 4 9 and younger divergent sequences 1 3 isochron maps of the sequences were used to interpret different deformation modes and their areal extends on the arc side of the basin of the subduction and initial collision zones we found relatively undisturbed strata showing little arc deformation on the trench side the growth strata in sequences 1 through 3 are the result of recent tectonic wedging along the rear of the accretionary prism tectonic wedging and back thrusts incorporate the forearc strata into the rear of the accretionary prism until they close the forearc basin at a region with a 2200 m basement relief this relief is not caused by active deformation as young flat forearc strata lap onto it and mark the transition from initial collision to collision where many growth strata to the north suggest abrupt increase in active arc basement deformation the 1 deforming basement 2 back thrusts and 3 other sedimentary processes affect the architecture of the successive basins in the collision zone until the arc is juxtaposed to the rear of the fold and thrust belt on land

role of preexisting topography and overburden on strain partitioning of oblique doubly vergent convergent wedges 1 scaled sandbox modeling was used to analyze the three dimensional aspects of strain partitioning along obliquely convergent margins that underwent a subduction polarity reversal event in the experiments the first phase of shortening produced a preexisting topography that affected wedge kinematics during the second phase increasing degrees of obliquity during the first shortening phase produced different amounts of inherited topography and overburden giving way to different effects on wedge response during the second phase of shortening during the second phase the models with an inherited heavy overburden show an anomalous orientation for riedel shears predating the development of a margin parallel strike slip fault these shears are oriented at an angle that is higher than kinematically predicted with respect to the subduction slot suggesting a transient rotation of the stress applied by the obliquity of subduction in contrast experiments with a lighter overburden do not show this inconsistency in addition all the models displayed an unexpectedly high accretion rate during the second phase of shortening which we interpret to be dependent on topographical slope breaks inherited after the first phase of shortening and the critical asymmetrical architecture of doubly vergent wedges

geodynamic evolution of the taiwan luzon mindoro belt since the late eocene abstract the structural framework of the taiwan luzon mindoro belt or festoon is described following three major transects the luzon transect with active subduction and active island arc the taiwan transect with active collision the mindoro transect with active subduction and inactive collision based on this geological study and on available geophysical data a model for the geodynamic evolution of this portion of the philippine sea and eurasia plates boundary is proposed in a succession of reconstructions between the late eocene and the present the major geodynamic events are 1 1 beginning of the opening of the south china sea s c s in lower oligocene times contemporaneous with obduction of the zambales and angat ophiolites on luzon 2 2 subduction of a mesozoic oceanic basin along the proto manila trench from the upper oligocene to the lower miocene 3 3 obduction of the south china sea oceanic crust onto the chinese and reed bank calamian passive margins in middle miocene time 14 15 ma related to a major kinematic reorganization end of opening of the s c s 4 4 beginning of collision between the luzon microblock and the two margins of the s c s in the upper miocene 7 ma collision is still active in taiwan whereas it stopped in mindoro during the pliocene

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia abstract siliciclastic supersequences of the kalgoorlie and gindalbie terranes post date 2660 ma deformation uplift and erosion associated with the amalgamation of arc related terranes but were tectonically buried to greenschist or amphibolite facies during the orogenic shortening that accreted the eastern goldfields superterrane to the yilgarn craton the supersequences are synclinal remnants of late stage basins that were linear zones of subsidence adjacent to north trending strike slip faults fluvial facies merougil navajo jones creek scotty creek and yandal basins are dominated by sheet sandstones that represent the deposits of medial braid plains but proximal channel and bar complexes of cobble and boulder conglomerates are also preserved submarine facies kurrawang basin range from boulder to pebble conglomerates but are dominantly bouma turbidites with rare black shales and record the filling of a proximal canyon that fed a distal submarine fan axial depositional systems are preferentially preserved in all basins but transverse systems are preserved at the base of some fluvial deposits the gross vertical succession in all basins is from proximal up to distal the basins developed during two tectonic stages separated by an intervening period of uplift tilting and erosion with the southern kalgoorlie terrane recording change from a stage i fluvial to a stage ii deep marine basin stage ii fluvial deposits are preserved in the northern kalgoorlie terrane and in the gindalbie terrane sparse palaeocurrents establish sediment dispersal was to the south or southeast implying uplift to the north or northwest controlled palaeoslopes stacking of lithofacies is aggradational and is consistent with limited lateral migration of facies tracts in fault confined basins similar lithofacies and aggradational styles of facies stacking characterise syncollisional sequences of the cenozoic coastal range basin of taiwan and the present day syncollisional basins of southeastern taiwan are good analogues of late stage basins of the kalgoorlie and gindalbie terranes

