evolution of 3 d subduction induced mantle flow around lateral slab edges in analogue models of free subduction analysed by stereoscopic particle image velocimetry technique abstract we present analogue models of free subduction in which we investigate the three dimensional 3 d subduction induced mantle flow focusing around the slab edges we use a stereoscopic particle image velocimetry spiv technique to map the 3 d mantle flow on 4 vertical cross sections for one experiment and on 3 horizontal depth sections for another experiment on each section the in plane components are mapped as well as the out of plane component for several experimental times the results indicate that four types of maximum upwelling are produced by the subduction induced mantle flow the first two are associated with the poloidal circulation occurring in the mantle wedge and in the sub slab domain a third type is produced by horizontal motion and deformation of the frontal part of the slab lying on the 660 km discontinuity the fourth type results from quasi toroidal return flow around the lateral slab edges which produces a maximum upwelling located slightly laterally away from the sub slab domain and can have another maximum upwelling located laterally away from the mantle wedge these upwellings occur during the whole subduction process in contrast the poloidal circulation in the mantle wedge produces a zone of upwelling that is vigorous during the free falling phase of the slab sinking but that decreases in intensity when reaching the steady state phase the position of the maximum upward component and horizontal components of the mantle flow velocity field has been tracked through time their time evolving magnitude is well correlated to the trench retreat rate the maximum upwelling velocity located laterally away from the subducting plate is 18 24 of the trench retreat rate during the steady state subduction phase it is observed in the mid upper mantle but upwellings are produced throughout the whole upper mantle thickness potentially promoting decompression melting it could thereby provide a source for intraplate volcanism such as mount etna in the mediterranean the chiveluch group of volcanoes in kamchatka and the samoan hotspot near tonga

slab pull and indentation tectonics insights from 3d laboratory experiments abstract we investigate using 3d laboratory experiments how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions lithospheric plates are modelled by sand silicone plates floating on glucose syrup and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced analogue experiments model the convergence between two lithospheric plates a small continent indenting a large continental plate we show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone slab break off following the subduction of the small continent favours the indentation process because it results in an increasing compression in front of the indenter and extension above the neighbouring oceanic subduction both of them being responsible for the appearance of the indenter like geometry of the plate boundary when the slab does not deform significantly at depth in contrast the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction during which the tectonic regime within the wide continent remains quite homogeneous comparing the presented analogue experiments with the subductions both part of the arabian indenter within eurasia our results suggest that the different tectonic regime on both sides of the arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern anatolia

dynamics of retreating slabs 2 insights from three dimensional laboratory experiments 1 a laboratory analogue of a three layer linear viscous slab upper mantle lower mantle system is established in a silicone putty honey and crystallized honey tank experiment the same setup as in the numerical investigation part 1 is used we focus on the interaction of the slab with the induced passive mantle flow by widely varying the mantle volume flux boundary conditions in our numerical experiments the lateral volume flux was set to zero in interpreting the results relative to the real earth the base of the box is taken as the bottom of the mantle convection system while the lateral boundaries may be associated with the presence of other nearby slabs dynamic force equilibrium assessed on the basis of an analytical review of forces is described for four different phases 1 the subduction initiation instability 2 the accelerating dynamic free fall phase of the slab 3 the dynamic interaction with the 660 km discontinuity and 4 a final phase of steady state trench retreat phase 3 is an important feature not observed in the numerical experiments this highly dynamic phase of interrupted trench retreat can therefore be attributed to boundary conditions on mantle volume flux on the basis of integration constants of force equilibrium in phases 2 and 4 we identify two different classes of volume flux one in which the lateral boundary can be considered open and the other class where it is closed closed boundary condition cases are obtained if any of the lateral box boundaries are 600 km away from the slab assuming a one to one relation between trench retreat and back arc spreading enigmatic observations of episodic opening of back arc basins can be explained by our experimental observations

