geometrical analysis of the punta del pedron shear zone asturias spain implications related to exploration of salave gold type mineralization abstract the salave gold deposit is located at the northern end of the oscos gold belt which forms part of the asturian leonese zone of the variscan massif the gold belt and the salave deposit are genetically related to the emplacement of post kinematic granitoids which were largely controlled by variscan fracture systems a geometrical analysis following the mccoss mccoss a m 1986 simple construction for deformation in transpression transtension zones journal of structural geology 8 6 715 718 method has been utilized to discriminate the transpressional transtensional and simple shear components and the displacement vectors s vectors of the punta del pedron shear zone a contour map of the s vector orientations is consistent with the contour map of the calculated extension of the whole area and shows those shear zones where extensional and contractional components have been determined extension is higher e 15 towards the east where transtension is predominant near the salave gold deposit this deposit is located at the intersection of the extensional sinistral shear zones striking between 130 and 140 which promoted dilation and the emplacement of the salave granodiorite with the dextral shear zones striking between 070 and 080 extension was transferred to the dextral shear zones and associated 030 pinnate veins in a transtensional stage which promoted connected vein systems and localized fluid flow this gave rise to the alteration patterns of the deposit and ore deposition in an area previously affected by the mondonedo thrust system the use of this geometrical method with limitations and several assumptions discussed in the text and the analysis of the scaling properties of the vein sets in traverses can be utilized in the field to aid in mineral exploration

heterogeneous strain associated with normal faulting evidence of mass transfer by pressure solution associated with fault displacement abstract in a well stratified flysch in the french pyrenees the offset of layers along a fault zone provide good data of relative displacement it is shown that the fault surface is composed of three right stepping fractures that opened tensile bridges along small left stepping fractures translation on the fault zone is parallel to the fault surface the displacement vector field shows that the movement between the two blocks was not a rigid body translation and that deformation in the hanging wall is greater than that in the foot wall volume loss within the rock is compensated by volume increase close to the fault surface calcite dissolution and reprecipitation by pressure solution is indicated by the occurrence of stylolites and numerous calcite filled veins around the fault calcite dissolution is more important in the hanging wall especially in layers where the calcite content is close to 60 both cathodoluminescence observations and rare earths element patterns are in favour of calcite in veins and dominos coming from units adjacent to the fault there is no evidence that some calcite coming from farther distance could have entered in the system

the mechanics of intersecting echelon veins and pressure solution seams in limestone abstract many studies that describe the formation of echelon vein arrays relate the causative stresses implicitly to the deformation reliant on simple shear kinematics such that the vein to array angle and the array width are the primary physical quantities in contrast we identify twelve physical quantities to describe echelon veins in two dimensions including coeval vein intersecting pressure solution seams a finite element method is used to reproduce vein shapes in linear elastic and elastic perfectly plastic model limestone model vein geometries are designed using values within the range of geometries measured from echelon veins at raplee anticline and comb monocline utah four physical quantities are significant for describing echelon vein shapes vein spacing vein array angle limestone elastic stiffness and closing of orthogonal pressure solution seams pressure solution seam closing influences the mechanical interaction between adjacent veins and for a range of conditions causes a nearly linear vein opening distribution triangular shapes and encourages straight vein propagation both of which approximate field measurements model results show that small spacing of veins with seams and large vein array angles promote straight vein traces in limestone with stiffness typical of laboratory measurements given the physical geologic conditions inferred from the burial history of the limestone strata

pull apart formation and strike slip partitioning in an obliquely divergent setting leka ophiolite norway abstract the leka ophiolite complex loc is located on the island of leka norway and belongs to the uppermost allochthon of the scandinavian caledonides the rocks of the adjacent mainland and most of the surrounding islands are basement gneisses and supracrustal rocks not related to the ophiolite complex paleostress analysis gravity inversion and regional geology support a fault bounded rhombochasm geometry for the loc the paleostress inversions revealed two types of tensors interpreted as small strains 1 horizontal extension generally e w to ne sw and 2 horizontal extension in the same direction with an added component of perpendicular horizontal contraction a strong positive gravity anomaly 25 mgal is centered on leka and gravity inversion indicates that the loc lies directly below its surface exposures with steep sided walls and a flat bottom located at 7 km depth the faults bounding the loc probably initiated during postorogenic extension in the scandinavian caledonides the faults are regional in scale and are parallel to other ne sw trending en echelon faults along the norwegian coastline and on the adjacent mainland a pull apart structure explains the down dropping and subsequent preservation of the loc as it is surrounded by rocks from lower structural positions within the nappe stack the paleostress directions from leka support a sinistral component of shear along these faults the gravity inversion is consistent with a fault bounded geometry this pull apart structure as uniquely recorded by the dense ophiolitic rocks suggests that strike slip partitioning was active in an obliquely divergent setting

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

the development of brittle structures in an alpine valley glacier pasterzenkees austria 1887 1997 brittle structures exposed in the ablation area of pasterzenkees austria were interpreted using aerial photographs and maps covering a period of 100 years the most common structural features observed in aerial photographs are 1 normal faults which are particularly well developed along the lateral margins of the glacier and at the terminus 2 large scale tension gashes and riedel shears that develop along the northeastern lateral margin of the glacier and between ice flow units 3 thrust faults which develop at the terminus and cross cut the full width of the glacier and 4 band ogives longitudinal and transverse topographic profiles are available for the period covered in this study and ice flow velocity data are available from 1927 these data provide a means for interpreting the variations of observed structures in terms of ice flow velocity thrust faults predominantly develop during periods of glacier retreat when the glacier snout becomes an obstacle normal faults typically develop in areas of high glacier surface relief and are interpreted as gravity collapse structures the orientation of sub vertical wide open crevasses along the lateral margin of pasterzenkees varied these variations are interpreted as reflecting changes of the flow regime and indicate a transition from simple shearing to transtension during a period of ice flow deceleration

fine fracture structures in the geothermal region of hakone volcano revealed by well resolved earthquake hypocenters and focal mechanisms abstract we investigated precise hypocentral distribution and the mechanisms of small earthquakes in the geothermal region of hakone volcano central japan where swarm activity has been frequently observed earthquake swarms were remarkably prevalent in 2001 and 2006 and were accompanied by crustal deformation we first determined initial hypocenters using station corrections and one dimensional velocity structures as estimated by the joint hypocenter determination method then we applied the double difference method to relocate the initial hypocenters using the differential arrival time obtained by both manual picking and waveform cross correlation analysis subsequently we determined the focal mechanisms from the absolute p and sh wave amplitudes and p wave polarities from the relocated hypocenter distribution we found that most swarm earthquakes are distributed on thin plane like zones with width length of 100 m to 1 km we found that these plane like hypocentral distributions range from the e w to n s strikes and are consistent with one of the nodal planes of the focal mechanism it is likely that most swarm earthquakes occurred on pre existing fracture planes shaping the plane like hypocenter distributions previous studies suggested that a highly permeable fracture system has developed in the fault interaction area and these highly permeable fractures affect the occurrence of swarm earthquakes and surface geothermal activity since hakone volcano is located in the interaction area of the active tanna and hirayama faults it is suggested that the fracture planes revealed by the relocated hypocenter distribution have been developed by the activity of the two faults the fracture planes in the caldera might be channels for the hydrothermal water of hot springs in the caldera of hakone volcano which are rich in sodium chloride and considered to be composed of fluid heated by a deep seated magma the strike of the fracture plane on which the swarm earthquakes of the 2001 activity occurred is inconsistent with the orientation of open crack models estimated from geodetic data it is therefore possible that the hydrothermal fluid aseismically intruded the open cracks during the 2001 activity

evolution of fault zones in carbonates with mechanical stratigraphy insights from scale models using layered cohesive powder abstract we present analogue models of the formation of dilatant normal faults and fractures in carbonate fault zones using cohesive hemihydrate powder caso 4 h 2 o the evolution of these dilatant fault zones involves a range of processes such as fragmentation gravity driven breccia transport and the formation of dilatant jogs to allow scaling to natural prototypes extensive material characterisation was done this showed that tensile strength and cohesion depend on the state of compaction whereas the friction angle remains approximately constant in our models tensile strength of the hemihydrate increases with depth from 9 to 50 pa while cohesion increases from 40 to 250 pa we studied homogeneous and layered material sequences using sand as a relatively weak layer and hemihydrate graphite mixtures as a slightly stronger layer deformation was analyzed by time lapse photography and particle image velocimetry piv to calculate the evolution of the displacement field with piv the initial predominantly elastic deformation and progressive localization of deformation are observed in detail we observed near vertical opening mode fractures near the surface with increasing depth dilational shear faults were dominant with releasing jogs forming at fault dip variations a transition to non dilatant shear faults was observed near the bottom of the model in models with mechanical stratigraphy fault zones are more complex the inferred stress states and strengths in different parts of the model agree with the observed transitions in the mode of deformation

