viscous flow and deformation of regional metamorphic belts at convergent plate boundaries 1 viscous flow and deformation of a newtonian fluid between rigid boundaries have been modeled for investigating deformation of a forearc wedge and a regional metamorphic belt as a weak deforming zone between the plates at convergent boundaries three types of analytic formulations together with numerical formulations for a newtonian fluid with a constant viscosity are used for investigating various flows and deformation 1 flows induced by squeezing between two parallel boundaries 2 flows induced by squeezing and heterogeneous mass influx in the wedge between two oblique boundaries e g accretionary wedge over the subducting plate with the continental plate as a backstop and 3 flows induced by dragging along the boundaries and by homogeneous mass influx in the wedge as in type 2 all cases include strike slip movements of the boundaries which allows us to investigate three dimensional 3 d deformation e g 3 d corner flow the corresponding flow deformation of infinitesimal and finite elements and the timescale of flow are calculated for each configuration with various mechanical boundary conditions the model results show that configuration and mechanism of the flow can be inferred from the spatial variation of finite deformation e g deformed radiolarians as a strain marker and geometry of folding as finite deformation of a large block in particular prolate strain nearly parallel to the strike of subduction zone together with a large scale folding can be a good indicator for deformation in the forearc wedge associated with 3 d corner flow induced by oblique subduction deformation observed in the cretaceous regional metamorphic belts in southwest japan can be explained by this mechanism

magmatic and structural controls on porphyry style cu au mo mineralization at kemess south toodoggone district of british columbia canada kemess south is the only cu au mo mine in the toodoggone district and a major cu and au producer in british columbia porphyry style cu au mo mineralization is mainly hosted by the tabular sw plunging 199 6 0 6 ma maple leaf granodiorite which intrudes tightly folded sw dipping permian asitka group siltstone and limestone and homogeneous triassic takla group basalt southwest dipping 194 0 0 4 ma toodoggone formation conglomerate volcaniclastic and epiclastic rocks overlie the granodiorite and asitka group rocks minor cu au mo mineralization is hosted by the immediate takla group basalt country rock whereas low tonnage high grade cu zones occur beneath a 30 m thick leached capping in supergene altered granodiorite and in exotic positions in overlying toodoggone formation conglomerate granodiorite has an intrusive contact with mineralized and altered takla group basalt but displays a sheared contact with unmineralized and less altered asitka group siltstone the north block fault is a deposit scale e striking steeply s dipping normal fault that juxtaposes the granodiorite basalt ore body against unmineralized asitka group rocks younger nw and ne striking normal dextral faults cut all rock types orebodies and the north block fault with displacements of up to 100 m and result in the graben and horst style block faulting of the stratigraphy and ore body both basalt and granodiorite host comparable vein sequence and alteration histories with minor variations in hydrothermal mineral assemblages caused by differing protolith chemistry early potassic alteration and associated early stage cu au mo mineralization is partly replaced by phyllic and intermediate argillic alteration associated with main stage cu au mo mineralization two main stage veins have re os molybdenite ages of 201 3 1 2 and 201 1 1 2 ma these mineralization ages overlap the 199 6 0 6 ma u pb zircon crystallization age for the maple leaf granodiorite late stage pyrite rich stringer veins and related phyllic alteration assemblages are cut by anhydrite rich carbonate rich and chlorite veins fluids and metals associated with early main and late stage veins were probably derived principally from the same deep magma chamber as the maple leaf granodiorite these magmatic derived fluids interacted with asitka and takla group country rocks and possibly with meteoric and metamorphic fluids prior to mineralization

mantle flow in subduction systems the subslab flow field and implications for mantle dynamics 1 the character of the mantle flow field in subduction zones remains poorly understood despite its importance for our understanding of subduction dynamics in particular little attention has been paid to mantle flow beneath subducting slabs in order to identify processes that make first order contributions to the global pattern of subslab mantle flow we have compiled shear wave splitting measurements from subduction zones worldwide from previously published studies and estimated average splitting parameters for the subslab region globally the subslab region is overwhelmingly dominated by trench parallel fast splitting directions we tested for relationships between splitting delay time a measure of the strength of anisotropy and parameters that are indicators of tectonic processes such as trench migration velocity convergence velocity and obliquity age of subducting lithosphere and slab dip curvature seismicity and thickness we used several different plate motion models to describe plate and trench motions and evaluated the differences among the models we find that only one parameter namely the trench migration velocity in a pacific hot spot reference frame appears to correlate well with the strength of the subslab splitting signal this finding supports a model in which the mantle beneath subducting slabs is dominated by three dimensional flow induced by trench migration we explore several implications of our model for various aspects of mantle dynamics including the choice of a suitable reference frame s for mantle flow the existence of a thin decoupling zone between slabs and the subslab mantle and consequences for mass transfer between the upper and lower mantle

fractal modeling and fry analysis of the relationship between structures and cu mineralization in saveh region central iran abstract the saveh region in the middle part of the urumieh dokhtar magmatic belt udmb central iran contains several cu mineralization and deposits that may have been localized by structural controls in the region along the major thrust fault the saveh region comprises intrusive bodies associated with various cu occurrences and deposits the nw se major faults especially the khalkhab and koshk e nosrat faults on the iranian plates created a sigmoid space for the emplacement of plutons during middle eocene the cu occurrences deposits are either vein or manto style with vein style being dominant the lineaments and faults in the saveh region were mapped using precise local data including remote sensing landsat etm digital elevation models dem geomagnetic airborne images geological maps and field observations the relationship between cu occurrences deposits and geological structures the latter being described by a lineament factor lf or fracture density is important for focusing of ore forming fluids and mineralization this was analyzed by concentration area c a fractal modeling and by fry analysis the results of the c a fractal modeling and fry analysis indicate that the vein style cu mineralization is associated with major nw se trending faults especially the khalkhab and koshk e nosrat faults manto style cu mineralization in the saveh region is associated with minor ne sw trending faults

synthetic fluid inclusions in natural quartz iii determination of phase equilibrium properties in the system h2o nacl to 1000 c and 1500 bars phase equilibria in the system h2o nacl have been determined to 1000 c and 1500 bars using synthetic fluid inclusions formed by healing fractures in inclusion free brazilian quartz in the presence of the two coexisting immiscible h2o nacl fluids at various temperatures and pressures petrographic and microthermometric analyses indicate that the inclusions trapped one or the other of the two fluids present or mixtures of the two salinities of the two coexisting phases were obtained from heating and freezing studies on those inclusions which trapped only a single homogeneous fluid phase results of the present study are consistent with previously published data on the h2o nacl system at lower temperatures and pressures and indicate that the two phase field extends well into the p t range of most shallow magmatic hydrothermal activity as a consequence chloride brines exsolved from many epizonal plutons during the process of second boiling should immediately separate into a high salinity liquid phase and a lower salinity vapor phase and produce coexisting halite bearing and vapor rich fluid inclusions this observation is consistent with results of numerous fluid inclusion studies of ore deposits associated with shallow intrusions particularly the porphyry copper deposits in which halite bearing and coexisting vapor rich inclusions are commonly associated with the earliest stages of magmatic hydrothermal activity

shear wave polarization anisotropy and subduction induced flow in the mantle wedge of northeastern japan abstract shear wave polarization anisotropy in the central part of northeastern ne japan was investigated we analyzed s phases of 293 intermediate depth earthquakes recorded at 77 stations and obtained 1286 splitting parameters the obtained results show the systematic variation in splitting parameters across the arc the leading shear wave polarization directions fast direction obtained at stations in the western side of the study area are oriented nearly e w which is sub parallel to the direction of relative plate motion between the pacific plate and the north american okhotsk plate in contrast fast directions obtained at stations in the eastern side of the study area are oriented approximately n s stations in the western side have a larger average delay time compared to those in the eastern side these variations suggest that the nature of anisotropy is quite different between the eastern and the western sides both experimental studies on the deformation of olivine and numerical simulations of plate driven flow predict that the lattice preferred orientation of olivine causes the fast direction sub parallel to the flow direction for the conditions in the mantle wedge of ne japan we thus infer that the lattice preferred orientation of olivine generated by flow induced strain is the most likely candidate for anisotropy that produces splitting with e w fast direction three possible causes of anisotropy in the eastern side are considered deformation of water rich olivine in the mantle wedge trench parallel flow in the mantle wedge due to along strike dip variations in the slab and anisotropy in the crust and the slab we could not however determine which causes are dominant further systematic study is required to reveal the cause of anisotropy in the eastern side

