culturable yeasts in meltwaters draining from two glaciers in the italian alps the meltwaters draining from two glaciers in the italian alps contain metabolically active yeasts isolable by culture based laboratory procedures the average number of culturable yeast cells in the meltwaters was 10 20 colony forming units cfu l 1 whereas supraglacial stream waters originating from overlying glacier ice contained 80 of isolated strains cryptococcus spp and rhodotorula spp were 33 3 and 17 8 of total strains respectively culturable yeasts were psychrotolerant predominantly obligate aerobes and able to degrade organic macromolecules e g starch esters lipids proteins to the authors knowledge this is the first study to report the presence of culturable yeasts in meltwaters originating from glaciers on the basis of these results it is reasonable to suppose that the viable yeasts observed in meltwaters derived predominantly from the subglacial zone and that they originated from the subglacial microbial community their metabolic abilities could contribute to the microbial activity occurring in subglacial environments

erosion and the mechanics of shallow foreland thrusts a simple model for the effects of erosion on the geometry and mechanics of shallow foreland thrusts allows prediction of maximum stable length of the thrust toe location of initial failure within the toe if total thrust displacement exceeds the maximum stable length and estimates of average pore fluid pressures along the fault during thrust advance for typical rates of erosion and thrust advance the maximum stable length of the toe may be very large over 50 km for relatively low values of fluid overpressure application of the theoretical results to the keystone muddy mountain thrust of southern nevada predicts maximum stable length location and degree of imbrication in agreement with observation relatively low pore fluid pressures along the fault between 0 5 and 0 6 and a rate of thrust advance between 4 and 8 km ma 1

structure of the mountain front flexure along the anaran anticline in the pusht e kuh arc nw zagros iran insights from sand box models this is a contribution of the group of dynamics of the lithosphere gdl financed by a collaborative project between the institute of earth sciences jaume almera csic of barcelona spain and statoilhydro tehran and statoilhydro research centre with the partial support of project team consolider ingenio 2010 no csd 2006 00041

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

tectonic evolution of the lachlan fold belt southeastern australia constraints from coupled numerical models of crustal deformation and surface erosion driven by subduction of the underlying mantle abstract we have used a coupled thermo mechanical finite element fe model of crustal deformation driven by mantle oceanic subduction to demonstrate that the tectonic evolution of the lachlan fold belt lfb during the mid palaeozoic late ordovician to early carboniferous can be linked to continuous subduction along a single subduction zone this contrasts with most models proposed to date which assume that separate subduction zones were active beneath the western central and eastern sections of the lachlan orogen we demonstrate how the existing data on the structural volcanic and erosional evolution of the lachlan fold belt can be accounted for by our model we focus particularly on the timing of fault movement in the various sectors of the orogen we demonstrate that the presence of the weak basal decollement on which most of the lachlan fold belt is constructed effectively decouples crustal structures from those in the underlying mantle the patterns of faulting in the upper crust appears therefore to be controlled by lateral strength contrasts inherited from previous orogenic events rather than the location of one or several subduction zones the model also predicts that the uplift and deep exhumation of the wagga omeo metamorphic belt womb is associated with the advection of this terrane above the subduction point and is the only tectonic event that gives us direct constraints on the location of the subduction zone we also discuss the implications of our model for the nature of the basement underlying the present day orogen

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

effects of mass waste events on thrust wedges analogue experiments and application to the makran accretionary wedge 1 olistostromes cover large portions of active thrust wedges like makran gulf of cadiz and offshore borneo olistostrome emplacement by submarine mass flow represents an instantaneous and massive mass redistribution that may influence thrust wedge mechanics different scenarios are experimentally tested they show that the postolistostrome wedge development depends on the thickness and extent of the added load these results are discussed after the example of the iranian makran wedge situated between the arabian and eurasian plates mass redistribution caused by a late miocene mass flow may explain a change in deformation style from intense folding and thrusting to gentle folding and eventually a jump of thrust imbrication toward the frontal offshore part of this active accretionary wedge

