applying a general triclinic transpression model to highly partitioned brittle ductile shear zones a case study from the torcal de antequera massif external betics southern spain abstract oblique convergence and subsequent transpression kinematics can be considered as the general situation in most convergent and strike slip tectonic boundaries to better understand such settings progressively more complex kinematic models have been proposed which need to be tested against natural shear zones using standardized procedures that minimise subjectivism in this work a protocol to test a general triclinic transpression model is applied to the torcal de antequera massif tam an essentially brittle shear zone our results given as kinematic parameters of the transpressive flow transpression obliquity extrusion obliquity and kinematic vorticity number wk suggest that the bulk triclinic transpressive flow imposed on the tam was partitioned into two different flow fields following a general partitioning type as such one flow field produced narrow structural domains located at the limits of the tam where mainly dextral strike slip simple shear dominated transpression took place outer domains ods in contrast the remaining part of the bulk flow produced pure shear dominated dextral triclinic transpression at the inner part of the tam inner domain id a graphical method relating internal wk to far field dip of the shear zone boundary angle of oblique convergence transpression parameters is proposed to obtain the theoretical horizontal velocity vector v which in the case of the tam ranges between 099 and 118 these results support the applicability of kinematic models of triclinic transpression to brittle ductile shear zones and the potential utility of the proposed protocol

using relief parameters in a discriminant analysis to stratify geological areas with different spatial variability of soil properties the spatial variation of soil properties within landscapes is controlled by the soil forming factors relief parent material climate organisms and time although this relation is a paradigm in soil survey it is rarely considered in the analysis of spatial variability of soil properties homogeneous soil units are mostly mapped according to the soil properties found close to the soil surface nevertheless a large heterogeneity may occur at greater depths for soils developed in two different geological strata this is often the case in former periglacial areas where pleistocene sediments cover older strata the aim of this paper is to show how discriminant analysis can be used to objectively determine the soil depth at which geology changes this information may then help to develop better soil surveys and improve the geostatistical regionalization of soil properties the study area is a 1 5 km 2 soilscape 50 km north of munich with large variability in relief and parent material at 450 nodes of a rectangular 50 50 m grid fundamental soil properties were measured for each soil horizon relief parameters were calculated using a digital elevation model dem derived from more than 4000 elevation measurements parent material of the soils may be sediments of the tertiary period ts or quaternary sediments qs altogether 86 soil horizons were classified with confidence to ts and 496 to qs they were the training data set for a discriminant analysis to distinguish horizons of ts from horizons of qs in addition to several relief parameters the horizons depth position within the soils was used as a discriminant variable the discriminant functions classified 87 of ts and 85 of qs training data set horizons correctly by using elevation above sea level depth slope and upslope watershed area as independent variables solving the discriminant functions with respect to the boundary depth between qs and ts and applying the result to the dem yielded a map of boundary depth for each location of the study area at 19 locations within the study area the predictions were validated

shear fracture pattern and microstructural evolution in transpressional fault zones from field and laboratory studies abstract zones of transpressional shear deformation accommodate strike slip and oblique slip displacements field work in a transpressive shear zone and transpressional analogue clay box modelling show that a p oriented foliation and associated p shears are preferentially developed over the more common r 1 riedel shears the carboneras fault system cfs in se spain is a left lateral transpressional shear zone with an internal geometry characterized by first order y oriented faults and widespread p oriented second order faults the mesoscopic to microscopic gouge fabric reflects the regional architecture of the shear zone being dominated by a pervasive poriented foliation and discrete y and p shears friction experiments carried out to investigate the textural evolution of gouge fabrics showed four textural stages of fabric development from foliation formation to extreme shear localization resulting in cross gouge failure transpression clay box models favoured the formation of secondary p oriented shear fractures and p oriented shear lenses further deformation caused differential shear lens rotation and shear lens orientations closer to the mean displacement direction our field studies and laboratory analogue experiments indicate that shear zones dominated by p shears are diagnostic of a transpressional deformation regime

experiments on simultaneous faulting and folding above a basement wrench fault abstract wrench zones commonly show en echelon patterns of folds in the stratified cover above a basement fault examples are the darien basin in panama and the inglewood fault trend in california folds are often associated with synthetic and antithetic wrench faults but the time relationships between folds and faults may not be obvious we have done experiments where simultaneous faulting and folding occur above a basement fault four experiments were performed using a simple apparatus capable of imposing localised strike slip motions this apparatus consists of two plastic plates one can be moved laterally past the other by a piston thus modelling lateral motion on a single basement fault models were properly scaled to account for gravitational forces brittle behaviour of sandstone and ductile behaviour of clay or shales in the upper crust each model is a vertical succession of silicone layers and sand layers each layer is 2 mm thick except for the basal silicone layer which is 2 4 6 or 8 mm thick in experiments 1 2 3 or 4 respectively all models were deformed at the same slip rate on the basal fault 1 cm h 1 experiments 1 2 and 3 with 8 cm total horizontal sinistral offset were designed to investigate the influence of basal silicone layer thickness on the deformation of a multilayered model experiment 4 with 20 cm of total offset was designed to investigate the influence of an increasing left lateral offset on folding and faulting with a 2 mm thick basal silicone layer experiment 1 synthetic strike slip faults appeared en echelon above the basement fault no folds were visible at the surface of the experiment but the interfaces between sand and silicone layers showed millimetric folds en echelon above the basement fault with a 4 mm thick basal silicone layer experiment 2 en echelon synthetic strike slip faults and folds appeared above the basement fault faults and folds rotated progressively anticlockwise and synclines were activated as dextral antithetic shear zones with a 6 mm thick basal silicone layer experiment 3 synthetic faults and en echelon folds appeared as before but the fold amplitude was larger than in experiment 2 an increasing left lateral offset produced anticlockwise rotation of faults and folds as before and synclines were activated as dextral antithetic shear zones in experiment 4 after 16 cm of left lateral offset the anticlockwise rotation of the folds was such that antithetic dextral shear zones became almost parallel to the basement fault and were then reactivated as synthetic sinistral shear zones

transfer zones of deformation in thrust wedges an experimental study abstract although numerous transfer zones of deformation have been observed in thrust wedges their mechanisms and conditions of development are poorly understood in this paper three basic questions are addressed 1 1 what are the parameters controlling the genesis of transfer zones 2 2 what are the kinematics of thrust propagation during transfer zone development 3 3 which kinds of geological structure link the two compartments on either side of the transfer zone we attempted to solve these problems using a 3 d experimental approach sand models were used to simulate the foreland a rigid but mobile backstop was used to produced a thrust coulomb wedge which was studied during the various stages of its formation shortening led to the development of transfer zones in the wedge separating two domains of homogenous behaviour and connecting thrust planes in different domains the experimental results show that the development of transfer zones is controlled by mechanical and or geometrical parameters such as 1 1 variations in the sedimentary thickness in the foreland 2 2 the steepness of the backstop 3 3 domains with different basal friction in the foreland 4 4 kinked backstop geometry during deformation of the models two types of thrust sequence were identified alternative thrust propagations on both sides of the transfer zone and synchronous thrust propagations which are anastomosed within the transfer zone 3 d reconstructions revealed that the thrust deformations observed in the transfer zone are oblique ramps the frontal thrust bending of the barbados accretionary complex as well as the imbrication of thrust in the castellane arc and the oblique ramp in the zanskar range are discussed in relation to the mechanisms and structures revealed by the models the results of analogue modelling suggest that the development of transfer zones is directly linked to variations in the boundary conditions mechanical and or geometrical between two adjacent parts of a thrust wedge

