reconciling subduction dynamics during tethys closure with large scale asian tectonics insights from numerical modeling we use three dimensional numerical models to investigate the relation between subduction dynamics and large scale tectonics of continent interiors the models show how the balance between forces at the plate margins such as subduction ridge push and far field forces controls the coupled plate margins and interiors evolution removal of part of the slab by lithospheric break off during subduction destabilizes the convergent margin forcing migration of the subduction zone whereas in the upper plate large scale lateral extrusion rotations and back arc stretching ensue when external forces are modeled such as ridge push and far field forces indentation increases with large collisional margin advance and thickening in the upper plate the balance between margin and external forces leads to similar convergent margin evolutions whereas major differences occur in the upper plate interiors here three strain regimes are found large scale extrusion extrusion and thickening along the collisional margin and thickening only when negligible far field forces ridge push and larger far field forces respectively add to the subduction dynamics the extrusion tectonics develops a strong asymmetry toward the oceanic margin driven by large scale subduction with no need of preexisting heterogeneities in the upper plate because the slab break off perturbation is transient the ensuing plate tectonics is time dependent the modeled deformation and its evolution are remarkably similar to the cenozoic asian tectonics explaining large scale lithospheric faulting and thickening and coupling of indentation extrusion and extension along the asian convergent margin as a result of large scale subduction process

the dynamics of extrusion tectonics insights from numerical modeling to elucidate the dynamics of extrusion tectonics i investigate the relation between subduction processes and intraplate deformation three dimensional numerical models of subducting upper plate systems show that subduction of a heterogeneous buoyancy slab that is hosting continental and oceanic lithosphere causes the retreat of the oceanic trench and the localization of deformation in the back arc similar trench evolution is found when the subducting slab partially detaches from the impinging continent however deformation in the upper plate interiors widens with indentation plastic yielding and rotation of a large block extruding laterally toward the retreating margin indentation stresses are consequence of the partial slab breakoff at depth and vanish when the detached slablet reaches the mantle transition zone resulting in transient extrusion tectonics the distance to which indentation deformation propagates depends on the ability of subducting lithosphere to propagate stress laterally and is linear with the lithospheric strength while in the stretching back arc the plate deformation and the underlying mantle flow are coupled they are uncoupled in the extrusion tectonics where mostly stresses propagated through the margin drive rotations the potential role of these diverse subduction processes in the eastern mediterranean is discussed suggesting that different mechanisms likely drive the tectonics of this area

constraints on the lateral strength of slabs from three dimensional dynamic flow models if the viscosity of subducted lithosphere is described purely by temperature and pressure it should remain considerably more viscous than the surrounding material as it descends through the upper mantle many dynamic models of the long wavelength geoid associated with slabs require an increase in viscosity from the upper to the lower mantle but assume the perturbation to the lateral viscosity structure arising from the slabs themselves can be ignored previous studies indicate that strong and localized viscosity variations should have a dramatic influence on the geoid we present 3d finite element models of the regional geoid of the western pacific subduction zones slab buoyancies and viscosities are defined using the distribution of seismicity the geoid is very sensitive to the lateral strength of the slab very viscous slabs penetrating a low viscosity mantle generate significant 10 50 m long wavelength geoid lows opposite to the geoid high which is observed over slabs to obtain a geoid high comparable to that observed the lower mantle viscosity must be 60 200 times greater than the upper mantle viscosity and the slab must be in contact with the lower mantle these strict requirements suggest that slabs have been weakened and cannot act as stress guides from the deep mantle to the surface

back arc strain in subduction zones statistical observations versus numerical modeling 1 recent statistical analysis by lallemand et al 2008 of subduction zone parameters revealed that the back arc deformation mode depends on the combination between the subducting vsub and upper vup plate velocities no significant strain is recorded in the arc area if plate kinematics verifies vup 0 5 vsub 2 3 cm a in the hs3 reference frame arc spreading shortening occurs if vup is greater lower than the preceding relationship we test this statistical law with numerical models of subduction by applying constant plate velocities far away from the subduction zone the subducting lithosphere is free to deform at all depths we quantify the force applied on the two converging plates to sustain constant surface velocities the simulated rheology combined viscous non newtonian and brittle behaviors and depends on water content the influence of subduction rate vs is first studied for a fixed upper plate after 950 km of convergence steady state slab pull the transition from extensional to compressive stresses in the upper plate occurs for vs 1 4 cm a the effect of upper plate velocity is then tested at constant subduction rate upper plate retreat advance with respect to the trench increases extension compression in the arc lithosphere and increases decreases the subducting plate dip our modeling confirms the statistical kinematic relationship between vsub and vup that describes the transition from extensional to compressive stresses in the arc lithosphere even if the modeled law is shifted toward higher rates of upper plate retreat using our set of physical parameters e g 100 km thick subducting oceanic plate and short term simulations our results make valid the choice of the hs3 reference frame for assessing plate velocity influence on arc tectonic regime the subduction model suggests that friction along the interplate contact and the mantle stokes reaction could be the two main forces competing against slab pull for upper mantle subductions besides our simulations show that the arc deformation mode is strongly time dependent

a new hypothesis on parameters controlling the formation and size of porphyry copper deposits implications on thermal gradient of subducted oceanic slab depth of dehydration and partial melting along the kerman copper belt in iran abstract porphyry copper deposits in the tethyan metallogenic belt broadly occur in early mesozoic late mesozoic paleogene and neogene within a wide range of tectonic setting these deposits in iran often occur within the cenozoic urumieh dokhtar magmatic arc udma mostly in the kerman porphyry copper belt kpcb located in the southeast of this arc these deposits along the udma are mainly associated with the granitoids of miocene age 18 82 9 20 ma in this research geochemical characteristics pb and sr isotopes tectonic environment oxidizing conditions and source of magmas for the most important porphyry copper deposits of the udma have been compared and discussed on the basis of trace element discrimination diagrams the kerman belt granitoids formed in a volcanic arc type setting whereas the jebal barez granitoids seem to have formed in a different tectonic setting the eu eu of granitoids from the kerman belt are greater than 1 2 representing the oxidizing conditions for the crystallization of the granitoid magma whereas jebal barez granitoids were formed under reducing conditions the sr y ratio for kerman granitoids is greater than 60 indicating adakitic affinities and la yb n for these granitoid rocks is between 17 and 35 suggesting that their parental magma was generated from a deep garnet bearing source based on 87sr 86sr i values for kerman belt granitoids of 0 704 0 705 it is suggested that parental magmas originated from a subducted oceanic slab in the sarcheshmeh porphyry copper deposit the thermal gradient of the oceanic slab at depth was less than 9 c km warm cold slab the oceanic slab was highly hydrated and more than 80 of the water within the oceanic slab was released in the deep zone of the sub arc region at a depth of 110 130 km under saturated conditions the oceanic slab partially melted 20 25 a large volume of magma and magmatic water formed sarcheshmeh as a giant porphyry copper deposit in the iju deposit a small porphyry copper deposit the oceanic slab was slightly hydrated and minor water was released at the depth of 110 130 km a small volume of magma was formed due to water undersaturated melting conditions finally a new hypothesis is introduced regarding the roles of down dip thermal gradient of the oceanic slab water content depth of dehydration and degree of partial melting of oceanic slab which are important controls on the formation and size of the porphyry copper deposits within continental volcanic arcs