b type olivine fabric in the mantle wedge insights from high resolution non newtonian subduction zone models several hypotheses have been proposed to explain trench parallel shear wave splitting in the mantle wedge of subduction zones these include 3 d flow effects parallel melt filled cracks and b type olivine fabric we predict the distribution of btype and other fabrics with high resolution thermal and stress models of subduction zones a composite viscous rheology is used that incorporates wet diffusion creep wet dislocation creep and a stress limiting approximated peierls creep law rheological parameters for dislocation and diffusion creep are based on deformation experiments the effects of variable viscous coupling between the slab and mantle are explored using kinematic boundary conditions that change along the top of the slab two end member models are observed which depend on the depth of partial viscous coupling between the slab and mantle 1 deep partial coupling which gives rise to cold high stress conditions in the forearc mantle and high temperature low stress conditions in the arc and back arc mantle 2 full viscous coupling at the base of a 40 km conducting lid which is characterized by high temperature and low stress the case with deep partial coupling which produces a better match with attenuation tomography and heat flow shows a large region with suitable conditions for b type fabric in the forearc mantle and a rapid transition toward the back arc to conditions that are more suitable for a c or e type fabrics full viscous coupling gives rise to high temperature low stress conditions unsuitable for b type fabric our modeling predicts that the best candidates for regions with b type fabric are the forearc mantle and a cold 10 15 km layer above the slab d 2005 elsevier b v all rights reserved

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

effect of three dimensional slab geometry on deformation in the mantle wedge implications for shear wave anisotropy shear wave splitting observations from many subduction zones show complex patterns of seismic anisotropy that commonly have trench parallel fast directions three dimensional flow may give rise to trench parallel stretching and provide an explanation for these patterns of seismic anisotropy along strike variations in slab geometry produce trench parallel pressure gradients and are therefore a possible mechanism for three dimensional flow in this study we quantify the effects of variable slab dip curved slabs oblique subduction and slab edges on flow geometry and finite strain in the mantle wedge of subduction zones temperature dynamic pressure velocity and strain are calculated with high resolution three dimensional finite element models these models include temperature and stress dependent rheology and parameterized slab and trench geometry thick layers 20 60 km with strong trench parallel stretching are observed in the mantle wedge when slab geometry involves a transition to slab dip less than 15 or strong curvature in the slab in these cases strong trench parallel stretching develops when flow lines have an oblique to trench normal orientation this suggests that trench parallel seismically fast directions may not indicate trench parallel flow lines in systems with large along strike variations an oblique component of stretching is confined to a 20 30 km layer above the slab in systems with oblique subduction the effects of slab edges include strong toroidal flow and focusing in the mantle near slab edges and trench parallel flow that extends 50 100 km into the core of the mantle wedge

control of barrier island shape by inlet sediment bypassing east frisian islands west germany abstract a study of the east frisian islands has shown that the plan form of these islands can be explained by processes of inlet sediment bypassing this island chain is located on a high wave energy high tide range shoreline where the average deep water significant wave height exceeds 1 0 m and the spring tidal range varies from 2 7 m at juist to 2 9 m at wangerooge an abundant sediment supply and a strong eastward component of wave power 4 4 103 w m 1 have caused a persistent eastward growth of the barrier islands the eastward extension of the barriers has been accommodated more by inlet narrowing than by inlet migration it is estimated from morphological evidence that a minimum of 2 7 105 m3 of sand is delivered to the inlets each year via the easterly longshore transport system much of this sand ultimately bypasses the inlets in the form of large migrating swash bars the location where the swash bars attach to the beach is controlled by the amount of overlap of the ebb tidal delta along the downdrift inlet shoreline the configuration of the ebbtidal delta in turn is a function of inlet size and position of the main ebb channel the swash bar welding process has caused preferential beach nourishment and historical shoreline progradation along the east frisian islands this process has produced barrier islands with humpbacked bulbous updrift and bulbous downdrift shapes the model of barrier island development presented in this paper not only explains well the configuration of the german barriers but also the morphology of barriers along many other mixed energy coasts

hydrodynamics and sedimentation in wave dominated coastal environmentscontrol of barrier island shape by inlet sediment bypassing east frisian islands west germany a study of the east frisian islands has shown that the plan form of these islands can be explained by processes of inlet sediment bypassing this island chain is located on a high wave energy high tide range shoreline where the average deep water significant wave height exceeds 1 0 m and the spring tidal range varies from 2 7 m at juist to 2 9 m at wangerooge an abundant sediment supply and a strong eastward component of wave power 4 4 103 w m 1 have caused a persistent eastward growth of the barrier islands the eastward extension of the barriers has been accommodated more by inlet narrowing than by inlet migration it is estimated from morphological evidence that a minimum of 2 7 105 m3 of sand is delivered to the inlets each year via the easterly longshore transport system much of this sand ultimately bypasses the inlets in the form of large migrating swash bars the location where the swash bars attach to the beach is controlled by the amount of overlap of the ebb tidal delta along the downdrift inlet shoreline the configuration of the ebbtidal delta in turn is a function of inlet size and position of the main ebb channel the swash bar welding process has caused preferential beach nourishment and historical shoreline progradation along the east frisian islands this process has produced barrier islands with humpbacked bulbous updrift and bulbous downdrift shapes the model of barrier island development presented in this paper not only explains well the configuration of the german barriers but also the morphology of barriers along many other mixed energy coasts

three dimensional structure of p wave anisotropy in the presence of small scale convection in the mantle wedge 1 as a possible explanation of hot fingers in the mantle wedge below the tohoku region japan the existence of small scale convection has been proposed in this study we performed numerical calculations around the subduction zone in 3d with composite rheology i e a combination of linear and non linear rheology and found that small scale convection could arise when the rheology determined from laboratory experiments is considered we also calculated 3d structure of expected p wave anisotropy for the case with and without small scale convection based on a theory of lpo development and an assumption that anisotropy is approximately represented as hexagonal symmetry and found that the fast axis of the p wave propagation projected on the horizontal cross sections is nearly in the same direction as that of plate motion in many places it implies that effects of large scale mantle flow associated with subducting slab is still dominant even in the presence of small scale convection in mantle wedge however in vertical cross sections the projected fast axis of the p wave propagation could tilt vertically while that without small scale convection is almost horizontal therefore future seismological studies that determine the fast direction of p wave propagation in 3d would give us critical information on the possible existence of small scale convection in the mantle wedge

examining potential genetic links between jurassic porphyry cu au mo and epithermal au ag mineralization in the toodoggone district of north central british columbia canada the toodoggone district comprises upper triassic to lower jurassic hazelton group toodoggone formation volcanic and sedimentary rocks which unconformably overlie submarine island arc volcanic and sedimentary rocks of the lower permian asitka group and middle triassic takla group some of which are intruded by upper triassic to lower jurassic plutons and dikes of the black lake suite although plutonism occurred episodically from ca 218 to 191 ma the largest porphyry cu au mo systems formed from ca 202 to 197 ma with minor mineralization occurring from ca 197 to 194 ma porphyry style mineralization is hosted by small volume 468 c saline and deposited metals at deep crustal depths 2 km sulfur c o and pb isotope data confirm the involvement of a magmatic fluid but also suggest that the ore fluid interacted with asitka and takla group country rocks prior to metal deposition in contrast in the shasta lawyers and griz sickle low sulfidation epithermal systems there is no clear association with magmatic fluids instead their fluid inclusion data indicate the involvement of low temperature 175 to 335 c low salinity 1 to 11 equiv wt nacl fluids that deposited metals at shallow depths 850 m their isotope i e o h pb data suggest interaction between meteoric and or metamorphic ore fluids with basement country rocks

physical conditions producing slab stagnation constraints of the clapeyron slope mantle viscosity trench retreat and dip angles abstract recent seismic tomography has revealed various morphologies in the subducted lithosphere in particular significant flattening and stagnation of slabs around the 660 km boundary are seen in some areas beneath the northwestern pacific subduction zones we examined the cause of slab stagnation in terms of the clapeyron slope of the phase transformation from ringwoodite to perovskite magnesiowustite trench retreat velocity dip angles and high viscosity of the lower mantle based on two dimensional 2 d numerical simulations of thermal convection in particular we examined the conditions necessary for slab stagnation assuming a very small absolute value of the clapeyron slope which were proposed based on recent high pressure high temperature high p t experiments our calculations show that slabs tend to stagnate above the 660 km boundary with an increasing absolute value of the clapeyron slope viscosity jump at the boundary and trench retreat velocity and a decreasing initial dip angle stagnant slabs could be obtained numerically for a realistic range of parameters obtained from high p t experiments and other geophysical observations combining buoyancy high lower mantle viscosity and trench retreat we found that a low dip angle of a descending slab at the bottom of the upper mantle plays an important role in slab stagnation two main regimes underlie slab stagnation buoyancy dominated and viscosity dominated regimes in the viscosity dominated regime it is possible for slabs to stagnate above the 660 km boundary even when the value of the clapeyron slope is 0 mpa k