simultaneous pure and simple shear the unifying deformation matrix abstract any simultaneous combination of finite simple shear and finite pure shear is a linear transformation which can be expressed as a single transformation matrix for two dimensions the matrix is upper triangular with an off diagonal term called the effective shear strain is a simple function of the pure and simple shear components for three dimensions a simultaneous combination of thrusting in the x direction thrusting in the y direction and a wrench in the x direction in addition to 3 orthogonal components of coaxial strain can also be represented by a 3 3 upper triangular matrix here three off diagonal terms xy x y and y z occur xy is a simple function of the horizontal coaxial strain values and thrusting in the x direction yz depends on the coaxial strain components in the y and z directions and the thrusting in the y direction while xz is related to all six strain components the matrix also allows for volume change either homogeneously or preferentially in a single direction a method of decomposing the deformation matrix into a series of incremental deformation matrices where each incremental deformation records the same kinematic vorticity number as the finite deformation is shown the orientation and magnitude of the finite strain ellipsoid ellipse is easily and accurately found at any increment during the deformation

analogue modelling of inclined brittle ductile transpression testing analytical models through natural shear zones external betics abstract the combination of analytical and analogue models gives new opportunities to better understand the kinematic parameters controlling the evolution of transpression zones in this work we carried out a set of analogue models using the kinematic parameters of transpressional deformation obtained by applying a general triclinic transpression analytical model to a tabular shaped shear zone in the external betic chain torcal de antequera massif according to the results of the analytical model we used two oblique convergence angles to reproduce the main structural and kinematic features of structural domains observed within the torcal de antequera massif 15 for the outer domains and 30 for the inner domain two parallel inclined backstops one fixed and the other mobile reproduce the geometry of the shear zone walls of the natural case additionally we applied digital particle image velocimetry piv method to calculate the velocity field of the incremental deformation our results suggest that the spatial distribution of the main structures observed in the torcal de antequera massif reflects different modes of strain partitioning and strain localization between two domain types which are related to the variation in the oblique convergence angle and the presence of steep planar velocity and rheological discontinuities the shear zone walls in the natural case in the 15 model strain partitioning is simple and strain localization is high a single narrow shear zone is developed close and parallel to the fixed backstop bounded by strike slip faults and internally deformed by r and p shears in the 30 model strain partitioning is strong generating regularly spaced oblique to the backstops thrusts and strike slip faults at final stages of the 30 experiment deformation affects the entire model box our results show that the application of analytical modelling to natural transpressive zones related to upper crustal deformation facilitates to constrain the geometrical parameters of analogue models

physical experiments of transpressional folding abstract in order to understand the process of folding in obliquely convergent settings we formed folds within a shear box capable of creating homogeneous transpressional deformations folds were created in a single layer of stiff mixed plasticine and silicone that overlay a newtonian silicone for a variety of plate convergence angles as small amplitude folds became visible they were parallel to the long axis of the horizontal finite strain ellipse with increasing deformation the fold hinges rotated parallel with the long axis of the horizontal finite strain ellipse for all angles of convergence this parallelism indicates that fold hinges once formed rotate with the horizontal strain ellipse rather than as material lines the experiments highlight several interesting effects of transpression dynamics the fold hinges initiate parallel to either 1 or 2 and are parallel to either s 1 or s 2 with increasing deformation neither infinitesimal strain stress nor finite strain is resolvable solely from fold geometry further the net amount of contraction determined by folding across the zone was overestimated in all cases except pure contraction this effect is obvious for the case of wrenching where folding implies that the zone contracts if elongation parallel to the fold hinge is not considered therefore attempts to balance cross sections in transpressional zones will tend to overestimate contraction unless the wrench component of deformation is addressed this result is validated by applying the modeling results in folding in central california adjacent to the san andreas fault where cross section balancing indicates higher amounts of contraction than predicted by plate motion

fabric attractors in general triclinic flow systems and their application to high strain shear zones a dynamical system approach high strain zones may deform by flow with a triclinic symmetry this paper describes triclinic flow in a reference frame where instantaneous stretching axes isa are fixed the operation of triclinic flow is described in two ways first in terms of flow and the nature of flow eigenvectors and in the second part of the paper in terms of finite strain in monoclinic flow at least one of the eigenvectors of the flow coincides with one of the isa and one or two of the eigenvectors act as attractors of foliation or lineation elements in triclinic flow some flow eigenvectors are undefined since the two largest eigenvalues controlling the flow are imaginary imaginary eigenvalues are particularly common at high kinematic vorticity and within flow with deviation of the vorticity vector of more than 20 from one of the isa strong deviation from monoclinic flow is therefore possible but this will not produce permanent foliations or lineations for triclinic flow that does produce permanent fabrics the angle between isa and the fabric is so small that it is unlikely that it can be recognised in nature a discussion of the potential application of such results within real shear zones is presented