analogue modelling of continental collision influence of plate coupling on mantle lithosphere subduction crustal deformation and surface topography abstract the role of the plate boundary in a continental collisional setting is investigated by lithospheric scale analogue models key variables in this study are the degree of coupling at the plate interface and along the moho of the lower plate as well as the geometry of the plate contact they control the onset of intra plate deformation orogenic architecture amount of mantle lithosphere subduction and basin development in all experiments deformation initiates at the plate interface by the formation of a pop up structure a vertical plate boundary with respect to the shortening direction results in buckling of the lithosphere whereas experiments with an inclined plate boundary show underthrusting and foreland basin development without orogenic wedge formation continental collision and coinciding mantle lithosphere subduction may occur only if the lower crust of the foreland plate is weak enough promoting crust mantle decoupling during decoupling the weak lower crust beneath the orogen thickens significantly by ductile flow as it detaches from the down going mantle lithosphere this lower crustal thickening effects the distribution of upper crustal deformation and topography subduction of weak lower crust is favored when the weak plate interface has a significant thickness 15 km in nature and a high amount of shortening is applied increasing coupling at the plate interface through time leads to intra plate deformation by thickening and gentle folding and influences surface uplift and subsidence above the plate interface the transition from a mechanically decoupled plate boundary with a significant amount of mantle lithosphere subduction towards stronger plate coupling resulting in intra plate deformation and topography development can be recorded in for instance the caucasus the colombian cordillera the pyrenees and the alps thickening of the lower crust as portrayed for the western alps does not demand a strong frictional type behavior of the lower crust but can also be the consequence of ductile processes

switching between alternative responses of the lithosphere to continental collision summary we study possible responses to arc continent or continent continent collision using numerical models our short term integration models show that the initial stage of deformation following continental collision is governed by the competition between three potential weakness zones 1 mantle wedge 2 plate interface and 3 lower continental crust depending on which of these is the weakest zone in the system three different responses can be recognized 1 subduction polarity reversal 2 continuation of subduction and 3 delamination and back stepping subduction polarity reversal occurs if the mantle wedge is the weakest zone in the system this happens only if the viscosity of the mantle wedge is at least one order of magnitudelowerthantheaverageviscosityofthelithosphere incontinent continentcollision one additional condition needs to be satisfied for subduction polarity reversal to occur for the subducting lithosphere the ratio of the viscosity of the lower continental crust to the viscosity of the upper lithospheric mantle must be equal to or higher than 0 006 the time required for polarity reversal depends on several parameters the convergence rate the sinking velocity of the detached slab and the relative strength of the mantle wedge arc and backarc the response to collision is continued subduction if the plate interface is the weakest zone and is delamination and back stepping if the lower continental crust is the weakest area in the system our finding that a low viscosity wedge is a prerequisite for a reversal of subduction polarity agrees with inferences about regions for which subduction polarity reversal has been proposed

crustal scale seismic profiles across taiwan and the western philippine sea abstract we have used combined onshore and offshore wide angle seismic data sets to model the velocity structure of the taiwan arc continent collision along three cross island transects although taiwan is well known as a collisional orogen relatively few data have been collected that reveal the deeper structure resulting from this lithospheric scale process our southern transect crosses the hengchun peninsula of southernmost taiwan and demonstrates characteristics of incipient collision here 11 km thick transitional crust of the eurasian plate eup subducts beneath a large rapidly growing accretionary prism this prism also overrides the n luzon forearc to the east as it grows just west of the arc axis there is an abrupt discontinuity in the forearc velocity structure because this break is accompanied by intense seismicity we interpret that the forearc block is being detached from the n luzon arc and philippine sea plate psp at this point our middle transect illustrates the structure of the developing collision steep and overturned velocity contours indicate probable large scale thrust boundaries across the orogen the leading edge of the coherent psp appears to extend to beneath the east coast of taiwan deformation of the psp is largely limited to the remnant n luzon arc with no evidence of crustal thickening to the east in the huatung basin our northern transect illustrates slab continent collision the continuing collision of the psp and eup as the psp subducts the collisional contact is below 20 km depths along this transect ne of hualien this transect shows elements of the transition from arc continent collision to ryukyu arc subduction both of our models across the central range suggest that the paleozoic to mesozoic basement rocks there may have been emplaced as thick coherent thrust sheets this suggests a process of partial continental subduction followed by intra crustal detachment and buoyancy aided exhumation although our models provide previously unknown structural information about the taiwan orogen our data do not define the deepest orogenic structure nor the structure of western taiwan additional seismic active and passive geologic and geodynamic modeling work must be done to fully define the structure the active deformation zones and the key geodynamic process of the taiwan arc continent collision

