duplex style and triangle zone formation insights from physical modeling duplexes are a common feature in thrust belts at many scales their geometries vary significantly from antiformal stacks with significant forethrusting in the cover e g southern pyrennes spain to triangle zones e g foreland canadian rockies to low displacement individually spaced ramp anticlines e g sub andean thrust belt bolivia we present a series of physical experiments demonstrating that the strength of the decollements relative to that of the intervening and overlying rock layers plays a significant role in controlling the duplex style the models comprise brittle layers made of dry quartz sand and decollements made of two types of viscous silicone polymers the strength of the decollements in the models is a function of the shortening rate applied to the model the relative strength of the decollements and surrounding rocks affects the development of active or passive roof duplexes triangle zones it also affects the amount of translation of individual thrust blocks and the spacing of thrust ramps which in turn determine if a duplex evolves into an antiformal stack or into individually spaced ramp anticlines model results indicate that specific associations of structural features form systematically under similar rheological and boundary conditions the presence of relatively strong decollements promotes local underthrusting of the cover individual ramp anticlines internal deformation of thrust sheets low early layer parallel shortening and sequential towards the foreland propagation of structures weak decollements promote forethrusting of the cover antiformal stacks coeval growth of structures and low internal strain with the exception of significant early layer parallel shortening no underthrusting at a regional scale occurred in any model

stagnant layers at the bottom of convecting magma chambers the evolution and crystallization of igneous complexes has received much attention from petrologists1 3 and more recently from physicists4 10 current models emphasize the role of compositional effects we present here a different viewpoint because compositional effects are due to crystallization they depend on the thermal structure and regime of cold boundary layers in convecting magma chambers particularly of the bottom layer where the thickest rock sequences form we have studied purely thermal convection in a large aspect ratio magma chamber which is cooled through both its upper and lower boundaries we made laboratory fluid dynamical experiments in turbulent and transient conditions and show that a stagnant layer develops at the bottom isolated from the convective part of the chamber the essential features of this layer are that it is not affected by mixing and that a significant thermal gradient is maintained across it these imply peculiar crystallization conditions

sandbox modelling of thrust wedges with fluid assisted detachments abstract we have used granular materials to model the development of thrust wedges where migrating pore fluids assisted in the formation of detachments the governing equations yield practical scales for linear dimensions stresses and time using compressed air as a pore fluid models a few centimetres thick were deformed in about half an hour model materials were sands of three different grain sizes and a loess they had suitable values of density permeability cohesion and internal friction fluid flow obeyed darcy s law at yield the materials satisfied a coulomb criterion for effective stresses models with various sequences of layers were submitted to horizontal shortening in a rectangular box compressed air entered through a sieve at the base the fluid pressure was uniform over the basal boundary in models made from a single material the style of deformation depended on the fluid pressure for no fluid flow the thrust wedge was short and high the surface slope attained large angles 30 and internal structures were mainly forethrusts for fluid pressures approaching lithostatic values thrust wedges were longer and lower and surface slopes attained smaller angles in models containing basal layers of small permeability detachments formed beneath them and the structural style was dominated by interacting forethrusts and backthrusts in multilayered models thin skinned detachments formed beneath less permeable layers in the sequence to understand how fluid flow controlled the first stages of detachment we calculated ideal vertical profiles of fluid pressure vertical normal stress effective stress and horizontal shear stress for multilayered models in the undeformed state the profiles are segmented because material properties vary from layer to layer sharp drops in shear strength occur at positions where detachments were observed in the sandbox models we infer that detachments resulted from large fluid pressures beneath relatively impermeable layers

detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

double evaporitic decollements influence of pinch out overlapping in experimental thrust wedges abstract this article focuses on how deformation and displacements are transferred between two decollements located at different stratigraphic levels by means of analogue modeling using brittle viscous sand silicone systems we present results from ten analogue models in which we varied key parameters such as the amount of horizontal offset or overlap between the pinch outs of the upper and lower decollements the total amount of shortening and the planform geometry of the upper decollement results indicate that i structures root onto the basal and upper decollement defining an inner and an outer domain and ii the offset overlap of the decollements controls the geometry of the transition zone located between the two decollements the propagation of deformation into the foreland both in space and time and the deformation style and kinematics in the different domains of the model when the pinch out of the upper decollement is at an angle with the backstop oblique structures form and the geometry and propagation mode of the structures change progressively along strike we compare our experimental results with other silicone sand analogue models and with the natural examples of the southern pyrenees where upper triassic and eocene oligocene syn tectonic evaporites acted as basal and upper decollements respectively

