rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

mountain building in taiwan a thermokinematic model the taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening however a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge we propose here a new thermokinematic model of the taiwan mountain belt reconciling existing kinematic thermometric and thermochronological constraints in this model shortening across the orogen is absorbed by slip on the most frontal faults of the foothills crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge tananao complex tc where the uplift rate is estimated to 6 3 mm a 1 and beneath the westernmost internal region of the orogen hsueshan range units hr where the uplift rate is estimated to 4 2 mm a 1 our model suggests that the tc units experienced a synchronous evolution along strike despite the southward propagation of the collision it also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures exhumation of the hr units increases northward but has not yet reached an exhumational steady state presently frontal accretion accounts for less than 10 of the incoming flux of material into the orogen although there is indication that it was contributing substantially more 80 before 4 ma the incoming flux of material accreted beneath the tc significantly increased 1 5 ma ago our results also suggest that the flux of material accreted to the orogen corresponds to the top 7 km of the upper crust of the underthrust chinese margin this indicates that a significant amount 76 of the underthrust material has been subducted into the mantle probably because of the increase in density associated with metamorphism we also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field by combining available geological data on the thermal and kinematic evolution of the wedge our study sheds new light onto mountain building processes in taiwan and allows for reappraising the initial structural architecture of the passive margin

use of rubidium to date loess and paleosols of the louchan sequence central china abstract rb concentrations analyzed at 20 cm intervals from the luochuan sequence of loess and paleosols are sensitive to the loess paleosol alternation controlled by monsoon climate because it is geochemically immobile rb can be well preserved in the loess paleosol sequence after deposition and its concentration depends mainly on properties of the winter monsoon blown dust and on intensity of the summer monsoon induced pedogenesis a curvilinear relation has been developed between the measured rb concentration and the apparent sedimentation rate for the last glacial interglacial cycle this relation provides a time scale that corresponds well with the presently accepted ages for paleomagnetic reversals of brunhes matuyama and jaramillo events with allowance for reduced rb concentrations caused by early pleistocene climate the rb based time scale is also consistent with the boundary ages of other major paleomagnetic reversals of the past 2 58 myr

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

inversion of the paleogene chinese continental margin and thick skinned deformation in the western foreland of taiwan abstract new structural data available seismicity data together with mechanical constraints on the eurasian continental lithosphere and reconstruction of paleostress trajectories are combined in order to re assess and discuss the dominant deformation mode thin skinned vs thick skinned in the western fold and thrust belt of the active taiwan collision zone serial balanced cross sections and computed paleostress tensors suggest that structural styles and stress trajectories at the front of the taiwan mountain belt may vary rapidly along strike depending on the presence of pre orogenic paleogene troughs in the chinese continental margin taihsi and tainan basins that are favourably oriented to be reactivated and inverted in localities of the western foreland where basin inversion and thick skinned basement involved shortening predominate the crustal seismic activity is important and characterized by strike slip faulting in these domains of the fold thrust belt the stress deviations with respect to the regional transport direction are also important by contrast in domains of significant syn orogenic subsidence a thin skinned style of deformation may be prominent due to the lack of available pre existing features the seismic activity is limited to few major faulted boundaries such as the active chelungpu sani thrust and the stress deviations are limited the timing of deformation at the belt front seems to be independent of the structural styles so that frontal folds are active since probably 0 5 ma however in inner parts of the western foothills of taiwan where superimposed thick skinned and thin skinned deformation are required out of sequence thrusting occurs to maintain the topographic profile finally we suggest that kinematics and structural styles of the western fold thrust belt are controlled by the mechanics of the eurasian continental margin in agreement with a recent study at the scale of the orogen the limited shortening amounts across the wf and in the central range as well as the absence of continental hp rocks better support a thick skinned collision model for taiwan

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

overturned marble layers evidence for upward extrusion of the backbone range of taiwan abstract the backbone range is part of the taiwan mountain belt which was formed due to the oblique collision between the luzon arc and the eurasian passive continental margin from plio pleistocene to the present stable isotope compositional profiles of thin marble layers from this mountain range show that marble layers from rock sections with an inverted metamorphic zonation were all overturned after the peak metamorphism and that marble layers from rock sections with a normal metamorphic zonation were not overturned exhumation folding seems to be the responsible process an upward extrusion exhumation model is therefore postulated as the probable mechanism for the mountain building process this model can well explain the fanning orientation of rock cleavage s dipping in a regional scale as well as the metamorphic characteristics across the mountain range the model also shows that the recorded stretching lineation is secondary in nature meaning the exact direction of rock movement during the initial exhumation stage in response to the oblique collision cannot be deduced

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

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

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

continental plate collision p t t z conditions and unstable vs stable plate dynamics insights from thermo mechanical modelling there was much debate recently on the mechanisms of continental convergence and related pressure temperature p t conditions both in modeling and petrologic community depending on the mechanisms of convergence subduction collision folding or rt instability one can argue about the possibility of large scale deviations of pressure and temperature in the accretion prism and below it from reference i e lithostatic conditions commonly used for petrologic reconstructions of evolution of exhumed metamorphic rocks these deviations can be caused for example by tectonic overpressure that as suggested in some studies may be responsible for formation of uhp ultra high pressure rocks however overpressure in exhumation zones can be built only in specific collision scenarios associated with plate coupling pure shear folding in this study we analyze conditions that define various mechanisms of convergence and consequently of exhumation these mechanisms can be represented as a superposition of 1 simple shear subduction 2 pure shear collision 3 folding and 4 rayleigh taylor instability we study these scenarios using a thermo mechanical model that accounts for brittle elastic ductile rheology surface processes and metamorphic changes it appears that stable oceanic type subduction may occur in the case of cold lithospheres tmohob550 c and relatively high convergence rates n3 5 cm yr depending on the lower crustal rheology strong or weak either the whole upper and lower crust or only the lower crust can be involved in subduction in case of weak metamorphic rheologies phase changes improve chances for stable subduction pure shear becomes a dominant mechanism when tmohon550 c or convergence rates are lower than 3 cm yr large scale folding is favored in case of tmoho 500 650 c and is more effective in the case of mechanical coupling between crust and mantle e g strong lower crust gravitational rayleigh taylor instabilities overcome other mechanisms for very high values of tmoho n800 c and may lead to development of subvertical cold spots however it is reasonable to assume that in most cases continental collision is initiated at oceanic subduction rate which is rarely slower than 5 cm yr this rate is sufficient to drive continental subduction during the first several myr of collision in this case the subduction channel is characterized by nearly lithostatic pressure conditions large scale zones of tectonic overpressure may be built outside the channel but do not affect the exhumed rocks overpressure may be built inside the channel in the short moment of its closure we suggest that most continental orogenic belts could have started their formation from continental subduction this evokes small tectonic overpressures and thus deep origin of the uhp rocks that may be brought to the surface via the suggested multi level mechanism of exhumation

transient hot channels perpetrating and regurgitating ultrahigh pressure high temperature crust mantle associations in collision belts abstract two dimensional numerical modeling of early continental collision associated with subduction of the lithospheric mantle shows that the formation and exhumation of coesite and diamond bearing rocks metamorphosed at 700 to 900 c in the presence of dense supercritical silicate fluids and melts may be explained by a transient hot channel effect anomalously high temperature is caused by intense viscous and radiogenic heating in the channel composed of deeply subducted radiogenic upper crustal rocks especially sediments of passive margin origin and mantle rocks heating is associated with partial melting of crustal rocks caused by pervasive flow of aqueous fluids relieved by rapid dehydration deserpentinization of the overriding mantle lithosphere that has been hydrated during earlier subduction stages the channel penetrates the plate interface to the bottom of the lithosphere of the overriding plate 150 200 km and is characterized by metamorphic temperatures reaching 700 to 900 c low effective viscosity of rocks subsequent to increased temperature partial melting and fluid infiltration permits profound mixing of hydrated mantle and crustal rocks the hot channel exists only during early collision but rapidly produces large amounts of ultrahigh pressure high temperature rocks further collision closes the channel by squeezing rheologically weak partially molten buoyant rocks between the strong lithospheric mantles of the two colliding plates assemblages of complicated p t paths with repetitive loops characterize exhumation of ultrahigh pressure rocks in the convoluted flow pattern of the hot channel

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

investigating the kinematics of mountain building in taiwan from the spatiotemporal evolution of the foreland basin and western foothills the taiwanese range has resulted from the collision between the luzon volcanic arc and the chinese continental margin which started about 6 5 myr ago in the north and has since propagated southward the building of the range has been recorded in the spatiotemporal evolution of the foreland basin we analyze this sedimentary record to place some constraints on the kinematics of crustal deformation the flexure of the foreland under the load of the growing wedge started with a 1 5 myr long phase of rapid subsidence and sedimentation which has migrated southward over the last 3 5 myr at a rate of 31 10 5 mm yr reflecting the structural evolution of the range and the growth of the topography during the oblique collision isopachs from the toukoshan 0 to 1 1 ma and cholan 1 1 to 3 3 ma formations as well as the sedimentation rates retrieved from a well on the pakuashan anticline indicate that the foreland basement has been moving toward the center of mass of the orogen by 45 50 mm yr during the development of the basin from there we estimate the long term shortening rate across the range to 39 5 44 5 mm yr by considering available data on the thrust faults of the foothills of central taiwan we show that most if not all the shortening across the range is accommodated by the most frontal structures with little if any internal shortening within the wedge the range growth appears therefore to have been essentially sustained by underplating rather than by frontal accretion in addition only the upper 7 to 9 km of the underthrusted crust participates to the growth of the orogen this requires that a significant amount of the chinese passive margin crust is subducted beneath the philippine sea plate

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

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

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

what drives orogeny in the andes the andes the world9s second highest orogenic belt were generated by the cenozoic tectonic shortening of the south american plate margin overriding the subducting nazca plate we use a coupled thermomechanical numerical modeling technique to identify factors controlling the intensity of the tectonic shortening from the modeling we infer that the most important factor was accelerated westward drift of the south american plate changes in the subduction rate were less important other important factors are crustal structure of the overriding plate and shear coupling at the plates9 interface the model with a thick 40 45 km at 30 ma south american crust and relatively high friction coefficient 0 05 at the nazca south american interface generates 300 km of tectonic shortening during 30 35 m y and replicates the crustal structure and evolution of the high central andes the model with an initially thinner

two dimensional crustal structures of taiwan from gravity data to delineate the tectonic character of taiwan an island wide gravity survey of taiwan was conducted between 1980 and 1987 the bouguer anomaly map shows that in general isogals trend nne in consonance with the overall structural trend of the island with seismic and other geophysical data as constraints the subsurface density structures were modeled along three profiles across the major structural trends the gravity data are consistent with average continental moho depths of 26 km in the coastal plain and the western foothills 28 km underneath the coastal range in eastern taiwan and 33 km under the central range a lack of significant correlation of the bouguer anomalies with the topography implies dynamic rather than isostatic support of topography in the taiwan region

light absorbing impurities in snow cover across northern xinjiang china light absorbing impurities lais e g black carbon bc organic carbon oc mineral dust md deposited on snow cover reduce albedo and accelerate its melting northern xinjiang nx is an arid and semi arid inland region where snowmelt leads to frequent floods that have been a serious threat to local ecological security there is still a lack of quantitative assessments of the effects of lais on snowmelt in the region this study investigates spatial variations of lais in snow and its effect on snow albedo radiative forcing rf and snowmelt across nx results showed that concentrations of bc oc only water insoluble oc md ranged from 32 to 8841 ng g 1 77 to 8568 ng g 1 and 0 46 to 236 g g 1 respectively weather research and forecasting chemistry model suggested that residential emission was the largest source of bc snow ice and aerosol radiative modelling showed that the average contribution of bc and md to snow albedo reduction was 17 and 3 respectively rf caused by bc significantly exceeded rf caused by md in different scenarios changes in snow cover duration scd caused by bc and md decreased by 1 36 0 61 to 6 12 3 38 d compared with md bc was the main dominant factor in reducing snow albedo and scd across nx

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

east asia plate tectonics since 15 ma constraints from the taiwan region abstract 15 ma ago a major plate reorganization occurred in east asia seafloor spreading ceased in the south china sea japan sea taiwan sea sulu sea and shikoku and parece vela basins simultaneously shear motions also ceased along the taiwan sinzi zone the gagua ridge and the luzon ryukyu transform plate boundary the complex system of thirteen plates suddenly evolved in a simple three plate system eu ph and pa beneath the manila accretionary prism and in the huatung basin we have determined magnetic lineation patterns as well as spreading rates deduced from the identification of magnetic lineations these two patterns are rotated by 15 they were formed by seafloor spreading before 15 ma and belonged to the same ocean named the taiwan sea half spreading rate in the taiwan sea was 2 cm year from chron 23 to 20 51 to 43 ma and 1 cm year from chron 20 43 ma to 5b 15 ma five plate kinematic reconstructions spanning from 15 ma to present show implications concerning the geodynamic evolution of east asia amongst them the 1000 km long linear gagua ridge was a major plate boundary which accommodated the northwestward shear motion of the ph sea plate the formation of taiwan was driven by two simple lithospheric motions i the subduction of the ph sea plate beneath eurasia with a relative westward motion of the western end a of the ryukyu subduction zone ii the subduction of eurasia beneath the philippine sea plate with a relative southwestward motion of the northern end b of the manila subduction zone the luzon arc only formed south of b the collision of the luzon arc with eurasia occurred between a and b east of a the luzon arc probably accreted against the ryukyu forearc