rheology and strength of the eurasian continental lithosphere in the foreland of the taiwan collision belt constraints from seismicity flexure and structural styles 1 deformation in western taiwan is characterized by variable depth frequency distribution of crustal earthquakes which are closely connected with along strike variations of tectonic styles thin or thick skinned around the peikang high a major inherited feature of the chinese margin to fit the calculated high crustal geotherm and the observed distribution of the crustal seismic activity a qz diorite and granulite composition for the upper and the lower crust is proposed we then model the plate flexure through te estimates using brittle elastic ductile plate rheology flexure modeling shows that the best fit combination of te boundary condition is for thrust loads acting at the belt front the calculated te vary in the range of 15 20 km these values are primarily a reflection of the thermal state of the rifted chinese margin inherited from the oligocene spreading in the south china sea however other mechanical properties such as the degree of crust mantle coupling and the thickness of the mechanically competent crust and mantle are considered south of the peikang high flexure modeling reveals lower te associated with thinner mechanically strong layers variable stress strain distribution associated with a higher degree of crust mantle decoupling is examined to explain plate weakening we first show that plate curvature cannot easily explain strength reduction and observed seismic activity additional plate boundary forces arising from the strong coupling induced by more frontal subduction of a buoyant crustal asperity i e the peikang high with the overriding plate are required favorably oriented inherited features in the adjacent tainan basin produce acceleration of strain rates in the upper crust and hence facilitate the crust mantle decoupling as attested by high seismic activity and thick skinned deformation the relative weakening of the lower crust and mantle then leads to weaken the lithosphere by contrast to the north more oblique collision and the lack of inherited features keep the lithosphere stronger this study suggests that when the eurasian plate enters the taiwan collision tectonic inheritance of the continental margin exerts a strong control on the plate deformation by modifying its strength

a model of palaeozoic obduction and exhumation of high pressure low temperature rocks in the southern urals abstract a new evolutionary geodynamic model of devonian continental subduction and exhumation of high pressure low temperature metamorphic rocks in the southern urals is proposed based on the results of physical modelling geological and geophysical data and on the comparison of this belt with other orogens the model includes the following principal phases 1 closure of the western uralian ocean by eastward intraoceanic subduction associated with the magnitogorsk volcanic arc 2 subduction of the european continental margin causing failure of the overriding plate in the arc area along a fault dipping eastward under the arc 3 subduction into the mantle of the fore arc block together with the underlying continental crust and sedimentary layer the sedimentary cover as well as the crustal and mantle fragments of this block are scraped off and accreted in front of and under the arc the continental crust shielded from the hot mantle by the fore arc block subducts to depths of more than 150 km remaining at a relatively low temperature the crust then fails at depths of several tens of kilometres 4 the subducted crustal slice starts to rapidly rise and intrude the interplate zone scraping and pushing up the sediments and slivers of the oceanic fore arc block previously dragged down to different depths 5 exhumation of the rising high pressure low temperature rocks within the uraltau dome separating the subduction accretionary complex from the magnitogorsk arc the eastern border of the uraltau dome coincides with the main uralian fault this fault represents a complex suture zone which at the stage of deep crustal subduction was associated with a major thrust subduction fault and at the exhumation stage with a major normal fault corresponding to the upper surface of the rising crustal sedimentary body