p wave anisotropic tomography of the crust and upper mantle under hokkaido japan abstract we determined a 3 d anisotropic velocity structure beneath hokkaido in northern japan using a large number of first p wave arrival times the travel time inversion is parameterized with an isotropic component and two anisotropic parameters for each grid node by assuming p wave azimuthal anisotropy with hexagonal symmetry axis distributed horizontally the geometries of the conrad and moho discontinuities and the upper boundary of the subducting pacific plate are taken into account in the model our results show that low velocity zones exist beneath active arc volcanoes in the crust and in the central portion of mantle wedge above the high velocity pacific slab which are similar to the previous tomographic images p wave anisotropy is revealed in the crust mantle wedge and the subducting pacific slab in the upper crust the anisotropy is possibly caused by microcracks and cracks in the lower crust the anisotropic structure is different from that in the upper crust and it may be affected considerably by the plastic flow deformation in the mantle wedge the fast velocity direction fvd is generally trench normal in most of the study area while it becomes trench parallel in the pacific coast areas close to the trench which agrees with the shear wave splitting results beneath the volcanic front the fvd is also trench parallel which may suggest the existence of complex 3 d mantle flow in the mantle wedge the fvd in the subducting pacific slab is nearly north south which likely keeps the original fossil anisotropy of the pacific plate formed at the mid ocean ridge or is affected by the olivine fabric transition from a type to b type fabric due to the changes in water content stress and temperature

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

reconciling surface plate motions with rapid three dimensional mantle flow around a slab edge a central axiom of the theory of plate tectonics is that the surface plates are coupled to and carried along by convection in the earth s mantle the situation is rather different at subduction zones however margarete jadamec and magali billen now present calculations that quantify this variance they use three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system to determine the surrounding mantle flow field they show that near a subduction zone edge mantle flow velocities can have magnitudes of greater than ten times the surface plate motions and that the complex mantle flow field is consistent with observations from seismic anisotropy these results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally implying large scale coupling between the mantle and surface plates but the fit is poor at subduction zones here three dimensional numerical models of buoyancy driven deformation for the alaska subduction transform system are used to find the origin of the regional decoupling of flow the results imply local rapid transport of geochemical signatures through subduction zones the direction of tectonic plate motion at the earth s surface and the flow field of the mantle inferred from seismic anisotropy are well correlated globally suggesting large scale coupling between the mantle and the surface plates1 2 the fit is typically poor at subduction zones however where regional observations of seismic anisotropy suggest that the direction of mantle flow is not parallel to3 4 5 6 7 and may be several times faster than6 plate motions here we present three dimensional numerical models of buoyancy driven deformation with realistic slab geometry for the alaska subduction transform system and use them to determine the origin of this regional decoupling of flow we find that near a subduction zone edge mantle flow velocities can have magnitudes of more than ten times the surface plate motions whereas surface plate velocities are consistent with plate motions8 and the complex mantle flow field is consistent with observations from seismic anisotropy5 the seismic anisotropy observations constrain the shape of the eastern slab edge and require non newtonian mantle rheology the incorporation of the non newtonian viscosity9 10 results in mantle viscosities of 1017 to 1018 pa s in regions of high strain rate 10 12 s 1 and this low viscosity enables the mantle flow field to decouple partially from the motion of the surface plates these results imply local rapid transport of geochemical signatures through subduction zones and that the internal deformation of slabs decreases the slab pull force available to drive subducting plates

mantle wedge flow pattern and thermal structure in northeast japan effects of oblique subduction and 3 d slab geometry abstract we develop a 3 d thermal model for the northeast japan subduction margin using a realistic slab geometry for the subducting pacific plate and investigate the effects of oblique subduction and 3 d slab geometry on the mantle wedge flow pattern and the thermal structure in the tohoku region the mantle wedge flow pattern is nearly two dimensional resulting in a thermal structure similar to those obtained by a 2 d model owing to the simple slab geometry and subduction nearly perpendicular to the margin however in hokkaido oblique subduction leads to 3 d mantle wedge flow with northerly inflow and west northwestward outflow and also results in lower temperatures in the shallow part of the mantle wedge than in tohoku due to lower sinking rate of the slab between hokkaido and tohoku the slab has a hinge like shape due to a relatively sharp change in the dip direction in this hinge zone northerly mantle inflow from hokkaido and westerly mantle inflow from tohoku converge discouraging inflow from northwest and resulting in a cooler mantle wedge the model predicted mantle wedge flow patterns are consistent with observed seismic anisotropy and may explain the orientations of volcanic cross chains the predicted 3 d thermal structure correlates well with the along arc variations in the location of the frontal arc volcanoes and help to provide new insights into the surface heat flow pattern and the down dip extent of interplate earthquakes

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

effects of oblique subduction on the 3 d pattern of small scale convection within the mantle wedge 1 we have developed a 3 d numerical model of obliquely subducting slab and mantle flow above using this model we explore the effects of oblique subduction on the small scale convection within the mantle wedge we find that the spatial pattern and time dependent characteristics of oblique subduction are similar to those of non oblique cases whose subduction speed is the same as the subduction velocity component normal to the strike of subducting slab this also implies that the axes of rolls of small scale convection are nearly normal to the plate boundary assuming that the plate boundary represents the strike of subducting plate only when the back arc lithosphere overlying the small scale convection moves along the strike of subduction a significant change of the orientation of roll axes is observed

evolution and facies architecture of the mesotidal guadiana river delta s w spain portugal abstract the guadiana river estuary and delta is one of the most important mesotidal fluvio marine systems of the southwestern iberian peninsula the river mouth was formed as a narrow channel excavated by fluvial incision during the pleistocene lowstand and then flooded 6500 yr ago during the flandrian transgression holocene the estuary is in an advanced state of sediment infilling in its proximal part due to its narrow morphology which prevents passage of sediment through to the open coast consequently sediment is accumulating in the river mouth causing progradation as response of the interaction between coastal and fluvial processes sedimentation is controlled by the interaction of sediment load delivered by the guadiana river and the active longshore current which also supplies sand eroded from barrier islands and friable cliffs in the portuguese algarve to the west tidal range is mesotidal 2 0 m and mean significant wave height is 0 6 m with an average period of 3 6 s morphological differences exist between the two sides of the river mouth the western side has a large spit separated from the mainland by a marsh and the eastern side shows an array of old barrier islands separated by salt marsh areas a vibracore study allows us to distinguish 12 different depositional facies in the system fluvial delta tidal inlet flood tidal delta washover beach dune estuarine channel lagoon tidal creek channel margin tidal flat and salt marsh furthermore a different architectural scheme of these facies is present on each side to the east there is a longitudinal repetition of the sandy facies corresponding to the barrier islands on the west side there is a transverse growth of a single spit containing eolian dunes these differences result from asymmetric interaction between the tidal and fluvial currents at the river s mouth and the waves and tidal currents of the open coastal zone

three dimensional structure of p wave anisotropy beneath the tohoku district northeast japan 1 we retrieve three dimensional structures of isotropic and anisotropic velocities of p waves of the tohoku district from first p arrival time data assuming azimuthal anisotropy to be caused by hexagonal symmetry axes distributed horizontally in the earth the results show that the high velocity pacific slab is clearly imaged in the isotropic velocity structure even though the azimuthal anisotropy is taken into account in addition small scale low velocity regions and prominent low velocity anomalies are found just below the active volcanoes and in the mantle wedge above the high velocity pacific slab respectively the fast propagation axis of p waves is in mostly e w direction in the upper crust nearly n s and e w directions in the lower crust e w direction in the mantle wedge and n s direction in the descending pacific slab these features of the p wave anisotropy structure are consistent with those of lateral variations of the fast polarization directions measured previously by shear wave splitting observations the plausible factor that causes the crust anisotropy is interpreted as being alignment or preferred orientation of microcracks and crust minerals the mantle wedge anisotropy is attributed to lattice preferred orientation of the mantle minerals arising from present day mantle process such as the mantle wedge convection and the plate motion however the fast propagation axis of p waves in the slab is almost perpendicular to the magnetic lineation of the oceanic plate under the northwest pacific and thus the slab preserves the original anisotropic property that the pacific plate gained when it formed