the age petrogeneis and tectonic significance of the frontenac formation basalts northern new hampshire and western maine within plate basalts are present across the connecticut valley gaspe trough in new england and canada proposed mechanisms for the extensional magmatism include back arc basin extension slab breakoff and extensional collapse the age and composition of the bimodal frontenac formation of northern new england and southern quebec has bearing on the topic we analyzed zircons from the meta felsic rocks of the formation and determined a silurian age of 432 8 ma we also analyzed the frontenac rocks for major and trace elements and compared their compositions to the other mafic rocks along strike in the connecticut valley gaspe trough these include the comerford intrusive suite and the standing pond volcanic member of the waits river formation of vermont the silurian chaleur group and the early devonian dalhousie group of new brunswick and the gaspe peninsula and to the piscataquis belt rocks of northern maine all these rocks are post taconic within plate tholeiites that span an age range from 432 ma frontenac formation to 419 ma comerford intrusive suite in spite of their similar tectonic setting subtle differences in trace element compositions are evident indicating a multiplicity of sources in the production of the siluro devonian magmas ce yb versus la ta values suggest that the frontenac magmas were derived from spinel peridotite sources in the asthenospheric mantle we suggest that slab rollback and back arc basin extension permitted asthenospheric mantle upwelling to the spinel peridotite stability field causing the frontenac partial melting event at depths as low as 35 km sediments of the frontenac formation were deposited as turbidite successions into a developing trough resulting from extension the coeval influx of sediment and intrusion of basalt produced a sediment sill complex because the upward migration of the basaltic magmas was hindered by the rapidly thickening sediment overburden subsequently slab breakoff may have opened an asthenospheric window generating the younger within plate magmas that occurred from 425 to 418 ma across the connecticut valley gaspe trough

the effect of rheological approximations in 3 d numerical simulations of subduction and collision abstract subduction and collision zones evolve differently from one another due to different rheological properties different amounts of regional isostatic compensation and the different mechanisms by which forces are applied to the convergent plates the rheology of mantle and lithosphere is known to have the largest influence on the dynamics of subduction and continental collision however previous 3 d geodynamic models of subduction collision processes have used various rheological approximations making their results difficult to compare since there is no clear understanding on the extent of these approximations on the dynamics here we test the effect of rheological approximations in a geometrically simplified 3 d model in which the dynamics of subduction and collision is entirely driven by slab pull i e free subduction the results exhibit a wide range of behaviors depending on the rheological law employed from linear viscous lv to temperature dependent visco elasto plastic vep rheology that takes into account both diffusion and dislocation creep rheological approximations exert a strong effect on slab morphology trench migration rates and topography in the upper plate for example we find that slab dynamics varies drastically between end member models in lv approximations slabs do not break off but instead buckle at the transition zone the dynamics is dominated by low strain rates and diffuse stresses and topography is controlled by lateral extrusion of material which homogenizes amplitudes in the upper plate in simulations with non linear vep rheology slab break off occurs at the corners of the indenting continent opening of a back arc basin is fast and topography has a laterally heterogenous distribution of amplitudes opening of a back arc basin is observed only in simulations with non linear vep rheology when the rheology is approximated with multiple discrete layers the dynamics also resembles more the non linear vep case

asymmetric dynamics at subduction zones derived from plate kinematic constraints abstract the lithospheric sinking along subduction zones is part of the mantle convection therefore computing the volume of lithosphere recycled within the mantle by subducting slabs quantifies the equivalent amount of mantle that should be displaced for the mass conservation criterion the rate of subduction is constrained by the convergence rate between upper and lower plates and the motion of the subduction hinge h that may either converge or diverge relative to the upper plate here starting from the analysis of the slab hinge kinematics we evaluate the subduction rate at 31 subduction zones worldwide useful to compute volumes of sinking lithosphere into the mantle our results show that 190 km3 yr and 88 km3 yr of lithospheric slabs are currently subducting below h divergent and h convergent subduction zones respectively we also propose supporting numerical models providing asymmetric volumes of the subducted lithosphere using the subduction rate instead of plate convergence as boundary condition furthermore h divergent subduction zones appear to be coincident with subductions having westward directed slabs whereas h convergent subduction zones are mostly compatible with those that have eastward to northeastward directed slabs on the basis of this geographical polarity our lithospheric volume estimation gives 214 km3 yr and 88 km3 yr of subducting lithosphere respectively this entails that w directed subduction zones contribute more than twice in lithospheric sinking into the mantle with respect to e to ne directed ones in accordance with the conservation of mass principle this volumetric asymmetry in the mantle suggests a displacement of 120 km3 yr of mantle material from west to east providing a constraint for global asymmetric mantle convection

the role of the miocene to pliocene transition in the eastern mediterranean extrusion tectonics constraints from numerical modelling abstract in the eastern mediterranean extension in the aegean sea and lateral anatolian extrusion are contrasting and seemingly unrelated examples of continental tectonics developed during tethys closure we use numerical modelling to investigate the relation of the tectonic regimes to the underlying subduction dynamics during subduction land locking and slab break off we find that the tectonics has a two phase evolution 1 an incipient phase with back arc spreading and transcurrent shear zone formation and lateral escape of a block in the upper plate interiors and 2 a reorganisation phase during which the transcurrent shear zone propagates and the extruding block internally stretches progressively separating from the opening back arc domain while the collisional margin reactivates into a transform plate boundary the regimes are explained by two concurring plate margin processes 1 mantle tractions following the subduction and retreat of a land locked oceanic slab and 2 stresses propagated through rigid indentation upon slab break off these have different spatial and temporal fingerprints long term trench retreat and convergence slow down follow continental subduction while stresses localise atop the newly formed slab edge upon slab break off fastening up margin reorganisation driving faulting and extrusion yet fading rapidly forcing local tectonics rearrangement a comparison with the eastern mediterranean allows an explanation for the time evolution of the tectonics here and emphasises the role of the miocene to pliocene tectonics transition previously not considered this offers a novel key to the dynamics of the enigmatic evolution of this area

new evidence for dislocation creep from 3 d geodynamic modeling of the pacific upper mantle structure laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth s upper mantle diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes each mechanism has very different and important consequences on the dynamical evolution of the mantle and the development of mantle fabric due to the lack of in situ observations it is unclear which deformation mechanism dominates in the upper mantle although observed seismic anisotropy in the upper mantle suggests the presence of dislocation creep we examined the thermo mechanical erosion of the lithosphere by thermal boundary layer instabilities in 3 d dynamical models this study demonstrates that the seismically derived thermal structure of the pacific lithosphere and upper mantle imposes an important constraint on the upper mantle deformation mechanism the predominant deformation mechanism in the upper mantle is dislocation creep consistent with observed seismic anisotropy the acceptable activation energy range of 360 540 kj mol is consistent with although at the lower end of those determined from laboratory studies

a theory for the tropical tropospheric biennial oscillation the key questions of how the tropospheric biennial oscillation tbo maintains the same phase from northern summer in south asia to southern summer in australia and how the reversed phase can last through three locally inactive seasons to the next monsoon are studied by a simple tropical atmosphere ocean land model the model has five boxes representing the south asian and australian monsoon regions and the equatorial indian and western and eastern pacific oceans the five regions interact with each other through the sst monsoon evaporation wind monsoon walker circulation and wind stress ocean thermocline feedbacks a biennial oscillation emerges in a reasonable parameter regime with model sst and wind variations resembling many aspects of the observed tbo warm sst anomalies ssta in july in the equatorial indian ocean cause an increase of surface moisture convergence into south asia leading to a stronger monsoon the monsoon heating on one hand induces a westerly wind anomaly in the indian ocean and on the other hand intensifies a planetary scale east west circulation leading to anomalous easterlies over the western and central pacific the westerly anomaly over the indian ocean decreases the local sst primarily by evaporation wind feedback the easterly anomaly in the central pacific causes a deepening of the ocean thermocline in the western pacific therefore increasing the subsurface and surface temperatures in addition a modest easterly anomaly in the western pacific opposes the seasonal mean westerlies so evaporation is reduced these effects overwhelm those of the cold zonal advection and anomalous upwelling the net result is warm ssta persisting in the western pacific through northern fall leading to a stronger australian monsoon meanwhile the warming in the western pacific also induces a stronger local walker cell and thus a surface westerly anomaly over the indian ocean this westerly anomaly helps the cold ssta to persist through the succeeding seasons leading to a weaker asian monsoon in the following summer during northern winter the westerly anomaly associated with the stronger australian monsoon through anomalous ocean downwelling and reduction of evaporation when the seasonal mean wind is easterly reinvigorates the warm ssta in the western pacific which has been weakened by the slow cold advection from the eastern pacific this further intensifies the eastern walker cell and helps to keep the eastern pacific cold the authors theory indicates that the tbo is an inherent result of the interactions between northern summer and winter monsoon and the tropical indian and pacific oceans thus it is an important component of the