from the highest to the deepest the gaoping river gaoping submarine canyon dispersal system abstract there are many different source to sink dispersal systems around the world and the gaoping river gpr gaoping submarine canyon gpsc provides an example especially as a canyon captured system the gpr a small mountainous river having an average gradient of 1 150 and the gpsc which links the river catchment to the deep sea basin represent two major topographic features around sw taiwan together they constitute a terrestrial to marine dispersal system that has an overriding impact on the source to sink transport of sediment in this region the gpsc extents from the mouth of the gpr through the shelf and slope and into the northeastern manila trench a distance of about 260 km it is a major conduit for the transport of terrestrial sediment and carbon to the south china sea and the landward transport of particles of marine and biological origin in the gpsc the dominant mode of suspended sediment transport is tidal oscillations and the net direction is up canyon in contrast sediment transport associated with episodic gravity driven events is down canyon the steady sedimentation of the tidal regime results in hemipelagic mud across the canyon floor whereas the gravity driven hyperpycnal regime causes turbidite erosion and deposition along the canyon thalweg typhoon induced river floods often lead to hyperpycnal plumes at the river mouth which directly and indirectly ignite hyperpycnal turbidity currents in the canyon forming an effective agent for transporting large amounts of terrestrial organic material modern and fossil carbon to the south china sea basin therefore the gpr gpsc represents a source to sink system in which terrestrial sediment in a mountainous catchment is promptly removed and transported to the deep sea by episodic gravity flows this is also a pathway by which modern terrestrial organic carbon is quickly and effectively delivered to the deep sea

development of arc continent collision melanges linking onshore geological and offshore geophysical observations of the pliocene lichi melange southern taiwan and northern luzon arc western pacific abstract although the lichi melange has been studied intensively over the last decade its enigmatic nature has generated debates regarding its origin and evolution two prominent models have been proposed to explain the lichi melange the olistostrome model with slumping sediments and the tectonic collision model with intensive shearing neither model can explain what causes the interpreted slumping and complex faulting processes for the sediments here we study the lichi melange using a time space equivalence approach in which the tectonics of the offshore continuation of the lichi melange should represent an earlier stage in its evolution our study of marine multichannel seismic data suggested that the backthrusts in the accretionary prism propagate arcward above and within the deforming forearc and arc basement to incorporate the sediment and basement materials into the rear of the accretionary prism therefore we proposed the retrowedge evolution model whose novel key feature is that the irregular topography of the arc basement affects the taper angle of the retrowedge the retrowedge has a greater taper than the minimum taper of the prowedge so the slope can be steeper and thus favors gravitational failure such processes would generate complex faulting and slumping processes in the backthrusted forearc ridge and basin in sum this retrowedge model reconciles the mixture of slumping and faulting processes found in the lichi melange

deep seismic structure of the northeastern south china sea origin of a high velocity layer in the lower crust we present a 2 d seismic tomographic image of the crustal structure along the obs2012 profile which delineates the moho morphology and magmatic features of the northeastern south china sea margin the image was created by forward modeling rayinvr and traveltime tomographic inversion tomo2d overall the continental crust thins seaward from 27 km to 21 km within the continental shelf across the zhu i depression and dongsha rise with slight local thickening beneath the dongsha rise accompanying the increase in the moho depth the dongsha rise is also characterized by 4 7 km thick high velocity layer hvl 7 0 7 6 km s in the lower crust and exhibits a relatively high velocity 5 5 6 4 km s in the upper crust with a velocity gradient lower than those of the zhu i depression and tainan basin across the continental slope and continent ocean transition cot which contain the tainan basin the crust sharply thins from 20 km to 10 km seaward and a 2 3 km thick hvl is imaged in the lower crust we observed that volcanoes are located only within the cot but none exist in the continental shelf the dongsha rise exhibits a high magnetic anomaly zone and different geochemical characteristics from the cot based on those observations we conclude that the hvl underlying the cot is probably extension related resulting from the decompression melting in the cenozoic whereas the hvl beneath the dongsha rise is probably arc related and associated with the subduction of the paleo pacific plate these findings are inconsistent with those of some previous studies

strain modes within the forearc arc and back arc domains in the izu japan and taiwan arc continent collisional settings 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

structural evolution and significance of a melange in a collision belt the lichi melange and the taiwan arc continent collision the analysis of melanges of various types sedimentary diapiric tectonic and polygenetic is generally difficult and depends on a variety of criteria however understanding the nature and origin of melanges is crucial to deciphering the evolution of some mountain belts the lichi melange of the taiwan coastal range is juxtaposed against remnant forearc basin sequences by thrust faults and is composed of exotic ophiolite and sedimentary blocks with sizes ranging from metres to kilometres and coherent turbidite beds all embedded in a sheared scaly argillaceous matrix the lichi melange has been interpreted either as a subduction complex or as an olistostrome by separating four main deformation levels based on the degree of disruption within the lichi melange and adjacent sedimentary rocks we have made new detailed geological maps and structural profiles in two key areas of the lichi melange we paid particular attention to the original stratigraphic relationships between the melange and the adjacent flysch formation our field results compared with submarine seismic profiles suggest that the present day structure of the lichi melange results mainly from the shearing of lower forearc basin sequences rather than from a subduction complex or a mere olistostrome in late miocene time because lithospheric subduction turned into arc continent collision in the southern taiwan area the site of the proto manila trench changed from an active plate boundary into a deformation zone with several thrusts a new plate suture zone between the eurasian plate eastern central range and the philippine sea plate coastal range was therefore formed along the longitudinal valley the longitudinal valley originated as a submarine arc prism boundary an innate weak zone within the overriding plate and has become a prominent tectonic feature of the arc continent collision this inference is supported by observations on the lichi melange in the coastal range and the huatung ridge off southeastern taiwan