the analogue shear zone from rheology to associated geometry the geometry of ductile strain localization phenomena is related to the rheology of the deformed rocks both qualitative and quantitative rheological properties of natural rocks have been estimated from finite field structures such as folds and shear zones we apply physical modelling to investigate the relationship between rheology and the temporal evolution of the width and transversal strain distribution in shear zones both of which have been used previously as rheological proxies geologically relevant materials with well characterized rheological properties newtonian strain hardening strain softening mohr coulomb are deformed in a shear box and observed with particle imaging velocimetry piv it is shown that the width and strain distribution histories in model shear zones display characteristic finite responses related to material properties as predicted by previous studies application of the results to natural shear zones in the field is discussed an investigation of the impact of 3d boundary conditions in the experiments demonstrates that quantitative methods for estimating rheology from finite natural structures must take these into account carefully

indentation of a continent with a built in thickness change experiment and nature orogens oblique to the direction of plate convergence are currently attributed to obliquity between the margins of one or both of the sutured continents to their direction convergence we use a single analogue experiment and natural examples to illustrate a potential additional factor variations in strength of the indented continent at a high angle to the convergence direction the wavelengths of structures in laterally shortened lithosphere depend on the strength of the most competent layers lateral variations in crustal thickness must therefore lead to structures oblique to any applied lateral compression an analogue experiment was performed to explore this phenomenon a two layer indented continent was modelled by a brittle upper crust of sand above a lower crust of high viscosity polymer floating on a single layer of low viscosity syrup representing the mantle the well known strike slip structures allowing lateral escape to distant weak boundaries were hindered by lateral boundaries in front of the indenter this allowed us to focus on the effects of a thickness change built into the indented continent along a zone parallel to the direction in which a vertical rigid wall advancing at a steady rate represented the indenter vertical escape led to an orogenic belt oblique to the advancing wall this obliquity influences subsequent lateral escape model scaling and interpretations are based on extended thin sheet approximation etsa and standard theories of faulting four sectors of the alpine himalayan orogen iran tunisia the eastern alps and the himalaya are oblique to the continental convergence direction and we point to thickness changes at high angles to the suture that may account for this geometry as crustal thicknesses north of oblique sectors of the himalayas are not yet known we speculate on them we infer from the main difference between our experiment and all our examples chosen from nature that vertical orogenic escape was oblique to our model suture but can be parallel to natural sutures

coupled crust mantle dynamics and intraplate tectonics two dimensional numerical and three dimensional analogue modeling 1 tectonic deformation of some intraplate regions may be caused by the rayleigh taylor rt instability of dense subcrustal lithosphere mantle lithosphere as it descends into the mantle we report on a series of scaled three dimensional 3 d analogue and 2 d numerical experiments of coupled crust mantle dynamics that study such a process the models investigate the effects of two geometries of rt instability linear versus axisymmetric and use different rheological stratifications of the crust the growth of the rt instability is strongly influenced by crustal rheology while rt growth rates are not greatly influenced by the geometry of the mantle lithosphere instability itself the surface is experiments having a viscous only crust are characterized by significant crustal contraction and thickening above the mantle downwelling and extension and thinning in adjacent regions in experiments with a brittle upper crust the surface deformation is much more subdued however strong mantle flow induced deformation still occurs in the ductile lower crust beneath the quiescent brittle upper crust when the lower crust is relatively strong localized styles of extensional and contractional structure develop in the brittle upper crust owing to the greater degree of coupling between upper crust and the mantle instability in all the experiments a portion of the ductile lower crustal material is entrained within the downgoing rt instability deep into the mantle the interplay between dynamic topography and crustal thickening thinning induced by the underlying mantle flow governs various time dependent phases of subsidence and uplift of the model surface the experiments help to account for a number of first order tectonic behaviors of the lithospheres of earth and other terrestrial planets for example intraplate orogens and basins complex localized tectonic structure in intraplate settings and deep crustal seismic fabrics may arise as the variable crustal response to underlying mantle lithosphere rt instabilities