role of indian ocean warming in the development of philippine sea anticyclone during enso 1 the anomalous low level anticyclone near the philippines and suppressed convection over the western pacific associated with the mature warm phase of el nino southern oscillation enso have been suggested as important elements in the interaction between enso and the east asian monsoon we examined the causes of these anomalies in the circulation and convection using a newly developed linear baroclinic model that includes interactive moist processes of the cumulus convection and surface heat fluxes a conventional version of the linear model forced by prescribed heating indicates that the diabatic cooling due to suppressed convection over the maritime continent generates the philippine sea anticyclone from a series of the moist linear model experiments we found that the modest warming of the indian ocean in addition to the strong warming in the central eastern pacific and weak cooling in the western pacific is significant to suppress the convection over the maritime continent observed data also show a coincidence of the development between the philippine sea anticyclone indian ocean warming and the ascending motion over the indian ocean supporting the model results the above results indicate that the atmosphere ocean system in the indian ocean may be one of important factors to improve predictability of the east asian climate during enso

maintenance of northern summer stationary waves in a gcm abstract the maintenance of northern summer stationary waves is studied with data from a 15 year integration of the general circulation model gcm experiment performed at the geophysical fluid dynamics laboratory the model has relatively high resolution rhomboidal 30 wavenumbers 9 vertical levels and simulates the summertime stationary waves reasonably well a steady linear baroclinic model is used to understand the various forcing mechanisms for the northern summer stationary waves the linear model response to global diabatic heating is found to play a dominant role in maintaining the summertime stationary waves in the gcm especially in the subtropics this response to diabatic heating shows a baroclinic structure in the vertical with a node at about 0 5 on the other hand stationary nonlinear interaction terms are found to be largely responsible for the extratropical equivalent barotropic stationary wave features it is hypothesized that this nonlinear interaction is a result of the therm

continental collision and slab break off a comparison of 3 d numerical models with observations abstract conditions and dynamics of subduction collision and subsequent 3 d slab break off and slab tear propagation are quantified for the first time using fully dynamic numerical models model results indicate that collision after the subduction of old strong subducting oceanic slab leads to slab break off at 20 25 myr after the onset of continental collision and subsequently a slab tear migrates more or less horizontally through the slab with a propagation speed of 100 150 mm yr in contrast young weak oceanic slabs show the first break off already 10 myr after continental collision and can experience tear migration rates up to 800 mm yr slab strength plays a more important role in the timing of slab break off and the speed of a propagating slab tear than negative slab buoyancy does slab break off is viable even for slabs that are supported by the viscosity jump and phase change between the upper and lower mantle the density of the oceanic slab and the subducting continental block is important for the amount of continental subduction and the depth of slab break off a 40 km thick continental crust can be buried to depths greater than 200 km although this maximum depth is significantly less for younger or very weak slabs or thicker continental crust slab break off typically starts at a depth of 300 km mostly independent of mantle rheology but like continental crustal burial can be shallower for young or buoyant plates our 3 d models illustrate how due to the difference in necking in 2 d and 3 d break off has an intrinsic small preference to start as a slab window within the slab s interior rather than as a slab tear at the slab edge however any significant asymmetry in the collision setting e g earlier collision at one end of the subduction zone would override this and leads to slab tearing starting near one edge of the slab these results put important new constraints on the dynamics of the collision and subsequent slab break off for modern collision belts for a proposed timing of the initial arabia eurasia collision at 35 ma break off of the 200 myr old neo tethys slab is unlikely to have occurred before 15 10 ma furthermore our results illustrate that shallow early break off of weak slabs provides a viable explanation for the absence of blueschists and ultra high pressure metamorphism in the precambrian geological record

the formation and evolution of the east china sea shelf basin a new view abstract back arc basins and the related subduction systems have been extensively studied however back arc basins exhibiting episodic jumps of extension centers by the subduction of different ocean slabs are poorly known the east china sea shelf basin ecssb comprises two eastward younging subparallel depression zones and its formation and evolution is accompanied by a complicated subduction history and regional tectonic events offer an excellent opportunity to decipher the various geological features of back arc basins here we review the tectonic and sedimentary features of the subbasins in the ecssb and its adjacent regions and then reconstruct the evolution of the sedimentary paleogeography the west depression zone wdz of the ecssb experienced rifting in the late cretaceous during the subduction of the izanagi plate at the eastern continental boundary in the northern wdz the changjiang depression was mainly dominated by fluvial to lacustrine deposits this depression experienced strong compression characterized by folds and erosion during the transition from a synrift to postrift setting at the end of the paleocene then another compression event occurred that resulted in extensive folds and uplift accompanied by a large scale alluvial fan in the eastern changjiang depression coinciding with the subparallel subduction of the izanagi pacific ridge in the early eocene however the lishui jiaojiang sag characterized by diffuse extension rather than focused rifting in its late rifting period this sag was mainly covered by paralic to marine deposits and experienced extensive erosion caused by tilted sequences from the late eocene to oligocene which shared the same characteristics as basins around the taiwan region it is widely accepted that the formation and evolution of basins around taiwan were controlled by the evolving of the south china sea scs and the related regional tectonics considering the eastward extent of scs it would seem that the southern ecssb was part of the passive margin of scs accordingly the southern ecssb might be significantly influenced by the scs the east depression zone edz commenced rifting in approximately the middle eocene as inferred from the absence of the compressional event that occurred in the early eocene and the existence of a thick layer reflection below the pinghu fm late eocene due to the subduction of the pacific plate the depocenters of the ecssb and the okinawa trough jumped eastward successively triggered by the three oceanic slabs of the izanagi plate at 72 ma the pacific plate at 50 ma and the philippine sea plate at 15 ma thus a new model for the formation and evolution of the ecssb is suggested in which a back arc basin of episodic extension with jumping depocenters in respond to subduction of three oceanic slabs meanwhile its differences between northern and southern part are caused by the dominant subduction and opening of scs respectively the ecssb and okinawa trough might formed mainly by rollback of the oceanic slab possibly due to slab stagnation and toroidal flow related to the subduction however the effects of large scale mantle flow cannot be exclusively identified in this research in addition further research in this region will give new insights into both the formation and evolution of the scs and the continental breakup process

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

transient landscape and stratigraphic responses to drainage integration in the actively extending central italian apennines abstract drainage networks in continental rifts are generally reported as dynamic features that produce transitions between endorheic and exorheic conditions while this is of major importance for landscape development sediment dispersal and basin stratigraphy the controls of drainage network evolution across an array of normal fault bounded basins are still not well understood in this study we use the central italian apennines an area that has been affected by active normal faulting and regional uplift over the last 3 myrs to determine the controls on drainage network evolution and its impact on transient landscape evolution and basin stratigraphy we compile previously published stratigraphic and fault related data with new geomorphological constraints for the aterno river system 1300 km2 for which a wealth of data has been collected following the destructive l aquila earthquake in 2009 we use this compilation to demonstrate how the different basins along the river system were initially isolated during the early pleistocene but became fluvially integrated with one another and the adriatic coast between ca 1 2 and 0 65 ma we conclude that the spatial and temporal pattern of drainage integration is mostly explained by a long term increase in sediment and water supply relative to basin subsidence due to the early to middle pleistocene climatic transition the progressive increase in fault related topography and the transport of sediment and water down system as drainage integration occurred overall we conclude that rates of sedimentation and basin subsidence in the central apennines are well matched allowing tipping points between over and under filled conditions to be easily reached we also show that consecutive drainage integration events produce discrete waves of river incision and terrace formation and conclude that drainage integration is of major importance at least equivalent to tectonics and climate in controlling transient landscape evolution and rift basin stratigraphy