tomographic evidence for the eurasian lithosphere subducting beneath south taiwan 1 a tomographic image of the crust and upper mantle beneath the taiwan island as derived from local regional and teleseismic data simultaneously revealed a high velocity zone from the surface down to a depth of 300 km locating beneath south taiwan to the south of latitude 24 n we interpret this high velocity zone to be the subducted eurasian lithosphere our result is different from a global tomography study that shows the eurasian plate subducting beneath most part of the taiwan island down to 670 km depth this down going model of the eurasian lithosphere implies that the tectonic framework of taiwan has been changing from subduction in the south to collision in the north which provides geophysical evidence supporting the previous proposed models the subducted eurasian lithosphere colliding with the subducted philippine sea plate would have contributed to the mountain building active seismicity and crustal deformation in the study region due to the lower part of the eurasian continental plate subducted beneath south taiwan

tandem suturing and disarticulation of the taiwan orogen revealed by its neotectonic elements taiwan s numerous active faults and folds demarcate distinct eastern and western neotectonic belts the western belt results from the attachment and subsequent detachment of a sliver of continental lithosphere to the eurasian continental margin the eastern belt is the product of the same continental sliver docking with and then separating from the luzon volcanic arc thus the active taiwan orogen is a tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin this progressive suturing and separation is a superb living demonstration of the fundamental weakness of lithospheric sutures furthermore this neotectonic architecture provides the basis for understanding the taiwan s seismic sources

a model for the termination of the ryukyu subduction zone against taiwan a junction of collision subduction separation and subduction boundaries 1 the nw moving philippine sea plate psp collides with the eurasian plate eup in the vicinity of taiwan and at the same time it subducts toward the north along sw ryukyu the ryukyu subduction zone terminates against eastern taiwan while the ryukyu trench is a linear bathymetric low about 100 km east of taiwan closer to taiwan it cannot be clearly identified bathymetrically owing to the deformation related to the collision making the location of the intersection of the ryukyu with taiwan difficult to decipher we propose a model for this complex of boundaries on the basis of seismicity and 3 d velocity structures in this model the intersection is placed at the latitude of about 23 7 n placing the northern part of the coastal range on eup as psp gets deeper along the subduction zone it collides with eup on the taiwan side only where they are in direct contact thus the eurasian plate on the taiwan side is being pushed and compressed by the nw moving philippine sea plate at increasing depth toward the north offshore of northeastern taiwan the wedge shaped eup on top of the ryukyu subducting plate is connected to the eup on the ryukyu side and coupled to the nw moving psp by friction at the plate interface the two sides of the eup above the western end of the subduction zone are not subjected to the same forces and a difference in motions can be expected the deformation of taiwan as revealed by continuous gps measurements geodetic movement along the east coast of taiwan and the formation of the hoping basin can be understood in terms of the proposed model

late archaean synorogenic basins of the eastern goldfields superterrane yilgarn craton western australia part iii signatures of tectonic escape in an arc continent collision zone abstract siliciclastic supersequences in the eastern goldfields superterrane are remnants of basins that were linear zones of subsidence between intra terrane faults fluvial deposits record proximal to medial braid plains deep marine canyon and fan deposits were linked across intra terrane compartments only by mud rich deposits axial depositional systems dominate with only minor evidence for slope aprons although transverse and axial systems are preserved in some fluvial deposits basin development occurred during two stages separated by an inversion event with the kalgoorlie terrane recording change from a fluvial to a deep marine basin and the kurnalpi terrane change from distal to proximal deep marine facies tracts sparse palaeocurrents establish that uplift to the north controlled sediment dispersal lithofacies stacking is aggradational whereas abrupt upwards change in facies tracts is back stepping within depositional sequences and between depositional sequence sets but forward stepping between depositional sequences the stratigraphic architecture is atypical of synorogenic basins but consistent with a strike slip regime characterised by pulsed uplift subsidence steady state basin lengthening and subsidence punctuating catastrophic subsidence and lengthening and tectonic anchoring the basins are interpreted to have been similar to graben and half graben of the western anatolian extensional province of turkey with linear zones of subsidence developing adjacent to strike slip oblique slip or normal dip slip faults controls on stratigraphic patterns are considered to have been regional rather than at the scale of each basin the envisaged tectonic setting is similar to projected collision between the philippine archipelago west of the philippine fault and continental crust of the south china sea but the orogenic architecture is similar to that of accreted superterranes in the canadian cordillera interpreted north or northwest convergence between the burtville terrane to the east and the ancestral yilgarn continent to the northwest produced a south propagating orogen with the kalgoorlie gindalbie and kurnalpi terranes trapped between in a tectonic escape corridor tectonic escape to the south between bounding strike slip faults produced back stepping of facies tracts that simulated basin lengthening whereas forward stepping of facies tracts was the response to south propagating uplift