the break back thrust splay of the main dun thrust himalayas of western nepal evidence of an intermediate displacement scale between earthquake slip and finite geometry of thrust systems abstract numerous studies have shown that development of a forward breaking sequence in a thrust belt is accompanied by reactivation of inner faults and development of break back thrusts the partitioning of shortening in the outer and lesser himalayan thrust belt follows these rules tectonic and sedimentary relationships in this thrust belt exemplify out of sequence thrusts in the lesser himalayas and break back imbricate fans close to the mbt main boundary thrust and mdt main dun thrust which are transported during their development above the himalayan basal detachment the displacement along a single splay of the imbricate fan of the mdt was 40 m before abandonment and nucleation of a new inner splay the development of the break back imbricate fan is discontinuous in time furthermore superimposition of ultracataclasite pressure solution cleavage extensional crenulation cleavage and tension gashes in the fault zones suggests that the 40 m displacement occurred by discrete slip events or most probably by a succession of several seismic aseismic deformations these data require several scales of sequential displacement in the outer and lesser himalayas consisting of forward propagation of the thrust system out of sequence reactivation break back nucleation of thrust splays and seismic aseismic fault slip our findings require an intermediate period of tectonism between the 500 ka deformation of the accretionary sediments of the himalayas

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

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

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

influence of syntectonic sedimentation on thrust wedges in analogue models scaled analogue sandbox models have been used to simulate the growth of coulomb thrust wedges that include syntectonic sedimentation during thrusting increases in the syncontractional sedimentation rate dramatically change the shape of the coulomb thrust wedge decreasing the number of thrust slices the internal shortening and the critical taper of the wedge thrust trajectories change from ramp flat to sigmoidal with increased syncontractional sedimentation the analogue models show many similarities to thrust fault geometries in accretionary prisms and foreland fold and thrust belts in which thrust slices prograded into basins with active sedimentation

a mechanical analysis of the keystone muddy mountain thrust sheet in southeast nevada abstract the keystone muddy mountain thrust sheet was displaced for several tens of kilometres across the land s surface in cretaceous times its movement is related to the emplacement of the sierra nevada batholith which provided a source of compressive stress over a period of about 140 ma the mechanical analysis presented here examines the stresses operating throughout the whole thrust sheet i e the toe ramp and main thrust block which extends for approximately 200 km from front to rear frictional sliding can explain only the motion of the toe the ramp and perhaps part of the main thrust block a composite model involving elastic upper and viscous lower layers is used to account for the movement of most of the main thrust block

erosion and exhumation in accretionary orogens experimental and geological approaches 1 this study examines the role of erosion on exhumation and deformation history of accretionary orogens through experimental and geological methods fault propagation kinematics and exhumation rates in an eroded thrust wedge are analyzed through scaled sandbox simulations by testing different parameters friction rheologic layering and sediment input output ratio a model coulomb wedge is submitted to erosion under flux steady state conditions that is the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during shortening results show that the way of exhumation depends on the internal dynamics of thrust wedges and conversely on how this dynamics is modified by erosion in the eroded thrust wedges the diversity of exhumation patterns is controlled by the mode of fault propagation depending on the basal friction high or low the vertical component of exhumation is generally higher for the wedges with high basal friction than for low friction wedges the uplift of material occurs along a cluster of subvertical thrusts in the middle part of the eroded thrust wedge with low basal friction the material is exhumed along a series of inclined 20 50 thrusts in the rear of the high friction wedge the zone of maximum exhumation is generally localized in the middle part of the thrust wedge and migrates toward the backstop with continued shortening the vertical exhumation rate increases with time and the material accreted later is rapidly transferred to the main exhumation zone compared to the material accreted during the early stages the exhumation occurs at rates 2 times faster in the wedges with half the thickness than in full thickness wedges the total quantity of eroded material at the end of convergence constitutes 36 50 of initial model area for the thrust wedges with low basal friction and 20 40 for the high basal friction wedges the extent of basal underplating increases with total shortening the area of basal underplated material constitutes up to 30 and 40 of the eroded thrust wedge area for the models with low and high basal friction respectively presence of decollements in the accreted series allows underplating of thrust units developing an anticlinal stack whose growth and location is favored by erosion our results are compared to different present day active and ancient convergent orogens himalaya taiwan southern alps of new zealand and cascadia orogen allowing the different specific exhumation processes to be characterized

mechanical model for the tectonics of doubly vergent compressional orogens a mechanical model of crustal shortening and deformation driven by the relative convergence of rigid underlying mantle plates explains many features of convergent orogens results based on numerical models and supported by sandbox models show that a coulomb crustal layer subject to basal velocity boundary conditions corresponding to asymmetric detachment and subduction of the underlying mantle passes through three stages of orogenic growth 1 block uplift bounded by step up shear zones 2 development of a low taper wedge over the underthrusting mantle plate and 3 development of a low taperwedge overlying the overthrusting mantle plate and verging in the opposite direction when modified by isostasy basal viscous flow surface erosion and denudation and sedimentation the resultant model orogens exhibit a variety of styles with characteristics in common with small rapidly denuded orogens large orogens with plateaus and extensional characteristics and active subduction margins with doubly vergent accretionary wedges and deformed fore arc basins