fore arc deformation at the transition between collision and subduction insights from 3 d thermomechanical laboratory experiments 1 three dimensional thermomechanical laboratory experiments of arc continent collision investigate the deformation of the fore arc at the transition between collision and subduction the deformation of the plates in the collision area propagates into the subduction collision transition zone via along strike coupling of the neighboring segments of the plate boundary in our experiments the largest along strike gradient of trench perpendicular compression does not produce sufficiently localized shear strain in the transition zone to form a strike slip system because of the fast propagation of arc lithosphere failure deformation is continuous along strike but the deformation mechanism is three dimensional progressive along strike structural variations arise because coupling between neighboring segments induces either advanced or delayed failure of the arc lithosphere and passive margin the modeling results suggest that orogenic belts should experience deeper subduction of continental crust and hence higher pressure metamorphism where the two plates first collided than elsewhere along the plate boundary where collision subsequently propagated furthermore during the initial stage of collision the accretionary wedge is partially subducted which leads to lubrication of the interplate zone and a reduction of shear traction therefore a large convergence obliquity angle does not produce a migrating fore arc sliver rather the pressure force generated by subduction of the buoyant continental crust causes fore arc motion it follows that convergence obliquity during collision does not yield trench parallel deformation of the fore arc and its influence on the collision process is limited however convergence obliquity may control the geometry of the active margin during the oceanic subduction stage prior to collision and inherited structures may influence the propagation mechanism

petrography and geochemistry of impactites and volcanic bedrock in the icdp drill core d1c from lake el gygytgyn ne russia the 3 6 ma old and 18 km diameter el gygytgyn impact structure in ne siberia was drilled in 2008 09 by icdp international continental scientific drilling program a 517 m long core hole d1c was drilled into the outer flank of the central uplift structure with an overall core recovery of approximately 63 thereby approximately 315 m lake sediments and approximately 202 m impactites were recovered here we present a detailed petrographic and geochemical assessment of the impact breccia and bedrock sections in this core the 97 m long lower bedrock unit 517 420 m below lake floor blf consists of an ignimbrite in the overlying upper bedrock unit 420 390 mblf the core recovered a sequence of similar ignimbrite and several decimeters of mafic rocks we interpret these units as rocks that are located close to their former preimpact position but have been somewhat rotated due to collapse of the central uplift i e it represents parautochthonous basement from about 390 to 328 mblf occurs a suevite package with an impact melt poor clast dominated matrix and lithic and mineral clasts that cover the entire range of volcanic target rocks known from the el gygytgyn region all stages of shock metamorphism unshocked to melted were observed in clasts and in microclasts of the matrix of suevite from different depths immediately below this package at the contact to the underlying bedrock occurs a 1 m wide sheared zone within vitrophyric ignimbrite which we consider the actual crater floor the uppermost approximately 12 m from 328 316 mblf depth seem to comprise reworked suevite consisting of a mixture of sediments and suevite with more and on average stronger shocked minerals than found in the main suevite unit this includes a small component of glassy spherules and impact melt fragments toward the top of this unit lake sediments progressively become the dominant material in this section we assume that this unit contains a fallback component from the ejecta plume that was mixed with the first sediments of the postimpact crater lake and possibly some rocks that slumped off the inner crater wall similar to a thin layer at the base of the sediment section of borehole lb 5a recovered in lake bosumtwi ghana

trench parallel shortening in the forearc caused by subduction along a seaward concave plate boundary insights from analogue modelling experiments abstract three dimensional thermo mechanical analogue experiments are employed to test the hypothesis that oceanic subduction along a seaward concave plate boundary can generate trench parallel shortening in the forearc near the axis of curvature the model deformation is analyzed with a particle imaging velocimetry piv system that allows for comparison of forearc deformation along the oblique limbs of the curved plate boundary and near the axis of curvature moreover piv allows for separation of the trench parallel and trench perpendicular components of strain regardless of trench orientation the resulting deformation maps show a remarkable symmetry and indicate drag of the forearc above the interplate coupling area towards the axis of curvature trench perpendicular profiles show that along the oblique limbs of the plate boundary the forearc is submitted to trench normal shortening and trench parallel shearing but not trench parallel shortening or extension this contrasts with the situation near the axis of symmetry where the forearc is submitted to trench parallel and trench perpendicular normal shortening but is not sheared the experimental results confirm that trench normal thrusts observed in the fore arc of the central andes can be a mechanical consequence of subduction along a seaward concave plate boundary if the degree of interplate coupling is large