epicenter distribution and magnitude of earthquakes in fold thrust belts insights from sandbox models scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth quakes in the sedimentary cover of active fold thrust belts model results suggest that in fold thrust belts shortenedabove low friction ductile decollements rock salt or over pressured mudstone low to moderate magnitude earth quakes mw 5 3 5 6 distributed over a wide area occuralong several long lived thrust faults conversely in areasshortened above high friction decollements large magnitudeearthquakes mw 6 6 6 8 distributed over a narrowzone are likely to occur along few short lived thrust ramps calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat tern from the zagros mountain belt which is partially short ened above a ductile decollement of hormuz salt formation model results also showed that erosion reactivates older in active thrusts and promotes formation of out of sequencethrusts

the influence of a weak upper ductile detachment on the longmen shan fold and thrust belt eastern margin of the tibetan plateau insights from sandbox experiments abstract the topic of the longmen shan fold and thrust belt has been vigorously debated due to the steep topography in contrast with the low convergence rate and earthquake hazards the longmen shan fold and thrust belt is characterized by two main detachments a strong lower detachment at 15 17 km depth in the hinterland and a weak upper detachment at 7 km depth in the sichuan basin nevertheless how the two detachments control deformation in the longmen shan remains unclear in this study we focus on the mechanical strengths of the two detachments in the study area and design three analog models to investigate the kinematics and mechanisms of the longmen shan fold and thrust belt all three model experiments have the same strong lower detachments at the basement but different upper detachments the results indicate that for model 1 with no upper detachment and model 2 with a strong frictional upper detachment the strain and deformation only concentrate near the mobile backwall and particle image velocimetry analysis reveals that both models deform in the forward in sequence style however for model 3 with a weak ductile upper detachment the strain and deformation propagate into the foreland and the model deforms in the out of sequence style consistent with the longmen shan fold and thrust belt the model results indicate that the spatial relation of strong lower detachment and weak upper detachment may be one of the important factors producing the current structural pattern and the out of sequence style of the longmen shan fold and thrust belt

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

topography reveals seismic hazard the devastating earthquake in the chinese province of sichuan struck an area that was not expected to suffer seismic activity of such magnitude yet topographic analyses of the region indicate active deformation suggesting a way of refining maps of earthquake risk elsewhere

deformation patterns and structural vergence in brittle ductile thrust wedges an additional analogue modelling perspective abstract scaled physical models of brittle ductile thrust wedges investigated the causes leading to the development of the various structural styles observed in fold and thrust belts and accretionary prisms this study focused on some potential controlling factors such as 1 relative strength between the brittle overburden and the viscous decollement layer brittle ductile coupling 2 the effect of very low basal friction and 3 pre shortening rheological stratigraphy including decollement strength type 1 models had a single basal decollement whereas in type 2 models the decollement was embedded in brittle material simulating an upper roof sequence and a lower floor sequence other models investigated the effects produced by an horizon of mechanical weakness at the base of the viscous decollement type 1a and the role of decollement offset type 3 the experiments suggest the occurrence of a genetic relationship between the absolute values of shear stresses and the development of dominating hinterland or foreland verging thrust faults or dually verging thrusts by controlling the orientation of the 1 axis basal friction and decollement offset is found to effectively influence the deformation pattern and structural vergence and could explain the development of dominating backthrusts in cascadian type margins the decoupling of a frontal monocline via the upper decollement type 2 models produced passive roof duplex structures termed composite roof duplex when the frontal monocline coexists with outward fold propagation

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

analogue modelling of intraplate strike slip tectonics a review and new experimental results abstract intraplate strike slip zones commonly display intricate 3 d geometries with rapid changes in structural style along strike and with depth strike slip deformation typically results in complex vertical and horizontal sections that can be difficult to interpret coherently physical modelling of strike slip fault systems is a powerful and graphic tool to help in providing a unified picture of the evolution of strike slip zones with considerable spatial and temporal detail a large number of experimental studies have investigated different aspects of strike slip tectonics using materials such as dry sand wet clay or silicone the choice of analogue material and experimental design exerts a strong control on the structures that form in the model here we present a review of different experimental setups used to investigate intraplate strike slip tectonics from the classical riedel experiment to more sophisticated setups using brittle and viscous analogue materials we review our current understanding from models of distributed shear transtension transpression pull apart basins formed in releasing stepovers and popups formed in restraining stepovers in addition we present the results of two new experimental series that investigated 1 the effect of crustal weak zones on strike slip fault zone segmentation and 2 strike slip and transpressional reactivation of extensional basins

thrust wedges and fluid overpressures sandbox models involving pore fluids the well known model for the critical taper of an accretionary wedge includes overpressure as a first order parameter fluid overpressures reduce frictional resistance at the base of a wedge but they also act as body forces on all material particles of the wedge in addition to that of gravity by means of sandbox modeling many workers have tried to verify the predictions of the critical taper model but few of them have so far incorporated true fluid pressures we have used scaled experiments in which compressed air flows through sand packs so as to model the deformation of overpressured wedges a new apparatus provides for a horizontally varying fluid pressure for example a linear variation as in the critical taper model we have done three series of experiments involving horizontal shortening of homogeneous or multilayered sand models for various gradients of fluid pressure as predicted by the critical taper model the apical angle of the resulting wedge depends on the overpressure gradient in homogeneous sand at a high overpressure gradient deformation becomes diffuse and looks ductile in multilayered models detachments form beneath layers of low permeability so that thrusts propagate rapidly toward the undeformed foreland the efficiency of a detachment and its ability to propagate depend not only on the fluid pressure but also on the permeability ratios between the various layers

effect of lateral thickness variation of an intermediate decollement on the propagation of deformation front in the lurestan and izeh zones of the zagros fold thrust belt insights from analogue modeling although the role of various basal decollement levels on structural style and deformation propagation is well documented in many folded belts the effect of lateral variation in intermediate decollements is poorly constrained this work uses results of three scaled sand box models shortened from one end to study the variation in structural development between areas with a ductile intermediate decollement and areas without or with a thinner intermediate decollement combined results of scaled models with field observations are used to argue that the presence of mechanically different intermediate decollement horizons within the zagros stratigraphy has resulted in deformation partitioning between the lurestan and izeh zones a thick intermediate decollement facilitates a faster propagation of deformation front and a lower taper in comparison with a thinner or non existing intermediate decollement during compression however the effect of lateral thickness variation in the intermediate decollement on propagation of deformation is less profound than the effect of mechanical differences in basal decollements

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

fault and fault rock characteristics associated with cenozoic extension and core complex evolution in the catalina rincon region southeastern arizona cenozoic extensional deformation in southern arizona included 1 a neogene phase of basin and range deformation recorded by high angle normal faults and 2 an earlier phase of detachment faulting and brittle ductile crustal shearing associated with tectonic denudation of metamorphic core complexes in the catalina rincon region exposed fault zones produced at different crustal depths during successive extensional episodes display differing fault geometries and types of fault rocks formed during progressive crustal extension detachment faults are associated with both mylonites produced by ductile shear and cataclasites produced by brittle shear younger faults formed at shallower depths are associated with less intense cataclastic deformation and with brittle fracturing that includes transtensile phenomena at the shallowest crustal levels represented qualitative measures of net displacement along individual fault zones are provided by 1 the nature of contrasts among successively overprinted fabrics and internal structures in the footwall and 2 the degree of contrast between fabrics and structures of footwall and hanging wall rocks footwalls of the oldest structures display varied brittle overprints of ductile fabrics and are juxtaposed across gouge zones along detachment surfaces with stratal successions cut by multiple brittle shear surfaces footwalls of younger structures formed at shallower depths display multiple generations of cataclastic features including brecciation of variable intensity and cataclasite dikes but are juxtaposed against hanging wall strata that are only moderately deformed by subsidiary faults the shallowest fault zones lack either structural overprints in their footwalls or any significant contrasts between footwall and hanging wall deformation exposures of mid crustal rocks within the core complexes reflect successive exhumation and uplift of fault footwalls during sequential episodes of deformation the present high elevation of mylonitic rocks in the catalina rincon metamorphic core complex reflects dip slip and isostatic footwall flexure during basin and range deformation as well as tectonic denudation during detachment faulting net uplift of core rocks resulted from multiple phases of deformation