3d numerical modeling of mantle flow crustal dynamics and magma genesis associated with slab roll back and tearing the eastern mediterranean case interactions between subduction dynamics and magma genesis have been intensely investigated resulting in several conceptual models derived from geological geochemical and geophysical data to provide physico chemical constraints on these conceptual models self consistent numerical simulations containing testable thermo mechanical parameters are required especially considering the three dimensional 3d natural complexity of subduction systems here we use a 3d high resolution petrological and thermo mechanical numerical model to quantify the relative contribution of oceanic and continental subduction collision slab roll back and tearing to magma genesis and transport processes our modeling results suggest that the space and time distribution and composition of magmas in the overriding plate is controlled by the 3d slab dynamics and related asthenospheric flow moreover the decrease of the bulk lithospheric strength induced by mantle and crust derived magmas promotes the propagation of strike slip and extensional fault zones through the overriding crust as response to slab roll back and continental collision reduction of the lithosphere asthenosphere rheological contrast by lithospheric weakening also favors the transmission of velocities from the flowing mantle to the crust similarities between our modeling results and the late cenozoic tectonic and magmatic evolution across the eastern mediterranean region suggest an efficient control of mantle flow on the magmatic activity in this region which in turn promotes lithospheric deformation by mantle drag via melt induced weakening effects

aegean tectonics strain localisation slab tearing and trench retreat abstract we review the geodynamic evolution of the aegean anatolia region and discuss strain localisation there over geological times from late eocene to present crustal deformation in the aegean backarc has localised progressively during slab retreat extension started with the formation of the rhodope metamorphic core complex eocene and migrated to the cyclades and the northern menderes massif oligocene and miocene accommodated by crustal scale detachments and a first series of core complexes mccs extension then localised in western turkey the corinth rift and the external hellenic arc after messinian times while the north anatolian fault penetrated the aegean sea through time the direction and style of extension have not changed significantly except in terms of localisation the contributions of progressive slab retreat and tearing basal drag extrusion tectonics and tectonic inheritance are discussed and we favour a model 1 where slab retreat is the main driving engine 2 successive slab tearing episodes are the main causes of this stepwise strain localisation and 3 the inherited heterogeneity of the crust is a major factor for localising detachments the continental crust has an inherited strong heterogeneity and crustal scale contacts such as major thrust planes act as weak zones or as zones of contrast of resistance and viscosity that can localise later deformation the dynamics of slabs at depth and the asthenospheric flow due to slab retreat also have influence strain localisation in the upper plate successive slab ruptures from the middle miocene to the late miocene have isolated a narrow strip of lithosphere still attached to the african lithosphere below crete the formation of the north anatolian fault is partly a consequence of this evolution the extrusion of anatolia and the aegean extension are partly driven from below asthenospheric flow and from above extrusion of a lid of rigid crust

subduction and the depth of convection in the mediterranean mantle 1 we tie together geological data paleotectonic reconstruction plate motion and tomographic analysis to unravel the history of subduction and back arc extension of the eastern and central mediterranean in these two regions extensional processes started contemporaneously around 30 myr ago but with marked differences in the eastern region the aegean basin opened slowly 1 cm yr behind a shallow dipping slab 40 45 the corresponding high velocity anomaly extends inside the upper mantle and can be also followed in the midmantle down to a depth of at least 1500 km its descent into the midmantle initiated most probably during the late cretaceous and the trench moved northeastward following the path of the eurasian plate and under the persistent push of the african plate conversely in the central mediterranean region subduction initiated later and the motion of the subducting slab is confined to the upper mantle causing punctuated and rapid episodes of back arc extension provencal and tyrrhenian basins behind a slab that dips steeply 75 we explore the causes that control how the slab subducted and interacted with the lower more viscous part of the mantle

sensitivity of the southern san andreas fault system to tectonic boundary conditions and fault configurations the southern big bend of the san andreas fault saf accommodates transpression along numerous non vertical non planar and intersecting active surfaces using three dimensional boundary element method bem models we test the sensitivity of fault slip rates to a range of tectonic boundary conditions constrained by global positioning system gps studies of the region 45 50 mm yr and 320 325 using this approach our models provide a range of distributed fault slip rates associated with both spatial variations in geometry and present day uncertainties in plate motion model slip rates match most of the available geologic slip rates and discrepancies may owe to inaccurate fault geometries more northerly plate velocity 325 produces greater transpression along the saf system associated with greater uplift of the san bernardino mountains greater reverse slip rates along range bounding reverse thrust faults lower strike slip rates along the san andreas and san jacinto faults and greater strike slip rates along the eastern california shear zone ecsz and garlock fault these results suggest that the degree of regional transpression controls the partitioning of deformation between uplift and slip along both the saf system and the ecsz the insensitivity of modeled slip rates to applied velocity along the southern san andreas and san jacinto faults suggests that fault geometry greatly influences slip rates within the san bernardino mountains region a northerly shift in plate velocity orientation could account for the abandonment of the mill creek strand of the saf 95 ka and development of the present day active geometry which accommodates greater uplift

geodynamic regimes of subduction under an active margin effects of rheological weakening by fluids and melts the dynamics of subduction under an active margin are analysed by using a 2d coupled petrological thermomechanical numerical model of an oceanic continental subduction system the model includes spontaneous slab bending dehydration of the subducted crust aqueous fluid transport partial melting of both crustal and mantle rocks as well as melt extraction processes resulting in magmatic arc crust growth based on our models the following five geodynamic regimes of subduction which may potentially form at active margins are identified i stable subduction with no backarc spreading centre and without plumes in the mantle wedge ii retreating subduction with a focused backarc spreading centre and without plumes iii retreating subduction with distributed intra arc extension and trans lithospheric sedimentary plumes iv advancing subduction with underplating laterally extending sub lithospheric plumes and v stable to advancing subduction with stationary laterally limited sub lithospheric plumes transitions between these different regimes are mainly caused by the concurrence of rheological weakening effects of i aqueous fluids percolating from the subducting slab into the mantle wedge and ii melts propagating from the partially molten areas formed in the mantle wedge towards the surface the aqueous fluids mainly affect the forearc region strong fluid related weakening promotes plate decoupling and reduces subduction drag and thus results in stacking of sediments in the accretion prism in contrast reduced weakening by fluids results in strong coupling of the plates and leads to advancing collision like subduction with enhanced subduction erosion thickening of the overriding plate and large sedimentary plumes in the mantle wedge are the consequences on the other hand melts extracted from the hot regions above the slab rheologically weaken the lithosphere below the arc which thus controls overriding plate extension and shortening strong rheological weakening by melts in combination with weak plate coupling trigger retreating subduction with a pronounced backarc spreading centre also weakening of the continental lithosphere by melts extracted from trans lithospheric sedimentary plumes generate a weak channel through which these structures may be emplaced into subarc crust if there is insufficient melt related weakening plumes cannot ascend but extend horizontally and thus underplate the lithosphere

the role of slab detachment processes in the opening of the western central mediterranean basins some geological and geophysical evidence abstract a review of the geological and geophysical data from the central and western mediterranean region and the present day upper mantle structure derived from tomographic studies are utilized in order to define the oligocene recent geodynamic evolution for the area in line with previous work we suggest that the miocene quaternary opening of the western and central mediterranean basins is the result of back arc extension due to the roll back toward the southeast of a northwestward subducting african slab in a geodynamic setting pinned between the alpine and betic collisional zones we find however that this general pattern is complicated by four different detachment events which occurred beneath the alps early oligocene the betic chain aquitanian northern africa langhian and the apennines late miocene pliocene we show that each of these events determines a major tectonic reorganization within the european plate

slab detachment beneath eastern anatolia a possible cause for the formation of the north anatolian fault in this paper we discuss the possibility that the north anatolian fault naf results from the deep deformation of the slab beneath the bitlis hellenic subduction zone we described the tectonic evolution of the anatolia aegean area in three main steps before during and after the formation of the naf we remark that the tectonic conditions that are assumed to have triggered the formation of the naf i e collision to the east and extension to the west was already achieved before the onset of that strike slip fault system we also highlight that the formation of the naf was accompanied by the uplift of the turkish iranian plateau and by a surge of volcanism in the eastern anatolia collisional area and probably by the acceleration of the aegean trench retreat we show tomographic images from global p wave model of piromallo and morelli c piromallo a morelli p wave tomography of the mantle under the alpine mediterranean area j geophys res 108 2003 doi 10 1029 2002jb001757 showing that the slab beneath the bitlis collisional belt is not continuous and that its possible rupture pursues to the west at least up to cyprus and possibly up to the eastern end of the hellenic trench all these observations suggest that the plate tectonic re organization occurred in the late miocene early pliocene in the region results from slab break off in the bitlis area and from its lateral propagation to the west this idea is tested in analogue laboratory experiments which confirm that the break of the slab under the collisional belt may trigger 1 the acceleration of slab retreat to the west due to the increase in slab pull force 2 the indentation of the continent in the collisional area and 3 produce the conditions that permit the lateral escape of material towards the west and the formation of the naf