influence of synkinematic sedimentation in a thrust system with two decollement levels analogue modelling abstract compressive systems in foreland domains are characterised by fold and thrust belts linked to the presence of one or several ductile layers in depth acting as a decollement level the main parameters controlling the structural evolution are the presence of a decollement level the amount and rate of shortening and the amount of synkinematic sedimentation the effect of these parameters has only been studied on a thrust belt scale furthermore only the effect of synkinematic sedimentation on a simple system with one decollement level has been studied at the scale of a single structure the aim of this study was to use analogue modelling to test the effect of shortening rate velocity and the localization of sedimentation on a single system characterised by the presence of two prekinematic decollement levels the main results showed variations in the structural vergence folding geometry symmetric or asymmetric the evolution of the deformation horizontal propagation versus vertical uplift and the decoupling of the lower and upper brittle structures in relation with the main parameters shortening rate and mass transfer the results of the experiments were then compared to natural examples from the sub andean thrust belt

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

impact of synkinematic sedimentation on the geometry and dynamics of compressive growth structures insights from analogue modelling analogue sandbox models have been set up to study the impact of synkinematic deposits on the geometry and evolution of single thrusts and folds according to different sedimentation modes a slow or rapid sedimentation rate that is constant or changing in space and time and rheological profiles thin or thick sedimentary series with or without a basal decollement level a first series of experiments documents the influence of synkinematic deposits according to their sedimentation rate and the rheology of the prekinematic materials a second series investigates the influence of changes in the sedimentation rate through time a third one considers the influence of changes in the sedimentation rate in space all these experiments suggest that the geometry and evolution of single compressive growth structures vary according to the sedimentation rate the number and dip of their frontal thrust segments change with the ratio r between the sedimentation rate at the footwall of the faults and the uplift rate of their hanging wall the latter is then more or less uplifted depending on the dip of the thrusts as a result the overall structure has either a fault bend fold or a fault propagation fold geometry these rules are verified when the ratio r changes in space or through time in addition the rheological profile of the models also affects the geometry and evolution of compressive growth structures their structural style as well as the synsedimentary splitting and steepening of the associated thrusts varies according to the occurrence and strength of the brittle and ductile layers according to this modelling study the ratio r and its changes in space and time along with the rheology of the deformed materials are key parameters to better understand the geometrical and kinematical complexities of natural growth thrusts and folds and to improve their interpretation

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

influence of syntectonic sedimentation on thrust geometry field examples from the iberian chain spain and analogue modelling abstract steep thrusts are usually interpreted as oblique slip thrusts or inverted normal faults however recent analogical and numerical models have emphasised the influence of surface mass transfer phenomena on the structural evolution of compressive systems this research points to sedimentation and erosion during deformation as an additional explanation for the origin of steeply dipping thrusts the present study uses both field observations and analogue modelling to attempt to isolate critical parameters of syntectonic sedimentation that might control the geometry of the upper part of thrust systems a field study of thrust systems bounding two compressive intermountain tertiary basins of the iberian chain is first briefly presented we describe the surface geometry of thrusts surrounding the montalban basin and the alto tajo syncline at the vicinity of deposits of oligocene early miocene alluvial fans at the footwall of faults field observations suggest that synthrusting sedimentation should influence the structure of thrusts indeed the faults are steeper and splitted at the edge of the syntectonic deposits effects of sedimentation rate on footwall of thrusts and of its change along fault strike are further investigated on two layer brittle ductile analogue models submitted to compression and syntectonic sediment supply two series of experiments were made corresponding to two end members of depositional geometries in the first series the sedimentation was homogeneously distributed on both sides of the relief developed above the thrust front in the second series deposits were localised on a particular area of the footwall of thrust front in all experiments the sedimentation rate controls the number and the dip of faults for low sedimentation rates a single low angle thrust develops whereas for high sedimentation rates a series of steeper dipping thrust is observed in experiments with changing sedimentation rate along fault strike the thrust geometry varies behind the areas with the thickest sediment pile