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

horizontal lithosphere compression and subduction constraints provided by physical modeling physical modeling of the subduction is performed with a two layered mantle model elastico plastic lithosphere and low viscosity asthenosphere and is governed by the criteria of similarity compression of the lithosphere in the area of a passive continental margin has been shown to produce a buckling instability in the oceanic plate with wavelengths of 200 km on the average later a localization of deformation occurs in sagging at some distance from the margin where a strongly dislocated linear ridge is formed due to the thrusting the plate then experiences a failure along the inclined zone and subduction starts the inner trench slope which forms therefore has a scraped structure and include a block of crushed and dislocated oceanic crust and sediments in the lower section if there is an old inclined fault striking across the compression of an oceanic lithosphere it is on that fault that a subduction zone is initiated the inner trench slope has then a different structure and forms due to normal faulting in the frontal part of the overriding plate the formation of a subduction zone requires a compression that is smaller than that in the preceding case by a factor of 2 or 3 the subducting plate experiences an elastico plastic bending and under specific conditions thrusting along the zone dipping from under the overriding plate oceanward and crossing the entire lithosphere the best agreement between generalized relief in subduction zone in the model and nature is achieved when a shear yield limit s 1 3 108 pa modulus of elasticity e about a few times 1011 pa and a thickness h 60 km are adopted for the real lithosphere

density and visco elasticity of natrosol 250 hh solutions determining their suitability for experimental tectonics abstract analogue models often require that materials with specific physical properties be engineered to satisfy scaling conditions to achieve this goal we investigate the rheology of aqueous solutions of natrosol 250 hh a rheology modifier employed in various industries to thicken viscous solutions we report the rheological properties as functions of the concentration and temperature and discuss the advantages and limitations of these materials in view of their use in analogue modelling experiments the solutions are linear visco elastic for low stresses or strain rates becoming shear thinning for larger stresses for the typically slow analogue experiments of tectonics the solutions can be considered linear visco elastic with a maxwell relaxation time much smaller than the characteristic observation time this simplification is even more appropriate when the solutions are employed at temperatures higher than 20 c since the solutions then display a behaviour that is more viscous less elastic at the same shear rate while the newtonian viscosity reduces and the shear rate limit between newtonian and shear thinning behaviours increases the newtonian viscosity is shown to increase non linearly with concentration and decrease non linearly with temperature with concentrations between 0 and 3 and temperature between 20 and 40 c the viscosity varied between 10 1 and 4000 pa s while the density remained close to the density of water natrosol 250 hh thus offers the possibility to control the viscosity of a solution without significantly affecting the density thereby facilitating the design and setup of analogue experiments