the structural styles and formation mechanism of salt structures in the southern precaspian basin insights from seismic data and analog modeling abstract using the seismic profiles and analog modeling this paper addresses the salt structures in the m and b blocks in the southern precaspian basin the salt structural features the formation mechanism and the controlling factors of structural deformation are investigated and discussed systematically the interpretation of the seismic profiles shows that typical salt related structures include salt wall flip flop salt diapir salt roller salt pillow dome salt weld salt withdrawal minibasin and drag structure or drape fold in addition model results demonstrate that the gravity spreading driven by progradation and aggradation is probably the primary factor in controlling the formation of the salt structures in the research area due to the differential loading driven by progradation passive salt diapir developed near the progradational front followed by the formation of intrasalt withdrawal minibasin bounded by two salt diapirs and secondary reactive triangle salt diapir or salt pillow might form within the intrasalt withdrawal minibasin model results also indicate that the pattern of the subsalt basement has important influence on the formation and evolution of salt structures salt diapirs primarily developed along the margin of the subsalt uplift basement where high shear deformation was induced by differential sedimentary loading between the uplift area and the slope area

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

structural geometry and deformation mechanism of the longquan anticline in the longmen shan fold and thrust belt eastern tibet abstract the 2008 mw 7 9 wenchuan earthquake is a consequence of ongoing india tibet collision and reflects the growth of the longmen shan fold and thrust belt in this paper we present new constraints on the deformation mechanism of the longmen shan fold and thrust belt by comparing the physical models to the example of the longmen shan fold and thrust belt the result indicates that the deformation mechanism of the belt is mainly dominated by the pre sinian layer whereas locally is controlled by the lower triassic layer such as the longquan anticline in addition we discuss the deformation style of the longquan anticline various along strike based on the seismic reflection data interpretations of structural cross sections and field observations as well as physical modeling the sandbox modeling suggests that the deformation of the central segment of longquan anticline is likely controlled by higher displacement rate higher erosion and lower sedimentation which is in contrast with the southern and northern segment moreover the structural geometry of the central segment of longquan anticline is more complex than the end member models of fault related folds which is mainly controlled by pure shear wedge fault bend fold and bounded by west verging thrust fault combining the studies of the structural geometry deformation mechanism and previous studies we infer that the longquan anticline is active and potentially seismogenic therefore a quantitative re evaluation of seismic hazard in longquan anticline and adjacent area directly beneath the densely populated sichuan basin is urgently needed

extension and compression in the northern apennines italy hinterland evidence from the late miocene pliocene siena radicofani basin and relations with basement structures 1 the northern apennines na hinterland area is characterized by a complex neogene quaternary tectonics where both crustal extension associated with the tyrrhenian basin opening and crustal shortening in the onshore area took part in the deformation analysis of synorogenic deposits preserved in the nnw trending siena radicofani basin srb extending along a large part of the na hinterland documents the evolution of deformation of this sector during the last 9 ma information from subsurface geology deep seismic lines commercial seismic lines and deep wells surface geology mapping and structural analysis and from analogue modeling was integrated and used to infer the tectono sedimentary history of the srb and its relation with structures in the substratum as well as the possible implications for the evolution of the na hinterland the results we obtain indicate that the srb and the adjoining hinterland basins were bounded by thrust anticlines controlling basin development and deformation seismic lines across the srb display various examples of compressional structures affecting the basin fill and the substratum such as thrust anticlines and reverse faults notably these basin scale structures exhibit a good correlation with those observed in the field and are consistent with the kinematics of the outcrop scale compressional structures the thrust anticlines bounding the basins are often cored by triassic evaporites burano formation suggesting that this weak layer decoupling the sedimentary cover from the underlying crystalline basement controlled their evolution in this circumstance three series of scaled brittle ductile physical models have been used to investigate the development of a basement cover system with a decollement ductile layer at the base of the sedimentary cover these models simulate the evolution of the northern apennines hinterland where the basement is involved in the thrusting and the sedimentary cover is shortened above a basal ductile layer given by the burano formation longitudinal models cross sections display similar deformation patterns to those observed in the na hinterland such as characteristic wavelength of both basement and cover structures as well as detachment and fault propagation folding in the cover extensional tectonics is instead found to control sedimentation in the southern part of the srb at 8 ma or representing recent deformation the older extensional event is here related to the forelandward propagation of tyrrhenian related extension that could reactivate suitably oriented basement thrusts transfer zones produced a differential propagation of extension such that along strike sectors of the hinterland were eventually deformed by different stress fields analysis of the srb and of other adjoining basins reveals that the na hinterland experienced alternated periods of forward and backward migration of the compression extension transition in our interpretation the competition between extension and compression in the hinterland is related to the nnw directed africa pelagian indentation responsible for the lateral extrusion of the na and the contemporaneous opening of the tyrrhenian basin in the inner zone increased marginal loading at the foreland promoting reactivation of hinterland thrusts may have influenced this process as well