evolution of strike slip duplexes and wrench related folding in the central part of al jabal al akhdar ne libya abstractthe deformation in the central part of al jabal al akhdar ne libya is dominated by e w right lateral strike slip fault zones that form a conjugate system with the n s left lateral strike slip faulting the dextral wrench dominated transpression is responsible for the formation of strike slip duplexes en echelon folds and thrusts that deform the cretaceous eocene sedimentary sequences the strike slip duplex is formed by the progressive linkage of horsetail like structures at the western tip of the al bayda strike slip fault that joined splays coming from other dextral strike slip faults the master linear fault branches into second order dextral or sinistral faults that regroup into a linear single fault faults started from arrays of en echelon extensional extensional shear fractures that then coalesced into throughgoing strike slip faults shortening was accompanied by significant n s striking left lateral strike slip displacements with the development of ne to ese and sw plunging major f

kinematics of throughgoing fractures in jointed rocks abstract throughgoing fractures play a major role in subsurface fluid flow yet the kinematics of their formation which directly impact rock flow properties are often difficult to establish we investigate throughgoing fractures in the monterey formation of california that developed by the coalescence of pre existing joints at lompoc landing throughgoing fractures fall into three main groups linked linked with aperture and breccia zones the segmented nature of their walls provides numerous piercing points to firmly establish the sense of displacement analysis of displacement vectors derived from piercing points demonstrates that the nw se trending throughgoing fractures often interpreted as strike slip faults are in fact extensional structures in origin we suggest that this method may be applied to throughgoing fractures that form by the same mechanism in other geologic settings establishing kinematics of throughgoing fractures will lead to a better understanding of their contribution to subsurface fluid flow

modeling river dune development and dune transition to upper stage plane bed large asymmetric bedforms known as dunes commonly dominate the bed of sand rivers due to the turbulence generation over their stoss and lee sides dunes are of central importance in predicting hydraulic roughness and water levels during floods in steep alluvial rivers dunes are observed to grow rapidly as flow strength increases undergoing an unstable transition regime after which they are washed out in what is called upper stage plane bed this transition of dunes to upper stage plane bed is associated with high transport of bed sediment in suspension and large decrease in bedform roughness in the present study we aim to improve the prediction of dune development and dune transition to upper stage plane bed by introducing the transport of suspended sediment in an existing dune evolution model in addition flume experiments are carried out to investigate dune development under bed load and suspended load dominated transport regimes and to get insight in the time scales related to the transition of dunes to upper stage plane bed simulations with the extended model including the transport of suspended sediment show significant improvement in the prediction of equilibrium dune parameters e g dune height dune length dune steepness dune migration rate dune lee side slope both under bed load dominant and suspended load dominant transport regimes the chosen modeling approach also allows us to model the transition of dunes to upper stage plane bed which was not possible with the original dune evolution model the extended model predicts change in the dune shapes as was observed in the flume experiments with decreasing dune heights and dune lee slopes furthermore the time scale of dune transition to upper stage plane bed was quite well predicted by the extended model

fluid and sediment dynamics of upper stage plane beds to understand more fully the fluid and sediment dynamics of upper stage plane beds laboratory experiments were conducted using mobile and fixed beds where turbulent motions of fluid and sediment were measured using laser anemometry bed elevation fluctuations on mobile upper stage plane beds reveal millimeter high bed waves vertical profiles of flow velocity mixing length and eddy viscosity diffusivity are represented well by the law of the wall for the mobile bed von karman s 0 33 and equivalent sand roughness to mean bed grain size varies from 9 to 17 because of the presence of bed load and low relief bed waves for fixed beds with no sediment transport 0 41 and equivalent sand roughness is equal to the mean bedgrain size the decrease in for mobile beds is related to the relative motion of grains and fluid mobile bed turbulence intensities are greater than those for sediment free fixed beds because of enhanced wake formation from the lee side of near bed grains and low relief bed waves sediment diffusivities es calculated in a similar way to fluid diffusivities e indicate that es e sediment diffusivities calculated using the equilibrium balance between upward diffusion and downward settling of sediment are similar to e in near bed regions y d 0 3 suggesting that larger more energetic turbulent eddies are responsible for sediment suspension higher in the flow

evidence for pre folding vein development in the oligo miocene asmari formation in the central zagros fold belt iran in order to understand the interplay between vein development and folding in the carbonates of the oligo miocene asmari formation one of the main hydrocarbon reservoir rocks in iran several anticlines have been investigated in the central part of the zagros folded belt combining observations of relative chronology between veins based on calcite filling phases and crosscutting abutting relationships as well as aerial satellite image interpretation on several anticlines allowed proposing a tectonic model highlighting the widespread development of veins and other extensional micro meso structures in the central zagros folded belt our data suggest that most of the veins affecting the asmari formation predated the main miocene pliocene folding episode an early regional vein set striking n50 marked the onset of collisional stress build up in the region then n150 and n20 trending vein sets were initiated in response to local extension caused by large scale flexure drape folds above n s and n140 basement faults reactivated under the regional ne compression at the onset and during miocene pliocene folding of the sedimentary cover the early formed veins were reactivated reopened and or sheared while duplexes low angle reverse faults and thrusts formed beyond regional implications this study puts emphasis on the need of carefully considering regional local vein development predating folding as well as influence of underlying basement faults in models of folded fractured reservoirs in fold thrust belts

extension tectonics in the wessex basin southern england the permian to cretaceous tectonic evolution of the wessex basin was controlled by horizontal tensional and vertical isostatic forces within the lithosphere the gross morphologies of its constituent structures were governed by the location of variscan thrust and wrench faults in the upper and middle crust which suffered extensional reactivation in tensional stress fields oriented approximately nw se several episodes of crustal extension can be resolved in early permian early triassic early jurassic and late jurassic early cretaceous times these were characterized by the rapid subsidence of fault bounded basins and commonly by erosion of adjacent upfaulted blocks superimposed upon the fault controlled subsidence dominant during periods of fault quiescence and becoming increasingly important with time a component of regional subsidence is considered to have a thermal origin this suggests that crustal extension was accompanied by some form of not necessarily uniform lithospheric thinning subsidence analyses assuming local airey isostasy give cumulative crustal extension factors of 20 28 beneath the grabens a more reasonable assumption of regional airey compensation indicates basinwide crustal extension of 13 17 which is consistent with birps offshore deep seismic reflection data

earthquake faulting as a structural process abstract structural geology is concerned with the history of movement in the earth s crust and the processes by which displacements occur in the upper one third to one half of deforming continental crust displacement is accommodated largely by seismic slip increments on existing faults it follows that earthquakes and related processes are an integral part of structural geology traditionally structural geologists have been preoccupied with the complexity of the finite deformation within fault zones and with the stress states prevailing at the initiation of faults in intact crust future structural work should be directed more towards understanding the dynamic character of fault reactivation during incremental slip and related effects questions of interest include rheological and geometrical controls on the initiation perturbation and termination of ruptures directivity effects associated with rupture propagation the recognition of structures resulting from repeated stress cycling within seismogenic crust and identification of structural features diagnostic of shear stress levels during faulting structures arising from the inter relationships between slip episodes and induced fluid flow are of special importance because these dynamic fault processes appear influential in the development of much fault hosted mineralization mesothermal gold quartz lodes hosted in high angle reverse shear zones of mixed brittle ductile character form illustrative examples of structures that arguably can only be interpreted by seismo structural analysis embodying the concepts listed above

displacement features associated with fault zones a comparison between observed examples and experimental models abstract fault zones commonly consist of discontinuous surfaces or are composed of different kinds of en echelon fractures tension cracks r or p type fractures which give the brittle shear zone a width translation along these faults and related features can occur by sliding on the elementary planes and or by solution deposition processes with opening of transtension zones and possible dilatation of the shear zone in order to understand how fault planes develop and to investigate the mechanical conditions corresponding to natural configurations displacement along an analogue fault model was examined under conditions of direct shear the experimental fracture patterns were then compared with the natural features the structural elements of certain faults created by testing and showing transpression and transtension zones were found to be similar to natural domino structures bounded by elementary shears and could be compared with computed situations it can be inferred that stresses are reoriented inside the shear zone the angle between elementary fractures depends on their order of development transpression and transtension zones occur systematically and the shear zone undergoes dilatancy under low normal stresses

measurement of geometry and linkage in vein arrays abstract veins in an array are characterised by measurement of their length l width w and orientation and by the number 0 1 or 2 of adjacent veins to which they are linked data from a single array 129 veins and two regions comprising 146 and 64 arrays have been measured and analysed the system for measurement provides a sound basis for the quantitative assessment of both the array geometry and the effects of interaction of adjacent veins linkage is achieved by a breaching of the bridges of wall rock between veins either by extension fractures shear failure or the development of stylolites it is primarily controlled by the strain as measured by vein width the size and shape of the veins is found to be controlled by two factors the degree of linkage and the kinematics of the array transtension transpression interplay of these produces variability both within and between arrays and this is examined for two large datasets from the lower jurassic of somerset and the lower carboniferous of the gower peninsula south wales

mesoscale strike slip faults and damage zones at marsalforn gozo island malta well exposed strike slip faults in limestones in the north western part of gozo show damage zones that can be grouped into three categories based on their location along faults tip damage linking damage and distributed damage the predominant fracture types within damage zones include extension fractures and secondary faults tip damage zones usually show wedge shaped patterns formed by antithetic faults and extension fractures commonly accompanied by block rotation several fractures are combined at linking damage zones typically with the concentration of a high intensity of fractures structures in distributed damage zones are typically similar to the classical riedel shear pattern evolutionary and 3d models are proposed in terms of the geometries of damage zones for small displacement strike slip fault zones different evolutionary routes depend on fault tip modes and locations