along arc variation in the 3 d thermal structure around the junction between the japan and kurile arcs the thermal structure in subduction zones has a strong influence on seismogenesis and arc volcanism traditional 2 d models have been used to provide reasonable agreement between models and observations but in a number of cases clear 3 d effects are present one such case is in the northern japan subduction system at the junction between japan and kurile arcs surface heat flow and the occurrence of intermediate depth seismicity are different than in the tohoku and hokkaido regions we investigate the effects of 3 d slab geometry and a local deepening of slab mantle decoupling depth on the thermal structure in this region based on 3 d finite element approach we find that both effects produce the along arc variation of slab surface temperature which could reach 100 c the warmer region arises through 3 d effects of thermal conduction and the colder region arises through localized slow incoming flow in the case where 3 d slab geometry is taken into account 3 d flow arises where a local deepening of slab mantle decoupling depth is assumed which leads to both warmer and colder regions the effects on surface heat flow are small while intermediate depth seismicity in the subducted crust is suggested to be controlled by temperature dependent phase transitions the predicted changes in thermal structure are not sufficient to cause the observed deepening of seismicity this suggests that the thermal structure of this subduction zone may be more strongly influenced by time dependent deformation of the overriding crust and slab

newtonian versus non newtonian upper mantle viscosity implications for subduction initiation 1 the effect of rheology on the evolution of the slab tip during subduction initiation is analyzed using 2 d numerical flow models experimentally determined flow laws have both strong temperature and stress dependence which leads to large local variations in viscosity with direct consequences for subduction initiation we find that models with newtonian viscosity lead to flat or coupled subduction due to hydrodynamic stresses that pull the slab tip up towards the overriding plate non newtonian rheology reduces these hydrodynamic stresses by decreasing the wedge viscosity and the slab coupling to wedge corner flow rendering the small negative slab buoyancy of the slab tip sufficient to maintain its dip during the early stages of subduction

interaction between wave and tide generated processes at the mouth of a microtidal estuary matanzas river florida u s a abstract the zone of transition between the wave dominated open coast and tide dominated mouth of estuaries is complicated a time series study of wave parameters longshore currents and tidal parameters at the mouth of an estuary on the northeast coast of florida has demonstrated that tidal influence on nearshore processes is modest and localized tidal currents are nearly undetectable less than 0 5 km from the estuary mouth along the open coast tidal currents reach 80 cm s in the throat of the main ebb channel but immediately seaward of the terminal lobe of the ebb delta the tidal component is barely detectable with longshore currents predominating lateral flood channels adjacent to the estuary mouth show that tidal currents are significant and dominate longshore currents near low tide stage but are suppressed by longshore currents near high tide weather patterns may have an important effect on tidal processes at the estuary mouth because they control wave impingement and therefore longshore current speed and direction longshore currents may reinforce or suppress tidal currents particularly in lateral flood channels

mapping convection in the mantle long period 100 250 sec love and rayleigh waves are used to map heterogeneity and azimuthal anisotropy in the upper mantle spherical harmonic descriptions of anisotropy up to l m 3 and 2 are derived azimuthal anisotropy obtains values as high as 1 there is good correlation of fast rayleigh wave directions with upper mantle return flow directions derived from kinematic considerations this is consistent with the a axis of olivine being aligned in the flow direction the main differences between the flow models and the rayleigh wave azimuthal variation maps occur in the vicinity of hotspots hawaii for example appears to perturb the return flow there is strong correlation of the geoid and surface wave velocity at l 4 and 5 slow regions at this scale are associated with geoid highs and high heat flow consistent with upwelling convective flow or with isostatically compensated regions of low density the correlation of azimuthal anisotropy with upper mantle return flow directions rather than with plate directions suggests that part of the return flow is in the upper mantle and this in turn implies a low viscosity channel

numerical simulations of mantle flow around slab edges abstract a simple kinematic dynamic model of mantle flow around the slab edge is constructed in order to understand the flow complexity there the flow velocity on the top and the small boundary region around the shallow plate boundary is kinematically imposed in order to achieve a subduction like feature and the flow in other part is dynamically calculated the geometry of the plate mimics the region around the junction of aleutian islands and kamchatka that are examples of the convergent transform fault plate boundaries in a simple model in which the overlying plate is almost stationary the lateral flow from the mantle under the subducting slab to the mantle under the neighboring plate is of minor importance once the slab penetrates into the high viscosity layer where the downward flow encounters the resistance similar situation was found when the trench is advancing that is the trench moves toward the overlying plate for the case with retreating trench that is the trench moves toward the subducting plate a lateral flow exists even after the slab penetrates into the high viscosity layer although its magnitude is significantly smaller than that of the plate velocity the presence of a low viscosity layer just beneath the subducting plate may promote the emergence of lateral flow a significant lateral flow is observed when the high temperature anomaly that is buoyant and low viscosity block carried by the movement of subducting plate approaches the slab these results may have important implications for the possible existence of trench parallel flow in the sub slab mantle

slab stagnation and detachment under northeast china abstract results of tomography models around the japanese islands show the existence of a gap between the horizontally lying stagnant slab extending under northeastern china and the fast seismic velocity anomaly in the lower mantle a simple conversion from the fast velocity anomaly to the low temperature anomaly shows a similar feature this feature appears to be inconsistent with the results of numerical simulations on the interaction between the slab and phase transitions with temperature dependent viscosity such numerical models predict a continuous slab throughout the mantle i extend previous analyses of the tomography model and model calculations to infer the origins of the gap beneath northeastern china results of numerical simulations that take the geologic history of the subduction zone into account suggest two possible origins for the gap 1 the opening of the japan sea led to a breaking off of the otherwise continuous subducting slab or 2 the western edge of the stagnant slab is the previous subducted ridge which was the plate boundary between the extinct izanagi and the pacific plates origin 2 suggesting the present horizontally lying slab has accumulated since the ridge subduction is preferable for explaining the present length of the horizontally lying slab in the upper mantle numerical models of origin 1 predict a stagnant slab in the upper mantle that is too short and a narrow or non existent gap preferred models require rather stronger flow resistance of the 660 km phase change than expected from current estimates of the phase transition property future detailed estimates of the amount of the subducted izanagi plate and the present stagnant slab would be useful to constrain models a systematic along arc variation of the slab morphology from the northeast japan to kurile arcs is also recognized and its understanding may constrain the 3d mantle flow there

variation in ebb delta morphologies along the west and east frisian islands the netherlands and germany abstract ebb delta morphologies in the west and east frisian islands differ mainly in terms of the direction and the degree of asymmetry of the ebb deltas in the east frisian islands the ebb tidal deltas and their main ebb channels are asymmetrically directed downdrift to the east in the west frisian islands they are asymmetrically directed updrift to the west except for a few of the small ebb tidal deltas which are asymmetrically directed downdrift earlier theories for the east frisian islands considered wind driven waves coming dominantly from the west to be the main cause of the downdrift asymmetry of the ebb tidal deltas theories for the west frisian islands related the updrift directed ebb tidal deltas to tidal currents none of these theories can explain the morphological variation in the ebb tidal deltas for both the west and east frisian islands observation of the ebb delta morphologies of the west and east frisian islands in relation to tidal and wave regimes shows that the above mentioned difference in the ebb delta morphologies is due to the varying importance of the tidal prism and the wave induced longshore drift for the different inlets the difference is especially pronounced between the large and the small ebb tidal deltas because their tidal prisms are different the inlets with a large tidal prism have large ebb tidal deltas and they are dominated by tidal currents interaction of marine shore parallel tidal currents with onshore offshore inlet tidal currents which is enhanced by the ebb delta shoals causes the large ebb tidal deltas and their main ebb channels to be asymmetrically directed updrift to the west the inlets with a small tidal prism have small ebb tidal deltas and they are dominated by waves eastward moving deep water wave and wave induced longshore drift drive the small ebb tidal deltas asymmetrically downdrift to the east the general model proposed not only explains the varying morphologies of the ebb tidal deltas of the west and east frisian islands but is also applicable to other ebb tidal deltas