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

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

mechanical behaviour of granular materials used in analogue modelling insights from grain characterisation ring shear tests and analogue experiments abstract the mechanical behaviour of several dry granular materials is investigated through ring shear tests grain characterisation and simple analogue experiments analysed by x ray computed tomography an improved knowledge of granular materials is essential to determine their suitability as analogues for upper crustal rocks in experimental models and to compare analogue and numerical experiments the ring shear tests show that the granular materials have an elastic frictional plastic behaviour with strain hardening preceding failure at peak strength followed by strain softening until a dynamic stable value is reached this is similar to the behaviour exhibited by experimentally deformed rocks the physical characteristics of the grains determine the amount of diffuse deformation before failure the percentage of strain softening and act on the thickness of the shear zones before broadening initial shear zone width in extensional and contractional experiments is between 11 and 16 times the mean grain size the angle of internal friction defining one of the mechanical properties of granular materials and thus fault dip is not only related to physical characteristics of the grains and to the handling technique used e g sieving or pouring but also to the overburden and to the experimental setup used

the role of salt layers in the hangingwall deformation of kinked planar extensional faults insights from 3d analogue models and comparison with the parentis basin abstract using an analogue modelling approach this work investigates the role played by salt in the hangingwall deformation of an extensional fault models set up included a wooden block simulating the footwall of different kinked planar fault geometries flattening at depth above these faults the hangingwall was modelled using only sand or sand overlain by pre or syn kinematic silicone putty regardless of the stage at which was deposited the silicone appears as an efficient decoupling level that changes the deformation mode of the overlying sand layers above the silicone layers the rollover panels only continue to develop up to the welding of the underlying silicone afterwards they do not grow anymore and all shearing induced by the underlying fault bends is accommodated along the tilted silicone layer that acts as an extensional shear band further fault slip produces near horizontal growth stratal geometries that can be easily misinterpreted as a syn rift post rift boundary in addition the differential sedimentary loading of syn kinematic layers triggers the upslope silicone flow from the hangingwall depocenters towards the rollover shoulders this migration results in the formation of silicone welds at the rollover limbs and the growth of gentle silicone cored anticlines above or near the rollover shoulder that are locally pierced by diapirs and walls these experimental results fit with the parentis basin structure that formed from the motion of lithosphere scale kinked planar extensional faults includes salt inflated anticlines above their rollover shoulders and an intra albian unconformity interpreted now as syn kinematic

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

analogue benchmarks of shortening and extension experiments we report a direct comparison of scaled analogue experiments to test thereproducibility of model results among ten different experimental modelling laboratories we present results for two experimen

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

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

effect of ductile and frictional decollements on style of extension abstract scaled analogue models were used to study the effect of frictional and ductile detachments on thin skinned extension models consisted of two halves one half is the ductile and the other has a frictional detachment extension occurred above two different basal configurations a stretchable rubber sheet and a folded banded sheet intended to produce homogeneous and heterogeneous extension respectively model parameters varied systematically and included the brittle ductile thickness ratio rheologies and bulk strain structures in the two halves are compared in profiles and plan views a series of graben developed above both halves of models extended above a banded sheet although there were differences in style propagation rate and width of the deformation zone between the two halves different rates of propagation of structures in the two halves led to the formation of an accommodation or transfer zone parallel to the extension direction most relay ramps and inflection of normal faults in this zone indicate differential extension between the two halves in contrast in models extended above a stretchable rubber sheet extensional structures such as horst and graben developed only above the ductile detachment model results indicate that heterogeneous mechanical stratigraphy and displacement rate have no effect on extensional structure above a rubber sheet however above 20 bulk extension deformation becomes heterogeneous along multiple sets of conjugate faults oblique to the extension direction