bridge structures as sense of displacement criteria in brittle fault zones abstract fault zones often occur as arrays of en echelon fractures there are two main types of en echelon patterns involving right or left stepping fractures in such arrays first generation fractures define compressive or tensile bridges the structural features of such natural bridges at any scale can be used as criteria to determine the sense of displacement small compressive bridges provide criteria based on the increase in linear density of solution seams related to the degree of asymmetry of the fault trace and to the sequence of formation of the different types of en echelon fractures the criteria deduced from large compressive bridges involve upward displacement of the material by folds and hill or mountain ranges asymmetry of the fault profile and relative chronology of the segments tensile bridges yield criteria based upon vein fillings asymmetry and relative chronolog in large scale structures some pull apart basins are shown to be bounded by normal faults parallel to but outside the strike slip segments from a comparison of analytical models with well known large scale fault zones a new criterion can be proposed in fault zones formed through coalescence of en echelon fractures the bridging segments are wide if facing leeward of the bulk movement sense and narrow if forward facing

mesozoic reactivation of variscan thrusting in the bristol channel area uk new seismic reflection data from the bristol channel area provide direct evidence of a major variscan thrust in the palaeozoic basement beneath the mesozoic bristol channel syncline the thrust has an average southerly dip of about 25 and it rises into the major fault the central bristol channel fault zone cbcfz at the northern margin of the bristol channel syncline the cbcfz is attributed to reactivation in extension of the variscan thrust probably during the early cretaceous there is no evidence for major synsedimentary movement on the cbcfz and the bristol channel syncline does not represent a rollover structure section restoration suggests that the cbcfz has cut up through a previously tilted sequence of triassic and jurassic strata pervasive nnw sse cross faults are interpreted as original variscan transfer faults that have been reactivated in the mesozoic and tertiary

strike slip relay ramps areas of reorientated bedding at contractional oversteps between strike slip faults are here called strike slip relay ramps metre scale examples are described from the jurassic sediments at east quantoxhead somerset u k larger strike slip relay ramps occur in the rio de peixe basin ne brazil along the newport inglewood trend california and in the bovey basin sw england although the geometry and development of strike slip relay ramps are similar to those of relay ramps in normal fault systems there are differences in the structures which accommodate the transfer of displacement between the overstepping faults whereas strike slip relay ramps are typically transpressional with pressure solution often occurring relay ramps in normal fault systems are dominated by extension or transtension care needs to be taken when interpreting areas of reorientated bedding between overstepping faults particularly when displacement directions are unknown for example when using seismic data this is because relay ramps can occur in both strike slip and normal fault zones

evolution of fracture normal stiffness due to pressure dissolution and precipitation abstract the normal stiffness of a fracture is a key parameter that controls for example rock mass deformability the change in hydraulic transmissivity due to stress changes and the speed and attenuation of seismic waves that travel across the fracture non linearity of normal stiffness as a function of stress is often attributed to plastic yield at discrete contacts similar surface altering mechanisms occur due to pressure solution and precipitation over larger timescales these processes partition the fracture surfaces into a flattened contact region and a rough free surface that bounds the void space under low loads contact occurs exclusively over the flattened part leading to rapid exponential stiffening at higher loads contact occurs over the rough surface fraction leading to the conventional linear increase of stiffness with stress it follows that a relationship exists between the history of in situ temperature and stress state of a rock fracture and its subsequent deformation behavior

scaling of transfer zones in the british isles widths of transfer zones between stepping normal faults obey power law scaling relationships probably from widths of millimetres to tens or hundreds of kilometres relay ramp widths in the mesozoic sedimentary rocks of the somerset coast obey a power law up to 50 m above which there is a censoring effect caused by the width of the wave cut platform a structural map of the british isles indicates that transfer zones obey a power law up to widths of at least 250 km this indicates that normal faults can interact over tens or hundreds of kilometres especially where transfer zones occur between stepping half grabens interaction is therefore another aspect of faulting that obeys fractal behaviour

a quantitative three dimensional depositional model of gravelly braided rivers a quantitative three dimensional depositional model of gravelly braided rivers has been developed based largely on the deposits of the sagavanirktok river in northern alaska these deposits were described using cores wireline logs trenches and ground penetrating radar profiles the origin of the deposits was inferred from observations of 1 channel and bar formation and migration and channel filling interpreted from aerial photographs 2 water flow during floods and 3 the topography and texture of the river bed at low flow stage this depositional model quantitatively represents the geometry of the different scales of strataset the spatial relationships among them and their sediment texture distribution porosity and permeability in the model are related to sediment texture the geometry of a particular type and scale of strataset is related to the geometry and migration of the bedform type e g ripples dunes bedload sheets bars associated with deposition of the strataset in particular the length to thickness ratio of stratasets is similar to the wavelength to height ratio of associated bedforms furthermore the wavelength and height of bedforms such as dunes and bars are related to channel depth and width therefore the thickness of a particular scale of strataset i e medium scale cross sets and large scale sets of inclined strata will vary with river dimensions these relationships between the dimensions of stratasets bedforms and channels mean that this depositional model can be applied to other gravelly fluvial deposits the depositional model can be used to interpret the origin of ancient gravelly fluvial deposits and to aid in the characterization of gravelly fluvial aquifers and hydrocarbon reservoirs

the dinevar transtensional pull apart basin nw zagros mountains iran a geological study and comparison to 2d finite element elastic models the dinevar transtensional pull apart basin is a nw se trending basin located in the northwest part of the zagros mountains sanandaj sirjan tectonic zone iran this basin was formed by oblique extension in a strike slip fault system which was controlled by the pre existing sahneh and the mianrahan faults in addition to a field study we constructed a 2d finite element elastic model based on the major fault segments according to the field study various geological structures are formed around the pre existing fault segments including pencil structures with 13 aspect ratio 19 tight to open asymmetric folds oblique normal faults synthetic and antithetic faults normal and reverse fault drags and negative and hybrid type flower structure fe model results show that around the fault step is a zone of displacement gradient that indicates extension transtension within the overlapping zone consequently subsidence is predicted over the releasing fault step the modelled stress distributions within the fault step and around the fault segment tips are asymmetric elastic modelling shows that the mean normal stress within the step is tensional which would impede plastic yield while the region outside the step is characterised by compressive mean normal stress the mean normal stress pattern is characterised by a regional minimum localised inside the extensional step transtension zone and two local maximum and minimum couples formed at the advancing and retreating sides respectively in the fault segment tips the results show that two main subsidence regions depocentres or sub basins form along and in the proximity of the fault segment tips the imposed relative motion is entirely accommodated by creep on the faults which causes plastic strain to accumulate outside the faults mostly localised within the fault step this localised strain between fault segments could initiate connecting faults or reactivate earlier faults generally at high angles relative to the master fault segments as suggested by the stress and strain patterns the rotation and magnitude variation in the stress and strain trajectories reflects heterogeneous deformation in general the dinevar transtensional pull apart basin is characterised by an elongate rhomboidal to trapezoidal shaped geometry the modelled stress distribution and strain localisations within the basin are in general agreement with the locations of fault segments within the dinevar transtensional pull apart basin

the distribution of faults and fractures and their importance in accommodating extensional strain at kimmeridge bay dorset uk the spatial distribution of extensional strain in interbedded mudstones and carbonates from around kimmeridge bay in southern england is examined using a variety of line samples normal faults and tensile fractures veins from the same deformation event show displacements ranging over 6 orders of magnitude the relative contribution of these structures to the overall extension varies with large faults 10 m heave accommodating about 65 smaller faults 1 10 m heave about 25 and veins less than 10 of the overall extension the heterogeneity of fracture density and strain can be quantified from cumulative plots by applying a non parametric method based on kuiper s test both the degree and statistical significance of strain heterogeneity can be determined and are shown to be scale dependent thin veins accommodate a fairly constant background strain across the region whilst thick veins and small faults take up localized higher strains in damage zones around larger faults fault strain is relatively homogenously distributed across the region the faults and veins do not share the same scaling relationship thus this study shows that it is not possible to simply extrapolate fracture frequencies and strain from fault scale to vein scale and that the heterogeneity of extensional strain is scale dependent

origin damping and pattern of development of faults in granite observations of brittle fractures in the granite of the massif de la borne as well as in other rocks allow us to discuss the different hypotheses regarding the origin of faults it seems that all faults originate by shear along a preexisting plane which can be an important fracture joint former fault or a microflaw pore grain boundary the shear on the plane gives rise to an array of en echelon cracks that makes the rock less resistant and permits the lengthening of the fault we also found an arrangement of horsetail fractures damping the movements on the faults we then propose a pattern for the development of the faults they originate on preexisting plane and propagate by initiating en echelon cracks the movements are damped by horsetails which permit by faults connection in relays the creation of larger faults