layered convection induced by phase transitions we report a systematic study on the conditions under which an endothermic phase transition can enforce layered convection two dimensional numerical calculations of convection in a domain containing a divariant phase change were performed in the framework of the extended boussinesq approximation i e considering the effects of adiabatic gradient latent heat and frictional heating in the energy equation we find that the critical value of the negative clapeyron slope which must be surpassed in order to induce layered convection decreases in magnitude with increasing rayleigh number ra in the range 104 ra 2 106 near the critical clapeyron slope vacillations between double and single layer convection or strongly leaking double layer convection are possible the breakdown into layers is influenced very little by the latent heat release but depends solely on the phase boundary deflection caused by lateral temperature differences the value of the critical clapeyron slope also seems little affected by the width of the transition zone or by its depth a possible superplastic rheology within the transition zone would tend to favor layered convection scaling the model results to the 670 km discontinuity in the earth s mantle as a possible endothermic phase boundary we estimate the critical clapeyron slope to be in the range of 4 to 8 mpa k 40 to 80 bar k the possibility that the spinel perovskite periclase transition is within this range appears to be remote but certainly cannot be neglected

a simple semi dynamic model of the subduction zone effects of a moving plate boundary on the small scale convection under the island arc summary a simple semi dynamic numerical model of the subduction zone which incorporates the plate velocity and a moving plate boundary as a priori constraints has been developed this model may be useful for studying specific subduction zones where a history of kinematic movements of plates is well constrained as an application of this model the effects of a moving plate boundary on the nature of the small scale convection in the mantle wedge were studied under the restriction of given relative velocity between two converging plates the absolute velocity of each plate was changed and i found that the characteristics of small scale convection are not significantly affected by the movement of the plate boundary at least within the parameter range used in this study i also found a small systematic change which may be related to the difference of the heat supply to the mantle wedge caused by the moving plate boundary thus the model with a fixed continental plate and moving oceanic plate with a given relative velocity may be sufficient for studying the present subject this model can be extended into a simple 3d subduction zone model

tearing of stagnant slab subducted slabs of oceanic lithosphere below the western pacific tend to be stagnant in the transition zone with poorly known mechanical properties typical examples are the izu bonin and japan slabs that meet each other to form a cusplike junction beneath southwest japan here we show that these two slabs are torn apart at their junction when they bend to flatten over the 660 kilometer discontinuity as is expected from a simple geometric argument we present three lines of evidence for this ongoing slab tear

sand transport patterns in the ebb tidal delta off texel inlet wadden sea the netherlands abstract sand transport patterns in the ebb tidal delta of texel inlet were studied using current and wave measurements calculations of sediment transport rate bedform orientations dips of cross beds and the morphological evolution a qualitative picture of sand transport patterns was formed sand supplied from the north sea and the adjacent coast is transported in and out through several neighboring flood and ebb dominated channels in the southwestern ebb delta along the seaward margin of the ebb tidal delta of texel inlet sand is transported in both directions parallel to the coast by tidal currents but predominantly northwards and landwards some sand is desposited where a weak rotational tidal current pattern is produced north of the inlet by the interruption of tidal currents parallel to the coast by the inlet waves transport the sand further onshore over the swash platform some of it returns to the main circulation of the inlet through the molengat sand transport through the inlet is flood dominated it is revealed that not only the interaction of tidal currents and waves but also the interaction between the tidal currents in the north sea and through the inlet greatly influence the system

evolution of the hazelton arc near terrace british columbia stratigraphic geochronological and geochemical constraints on a late triassic early jurassic arc and cu au porphyry belt understanding the development of island arcs that accreted to the north american craton is critical to deciphering the complex geological history of the canadian cordillera in the case of the hazelton arc part of the stikine terrane or stikinia in northwestern british columbia understanding arc evolution also bears on the formation of spatially associated porphyry cu au epithermal and volcanogenic massive sulfide deposits the hazelton group is a regionally extensive long lived and exceptionally thick upper triassic to middle jurassic volcano sedimentary succession considered to record a successor arc that was built upon the paleozoic and triassic stikine and stuhini arcs in central stikinia near terrace british columbia the lower hazelton group telkwa formation comprises three volcanic intrusive complexes mt henderson mt o brien and kitselas that at their thickest constitute almost 16 km of volcanic stratigraphy basal telkwa formation conglomerates and volcanic rocks were deposite

d rex a program for calculation of seismic anisotropy due to crystal lattice preferred orientation in the convective upper mantle summary models of development of lattice preferred orientation lpo of crystals aggregates in convec tive flow are necessary to interpret the anisotropic seismic signature of the earth s upper mantle for that purpose we previously developed a model of lpo evolution in olivine aggregates by plastic deformation and dynamic recrystallization by subgrain rotation and grain boundary migration this paper presents a refined version of that model called d rex for dynamic recrystallization induced lpo a public version of which is made available on our web site the code displays two new features 1 enstatite is incorporated in the aggregates and 2 grain boundary sliding gbs of small grains is taken into account enstatite is incorporated on the assumption of no direct interaction with olivine the fast a axis of enstatite grains tend to be parallel to the slow c axis of olivine which dilutes the total anisotropy grain boundary sliding is included using a threshold dimensionless volume fraction defined as the ratio of the initial size of the grains over the size for which gbs is the dominant mechanism of deformation grains with a dimensionless volume smaller than do not rotate by plastic deformation and their strain energy is set to zero comparison with torsion experiments at very large strain constrains the threshold dimensionless volume to 0 3 0 1 the incorporation of grain boundary sliding prevents the lpo from becoming singular at large strains and yields more realistic predictions our kinematic formalism and the model s semi analytical character insures that it is fast robust and stable it can be applied efficiently to arbitrary 3 d convective flows

the influence of olivine metastability on the dynamics of subduction abstract both seismological observations and mineral physics experiments suggest that old and cold subducting slabs might contain a wedge of metastable olivine mo dynamically consistent models of subducting slabs in which the kinetics of the olivine to spinel wadsleyite or ringwoodite transition is treated in a simplified way are carried out to evaluate the buoyancy effect of mo on the subduction velocity assuming slab thicknesses according to the cooling half space model we find that mo forms in slabs with ages greater than approximately 70 myr and that a significant slowing down of subduction velocity occurs for ages greater than 100 myr because a decrease in the subduction velocity for old lithospheric ages is not observed our models suggest that the amount of mo in slabs is less than approximately 5000 km2 in cross section and that for old lithosphere the cooling half space model is not applicable

mantle flow and deformation of subducting slab at a plate junction abstract at junctions between plate boundaries there are several general characteristic features these include trench normal fast polarization direction of s wave splitting in the mantle wedge along arc variation of the angle of subduction and the different behavior of slab stagnation along the strike of the trench in this paper we focus on the junction of the tohoku kurile arc we show the dynamical effects of the junction using a numerical model of mantle convection with a realistic curved shape of the trench we obtain 3d flow in the mantle wedge which is consistent with the observation of seismic anisotropy even with the oblique subduction we also find the along arc variation of subduction angle which agrees with the observations although the match becomes worse when we include the effect of dislocation creep that is non linear viscosity along arc variation of the angle of subduction partly contributes to the different behavior of slab stagnation in the tohoku kurile arc our results show that the shape of the trench is an important factor which considerably affects mantle flow and deformation of subducting slabs thus 3d modeling is necessary to constrain the dynamics of subduction zones near the junction

surface sediments and sequence models in the ebb tidal delta of texel inlet wadden sea the netherlands abstract grain size and primary sedimentary structures in the ebb tidal delta of texel inlet are described with the emphasis on the relations with tidal and wave processes grain size distribution curves represent two major types wave dominated very well sorted sand with dominantly saltation population and tide dominated less well sorted with relatively large suspension and traction populations areal distribution of mean grain size sorting and different distribution curves is closely related to sediment transport patterns the deep inlet channel and the offshore area serve as source areas for the ebb tidal delta and have coarse relatively poorly sorted sediments deposition of very well sorted fine sand occurs on the shallow ebb delta shoal the size and sorting of the sands are the result of selective transport and wave processes sedimentary structures formed by waves and tidal currents are distinctly distributed over the shallow ebb delta shoal the channels and the adjacent inner shelf the areal distribution of mud drapes in the ebb tidal delta is a combined effect of the local tidal current pattern and the related locally high concentrations of fine grained suspended sediment alternation of tidal current dominance during and immediately after storms with wave dominance during fair weather conditions results in the formation of storm deposits at specific locations in the ebb tidal delta i e seaward of the main ebb channel on the basis of this study sequential models are proposed for the migrational inlet channel the progradational ebb delta lobe and the landward migrating ebb delta shoal the transgressive sequence formed after abandonment of the ebb delta lobe

spherical shell tectonics effects of sphericity and inextensibility on the geometry of the descending lithosphere the shape of a deep seismic zone is thought to represent that of the descending slab of lithosphere the lithosphere before subduction is a spherical shell and the shape of the descending slab is the result of the deformation of the spherical lithosphere at the subduction zone upon bending a spherical shell often deforms in a very different way from a simple plate we examine whether the actual shape of the descending slab can be explained by a simple bending of an inextensible spherical shell which shows little surface deformation under moderate stress this examination is made region by region for most of the subduction zones in the world by means of an analogue method the lithosphere is simulated by an inextensible spherical shell made of polyvinyl chloride resin the wadati benioff zone is shaped by plaster by referring to the reliable hypocentral data selected from the international seismological centre isc bulletins the spherical shell is forced to fit the miniature of the wadati benioff zone fitting is first attempted only by bending if a good fit is not attainable and if a discontinuity or gap in seismic activity is observed in the relevant region the spherical shell is torn along this discontinuity or gap and the goodness of fit is reexamined the results of the analysis are summarized as follows 1 the shape of the wadati benioff zone can be simulated largely by a simple bending of a spherical shell without surface deformation 2 in almost all of the regions of poor fit with bending a good fit can be achieved by tearing the spherical shell along the trace of low seismicity the sphericity of the lithosphere and the inextensibility upon deformation are the two essential factors in controlling the slab shape this means that the lateral constraint is most important for understanding the geometry of the downgoing slab of lithosphere and the stress state within it further several problems related to the deformational characteristics of the spherical lithosphere are also reviewed and discussed in connection with subduction tectonics

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

slab1 0 a three dimensional model of global subduction zone geometries 1 we describe and present a new model of global subduction zone geometries called slab1 0 an extension of previous efforts to constrain the two dimensional non planar geometry of subduction zones around the focus of large earthquakes slab1 0 describes the detailed non planar three dimensional geometry of approximately 85 of subduction zones worldwide while the model focuses on the detailed form of each slab from their trenches through the seismogenic zone where it combines data sets from active source and passive seismology it also continues to the limits of their seismic extent in the upper mid mantle providing a uniform approach to the definition of the entire seismically active slab geometry examples are shown for two well constrained global locations models for many other regions are available and can be freely downloaded in several formats from our new slab1 0 website http on doi gov d9arbs we describe improvements in our two dimensional geometry constraint inversion including the use of average active source seismic data profiles in the shallow trench regions where data are otherwise lacking derived from the interpolation between other active source seismic data along strike in the same subduction zone we include several analyses of the uncertainty and robustness of our three dimensional interpolation methods in addition we use the filtered subduction related earthquake data sets compiled to build slab1 0 in a reassessment of previous analyses of the deep limit of the thrust interface seismogenic zone for all subduction zones included in our global model thus far concluding that the width of these seismogenic zones is on average 30 larger than previous studies have suggested

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

the red chris porphyry copper gold deposit northern british columbia canada igneous phases alteration and controls of mineralization red chris is a late triassic porphyry cu au mo deposit in the stikinia island arc terrane in northern b c late triassic sedimentary and volcanic rocks of the stuhini group host a series of late triassic to early jurassic 204 198 ma diorite to quartz monzonite stocks and dikes the red chris deposit is hosted in the 204 ma red stock the largest 6 5 1 5 km and most altered intrusion in the area volcanic rocks approximately time equivalent with the stock are exposed 2 km to the southwest and west postmineral early and middle jurassic sedimentary rocks unconformably overlie the stuhini group and red stock to the south and southeast the composite red stock consists of multiple phases of crowded porphyries 30 65 plagioclase hornblende biotite phenocrysts including abundant premineral p1 leucodiorite multiple subphases of synmineral p2 quartz monzonite porphyries and volumetrically minor late mineral monzonite p3 and monzodiorite p4 porphyries the stock evolved from subalkaline to silica saturated alkalic composition with the mineral related p2 porphyries being high k calcalkalic and high sr y common septa of stuhini biotitic hornfels are entrapped within the stock minor postmineral weakly altered mafic dikes cut the stock the zone of 0 25 cu equiv cu au is 2 km long wsw ene and up to 650 m wide early a type quartz veins with disseminated bornite accompanied biotitic and k feldspar magnetite alteration which was coeval with p2 porphyries higher cu and au grades correlate in a general way with zones of more abundant a veins chlorite carbonate epidote actinolite replaced hornblende peripheral to biotitic alteration and chlorite overprinted much of the secondary biotite late alteration affected all porphyry phases and is subdivided into earlier sericite clay pyrite and later low sulfide carbonate clay hematite late sericite clay pyrite alteration sulfidized much of the primary bornite to chalcopyrite with or without pyrite and carbonate clay hematite alteration converted most magnetite to hematite highest cu au grades 2 cu equiv occur in and around the early and intermediate stage p2 porphyries zoning of cu au au cu ratios sulfides and quartz veins is centered and mostly symmetrical around a core of high grade cu au within and surrounding apices of p2 porphyry contact relationships confirm the close association of p2 porphyry phases with cu au zones of 50 ppm mo surround the highest grade cu au zone at depth west northwest and east northeast strike slip to oblique slip faults offset sulfide cu au and mo patterns several lines of evidence indicate 15 to 20 of southward tilt since the system formed due to glaciation oxidation is very thin and supergene enrichment negligible red chris was previously considered by most workers as an alkalic or hybrid alkalic deposit new chemical data on synmineral porphyry phases instead suggest high k calc alkalic composition similar to the monzonitic cu mo au class of porphyry deposits which includes bingham and bajo de la alumbrera red chris is also classified as an a vein type deposit due to strong control of higher grade cu au by a vein stockworks with abundant disseminated cu sulfides

modeling the equilibrium of tide dominated ebb tidal deltas 1 this study focuses on identifying physical mechanisms that lead to symmetric tide dominated ebb tidal deltas an idealized morphodynamic model is developed and analyzed to demonstrate that these deltas can be modeled as morphodynamic equilibria no evolving bathymetry it is assumed that the large scale alongshore tidal currents are small compared to the cross shore tidal currents that waves have shore normal incidence that the tidal velocity profile over the inlet is symmetric with respect to the midaxis and that the coriolis force can be ignored the modeled tidal hydrodynamics are characterized by an ebb jet during the ebb phase of the tide and a radial inflow pattern during flood two residual eddies are formed the mechanism behind these current patterns is explained with vorticity concepts the modeled bottom patterns are similar to those of observed symmetric tide dominated ebb tidal deltas in the center of the tidal inlet an ebb dominated channel is observed that branches further offshore into two flood dominated channels at the end of the ebb dominated channel a shoal is present varying the tidal prism the width of the tidal inlet the wave height and the bed slope coefficient in the sediment transport formulation within the range of observed values leaves these patterns qualitatively unchanged however the exact extent and shape of the modeled deltas are affected by these parameters compared to observations the modeled ebb tidal delta is smaller and the ebb dominated channel is shorter the observed exponent in the power law relation between sand volume of the delta and the tidal prism is recovered and explained with the model

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

geological and isotopic evidence for magmatic hydrothermal origin of the ag pb zn deposits in the lengshuikeng district east central china the lengshuikeng ore district in east central china has an ore reserve of 43 mt with an average grade of 204 53 g t ag and 4 63 pb zn based on contrasting geological characteristics the mineralization in the lengshuikeng ore district can be divided into porphyry hosted and stratabound types the porphyry hosted mineralization is distributed in and around the lengshuikeng granite porphyry and shows a distinct alteration zoning including minor chloritization and sericitization in the proximal zone sericitization silicification and carbonatization in the peripheral zone and sericitization and carbonatization in the distal zone the stratabound mineralization occurs in volcano sedimentary rocks at 100 400 m depth without obvious zoning of alterations and ore minerals porphyry hosted and stratabound mineralization are both characterized by early stage pyrite chalcopyrite sphalerite middle stage acanthite native silver galena sphalerite and late stage pyrite quartz calcite the 34s values of pyrite sphalerite and galena in the ores range from 3 8 to 6 9 with an average of 2 0 the c o isotope values of siderite calcite and dolomite range from 7 2 to 1 5 with an average of 4 4 v pdb and from 10 9 to 19 5 with an average of 14 8 v smow respectively hydrogen oxygen and carbon isotopes indicate that the hydrothermal fluids were derived mainly from meteoric water with addition of minor amounts of magmatic water geochronology employing la icp ms analyses of zircons from a quartz syenite porphyry yielded a weighted mean 206pb 238u age of 136 3 0 8 ma considered as the emplacement age of the porphyry rb sr dating of sphalerite from the main ore stage yielded an age of 126 9 7 1 ma marking the time of mineralization the lengshuikeng mineralization classifies as an epithermal ag pb zn deposit

porphyry deposits of the northwestern cordillera of north america edited by t g schroeter special volume 46 canadian institute of mining metallurgy and petroleum montreal 1995 888 pp canadian 95 plus 15 handling isbn 0 919086 56 x

jurassic epithermal deposits in the toodoggone river area northern british columbia examples of well preserved volcanic hosted precious metal mineralization epithermal gold silver deposits in the toodoggone river area are hosted by early jurassic high k trachyandesite and trachydacite volcanic rocks that erupted during two major cycles spanning roughly 7 m y volcanism and related plutonic activity is intimately associated with the structural development of an elongate volcano tectonic depression in which extensional fracture zones confine the epithermal deposits younger sedimentary rocks overlay and protected the deposits from erosion gold and silver in the toodoggone district occur most commonly in quartz veins associated with adularia sericite and calcite locally gold barite veins cut volcanic rocks that are pervasively replaced by varying proportions of fine grained silica dickite and natroalunite fluid inclusions in quartz from most precious metal vein deposits are typical of epithermal environments they contain low temperature dilute hydrothermal fluids of predominantly meteoric origin t h 300 degrees c and 30 equiv wt nacl light stable isotope analyses show marked 18 o enrichment in the volcanic rocks hydrothermally altered host rocks and mineralized vein quartz with adularia or sericite of about 8 per mil the isotopic composition of the hydrothermal fluid is calculated to be about delta 18 o 0 per mil these hydrothermal fluids are isotopically evolved mixtures derived from meteoric and magmatic waters with possible metamorphic input whole rock analyses of mainly fine grained quartz dickite mineral mixtures document the largest 18 o shifts with values up to 15 7 per mil this is interpreted to be due to lower temperatures and or the presence of significant quantities of magmatic fluids in these altered zones k ar age determinations on alunite from several zones of intensely acid leached rocks suggest that an early mineralizing episode apparently occurred around 190 ma or earlier during a depositional hiatus between the two major volcanic cycles this coincides with the uplift and cooling of several plutons k ar dates on adularia and sericite from precious metal bearing quartz veins some of which are from volcanic rocks of the upper cycle suggest that there was also a younger mineralizing event recent argon step heating dates indicate that the major gold silver deposits with adularia sericite range from 189 7 or 2 6 to 186 7 or 1 7 ma clark and williams jones 1991 this closely follows the latest stages of toodoggone volcanism and fault block subsidence a depth zoning model for mineralization illustrates the two types of epithermal regimes adularia sericite and acid sulfate gold barite in the extensive advanced argillic and argillicly altered zones at the al deposit represent high level near surface acid sulfate alteration formed on the flanks of a stratovolcano the advanced argillic altered zone at silver pond next to the major lawyers adularia sericite deposit represents a downfaulted acid sulfate outflow i e the upper portion of the lawyers hydrothermal system the lawyers deposit and most of the other occurrences are adularia sericite type deposits formed at slight depth these deposits occur in grabens or half grabens in an extensional fault regime that created the central toodoggone depression nested within the broader volcanic belt

morphodynamics of ebb tidal deltas a model approach abstract the results of 2dh numerical models of the frisian inlet located in the dutch wadden sea are discussed to gain further knowledge about the physical mechanisms causing the presence of both ebb tidal deltas and of channels and shoals in tide dominated inlet systems a hydrodynamic model extended with sediment transport formulations was used to verify earlier conceptual models that deal with ebb tidal delta characteristics the model does not confirm their hypothesis concerning the observed spatial asymmetry of ebb tidal deltas and suggests that long term morphological simulations are needed to understand this aspect furthermore the model indicates that the initial formation of the ebb tidal delta is mainly due to convergence of the tidally averaged sediment flux related to residual currents whilst the net sediment transport in the basin is mainly caused by tidal asymmetry a second model accounting for feedbacks between tidal motion and the erodible bottom was used to simulate the long term bathymetric evolution of the frisian inlet under fair weather conditions this model reproduces the gross characteristics of the observed morphology the presence of a double inlet system with two distinct ebb tidal deltas having different sizes and the presence of channels and shoals the role of the engelsmanplaat a consolidated shoal in the middle of the frisian inlet was not found to be crucial for the morphodynamic stability of this inlet system

strength of slab inferred from the seismic tomography and geologic history around the japanese islands i analyze the seismic tomography around the japanese islands to elucidate the present slab morphology a simple conversion from the high speed to the temperature anomaly is done based on the recent study of the conversion coefficient from the velocity to the thermal anomaly and on the study of the relation between the seismicity and the temperature in the slab i find recognizable amount of cold temperature anomalies under the subducting slab this suggests a rather continuous slab throughout the mantle consistent with the results of many recent numerical models however there still is a gap in the slab or diluted slab under the transition zone to understand this i construct a simple half kinematic model of subduction zone in which a byerlee s type yield stress and the depth independent yield stress are assumed taking into account the geologic history around the japanese islands i find that the slab morphology similar to the tomographic image is obtained when the yield stress is o 100 mpa the present study shows that the detailed studies of seismic tomography and the tectonic history of the surveyed area can provide the constraints on the slab dynamics

carbon and oxygen isotopic covariations in hydrothermal calcites isotopic covariations of carbon and oxygen in hydrothermal calcites are quantitatively modeled in terms of the following three mixing processes 1 mixing between two different fluids which leads to the precipitation of calcite 2 mixing between fluid and rock a calcite precipitation due to fluid rock interaction b secondary alteration of primary calcite by interaction with a subsequent fluid the models are derived from mass balance equations a distinction among the three mixing processes can be made on a 13c vs 18o diagram which places important constraints on the genesis of hydrothermal mineralization the variables which control the ultimate isotopic composition of hydrothermal calcites include the composition of the initial fluid and the wallrock temperature and dissolved carbon species owing to significant temperature dependent fractionation effects during equilibrium precipitation of calcite from a hydrothermal fluid the mixing processes may be distinguished by telltale patterns of isotopic data in 13c vs 18o space in particular caution must be exercised in postulating the fluid mixing as the cause for mineral deposition this is demonstrated for hydrothermal pb zn deposits in the western harz mountains germany a positive correlation between 13c and 18o values is observed for calcites from the bad grund deposit in the upper harz two sample profiles through calcite veins show similar correlations with the lowest values at the center of the veins and the highest values at the vein margins because the correlation array has a greater slope than for calcite precipitation at equilibrium in a closed system and because fluid mixing may not proceed perpendicular to the vein strike it is assumed that a fluid rock interaction is responsible for the observed correlation and thus for the precipitation of calcite a deep seated fluid is inferred with a 13c value of 7 and a 18o value of 10 as well as h2co3 as the dominant dissolved carbon species precipitation temperatures of the calcites are estimated to be about 280 170 c quite different isotopic distributions are observed for calcites from the st andreasberg deposit in the middle harz an alteration model is suggested based mainly on the isotopic distribution through a calcite vein in addition to a primary fluid which has the same isotopic composition as that in the bad grund deposit and thus seems to be responsible for the precipitation of calcite associated with sulfides an evolved hco 3 dominant subsurface fluid with 13c about 20 15 and 18o 0 is deduced to alter the primary calcite at low temperatures of 70 40 c

macflincor and its application to fluids in archean lode gold deposits abstract macflincor was developed to process laboratory data gathered on fluid inclusions and to calculate isochores for geologically important fluids composed of h2o c02 ch4 nacl and n2 within the program interactive diagrams are available to describe those chemical systems which cannot be adequately constrained numerically the user can choose from various published equations of state describing fluid behavior and can easily compare the results obtained by using different equations the program once the basic fluid parameters have been established allows the data to be used to determine the p t trapping conditions to evaluate possible pressure corrections and to compare different depths of formation based on the pressure calculations and given geothermal gradients for illustrative purposes macflincor has been utilized here to constrain different physical chemical parameters of fluid inclusions trapped in ore related quartz veins and breccias of archean lode gold deposits in western australia inferred pressures from individual deposits show a wide range of values which may be due to post entrapment modifications and or observational uncertainties including estimation of liquid vapor ratios