structural trend line pattern and strain partitioning around the gibraltar arc accretionary wedge insights as to the mode of orogenic arc building 1 mediterranean tectonics results in tight orogenic arcs enclosing back arc basins of oceanic or thinned continental lithosphere the gibraltar arc cannot be explained solely by the europe africa plate convergence therefore complementary mechanisms have been proposed most of them imply a westward motion of the arc and a general transpressive regime on both branches betic and rif chains a structural revision made along the western gibraltar arc allows us to generate a detailed kynematic map and to introduce new constraints on the possible arc formation mechanisms our results suggest that the strain partitioned into two main types of structures structures accommodating suborthogonal shortening folds and thrusts and structures accommodating arc parallel stretching normal faults conjugate strike slip faults and distributed minor structures on the basis of the fan pattern depicted by the slip direction of contractional structures and the homogeneous distribution of arc parallel stretching an arc formation mode close to the piedmont glacier type is suggested

strain distribution and fabric development modeled in active and ancient transpressive zones 1 a model based on kinematics of transpression allows the measurable internal parameters simultaneous strain fabric and vertical elevation to be simulated in relation to the macroscopically determined external parameters of transpressive zones i e zone width velocity angle of convergence and zone depth we present a diagram of convergence angle against time for homogeneous transpression where isolines of strain intensity d strain symmetry k and vertical elevation of rock samples are superposed however the distribution of internal strain parameters is sensitive to three types of strain partitioning 1 discrete partitioning results in general decrease of finite strain accumulations and in increase of pure shear component 2 ductile partitioning splits the transpressional domain into a pure shear zone where strain accumulations decreases and in a wrench dominated zone where strain accumulations increases and 3 viscosity partitioning is marked by different strain rates in zones of different viscosity and therefore by different strain parameters

helium isotopes in paleofluids and present day fluids of the larderello geothermal field constraints on the heat source 1 the he isotope composition of paleofluids entrapped in fluid inclusions of hydrothermal minerals is compared with the present day fluid composition of the larderello geothermal field almost constant values of 3he 4he m 3he 4he air r ra over time indicate that no important changes have occurred in the deep source of gases at least during the last 3 8 million years on a regional scale a correlation has been found between the r ra spatial distribution heat flow and bouguer gravity anomaly high values of r ra and heat flow and low bouguer anomaly values indicate that the larderello field is an area of preferential escape for mantle derived fluids a positive correlation has also been found between the r ra spatial distribution and a major seismic reflector named the k horizon a deep magma source refilled by periodic gas input from the mantle is the most likely source of 3he enriched fluids and the anomalously high heat flow the nearly constant value of r ra clearly indicates that input of fresh mantle material has occurred up to recent times clear evidence of mixing between mantle and crustal fluids indicates that the high r ra is the lower limit of the actual mantle value which is suggested to be similar to the subcontinental european mantle the decrease of r ra over time in the peripheral part of the larderello field indicates that important changes in the feeding fracture system and or cooling rate have occurred in these areas

mechanics of fore arc slivers insights from simple analog models 1 convergent margins with oblique subduction commonly include a fore arc sliver a portion of the overlying plate bounded by the trench and a major strike slip fault system it has long been noted that relative plate motion near the deformation front as indicated by earthquake focal mechanisms is generally closer to margin normal than would be expected from overall relative plate motion this results from sliver motion as well as from shear within the fore arc we carry out some simple calculations to determine how the rate of sliver motion should vary with plate convergence obliquity we find that the results are related to rheology but that the measurement of sliver rates at natural fore arcs is unlikely to yield real insight into physical properties even for very simple models the system is too complicated and its relation to rheology is not unique the proportion of oblique convergence taken up by sliver motion in simple tabletop experiments depends on the rate of slip and the smoothing of asperities similarities in taper and style of strain between frontal wedges forming with and without slivers suggest that structural observations of exhumed accretionary wedges are unlikely to allow geologists to draw definitive conclusions about the degree of obliquity of relative plate motion at the time when the wedges were formed and in some cases not even whether or not a sliver plate was present at the time of deformation