rheology and density of glucose syrup and honey determining their suitability for usage in analogue and fluid dynamic models of geological processes abstract analogue models of lithospheric deformation and fluid dynamic models of mantle flow mostly use some kind of syrup such as honey or glucose syrup to simulate the low viscosity sub lithospheric mantle this paper describes detailed rheological tests and density measurements of three brands of glucose syrup and three brands of honey additional tests have been done for one brand of glucose syrup that was diluted with water to various degrees 2 5 and 10 by weight the rheological tests have been done to test the effect of shear strain shear rate and temperature on the dynamic viscosity of the syrup the results show that the viscosity of all glucose syrups and honeys is independent of shear strain i e no strain hardening or softening the viscosity of the glucose syrups is independent of shear rate i e linear viscous or newtonian in the range 10 4 10 0 s 1 with stress exponents that are almost identical to one n 0 995 1 004 all the honeys show a very weak but consistent decrease in viscosity with increasing shear rate of 7 14 from 10 3 to 100 s 1 and have stress exponents more distinct from one n 1 007 1 026 all syrups have a viscosity that is strongly dependent on temperature in the range 0 50 c where viscosity decreases with increasing temperature such decrease can be fitted with exponential and arrhenius functions with the latter giving the best results furthermore the viscosity of glucose syrup decreases approximately exponentially with increasing water content oscillation tests indicate that the rheology of all the syrups is entirely dominated by viscous behaviour and not by elastic behaviour at frequencies of 10 3 102 hz finally the density investigations show that the density of glucose syrup and honey decreases approximately linearly with increasing temperature in the range 10 70 c with coefficients of thermal volumetric expansion at 20 c of 3 89 3 95 10 4 c 1 and 4 57 4 81 10 4 c 1 for glucose syrup and honey respectively the new results demonstrate that glucose syrups and to a lesser degree honeys are well suited for usage in analogue and fluid dynamic experiments to represent linear viscous strain independent and shear rate independent rheologies to model geological processes glucose syrups have the added advantage of being more transparent than honeys allowing for accurately resolving and quantifying flow patterns in the fluid during a model run

another word on the rheology of silicone putty bingham abstract silicone putty a material commonly used as a rock analog in tectonic scale model studies exhibits rheological behavior that is similar to the bingham rheological model over a wide range of strain rate nevertheless at low strain rates a power law is a useful approximation similarly at high strain rates a linear viscous model can be applied thus the choice of rheologic expression can be based on knowledge of the range of stress levels that are achieved in a given model conversely models can be designed to develop appropriate stress levels so that the rheological formulation appropriate to the relevant prototype material will be applicable

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

internal strain within lava flows from analogue modelling internal strain within lava flows can be measured in the field from deformed bubbles or vesicle foliations preferred crystal orientation or ams studies these measurements have important implications for the determination of vertical velocity profiles and flow directions recent field studies show very contrasting strain patterns especially in vertical profiles an experimental study was conducted to relate variations in internal strain to different boundary conditions during flow results show that viscous flow in a straight channel along a basal slope produces three successive stretch trajectories in vertical flow planes these trajectories are related to the distribution with time of a simple shear component and a pure shear component viscous flow in a straight channel along a horizontal base reveals convex stretch trajectories in the vertical flow plane radial spreading at the mouth of a straight channel reveals concentric stretching perpendicular to the radial direction of displacement in the upper part of the flow strain components deduced from experiments may also explain fold formation during motion these experimental results provide a few end member strain patterns which may facilitate the interpretation of strain measurements in natural lava flows in terms of emplacement mechanisms

evolutionary model of the himalaya tibet system geopoem based on new modelling geological and geophysical data a two dimensional thermo mechanical laboratory modelling of continental subduction was performed the subducting continental lithosphere includes a strong brittle upper crust a weak ductile lower crust and a strong upper mantle the lithosphere is underlain by a low viscosity asthenosphere subduction is produced by a piston push force and the pull force from the mantle lithospheric layer which is denser than the asthenosphere the lithospheric layers are composed of material whose strength is sensitive to and inversely proportional to temperature throughout the experiment the model surface was maintained under relatively low temperature and the model base at higher temperature the subduction rate satisfied the peclet criterion modelling confirms that the continental crust can be deeply subducted and shows that slab break off delamination and tectonic underplating are fundamental events with drastic consequences on the subsequent evolution of the convergent system combining these results with previous purely mechanical modelling we elaborate a new evolutionary model for the himalaya tibet convergent system the principal successive stages are 1 subduction of the indian continental lithosphere to 200 250 km depth following subduction of the tethys oceanic lithosphere 2 failure and rapid buoyancy driven uplift of the subducted continental crust from ca 100 km depth to some depth that varies along the mountain belt 20 30 km on average 3 break off of the indian subducted lithospheric mantle with the attached oceanic lithosphere 4 subduction underplating of the indian lithosphere under asia over a few to several hundred kilometers 5 delamination roll back and break off of the indian lithospheric mantle 6 failure of the indian crust in front of the mountain belt formation of the main central thrust and underthrusting of the next portion of indian lithosphere beneath tibet for a few hundred kilometers at the beginning of stage 6 the crustal slice corresponding to the crystalline himalayas undergoes erosion activated uplift and exhumation fl 2000 elsevier science b v all rights reserved

the mechanics of sill inception propagation and growth experimental evidence for rapid reduction in magmatic overpressure abstract a model of magma propagation in the crust is presented using a series of analogue experiments where dyed water is injected at a constant flux into layers of solidified gelatine the gelatine layers are transparent and when intruded deform in an almost ideal elastic manner under the experimental conditions low gelatine concentration 2 5 or 3 wt and low temperature 5 10 c the upper gelatine layer was 1 0 to 1 5 times stiffer than the lower layer with either a weak or strong interface strength between the gelatine layers the gelatine is seeded with 20 50 m diameter pmma rhb neutrally buoyant particles that are fluoresced by a pulsed vertical laser sheet centred on the injection point digital image correlation dic is used to calculate incremental strain and finite strain in the deforming host material as it is intruded this is mapped in 2d for the developing experimental volcanic plumbing system that comprises a feeder dyke and sill since the gelatine deforms elastically strain measurements correlate with stress our results indicate that for constant magma flux the moment of sill inception is characterised by a significant magmatic pressure decrease of up to 60 this is evidenced by the rapid contraction of the feeder dyke at the moment the sill forms sill propagation is then controlled by the fracture properties of the weak interface with fluid from the feeder dyke extracted to help grow the sill pressure drops during sill inception and growth are likely to be important in volcanic systems where destabilisation of the magmatic plumbing system could trigger an eruption

on the transient nature of mantle plumes 1 we present new experiments focussing on the transient behaviour of thermal plumes in a fluid heated from below plumes develop once the hot thermal boundary layer tbl reaches a critical thickness howard 1964 they rise through the fluid owing to their thermal buoyancy and comprise tbl material which empties itself into the plumes as the tbl becomes exhausted plumes start disappearing from the bottom up sometimes even before reaching the upper boundary depending on the convection intensity then they finally fade away by thermal diffusion this sequence of events shows that time dependence is a key factor when interpreting present day tomographic images of mantle upwellings in particular it could be erroneous to identify the depth of a present day slow seismic anomaly with the depth of its origin or to interpret the absence of a long tail as the absence of a plume

quantifying the net slab pull force as a driving mechanism for plate tectonics 1 it has remained unclear how much of the negative buoyancy force of the slab fb is used to pull the trailing plate at the surface into the mantle here i present three dimensional laboratory experiments to quantify the net slab pull force fnsp with respect to fb during subduction results show that fnsp increases with increasing slab length and dip up to 8 12 of fb making fnsp up to twice as large as the ridge push force the remainder of fb is primarily used to drive rollback induced mantle flow 70 to bend the subducting plate at the trench 15 30 and to overcome shear resistance between slab and mantle 0 8

rheology of petrolatum paraffin oil mixtures applications to analogue modelling of geological processes abstract paraffins have been widely used in analogue modelling of geological processes petrolatum and paraffin oil are commonly used to lubricate model boundaries and to simulate weak layers in this paper we present rheological tests of petrolatum paraffin oil and several homogeneous mixtures of the two the results show that petrolatum and all petrolatum paraffin oil mixtures are strain strain rate and temperature dependent under typical experimental strain rates 10 3 10 1 s 1 for the same conditions pure paraffin oil is a slightly temperature dependent linear newtonian fluid all mixtures have yield stress and flow stress strain softening values that decrease with decreasing shear rate and with increasing relative amounts of paraffin oil the degree of strain rate dependence shear thinning also decreases with increasing paraffin oil content because these materials have rheologies that can be characterized and controlled they are suitable for use in a large number of analogue model settings either as a lubricant or to simulate weak layers when used as a lubricant mixtures with higher paraffin oil content should perform better than pure petrolatum