differential exhumation in response to episodic thrusting along the eastern margin of the tibetan plateau abstract thermochronological data from the songpan ganze fold belt and longmen mountains thrust nappe belt on the eastern margin of the tibetan plateau in central china reveal several phases of differential cooling across major listric thrust faults since early cretaceous times differential cooling indicated by distinct breaks in age data across discrete compressional structures was superimposed upon a regional cooling pattern following the late triassic indosinian orogeny 40ar 39ar data from muscovite from the central and southern longmen mountains thrust nappe belt suggest a phase of differential cooling across the wenchuan maouwen shear zone during the early cretaceous the zircon fission track data also indicate differential cooling across a zone of brittle re activation on the eastern margin of the wenchuan maouwen shear zone during the mid tertiary between 38 and 10 ma apatite fission track data from the central and southern longmen mountains thrust nappe belt reveal differential cooling across the yingxiu beichuan and erwangmiao faults during the miocene forward modelling of apatite fission track data from the northern longmen mountains thrust nappe belt suggests relatively slow regional cooling through the mesozoic and early tertiary followed by accelerated cooling during the miocene beginning at ca 20 ma to present day regional cooling is attributed to erosion during exhumation of the evolving longmen mountains thrust nappe belt lmtnb following the indosinian orogeny differential cooling across the wenchuan maouwen shear zone and the yingxiu beichuan and erwangmiao faults is attributed to exhumation of the hanging walls of active listric thrust faults thermochronological data from the longmen mountains thrust nappe belt reveal a greater amount of differential exhumation across thrust faults from north to south this observation is in accord with the prevalence of proterozoic and sinian basement in the hanging walls of thrust faults in the central and southern longmen mountains the two most recent phases of reactivation occurred following the initial collision of india with eurasia suggesting that lateral extrusion of crustal material in response to this collision was focused along discrete structures in the lmtnb

enigmatic structures within salt walls of the santos basin part 2 mechanical explanation from physical modelling abstract jackson et al this volume used 3d seismic reflection data to describe intrasalt deformation in salt walls in the santos basin they focused on the origin of enigmatic allochthonous salt sheets of older evaporites a1 unit emplaced above overlying stratified evaporites a2 a4 units their kinematic model incorporates i initial inward flow and thickening of a1 salt within the rising wall and arching of a2 a4 overburden ii breaching of the arched overburden ascent of mobile a1 evaporites along single or multiple feeders and emplacement of upper wall sheets or canopies and iii a component of regional shortening within the salt this companion paper uses physical modelling to explain how and why these structures occur and proposes a mechanical basis for the kinematic model our first two models simulated salt having uniform internal density with walls growing by i initially symmetric differential loading and ii initially symmetric differential loading plus shortening these models reproduced anticlines and injection folds seen in the simpler deformed walls in the santos basin however neither model reproduced the most complex structures within the santos evaporites which are i allochthonous intrusions ii steep feeders and iii recumbent synclines thus differential loading and shortening alone are insufficient to generate these complex structures in our third model a less dense lower evaporite a1 was overlain by denser upper evaporites a2 a4 similar to the density structure found by santos basin wellbores the wall rose solely by differential loading in this model a1 breached the overlying evaporites to form vertical diapirs feeding salt sheets and salt wings in the upper part of the salt wall breakthrough of a1 folded a2 a4 evaporites into recumbent synclines model sections closely resemble santos seismic examples suggesting that the key to forming these complex intrasalt structures is a density inversion within the evaporite sequence that creates a rayleigh taylor instability

late cenozoic east west crustal shortening in southern longmen shan eastern tibet implications for regional stress field changes abstract the co seismic slip sense of the 2008 wenchuan earthquake mw 7 9 has resulted in the present east west e w crustal shortening and oblique thrusting across longmen shan which are inconsistent with southeast directed thrusting that occurred during the late triassic although the two major periods of compressional deformations in longmen shan have long been recognized the fault slip rate of the late cenozoic deformation and the initial e w crustal shortening remain poorly investigated this study confirms the fault slip rate in the dayi thrust fault system dyfs based on data from the petroleum industry and shallow seismic reflection profiles and well data folded late pliocene to present strata are analyzed and yield with an average slip rate of 0 2 mm yr on the dyfs an average fault slip rate of 0 25 mm yr is then obtained from the late pliocene to present for the range front thrust of longmen shan the e w crustal shortening is investigated by using 3 d seismic reflection data interpreting satellite image and conducting a field investigation in the dyfs to determine stress field changes during the late cenozoic two period tectonic deformations during the late cenozoic are found in the dyfs which correspond to the ne and ns trending structures respectively the activities of the dyfs may reflect a change in the field direction of the regional stress from nw se during the oligocene to early pliocene to e w during the late pliocene to holocene which is consistent with the present stress measurements the 120 km ns trending structures in the southern longmen shan range front as well as the wenchuan earthquake co seismic ruptures are assumed to reflect the active e w crustal shortening in longmen shan