the effect of convergence angle on the kinematic evolution of strain partitioning in transpressional brittle wedges insight from analog modeling and high resoluiton digital image analysis 1 using analog modeling aided by digital image analysis dpiv we constrained the long term kinematic evolution of strain partitioning in transpressional brittle wedges as a function of convergence angle we ran a series of dry quartz sand experiments representing highly oblique continent continent collision convergence angles of 4 to 30 the digital image analysis provided high resolution constraints on the long term kinematic evolution of these wedges which could be subdivided in distinct kinematic stages comprising 1 an initial distributed strain stage and 2 an oblique wedge stage before 3 the stage of strain partitioning is reached thus we document the evolution of different deformation stages from a single plate tectonic boundary condition in addition the relationship between convergence angle kinematic stages and wedge geometry including fault dips and fault hierarchy was established the modeling results show that smaller convergence angles lead to steeper faults besides for a constant convergence angle the proshears that evolved during the strain partitioning stage were less steep than those formed during the oblique wedge stage the fault slip vector on individual fault segments was derived from the dpiv data set for each time increment quantifying the magnitude and orientation of slip on fault segments during the different kinematic stages in addition in the 7 5 and 15 models rotation of the slip vector by up to 40 was observed on a single proshear during the strain partitioning stage these observations allow to some degree a validation of existing analytical models of strain partitioning in particular the assumption of steady state

sustainable transpression an examination of strain and kinematics in deforming zones with migrating boundaries most orogenic belts owe their development to oblique convergence and commonly have many orogen parallel transpressional high strain zones to constrain the tectonic history of orogenic belts by structural and fabric analysis of rocks it is desirable to understand quantitatively the relationship between the boundary conditions and the resulting strain distribution and kinematics in these zones most current models for transpression assume homogeneous deformation confined by boundaries that are fixed to material planes this creates a strain compatibility problem at the margins of the active deforming zone and also requires that the strain rate normal to the zone boundaries increase to implausibly high values soon after the onset of oblique convergence transpressional motion the latter contradicts with the observation that transpressional motion can be sustained throughout an orogeny the assumption that zone boundaries are fixed to material planes is unrealistic the outstanding problems of current transpressional models are resolved in this paper by allowing the zone boundaries to migrate through the rock material the consequence of zone boundary migration for the strain field and kinematics within a transpressional high strain zone is investigated mathematically the implications of the modeling for fabric interpretation are discussed the modeling makes general predictions consistent with observed planar and linear fabric patterns in natural transpressional high strain zones it predicts that foliations in transpressional high strain zones are subparallel to the zone boundaries regardless of variation in the imposed boundary conditions lineations cluster along the great circle girdle subparallel to the average foliation the spread of the lineations may vary from point maxima to complete girdles

kinematics of compressional fold development in convergent wrench terranes abstract kinematic models are presented for compressional fold development in wrench and convergent wrench terranes that relate fold shortening axial rotation and axial extension fold shortening may be derived from final fold geometry existing fold geometry and axial orientation two readily measurable quantities provide the data needed to determine the relative components of shearing and convergence within the fold system analyses utilizing these kinematic models indicate that folds developed in sedimentary rocks in the wrench borderlands of both the rineonada and san andreas wrench faults in central california are the product of strongly convergent wrenching the axes of these folds have been rotated no more than a few degrees during the course of their development in contrast folds developed in the alpine schists along the alpine fault in new zealand and in pleistocene sediments along the southern limit of the san andreas fault suggest an almost pure wrench setting and large 25 axial rotations significant axial extension is inherent in wrench related compressional folds this axial extension is commonly manifest in the form of normal and strike slip faults that are internal to the folds and trend at high angles to the fold axes the relative amount of axial extension diminishes as the degree of convergence increases this axial extension and the associated extensional features can be a diagnostic indication of the influence of wrenching