meso to microscale fracture porosity in tight limestones results of an integrated field and laboratory study abstract the complex fluid saturation distribution and influence of microscale and mesoscale fractures on the fluid accumulation and flow properties of carbonates are still interesting challenges for petroleum geologists for this reason in order to know the relative role played by the aforementioned features on the storage and migration properties of tight limestones the present work focuses on a surface analogue cropping out in southern italy by first applying a deterministic discrete fracture network dfn modelling to a 1 m3 geocellular volume an amount of 0 3 of fracture porosity and a fracture connectivity configuration above the percolation threshold are computed in addition to mesoscale fracture porosity in order to gather information on matrix porosity and microscale fractures we investigate the pore type geometry and textural anisotropy of selected rock plugs by mean of integrated petrophysical ultrasonic and optical microscopy analyses experiments results show values of connected porosity ranging between 1 and 6 presence of vugs localized along pre existing structural heterogeneities and the predominance of stiff pores within the carbonate matrix the rare microfractures are mainly oriented orthogonal to bedding the estimated crack density 0 19 shows that the contribution of fracture porosity at microscale 0 078 is very low if compared to that of matrix porosity and also a structural configuration above the percolation the present study therefore documents that the carbonate matrix forms an isotropic medium which profoundly affects the storage capability of the study limestones in fact the amount of storage provided by carbonate matrix and microscale fractures is greater than that due to mesoscale fractures moreover we document that the matrix contribution on porosity is much more significant than the contribution provided by microfractures finally the present work shows the importance of integrating different methodologies on the assessment of fracture porosity at different scales of observation in fact a great benefit for development and production operations can be obtained by performing studies of surface analogs which allow the detailed investigation of rock masses below seismic resolution

the temporal relationship between joints and faults abstract examples are presented of three temporal relationships between joints and faults joints that pre date faults joints that are precursors to or synchronous with faults and joints that post date faults emphasis is placed on strike slip faults in carbonate beds but other examples are used general rules are given for identifying the three temporal relationships between joints and faults joints that formed before faults can be dilated sheared or affected by pressure solution during faulting depending on their orientation in relation to the applied stress system faulted joints can preserve some original geometry of a joint pattern with pinnate joints or veins commonly developing where faulted joints interact joints formed synchronously with faults reflect the same stress system that caused the faulting and tend to increase in frequency toward faults in contrast joints that pre or post date faults tend not to increase in frequency towards the fault joints that post date a fault may cut across or abut the fault and fault related veins without being displaced by the fault they may also lack dilation near the fault even if the fault has associated veins joints formed either syn or post faulting may curve into the fault indicating stress perturbation around the fault different joint patterns may exist across the fault because of mechanical variations geometric features may therefore be used in the field to identify the temporal relationships between faults and joints especially where early joints affect or control fault development or where the distribution of late joints are influenced by faults

stress fields about strike slip faults inferred from stylolites and tension gashes abstract in general the long axis of the tension gashes and stylolitic columns developed in limestones during a single phase of compressional deformation occur parallel to the direction of the maximum compressive stress 1 this is the case in the languedoc for structures developed in the jurassic limestones during the n s pyrenean compression exceptionnally however these microstructures turn in direction and become oblique even orthogonal one to the other probably as a consequence of a variation in intensity and direction of the stress field at the end of a microfault this mechanism also occurs in a larger scale structure involving segments of pre tectonic joints that act as en echelon microfaults in a brittle kink band equivalent to a peculiar type of potential wrench fault

flow and turbulence structure across the ripple dune transition an experiment under mobile bed conditions current knowledge of flow and turbulent processes acting across the sand bed continuum is still unable to unequivocally explain the mechanism s by which ripples become dunes understanding has been improved by comparative high resolution studies undertaken over fixed bedforms at different stages in the continuum however these studies both ignore the role of mobile sediment and do not examine flow structure during the actual transition from ripples to dunes the aims of the paper are i to describe flow and turbulence characteristics acting above mobile bedforms at several stages across the transition and ii to compare these data with those arising from experiments over fixed ripples and dunes laboratory experiments are presented that examine the turbulence structure across seven distinct stages of the transition from ripples to dunes single point acoustic doppler velocimeter sampling at three flow heights above a developing mobile boundary was undertaken time averaged statistics and the instantaneous quadrant record reveal distinct changes in flow structure either side of the change from ripples to dunes initially shear related high frequency vortex shedding dominates turbulence production this increases until two dimensional 2d dunes have formed thereafter turbulence intensities and reynolds stress decline and three dimensional dunes exhibit values found over 2d ripples this is the result of shear layer dampening which occurs when the topographically accelerated downstream velocity increases at a faster rate than flow depth activity at reattachment increases due to high velocity fluid imparting high mass and momentum transfer at the bed and or wake flapping suspended sediment may also play a role in turbulence dampening and bed erosion ejections dominate over sweeps in terms of event frequency but not magnitude strong relationships between inward interactions and sweeps and ejections and outward interactions suggest that mass and momentum exchanges are dependent upon activity in all four quadrants the results contradict the notion present in most physical models that larger bedforms exhibit most shear layer activity consequently an improved model for the ripple dune transition is proposed

influence of p t conditions on the style of normal fault initiation and growth in limestones from the se basin france abstract a conventional and cathodoluminescence microscopy stable isotope and fluid inclusion study was undertaken on normal fault zones exposed on vertical cliffs in tithonian limestones of the french se basin the aim was to determine the chronology of deformation and factors controlling normal fault nucleation and evolution in carbonate rocks two models are proposed for fault zone development depending on the depths at which deformation takes place at depths of 3 3 5 km incipient shear zones consist of en echelon veins filled by fibrous calcite and confined to limestone layers bounded by thin clayey interlayers as deformation increases and the layers rotate slip occurs along the clay rich interlayers a system of pull aparts forms allowing displacement to increase pull aparts are commonly filled by fibrous calcite crystals at depths of 1 5 2 km faults initiate as small slip surfaces early nucleating in some limestone layers their propagation is impeded by thin clayey interlayers which enhances fracturing and bending of the limestone layers as slip surfaces propagate they overlap and can connect with one another by means of dilational jogs that are filled by large euhedral calcite crystals in the first case pull aparts are coupled with the solution seams that reuse preexisting rotated clay rich interlayers as they formed they progressively filled and the fluid circulation remained local in the second case longer slip planes connect by dilation jogs that are not immediately filled which enhance the circulation of fluids which show chemical variations it appears that p t conditions strongly control the relative role of brittle processes and solution crystallization mechanisms and the style of the early stages of normal faulting in the same limestone rocks

the formation and growth of pressure solution seams in clastic rocks a field and analytical study abstract pressure solution seams psss are closing mode structures of localised dissolution resulting in a volume reduction we present new observations constraining the processes by which psss initiate and grow in low porosity clastic rocks from southern ireland psss initiate as inter granular psss at quartz grain to grain contacts as quartz dissolves clay remains as a residue along the contacts as well as filling the adjacent pores to form incipient psss involving multiple grain boundaries further lengthening and thickening occurs by lateral linkage and transverse coalescence of neighbouring segments of incipient psss multiple pss segments are observed to concentrate in thin tabular zones that appear as single macroscopic psss visible in hand samples published numerical modelling results show the ability of both lateral and transverse growth of psss due to the presence of asperities on their flanks which confirm our interpretations based on our laboratory and field observations

fracture development and mechanical stratigraphy of austin chalk texas the mechanical stratigraphy of the upper cretaceous austin chalk is established from study of fracture intensity along its outcrop trend from dallas to san antonio and westward to langtry texas and in the subsurface from study of cores and or fracture identification logs from 30 wells three mechanical stratigraphic units are recognized 1 an upper fractured massive chalk corresponding to the big house chalk member 2 a middle ductile chalk marl corresponding to the dessau chalk and burditt marl members and 3 a lower fractured massive chalk corresponding to the atco chalk member representative samples from the three mechanical stratigraphic units were experimentally shortened dry at 10 17 34 and 70 mpa confining pressure at 24 c and at a strain rate of 2 5 10 4 sec 1 to determine if the relative mechanical behavior observed at the surface could be extrapolated into the subsurface at different simulated burial depths the experimentally determined ductilities parallel those determined from outcrop and subsurface studies multiple linear regression analysis indicates that porosity is most strongly correlated with fracture strength smectite content has the second strongest correlation for low porosity specimens 9 13 5 the strength of specimens with 4 smectite is reduced 30 42 compared to specimens with no smectite the coefficient of internal friction at 17 mpa confining pressure decreases from 1 66 to 0 61 as smectite content increases from 0 to 4 sem photomicrographs of undeformed specimens show that smectite and other clays are distributed as large 30 m discrete amorphous concentrated masses throughout the chalk they are comminuted along the induced fracture surfaces where their grain size is 0 5 m or less these observations suggest that smectite acts as a soft inclusion localizing shear failure and correspondingly weakening the material

simple constructions for deformation in transpression transtension zones abstract a simple geometrical construction is demonstrated for determining the orientations of the principal axes of the infinitesimal strain ellipsoid in tectonic zones where boundaries obliquely converge or diverge the construction may also be used to determine the relative magnitudes of the principal axes and the ellipsoid shape for infinitesimal and finite transpressional transtensional strains the analysis leads to a tightening of the definitions of the loosely used terms compression wrench and extension applications of the simple construction and convenient graphical solution are illustrated by brief examples