styles of crustal deformation in compressional orogens caused by subduction of the underlying lithosphere abstract crustal scale deformation is calculated for models in which the driving mechanism corresponds to the asymmetric detachment and underthrusting of the underlying mantle lithosphere the plane strain finite element model results provide indications of the styles of deformation to be expected in small compressional orogens in particular these styles occur where shortening of the mantle lithosphere is achieved by the nearly rigid convergence between lithospheric mantles and the subduction of one mantle beneath the other the crust is modelled using coulomb plastic frictional and thermally activated power law viscous rheologies and the effects of compositional layering and variable geothermal gradients are included results are presented for a range of models in which the strength of the coupling between the model crust and its basal boundary surface denudation partial and total subduction of the crust and compositional layering are examined the results show the development of inclined step up shear zones which are a consequence of conjugate thrusting in regions of coulomb controlled rheology these zones link to sub horizontal shear zones which occur where composition and temperature render the crust viscously weak the model strain fields are interpreted in terms of deformation on discrete planes and the seismic reflectivity fabric that may be associated with this discrete deformation finally we ask whether similar seismic reflectivity fabric can be recognized in observations from small compressional orogens

the role of syntectonic sedimentation in the evolution of doubly vergent thrust wedges and foreland folds this paper shows the evolution of time constrained two dimensional scaled analogue models of doubly vergent thrust systems in the presence of syntectonic sedimentation two sets of experiments were considered 1 the addition of a syntectonic layer composed of a polymer and overlying sand in the prowedge and 2 the addition to the previous condition of a progradational sedimentary load results from the first set of experiments indicate that the foreland fold and thrust belt has a strong relationship with the competence of the syntectonic layers when the competence is low the deformation produces tight asymmetric detachment folds as the competence increases the fold and thrust belt shows break trough folds with longer and better defined foreland vergence results from the second set of experiments indicate that structural vergence is determined by the sense of progradation of the syntectonic layers and in the case of strong aggradation at the prowedge extension and reactive diapirism form contemporaneously with the contraction three end members are proposed for mountain front thrust systems formed in the presence of syntectonic polymer and sand sedimentation 1 outcropping fold and thrust belt sequence in the case of no syntectonic sedimentation 2 long displacement blind thrust sheets in the case of under filled basins and 3 short displacement blind thrust sheets in the case of over filled basins all results indicate that ductile units at the base of syntectonic layers increase the displacement of the underlying frontal thrusts at the prowedge and reduce the critical taper results also indicate that at very high sedimentary rates and hyper critical taper conditions the prowedge collapses conclusions drawn from this research may be applied as an analogue to foreland evolution and to evaluate hydrocarbon generation migration and entrapment in thrust belts in areas where seismic imaging is generally poor

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

thrust geometry controlled by erosion and sedimentation a view from analogue models analogue sandbox models have been set up to study thrust systems formed above two decollements and affected by erosion and sedimentation the deformation was imaged by x ray scanner three erosion sedimentation conditions were tested for all the experiments a duplex develops between the two decollement levels for the experiment without erosion and without sedimentation ramp anticlines form in the upper series for the model with syntectonic sedimentation and without erosion the shortening in the upper series is first characterized by fault related folds and then by a forward propagation of the decollement that induces the development of a piggy back basin for the experiment with erosion and sedimentation a passive roof duplex is formed relationships between structural style and syntectonic superficial conditions in classical thin skinned thrust belts are similar to those found in the analogue models the ramp anticlines of the jura developed with low erosion and low sedimentation and the large sub andean thrust belt is controlled by syntectonic sedimentation whereas the passive roof duplex of pakistan is synchronized with intense erosion this study outlines the crucial effect of the superficial mass transport phenomena in the tectonic style of thrust belts

growth and erosion of fold and thrust belts with an application to the aconcagua fold and thrust belt argentina 1 the development of topography within and erosional removal of material from an orogen exerts a primary control on its structure we develop a model that describes the temporal development of a frontally accreting critically growing coulomb wedge whose topography is largely limited by bedrock fluvial incision we present general results for arbitrary initial critical wedge geometries and investigate the temporal development of a critical wedge with no initial topography increasing rock erodibility and or precipitation decreasing mass flux accreting to the wedge front increasing wedge sole out depth decreasing wedge and basal decollement overpressure and increasing basal decollement friction lead to narrow wedges large power law exponent values cause the wedge geometry to quickly reach a condition in which all material accreted to the front of the wedge is removed by erosion we apply our model to the aconcagua fold and thrust belt in the central andes of argentina where wedge development over time is well constrained we solve for the erosional coefficient k that is required to recreate the field constrained wedge growth history and these values are within the range of independently determined values in analogous rock types using qualitative observations of rock erodibilities within the wedge we speculate that power law exponents of 1 3 m 0 4 and 2 3 n 1 characterize the erosional growth of the aconcagua fold and thrust belt this general model may be used to understand the development of mountain belts where orogenic wedges grow as they deform at their coulomb failure limit