coupling bedform roughness and sediment grain size sorting in modelling of tidal inlet incision abstract a key problem in the decadal morphodynamic modelling of tidal inlet system is on the evolution of the inlet channels especially the unrealistic channel incision the present study attempts to couple two processes including the bedform roughness and sediment grain size sorting in the two dimensional depth averaged process based model to solve the problem based on the comparison of the modelling results and relevant field observations in the dutch wadden sea it is suggested that bedform roughness height predictor is a useful tool for determining spatial and temporal heterogeneous bed frictions within tidal channels bedform roughness is dominated by dune roughness in order to represent the memory of old bedforms a relaxation time method was implemented the corresponding large relaxation time 2 m2 tidal periods smooths the tidal variations of dune roughness and makes it respond to hydrodynamic changes on a longer time scale when decadal morphological modelling is carried out the model performance can be significantly improved by introducing either bedform dune roughness predictor or sediment sorting processes the mechanisms are twofold first in the deep channels where flow velocities are high large dunes develop and cause large bed drag coefficients second coarser bed sediments within the channel area induced by sorting prevent the channel incision if both effects are coupled in the morphodynamic modelling the inlet channel incision is further controlled which is not just a result of the linear superposition of both effects because sorting can further promote the development of dunes within the deep channels

application of the model of small scale convection under the island arc to the ne honshu subduction zone 1 we compare the results of 2 d 3 d time dependent models of small scale convection under the island arc with the geophysical and geologic data observed in the ne honshu subduction zone northeast japan assuming that the temperature anomalies have a close connection with the seismic anomalies we may constrain the geometry of the low viscosity wedge lvw overlying the slab which may be produced by the water dehydrated from the subducting slab our preferred model predicts step like low velocity anomalies above the subducting slab rather than smooth anomalies subparallel to the subducting slab since the shallow nature of the lvw is required for the small scale convection to occur at the back arc end of the lvw a movement of cold plumes generated at the back arc end of the lvw may be related to a possible migration of volcanism from back arc to volcanic front side to be consistent with the observation which may suggest the migration rate of 2 cm yr models require weak viscous couplings between the mantle wedge and the underlying subducting slab whose speed of subduction is 10 cm yr three dimensional models showing 3 d temperature variation consist of fairly continuous and strong temperature anomalies several hundreds of degrees under the volcanic front and weak finger like temperature anomalies several tens of degrees behind them which are similar to the pattern of the seismic tomography the time dependent behavior of the temperature field shows that the pattern of fingers flip flops with a timescale equal to the ratio of the horizontal extent of the lvw to the migration speed of cold plumes this change of pattern of fingers may have an important implication for understanding the past distribution of volcanism further studies related to 1 the detailed morphology of the low velocity zone above the subducting slab 2 the spatial and temporal evolution of volcanism and 3 the dynamic 3 d model studies which self consistently determine the distribution of water volatiles and the resultant weak rheology are important for checking the validity of our model or developing alternative models

the influence of rheological weakening and yield stress on the interaction of slabs with the 670 km discontinuity results of high resolution seismic tomography showing subducting slabs deflected in the transition zone and thickened in the lower mantle seem to call for slab material weaker than inferred from mineral physics deformation mechanisms a possible mechanism suggested by several authors could be the weakening due to grain size reduction which should occur in the cold portion of fast slabs after an exothermic phase transition at a depth of 400 km since the amount of weakening as well as the rate of subsequent strengthening due to the grain growth are not precisely known we present here a parametric study of slab behavior in the transition zone and upper part of the lower mantle we simulate a subducting slab in a two dimensional 2 d cartesian box in the numerical model with composite rheology including diffusion creep dislocation creep and a general stress limiting rheology approximating peierl s creep we concentrate on two rheologic effects the dynamic effect of slab weakening due to grain size reduction at the phase boundary and the effect of yield stress of stress limiting rheology the effect of trench migration on slab deformation is also included in our study results show that the slab ability to penetrate into the lower mantle is not significantly affected by a trench retreat in the absence of grain size weakening however in case of a 4 cm yr trench retreat grain size weakening provides a viable mechanism to deflect the slab in the transition zone provided that stress limiting deformation mechanism would limit the effective viscosity outside the areas of grain size weakening to about 10 24 pa s 2002 elsevier science b v all rights reserved

shear wave splitting beneath the southwestern kurile arc and northeastern japan arc a new insight into mantle return flow 1 shear wave splitting in the southwestern part of the kurile arc and the northeastern ne japan arc is investigated using the waveforms from local earthquakes for both arcs observed shear wave splitting shows clear evidence for a striking rotation of fast direction across the arc suggesting the different feature of anisotropy between the fore arc and back arc sides trench parallel fast directions are observed in the fore arc side which is consistent with the anisotropy expected from the deformation of the b type olivine fabric as well as the anisotropy in the slab fast directions observed in the back arc side show approximately e w and ese wnw in the ne japan arc and n s in the southwestern kurile arc which are characterized by the local maximum dip direction of the subducted pacific plate not by the direction of plate convergence this relationship suggests that the direction of the mantle return flow is governed by the local slab geometry

subduction of oceanic asthenosphere a critical appraisal in central alaska song and kawakatsu 2012 have shown that the sub slab fast splitting pattern observed in most subduction zones can be a direct consequence of subduction of the oceanic asthenosphere that has strong radial anisotropy this model not only explains the non intuitive trench parallel splitting pattern in most of subduction zones but also predicts the trench normal behavior fast polarization direction sub parallel to the absolute plate motion of the incoming plate observed in several shallow subduction zones the general validity of such a scenario is crucial to fundamental understandings of the development of mantle anisotropy in sub lithosphere or and sub slab conditions the nature and formation of oceanic asthenosphere as well as the flow pattern and mass transport near subduction zones to validate this scenario we examine sks splitting patterns observed across the fore arc in central alaska here the fast splitting direction varies from plate motion sub parallel near the trench to mostly trench parallel beyond the 100 km slab isodepth contour while being strongly variable in between after taking into account the rotation of anisotropy symmetry in the oceanic asthenosphere with respect to the local plate motion obliquity and down dip variations in the slab dip we reproduce a general 90 degree switch in fast splitting direction as well as the back azimuth dependent splitting pattern across the entire fore arc the current validation further augments the idea that apart from anisotropy in the mantle wedge and the subducting slab subduction of the oceanic asthenosphere is likely to be the dominant source of seismic anisotropy in central alaska and potentially in many subduction zones furthermore this result also provides alternative views to models of seismic anisotropy in the mantle wedge and on the length scale in which the 3d mantle flow may be important

evolution of mantle structure beneath the northwest pacific evidence from seismic tomography and paleogeographic reconstructions 1 plate motions and subducting slab morphology are intricately connected and through the integration of seismicity tomographic images and relative plate motions the evolution of mantle structure can be interpreted tomographic images of p wave shear wave speed and bulk sound speed perturbations of the northwest pacific region have been interpreted to define the extent and geometry of the subducting pacific plate we have found that the subducted pacific plate beneath the japan and kurile arcs is coherent but is very complex at the junction of the two arcs near the hokkaido corner as the slab subduction angle decreases from north to south while the slab thickens the pacific slab beneath the japan arc is slightly thinner and subducting through the upper mantle at a less steep angle than the slab beneath the kurile arc as the slab reaches the 660 km discontinuity it becomes stagnant and lies in a horizontal position on top of the transition zone both beneath the izu and japan arcs in contrast the slab beneath the kurile arc is subducting at a steeper angle and penetrates through the transition zone into the lower mantle the difference in slab morphology appears to be due to a combination of change in dip of the subducting plate and the convergence velocity of the pacific plate along the margin a new paleogeographic reconstruction of northeast asia was assembled to evaluate the plate motions that could explain the foundation of the current slab morphology the plate reconstruction was based on euler pole motions of the pacific philippine amurian okhotsk and north american plates relative to stable eurasia plate the new tectonic model illustrates the collision of the japan and kurile arcs the opening of the kurile basin disparity in pacific plate velocities along the arc and different rates of trench retreat along the izu japan and kurile segments of the western pacific margin the plate motion model was interpreted in conjunction with the physical properties of the mantle imaged with the p wave and joint tomography to assess the evolution of the pacific plate morphology since the mid miocene and to provide constraints on the plausible plate motions in the region

slab2 a comprehensive subduction zone geometry model subduction zones are home to the most seismically active faults on the planet the shallow megathrust interfaces of subduction zones host earth s largest earthquakes and are likely the only faults capable of magnitude 9 ruptures despite these facts our knowledge of subduction zone geometry which likely plays a key role in determining the spatial extent and ultimately the size of subduction zone earthquakes is incomplete we calculated the three dimensional geometries of all seismically active global subduction zones the resulting model called slab2 provides a uniform geometrical analysis of all currently subducting slabs