northward migration of the southern diagonal fault of the hula pull apart basin dead sea transform northern israel abstract the hula valley located in northeastern israel is a 4 million year old pull apart basin bounded by two left stepped segments of the dead sea transform basic models of pull apart basins suggest four faults at all sides of the basin a situation which is not always the case in the hula pull apart basin the longitudinal n s faults are clearly evident while the transversal e w faults are less explicit an nw oriented lineament expressed as a north facing continuous scarp 1 3 m high was recognized in the southern part of the valley morphological seismic and sedimentary considerations suggest that this scarp is the surface expression of a deep seated fault this fault termed the yesod hama ala fault forms the present southern boundary of the hula pull apart basin and appears to be the southern diagonal fault which links the jordan fault in the east with the yammunneh fault in the west it is suggested that this fault scarp formed a shallow morphological barrier that partly blocked the southern outlet of the valley enabling a permanent lake in the southern part of the hula valley thus the uplifted southern block determined the sw shoreline of the lake it is proposed that the hula basin is a version of the classic pull apart model it is also suggested that in the absence of upwelling mantle material and extension along the length of the basin a crustal thinning and subsidence might have occurred through normal faulting of the upper brittle crust the thick depositional sequence within the southern part of the basin shows that the present margins have been a major depositional site for a long time and that the hula valley has thus developed as an asymmetric pull apart rhomb shaped basin bounded by steep north striking boundary normal as well as strike slip faults w nw striking and northward dipping normal faults and a south facing bending flexure as activity within the basin continued and northward migration of the faulting occurred a new fault developed according to this perception the present active fault is the yesod hama ala fault while the future fault will be located northward as can be presumed from the present micro seismic activity in the valley

strike slip fault propagation cleavage in carbonate rocks the mattinata fault zone southern apennines italy disjunctive spaced solution cleavage in carbonate rocks is genetically associated with the propagation of the left lateral strike slip mattinata fault in the gargano promontory italy typical cleavage development is restricted within the 200 300 mwide fault zone which is bounded by virtually unfractured wall rocks the cleavage consists of sub parallel solution surfaces which are often reactivated as sheared solution planes geometrical and kinematic relationships exist between the fault and the associated cleavage planes thus 1 cleavage fault intersection lines lie parallel to the fault and the sheared cleavage rotational axes and 2 the cleavage fault angle is almost constantly equal to 408 a model for the development of the mattinata fault is proposed in which the cleavage surfaces are interpreted as fault propagation deformations cleavage nucleates as solution planes at the front of the advancing fault as the result of stress concentration in this region two distinct time sequential processes are shown to operate during the fault propagation 1 typical millimetre to centimetre spaced solution surfaces form in the distal tip zone of the advancing fault plane 2 as the tip advances the fault plane breaks through the cleavage as minor shear displacements reactivate some of these nascent surfaces these observations may prove useful in understanding mechanisms for fault controlled enhanced reduced permeability and fluid pathways 1999 elsevier science ltd all rights reserved

critical displacement for normal fault nucleation from en echelon vein arrays in limestones a case study from the southern apennines italy abstract the process of fault initiation by the coalescence of en echelon arrays of tensile cracks has been discussed by several workers and is now well established however not many studies have tried to quantitatively describe this process in terms of displacement and shear strain that control the early stages of fault nucleation in this study a large number of conjugate en echelon vein arrays showing extensional offsets have been analysed these structures are exposed in well bedded micritic limestones deformed at very low grade conditions in the apennine mountain belt of southern italy three different types of structures can be distinguished i brittle ductile shear zones characterised by arrays of en echelon calcite filled tension gashes ii shear zones showing incipient development of discontinuous shear parallel fractures cutting through the vein array and iii faulted shear zones in which a continuous discrete normal fault breaks through and clearly developed from an original en echelon vein array critical values of displacement and shear strain have been determined for the onset of normal fault nucleation from brittle ductile shear zones therefore suggesting that these parameters exert a major control on fault initiation a diagram of shear zone population vs displacement also shows that this parameter obeys a power law of the type generally followed by normal faults in the frictional regime our results suggest that during the early stages of fault nucleation displacement and shear strain control the switch from dominant ductile viscous deformation mechanisms accompanied by brittle fracturing responsible for vein formation to the frictional regime

morphology paleogeographic setting and origin of the middle wilcox yoakum canyon texas coastal plain the yoakum canyon is the largest of the gulf coast eocene erosional gorges and is interpreted as a buried submarine channel the canyon can be traced for 67 mi 108 km from the wilcox fault zone which defines the position of the early eocene shelf edge nearly to present outcrop in this paper we expand on previously published descriptions of the canyon and use a more extensive subsurface database decompaction of the canyon shale fill reveals that original depths of the canyon exceeded 3500 ft 1067 m apparent canyon wall slump scarps and a peripheral chaotic zone interpreted as an incipient slump feature are comparable to similar features of the late quaternary mississippi submarine canyon the yoakum canyon formed within the garwood subembayment to the west of and adjacent to the middle wilcox rockdale delta system quantitative mapping of facies adjacent to the yoakum shale indicate the following sequence of events l muddy distal deltaic and shelf facies of the lower middle wilcox subgroup were deposited during a retrogradation 2 a resurgence of progradation deposited upper middle wilcox deltaic facies atop the unconsolidated lower middle wilcox continental margin muds loading the shelf edge and initiating slump failure of the continental margin 3 headward erosion of the canyon across the shelf occurred contemporaneously with a subsidence induced transgression that coincided with a disruption in sediment supply the yoakum canyon was excavated by a combinat on of slumping and current scour 4 the canyon was filled by hemipelagic and prodelta muds of the upper wilcox subgroup

crustal scale en echelon p shear tensional bridges a possible solution to the batholithic room problem the apparent paradox of voluminous granitoid emplacement in an overall compressional magmatic are has been somewhat alleviated by the idea of pluton emplacement in tension cracks and dilational jogs within arc parallel strike slip fault systems as an alternative hypothesis we propose that an en echelon p shear array provides a continuous batholith scale zone of dilation along the trend of active magmatism and that it is favored by transpressional tectonics in the sierra nevada california the late cretaceous granitoids of the cathedral range intrusive epoch are consistent with emplacement into bridges between p shears because 1 they are elongated oblique to the magmatic trend consistent with p shear orientation within a dextral system 2 they were all emplaced within 5 10 m y along a 300 km trend resulting in a displacement rate of 1 cm yr across the arc and 3 syn to late magmatic dextral shear zones bound and crosscut the plutons as in a p shear tensional bridge

microstructures of bedding parallel faults under multistage deformation examples from the southeast basin of france abstract we conducted a microstructural analysis of bedding parallel faults bpfs in mesozoic clay rich layers of the southeast basin of france various microstructures are recognized in thin sections under a petrographic microscope and by cathodoluminescence the microscale observations are combined with outcrop observations from previous studies to provide insight into the origin of the bpfs and their evolution during successive phases of deformation in a basin that had a polyphase tectonic history the bpfs slipped while normal faults were formed during the oligocene extension then another phase of slip occurred later during the basin inversion these two phases of deformation are expressed by recurrent crack seal veins pull apart veins and stylolites in addition calcite veins with an elongate blocky morphology suggest an opening normal to bedding before the reactivation the bpfs initiated in clay layers that were shallow dipping such conditions may appear mechanically unfavourable for an opening normal to bedding or a shearing parallel to bedding we suggest that the role of rock anisotropy is critical this study furthermore demonstrates that bpfs can be long lived brittle structures that may record successive tectonic events

insights into the mechanics of en echelon sigmoidal vein formation using ultra high resolution photogrammetry and computed tomography abstract two novel techniques photo based reconstruction photogrammetry and computed tomography ct are used to investigate the formation of an exceptional array of sigmoidal veins in a hand sample from cape liptrap southern victoria and to provide constraint on models for their development the accuracies of the photogrammetric models were tested by comparison with a laser scan generated three dimensional 3d model the photogrammetric model was found to be accurate to at least 0 25 mm and substantially more detailed than the laser scan a methodology was developed by which 3d structural measurements could be extracted from the photogrammetric model this was augmented with the ct model which through its capacity to elucidate internal structure was used to constrain the geometry and linkage of structures within the rock volume the photogrammetric and ct data were then combined with detailed photomicrographs to evaluate the evolution of the sigmoidal veins in the sample the angle between the sigmoidal vein margins and an inferred shear zone as well as the orientations of the crystal fibres were found to imply a rotation of 27 however coeval pressure solution seams and older veinlets in the rock bridges between the veins were only found to have rotated by 10 an observation not easily explained using existing models for sigmoidal vein formation a new model is proposed in which a significant component of sigmoidal vein geometry is due to localised dilation caused by slip on the pressure solution seams the process involves strain partitioning onto pressure solution seams which leads to exaggeration of sigmoidal vein geometries if not accounted for the apparent vein rotation due to slip partitioning introduces errors into calculations of simple shear and volume strain based on sigmoidal arrays of this type furthermore the ct data demonstrated that in 3d the veins are continuous and channel like implying a far higher degree of connectivity and fluid transport than is suggested by their 2d form

fluvial dunes initiation characterization flow structure research into fluvial dunes spans disciplines studies at grain to reach scales and methodological approaches that include theoretical experimental numerical and field investigations despite significant research efforts to date it remains difficult to provide definitive answers to some fundamental questions regarding dunes this paper reviews three notable challenges that remain regarding fluvial dunes namely scale consistent linking of bed morphologies with turbulent flow fields the intriguing question of what causes trains of highly ordered sediment waves to form in beds of river sediments and how to define the important characteristics of a dune covered bed including lengths shapes and their statistical nature in each case the particular challenge is discussed and then recent research and ways forward are presented copyright 2010 john wiley sons ltd

the role of pressure solution seam and joint assemblages in the formation of strike slip and thrust faults in a compressive tectonic setting the variscan of south western ireland abstract the ross sandstone in county clare ireland was deformed by an approximately north south compression during the end carboniferous variscan orogeny the initial assemblage consists of mutually abutting orthogonal arrays of 170 oriented set 1 joints veins jvs and approximately 75 oriented set 1 pressure solution seams psss formed under the same stress conditions orientations of splay jvs and psss set 2 suggest a clockwise remote stress rotation of about 35 responsible for the contemporaneous shearing of the set 1 arrays among these nearly orthogonal strike slip faults the prominent set is sub parallel to set 1 jvs these faults are formed by the linkage of en echelon segments with broad damage zones responsible for right lateral offsets of hundreds of meters thrust faults with up to 30 m of offset initiate within shale horizons and follow either the psss in the sandstones or high angle shales within tilted sequences within the large thrust fault zones compartmentalised blocks of rocks are bounded by thrust faults segments with various dip angles strike slip and thrust faults are contemporaneous and owe their existence to initial weaknesses in the form of jvs and psss rather than by switching relative stress magnitudes and orientations associated with andersonian models of faults and related stress orientations

relationships between faults extension fractures and veins and stress faults are commonly related to extension fractures defined here as including extension veins extension fracturing is integral to fault initiation and propagation and extension fractures also form after fault slip in these situations fault planes contain the intermediate principal stress 2 and slip is perpendicular to the line of intersection between the fault and the extension fractures however for reactivated faults multiple fault sets and faults formed according to the healy theory 2 is not necessarily within the fault plane a theoretical analysis shows that the trace of an extension fracture on a fault can make angles from 0 to 90 with the maximum resolved shear stress the angle depends on the fault orientation relative to the principal stresses and the ratio between the stresses extension fractures only intersect faults perpendicular to the maximum resolved shear stress on faults containing the maximum or intermediate principal stresses or when their magnitudes are equal 1 2 field observations show that extension fractures can intersect faults along lines at oblique angles to slip directions as predicted by the theory such angles may be indicators of fault reactivation multiple sets of faults or healy theory faulting

solution slip and separations on strike slip fault zones theory and application to the mattinata fault italy we present a set of relationships to determine the component of slip and separations generated by the cleavage controlled volume contraction in strike slip fault zones the fault walls can translate toward each other along the cleavage normal axis of maximum shortening as rock is dissolved by pressure solution along patterned cleavage surfaces within strike slip fault zones the fault zone shortening produces an apparent slip and possible separations of reference stratigraphic surfaces across the fault zone solution related slip and separations can differ in magnitude and have either the same or the opposite sense these discrepancies depend upon the amount of fault zone shortening and upon the angles between the fault and the shortening axis and between the fault and the reference stratigraphic surface separations can be considerable at any scales even for very low amounts of fault zone thinning apparent slip can be appreciable for large amounts of fault zone thinning and or high fault to cleavage incidence angles with the proper geometrical conversions the relationships here presented can apply to any fault type the application of this technique to the left lateral mattinata fault italy demonstrated that both left and right lateral strike separations can occur along the fault even for low amounts of fault zone contraction by rock dissolution q 2002 elsevier science ltd all rights reserved

formation and growth of normal faults in carbonates within a compressive environment normal faults were initiated and grew through hierarchical formation of pressure solution structures and their subsequent shearing in cretaceous carbonates in the leading thrust front of maiella mountain italy through mapping in the field we have documented the detailed architecture of faults with increasing slip values from a few millimeters to 50 m and have identified pretilting structural elements and four stages of fault development each stage representing addition of a new structural element the result is a conceptual model that begins with pretilting structures bed parallel and bed perpendicular solution surfaces that were reactivated in shear upon tilting of the beds at the frontal limb of the maiella anticline slip on mechanical layer boundaries and on bed perpendicular solution surfaces resulted in oblique solution surfaces linkage of solution surfaces and fragmentation of rock oblique zones of fragmented rock in adjacent mechanical layers linked to form a continuous breccia and facilitated fault growth these normal faults formed through mechanical processes strictly in a compressional regime

extensional faults in fine grained carbonates analysis of fault core lithology and thickness displacement relationships abstract a study of 103 extensional faults hosted by fine grained carbonates in western sinai svalbard and oman reveals that faults vary geometrically between simple cores and cores comprising fault splays lenses segment linkages and overlap structures fault core rocks are typically carbonate breccias carbonate and shale gouge shale smear secondary calcite cement and veins and host rock lenses there is a significant scatter in the core thickness for any given displacement but the overall pattern is that the thickness increases with displacement this increase best fits a power law function 0 29d 0 56 that describes a gradual decrease in the thickness displacement relationship for increasing slip along faults in more detail the general function can be seen as the sum of two power law trend lines the first representing thin localized fault cores with generally simple and planar geometry the second representing thicker fault cores with complex geometry of lenses and overlap structures and with fault rock membranes the studied faults show a significant change in composition and geometry from small 0 1 m to moderate 1 10 m and to large offset faults 10 400 m the overall pattern is that fault initiates as fractures filled with calcite veins and thin shear fractures that hosts gouge membranes with increased fault offset complexity increases with breakdown of veins more extensive fault rock membranes and a trend towards development of lenses when offset exceeds 100 m cores become complex with multiple slip zones cemented breccia and shale smear membranes and various types of lenses we envision that the fault development as reflected by offset is dominated by forces extension compression acting in the fault mechanical heterogeneity of wall rocks the core lithologies and their developing rheology and especially geometric effects arising from fault irregularities

linkage and evolution of conjugate strike slip fault zones in limestones of somerset and northumbria conjugate strike slip fault zones that cover metre scale areas at beadnell northumbria and kilve somerset were initiated as conjugate vein arrays early conjugate faults are linked by the propagation of one fault that eventually by passes the other fault a model for the development of strike slip faults is presented using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the propagation direction this model includes the evolution of networks from 1 the initial random development of vein arrays to 2 the isolated development of several unconnected conjugate fault segments that pass into vein arrays through 3 the intersection of a conjugate set of master faults and linkage with minor antithetic faults and the formation of new vein arrays with extensional geometries after a linked network of faults is established to 4 breaching of intersection points by dominant faults and finally 5 the propagation towards oversteps that are breached to form a through going fault the geometry of the active structures simplifies with time as strain is localised along the master fault but the complexities are preserved in the fault walls

volume loss and deformation around conjugate fractures comparison between a natural example and analogue experiments abstract in well stratified sedimentary rocks measurement of the bedding offsets along fractures gives a value for the relative displacement at each location to restore the undeformed geometry of the layers the offset along each fracture must be cancelled restoration of the geometry enables the location of places where shortening is concentrated to be established namely at the fracture intersection and at fracture tips slow displacement during deformation is demonstrated by the growth of fibres on the fault surfaces pressure solution inside the layers is responsible for the internal strain with associated volume loss this mechanism is compatible with low strain rates giving aseismic displacements along the fractures to model rock rheology dominated by pressure solution a viscous material paraffin wax has been employed in the analogue model volume loss in nature is represented by area changes during the analogue experiments in the experiments shortening is concentrated around the fractures in exactly the same geometrical positions as in nature when the amount of displacement is different on each of the two fractures one of the fractures is observed to offset its conjugate fracture when this is the case relative timing of displacement along conjugate fractures cannot be determined without ambiguity from the observation of fracture offsets

the structural evolution of dilational stepovers in regional transtensional zones we propose a theoretical model supported by a field study to describe the patterns of fault fracture meshes formed within dilational stepovers developed along faults accommodating regional scale wrench dominated transtension the geometry and kinematics of the faulting in the dilational stepovers is related to the angle of divergence and differs from the patterns traditionally predicted in dilation zones associated with boundary faults accommodating strike slip displacements where 0 for low values of oblique divergence 30 and low strain the fault fracture mesh comprises interlinked tensile fractures and shear extensional planes consistent with wrench dominated transtension at higher values of strain a switch occurs from wrench to extension dominated transtension leading to the reactivation and or disruption of the early formed structures these structural processes lead to the development of a geometrically complex and kinematically heterogeneous fault pattern which may affect and or perturb the development of a through going fault linking and facilitating the slip transfer between the two overlapping fault segments as a result dilational stepover zones will tend to form long lived sites of localized extension and subsidence in regional transtensional tectonic settings cyclic increases decreases of structural permeability will be related to slip on the major boundary faults that control the distribution of fluid flow paths and consequently the long and short term structural evolution of these sites our model also predicts complex and more realistic subsurface fluid migration pathways relevant to our current understanding of hydrothermal ore deposits and hydrocarbon migration and storage

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

spectral behavior of gravel dunes abstract spectral behavior of gravel dunes formed under different flow discharges is analyzed with an attempt to verify the 3 spectral law that has been confirmed extensively for sand dunes a schematic spectrum of gravel dunes is proposed based on the spectral analysis as well as results from the literature the results of spectral analysis show a significant deviation from the 3 spectral law for gravel dunes and the magnitude of deviation correlates with flow discharge possible explanations for the deviation from the 3 spectral law being associated with kinetic and geometrical characteristics have been explored to investigate the kinetic characteristics of gravel dunes a wavelet based method that calculates the celerity of dunes based on a pair of elevational time series is quantitatively tested our results suggest that 1 the kinetic explanation based on the relationship between dune celerity and dune length cannot fully explain the spectral behavior of gravel dunes 2 the geometrical explanation based on the self similarity hypothesis is confirmed by the relationship between dune length and dune height and 3 the development of gravel sheets accounts for the differences in kinetic and geometrical characteristics between gravel dunes and sand dunes

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

discrete fracture network modelling of a hydrocarbon bearing oblique slip fault zone inferences on fault controlled fluid storage and migration properties of carbonate fault damage zones abstract discrete fracture network dfn modelling is a useful tool to assess both fluid storage and migration properties of naturally fractured carbonate rocks this work presents the results of multiple dfn models which represent the structural network associated with a ca 100 m offset oblique slip normal fault zone crosscutting miocene ramp carbonates of the majella mountain italy specifically by taking advantage of a previously published conceptual model of fault nucleation and growth the dfn models are aimed at computing the amount of fracture porosity and equivalent permeability of representative portions of the evolving fault damage zone in fact by first considering only background structural elements those pre dating the fault nucleation stage all fault related structural elements such as joints small and medium faults are added one by one according to their relative time of formation small faults are characterized by several cm offset whereas the latter ones have several 10 s of cm offset the following fracture parameters are inputted for each structural element i length ii aspect ratio iii mechanical and hydraulic aperture iv fracture intensity and v orientation a sensitivity analysis is carried out in order to test the seeding procedure of the software and the input fracture aperture values results of dfn modelling are consistent with the small faults forming the main repository for underground geofluids differently the fluid migration paths through the fault damage zone are mainly controlled by opening mode related fractures which mainly form clusters at the extensional quadrants of sheared structural elements due to their attitude and distribution these features mainly enhance fault parallel fluid migration paths in fact the computed values of horizontal equivalent permeability obtained along this direction are about one order of magnitude higher than those along the orthogonal direction the approach and methodologies applied in this work together with the results of the multiple dfn model configurations show the relative influence and role of the different structural elements on fluid storage and migration properties of limestone hosted fault damage zones

sedimentary stylolite networks and connectivity in limestone large scale field observations and implications for structure evolution stylolites are rough surfaces formed by localized rock dissolution and prevalent in carbonates and other sedimentary rocks their impact on porosity and permeability and capacity to accommodate compactive strain are well documented this paper presents a meso scale field study on sedimentary stylolites in carbonates characterizing large scale distributions of stylolites including measurements conducted on longer than kilometer long stylolites our field study suggests that on large scales connections between stylolites become important since connectivity and also lack of connectivity are expected to play a significant role in strain accommodation and hydraulic rock properties we suggest that large scale analysis may require a new characterization scheme for stylolites populations based on their connectivity we therefore divide sedimentary stylolite populations into three end member types which are correlated with the three possibilities for percolation of such systems isolated stylolites with zero percolation connectivity long parallel stylolites with 2 dimensional percolation connectivity and interconnected stylolite networks with 3 dimensional percolation connectivity new statistical parameters and measures are devised and used to quantitatively characterize the different population types schematic mechanistic models are then offered to explain the evolution of the three end member connectivity classes in addition we discuss the effect on fluid flow of the different population types

possible variscan thrusting beneath the somerton anticline somerset vibroseis seismic data were acquired by goal petroleum plc during 1982 in the vicinity of the somerton anticline somerset these data show the simple form of the anticline but in addition show a southward dipping discontinuous seismic event beneath gravity modelling demonstrates that this event may be correlated with an e w trending gravity gradient which can be followed for approximately 150 km the dipping seismic event may represent a variscan thrust plane which dips to the ssw in contrast to similar planes seen to the east which dip to the sse the variation in dip seen between these postulated thrust planes may explain the curvature of structural trends seen within and to the east of the mendip hills the polden hills fault runs sub parallel to the proposed thrust plane beneath the somerton anticline and may be linked to a mesozoic reactivation of the postulated thrust

structural and hydrothermal evolution of the shear zone related iron oxide enrichment in metavolcano sedimentary rocks of the intracontinental aracuai orogen the case of the espirito santo iron deposit abstract the rio sao joao metavolcano sedimentary sequence is located in the eastern border of the northern espinhaco fold thrust belt in the intracontinental aracuai west congo orogen mafic schist quartz amphibole and carbonate itabirites as well as a carbonate silicate rock occur in the study area these contain mineral assemblages compatible with the amphibolite facies metamorphic conditions magnetite and hematite rich itabirites form a series of iron deposits in the region near igapora caetite bahia state brazil the espirito santo iron deposit has compact hematite layers truncating quartz itabirite with magnetite varying from 10 to 55 vol of the rock volume siliciclastic and mafic rocks also host iron rich domains variably enriched in magnetite and hematite the deposit is hosted in compressional duplexes with structural top towards the sw these structures have an sn 1 sn foliation represented by compositional banding and parallel schistosity that is observed at all scales other common features are s c c boudins pinch and swell structures as well as sheath syn tectonic folds and a mineral stretching lineation lxn hydrothermal alteration was contemporaneous to the development of duplex and the sn 1 sn foliation a distal alteration zone is dominated by a potassic muscovite and or biotite chlorite assemblage and the intermediate zone by carbonate development the proximal alteration zone constitutes the iron oxide magnetite and hematite domains sulfide minerals as well as quartz veins silicification in association with other phases also formed hydrothermal magnetite is associated with c structures which grows either including silicates and skeletal carbonates or forming corrosion borders in these minerals lamellar hematite forms polycrystalline aggregates characterizing the s c structure in the sn 1 sn foliation as well as the axial planar foliation sn in intrafolial folds and the mineral stretching line lxn data obtained by the la icpms technique show that in general in quartz rich and amphibole itabirites hydrothermal magnetite is richer in ree than an early stage magnetite hydrothermal magnetite ree pattern is close to that of the country rock of the mineralization the formation of hematite and magnetite rich domains is related to the percolation of hydrothermal fluids that leached all components of the original silicates quartz and the carbonates of all host rocks and precipitated new hydrothermal phases taking advantage of the ediacaran shear structures

effects of layering and anisotropy on fault geometry the geometry and orientation of faults are examined using several field examples of small scale 1 with dihedral angles usually of about 50 as predicted by the coulomb theory of failure in layered rocks the geometry of faults varies with the orientation of layering with respect to the stress field where 1 is approximately normal to layering or anisotropy conjugate faults also develop symmetrically about 1 where rocks have interbedded layers with different mechanical behaviours however faults tend to initiate orthogonal to the more brittle layers i e originate as extension fractures sub parallel to 1 but oblique to the less brittle layers as the fault steps through the layering pull aparts are developed which may reduce the dihedral angle where 1 is oblique c 25 75 to anisotropy one set of faults is developed at a high angle to layering with another at a low angle usually showing a ramp flat geometry large dihedral angles up to 90 may result and 1 does not bisect this angle where 1 is approximately parallel to layering two cases can be recognized where 3 is approximately normal to layering faults with layer parallel flats and contractional ramps develop where 2 is approximately normal to layering conjugate faults develop which are symmetrical about 1 the geometry resembling that in isotropic rocks these observations are in agreement with rock deformation experiments which show the strong effect of anisotropy on fault orientation but the observations incorporate the effects of layering of materials with different deformation characteristics

initiation and growth of strike slip faults within intact metagranitoid neves area eastern alps italy exhumed strike slip faults exposed in the neves area of the tauern window eastern alps italy formed in the lower brittle crust under hydrous conditions within intact metagranitoids where any precursor fractures were already healed due to earlier amphibolite facies metamorphism faults initiated as newly formed en echelon fractures delineating shear bands with segmentation occurring over scales of 10 3 to 10 2 m due to the initial en echelon pattern stepovers between fault segments were almost invariably contractional during subsequent slip accumulation in initial low slip centimeter to decimeter stages synthetic slip on the segments was associated with the development of a set of antithetic faults in the contractional stepovers oriented at an angle of 30 45 to the bounding faults slip on this antithetic set did not fully compensate for the decrease in slip on the main faults implying an additional deformation mechanism within the stepovers e g block rotation and or out of plane movement in larger faults with slip on the order of a few meters the antithetic faults within the stepover were crosscut by synthetic sigmoidal faults that connected the overstepped fault segments and accommodated most of the subsequent displacement transfer this second stage of evolution involving fault linkage is well documented in the mesule fault which has a current maximum offset of 10 m in the mesule fault the total horizontal slip summed along all secondary faults within the stepover accounts almost entirely for the net slip decrease toward the tips of the overstepping faults however the boundary faults remain nearly straight in spite of the sigmoidal ramp like geometry of the connecting faults since the adjacent blocks are little deformed and there is no evidence for appreciable volume loss or block rotation in the stepover significant out of plane movement is implied although it is difficult to quantify the neves area provides unusually detailed field constraints on fault initiation linkage and displacement accumulation within nonbedded and relatively isotropic granitoid rocks at the base of the brittle crust where neither a free upper surface nor substantial volume change e g by veining and pressure solution was a controlling factor in accommodating fault linkage and displacement transfer

rupture propagation inferred from damage patterns slip distribution and segmentation of the 1957 mw8 1 gobi altay earthquake rupture along the bogd fault mongolia 1 a detailed analysis of the rupture patterns and slip changes along the surface rupture associated with the 1957 gobi altay earthquake mw 8 1 in mongolia which occurred along the bogd left lateral strike slip fault was carried out to better understand segmentation and propagation the major surface ruptures show a simple linear pattern whereas minor ruptures along the major ruptures which are concentrated at rupture step overs and tip zones show complex patterns in the latter case their patterns strongly resemble the geometric and kinematic characteristics of previously reported mesoscale fault damage patterns the geomorphologic offsets show that left lateral slip dominated with an average displacement of 3 5 to 4 0 m but it decreased or transferred to dip slip components mainly at rupture step overs and tip zones abrupt changes of rupture patterns and slip distribution indicate that the coseismic surface rupture along the bogd fault comprises three major segments from west to east namely the north ih east ih and north baga bogd segments and a highly damaged eastern tip zone based on the location of the epicenter as well as the asymmetrically distributed damage structures and slips we infer that the surface rupture propagated eastward unilaterally through several segments and reached the easternmost step over which acted as a tough barrier the rupture finally terminated producing a highly deformed tip damage zone developed to accommodate released stress we argue that detailed analysis of damage patterns slip distribution and slip transfer can help us to better understand fault segmentation and rupture propagation

structural characteristics and re os dating of quartz pyrite veins in the lewisian gneiss complex nw scotland evidence of an early paleoproterozoic hydrothermal regime during terrane amalgamation in the archaean basement rocks of the assynt and gruinard terranes of the mainland lewisian complex in nw scotland a regional suite of quartz pyrite veins cross cut regional palaeoproterozoic badcallian ca 2700 ma inverian ca 2480 ma fabrics and associated scourie dykes the quartz veins are overprinted by amphibolite greenschist facies laxfordian deformation fabrics ca 1760 ma and later brittle faults the hydrothermal mineral veins comprise a multimodal system of tensile hybrid hydraulic fractures which are inferred to have formed during a regional phase of nw se extension the almost orthogonal orientation of the quartz veins ne sw to the scourie dykes nw se are incompatible and must result from distinct paleostress regimes suggesting they are related to different tectonic events this hypothesis is supported by rhenium osmium dating of pyrite that yields an age of 2249 77 ma placing the vein hosted mineralisation event after the oldest published dates for the scourie dykes 2420 ma but before the youngest ages 1990 ma sulphur isotope analysis suggests that the sulphur associated with the pyrite is isotopically indistinguishable from primitive mantle the presence of the ca 2250 ma quartz pyrite veins in both the assynt and gruinard terranes confirms that these crustal units were amalgamated during or prior to inverian deformation the absence of the veins in the rhiconich terrane is consistent with the suggestion that it was not finally amalgamated to the assynt terrane until the laxfordian

impacts of off fault plasticity on fault slip and interaction at the base of the seismogenic zone direct observations of faults exhumed from mid crustal depths indicate that distributed inelastic deformation enhances fault slip and interaction across steps constrained by field measurements finite element models demonstrate that the slip distribution for a fault in a mises elastoplastic continuum differs significantly from that of a linear elastic model fault lobes of plastic shear strain align with fault tips and effectively lengthen the fault resulting in greater maximum slip and increased slip gradients near fault tips additionally distributed plastic shear strain facilitates slip transfer between echelon fault segments fault arrays separated by contractional steps which are subjected to greater mean normal stress and mises equivalent stress produce greater maximum slip than do those separated by extensional steps with no fractures these results provide insight into fault behavior at the base of the seismogenic zone with implications for rupture dynamics of discontinuous faults

evolution of fracture and fault controlled fluid pathways in carbonates of the albanides fold thrust belt the process of fracture and fault formation in carbonates of the albanides fold thrust belt has been systematically documented using hierarchical development of structural elements from hand sample outcrop and geologic map scales the function of fractures and faults in fluid migration was elucidated using calcite cement and bitumen in these structures as a paleoflow indicator two prefolding pressure solution and vein assemblages were identified an overburden assemblage and a remote tectonic stress assemblage sheared layer parallel pressure solution surfaces of the overburden assemblage define mechanical layers shearing of mechanical layers associated with folding resulted in the formation of a series of folding assemblage fractures at different orientations depending on the slip direction of individual mechanical layers prefolding and folding related fracture assemblages together formed fragmentation zones in mechanical layers and are the sites of incipient fault localization further deformation along these sites was accommodated by rotation and translation of fragmented rock which formed breccia and facilitated fault offset across multiple mechanical layers strike slip faults formed by this process are organized in two sets in an apparent conjugate pattern calcite cement and bitumen that accumulated along fractures and faults are evidence of localized fluid flow along fault zones by systematic identification of fractures and faults their evolution and their fluid and bitumen contents along with subsurface core and well log data we identify northeast southwest trending strike slip faults and the associated structures as dominant fluid pathways in the albanides fold thrust belt

tan lu fault system and its significance in oil accumulation in the central liaodong bay subbasin bohai bay basin china the tan lu fault system in the central liaodong bay subbasin bohai bay basin has complex structural characteristics and its tectonism during the cenozoic is an important factor in oil accumulation three dimensional seismic data were used to document the structural features and evolution of the system variations in source rock occurrence oil catchment area and faulting intensity were comprehensively evaluated to discuss the heterogeneity of oil occurrence along the system detailed analysis of the seismic data indicates a right lateral slip for the tan lu fault system transpression and transtension occur on two branches of the tan lu fault with different orientations indicating a likely slip azimuth that is between the two orientations i e 30 35 the strike slip began at the middle stage of deposition of the shahejie formation and reached its climax during deposition of the first and second members of the dongying formation to date the slip is still continuing in the transpressional system the lower strata on opposite sides of the strike slip fault were shortened and folded whereby the upper strata were stretched and normal faulted as a result a negative flower structure developed immediately above a positive flower structure strain distribution in this system is similar to that in a classic fold moderate tectonic deformation could enlarge the oil catchment area benefiting oil accumulation weak or intense deformation is unfavorable for commercial oil accumulation because of a small oil catchment area and poor oil preservation respectively

tension vein arrays in progressive strain complex but predictable architecture and major hosts of ore deposits abstract most en echelon vein arrays are extensional and can be termed tension vein arrays tvas tvas in major fault and shear zones fszs are subject to progressive deformation this deforms the initial tva whose geometry is well documented in the literature via discrete stages first into progressively more complex architecture involving folding of the tension veins then into progressively more simple architecture ultimately forming pipes during this progression the tva axis new definition rotates within the shear plane from normal to parallel to the displacement vector the deforming tva axis has simpler geometry than the complex tension veins and it can be employed to precisely track the deformation state of the fsz its displacement vector and shear sense through all the strain stages five structural metasomatic stages are defined by discrete steps in the strain evolution tvas are difficult to recognise and are under recognised in ore systems for a number of inherent geological reasons orebodies founded on dilation form parallel to the tva axis which is also parallel to dilational jogs in the parent fsz orebodies formed early in the fsz history are normal to the displacement vector and in progressive shear rotate with the tva axis toward the displacement vector orebodies formed late in the fsz history overprint apparently complex to chaotic vein stockwork which nevertheless has analysable geometry tva hosted orebodies are not necessarily parallel to the displacement vector of the host fsz but occupy elongate orientations over a 90 range within the fsz large orebodies are favourably developed in tvas in unfoliated fszs type 1 shear zones which may form fluid superhighways type 1 shear zones form in predictable circumstances involving particularly host rocktype and crustal position strike slip fszs possess a downdip tva axis and are especially able to tap deep crustal fluid tva hosted orebodies form a major deposit style exploration requires careful analysis of the prospect geometry at an early stage and recognition of the multi faceted tva architecture the relationship between the parent shear zone or fault including fault veins and the component tension veins is complex and search strategies depend critically on the strain stage the type of host fsz and the type of exposure deciphering the architecture of tvas involves a combination of vector orientational parameters and scalar angular relationship parameters this permits ready analysis in oriented rock outcrop and oriented drillcore and in unoriented rock unoriented drillcore mine dumps and float