monsoons and the dynamics of deserts the existence of subtropical deserts such as the sahara has often been attributed to the annual mean zonal mean hadley circulation which shows strong descent in the subtropics however the zonal mean hadley circulation shows considerable evolution over the course of the year with very strong subtropical descent during winter but practically no zonal mean subtropical descent during summer when rainfall over the eastern sahara and the mediterranean is least charney 1975 proposed a biosphere albedo feedback mechanism whereby local anthropogenic effects related to over grazing could affect the radiative balance enhancing summertime diabatic descent and leading to desertification of the subtropics in general the present study which uses an idealized model suggests a monsoon desert mechanism for desertification whereby remote diabatic heating in the asian monsoon region can induce a rossby wave pattern to the west integral with the rossby wave solution is a warm thermal structure that interacts with air on the southern flank of the mid latitude westerlies causing it to descend this adiabatic descent is localized over the eastern sahara and mediterranean and over the kyzylkum desert to the south east of the aral sea by the mountains of north africa and south west asia trajectories indicate that the monsoon desert mechanism does not represent a simple walker type overturning cell instead the descending air is seen to be mainly of mid latitude origin it is speculated that the monsoon forced adiabatic descent may result in clear air and therefore a local diabatic enhancement which effectively doubles the strength of descent with this mechanism desertification can be forced by remote changes in monsoon strength rather than by local effects this conclusion is supported by the observed dramatic strengthening of descent over the mediterranean and east sahara during the onset of the asian monsoon and on the longer timescale by relating prehistoric lake levels to milankovitch monsoon forcing the latter may help to explain the perceived discrepancies between the palaeoclimate of the eastern sahara and the strength of a tropic wide monsoon the monsoon desert mechanism may not be confined to the asian monsoon alone and the existence of other monsoon climate regions over the globe may in a similar way explain the observed summertime strengthening of the oceanic sub tropical anticyclones and the existence of western continental deserts and mediterranean type climate regions

the effect of slab gaps on subduction dynamics and mantle upwelling abstract gaps within a subducting plate can alter the surrounding mantle flow field and the overall subduction zone dynamics by allowing hot sub slab mantle to flow through the gaps and into the mantle wedge this through slab flow can produce melting of the slab gap edges as well as significant upwelling that can lead to anomalous alkaline volcanism and or dynamic uplift in the overriding plate while the altered mantle flow patterns affect the trench evolution numerous geodynamic models have investigated the processes that form slab gaps but few studies have examined the dynamics of slab gap altered mantle flow its effects on trench morphology and kinematics or the controlling parameters on these processes here laboratory subduction models with a pre cut gap in a subducting silicone plate are used to explore how slab gap size and slab gap depth influence the surrounding mantle flow field and trench dynamics results suggest that both the vertical extent and the depth of the top trailing edge of the slab gap are crucial parameters for modulating overall subduction dynamics they show that a slab gap which occurs near the surface and initially comprises 30 of the subducting plate width can extend enough vertically in the slab to produce significant vertical flow through the gap changes to the trench geometry and kinematics are also evident in the models such that double and triple arc geometries are formed during subduction of a shallow slab gap all of these results are consistent with observations of slab gaps and their induced surface expressions or the lack thereof in eastern anatolia east java italy and argentina

p wave tomography of the mantle under the alpine mediterranean area 1 we study the upper mantle p wave velocity structure below the euro mediterranean area down to 1000 km depth by seismic travel time tomography we invert summary residuals constructed with both regional and teleseismic first arrival data reported by the international seismological centre isc 1964 1995 introducing some alternative strategies in the travel time tomographic approach and a new scheme to correct teleseismic data for global mantle structure our high resolution model pm0 5 is parameterized with three dimensional 3 d linear splines on a grid of nodes with 0 5 spacing in both horizontal directions and 50 km vertical spacing we obtain about 26 root mean square rms reduction of residuals by inversion in addition to roughly 31 reduction after summary rays formation and selection sensitivity analyses are performed through several test inversions to explore the resolution characteristics of the model at different spatial scales the distribution of large scale fast anomalies suggests that two different stages of a convection process presently coexist in very close regions the mantle dynamics of western central europe is dominated by blockage of subducted slabs at the 660 km discontinuity and ponding of seismically fast material in the transition zone contrarily in the eastern mediterranean fast velocity material sinks into the lower mantle suggesting that the flow of the cold downwelling here is not blocked by the 660 km discontinuity on a smaller scale the existence of tears in the subducted slab lithospheric detachment all along both margins of the adriatic plate as proposed by some authors is not supported by our tomographic images

subducting slab transition zone interaction stagnation penetration and mode switches seismic tomography shows that subducting slabs can either sink straight into the lower mantle or lie down in the mantle transition zone moreover some slabs seem to have changed mode from stagnation to penetration or vice versa we investigate the dynamic controls on these modes and particularly the transition between them using 2d self consistent thermo mechanical subduction models our models confirm that the ability of the trench to move is key for slab flattening in the transition zone over a wide range of plausible clapeyron slopes and viscosity jumps at the base of the transition zone hot young slabs 25 myr in our models are most likely to penetrate while cold old slabs 150 myr drive more trench motion and tend to stagnate several mechanisms are able to induce penetrating slabs to stagnate ageing of the subducting plate decreasing upper plate forcing and increasing clapeyron slope e g due to the arrival of a more hydrated slab getting stagnating slabs to penetrate is more difficult it can be accomplished by an instantaneous change in the forcing of the upper plate from free to motionless or a sudden decrease in the clapeyron slope a rapid change in plate age at the trench from old to young cannot easily induce penetration on earth ageing of the subducting plate with accompanying upper plate rifting may be the most common mechanism for causing slab stagnation while strong changes in upper plate forcing appear required for triggering slab penetration

structural and geomorphological constraints on active normal faulting and landscape evolution in calabria italy calabria is one of the fastest uplifting and most seismically active regions in the mediterranean yet the time averaged c 10 6 years rates of normal faulting remain poorly constrained here we use digital elevation model analysis geological cross sections and a compilation of published data to quantify systematically along strike the fault throws and time averaged throw rates of the serre cittanova armo east crati and west crati faults we show that regional uplift has uplifted both their hanging wall and footwall blocks by c 200 400 m and the aspromonte massif by up to c 1150 1300 m we find that these faults have throws between c 640 and 1430 m and throw rates between c 0 6 and 1 4 mm a 1 their footwall ranges have variable proportions of inherited relief up to c 300 800 m the channels draining these ranges reflect the active normal faulting and relief in their steepness indices becoming c 5 8 m 0 9 steeper for each 0 1 mm a 1 throw rate increment and each 100 m relief increase finally the presence of knickpoints suggests that these channels are transiently responding to changes in relative base level which could be due to fault linkage or regional strain rate increases for the southern calabrian faults and to regional uplift acceleration in the case of the crati faults supplementary material topographic profiles of the marine terraces and long profiles of rivers are available at https doi org 10 6084 m9 figshare c 3689464

constraints on mantle circulation around the deforming calabrian slab 1 combining tectonics with seismological and geochemical data we reconstruct the deformation history of the presently narrow calabrian slab and the path of mantle circulation during the last 10 ma we show that during the slab deformation the mantle laterally flowed inside the back arc region permitting its retrograde motion and giving a seismological and volcanological record after 1 2 myr