collisional tectonics between the eurasian and philippine sea plates from tomography evidences in southeast china abstract the upper mantle structure of southeast china is important for us to understand the deformation and mantle dynamics process associated with the interaction between the eurasian plate and philippine sea phs slab we determined a detailed three dimensional p wave velocity vp structure of the crust and upper mantle down to 400 km depth beneath southeast china by applying teleseismic tomography to 6869 high quality p wave arrival times the data were collected very carefully from the original seismograms of 635 teleseismic events recorded by 65 broadband stations deployed in southeast china our images show that the high vp phs slab subducts toward the north along the ryukyu trench at the latitude of about 24 n and extends down to 350 km depth and even more high vp anomalies are imaged in the upper mantle under central and southern taiwan which represent the subducted eurasian plate break off eurasian plate at a big angle subducting eastward is revealed under central taiwan at depths from the upper mantle to 400 km while continuous eurasian plate under south taiwan is mainly imaged from the moho down to 400 km depth a torn mantle window within the eurasian continent beneath central and northern taiwan created by the northward motion of the philippine sea plate is the upwelling path of the asthenosphere the tomographic images also show the low vp anomalies spread widely under the coastal areas of mainland china and taiwan strait the structure of the crust and upper mantle suggests that the mountain building process in the central part of taiwan is mainly attributed to the subduction collision tectonics at the boundary between the eurasian continental lithosphere and the subducting oceanic lithosphere of the phs slab

arc continent collision and subduction reversal in the cenozoic evolution of the northwest pacific an example from kamchatka ne russia abstract the principal new feature in the cenozoic evolution of the northwest pacific is based on the fact that two arc terranes of upper cretaceous paleogene age were incorporated in the kamchatka orogen during the early tertiary and at the end of the miocene respectively these two arc terranes so called achaivayam valaginskaya campanian lower paleocene and kronotskaya coniacian eocene arcs are separated by a suture zone that contains deformed slices of young paleocene lower eocene oceanic crust paleomagnetic data on the original paleolatitudes of the arc positions as well as geochemical data characterized the arcs as intraoceanic originated in the northwest pacific the arcs were separated by the vetlovka oceanic plate suggested to be a trapped fragment of the kula plate in which a new spreading zone developed in the early tertiary the principal event in the reconstructed evolution is the eocene collision of the extended achaivayam valaginskaya arc terrane with the continental margin of asia the margin is interpreted as the southeastern facing the pacific cretaceous accretionary boundary of the okhotsk microplate docked against the asian continent at 55 65 ma the arc continent collision developed progressively northward from the end of the paleocene early eocene in southern kamchatka to the middle eocene in the olutorka region the different stages of the collision occurred simultaneously along strike of the achaivayam valaginskaya arc according to the geodynamic model based on geological data for southern kamchatka collision included 1 the entrance of the continental margin in the subduction zone deformation of the overriding plate and subduction of fore arc block 2 arc obduction on the continental margin blocking of continental margin subduction and 3 subduction reversal with onset of oceanic subduction at the eastern side of the deformed arc this subduction reversal produced deformation and reverse faulting along the eastern side of the arc thus allowing accretion of tectonic slices of young oceanic crust of the vetlovka plate which began to subduct during the subduction reversal the subducted plate dipping to the southeast was broken off and detached at depth under the arc area the subduction polarity reversal the most characteristic feature of the collision model is strongly supported by structural and geologic data of southern kamchatka and explains the main tectonic metamorphic and magmatic events related to and postdating the collision

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities