simultaneous mountain building in the taiwan orogenic belt the obliquity of the arc continent collision in taiwan is thought to have produced a southward propagating orogenic system starting as early as 8 ma we combine 62 new zircon fission track ages with timing of rapid subsidence in the foreland basin to identify the timing of the onset of exhumation and orogenesis the oldest completely reset zircon fission track ages and the onset of rapid tectonic subsidence in both the northern and southern parts of the foreland basin are ca 5 6 ma we propose that north south rifting in the south china sea created a north trending continental margin before the collision rather than the commonly assumed northeast trending margin consequently both this north trending continental margin and the luzon arc of the philippine sea plate were subparallel resulting in an initial collision that was simultaneous along strike

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

magnitude of cenozoic erosion from mean sonic transit time offshore taiwan abstract mean sonic transit times from eight stratigraphic units in forty four wells in western and northern offshore taiwan were plotted against depth apparent erosion displacement on the depth axis from the normal compaction was determined for each unit in each well cretaceous and eocene units show greater apparent erosion than miocene and pliocene units in the same well which in turn show more erosion than pleistocene units apparent erosions derived from two different units are plotted against each other for correlation analysis based on the analysis the main periods of erosion were during the oligocene and plio pleistocene the timing of erosion inferred from sonic interval transit is consistent with recognized unconformities and its areal distribution is consistent with the observed structural evolution of the region the maximum true erosion corrected for post erosion burial at the oligocene unconformity was 3500 m on the penghu platform approximately 2500 m of true erosion occurred on the kuanin ulift and the pengchiahsu platform due to moderate to minor erosion and a great amount of post erosion burial true magnitude of erosion is masked at the miocene unconformity in most of the area erosion of up to 500 m on the eastern side of the penghu island at the pleistocene unconformity defines the shape of the present day penghu waterway in the northern offshore area up to 1000 m of plio pleistocene true erosion occurred in the taiwan sinzi folded zone where miocene folds are observed the magnitude of true erosion decreased west of the taiwan sinzi folded zone to 500 m in the pengchiahsu basin a maximum of 500 m of true erosion is also observed in the west offshore area along hsing chu to miaoli coast

the role of basement involved normal faults in the recent tectonics of western taiwan in the foreland area of western taiwan some of the pre orogenic basement involved normal faults were reactivated during the subsequent compressional tectonics the main purpose of this paper is to investigate the role played by the pre existing normal faults in the recent tectonics of western taiwan in nw taiwan reactivated normal faults with a strike slip component have developed by linkage of reactivated single pre existing normal faults in the foreland basin and acted as transverse structures for low angle thrusts in the outer fold and thrust belt in the later stage of their development the transverse structures were thrusted and appear underneath the low angle thrusts or became tear faults in the inner fold and thrust belt in sw taiwan where the foreland basin is lacking normal fault reactivation the pre existing normal faults passively acted as ramp for the low angle thrusts in the inner fold and thrust belt some of the active faults in western taiwan may also be related to reactivated normal faults with right lateral slip component some main earthquake shocks related to either strike slip or thrust fault plane solution occurred on reactivated normal faults implying a relationship between the pre existing normal fault and the triggering of the recent major earthquakes along strike contrast in structural style of normal fault reactivation gives rise to different characteristics of the deformation front for different parts of the foreland area in western taiwan variations in the degree of normal fault reactivation also provide some insights into the way the crust embedding the pre existing normal faults deformed in response to orogenic contraction

deformation of incompletely crystallized magma systems granitic gneisses and their tectonic implications certain textures in two feldspar calc alkaline granitic gneisses have been identified as indicators of the presence of intercrystalline melt during deformation of crystal melt mushes fluid relocation or fracting is to be expected in an incompletely crystallized magmatic system as deviatoric stresses are applied to it relocation of late stage fluids capable of crystallizing k feldspar quartz microaplite and myrmekite to low pressure zones such as the pressure shadow region around earlier crystals occurs within some developing mylonitic gneiss fabrics and results in a distinctive assemblage of textures strain in these rocks is expressed by various brittle and ductile features and by fluid relocation textures the petrogenesis of these particular gneisses is therefore both magmatic and metamorphic contrasting with gneiss forming processes that had no participating magmatic component migmatitic complexes evolving by partial anatexis of non magmatic rocks in a tectonically active environment are not

the structure of southwest taiwan the development of a fold and thrust belt on a margins outer shelf and slope d b j a m and c b acknowledge funding provided by the spanish ministerio de economia y competividad grant cgl2013 43877 p h k c acknowledges funding by most 104 2628 m 008 005 my3

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

exhumation and doming of the thasos metamorphic core complex s rhodope greece structural and geochronological constraints abstract the thasos island metamorphic core complex s rhodope n aegean sea was generated between 26 and 13 ma progressive extensional tectonics was associated with upwarping of the deeper parts of this core complex to a narrow gneiss dome and with formation of a steep topographic high we present a combined structural microstructural and geochronological study that constrains the deformation time path of progressive extension and exhumation thasos island consists of three superimposed more or less flat lying metamorphic units with downward decreasing geochronologic ages which are separated by two systems of low angle normal detachment surfaces trending nw se the upper unit stayed in supracrustal level since 50 ma representing the upper plate during an early phase of extension not later than 26 23 ma upper levels of the core complex intermediate unit underwent pervasive mylonitization with top to the sw shear from about 21 ma onward the intermediate unit was rigid and top to the sw slip continued at least until 13 8 ma on the discrete detachment surface that separates the core complex from the upper plate yet in the 21 15 ma period deeper levels lower unit still deformed plastically and deformation successively concentrated in zones of high strain and in discrete detachment surfaces that caused decoupling of the lower from the intermediate unit these indicate downdip movements in opposite sense associated with doming of the lower unit at that stage simultaneously the intermediate unit was fragmented on high angle normal faults that sole into the dome bounding detachment surface and roof into the core complex bounding detachment surface these faults confine tilt blocks that are arranged around the lower unit gneiss dome doming of the core complex occurred simultaneously with subsidence of basins located on the upper plate

the geodynamics of lithospheric extension lithospheric extension is a fundamental plate tectonic process controlling the collapse of mountain belts the break up of continents and the formation of new oceanic basins this review summarises major advances on understanding a the nature of the ocean continent transition b the origin and evolution of detachment faults c the dynamic strength of continental lithosphere during extension and d the role of magmatism during extension major steps have been made in mapping out the complexities of the ocean continent transition zone particularly in magma poor rifted margins where extensional structures are not masked by voluminous magmatism the role of detachment faulting during rifting seems to be crucial and explains observations on depth dependent stretching of the lithosphere despite new insights into the dynamic behaviour of the lithosphere its rheological response remains a major uncertainty in modelling the evolution of extensional systems likewise the multiple roles that basaltic magmatism may have in modifying extension remain a key question future insights into the global behaviour of extensional systems will be gained by constraining lithospheric rheology through integrating structural evolution and magmatism in the field geodetic measurements of active extension thermochronology seismic surveys and drilling programs 2008 elsevier b v all rights reserved

effects of initial rift inversion over fold and thrust development in a cratonic far foreland setting abstract the effects of initial rift inversion over the geometry of a far foreland intracratonic fold and thrust belt are investigated a total of 25 seismic reflection lines and stratigraphic data from 9 wells are used in association to digital elevation and field geological data to investigate the geometric relationship between shallow thrust development and initial positive inversion of buried rift faults in a cratonic environment where inversion tectonics is not common the study case is conducted in the meeting region of the opposed verging brasilia and aracuai foreland fold and thrust neoproterozoic belts located in central brazil formed in the first stages of west gondwana amalgamation seismic reflection sections are used to map buried paleorift faults and trust ramps the best 5 sections are also interpreted in detail in terms of fold and thrust geometry and their relationship to the inverted rifts is analyzed they show high correlation between shallow fold and thrust geometry and the shortening of synrift strata caused by rift inversion results indicate that initial positive rift fault reactivation exerts a determinant control over the locus of thrust ramp nucleation by causing syn rift strata to overfold and drape fold the passive folding propagates upwards forming gentle folds in the decollement plane where thrust ramps tend to nucleate back thrust forethrust pairs tend to form over elevated horsts where higher topographic plateaus are preserved multiple thrusting and lower relief occur over buried rifts with multiple inverted faults strata over non rifted basement remain practically unaffected by thrusting and folding moreover the development of thrust salients and recesses are demonstrated to be conditioned by the morphology of buried rifts the study also contributes with a more precise mapping of the buried rift system and thrust system in the area and brings new insights about the structural evolution of the brasiliano pan africano orogeny affecting the sao francisco craton basement and covers

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

frontal belt curvature and oblique ramp development at an obliquely collided irregular margin geometry and kinematics of the nw taiwan fold thrust belt 1 combined structural and tectonic analyses demonstrate that the nw foothills of the taiwan collision belt constitute mainly an asymmetric primary arc type fold thrust belt the arcuate belt developed as a basin controlled salient in the portion of the foreland basin that was initially thicker due to the presence of a precollisional depocenter the taihsi basin additional but limited buttress effects at end points related to interaction with foreland basement highs kuanyin and peikang highs may have also slightly enhanced curvature the complex structural pattern results from the interaction between low angle thrusting related to shallow decollement tectonics and oblique inversion of extensional structures of the margin on the southern edge of the kuanyin basement high the tectonic regimes and mechanisms revealed by the pattern of paleostress indicators such as striated outcrop scale faults are combined with the orientation and geometry of offshore and onshore regional faults in order to accurately define the quaternary kinematics of the propagating units the kinematics of this curved range is mainly controlled by distributed transpressional wrenching along the southern edge of the kuanyin high leading to the development of a regional scale oblique ramp the kuanyin transfer fault zone which is conjugate of the nw trending pakua transfer fault zone north of the peikang basement high the divergence between the n120 regional transport direction and the maximum compressive trend that evolved from n120 to n150 and even to n s in the northern part of the arc effectively supports distributed wrench deformation along its northern limb during the pleistocene the geometry and kinematics of the western taiwan foothills therefore appear to be highly influenced by both the preorogenic structural pattern of the irregularly shaped chinese passive margin and the obliquity of its plio quaternary collision with the philippine sea plate

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

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

how the structural architecture of the eurasian continental margin affects the structure seismicity and topography of the south central taiwan fold and thrust belt studies of mountain belts worldwide show that along strike changes are common in their foreland fold and thrust belts these are typically caused by processes related to fault reactivation and or fault focusing along changes in sedimentary sequences the study of active orogens like taiwan can also provide insights into how these processes influence transient features such as seismicity and topography in this paper we trace regional scale features from the eurasian continental margin in the taiwan strait into the south central taiwan fold and thrust belt we then present newly mapped surface geology p wave velocity maps and sections seismicity and topography data to test the hypothesis of whether or not these regional scale features of the margin are contributing to along strike changes in structural style and the distribution of seismicity and topography in this part of the taiwan fold and thrust belt these data show that the most important along strike change takes place at the eastward prolongation of the upper part of the margins necking zone where there is a causal link between fault reactivation involvement of basement in the thrusting concentration of seismicity and the formation of high topography on the area correlated with the necking zone the strike slip reactivation of east northeast striking extensional faults is causing sigmoidal offset of structures and topography along two main zones here basement is not involved in the thrusting there is weak focusing of seismicity and localized development of topography we also show that there are important differences in structure seismicity and topography between the margins shelf and its necking zone

a classification of thrust fronts variations in structural style at thrust fronts are examined to determine whether they represent different stages of typical thrust sheet development or unique events as orogenic stresses declined thrust fronts are classified as buried or emergent in which either the sole thrust died out in the subsurface or emerged to the synorogenic surface buried thrust fronts are subdivided into two types type 1 fronts end in broad zones of low strain type 2 fronts end in zones of high strain emergent thrust fronts may display significant horizontal displacement strongly emergent or limited displacements of about 1 km weakly emergent tip stick thrust fronts exhibit high strains and out of sequence thrusting different types of thrust fronts are linked by transitional tip li e anticlines and strike slip zones most thrust front types represent different stages of typical thrust sheet development but those in type 1 display atypical development unique to thrust fronts

origin of the west taiwan basin by orogenic loading and flexure of a rifted continental margin 1 seismic and well data suggest that the west taiwan basin developed by orogenic loading and flexure of a rift type continental margin the most likely source of the loading is taiwan where oblique convergence between the eurasian and philippine sea plates has produced an orogenic belt up to 300 km in length 100 km in width and 4 km in height flexure modeling shows that surface loading is unable to explain the depth of the west taiwan basin other subsurface or buried loads are required combined surface and buried loading explains the depth and width of the basin it also accounts for a bouguer gravity anomaly high and flanking low over the orogenic belt a lateral offset of 20 30 km between the peak topography and the maximum depth to the seismic moho and evidence for tectonic uplift in the penghu islands the depth of the base of the foreland sequence in the northern part of the west taiwan basin can be explained well by an elastic plate model with an effective elastic thickness te of 13 km while this value is low when compared to most other foreland basins it is within the range of values derived from rifted continental margins the northern part of the west taiwan basin unconformably overlies a passive margin sequence and therefore appears to have inherited the long term 1 myr flexural properties of the margin in the southern part of the basin however the depth to the base of the foreland sequence dips too steeply to be explained by elastic plate models this part of the basin therefore appears to be yielding rather than flexing differences in the flexural behavior along strike of the west taiwan foreland basin lithosphere are reflected in seismicity patterns west of the thrust front the northern part of the basin is associated with a low level of seismic activity while the south correlates with an abundance of earthquakes especially at shallow 25 km depths there is a cluster of earthquakes along two extensional faults that were active during rifting of the underlying margin therefore lithospheric flexure and fault reactivation may be important contributors to the seismicity of the taiwan region

evidence for deformation induced k feldspar replacement by myrmekite several examples of deformation induced myrmekite have been found in two amphibolite facies mylonites derived from granitic protoliths namely a muscovite poor s c mylonite and a single foliation muscovite poor mylonitic gneiss back scattered sem and conventional optical microscopy show that in both rock types syntectonic myrmekitic intergrowths of oligoclase and quartz formed on the two sides of k feldspar grains that faced the local inferred incremental shortening direction for the mylonite myrmekite does not occur on the two ends of the grain that faced the incremental stretching direction the replacement of k feldspar by plagioclase and quartz results in a volume decrease and is favoured on high normal stress sites around the grains we suggest that the ambient temperature pressure and chemical activities were such that the replacement reaction was favoured but the addition of extra strain energy along the high pressure sides of the grains localized the reaction at these sites this energy could arise from elastic strain or strain associated with tangled dislocations or twin boundaries the relative roles of stress and strain energy concentrations in driving the replacement reaction are not known but both were probably important

emplacement in an extensional setting of the mont lozere borne granitic complex se france inferred from comprehensive ams structural and gravity studies the emplacement mode and setting of the late hercynian mont lozere borne granitic complex french massif central which consists of several plutons is investigated structural and anisotropy of magnetic susceptibility ams studies have been carried out to characterize the internal fabrics of the granitic plutons throughout the pont de montvert borne pluton an e w trending magnetic lineation is well developed in the host rock and the thermal aureole a conspicuous e w trending lineation is interpreted as an evidence of a late orogenic extensional event to the east of the pluton the ams fabric is characterized by values of anisotropy degree p around 4 5 with a prolate ellipsoid and subsolidus structures whereas to the west the p parameter is weaker with an oblate ellipsoid and purely magmatic microstructures a gravity investigation allows determination of the 3d shape of the pluton the western part of the granitic complex is thicker than the eastern one and is interpreted as the feeder zone this suggests an eastward spreading of the magma the consistency between regional stretching and directions of ams lineations in the pluton and the shape of the complex deduced from gravity strongly argues that the emplacement mode of the complex was influenced by the regional extensional tectonic setting during the collapse of the hercynian belt

structural geodetic and seismological evidence for tectonic escape in sw taiwan abstract recent structural geodetic and seismological data in sw taiwan are analysed and discussed in terms of present day tectonic escape occurring in response to the active n100 collisional shortening the escaping area corresponds to the onland extension of the manila accretionary wedge this region comprises a rheologically weak thick muddy cover which is decoupled from the underlying basement by a decollement and which deforms mainly by aseismic creep it is separated from the northern actual collisional area by a major wnw to nw trending structural and kinematic transition zone oblique to the structural grain of the belt the chishan transfer fault zone geodetic data are further used to define several poorly deforming blocks undergoing nearly uniform displacement velocities and bounded by kinematic discontinuities that fit the major faults and to determine the present day across strike and along strike motions on these major faults although direct onland structural evidence of tectonic escape is poor reconstruction of quaternary paleostress patterns demonstrate that this escape probably began during the late pleistocene later than in northeastern taiwan as a result of the southward migration of the collision through time offshore structural data help to constrain the geometry and the southern extension of the escaping blocks finally a tentative model of lateral extrusion in sw taiwan is proposed