kinematics of the torcal shear zone transpressional tectonics in a salient recess transition at the northern gibraltar arc abstract complex strain patterns in the gibraltar arc derive from the interaction between the westward drift and concomitant back arc extension of the arc hinterland alboran domain and the europe africa convergence in order to explore strain partitioning modes within the arc and the role played by large scale oblique structures we have studied the kinematics of the torcal shear zone located at the northern branch of the gibraltar arc the torcal shear zone is a 70 km long e w brittle ductile shear zone that underwent overall dextral transpression during the late miocene to quaternary time within the torcal shear zone strain is highly partitioned at multiple scales into shortening oblique extensional and strike slip structures moreover strain partitioning is heterogeneous along strike giving rise to four distinct structural domains in the central sector the strain is pure shear dominated although narrow sectors parallel to the shear walls are simple shear dominated a single n99 e n109 e trending horizontal velocity vector v could explain the kinematics of the entire central sector of the torcal shear zone lateral domains have different strain patterns and are comparable to splay dominated and thrust dominated strike slip fault tips the torcal shear zone provokes the subvertical extrusion of the external betics units against the alboran domain and a dextral deflection of the structural trend moreover the estimated v points to the importance of the westward motion of the hinterland relative to the external wedge and fits well with the radial outward thrusting pattern identified in the arc

mantle lithosphere bodies in the alboran crustal domain ronda peridotites betic rif orogenic belt abstract geological and geophysical data are used to demonstrate the existence of intracrustal high density high p wave velocity bodies in the western betics these bodies appear to correspond to buried peridotites similar to those that outcrop in the ronda area a gravity study shows how the gravity field is mainly the result of a combined effect of crustal thinning and the presence of ultramafic bodies the size of the buried high density body as interpreted from gravity and seismic results shows maximum dimensions of about 40 km in length nnw sse about 8 km in thickness and a lateral extension ene wsw of about 70 km the thinning of the crust from 32 35 km to 20 22 km takes place in a narrow area less than 35 km wide our results are compatible with an interpretation in terms of an unrooted peridotite slab dismembering of an initial slab of ultramafic rocks is a possible consequence of the extensional regime that originated the alboran basin

3d seismic survey for geothermal exploration in crystalline rocks in saxony germany a 3d seismic survey was recorded in 2012 to explore a petrothermal reservoir in a late variscan granitic pluton within the erzgebirge ore mountains in saxony germany the main objective was to test this area in the context of the enhanced geothermal system concept and to test the 3d seismic technique as an exploration tool the intention and challenge are to image and characterize potentially permeable fracture zones at target depths of 5 6 km with temperatures above 150 c unconventional methods were applied for field acquisition and data processing the vibroseis technique was used in the core experiment accompanied by a special explosive seismic experiment field acquisition was characterized by severe noise conditions and a highly irregular layout these conditions required extensive preprocessing and data conditioning the imaging started with conventional common midpoint processing for quality control and for a first reference better images were obtained by common reflection surface processing with subsequent post stack time migration prestack time migration was also used for comparison outstanding results were obtained by the operator oriented version of the common reflection surface technique a rich repertoire of structures within the granite pluton was imaged including steeply dipping fault zones and conjugate faults images and indications of fracture and crack porosity of a prominent fault zone provide the background to define an optimum drill path this is considered as the next stage for a possible geothermal plant if a decision is taken to drill a research well in the future the 3d seismic reflection technique was shown to be an indispensable tool for geothermal exploration even in crystalline basement rocks

kinematic analysis of the southern iberian shear zone and tectonic evolution of the acebuches metabasites sw variscan iberian massif 1 the acebuches metabasites constitute a slice of oceanic crust located at the variscan suture between the ossa morena and the south portuguese zones iberian massif the emplacement of the metabasites onto the accretionary prism was associated with the activity of the southern iberian shear zone careful measurements of the fabrics and structures related to this shear zone show consistent kinematic criteria pointing to the presence of a simple shear component with an oblique predominantly left lateral sense of displacement the data are consistent with existing models of triclinic or oblique shear zones considering coeval simple shear and pure shear components these models provide a satisfactory explanation of the observed spatial variations in the foliation lineation and fold hinge data the kinematics of other shear deformations older and younger than the southern iberian shear zone have also been established these results offer new insights into the tectonic evolution of this suture of the variscan belt and show how complex transpressional strains can arise during oblique crustal deformation associated with the motions of tectonic plates