upper plate deformation and trench retreat modulated by subduction driven shallow asthenospheric flows upper plate deformation within a subduction zone depends on the complex relationship between surface plate motions trench motion slab pull and asthenospheric flow previous modelling studies suggest that trench motion rates should be related to slab buoyancy but this relationship is neither clear nor verified by observations of natural subduction systems trench motion is also thought to induce upper plate deformation however no clear correlation has been identified between the direction of trench motion and the mode of upper plate deformation in this study we construct 2 d thermo mechanical models to explore the relationship between slab pull trench retreat and upper plate deformation focusing on subduction systems with retreating trenches we start with quasi steady state subduction and introduce a positive density anomaly into the slab to transiently increase slab pull we vary both the value of the density anomaly and the properties of the upper plate to isolate key controls on trench retreat and upper plate deformation our models indicate that asthenospheric flow responds to changes in slab pull and influences both trench retreat and upper plate deformation we propose that trench retreat depends on the competition between shallow and opposite asthenospheric flows below the subducting and upper plates and that a fast sub slab flow can hamper trench retreat even when slab buoyancy is high after a transient slab pull increase the mode of upper plate deformation partly depends on the upper plate s ability to translate horizontally an upper plate with a ridge at its trailing edge deforms by shortening while a fixed upper plate may deform by extension finally in some cases upper plate deformation seems to allow trench retreat if the upper plate is weak enough to be deformed by the basal shear from underlying asthenospheric flow our results provide insights into retreating subduction systems with contrasting upper plate deformation modes such as the compressive andes and the extensional aegean

history of subduction and back arc extension in the central mediterranean summary geological and geophysical constraints to reconstruct the evolution of the central mediterranean subduction zone are presented geological observations such as upper plate stratigraphy hp lt metamorphic assemblages foredeep trench stratigraphy arc volcanism and the back arc extension process are used to define the infant stage of the subduction zone and its latest back arc phase based on this data set the time dependence of the amount of subducted material in comparison with the tomographic images of the upper mantle along two cross sections from the northern apennines and from calabria to the gulf of lyon can be derived further the reconstruction is used to unravel the main evolutionary trends of the subduction process results of this analysis indicate that 1 subduction in the central mediterranean is as old as 80 myr 2 the slab descended slowly into the mantle during the first 20 30 myr subduction speeds were probably less than 1 cm year x1 3 subduction accelerated afterwards producing arc volcanism and back arc extension and 4 the slab reached the 660 km transition zone after 60 70 myr this time dependent scenario where a slow initiation is followed by a roughly exponential increase in the subduction speed can be modelled by equating the viscous dissipation per unit length due to the bending of oceanic lithosphere to the rate of change of potential energy by slab pull finally the third stage is controlled by the interaction between the slab and the 660 km transition zone in the southern region this results in an important re shaping of the slab and intermittent pulses of back arc extension in the northern region the decrease in the trench retreat can be explained by the entrance of light continental material at the trench

summertime quadruplet heating pattern in the subtropics and the associated atmospheric circulation 1 a quadruple heating pattern is found over each subtropical continent and its adjacent oceans in summer based on data diagnosis the ocean region to the west is characterized by strong longwave radiative cooling lo the western and eastern portions of the continent are dominated by sensible heating se and condensation heating co respectively and the ocean region to the east is characterized by double dominant heating d with lo prevailing co these compose a losecod heating quadruplet its general feature is heating over the continent and cooling over the oceans a distinct circulation pattern accompanies this heating pattern in the upper troposphere anticyclonic circulation over the continent is accompanied by cyclonic circulations over the oceans on its western and eastern sides near the surface cyclonic circulation over the continent is accompanied by anticyclonic circulations over the oceans on both sides this circulation feature is interpreted as the atmospheric thermal adaptation to the quadruplet heating it is further demonstrated that the global summer subtropical heating and circulation may be viewed as mosaics of such a quadruplet heating and circulation patterns respectively

spreading pulses of the tyrrhenian sea during the narrowing of the calabrian slab the opening of the tyrrhenian sea has been punctuated by short lived episodes of oceanic accretion on separate small backarc basins during early pliocene vavilov basin and early pleistocene marsili basin time these spreading pulses are related to slab rollback and are synchronous with the reduction of the subduction zone width during the formation of the narrow calabrian arc using laboratory models we investigated the long term and transient effects of the reduction of slab width on the subduction kinematics we found that the abrupt reduction in slab width results in a pulse of acceleration of the trench retreat velocity as the balance between driving and resisting forces acting on the slab is temporarily modified our findings also show that the time scale and amplitude of spreading observed in the tyrrhenian sea can be experimentally fitted if the scaled viscosity of the uppermost part of the mantle ranges between 10 19 and 10 20 pa s

collision of continental corner from 3 d numerical modeling abstract continental collision has been extensively investigated with 2 d numerical models assuming infinitely wide plates or insignificant along strike deformation in the third dimension however the corners of natural collision zones normally have structural characteristics that differ from linear parts of mountain belt we conducted 3 d high resolution numerical simulations to study the dynamics of a continental corner lateral continental oceanic transition zone during subduction collision the results demonstrate different modes between the oceanic subduction side continuous subduction and retreating trench and the continental collision side slab break off and topography uplift slab break off occurs at a depth 100 km to 300 km that depends on the convergence velocity the numerical models produce lateral extrusion of the overriding crust from the collisional side to the subduction side which is also a phenomenon recognized around natural collision of continental corners for instance around the western corner of the arabia asia collision zone and around the eastern corner of the india asia collision zone modeling results also indicate that extrusion tectonics may be driven both from above by the topography and gravitational potentials and from below by the trench retreat and asthenospheric mantle return flow which supports the link between deep mantle dynamics and shallower crustal deformation

episodicity in back arc tectonic regimes abstract the evolution of back arc basins is tied to the development of the dynamics of the subduction system they are a part of we present a study of back arc basins and model their development by implementing 3d time dependant computer models of subduction including an overriding plate we define three types of episodicity pseudo quasi and hyper episodicity and find evidence of these in nature observations of back arc basin ages histories of spreading quiescence and compression in the overriding plate give us an understanding of the time development of these subduction zones and back arc basins across the globe today a number of trenches are advancing the izu bonin trench the mariana trench the japan trench the java sunda trench and the central portion of the peru chile trench the andes subduction zone the izu bonin mariana and japan all have established back arc basins while the others have documented episodes of spreading quiescence compression or a combination of these the combination of advancing and retreating trench motion places these subduction zones in the category of hyper episodicity quasi episodicity in which the back arc shifts between phases of rifting spreading and quiescence is the dominant form of episodic back arc development in the present we find this type of episodicity in models for which the system is dynamically consistent that we have allowed the subducting plate s velocity to be determined by the sinking slabs buoyancy quasi and hyper episodicity are only found in subduction zones with relatively high subducting plate velocities between 6 and 9 cm year finally those subduction zones for which the subducting plate is moving slowly such as in the mediterranean or the scotia sea experience only pseudo episodicity where the spreading moves linearly towards the trench but often does so in discrete ridge jump events

subduction hinge migration abstract it has been argued that back arc tectonics is controlled principally by the absolute motion of the overriding plate and the migration of the hinge of the downgoing plate thus hinge migration rollback is fundamentally important to understanding the geodynamics of back arc regions but even rates of hinge migration are unknown the rate of hinge migration can be estimated if the rate of back arc extension and the motion of the overriding plate are known rates of rollback in a hotspot reference frame range from near zero in the case of the new hebrides arc to 50 70 mm a at the south sandwich arc and may be as high as 100 mm a at the tonga trench but the hinge is actually advancing along the izu bonin trench as evidenced by the fact that there is no significant active extension behind the izu bonin arc the rate of hinge advance increases from north to south along the izu bonin trench and correlates well with the dip of the subducted slab active spreading in the mariana trough may be attributed to a rate of hinge advance which is lower than the rate of retreat of the philippine plate all of the possible motions of overriding plates and subduction hinges which might give rise to back arc opening are represented among the examples considered thus there is no unique circumstance in which back arc extension occurs finally there appears to be no clear correlation between hinge motion and the age of the subducted lithosphere

episodic back arc extension during restricted mantle convection in the central mediterranean abstract in the central mediterranean during the last 80 myr africa has been slowly converging toward eurasia with an average relative velocity of less than 1 cm yr 1 for 50 myr this slow convergence led to the build up of the alpine orogenic belt and to the initiation of consumption of the former tethys ocean in the last 30 myr however the whole central western mediterranean has been swept by rapid episodes of trench migration up to 6 cm yr 1 and back arc opening which consumed the whole former tethys ocean we combine plate tectonic history geological timing and laboratory modelling to reconstruct the subduction history and the evolution of the central mediterranean over the last 80 myr we find that the dynamic evolution of the subducting oceanic lithosphere can reconcile the rapid episodic back arc migration with the slow african convergence but only if the subduction process is restricted to the upper mantle

development of topography in 3 d continental collision models understanding the formation and evolution of high mountain belts such as the himalayas and the adjacent tibetan plateau has been the focus of many tectonic and numerical models here we employ 3 d numerical simulations to investigate the role that subduction collision and indentation play on lithosphere dynamics at convergent margins and to analyze the conditions under which large topographic plateaus can form in an integrated lithospheric and upper mantle scale model distinct dynamics are obtained for the oceanic subduction side trench retreat slab rollback and the continental collision side trench advance slab detachment topographic uplift lateral extrusion we show that slab pull alone is insufficient to generate high topography in the upper plate and that external forcing and the presence of strong blocks such as the tarim basin are necessary to create and shape anomalously high topographic fronts and plateaus moreover scaling is used to predict four different modes of surface expression in continental collision models i low amplitude homogeneous shortening ii high amplitude homogeneous shortening iii alpine type topography with topographic front and low plateau and iv tibet himalaya type topography with topographic front and high plateau results of semianalytical models suggest that the argand number governs the formation of high topographic fronts while the amplitude of plateaus is controlled by the initial buoyancy ratio of the upper plate applying these results to natural examples we show that the alps belong to regime iii the himalaya tibet to regime iv whereas the andes altiplano fall at the boundary between regimes iii and iv

how collision triggers backarc extension insight into mediterranean style of extension from 3 d numerical models the formation and evolution of a backarc basin are linked to the dynamics of the subduction system the opening of the central mediterranean basins is a well documented example of backarc extension characterized by short lived episodes of spreading the underlying reasons for this episodicity are obscured by the complexity of this subduction system in which multiple continental blocks enter the subduction zone we present results from three dimensional numerical models of laterally varying subduction to explain the mechanism of backarc basin opening and the episodic style of spreading our results show that efficient backarc extension can be obtained with an along trench variation in slab buoyancy that produces localized deformation within the overriding plate we observe peaks in the trench retreating velocity corresponding first to the opening of the backarc basin and later to the formation of slab windows we suggest that the observed episodic trench retreat behavior in the central mediterranean is caused by the formation of slab windows

the effects of back arc spreading on arc magmatism abstract mantle flow is a key feature that can affect melt production and composition in and around subduction zones in this study i use three dimensional numerical models to investigate the role of mantle flow on subduction related volcanism during back arc extension results show that for a time interval of about 10 15 myr during back arc basin formation and spreading a wide convection cell brings mantle that has already partially depleted at the back arc to the mantle wedge before and after this phase the mantle reaching the sub arc melting region is fertile thus changes in back arc activity and mantle flow pattern can be responsible for changes in magmatic composition and the amount of magmatism at the arc these results are consistent with many examples of present day subduction zones in which phases of actively spreading back arc correspond to a gap or a decrease of the arc volcanic activity

the future of earth s oceans consequences of subduction initiation in the atlantic and implications for supercontinent formation subduction initiation is a cornerstone in the edifice of plate tectonics it marks the turning point of the earth s wilson cycles and ultimately the supercycles as well in this paper we explore the consequences of subduction zone invasion in the atlantic ocean following recent discoveries at the sw iberia margin we discuss a buoyancy argument based on the premise that old oceanic lithosphere is unstable for supporting large basins implying that it must be removed in subduction zones as a consequence we propose a new conceptual model in which both the pacific and the atlantic oceans close simultaneously leading to the termination of the present earth s supercycle and to the formation of a new supercontinent which we name aurica our new conceptual model also provides insights into supercontinent formation and destruction supercycles proposed for past geological times e g pangaea rodinia columbia kenorland

subduction and slab breakoff controls on asian indentation tectonics and himalayan western syntaxis formation 1 we test the link between large scale asian continent deformations and indian slab subduction and breakoff during convergence by means of three dimensional numerical models of the subducting upper plates system we find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the indian motions yet the upper plate deformation remains accommodated in a narrow belt along a straight margin comparable rates are measured when the subducting slab breakoff is modeled although the convergent margin deforms and curves markedly with large underplating contiguous to ongoing subduction similar to what observed along the himalayan range the models support the interpretation of the himalayan western syntaxis evolution the progressive curvature of the indian margin and the underthrusting as a consequence of the indian slab breakoff the modeled slab detachment is followed by short lived large stresses in the upper plate interiors propagating at large distance from the margin with a trend similar to several major asian lithospheric faults such localized stress has likely provided the conditions for the formation of the central asian intracontinental faulting the bangong red river and the altyn tagh faults that followed successive indian slab breakoff episodes continent subduction and breakoff during india asia convergence offer an explanation for the different deformation mechanisms as the long lived understhrusting and the episodic lithospheric faulting in the asian continent and their link to deep processes

slab rollback orogeny model a test of concept buoyancy forces associated with subducting lithosphere control the dynamics of convergent margins in the post collisional stage these forces are significantly reduced yet mountain building and seismicity are ongoing albeit at lower rates we leverage advances of a newly developed seismo thermo mechanical modeling approach to simulate tectonic and seismicity processes in a self driven subduction and continental collision setting we demonstrate that the rearrangement of forces due to slab breakoff in the post collisional stage causes bending and rollback of the residual slab suction forces and mantle traction at the base of the upper plate while stress coupling transfers to the shallow crust our results provide an explanation for the post collisional evolution of the central alps where the so called slab rollback orogeny models explains the slow yet persistent upper plate advance the height of the mountain range and a seismicity pattern consistent with the different tectonic regimes throughout the orogen

geodynamic regimes of intra oceanic subduction implications for arc extension vs shortening processes abstract 40 of the subduction margins of the earth are intra oceanic they show significant variability in terms of extension and shortening we investigated numerically the physical controls of these processes using a 2d petrological thermo mechanical intra oceanic subduction model with spontaneous volcanic arc growth and deformation we varied the fluid and melt related weakening the ages of both the subduction slab and the overriding plate the subducting plate velocities and the cohesive strength of rocks three main geodynamic regimes were identified retreating subduction with opening of a backarc basin stable subduction and advancing compressive subduction the main difference between these regimes is the degree of rheological coupling between plates which is governed by the intensity of rheological weakening induced by fluids and melts retreating subduction regimes require plate decoupling which results from strong weakening due to both fluids and melts spreading centers nucleate either in forearc or in intraarc regions episodic trench migration is often due to variations of plate coupling with time which is caused by fore arc deformation stable subduction regime with little variation in the trench position forms at an intermediate plate coupling and shows a transient behavior from the retreating to advancing modes the advancing subduction regime results from strong plate coupling at the mature stage this subduction mode is associated with both partial fragmentation and subduction of the previously serpentinized forearc region forearc subduction is typically associated with a magmatic pulse which is caused by dehydration of subducted serpentinized forearc fragments our models demonstrate distinct differences in thermal and lithological structure of subduction zones formed in these different geodynamic regimes results compare well with variations observed in natural intra oceanic arcs

interannual relationships between the tropical sea surface temperature and summertime subtropical anticyclone over the western north pacific 1 the interannual variability of the western north pacific subtropical high wnpsh in boreal summer is investigated with the use of the ncep ncar reanalysis data the most significant change of the 500 hpa geopotential height field appears at the western edge of the wnpsh with dominant 2 3 year and 3 5 year power spectrum peaks the 2 3 year oscillation of the wnpsh and associated circulation and sea surface temperature sst patterns possess a coherent eastward propagating feature with a warm sst anomaly ssta and anomalous ascending motion migrating from the tropical indian ocean in the preceding autumn to the maritime continent in the concurrent summer of a strong wnpsh a strong wnpsh is characterized by anomalous anticyclonic circulation and maximum subsidence in the western north pacific wnp the anomalous wnpsh circulation has an equivalent barotropic vertical structure and resides in the sinking branch of the local hadley circulation triggered by enhanced convection over the maritime continent a heat budget analysis reveals that the wnpsh is maintained by radiative cooling the 3 5 year oscillation of the wnpsh exhibits a quasi stationary feature with a warm ssta anomalous ascending motion located in the equatorial central eastern pacific and indian ocean and a cold ssta anomalous descending motion located in the western pacific the anomaly pattern persists from the preceding winter to the concurrent summer of a high wnpsh the greatest descent is located to the southeast of the anomalous anticyclone center where a baroclinic vertical structure is identified the zonal phase difference and the baroclinic vertical structure suggest that the anomalous anticyclone on this timescale is a rossby wave response to a negative latent heating associated with the persistent local cold ssta echam4 model experiments further confirm that the 2 3 year mode is driven by the ssta forcing over the maritime continent while the 3 5 year mode is driven by the local ssta in the wnp

numerical models of the magmatic processes induced by slab breakoff abstract after the onset of continental collision magmatism often persists for tens of millions of years albeit with a different composition in reduced volumes and with a more episodic nature and more widespread spatial distribution compared to normal arc magmatism kinematic modelling studies have suggested that slab breakoff can account for this post collisional magmatism through the formation of a slab window and subsequent heating of the overriding plate and decompression melting of upwelling asthenosphere particularly if breakoff occurs at depths shallower than the overriding plate to constrain the nature of any melting and the geodynamic conditions required we numerically model the collision of two continental plates following a period of oceanic subduction a thermodynamic database is used to determine the de hydration reactions and occurrence of melt throughout this process we investigate melting conditions within a parameter space designed to generate a wide range of breakoff depths timings and collisional styles under most circumstances slab breakoff occurs deeper than the depth extent of the overriding plate too deep to generate any decompressional melting of dry upwelling asthenosphere or thermal perturbation within the overriding plate even if slab breakoff is very shallow the hot mantle inflow into the slab window is not sustained long enough to sufficiently heat the hydrated overriding plate to cause significant magmatism instead for relatively fast shallow breakoff we observe melting of asthenosphere above the detached slab through the release of water from the tip of the heating detached slab melting of the subducted continental crust during necking and breakoff is a more common feature and may be a more reliable indicator of the occurrence of breakoff we suggest that magmatism from slab breakoff alone is unable to explain several of the characteristics of post collisional magmatism and that additional geodynamical processes need to be considered when interpreting magmatic observations

absolute plate motions and regional subduction evolution we investigate the influence of absolute plate motion on regional 3 d evolution of subduction using numerical thermomechanical modeling building on our previous work we explore the potential impact of four different absolute plate motion frames on subduction evolution in the western mediterranean region during the last 35 my one frame is data based and derived from the global moving hotspot reference frame gmhrf of doubrovine et al 2012 and three are invented frames a motion frame in which the african plate motion is twice that in the gmhrf and two frames in which either the african plate or the iberian continent is assumed fixed to the mantle the relative africa iberia convergence is the same in all frames all motion frames result in distinctly different 3 d subduction evolution showing a critical dependence of slab morphology evolution on absolute plate motion we attribute this to slab dragging through the mantle forced by the absolute motion of the subducting plate which causes additional viscous resistance affecting subduction evolution we observed a strong correlation between increase in northward africa motion and decrease in the speed of westward slab rollback along the african margin we relate this to increased mantle resistance against slab dragging providing new insight into propagation and dynamics of subduction transform edge propagator step faults our results demonstrate a large sensitivity of 3 d slab evolution to the absolute motion of the subducting plate which inversely suggests that detailed modeling of natural subduction may provide novel constraints on absolute plate motions

new constraints on the pb and nd isotopic evolution of ne atlantic water masses 1 time series of lead pb and neodymium nd isotope compositions were measured on three ferromanganese crusts recording the evolution of ne atlantic water masses over the past 15 ma the crusts are distributed along a depth profile 700 4600 m comprising the present day depths of mediterranean outflow water and north east atlantic deep water a pronounced increase of the 206pb 204pb in the two deeper crusts starting at 4 ma and a decrease in 143nd 144nd in all three crusts took place between 6 4 ma and the present these patterns are similar to isotope time series in the western north atlantic basin and are consistent with efficient mixing between the two basins however the changes occurred 1 3 ma earlier in the eastern basin indicating that the northeastern atlantic led the major change in pb and nd isotope composition probably due to a direct supply of labrador seawater via a northern route the pb isotope evolution during the pliocene pleistocene can generally be explained by mixing between two end members corresponding to mediterranean outflow water and north east atlantic deep water but external sources such as saharan dust are likely to have played a role as well the pb isotope composition of the shallowest crust that grew within the present day mediterranean outflow water does not show significant pb isotope changes indicating that it was controlled by the same pb sources throughout the past 15 ma

mantle exhumation and sequence of magmatic events in the magnaghi vavilov basin central tyrrhenian italy new constraints from geological and geophysical observations highlights a serpentinised peridotite basement is strongly supported by s waves analysis depth dependent serpentinisation resembles to that observed at magma poor margins mantle exhumation was preceded by mor type magmatism and later intraplate volcanism summary the tyrrhenian basin opened in the neogene following the e se retreat of the appenines calabrian subduction system and the subsequent back arc extension of an orogenic crust the resultant crustal structure includes a complex distribution of continental back arc magmatism and mantle exhumation domains a clear example of this complex structure is found in the central and deepest part of the basin i e magnaghi vavilov sub basin where geophysical data supported that the bulk of the basement is composed of partially serpentinised peridotite representing exhumed mantle rocks and intruded by basalts forming low ridges and volcanic edifices however those data sets cannot univocally demonstrate the widespread presence of serpentinised mantle rocks let alone the percentage of serpentinisation here we use s wave arrivals and available geological information to further constrain the presence of mantle serpentinisation travel times of converted s waves were used to derive the overall vp vs and poisson s ratio as well as s wave velocity of the basement in the magnaghi vavilov basins this analysis reveals vp vs 1 9 0 3 that strongly supports a serpentinised peridotite forming the basement under the basins rather than oceanic type gabbro diabase p wave velocity models is later used to quantify the amount of serpentinisation from fully serpentinised up to 100 at the top of the basement to 10 at 5 7 km deep with a depth distribution similar to continent ocean transition zones at magma poor rifted margins seismic reflection profiles show normal faulting at either flank of the magnaghi vavilov basin that is potentially responsible for the onset of serpentinisation and later mantle exhumation these results together with basement sampling information in the area suggests that the late stage of mantle exhumation was accompanied or soon followed by the emplacement of mor type basalts forming low ridges that preceded intraplate volcanism responsible for the formation of large volcanoes in the area

ultrafast oceanic spreading of the marsili basin southern tyrrhenian sea evidence from magnetic anomaly analysis spectral analysis of both shipborne and airborne magnetic maps of the southern tyrrhenian sea reveals seven subparallel positive negative magnetic anomaly stripes over the flat lying deep floor of the marsili oceanic basin this represents the first evidence of oceanic magnetic anomalies in the tyrrhenian sea the central positive stripe is along the marsili seamount a superinflated spreading ridge located at the basin axis the stratigraphy of ocean drilling program site 650 and k ar ages from the marsili seamount suggest that the marsili basin opened at the remarkable full spreading rate of 19 cm yr between ca 1 6 and 2 1 ma about the olduvai subchron this is the highest spreading rate ever documented including that observed at the cocos pacific plate boundary renewed but slow spreading during the brunhes chron after 0 78 ma coupled with huge magmatic inflation gave rise to the marsili volcano our new data and interpretation show that backarc spreading of the tyrrhenian sea was episodic with sudden rapid pulses punctuating relatively long periods of tectonic quiescence