model for a passive to active continental margin transition implications for hydrocarbon exploration this paper proposes a model for the transition of a passive atlantic type continental margin to an active one with reverse polarity prior to its ultimate collision with an island arc or continent significant morphological and stratigraphic patterns which are believed to characterize this transition include 1 reactivation as reverse faults of preexisting listric normal faults not gulf coast type growth faults but those affecting basement as well that were established during the margin s most recent period of extension 2 landward migration with time of this fault rejuvenation 3 development of deeper water shallower water deeper water or deeper water unconformity deeper water stratal assemblages on the margin 4 regional flexure of the continental margin a in to that known for the outer rise area of oceanic plates landward of the subduction zone and 5 landward migration of major unconformities coeval with continental margin flexure this model creates implications for hydrocarbon exploration because 1 it predicts the presence or absence of unconformities and thus potential stratigraphic traps among units of a particular basin 2 provides spatial and temporal constraints for secondary porosity development in potential reservoirs 3 allows more accurate interpretations to be made of thermal or burial history diagrams constructed for the purpose of determining relative thermal maturities of potential source units and 4 helps distinguish between basement reactivation and decollement or gulf coast type growth faulting the orogenic phase of the margin s development however may later overprint or conceal these morphological and stratigraphic patterns to the extent that they might be unrecognizable because they have implications from both academic and economic perspectives the role of these patterns in the margin s evolution should not be overlooked

constraining the long term evolution of the slip rate for a major extensional fault system in the central aegean greece using thermochronology the brittle ductile transition is a major rheologic boundary in the crust yet little is known about how or if rates of tectonic processes are influenced by this boundary in this study we examine the slip history of the large scale naxos paros extensional fault system npefs cyclades greece by comparing published slip rates for the ductile crust with new thermochronological constraints on slip rates in the brittle regime based on apatite and zircon fission track aft and zft and u th he dating we observe variable slip rates across the brittle ductile transition on naxos zft and aft ages range from 11 8 0 8 to 9 7 0 8 ma and 11 2 1 6 to 8 2 1 2 ma and u th he zircon and apatite ages are between 10 4 0 4 to 9 2 0 3 ma and 10 7 1 0 to 8 9 0 6 ma respectively on paros zft and aft ages range from 13 1 1 4 ma to 11 1 1 0 ma and 12 7 2 8 ma to 10 5 2 0 ma while the u th he zircon ages are slightly younger between 8 3 0 4 ma and 9 8 0 3 ma all ages consistently decrease northwards in the direction of hanging wall transport most of our new thermochronological results and associated thermal modeling more strongly support the scenario of an identical fault dip and a constant or slightly accelerating slip rate of 6 8 km myr 1 on the npefs across the brittle ductile transition even the intrusion of a large granodiorite body into the narrowing fault zone at 12 ma on naxos does not seem to have affected the thermal structure of the area in a way that would significantly disturb the slip rate the data also show that the npefs accomplished a minimum total offset of 50 km between 16 and 8 ma

structural evolution from paleogene extension to latest miocene recent arc continent collision offshore taiwan comparison with on land geology marine structures observed in seismic profiles across the ne south china sea taiwan strait luzon arc region show that they are comparable to those observed onshore taiwan the hanjiang depression and dongsha uplift off the se china coast extend to the penghu basin and penghu platform respectively in the taiwan strait while the tainan basin in the south of penghu platform is connected to the chaoshan depression south of the dongsha uplift the hanjiang depression and the penghu basin are composed of paleogene syn rift sequences on the mesozoic basement and are uncomformably overlain by neogene post rift strata similar successions are found underneath the coastal plain or have been thrust up as a fold and thrust belt bordering the peikang basement high onshore central taiwan east of the manila trench off southwestern taiwan parts of the tainan basin are thrust into the submarine syn collision accretionary wedge the fold and thrust kaoping slope in the initial arc continent collision zone they have also been exposed in the fold and thrust western foothills south of the peikang basement high in southern taiwan during an advanced stage of arc continent collision since the late pliocene further east the pre collision accretionary wedge the hengchun ridge shoals northward to the hengchun peninsula with late miocene turbidites unconformably overlain by plio pleistocene shallow marine slope basin sequences in the arc domain cast of the arc prism boundary fault the western forearc sequences in the north luzon trough are deformed two normal faulted intra arc basins occur on the eastern part of the lanhsu island in the luzon arc the scenario of the deformed forearc sequences and the development of the two intraarc basins in the initial arc continent collision zone are analogous to the lichi melange taiyuan basin and the intra arc basins in the southern coastal range eastern taiwan additionally the lateral change in the marine structure from the passive asian continental margin to the manila subduction system is comparable to the temporal evolution from paleogene normal faulting through neogene subduction to latest miocene recent are continent collision observed onshore taiwan c 2001 elsevier science ltd all rights reserved

mechanisms of margin inversion in the external western alps implications for crustal rheology the kinematics of the collisional crustal wedge in the external western alps is discussed in the light of new cross sections of the whole external zone at the latitude of the belledonne grandes rousses oisans massifs external crystalline massifs ecm as well as a detailed analysis of the deformation of their basement and cover the cross sections were built from new field data and published geological maps and were restored through time oligo miocene times to unravel the successive stages of the dauphinois margin contractional deformation during oligocene times the variscan basement was deformed essentially by greenschist facies alpine distributed shear zones with no significant reactivation of the inherited jurassic normal faults or the variscan foliation however the inherited syn rift basins localized the deformation characterized by a thick skinned style and a cover disharmonically folded over basement shear zones with no major decollement in between shortening of 11 5 km 20 those early deformations progressively localized on the frontal crustal ramp and caused shortening in the folded belt 16 5 km of shortening 23 a similar sequence of deformation has been inferred in other alpine ecms this strongly suggests that the crust of dauphinois proximal passive margin was thin enough and its buoyancy low enough as a result of the liassic rifting to experience significant tectonic burial during the tertiary collision as a consequence of a weakening by both the presence of inherited basins and their weak syn rift sediments and the p t conditions greenschist facies the crust was shortened and the structural style was thick skinned

the structure and kinematics of the central taiwan mountain belt derived from geological and seismicity data 1 the structure of the taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment in recent years however a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment imbricate thrust belt model to address this issue we present new geological mapping together with earthquake focal mechanism and seismic energy release data from the central part of taiwan we concur with the interpretation that the foreland basin part of the western foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth to the east of the foreland basin however in the hsuehshan and central ranges our data show the presence of two fault systems an earlier inactive thrust system with a well developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more in the hsuehshan range the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal scale positive flower structure eastward in the central range mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first now inactive thrust system the involvement of deep crustal levels and mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin bounding faults that were located on the eurasian continental margin

mesozoic extensional tectonics in eastern asia the south liaodong peninsula metamorphic core complex ne china abstract in the north china block the south liaodong peninsula massif is an elliptical metamorphic core complex mcc with a long axis trending ne sw in cross section view it is asymmetric with a steeply dipping northwestern flank and a gently dipping southeastern flank it consists of three lithotectonic units a gneissic migmatite unit a paleo to meso proterozoic micaschist slate unit and a neoproterozoic to mesozoic sedimentary cover three deformation events related to extensional tectonics are distinguished in the study area d1 is a ductile deformation related to the exhumation of the mcc the following event d2 corresponds to the development of recumbent folds formed during the early exhumation of the mcc and the youngest event d3 corresponds to brittle normal faulting that controlled the opening of a cretaceous continental half graben basin a pre d1 event characterized as northward verging is interpreted as the result of n s shortening that occurred in the late triassic during the fin

development of tectonostratigraphy in distal part of foreland basin in southwestern taiwan abstract in the young and active tectonic belt of southwestern taiwan reconstructed stratigraphy in the distal part of the foreland basin reveals at least two regional unconformities with the younger ones covering the areas farther from the mountain belt in contrast with the previously proposed monotonous basin development the temporal spatial distribution of the unconformities indicates the back and forth migration of the foreland basin margin three distinct episodes of rapid subsidence during the foreland basin development have also been identified the onset of the basin development can be well constrained by the initial rapid subsidence at 4 4 4 2 ma which happened only in the proximal part of the basin this was followed by two younger episodes of rapid subsidence events at 2 1 8 ma and 0 45 ma which were encountered initially in the areas progressively farther from the orogenic belt we propose a model of episodic tectonic evolution in the distal part of the foreland basin in southwestern taiwan during each episode of rapid subsidence uplifting that corresponds to the forebulge began with a concurrent rapid subsidence in the areas closer to the basin center and was followed by rapid subsidence and deposition of widespread strata onlapping toward the basin margin part of the widespread strata and its overlying deposits would be eroded in the beginning of the next episode when the forebulge shifted toward the orogenic belt in general rate of forebulge migrating away from the orogenic belt during the early stage was slower than that derived from a previously proposed kinematic model of a steady migration of the orogenic belt this might be due to a rifted and weaker lithosphere beneath the foreland basin once the foreland basin migrated onto the less stretched lithosphere the basin would expand rapidly into the craton

the timing of partial melting barrovian metamorphism and granite intrusion in the naxos metamorphic core complex cyclades aegean sea greece abstract the relationship between partial melting and granite intrusion in a classic barrovian metamorphic terrane has been assessed thirteen samples were dated by shrimp u pb zircon geochronology from the island of naxos greece one of the aegean metamorphic core complexes the effect of partial melting during peak barrovian metamorphism on naxos is recorded by fine

magnetic fabric vs magnetite and biotite shape fabrics of the magnetite bearing granite pluton of gameleiras northeast brazil abstract a well defined orientation pattern has been evidenced by the magnetic fabric lineation and foliation of the granite pluton of gameleiras northeast brazil this magnetic fabric is roughly parallel to the magmatic fabric defined by the elongate mafic enclaves and by the planar arrangement of tabular k feldspar phenocrysts low field anisotropy of magnetic susceptibility properties as well as magnetic mineralogy studies and optical microscopy observations indicate that multidomian iron rich magnetite is the main carrier of the magnetic susceptibility and its anisotropy to examine in more detail the relationships between the magnetic and magmatic fabrics measurements of two dimensional shape fabrics of grain populations of biotite and magnetite have been carried out on a total of 500 grains using an automatic shape fabric analysis procedure on carefully selected and oriented thin sections angular departure has been calculated between the maximum elongation of the mineral shape fabric of the given grain population and the maximum susceptibility axis of the corresponding macroscopic specimen we found that the fabric of biotite correlates strongly with the magnetic fabric 7 8 the fabric of magnetite although not as well defined mainly because of its weak shape anisotropy still correlates with the magnetic fabric 12 18 origin of low field magnetic fabric in the pluton of gameleiras is concluded to be controlled principally by the statistical alignment of the long axes of inequant magnetite grains magnetic interactions between the grains of magnetite where they form clusters may account for the observed scattering or abnormal magnitudes of the magnetic anisotropy concerning the orientation of the magnetic fabric as the long dimensions of the magnetites preferentially align with the boundaries of the other minerals particularly biotite and titanite the magnetic fabric as defined by the grains of magnetite is concluded to approximate closely the magmatic fabric defined by the shape fabric of biotite however as no correlation exists between shapes or clustering of magnetites and strain undergone by the deforming magma the strength of the magnetic fabric in ferromagnetic granites cannot be used in a simple way as a measure of strain intensity

age and evolution of late mesozoic metamorphic core complexes in southern siberia and northern mongolia numerous cretaceous metamorphic core complexes mccs extend from transbaikalia in russia to northern mongolia within the central asian orogenic belt we investigated the buteel and zagan mccs in detail shear sense indicators in mylonitized rocks show footwall to the nw tectonic transport single zircon dating of footwall rocks in the buteel mcc establishes the emplacement of granitoid orthogneiss precursors at 240 211 ma a felsic metavolcanic rock at 265 0 1 2 ma a syenite at 265 5 1 2 ma and a metarhyolite of the pre granitoid basement at 553 6 2 9 ma a peralkaline granite intruding orthogneisses of the zagan mcc has a new u pb zircon age of 151 6 0 7 ma 40 ar 39 ar ages of 133 5 1 8 ma of hornblende from amphibolite and 122 6 1 8 ma of biotite from mylonitized gabbro dolerite of the buteel mcc are interpreted as cooling ages representing the time of deformation in the footwall geological data suggest that the mccs in transbaikalia and northern mongolia formed as a result of extension in a crust that had previously been thickened by abundant calc alkaline magmatism in an andean type setting on the border of the closing mongol okhotsk ocean by widespread collisional to post collisional thrusting and by extensive alkaline peralkaline magmatism

granite intrusion in a metamorphic core complex the example of the mykonos laccolith cyclades greece abstract the aegean domain is a well suited place to study the formation of metamorphic core complex mcc and to investigate the role of syn tectonic granites on their development in the northern cyclades the mykonos delos rhenia mcc is characterized by the intrusion of a kilometer scale late miocene pluton of i type granitoids within a migmatitic gneiss dome new combined ams anisotropy of magnetic susceptibility and microstructural studies on the mykonos granitoids together with recently published thermochronological data allow us to use the granitoids as strain markers the mykonos granitoids form a laccolith like intrusion with a n70 e long axis the laccolith is strongly asymmetric with an outlying root zone to the sw and a major body mainly developed to the ne the laccolith construction is due to successive pulses of more or less differentiated magma that intruded the cycladic blueschist unit the attitude of stretching markers suggests an important about 60 vertical axis local rotation phenomenon in the cycladic upper crust during the exhumation of the mykonos mcc structural data suggest a four stage evolution of the mykonos mcc i a first stage characterized by flat shearing toward the n ne and by the formation of a domal structure in migmatitic paragneisses with multi scale generation of folds with axes either perpendicular or parallel to the regional stretching as a result of the interplay between regional n20 e directed extension and ew shortening ii a second stage marked by the emplacement of the mykonos laccolith at 13 5 0 3 ma at the top of the migmatitic paragneisses iii the third stage corresponding to the development of protomylonitic foliations and lineations in the whole laccolith in high to medium temperature conditions and iv the late stage marked by an acceleration of the exhumation of the mykonos mcc this exhumation was accommodated by important rotations of upper crustal blocks during the end of the exhumation processes around 10 ma deformation localized at the top of the laccolith in semi ductile conditions and then in brittle conditions in the major detachment plane our study shows that the cycladic plutonism event had no role on the initiation of the mcc however the geometry of the mykonos intrusion supports that the magmas are sucked into the direction of regional extension and that the intrusion of magmas has caused an acceleration of the last stages of the mcc development this acceleration was marked by a very fast exhumation of the laccolith after its emplacement

pervasive melt migration from migmatites to leucogranite in the shuswap metamorphic core complex canada control of regional deformation abstract the shuswap metamorphic core complex exhumed in the hinterland of the canadian cordillera displays a 15 km structural section from migmatites to leucogranite it comprises a lower unit dominated by anatectic migmatites exposed in the core of domes at higher structural level the transition from a middle amphibolite facies unit to an upper crustal unit is marked by a low angle detachment associated with the emplacement of laccoliths of leucogranite the amphibolite facies middle unit is permeated by a network of granitic veins feeding the laccoliths and structurally connected to the migmatites of the lower unit this paper describes the geometric textural and structural characteristics and the distribution of the granitic fraction at the outcrop scale in the amphibolite facies unit separating the migmatites from the leucogranite this analysis constrains the mechanisms of melt migration within a plurikilometer scale section across high grade rocks of the middle crust in fertile lithologies metapelites felsic amphibolites the granitic fraction in part generated in situ forms a diffuse network of concordant veins feeding discordant veins and structural sites such as the foliation shear zones and boudin necks discordant granitic veins are oriented perpendicular and to a lesser extent parallel to the mineral and stretching lineation in refractory lithologies the granitic fraction is dominantly intrusive and displays sharp contacts with the host rock however distribution of the granitic fraction shows the same characteristics as for fertile lithologies the melt fraction migrated through a network of fractures taking advantage of mechanical weaknesses such as the foliation plane or forming dikes oriented dominantly perpendicular to the regional stretching and mineral lineations these geometric and textural characteristics suggest that granite migration in these rocks is achieved dominantly by viscous flow of the melt solid through the solid matrix driven by its buoyancy and controlled by mechanical anisotropy of the rock and local dilation created by heterogeneous deformation the relationship between the regional fabric and the distribution of the granitic fraction indicates that regional deformation incremental and finite played a major role in providing pathways for melt migration the formation of laccoliths of leucogranite at higher structural levels suggests that upward melt migration led to accumulation of granitic magmas these observations are consistent with a model of pervasive melt migration through a network of interconnected concordant and discordant granitic veins feeding laccolithic plutons extracted from the dominantly solid matrix during vertical thinning and compaction at a regional scale the presence of both transposed and intact granitic networks indicate an overlap between deformation and granite migration as a continuum or in pulses the methodology and terminology proposed in this paper provide some insights on the behavior of the granitic fraction in the middle crust this approach should be applicable to other high grade terrains exhumed in the cores of orogenic belts

a midcrustal ramp fault structure beneath the taiwan tectonic wedge illuminated by the 2013 nantou earthquake series 1 taiwan s active mountain belt is a spotlight for orogenic studies and was first used to test the critical taper wedge mechanics the concept of an orogenic wedge above a shallow detachment surface has been highly influential on current understanding of orogenic processes in taiwan however the recent ml 6 2 and ml 6 5 2013 nantou reverse faulting earthquakes in central taiwan have nucleated below the proposed detachment indicating that active mountain building is occurring below the orogenic wedge we estimate the coseismic slip distributions and fault geometry using the uniform stress drop slip inversions the earthquakes occur on essentially the same 30 dipping fault plane ramping up from 20km depth near a cluster of 1999 chi chi earthquake aftershocks to the shallow detachment and the chi chi fault plane the fault could be a deep extension of a mature shallow fault or a newly developed deep ramp fault that is not reflected in the surface geology

palaeomagnetic constraints from granodioritic plutons jiaodong peninsula new insights on late mesozoic continental extension in eastern asia mechanism and kinematics of the late mesozoic continental extension event of eastern asia are still debated in order to better constrain its evolution two granodioritic plutons of the jiaodong peninsula have been chosen as targets for a time constrained palaeomagnetic study indeed plutons are devoid of visible deformation did not experience rotation along horizontal axis and are precisely dated by u pb and 40ar 39ar methods multidomain md magnetite has been identified as the principal magnetic remanent carrier the interpolation of existing and new u pb and 40ar 39ar ages revealed that characteristic remanent magnetisation was acquired in a narrow range of 116 2 ma twenty out of 27 sites present stable magnetic directions calculated from high temperature or high coercive components the observations of the solo normal magnetic polarity for this palaeomagnetic collection and of the magnetic remanent age consistent with the cretaceous normal superchron cns argue that the characteristic magnetic remanence may be considered as primary detailed field observations of the intrusive relationship between the plutons and country rocks and anisotropy of magnetic susceptibility ams study reveal the absence of the subsequent deformation of plutons or rigid rotation of plutons along a horizontal axis two palaeomagnetic poles have been therefore calculated from these plutons among 12 out 15 cretaceous palaeomagnetic poles including the two new poles provided by this study from the jiaodong peninsula and on both sides of tan lu and muping jimo faults are statistically consistent as a result the jiaodong peninsula behaved as a rigid block as internal deformation appears negligible the remaining three derived poles are probably due to the secular variation or and the vicinity of fault zones near of the palaeomagnetic sampling site thus they can not be applied to the peninsula scaled tectonics comparison of these time52 constrained cretaceous palaeomagnetic results of the jiaodong peninsula with those of north china block ncb indicate that the jiaodong peninsula was rigidly attached to ncb since 3 at least the cretaceous as residual difference is clearly insignificant with respect to the error brackets these new palaeomagnetic results confirm that the relative clockwise cw rotation of eastern liaoning korea block elkb with respect to ncb does not affect the jiaodong peninsula as a rigid block nevertheless some tectonic structures have been reactivated since cenozoic and local rotations could be produced this palaeomagnetic study reveals that the late mesozoic extension in eastern asia is heterogeneously expressed in time and space the complete understanding of the mechanism s of this extensional event needs further multidisciplinary investigations

metamorphic core complex dynamics and structural development field evidences from the liaodong peninsula china east asia metamorphic core complexes mcc constitute remarkable features within wide rifts based on analogue and numerical modelling mcc dynamics and structural development are mainly controlled by first geothermal gradient second the compositional layering and after the strain rate and partial melting in the late mesozoic continental extension occurred in east asia leading to the development of mcc magmatism and extensional sedimentary basins based on an integrated study i e structural and finite strain analysis petrofabrics anisotropy of magnetic susceptibility ams and u pb on zircon dating this paper aims at constraining the tectonic evolution and deformation mechanisms in the south liaodong peninsula ne china the gudaoling massif is identified as a migmatitic mcc developed from upper jurassic ca 157 154 ma to early cretaceous ca 128 113 ma intrusion of the yinmawanshan synkinematic pluton early cretaceous to the south of the dome marks out the final stages of shearing along the gudaoling detachment zone and of exhumation of the mcc into the upper crust the gudaoling mcc and the yinmawanshan pluton stay in line with the coeval south liaodong mcc to the south all making a 140x30km wide extensional band formed during a regional e w to nw se crustal stretching the area shows a bi phased development with a slow and a fast stage which correspond to 1 crustal necking and 2 dome amplification exhumation stages according to published thermo mechanical modelling results finally the gudaoling mcc lower unit almost exclusively displays migmatites and anatectic granitoids of late jurassic and early cretaceous respectively occurrence of partial melting during earlier stages of extension seems controlling the initiation of mcc as a soft anomaly within lower crust in east asia a regional scale thermal event during jurassic cretaceous times may have significantly reduced the bulk lithosphere strength and locally induced partial melting emphasizing pervasive deformations and development of a wide rift system

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

structural complexities in a foreland thrust belt inherited from the shelf slope transition insights from the alishan area of taiwan the alishan area of taiwan spans the transition from the platform with full thickness of the eurasian continental margin in the north to the thinning crust of its slope in the south this part of the foreland thrust and fold belt includes important along strike changes in structure stratigraphy and seismic velocities in this paper we present the results of new geological mapping from which we build geological cross sections both across and along the regional structural trend fault contour stratigraphic cutoff and branch line maps provide 3 d consistency between the cross sections minimum shortening is estimated to be 15 km with displacement overall to the northwest a p wave velocity model helps constrain the structure at depth by providing insight into the possible rock units that are present there p wave velocities of 5 2 km s point toward the presence of basement rocks in the shallow subsurface throughout much of the southeastern part of the area forming a basement culmination the changes in strike of thrusts and fold axial traces the changing elevation of thrusts and stratigraphic contacts and the growing importance of middle miocene sediments that take place from north to south are interpreted to be associated with a roughly northeast striking lateral structure coincident with the northern flank of this basement culmination these transverse structures appear to be associated with the inversion of eocene and miocene age extensional faults along what was the shelf slope transition in the early oligocene uplifting the margin sediments and their higher p wave velocity basement during pliocene pleistocene thrusting

dynamics and structural development of metamorphic core complexes the development of metamorphic core complexes mccs in a thickened continental lithosphere is studied using fully coupled thermomechanical numerical code accounting for elastic brittle ductile properties of constituent rocks for mccs to develop the middle lower crust and the sub moho mantle are required to be weak enough to flow laterally so as to simultaneously feed the exhuming dome and enable the moho to keep a flat geometry the conditions are satisfied with initial moho temperatures of 800 c or higher with crustal thicknesses of 45 km or greater and with initial effective viscosities lower than 1020 pa s and 1022 pa s in the lower crust and the underlying mantle respectively a compositional mainly density anomaly with the properties of granite is placed centrally in the crust to localize strain at the onset of deformation during a first stage of upper crust necking the deformation pattern is relatively symmetrical and dominated by graben formation in the upper crust when the first ductile layers reach the surface a second stage of dome amplification and widening occurs dome amplification is accommodated by horizontal flow in the ductile crust giving an early symmetrical pattern of conjugate shear zones with no obvious detachment zone the system then rapidly becomes asymmetric with the localization of a detachment zone along one dome limb further accommodating dome widening thus the exhumation process of a metamorphic dome results in the progressive development of a detachment zone depending on initial moho temperature the detachment zone can migrate in space or die out and be replaced by a new one with an opposite dip

introduction tectonic evolution and mechanics of basement involved fold and thrust belts defining the structural style of fold and thrust belts is an important step for understanding the factors that control their long and short term dynamics for comprehending seismic hazard associated with them and for assessing their economic potential while the thin skinned model no basement involvement has long been the driving methodology for cross section construction and restoration of foreland fold and thrust belts a wealth of new geological and geophysical studies have shown that they are often thick skinned that is basement involved

gravity inversion ams and geochronological investigations of syntectonic granitic plutons in the southern part of the variscan french massif central magnetic fabric analyses gravity inversion associated with chemical u th pb dating and structural observations are carried out to elucidate relationships between faulting and magmatic processes this multidisciplinary study has been undertaken on late carboniferous plutons situated in the southern part of the variscan french massif central fmc the glenat omps and boisset plutons crop out on both sides of the crustal scale sillon houiller fault shf the anisotropy of magnetic susceptibility ams measurements and structural observations show that i the plutons acquired their final structure during the magma crystallization and record a nw se maximum stretching trend ii in the boisset pluton post magmatic fabrics predominate with a nnw sse trending lineation the structural pattern deduced from the ams study is thus consistent with the nw se late orogenic extensional tectonic regime that has been documented in other parts of the fmc during late carboniferous the 3d geological modelling refined by 3d gravity inversion does not show any evidence of rooting of the granites along the shf therefore despite the apparent cartographic relationship between the shf and the three plutons our study does not support a genetic link between fault and plutons it also questions the existence of the shf in this part of the massif central at the time of pluton emplacement and emphasises the dominant role of the regional tectonic framework rather than local faulting as a factor controlling pluton emplacement

blind thrust systems blind faults are documented from 20 thrust systems throughout the world they occur as single faults sets of faults or entire thrust systems the overlying cover responds to the formation of the blind system by backthrusting coupling forethrusting and deposition the relative importance of the first three responses for pretectonic cover is represented in a ternary backthrusting coupling forethrusting diagram pretectonic cover of blind systems deforms by either a combination of coupling and forethrusting or a combination of backthrusting and coupling

the montagne noire migmatitic dome emplacement french massif central new insights from petrofabric and ams studies in the southern french massif central the montagne noire axial zone is a ne sw elongated granite migmatite dome emplaced within visean south verging recumbent folds and intruded by syn to late migmatization granitoids the tectonic setting of this dome is still disputed thus several models have been proposed in order to better understand the emplacement mechanism of this dome petrofabric and anisotropy of magnetic susceptibility ams studies have been carried out in the granites and migmatites that form the dome core magmatic texture and to a lesser extent weak solid state texture are dominant as a paramagnetic mineral biotite is the main carrier of the magnetic susceptibility on the basis of 135 ams sites the magnetic fabrics appear as independent of the lithology but related to the dome architecture coupling our results with previous structural and geochronological studies allows us to propose a new emplacement model between 340 325 ma the palaeozoic series underwent a compressional deformation represented by nappes and recumbent folds involving the thermal event leading to partial melting until 325 310 ma the dome emplacement was assisted by diapiric processes an extensional event took place at 300 ma after the emplacement of the late to post migmatitic granitic plutons in the northeast side of the dome a brittle normal dextral faulting controlled the opening of the graissessac coal basin

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

geodynamic scenario and structural styles of mesozoic and cenozoic basins in china the continental lithosphere of china is situated at the junction of the marginal pacific and tethys himalayan tectonic domains the most manifest tectonic movements responsible for the deformation of the continental lithosphere of china are taphrogenic collisional and shearing these movements played an important role in the mesozoic and cenozoic tectonic evolution of china and formed various types of mesozoic and cenozoic basins in china the marginal pacific crust in eastern china was attenuated by rifting and developed north northeast trending mesozoic and cenozoic basins e g the songliao bohai bay and jianghan basins rifting mainly followed preexisting lineaments or shear zones in the basement then basin range graben horst structures and large fault bounded basins developed extensional structural styles have prevailed in mesozoic and cenozoic basins in eastern china with listric faults and tilted blocks in the basement and detached faults growth faults and rollover anticlines or drape folds in the cover rocks these structures are favorable for hydrocarbon accumulation thus the famous daqing and zhongyuan oil fields formed in songliao basin and bohai bay basin respectively in western china the continental crust thickened by collision and formed a series of mesozoic and cenozoic intermontane and foreland basins such as the junggar dzungaria tarim and qaidam basins contraction structural styles are predominant in mesozoic and cenozoic basins in western china with shortened fault blocks and ramps in basement and thrust faults and folds in the cover rocks the kelamayi and laojunmiao oil fields formed in these compressional basins in addition many great wrench faults played an important role in the evolution of china such as the tan lu fault in eastern china and the altunshan and talaso fergana faults in western china many mesozoic and cenozoic basins of china were characterized by transtension and transpression the mesozoic and cenozoic basins of china have undergone numerous tectonic events the extensional structures have been changed into contractional structures or conversely thus tectonic inversion occurred in successive events and different structural styles may be found in different tectonic levels of these basins these superposed deformations and structures have complicated petroleum exploration but they also enlarge prospective exploration targets and potential hydrocarbon reserves in china

the structure of mountain fronts commonly the part of a mountain front which is visible at the surface consists of foreland dipping thrust belt rocks elevated above their regional structural position and overlain more or less conformably by molasse several explanations for their geometry are possible 1 major detachments exist within or beneath the molasse resulting in transport of the foreland basin examples of this geometry come from the swiss molasse plain the southern pyrenees and the mackenzie mountains of canada 2 displacement is lost on major backthrusts beneath the frontal monocline examples cited here are the rockies of alberta the sulaiman ranges of pakistan the mackenzies and the andes in peru 3 thrust sheets travelled over an old land surface and syntectonic molasse contemporaneously offlaps the topographic high of the thrust front this phenomenon occurs along the alpine thrust front in haute provence 4 the frontal fold represents deformation above a large scale thrust tip no unequivocal example of tip line strain at this scale has been recorded although this type of deformation may occur in the brooks range of alaska in many areas mountain fronts show a combination of these idealized geometries

from submarine continental accretion to arc continent orogenic evolution the thermal record in southern taiwan constraining the timing of initial collision is critical for understanding how long term plate convergence is accommodated at collisional plate boundaries reevaluation of the age of collision from orogenic thermal evolution requires distinguishing the onset of submarine continental accretion from earlier oceanic subduction and subsequent subaerial orogenic evolution we present new thermochronological constraints from the first age elevation relationship transect in taiwan and zircon and apatite fission track ages from sediments in the western foreland our data reveal the onset of cooling from at least 7 1 1 3 ma at a minimum rate of 21 c m y in the submarine sedimentary wedge followed by a marked acceleration of subaerial exhumation after ca 3 2 0 6 ma at an average rate of 1 7 km m y our data reflect the effect of margin architecture as taiwan evolved from submarine accretion of the distal extremely thinned continental margin to crustal thickening of the proximal margin and orogenic development

structural inheritance in mountain belts an alpine apennine perspective abstract the geological structure of continental lithosphere shows complex variety that is inherited into orogenic belts and influences the localization and amplification of contractional structures during mountain building in the alpine apennine sector together with other sectors of the tethyan orogenic system the pre orogenic crustal template can include arrays of extensional faults other faults can form adjacent to the evolving mountain belt and subsequently become incorporated as the thrust belts migrate into their forelands while in some areas these inherited features may simply reactivate under inversion more commonly faults show complex partial reactivation structures in volumes of distributed strain faults may serve to nucleate large scale buckle folds for example along basement cover interfaces these different patterns of basement reactivation may reflect spatially varying strength depth profiles in continental lithosphere that are themselves inherited from spatially distinct geological histories even when not themselves reactivating basement faults can control deformation in the overlying sedimentary cover by offsetting otherwise regionally extensive detachment horizons the 3d form of thrust systems can be strongly compartmentalized by pre existing cross faults such as the oblique lineaments of the apennines on a large scale the distribution of pre existing faults and other weaknesses may affect the propensity for orogenic contraction in basement and therefore directly control larger scale tectonic processes in the central mediterranean the evolution of slab roll back and the related growth of overlying extensional basins e g tyrrhenian sea may be strongly modulated by the distribution of rift related weak zones in the adjacent continental crust the subduction of continental crust will strongly depend on the inherited structure of this crust specifically the distribution of deep crust of basic composition this develops relatively higher densities associated with eclogite metamorphism which act in turn to reduce the buoyancy of thickened continental crust that otherwise serves to inhibit further shortening investigating all these aspects from the scale of bulk crustal compositions to the geometry timing and strength of earlier fault zones preserved in orogenic belts requires the integration of substantial multidisciplinary geological data sets the extent to which continental orogenic belts represent the amplification of inherited geological heterogeneities as opposed to self ordered phenomena modulated by the syntectonic environment remains unclear

metamorphic core complexes vs synkinematic plutons in continental extension setting insights from key structures shandong province eastern china abstract continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust though a metamorphic core complex mcc reveals a much stronger crustal extension than a synkinematic pluton the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations in eastern asia a major continental extensional event occurred during mesozoic and early cenozoic times the resulting various extensional events described in previous studies consist in large intracontinental basins important volcanism emplacement of plutons in the upper crust and exhumation of mccs an efficient description of mccs and plutons in eastern asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations in that way an integrated structural and geophysical study has been realized to precisely discriminate the structure in the jiaodong peninsula shandong province eastern china previously regarded as simple sheared plutons a succession of three main stages have been identified all pertaining to a nw se extensional setting 1 the exhumation of the late jurassic early cretaceous linglong mcc below the se dipping linglong detachment fault 2 the emplacement of the guojialing syntectonic pluton below the n dipping extensional guojialing intracrustal shear zone 130 124 ma and 3 a penetrative brittle normal faulting associated with gold mineralizations 120 ma as a result the maximum amount of extension in jiaodong peninsula characterized by partially melted lower to middle crust upward into the linglong mcc should be revised to late jurassic early cretaceous period

petrogenesis of late triassic granitoids and their enclaves with implications for post collisional lithospheric thinning of the liaodong peninsula north china craton abstract major and trace element sr nd and hf isotope zircon u pb and hf isotope data are reported for mafic microgranular enclaves and host granitoids from the xiuyan pluton in the liaodong peninsula of the eastern north china craton in order to investigate their sources petrogenesis and tectonic implications the zircon u pb age of the enclaves 211 1 ma is identical to that of the host granite 210 1 ma establishing that the mafic and felsic magmas were coeval the enclaves have high mgo concentrations at low silica contents and positive ehf t values they are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements which can be explained as melts derived from a depleted asthenospheric mantle with some crustal contamination the host granitoids have high sio2 contents variable initial 87sr 86sr ratios and highly negative end t and ehf t values suggesting they were mainly derived from an ancient crustal source heated by the input of asthenospheric mantle derived magmas field observations geochronology geochemistry sr and nd isotopic and zircon hf isotopic compositions point to a complex petrogenesis where asthenospheric mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between enclaves and host rocks identification of an asthenospheric mantle component in the xiuyan granitoids suggests asthenospheric mantle upwelling and decompressional melting of the mantle indicating that post collisional lithospheric thinning in the liaodong peninsula was initiated in the late triassic

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

emplacement of an archean gneiss dome northern ontario canada inflation inferred from magnetic fabrics 1 previous field structural studies of the ash bay gneiss dome revealed an upward convex foliation with an integral east west lineation defined by a quartzo felspathic matrix unfortunately the amphibolite facies gneisses lack traditional indicators of microfabric evolution such as kinematic indicators so that it is difficult to relate the foliation s orientation distribution to an emplacement mechanism for the dome fortunately anisotropy of magnetic susceptibility isolates a distinct microfabric because of the preferred orientation of high susceptibility accessory magnetite the magnetite subfabric developed late in the metamorphic crystallization history and its magnetic foliation and magnetic lineation are similarly oriented to the s l fabric of the quartz feldspar matrix however the magnetite foliation dips less steeply and forms a less convex domal surface than the field schistosity the metamorphic schistosity and the magnetite foliation thus isolate the domal deflection at different stages confirming the inflation and upward motion of the ash bay diapir during the closing stages of amphibolite facies metamorphism

the role of a hidden fault in stress triggering stress interactions within the 1935 mw 7 1 hsinchu taichung earthquake sequence in central taiwan abstract hidden faults often lead to misestimation of earthquake hazard in western taiwan where many blind faults are located how the stress interactions correlate with potentially significant earthquakes and what is the role of blind faults in earthquake triggering are the important questions for earthquake hazard assessment given sequential rupture of active faults with an unexposed fault segment involved the 1935 mw 7 1 hsinchu taichung earthquake sequence in central taiwan provides an exceptional case to study this destructive earthquake sequence took 3000 lives and was composed of four m 6 earthquakes occurred within three months the mw 7 1 mainshock and a subsequent mw 6 8 event that occurred 12 s later caused surface ruptures on the tuntzuchiao fault ttcf and shihtan fault stf which are separated by 25 km these two ruptures were characterized by different types of faulting thrust faulting on the stf and right lateral faulting on the ttcf fault about 24 min later an mw 6 0 event occurred 45 km north of the mainshock three months later on july 17 the last event mw 6 2 occurred 30 km northwest of the mainshock in this study we revisit the data available for the 1935 sequence in an effort to place constraints on the fault models using five different fault models a series of coulomb stress calculations are conducted to understand whether static stress transfer advances slip during the subsequent events we propose that key features of the 1935 hsinchu taichung earthquake triggering can be explained by the existence of an unexposed fault segment in between the segments of ttcf and stf we also show that the 1935 earthquake sequence may play an important role in activating post 1935 earthquake activity along the sanyi puli seismic zone where the sequential ruptures of the 1935 events encourage ruptures of a nw se trending seismic zone at later times

distinct lateral variation of lithospheric thickness in the northeastern north china craton abstract a detailed knowledge of the thickness of the lithosphere in the northeastern north china craton ncc is important for understanding the significant tectonic reactivation of the craton in the mesozoic and cenozoic time we achieve this goal by applying the newly proposed wave equation based migration technique to the s receiver functions recently collected in the region distinct negative signals are identified below the moho in all the s receiver function migrated images and stacks which we interpret as representing the s to p conversions from the lithosphere asthenosphere boundary lab the imaged lab is as shallow as 60 70 km in the southeast basin and coastal areas and deepens to no more than 140 km in the northwest mountain ranges and continental interior these observations indicate widespread lithospheric thinning in the study region in comparison with the 180 km lithospheric thicknesses typical of most cratonic regions the revealed topography of the lab generally agrees with the lateral variation in upper mantle seismic anisotropy previously measured through sks splitting analysis in particular a sharp lab step of 40 km is detected at the triple junction of the basin and mountains at almost the same place where an abrupt change from nw se to ne sw in fast polarization direction of shear waves was found these findings suggest a close correlation between the seismic anisotropy and hence deformation of the upper mantle the lithospheric thickness and the surface tectonics of the northeastern ncc while the thinned lithosphere and the nw se fast shear wave polarizations in the east areas probably are related to the dominant nw se tectonic extension in the late mesozoic cenozoic time the thicker lithosphere and the ne sw fast polarization direction in the west mountain ranges may reflect earlier contractional deformations of the region synthetic tests indicate that the lab beneath the northeastern ncc is a well defined zone 10 20 km thick combined with seismic tomography results and geochemical and petrological data this suggests that complex modification of the lithosphere probably accompanied significant lithospheric thinning during the tectonic reactivation of the old craton

thrust related diapiric and extensional doming in a frontal orogenic wedge example of the montagne noire southern french hercynian belt abstract the montagne noire which is situated at the toe of the orogenic wedge of the french massif central south european variscides appears to be a well suited area for studying the origin and evolution of middle to upper crustal domes adjacent to foreland basins the data reported in the present paper show that the montagne noire dome is a particular type of basement involved frontal culmination in an orogenic wedge and foreland basin system this frontal culmination is characterized by a syn contractional ht decompression recorded by clockwise ptt paths and widespread strata overturning in thrust and fold structures which controlled the sedimentation in the adjacent foreland basin these unusual characteristics are interpreted to be a result of the succession of thrusting diapirism and extensional collapse antiformal stacking of syn metamorphic thrust sheets controlled the first stages of the foreland basin development diapirism was essentially responsible for the ht decompression and widespread strata overturning extensional doming was a result of late to post metamorphic collapse acting on the pre existing high amplitude dome diapirism and associated isothermal decompression metamorphism which constitute the essential difference between the montagne noire and ordinary frontal ridges in orogenic wedges were probably enhanced by a local partial melting of the upper to middle crust it is suggested that the occurrence of these phenomena in front of an orogenic wedge was related to local over thickening due to the superposition of an upper crustal antiformal stack on top of a lower crustal ramp anticline

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

deformation history of the southwestern taiwan foreland thrust belt insights from tectono sedimentary analyses and balanced cross sections abstract analysis of the basin scale and local deformation history and estimates of shortening rates are performed in the southwestern foreland thrust belt of the plio pleistocene taiwan orogen timing of deformational events is constrained using both syntectonic unconformities and other markers of syndepositional tectonic activity three cross sections are investigated and balanced intermediate shortening rates are estimated based on balanced and restored cross sections the total amount of shortening along studied balanced sections results from superimposed thin skinned and thick skinned styles a shallow aseismic thick decollement is located to depth of 6 8 km at the base of thick late miocene shales that behaves as ductile layer the occurrence of a deep seismic decollement to depth of 12 15 km is confirmed by seismicity fault plane solutions of focal mechanisms and a seismic reflection profile providing evidence of reactivated and inverted inherited extensional features beneath the coastal plain three major tectonic stages are recognized within the southwestern foothills which are correlated with local thrusting events the first stage begins at 5 ma with the onset of the taiwan collision and ends at 2 1 6 ma it reflects an initial submarine accretionary stage associated with moderate tectonic activity the second major stage occurs during late pliocene early pleistocene this intermediate collision stage sealed the evolution of the southern foreland thrust wedge from submarine to continental environment in relation with exhumation and denudation of the central range the last stage of deformation begins in the middle pleistocene and continues until present it is associated with high rates of sedimentation and most of the thrusts are activated or reactivated at that time and out of sequence thrusting occurs the collision started synchronously near 5 ma throughout the southwestern taiwan total and intermediate shortening rates are more or less constant through time in studied sections that may suggest that long term deformation in the taiwan foreland thrust belt occurred more or less at steady state since 5 ma the southward decrease of rates of shortening from 3 6 to 4 8 mm year in northern sections to 2 2 mm year in southern section might be related to both influence of indentation by the peikang high to the north and southward transition at the scale of the southwestern foothills from collision to subduction setting the effect of the obliquity of the convergence resulting in regional southward migration of the collision cannot be definitely inferred from this analysis our results place new kinematic and time constraints which must be taken into account in forthcoming geodynamic models of the taiwan collision

modelling of structural complexity in sedimentary basins the role of pre existing faults in thrust tectonics abstract analogue and numerical models have been used to study the role of pre existing faults in compressive regimes from a theoretical point of view reactivation is mainly controlled by fault attitude stress regime and frictional properties of fault planes in scaled down sandbox experiments precut faults are introduced in the homogeneous granular media with a nylon wire which is forced through the sand cake producing a thin planar disturbed zone systematic experiments of thrust inversion with various dips and strikes of such planar discontinuities have been modelled comparison of experimental results with theoretical diagrams indicate that disturbed zones have a friction angle which is 10 20 lower than the homogeneous sand and that the compressive regime in the sandbox has a shape factor close to 0 4 the static analysis of fault reactivation is in accordance with the experimental observations except for pre existing faults dipping at very low angle however numerical modelling using the udec code shows that low angle faults can be reactivated as a result of stress concentration in the lower part of the fault in addition sandbox experiments indicate that in thrust systems reactivation of pre existing faults is not only dependent on their attitude but also on their spacing and location relative to the thrust system

the influence of inherited continental margin structures on the stress and strain fields of the south central taiwan fold and thrust belt in this paper we test whether or not structural and morphological features inherited from the eurasian continental margin are affecting the contemporary stress and strain fields in south central ta

seismotectonic characteristics of the taiwan collision manila subduction transition the effect of pre existing structures abstract based on the distribution of an earthquake swarm determined from an ocean bottom seismometer obs network deployed from 20 august to 5 september 2015 in the northernmost part of the south china sea scs and data from inland seismic stations in taiwan we resolved a ml 4 1 earthquake occurring on 1 september 2015 as a ne sw trending left lateral strike slip event that ruptured along the pre existing normal faults generated during the scs opening phases the direction of the t axes derived from the ml 4 1 earthquake and the background seismicity off sw taiwan present high consistency indicating a stable dominant nw se tensional stress for the subducted eurasian plate eup the distinct stress variations on the two sides of these reactivated ne sw trending features suggest that the presence of pre existing normal faults and other related processes may lessen the lateral resistance between the taiwan collision and manila subduction system and facilitate the slab pull process for the subducting portion which may explain the nw se tensional stress environment near the transition boundary in the northernmost part of the scs

flow of partially molten crust and the internal dynamics of a migmatite dome naxos greece 1 migmatite domes are common in metamorphic core complexes dome migmatites deform in the partially molten or magmatic state and commonly record complex form surfaces folds and fabrics while units mantling the dome display a simpler geometry typically formed by transposition during crustal extension we use field observations and magnetic fabrics in the naxos dome greece to quantify the complex flow of anatectic crust beneath an extensional detachment system the internal structure of the naxos dome is characterized by second order domes subdomes pinched synforms and curved lineation trajectories which suggest that buoyancy driven flow participated in dome evolution subdomes broadly occur within two compartments that are separated by a steep n s oriented high strain zone this pattern has been recognized in domes formed by polydiapirism and in models of isostasy dominated flow the preferred model involves a combination of buoyancy and isostasy driven processes the naxos dome may have been generated by regional n s extension that triggered convergent flow of partially molten crust at depth and the upwelling of anatectic migmatites within the dome this pattern is complicated by gravitational instabilities and or overturning of the high melt fraction crust leading to the growth of subdomes as the migmatites within the naxos dome reached a higher structural level they were affected by regional top to the nne kinematics of the detachment system dome formation therefore occurred by a combination of coeval and coupled processes upper crustal extension deep crust contraction during convergent flow of anatectic crust diapirism and or density driven crustal convection forming subdomes and north directed detachment kinematics

controls on the geometry of fold thrust belt salients salients convex to the foreland curves in the map traces of orogens typically involve fold thrust belts formed along the foreland margin of orogens an examination of the map view shape degree of asymmetry dimensions and structural trend line patterns i e the variation in fold trend and fault strike along the length of the belt of 20 fold thrust belt salients worldwide illustrates relationships between salient geometry and the geologic setting in which the salient formed in order to understand these relationships we used simple sandbox models to simulate the formation of three of the several types of salients specifically we examined indenter controlled salients the geometry of which reflects interaction of a fold thrust belt with a hinterland indenter basin controlled salients the geometry of which reflects lateral variations in the thickness of predeformational basin fill and detachment controlled salients the geometry of which reflects lateral variations in the strength of a detachment surface our models demonstrate that thrusts in these three types of salients initiate with a curved shape and that rocks within thrust sheets on the limbs of salients can undergo a vertical axis rotation in response to simple shear without requiring major rotation of the fault trace furthermore trend line patterns distinguish basin controlled from indenter controlled salients specifically structural trend lines in basin controlled salients converge at the end points of the curve while in indenter controlled salients they diverge at the end points of the curve the asymmetry of a salient correlates with the asymmetry of the predeformational basin and or of the indenter and with the convergence direction thus our results explain geometric characteristics of individual salients and address controversies concerning paleomagnetic data in salients they also may help prioritize petroleum exploration targets in salients foreland basin oil fields concentrate at the apex of basin controlled salients because the geologic factors that generate the salient also contribute to localizing oil fields

postseismic rebound due to creep of the lower lithosphere and asthenosphere postseismic surface deformations are attributed to the inelastic flow of the subcrustal regions of the earth following an earthquake a multilayer representation of the earth s rheological properties is used in conjunction with a finite element computational scheme to calculate time dependent displacements and strains subsequent to a strike slip earthquake the deviatoric stress strain relation for the uppermost layer is assumed elastic lower layers are assumed to be in order of increasing depth a standard linear three element viscoelastic solid a linear viscoelastic fluid and another elastic solid physically these layers correspond to the upper lithosphere lower lithosphere asthenosphere and lower mantle respectively elastic dilatational properties are assumed throughout appreciable postseismic displacements possibly approaching meters for large earthquakes arise from the viscoelastic relaxation following the sudden coseismic slip furthermore compared to the simpler case of an elastic lithosphere over a viscoelastic asthenosphere the near fault postseismic shear strain is increased by a factor of two or more in some cases by the presence of a viscoelastic lower lithosphere also the duration of postseismic straining is increased if the viscosity of the lower lithosphere is greater than that of the underlying asthenosphere

metamorphic core complexes of cordilleran type in the cyclades aegean sea greece the islands of ios and naxos in the cycladic archipelago greece contain elongate domes over which a pervasive north to north northeast stretching lineation is warped these islands may be metamorphic core complexes of cordilleran type involving middle crustal rocks drawn upward and outward from underneath the sedimentary basins now 100 km to the south from ca 25 ma onward during uplift the crystalline rocks now exposed on the islands were deformed noncoaxially in the deeper levels of a major shallow dipping ductile shear zone this shear zone may have connected with low angle normal faults in its upper levels because it is probable that its later history involved the metamorphic complexes being dragged out from under a stretching and fracturing upper plate composed mainly of unmetamorphosed sedimentary and ophiolite suite rocks this model can be extended to explain the exhumation of the high pressure low temperature metamorphic rocks on crete which with the cyclades forms a distended paired metamorphic belt separated by an active sedimentary basin

viscous collision in channel explains double domes in metamorphic core complexes in hot orogens gneiss domes are a response to upper crustal stretching and lower crustal flow two dimensional thermal mechanical modeling shows that localization of extension in the upper crust triggers in the deep crust oppositely verging horizontal flows that converge beneath the extended region upon viscous collision both flowing regions rotate upward to form two upright domes of foliation double domes separated by a steep median high strain zone in such systems horizontal shortening in the infrastructure develops in an overall extensional setting dome material follows a complex depth dependent strain history from shearing in the deep crustal channel to contraction upon viscous collision in the median high strain zone to extension upon advection into the shallow crust this depth dependent strain history is likely a general feature of dome evolution and is arguably well preserved in double domes such as the montagne noire france and naxos greece gneiss domes

tomographic imaging of lithospheric structures under taiwan abstract tomographic images of the crustal and mantle velocity structures under taiwan are obtained by simultaneous inversion of local earthquake p wave arrival times for hypocenters and p wave velocity structures in northern taiwan a high velocity zone coinciding with the wadati benioff zone can readily be identified as the subducted philippine sea plate the imaged zone dips toward the north at an angle of 40 from a depth range of 20 55 to 100 130 km an upper mantle low velocity wedge ranging from 40 to 80 km in depth exists above the subducted slab above this wedge is the ilan plain of northern taiwan which lies at the west end of the okinawa trough a well recognized back arc basin the crustal velocities under the plain are also relatively low the well defined high velocity zone and the low velocity wedge provide some constraints on the thermal structures of the subduction system under northern taiwan in tomographic images across the central section of taiwan thickening of the crust and up arching of the lower crustal materials under the central range are commonly observed the crust under the western foothills region is clearly thinner and the near surface low velocity layers are well developed the structures under the central range show that although the taiwan orogeny is quite young a root deeper in the north and shallowing to the south has formed the results of our tomography show that a significant portion of the lithosphere is involved in the taiwan orogeny

seismic tomography of taiwan improved constraints from a dense network of strong motion stations in this study a large collection of 41 141 s p times from the untapped records of the taiwan strong motion instrumentation program tsmip network is combined with the p and s wave arrival times from the taiwan central weather bureau seismic network cwbsn to image the v p and v p v s structures beneath taiwan the records from the 680 tsmip stations throughout taiwan in the past 15 years enhance the path coverage and the resolution in the tomography inversions tremendously our result for the v p structure largely confirms previous studies but brings better constraint on the v p v s structure the colliding luzon volcanic arc is characterized by a belt of high v p and high v p v s with high seismicity that includes the offshore islands of lutao and lanyu and the coastal ranges in eastern taiwan at the depth between about 13 and 25 km this high v p v s belt can be traced to the subduction zone in the region between hualian and ilan in the deeper portion the shallow portions of the southwestern coastal plain and the pingtung region are also characterized by a belt of high v p v s with lower seismicity most of the events occurred at the base of the high v p v s zones we suggest that material strength in those regions may be too low to accumulate stress which may indicate water saturated young sediments finally the central range region is characterized by a low v p v s belt