a transpressional origin for the west spitsbergen fold and thrust belt insight from analog modeling 1 the west spitsbergen fold and thrust belt formed along the transform plate boundary between greenland and the western barents sea during paleocene eocene breakup in the northern north atlantic approximately 20 40 km margin perpendicular shortening accumulated in the belt has been attributed to transpression and strain partitioning in a restraining bend but also to head on collision we have applied scaled analog tectonic modeling to test the former hypothesis a pack of brittle quartz sand with a shallow thin layer of silicon putty was deformed by transpression at a 15 convergence angle by movement of a basal plate the kinematics was quantified by means of digital particle image velocimetry the result was a doubly vergent transpressional wedge consisting of a steeply tapered retrowedge and a strongly internally deformed steeply tapered prowedge separated by a central strike slip zone and an adjacent low taper thin skinned fold and thrust belt the doubly vergent wedge evolved through several kinematic phases three main stages were identified namely 1 initial distributed deformation 2 development of an oblique doubly vergent wedge with progressive evolution of local strain partitioning along the marginal shear zones and finally 3 a stage of full strain partitioning between a central strike slip zone and reverse displacement along marginal shear zones with folding and thrusting in a thin skinned belt on the proside the analog model convincingly reproduced the geometry and the kinematic evolution of the west spitsbergen fold and thrust belt supporting the hypothesis of its formation by strain partitioning in transpression with a small angle of convergence and significant lateral displacement

high strain zones a unified model abstract where a shear zone is bounded by undeformed wall rocks and there is no volume change the deformation path within the zone on the bulk scale approximates a simple shear where the zone boundaries are stretched and the shear direction between the two boundaries is parallel to one of the principal stretching directions of the boundaries the deformation path within the zone is not a simple shear but still has monoclinic symmetry both simple shear and general monoclinic deformation paths should be regarded as special cases in nature because generally not only are the zone boundaries stretched but also the shear is oblique to the principal stretching directions of the boundaries in this general case the deformation path is triclinic we establish a model which includes this general case also taking into consideration volume change five independent parameters are required to characterize the rate of deformation of the flow four are sufficient to characterize the flow kinematics the model is generally triclinic and orthorhombic and monoclinic deformations are subgroups by varying the values of the characterizing parameters the various types of high strain zones can be represented the kinematics of flow within such zones and the accumulated finite deformation geometry are investigated many field observations such as for example lineations in transcurrent shear zones that vary between vertical and horizontal cleavage transected folds and the absence of sheath folds in some shear zones where folds have been significantly rotated can sometimes be better interpreted in the context of our general model

slip partitioning and inclined dextral transpression along the zagros thrust system iran abstract flexural duplex structures and shear zones are well developed in the heneshk area in southwestern iran the zagros thrust system in this area consists of eight sheets of nw striking ne dipping dextral strike slip duplexes that are linked with imbricate fans and oblique slip thrusts the zagros thrust system is a portion of the internal zone of the zagros orogenic belt this internal zone is characterized by penetrative plastic deformation and metamorphism based on the kinematic vorticity number w k 0 73 0 02 calculated from quartz porphyroclasts of the goshti shear zones along the zagros thrust system the estimated angle between the maximum instantaneous strain axis isa and the transpressional zone boundary is 33 the estimated angle of the plate convergence or the flow apophysis of the displacement field is 25 the presence of dominantly dextral shear sense indicators in the area is consistent with dextral inclined transpressional convergence the mean estimated finite deformation w m value indicates relative contributions of 47 pure shear and 53 simple shear for the deformation which involved both strike slip and oblique slip displacements in this inclined transpression about 40 strike slip partitioning was required to accommodate the finite strain and re orientation of instantaneous strain

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction