transient seepage model for saturated unsaturated soil systems a geotechnical engineering approach a two dimensional finite element model is proposed to simulate transient seepage for complex groundwater flow systems the complete soil system is treated as a continuum encompassing flow in both saturated and unsaturated zones in the unsaturated zone the air phase is assumed to be continuous and open to atmospheric pressure the coefficient of permeability of the unsaturated soil is assumed to be a function of pore water pressure the governing differential equation is derived within a framework familiar to geotechnical engineers the stress state variables and the constitutive relationships for an unsaturated soil are used in the derivation the finite element solution to the governing differential equation is based on the galerkin weighted residual method the nonlinearity of the equation is solved by iterative procedures the finite element formulation is implemented into a computer model named trasee the model can be applied to a wide variety of problems involving complex boundary conditions and geo

hydrogeology of two saskatchewan tills i fractures bulk permeability and spatial variability of downward flow groundwater flow patterns were compared and contrasted in two deposits of clayey till of different thicknesses both of which overlie regional aquifers in a flat upland recharge area analysis of 67 field and laboratory hydraulic conductivity determinations indicated that conductive fractures in the unoxidized zone of the thinner till dalmeny site give rise to an isotropic bulk permeability of approximately 5 10 9 ms 1 which is two orders of magnitude greater than the bulk permeability of unoxidized till in the thicker deposit warman site vertical pore water velocities estimated using hydraulic and isotopic evidence vary greatly at dalmeny and appear to be of the order of 8 m in 10 000 yr at warman the association of vertical groundwater flux depth to water table and depth of oxidized zone at a given location is referred to as the flow regime there spatially detailed water level monitoring and test drilling indicated substantial variation of the flow regime at dalmeny on a horizontal scale of tens of meters no such variation exists at warman the differentiation of the flow regime at dalmeny is due to higher till permeability which permits a spatially variable response to microtopographically focussed infiltration of surface water recognition of the causes and symptoms of flow regime variability beneath flat till landscapes has implications for environmental assessment procedures agricultural practices wetland management and waste disposal

the geometry of echelon fractures in rock implications from laboratory and numerical experiments abstract the traces of echelon joints veins and dikes in rock range from curving to straight theoretical analyses using boundary element numerical methods have concluded that straight open fractures imply a significant remote differential stress whereas curving traces imply a more nearly isotropic stress we present a series of laboratory experiments which investigate the two dimensional propagation paths of echelon fractures in pmma plates as a function of the applied biaxial loading and the initial geometry of a simple fracture array the experimental results support the theoretical conclusions and verify the accuracy of the numerical method at the grain scale rock does not rigorously conform to the assumptions of isotropy homogeneity and linear elasticity demanded by the numerical method nevertheless results from crack path stability theory suggest that small scale deviations of a fracture from the ideal path generally do not affect its large scale behavior fracture paths which become kinked or curved by local heterogeneities are found to self correct to a path governed by competition between the fracture tip and remote stress fields provided the remote differential stress is non zero this enhances our confidence that the numerical method can be used to produce and explain realistic fracture geometries in rock an unexpected experimental result is the non perpendicular intersection of fractures grown in the laboratory free surface boundary conditions require that the walls of an open fracture be free of shear stress the principal stresses are therefore aligned with the crack wall and we might consequently expect an approaching opening mode fracture either to intersect the free surface at a right angle or to turn away and follow an asymptotic nonintersecting path experimental and numerical modeling however shows how the near tip stresses generated by an approaching fracture dominate the local stress field and allow it to propagate along an oblique path very close to intersection with the adjacent free surface

tectonics and hydrogeology of accretionary prisms role of the decollement zone abstract at convergent margins the decollement zone comprises the plate boundary and is marked by profound structural disharmony by changes in stress orientation and by a discontinuity in plate velocity the decollement zone initiates in a weak sediment layer typically a low permeability hemipelagic mud lying below a more rapidly deposited stronger more permeable trench turbidite sequence at the deformation front trench turbidites tend to be offscraped whereas the finer grained hemipelagic and pelagic sediments are more likely to be underthrust offscraped materials may undergo only limited burial whereas underthrust deposits can be deeply buried undergo high pressure metamorphism and are more likely to be preserved in the stratigraphic record burial rates associated with underthrusting are high exceeding 20 km my with high rates of underthrusting sediment descending below the decollement zone is probably buried faster than it can dewater resulting in emplacement of relatively high porosity deposits at depth fluids flowing from modern decollement zones have migrated substantial distances laterally and tapped deep sources the episodicity of flow suggests pumping of fluid by cycles of dilation and flow to the decollement zone followed by failure and fluid expansion along the decollement zone possible pressure gradients below the decollement zone allow flow upward into it while maintaining minimum effective stress along it the thickness of sediment underthrust beneath the decollement zone determines whether these deposits are emplaced by diffusive underplating with stratal disruption and efficient dewatering or by coherent underplating with the formation of macroscopic duplexes and transfer of fluid to the base of the accretionary prism deformation mechanisms affecting accreted sediment depend on depth of entrainment into the decollement zone and duration of residence

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

a geometrical and kinematical approach to the nappe structure in an arcuate fold belt the cantabrian nappes hercynian chain nw spain abstract in northwest spain thrust sheets occur in an arcuate fold belt the fault style consists of an array of thrusts merging downdip into a single decollement surface most of the thrust sheets were initiated as thrusts cutting across flat lying beds folds above the hanging wall ramps and some minor structures indicate that the body of the nappes has been subjected to an inhomogeneous simple shear parallel to bedding y 1 15 with slip concentrated along bedding planes this allows the rocks forming the nappe to remain unstrained at the base of the nappes a thin zone of deformed rock exists the thrust sheets die out laterally against an anticline syncline couple oblique to the thrust direction a geometrical analysis shows that if anticline and syncline axes are oblique the thrust sheet was emplaced with a rotational movement which can be evaluated as deformation progressed two sets of folds were formed a circumferential set following the arc and a radial set an arcuate trace of the thrust structures remains after unfolding the radial folds with a rotational emplacement the displacement vector for successive points has a progressively greater length and forms a progressively lower angle with the thrust the main thrust units are broken into several slices with rotational movements so that each unit was curved as it was being emplaced producing a first tightening of the arc later folding increased the arc curvature to its present shape the palaeomagnetic data available support the above conclusions

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

glacial lake saskatchewan and lake agassiz deltas in east central saskatchewan with special emphasis on the nipawin delta the nipawin delta extends eastward from the town of nipawin in east central saskatchewan the prince albert and fort a la corne deltas formed in lake saskatchewan at the mouths of the south and north saskatchewan rivers whereas the nipawin and mossy vale deltas formed in lake agassiz at the mouth of the saskatchewan river these deltas became lower in elevation and younger eastward clays beneath the nipawin and mossyvale deltas can be traced beneath the prince albert and fort a la corne deltas with little change in thickness suggesting that most of the clays beneath the nipawin and mossyvale deltas were deposited during the formation of the prince albert and fort a la corne deltas the nipawin delta formed between 10 200 and 9500 bp the campbell strandline emerson phase was the shoreline of the nipawin delta the mossyvale delta formed about 9500 bp the surface of the mossyvale delta mccauleyville level is about 40 m below the surface of the nipawin delta campbell level

nucleation of ductile shear zones on dilatant fractures small shear zones in granitic rocks of the sierra nevada california and near roses rosas northeast spain display features which indicate that dilatant fracturing preceded the localization of ductile shear deformation many zones have sharp nearly planar boundaries between their highly deformed interiors and the undeformed wall rock the roses shear zones narrow continuously to hairline fractures at their ends mineralized microcracks oriented parallel to the shear zones cluster near the zone boundaries and are interpreted as relicts of the earlier fracturing episode dynamic recrystallization of minerals filling these microcracks demonstrates that fracturing predated the ductile deformation gradients in ductile strain suggest that deformation spread laterally into the wall rocks after nucleation of the shear zones we suggest that cracks enhance the wall rock ductility by increasing local fluid fluxes thereby promoting chemical alteration and or hydrolytic weakening

erratum the gronlid crossing saskatchewan provincial highway no 6 at the saskatchewan river a traffic connection between regina and the northeastern part of saskatchewan required a crossing of the saskatchewan river north of gronlid slope instability developed in lacustrine and deltaic sands on the approaches to a ferry site installed in the early 1960s alternative ferry sites were considered but a river hydraulics study showed that other sites would not offer any improvement the creation of a reservoir by projected dam at nipawin and potential mining development in the area added incentive for the construction of a bridge to replace the original ferry installation valuable information was obtained from the ferry site for locating the new bridge and designing the approach roadways it was possible to locate the bridge and approaches to minimize seepage foundation and slope instability problems in a deposit of over 100 m of saturated interbedded deltaic sand lacustrine silt and clay a major artesian groundwater system was found in the bedrock sand of the swan river group whereas groundwa

cataclasites along the saltville thrust u s a and their implications for thrust sheet emplacement abstract cataclasis and frictional wear are the primary bulk deformation mechanisms along steeply dipping portions of the saltville thrust in the southern appalachian foreland zone u s a fault character ranges from a single discrete sliding surface with negligible gouge to a zone of several discrete sliding surfaces or a zone up to 0 3 m thick of pervasive cataclasite marked fracturing occurs up to 20 m above the fault whereas minimal deformation is found in the footwall rocks hanging wall dolomites range from crush breccias less than 5 matrix to ultracataclasites with 90 matrix although cataclasites 50 70 matrix are predominant foliated cataclasites occur where dolomite is thrust over shale progressive development of cataclastic fabrics is due to comminution by fracturing and grinding along intersecting fractures continued frictional grinding results in complete disruption of the original fabric to produce cataclasite and minor ultracataclasite grain alignment occurs by rigid body rotation with subsequent local enhancement by pressure solution microstructural relations of the fault gouge suggest periodic fluctuations in fluid pressure where v ratio of fluid to overburden pressure probably ranged between 0 45 and 1 the saltville thrust sheet emplacement must have occurred in a caterpillar like fashion involving aseismic and seismic shear shear stresses accompanying fault motion as determined from dolomite twin lamellae are in the order of 65 mpa

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

evolution of a turbiditic foreland basin and analogy with an accretionary prism example of the eocene south pyrenean basin the south pyrenean tertiary basin was an east west trending foreland trough which developed from early eocene to miocene times in a north south trending compressive regime a turbiditic series of lower and middle eocene age hecho group enables us to define the typical features of the tectono sedimentary evolution of the basin 1 slope and shelf derived carbonate turbidites and megaturbidites bear witness to the seismic activity of the basin borders 2 the southern basin border evidenced by the onlap of the turbidites onto slope and shelf deposits migrated progressively southwards in time and 3 the deformation pattern is characterized in the meso cenozoic sediments by a complex thrust fold system of thin skinned tectonics style its specific geometry and kinematics were influenced by the pre deformation geometry onlap this thrust fold system is related to south directed basement nappes and its front advanced progressively southwards in time from this data we infer an evolutionary model for this highly mobile basin it was a flexural basin linked to the northward bending of the lithosphere in the foreland of a south directed crustal accretionary prism as the nappes advanced the basin migrated progressively southwards in the foreland direction as for the actual basin evolution many analogies with accretionary prism trench systems of active margins exist

tertiary compressional overprint on aptian albian extensional magnetic fabrics north pyrenean zone abstract the mauleon basin constitutes part of the north pyrenean mesozoic extensional basins inverted during pyrenean late cretaceous tertiary orogeny a structural and magnetic fabric study of the aptian albian black marls of the mauleon basin north pyrenean zone provides new data indicating that when there is an intense deformation associated with the compressional stage formation of a pervasive foliation the magnetic lineation is strongly controlled by the latter tectonic deformation recorded in the basin however some areas of the sedimentary basin can still preserve the primary extensional event depending on its position with respect to basin margin faults and heterogeneous deformation areas structural and ams data define a fabric transition from extensional fabrics indicating an approximate n s extension in the central inner domain of the basin where compressional deformation was moderate to ne sw compressional fabrics in boundary domains close to the inverted faults where compressional deformation was more important k max becomes nearly parallel to the main pyrenean direction nw se consequently fabrics in the mauleon basin can be interpreted as the result of the overprint of compressional deformation onto a primary extensional fabric which in turn endures in the central domain of the basin in spite of its complicated pattern ams is revealed useful when considering the long term history of sedimentary basins undergoing several deformation events

stratigraphy and paleomagnetism of late pliocene and pleistocene sediments in the wellsch valley and swift current creek areas southwestern saskatchewan canada the late pliocene and pleistocene are represented in southern saskatchewan by sequences of preglacial glacial and nonglacial deposits these have been studied in surface exposures and bore cores and have been subdivided and correlated on the basis of their lithologies in this study new observations of magnetic polarity are presented they reveal a lower preglacial sequence empress group with reversed polarity and an upper normally magnetized sequence which contains glacial deposits of pre illinoian illinoian and wisconsinan age and which are correlative with the saskatoon and sutherland groups of central saskatchewan the reversed preglacial sequence is referred to the matuyama zone late pliocene to early pleistocene 2 58 0 78 ma and the normal glacial sequence to the brunhes zone middle to late pleistocene and holocene 0 78 ma to present in southern saskatchewan there is no evidence of glaciation during the late pliocene and early pleistocene matuyama chron which is in marked contrast w

marble mylonites in the bancroft shear zone ontario canada microstructures and deformation mechanisms abstract mylonitization of medium grade marbles in the bancroft shear zone ontario canada is characterized by decreasing grain size of both calcite and graphite and a variety of textures calcite grain sizes vary from several millimeters in the protolith to 50 200 m in mylonite to m in ultramylonite corresponding calcite grain shapes are equant in the protolith elongate in protomylonite first developed dimensional preferred orientation equant in coarse mylonite elongate in fine mylonite second developed dimensional preferred orientation and generally equant in ultramylonite which suggests that external energy applied stress that tends to elongate grains competed with internal energy sources e g distortional strain that favor equant shapes graphite grain size changes from several millimeters to centimeters in the protolith to submicroscopic in ultramylonite in the mylonitic stages graphite is present as dark bands while in the ultramylonitic stage it is preserved as a fine coating on calcite grains based on textural evidence twinning exponential creep regime i dynamic recrystallization power law creep regime ii and possibly grain boundary sliding superplasticity regime iii are considered the dominant deformation mechanisms with increasing intensity of mylonitization their activity is largely controlled by calcite grain size calcite grain size reduction occurred predominantly by the process of rotation recrystallization during the early stages of mylonitization as indicated by the occurrence of core and mantle or mortar structures and by the grain size of subgrains and recrystallized grains grain elongation in s c structures indicates the activity of migration recrystallization these structures are not the result of flattening of originally equant grains differential stress estimates in coarse mylonites and ultramylonites based on recrystallized grain size are 2 5 and 14 38 mpa respectively initial grain size reduction of graphite occurred by progressive separation along basal planes analogous to mica fish formation in quartzo feldspathic mylonites calcite graphite thermometry on mylonitic and ultramylonitic samples shows that the metamorphic conditions during mylonitization were 475 50 c which combined with a differential stress value of 26 mpa gives a strain rate of 1 2 x 10 10 s 1 based on constitutive equations corresponding displacement rates are mm yr 1

the petrofka landslide saskatchewan both abutments and all piers of the petrofka bridge are on a landslide the bridge has performed satisfactorily for 23 years indicating the factor of safety of the petrofka landslide is greater than unity this stability is abnormal because landslide slopes on bedrock clays shale in this region are notoriously unstable a dormant landslide is difficult to analyze because the input parameters must represent a condition of limiting equilibrium the petrofka landslide is 70 m high 880 m long 3000 m wide and up to 100 m thick the shear zone is in highly plastic montmorillonitic clays in an unnamed formation of probable tertiary age the upper cretaceous lea park judith river and bearpaw formations and the unnamed formation underly the landslide and are restricted to a collapse structure resulting from dissolution of devonian evaporites a retrogressive mechanism developed as valley downcutting progressed the pore water pressures could be estimated from the hydraulic head in the artesian aquifer of th

low temperature deformation of limestone isola palmaria northern apennine italy the role of primary textures precursory veins and intracrystalline deformation in localization abstract fine grained limestones of the tuscan nappe from isola palmaria northern apennine italy contain sporadically developed bedding parallel shear zones some of which exhibit well developed calcite mylonites the presence of shear zones that formed at temperatures less than 250 c allows the study of limestone deformation mechanisms active under low temperature upper crustal conditions two materially distinct types of shear zones developed during the syn nappe stage of deformation and have been characterized by integrated field strain microstructural optical microscopy cathodoluminescence transmission electron microscopy and ebsd fabric studies type a shear zones occur within decametre thick packages accommodating heterogeneously distributed strain in very fine grained limestone micrite type b shear zones are localized within calcite veins that develop into recrystallized calc mylonites both types form at the contact with dolomite although this does not play an important role in strain localization in both cases low temperature ductility occurs by extensive dislocation glide sustained by athermal network accommodated recovery although the end state microstructures of both shear zone types cannot be differentiated optically differences do exist in the crystallographic preferred orientations cpo and the grain boundary structure of deformed micrite and vein calcite deformed micrite grain boundaries are rich in voids consistent with extensive fluid flux that can enhance material transport and independent grain displacements while suppressing cpo development the crystallographically defined grain boundaries in recrystallized vein calcite suggest that lower grain boundary diffusivity enables more typical dislocation mediated cpo formation

ice thrust features and the maymont landslide in the north saskatchewan river valley the battleford glacier created shearing and softening of bedrock clays contributing to widespread slope instability along the valley of the north saskatchewan river the battleford glacier flowed southeastward down the valley of the north saskatchewan river during its final stage in west central saskatchewan it created flutings crevasse fillings folding and faulting in ice thrust ridges and extensive horizontal gouge zones filled with soft malleable clay extensive drilling and testing for the foundations of the maymont bridge provided definitive data outlining at least three gouge zones the shallowest gouge zone at an elevation of 465 m defines the base of the most severe glacial folding and deformation of the bedrock in at least one of the ice thrust ridges the deeper gouge zones are at about 433 and 438 m elevation postglacial landslides slumps along the southern side of the north saskatchewan river are controlled by the gouge zones which are low friction slide surfaces along which large ho

movement and stability analysis of the beaver creek landslide saskatchewan canada this paper presents a case history of a multiblock landslide where the blocks move at varying rates along a common horizontal slip surface which follows the contact between stratified drift and underlying till movement measurements indicate that the blocks towards the toe move at a higher rate than blocks towards the scarp stability analyses show that the entire slide mass can be analyzed as a single unit as opposed to considering each block separately this finding is compared with the analysis of other multiblock slides the friction angle mobilized along the horizontal slip surface falls within the range of residual values measured in the laboratory key words landslides stability analysis translational slides residual strength

the structure of the helvetic nappes and its relation to the mechanical stratigraphy abstract this paper discusses structure and variations in structural style due to changes in mechanical stratigraphy of the helvetic nappes based on five cross sections the ratio n of the thickness of mechanically weak to the thickness of adjacent mechanically strong layers is of particular importance a low value of n favours imbricate thrusting and harmonic folding a high value favours detachment and disharmonic folding the transition at around n 0 5 is characterized by polyharmonic folding stratigraphic thickness variations due to local basin subsidence resulted in arcuate fold hinges and important plunges upon basin inversion lateral variations in the overall structure of the helvetic nappes is largely controlled by the initial irregular arrangements of the various small basins one more or less coherent thrust sheet the cretaceous stockwerk of the wildhorn drusberg santis nappe can be traced along the entire fold and thrust belt

calcite mylonites in the central alpine root zone abstract north of the insubric line in the central alpine root zone carbonate rocks are concentrated in very narrow zones and have been metamorphosed under amphibolite facies conditions by the tertiary lepontine metamorphism grain size 1 mm post metamorphic deformation under greenschist facies conditions produced calcite mylonite bands a few millimeters to tens of meters wide in these marble zones microstructural development begins with twin formation bending of twin boundaries grain and twin boundary migration and recrystallization in high stress regions progressive mylonitization by dynamic recrystallization results in a microstructure with elongated calcite crystals long axis 20 50 m axial ration 1 4 in this fine grained matrix porphyroclasts of calcite quartz white mica biotite diopside tremolite scapolite and plagioclase are preserved ultra mylonite bands in pure calcite rocks show an even finer grain size of 5 10 m lattice preferred orientation is not present in the undeformed marbles but it develops during mylonitization the c axis orientation in the mylonites forms an asymmetric point maximum in the ultra mylonite no preferred orientation is left it is concluded from microstructural and textural aspects that during mylonitization dislocation creep accompanied by dynamic recrystallization were the most important processes whilst grain boundary sliding was the dominant mechanism during the formation of the ultra mylonites shear sense determinations indicate a horizontal right lateral strike slip shear system this is in good agreement with evidence regarding other movements along the insubric line which can be observed in ductile and brittle shear zones

laminated veins and hydrothermal breccia as markers of low angle faulting rhenish massif germany abstract the emplacement of bedding veins and vein breccia in a fold and thrust belt setting is discussed we relate vein types to thrusting regimes using the rhenish massif in germany as case example the rhenish massif is a slate belt in a hercynian fold and thrust system the slate belt cleavage generally dips to the southeast and locally has been rotated into low angle shear zones parts of these are parallel to bedding and marked by quartz carbonate veins both shear veins and extensional veins are distinguished on the basis of fibrous crack seal microstructures most shear veins grew by incremental pull apart between en echelon slip surfaces s0 the overlap of which produced a vein stack the stacks have a lineation l0 resulting from a combination of slip fibre growth and dissolution pressure solution slip the attitude of l0 relative to fold axes and the asymmetry of vein microstructures are consistent with vein emplacement during the hercynian thrusting early shear zone veins were thrusted mylonitized and finally boudinaged or folded depending on their setting the shear veins include coeval sheets of vein hosted breccia the breccia contains angular fragments of mylonitized veins and slate the orientation of s0 and s1 in the breccia varies randomly per fragment indicating random fragment rotation unencumbered spin of country rock debris implies rock expansion possibly by rapid pull apart events during the thrusting

three dimensional geometry strain rates and basement deformation mechanisms of thrust bend folding abstract models for thrust bend folding of an isotropic medium are used to predict initial basement thrust sheet geometries and sub surface thrust fault shapes from final basement thrust sheet structure predicted strains and strain rates from these models are compared with data on deformation fabrics in an example of a basement thrustbend fold in order to characterise the deformation response to thrust bend folding the glencoul thrust sheet in the moine thrust zone of north west scotland is restored to an initial thrust sheet geometry spatial and orientation distribution data of syn emplacement fractures and cataclastic fault zones from within the glencoul thrust sheet are then compared with the strain and strain rate histories predicted by thrust bend folding models a different set of cataclastic fault seams is demonstrated to have been generated at each frontal thrust bend cataclastic failure is restricted to portions of the thrust sheet that have moved over frontal bends with smaller radii of curvature from model thrust bend geometries and an assumed slip rate of 1 x 10 10 ms 1 estimated minimum critical strain rates required for fracture failure of the lewisian basement are 10 11 to 10 14 s 1 for shear strain rates and 10 12 to 10 15 s 1 for extensional strain rates

structural lithic units in external orogenic zones abstract changes in types of thrust fault structures are typical of external orogenic zones and are inferred here to be related to thickness and facies changes in stratigraphie sequences obvious deformation style changes occur from external to intermediate thrust sheets similar changes in style are observed and most easily interpreted along strike within individual thrust sheets to correlate stratigraphic and structural changes stratigraphic sections are divided into structural lithic units the subdivisions are based on the dominant deformation styles vertically in individual cross sections the major variables in determining deformation style are controlling stratigraphic members within individual stratigraphic structural units and the stacking sequence of lithologie types into different structural units in many areas the critical taper of one major dominant member regionally controls where structural style changes will occur areal change in either internal composition or in stacking sequence causes lateral change in deformation style lithological changes in structural units are coincident with changes in frontal thrust ramp positions connected by major lateral ramps and with changes in thrust zone geometries imbricate thrusts in one area versus a duplex zone along strike they are also associated with changes in thrust shapes from listric to stepped and changes from fault bend fold to fault propagation fold structures controlling members may be either strong or weak fold dominated regions and thrust faulted regions without major shales or evaporites are usually controlled by strong controlling members weak controlling members are major evaporite horizons or thick shales a thorough understanding of stratigraphic facies realms therefore may allow predictions of types and changes in structural styles it can also be very useful in the interpretation of less well exposed thrust terranes

antitaxial crack seal vein microstructures and their relationship to displacement paths abstract the microstructures developed in an example of a syntectonic crack seal vein indicate that antitaxial fibres do not necessarily track the incremental opening history during crack seal vein growth this observation serves as a caution against the uncritical use of fibrous microstructures to make inferences about displacement histories during fibre formation it is demonstrated that crack seal processes can lead to the development of both irregular and laminated vein microstructures as well as fibrous microstructures the types of microstructures which develop in crack seal veins and the extent to which they reflect the opening paths of veins depend on a range of factors the most important of these include the nucleation and growth kinetics of phases precipitated from fluids in opening fractures and the location of sites of material accretion during successive crack seal increments

a transient analysis of slope stability following drawdown after flooding of a highly plastic clay the stability of slopes at bridge abutments across the carrot river in east central saskatchewan was not influenced significantly by drawdown after flooding in the spring of 1995 traditional metho

magnetic fabrics in the western central pyrenees an overview abstract in the western central pyrenees numerous investigations during the past years have yielded an exceptional high density of localities more than 700 sites where the ams and rock magnetic properties have been determined this unique ams dataset helps in understanding the orogenic evolution of the pyrenees and its foreland basins processes related to ams development in different structural units permit to identify i an early recording of strain related to the transtensional or transpressional stages during the early triassic and early cretaceous ii a moderate shortening related to the fold and thrust belt and foreland basin evolution during the cretaceous tertiary orogenic stage and iii a relatively strong deformation that produced cleavage related to the emplacement of basement thrusts in the axial zone during the middle late eocene the main achievement of this contribution is the integration in cross section and map view of magnetic fabrics orientation and parameters in the western central pyrenees which allow constraining the processes affecting magnetic fabrics at the orogen scale ams results indicate i a dominant bedding controlled foliation very sensitive to subtle layer parallel shortening lps processes especially in the foreland basins ii magnetic lineations parallel to fold axes or strike of thrusts outside the cleavage front that can be deflected by vertical axis rotations in particular areas and iii an overall decrease of the definition of ams fabrics magnetic lineation or the anisotropy of the ellipsoid associated with incipient cleavage and intersection lineation fabrics in the internal zones of the orogen therefore ams is a sensitive indicator to delineate the strain patterns at the orogen scale in particular in those areas undergoing a modest degree of deformation

impact of the late triassic dashtak intermediate detachment horizon on anticline geometry in the central frontal fars se zagros fold belt iran abstract integration of 2 d seismic lines well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific central frontal fars region in the se zagros fold belt these variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level located along the late triassic dashtak formation anticlines of short wavelength contain a significant over thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m from an original thickness of 550 800 m folds containing thick dashtak evaporites show decoupling across the detachment level and thus a shift of the anticline crest in the underlying permo triassic carbonates of the dehram group which form the major gas reservoir in the central frontal fars four main parameters control the extent and distribution of the decoupled anticlines in the study area a original large thickness of the late triassic evaporitic basin b coinciding larger amounts of anhydrites with increasing total thickness of formation c parallel occurrences of abnormally high fluid pressures and d shortening variations across and along the strike of specific folds the present work relating the different parameters of the dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth which is applicable to oil and gas exploration in the se zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons

thrust sheet motion and earthquake mechanisms abstract the mechanism of thrust sheet motion and that of earthquake generation are two aspects of the same phenomenon studies of earthquake mechanisms show that only a part of the thrust fault generally less than 10km in length is in motion at any given instant this part sweeps the length of the fault moving at approximately 3 km s since shear fracture propagation is inherently a dynamic phenomenon it cannot be understood on the basis of the equations of static equilibrium the previously proposed mechanisms all rest on such an equilibrium which necessarily implies that the motion of a thrust sheet occurs simultaneously over its whole length since the latter may exceed 100 km the motion becomes a mechanical enigma this enigma vanishes once the dynamic nature of the problem is recognized the proposed mechanism also suggests that solution features on the fault result from the dissolution of barriers thus explaining the motion of only part of a thrust sheet

the anso transect of the southern pyrenees basement and cover thrust geometries a balanced geological section through the western central pyrenees allows the alpine geometry of hercynian basement to be determined this shows marked differences with other transects of the southern part of the chain basement involved thrust sheets do not form an antiformal stack but are imbricated and define steps separated by frontal culmination limbs basement thrusts propagate upwards and have formed distinct thrust systems in the cover in this transect the north pyrenean zone is bounded to the south by gently dipping thrusts of large displacement and the axial zone massif at its western termination area is a flat topped culmination caused by a single thrust fault the gavarnie thrust this thrust emerges to the south in the interior of the syntectonic jaca basin the geometry of which is also controlled by underlying basement thrusts various generations of structures can be correlated with distinct episodes of syntectonic sedimentation a sequential restoration of the section illustrates how successive foreland sedimentary wedges were generated and progressively involved in deformation tectonic shortening is 48 km almost half of that estimated further to the east for the southern pyrenees the structure deduced at the ecors pyrenees seismic section cannot be translated to this transect

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

microtectonic and geochemical characterization of thrusting in a foreland basin example of the south pyrenean orogenic wedge spain abstract in orogenic systems thrust faults play a major role in stacking different tectonic units and may act as conduits for the expulsion of large amounts of fluid of different origins metamorphic diagenetic meteoric this study focuses on the monte perdido thrust unit emplaced in the paleogene jaca thrust sheet top basin in the sw central pyrenees we aim to decipher the mechanisms and p t conditions of deformation in fault zones and characterize the related fluid involvement through combined microstructural geochemical and microthermometry analyses two thrust faults cutting platform limestones marls and siliciclastic turbidites of the lower part of the basin fill paleocene lower eocene have been studied the fault zones are characterized by metre thick shear zones with highly deformed foliated clay rich sediments foliation is underlined by preferentially oriented phyllosilicates several generations of shear and extension calcite quartz and chlorite bearing veins attest to fluid rock interactions during a multi stage deformation microstructural observations and stable isotope analyses on calcite from veins and host sediments suggest that deformation was aseismic and dominated by diffusive mass transfer from pressure solution sites along cleavage and stylolites to the precipitation sites in veins with mineralizing fluids in equilibrium with the host sediments our results suggest an essentially closed hydrologic system and imply the absence of significant fluid flow along the studied fault zones microthermometric study on fluid inclusions present in calcite and quartz veins and calcite quartz oxygen isotopic fractionation determined for the first generation shear veins allow a geothermal gradient of 34 c km to be estimated analytical results demonstrate an evolution of the fault zones in three stages the first stage was related to the emplacement of the monte perdido thrust unit during the middle eocene at a temperature of 208 c and a burial depth of 5 7 km the second stage corresponds to a fault reactivation at a temperature of 240 c and a burial depth of 6 5 km the latter deformation may have been related to folding of the monte perdido thrust unit during the emplacement of the underlying gavarnie thrust unit during the late eocene early oligocene with deeper burial resulting from aggradation of the thrust sheet top basin fill the last event corresponds to the formation of a dilatant vein system likely related to the exhumation of the massif

the hepburn landslide an interactive slope stability and seepage analysis mechanisms of active landslides are continuous processes involving the dynamics of slope failure interacting with the groundwater regime this process is simulated in phases by combining stability calculations interactively with a seepage analysis to determine the factor of safety for a dormant landslide near hepburn saskatchewan the landslide is a multiple retrogressive failure with two parallel slip surfaces at different elevations the slip surfaces are in originally overconsolidated cretaceous and tertiary clays softened by shear from glaciation an artesian aquifer is present at the base of the slip surface causing saline springs at the base of the valley slope a residual effective friction angle of 6 7 with zero cohesion was found to best characterize the shear strength of the clays in the failure zone potential nets and head profiles from the seepage analysis illustrate the strong influence of changing topography on the groundwater flow system the present day factor of safety for the dormant

structural evolution of the sierras interiores aragon and tena valleys south pyrenean zone tectonic implications abstractthe sierras interiores preserve an outstanding record of the alpine deformation along the northern border of the south pyrenean zone in northern spain new mapping and structural data illustrate the existence of two thrust systems developed from competent sandstones and limestones of cenomanian to paleocene age a deeper thrust system duplicates the massive limestones of the lower calcareous section cenomanian to early campanian at the base of the mesozoic cover of the sierras interiores that rests unconformable over paleozoic rocks of the pyrenean axial zone there is an upper thrust system that comprises a duplex leading to duplications of the marbore sandstones campanian to maastrichtian and the light limestones and dolostones paleocene from the regional point of view the relevance of the deeper thrust system is evidenced by its great lateral continuity and because it constitutes the higher thrust of a large antiformal stack made up by at least four paleozoic involving allochthonous sh

a fluid inclusion study of blueschist facies lithologies from the indus suture zone ladakh india implications for the exhumation of the subduction related sapi shergol ophiolitic melange abstract the best occurrence of blueschist facies lithologies in himalaya is that of the shergol ophiolitic melange along the indus suture zone in ladakh region of north western india these lithologies are characterized by well preserved lawsonite glaucophane garnet quartz assemblages this paper presents for the first time the results of a detailed fluid inclusion study on these lithologies in order to understand the fluid p t evolution and its tectonic implications the blueschist rocks from shergol ophiolitic melange record metamorphic peak conditions at 19 kbar 470 c several types of fluid inclusions are trapped in quartz and garnet most of them being two phase at room temperature three types of fluid inclusions have been recognised basing on microtextures and fluid composition type i are primary two phase carbonic aqueous fluid inclusions v co2 l h2o type ii are two phase l h2o v h2o aqueous fluid inclusions either primary type iia or secondary type iib type iii are re equilibrated fluid inclusions in the type i primary carbonic aqueous inclusions h 2 o is strongly predominant with respect to co 2 the homogenization temperature of co 2 range from 7 to 2 c the clathrate melting temperature in such inclusions varies in between 7 1 and 8 6 c type ii two phase aqueous fluid inclusions show a wide range of salinity from 7 8 14 wt nacl eq type iia to 1 65 6 37 wt nacl eq type iib with accuracy 0 4 wt nacl eq type i and type iia primary fluid inclusions are hosted in peak minerals garnet and quartz included in garnet therefore they were likely entrapped at or near to peak p t conditions the dominantly aqueous fluid of both type i and type iia inclusions was most likely produced through metamorphic devolatilization reactions occurring in the subducting slab despite their primary nature the isochores of type i and type iia inclusions do not intersect the peak metamorphic conditions of the blueschist mineral assemblage suggesting that these inclusions stretched or re equilibrated during nearly isothermal decompression from 19 kbar to 3 kbar or less at t 290 c this conclusion is further supported by their large variability in shapes and sizes which range from irregular inclusions c arc shaped hook shape and satellite type this decompression stage was followed by nearly isobaric cooling testified by the occurrence of dendritic networks of decrepitated and imploded fluid inclusions

deformation of the deer creek bridge by an active landslide in clay shale two parallel concurrently active slip surfaces of a landslide in clay shale of the cretaceous lea park formation are causing deformation of a bridge structure across the north saskatchewan river n

stratigraphy and structure of a late wisconsinan salt collapse in the saskatoon low south of saskatoon saskatchewan canada an update the saskatoon low is a collapse structure that formed as a result of dissolution of salt from the middle devonian prairie evaporite formation in this study the collapse has affected the upper cretaceous lea park judith river and bearpaw formations of the montana group the early and middle pleistocene mennon dundurn and warman formations of the sutherland group and the late pleistocene floral battleford and haultain formations of the saskatoon group locally the collapse is about 180 m which is about equal to the thickness of the salt the first phase of collapse took place after deposition of the ardkenneth member of the bearpaw formation and before glaciation or during a pre illinoian glaciation the second phase of collapse occurred during the battleford glaciation late wisconsinan prior to deposition of the battleford formation the saskatoon low was glacially eroded removing the sutherland group and the floral formation after the glacial erosion up to 110 m of soft till of the battle

kinematic model for the curvature of the northern subalpine chain france abstract analyses of cross sectional shortening mapped faults and calcite twin strain are used in conjunction with geometric kinematic modeling to interpret the mechanism of curvature formation in the northern subalpine chain of france there is a 45 change in strike around the chain that is convex towards the foreland northwest five models for fold thrust belt curvature are applied to the northern subalpine chain they can reproduce the geometry and the kinematic history of a curved fold thrust belt and can be used to predict the magnitude and orientations of strains and the three dimensional geometry of the curvature the models are pure bending radial thrusting curve parallel simple shear uniform displacement uniform shortening and transport parallel simple shear two principal criteria for distinguishing among the models geometrically are the horizontal tangential strain extension or contraction parallel to strike and cross sectional shortening the transport parallel simple shear model predicts no tangential extension in the central domain and greater radial shortening and significant tangential extension in the northeastern and southern domains this is the pattern observed in the northern subalpine chain therefore the curvature of the northern subalpine chain is attributed to a transport parallel simple shear mechanism

genesis of natural hydraulic fractures as an indicator of basin inversion abstract satin spar fibrous gypsum veins which occur in evaporite basins worldwide provide significant insights into host rock deformation and fluid flow although the genetic mechanism remains obscure satin spar veins in the red marls of the triassic mercia mudstone of the bristol channel basin were characterized in the context of regional and local setting the vein network in the keuper marl lower mercia exhibits a lack of systematic cross cutting between three distinct vein sets two sets of veins are observed in the overlying tea green marl with one set clearly crossing the other the gypsum veins commonly contain a blocky median zone of multiple thin bands of host rock inclusions and alabastrine gypsum crystals exhibiting crack seal patterns fibrous zones on either side of the median zone consist of pure parallel aligned gypsum fibres that are oblique to vein walls indicating a hybrid shear extensional mode of vein widening veins developed within reverse reactivated faults contain fibre lineations in the median zones and also on vein surfaces suggesting a minimum of two phases of fault slip the veins are interpreted to have formed as a result of overpressure in the low permeability mudstones by tectonic compression during basin inversion giving rise to the median zone growth of gypsum fibres commenced when the initial fractures were completely sealed the timing of vein formation is suggested to be miocene based on cross cutting relationships with folds formed during the latest phase of basin inversion because the fractures initiated in response to fluid overpressures they provide a useful analog to subsurface hydraulic fracture systems in low permeability rocks subjected to tectonic compression the fibrous widening of the veins post dates their initiation and led to continued propagation and increased connectivity

low temperature recrystallization in calcite mechanisms and consequences vein calcite dominated fault rocks collected from several locations show evidence for intense intracrystalline plasticity and interface twin and grain boundary mobility leading to dynamic recrystallization of calcite at temperatures 150 250 c significantly below those at which these features are commonly anticipated these observations require a reappraisal of calcite deformation at low temperature particularly the capability for dynamic recrystallization in the apparent absence of significant thermally activated recovery processes the cyclic introduction of coarse grained calcite veins is observed to be essential for the initiation of intracrystalline deformation and associated dynamic recrystallization the introduction of veins generates an essentially monomineralic rock of a grain size larger than the protolith as a result the mylonitization does not occur within a given protolith but rather in the introduced secondary calcite through hall petch type grain size dependent dislocation interactions stress is locally increased and the resulting increase in dislocation densities promotes grain boundary migration the recognition that nominal high temperature creep processes and associated microstructures can occur outside their expected temperature range has implications for fault rheology strength and fault permeability and porosity

water sill hypothesis for the origin of certain veins in the meguma group nova scotia canada certain bedding parallel quartz veins some gold bearing in the cambrian ordovician meguma group nova scotia are believed to indicate the former presence of water sills the veins contain primary subhedral quartz crystals which tend to be oriented normal to the vein walls and display brazil twins twinned crystals commonly show hexagonal sections with dark solid inclusion rich centers and white fluid inclusion rich rims viewed in a plane perpendicular to bedding the dark centers of crystals exhibit millimetre thick quartz plates bounded by bedding parallel micrometre thick inclusion bands of white micas the inclusion bands are aligned parallel to the vein walls and terminate within tapered crystals that have an outer zone of milky quartz the quartz veins are on limbs and hinges of folds particularly anticlines from these observations we conclude that 1 the solid inclusion banded quartz resulted from episodic hydraulic extension fracturing and incremental growth of dispersed quartz bridges across water sills 2 the milky quartz filled the vein by growing in optical continuity with the solid inclusion banded quartz 3 localization of certain bedding parallel quartz veins is due to ponding of water beneath aquacludes in very broad domes formed by differential compaction in the meguma group 4 during tectonic shortening these intensely veined rocks localized some of the major anticlines

disentangling magnetic subfabrics and their link to deformation processes in cleaved sedimentary rocks from the internal sierras west central pyrenees spain abstract here we present a detailed study of the magnetic fabrics and subfabrics of remagnetized upper cretaceous limolites that crop out in the internal sierras west central pyrenees affected by a penetrative pressure solution cleavage the bulk magnetic fabrics of these rocks rt ams show variable orientations that do not conform to what is typically reported for cleaved sedimentary rocks in contrast the paramagnetic subfabrics lt ams show remarkably constant directional properties so that their k max and k min axes cluster parallel to the intersection lineation and to the poles to bedding respectively these lt ams subfabrics indicate a preferred orientation of phyllosillicates that is consistent with a syn sedimentary late cretaceous period of nne oriented layer parallel shortening noticeably these phyllosillicate subfabrics are not further altered by the subsequent formation of cleavage in the late eocene early oligocene the ferrimagnetic subfabrics aarm also show remarkably constant orientation so that their k max axes are strikingly parallel to the shortening direction in the area we interpret this preferred orientation of ferrimagnetic grains as being caused by subhorizontal shear associated to cleavage formation which is consistent with the age and mechanisms authigenic growth and rotation of pre existing magnetite grains proposed for the pervasive remagnetization that affects the studied rocks

multiple origin and regional significance of bedding parallel veins in a fold and thrust belt the example of a carbonate slice along the appalachian structural front abstract the development and evolution of bedding parallel veins bpv are investigated in the saint dominique carbonate slice southern quebec appalachian structural front in order to emphasize the regional significance of bpv in a fold and thrust belt and their importance in establishing its structural and diagenetic evolution structural and microstructural analyses reveal that most bpv display a laminated structure locally crosscut by a massive one both structures show mutual crosscutting relationships with bedding parallel or bedding perpendicular stylolites and with bedding perpendicular veinlets indicating that bpv cementation and deformation are continuous processes opening both sub parallel and sub perpendicular to the bpv walls are documented early bpv are planes of weakness that focus later reactivation and evidence of successive and sometimes opposite senses of opening are locally preserved within a single bpv the bedding parallel orientation of these veins proved particularly helpful in establishing the structural evolution of an area mostly characterized by front parallel structures with little crosscutting relationships otherwise petrographic and geochemical 18 o vpdb and 13 c analyses of structural cements suggest a common locally derived source for the fluids that percolated through bpv non bedding parallel veins and faults the isotopic ratios also reveal a significant enrichment in 18 o and 13 c through time this evolution is tentatively correlated with tectonic syn convergence exhumation of the saint dominique slice during its imbrication along the appalachian structural front after its burial under taconian thrust sheets

the role of veining and dissolution in the evolution of fine grained mylonites the mcconnell thrust alberta microstructural observations of the mcconnell thrust fault rocks demonstrate the importance of vein formation and calcite dissolution in the evolution of the mcconnell thrust limestone mylonites the protolith to the mylonite is a micritic limestone the mylonite contains numerous discontinuous bedding parallel calcite veins that range from relatively undeformed except for twinning and undulose extinction to highly sheared the highly sheared veins show evidence for dynamic recrystallization and grain size reduction along grain and twin boundaries that can lead to complete recrystallization to a grain size of approximately 1 3 m the bulk of the calcite matrix within the mcconnell thrust mylonite is interpreted to have formed by dynamical recrystallization of veins the emplacement of relatively coarse grained veins promoted the activation of dislocation creep within the fault rocks of the thrust in the absence of the increase in grain size afforded by vein emplacement it is anticipated that the fine grained protolith would have deformed predominantly by solution transfer with grain boundary sliding and localized brittle shearing the layer parallel calcite veins are found in close proximity to sheared clay seams which are interpreted to represent the insoluble residue left behind after dissolution of calcite these clay seams may have contributed to the build up of high pore fluid pressures which if intermittently reaching lithostatic conditions during displacement would result in transient brittle failure and thrust surface parallel vein emplacement in an otherwise ductilely deforming rock

the mechanical paradox of large overthrusts the mechanical paradox of large overthrusts originates with a fallacious assumption in the conceptual model upon which mechanical analyses of overthrust faulting have been based the notion that the maximum width of a sheet of rock that may be displaced along an overthrust fault can be determined by using the mohr coulomb failure criterion to compare the strength of the rocks with the stress required to overcome the total frictional resistance to slip and the total cohesion or adhesion over the entire fault surface tacitly assumes that slip is initiated and occurs simultaneously over the entire fault surface this unstated and untenable assumption which is incompatible with what is known about real faults is the real explanation for the mechanical paradox a realistic model for overthrust faulting must be compatible with the nature of real overthrust faults and particularly with the way in which displacements including earthquake displacements occur on real faults most large overthrusts are discrete shear surfaces within a coherent mass of rock that is physically continuous around their ends total displacement clearly varies from place to place over these discrete shear surfaces and moreover must be the cumulative result of many relatively small incremental displacements that also varied from place to place over the finite part of the fault surface on which they occurred each increment began as a local shear failure and propagated along the fault as a smeared out somigliana dislocation at a velocity that was small considering the time required for propagation over the total area of the fault during any individual displacement event whether a megathrust earthquake or a creep event only a small part of the fault surface was in relative motion at any one time fault displacements may appear to occur simultaneously across laboratory specimens that are very small relative to the velocity of propagation of displacement because the transit time is so short when the linear scale is expanded over six orders of magnitude to encompass an entire surface of a large overthrust fault however the transit time is much longer because the velocity of propagation is very small relative to the area of the fault surface and the displacement clearly involves only a very small part of the fault surface at any one time the shape and size of overthrust faults result from the propagation of dislocations and this process is controlled by the strength heterogeneity and anisotropy of the rock mass as well as by variations in the regional stress field but not by the frictional resistance to sliding integrated over the entire fault surface

a new type of decollement thrusting one of the fundamental rules of decollement tectonics is that decollement horizons form in mechanically weak layers here we document two examples of decollement style thrust faults that detach within thick platformal dolostones in preference to apparently weaker layers of shale siltstone and limestone underlying the dolostones the thrusts are the keystone muddy mountain glendale thrust system the kmg thrust system and the underlying contact red spring north buffiington mormon thrust system the crm thrust system both of southern nevada they form part of the sevier orogenic belt and extend for roughly 250km along strike together showing at least 65 km tectonic overlap fig 1 although the thrust systems are closely related spatially the higher kmg system is younger than the underlying crm thrust system and the two developed essentially independently three points are important first that both the kmg and the crm thrust systems are decollement style thrusts second that the decollement horizon is primarily restricted to a narrow stratigraphical interval within a bedded sequence of essentially homogeneous dolostones of the middle cambrian bonanza king formation the third that the thrust faults formed at a very shallow crustal level 5 km

strain hardening and strain softening in fault zones from foreland thrusts the movement of thrust sheets is accomplished in part by deforming the rocks adjacent to thrust faults in foreland fold and thrust belts emplacement generates an array of mesoscopic faults in a thick layer along the base of a sheet ductile deformation of rocks in the layer occurs by displacing fault bounded blocks relative to one another in a kind of mesoscopic grain boundary sliding analyses of data from three southern appalachian thrust sheets indicate that this block sliding is first accompanied by strain hardening then by strain softening and it is accommodated by intra block fractures small faults and veins the density of accommodation features increases near thrusts and where these features become sufficiently numerous a layer of cataclastic rocks forms along the thrust we describe foliated cataclasites from two thrusts the microstructures of which indicate that the cataclasites exhibited extreme ductility interrupted occasionally by brittle processes deformation of the cataclasites was accompanied by strain softening strain softening deformation in fault arrays near thrusts is genetically related to strain softening deformation in cataclasites during the formation of the cataclasite rocks in the sheet are impelled to cross a strain energy hump after which they deform at either higher rates or lower stresses

syn diagenetic evolution of shear structures in superficial nappes an example from the northern apennines nw italy abstract in the superficial nappes of the northern apennines meso and microstructures in sheared mudstones and fine grained turbidites consist mainly of networks of striated faults and calcite vein arrays the striated faults correspond to the first generation of structures they form two sets respectively synthetic and antithetic to the general shearing locally a sigmoidal microfabric is associated with the synthetic faults in scaly deformation bands up to a few metres thick late laterally extensive calcite veins are superposed on these structures they result from the opening of multiple releasing oversteps between shear surfaces the crack seal mechanism of deformation played a major role in their formation structures of the first generation result from heterogeneous ductile deformation of initially poorly lithified and water rich sediments the late formation of the calcite veins corresponds to a transitional ductile brittle behaviour in sufficiently lithified sediment evolution of structures probably depended on a strain hardening process and was dependent on the progressive compaction and dewatering of the sediment the gently dipping faults and veins probably formed the main pathway for the interstitial fluids possibly overpressured expelled from the sediment we emphasize that the geometry of the structures described provides important shear sense criteria for the study of superficial nappe tectonics

rotational basement kinematics deduced from remagnetized cover rocks internal sierras southwestern pyrenees 1 paleomagnetic data from the internal sierras unravel the kinematic relationship between basement guarga gavarnie bielsa and cover thrusts larra monte perdido the new data come from an area of 100 km along strike and 5 15 km across strike of the southwestern pyrenees the area covers a variety of structural positions that range from cover to basement thrusts from 84 sites located in upper cretaceous two meaningful magnetic components are found 1 the higher temperature c component unblocks at 575 c presents two polarities is prefolding has a mean declination and inclination d i of 010 44 95 8 k 15 and is considered primary and 2 the intermediate b component unblocks between 250 c and 450 c has a mean d i of 198 43 95 4 k 18 and has always reverse polarity and postfolding the nine sites located in the eocene flysch south of the upper cretaceous show the same postfolding component b the acquisition of this intermediate component alludes to a widespread tectonic related remagnetization event affecting the internal sierras this event must be younger than the folding of the flysch deposits middle upper eocene the tilting induced by the basement thrust gavarnie bielsa in the axial zone does not alter the inclination of the b so that the sediments acquire the b component later than priabonian emplacement age of the gavarnie thrust the b component is rotated clockwise with respect to the tertiary reference this means that the rotation takes place after the remagnetization event the position of the c component before the rotation of the b component is negligibly rotated d i of 002 44 95 7 k 94 with respect to the cretaceous reference therefore the b component records the last and only rotational event in the region the rotation is related to the latest basement deformation guarga thrust during upper oligocene times and it reflects the regional shortening gradient in the southwestern pyrenees the emplacement of the larra monte perdido cover thrust system that took place prior to basement thrusts mentioned above did not undergo any significant rotation

anatomy of a fossil landslide from the pleistocene of se spain abstract pleistocene landslide failures are rarely recorded in the literature due to difficulties in recognition in the field an adaptation of standard landslide classification based on activity is used to identify and examine the significance of a fossil pleistocene landslide from the mocatan catchment of the sorbas basin se spain recognition of the landslide is based on identifying key but subtle anomalies in the geology and drainage the fossil landslide at mocatan developed principally in response to a rapid increase in valley incision rates associated with capture induced base level changes in the master drainage this was facilitated by the weak sand and silt lithology of the study area the landslide was a significant morphological modifier of the environment holocene drainage follows the original landslide morphology whilst more recent gullying and piping exploits planes of weakness developed within the internal body of the landslide feature in addition the landslide removed much of the pleistocene divide facilitating future river capture

mechanisms of thrust faulting in the gran sasso chain central apennines italy abstract the gran sasso chain in central italy is made up of an imbricate stack of eight thrust sheets which were emplaced over the upper miocene lower pliocene laga flysch the thrust sheets are numbered from 1 to 8 in order of their decreasing elevation in the tectonic stack and their basal thrusts are numbered from t 1 to t 8 accordingly on the basis of their different deformation features the major thrust faults fall into three groups 1 thrust faults marked by thick belts of incoherent gouges and breccia zones t 1 t 2 t 3 2 thrust faults characterized by a sharp plane which truncates folds that had developed in the footwall rocks t 5 t 6 and 3 thrust faults truncating folds developed in both the hangingwall and footwall units and bordered by foliated fault rocks t 7 the deformation features observed for the different faults seem to vary because of two combined factors 1 lithologic changes in the footwall and hangingwall units separated by the thrust faults and 2 increasing amounts of deformation in the deepest portions of the imbricate stack the upper thrust sheets from 1 to 6 are characterized by massive calcareous and dolomitic rocks they maintain a homoclinal setting and are truncated up section by the cataclastic thrust faults the lowermost thrust sheets 7 and 8 are characterized by a multilayer with competence contrasts which undergoes shear induced folding prior to the final emplacement of the thrust sheets bedding and axial planes of folds rotate progressively towards the t 5 t 6 t 7 and t 8 thrust boundaries and are subsequently truncated by propagation of the brittle thrust faults the maximum deformation is observed along the t 7 thrust fault consistent with horizontal displacement that increases progressively from the uppermost to the lowermost thrust sheet in the tectonic stack the axial planes of the folds developed in the hangingwall and footwall units are parallel to the t 7 thrust fault and foliated fault rocks have developed field data and petrographic analysis indicate that cleavage fabrics in the fault rocks form by a combination of cataclasis cataclastic flow and pressure solution slip associated with pervasive shearing along subtly distributed slip zones parallel to the t 7 thrust fault the development of such fabrics at upper crustal levels creates easy slip conditions in progressively thinner domains which are regions of localized flow during the thrust sheet emplacement

the interplay between fluids folds and thrusts during the deformation of a sedimentary succession abstract in this paper field evidence is presented to support the idea that fluid pressures in excess of lithostatic pressure were operating during the initiation and reactivation of large thrusts and folds in the wenlock shales of llangollen north wales it is also argued that as major thrusts are reactivated and as major folds amplify into finite structures they in turn exert an influence on the subsequent migration and concentration of fluids within the deforming sedimentary succession

the complexity of 3d stress state changes during compressional tectonic inversion at the onset of orogeny compressional tectonic inversions are classically represented in 2d brittle failure mode bfm plots that illustrate the change in differential stress s1 2 s3 versus the pore fluid pressure during orogenic shortening in these bfm plots the tectonic switch between extension and compression occurs at a differential stress state of zero however mostly anisotropic conditions are present in the earth s crust making isotropic stress conditions highly questionable in this study theoretical 3d stress state reconstructions are proposed to illustrate the complexity of triaxial stress transitions during compressional inversion of andersonian stress regimes these reconstructions are based on successive late burial and early tectonic quartz veins which reflect early variscan tectonic inversion in the rhenohercynian foreland fold and thrust belt high ardenne slate belt belgium germany this theoretical exercise predicts that no matter the geometry of the basin or the orientation of shortening a transitional wrench tectonic regime should always occur between extension and compression to date this intermediate regime has never been observed in structures in a shortened basin affected by tectonic inversion our study implies that stress transitions are therefore more complex than classically represented in 2d ideally a transitional wrench regime should be implemented in bfm plots at the switch between the extensional and compressional regimes extension mode i fractures are classically interpreted to form at low differential stresses less than four times the tensile strength t of rock e g secor 1965 they open perpendicular to the minimum principal stress s3 and propagate in the plane of the maximum s1 and intermediate s2 principal stresses the alignment of fractures has therefore often been used in orogenic belts to determine the orientation of the palaeostress field at the time of fracturing cox et al 2001 gillespie et al 2001 laubach et al 2004 if veins which initiated as extension fractures are uniform in trend over a large area then they can also be used as such a palaeostress indicator e g boullier robert 1992 cosgrove 2001 gillespie et al 2001 mazzarini et al 2010 van noten sintubin 2010 different cross cutting or successive vein generations are even more interesting because they have the potential 1 to serve as a tool to decipher changes in the overall stress regime during multiple phases of fracturing and 2 to define the p2t conditions at which these stress changes occurred on the one hand different crosscutting fracture and or vein generations have been used in many studies to deduce local stress field rotation in a consistent remote stress regime jackson 1991 crespi chan 1996 stowell et al 1999 laubach diaz tushman 2009 wiltschko et al 2009 on the other hand successive cross cutting veins i e vein sets that are oriented differently with respect to bedding have often been used to determine a transition in regional stress regime from extension to compression or reversely manning bird 1991 boullier robert 1992 teixell et al 2000 hilgers et al 2006b van noten et al 2008 2011 laubach diaz tushman 2009 alternatively cross cutting vein sets are observed in close relationship to faults in which they represent fluctuating fluid pressures during fault valve activity and are related to short lived local stress transitions in a consistent remote stress regime boullier robert 1992 sibson 1995 nielsen et al 1998 muchez et al 2000 collettini et al 2006 local mutually cross cutting vein sets may also develop in the presence of mechanical anisotropy around fault planes in a consistent remote stress field healy 2009 fagereng et al 2010 in all these studies transitions between regional stress regimes are defined as tectonic inversions a positive compressional tectonic inversion corresponds to a transition from an extensional to a compressional stress regime while a negative extensional tectonic inversion reflects the transition from compression to extension from healy d butler r w h shipton z k sibson r h eds 2012 faulting fracturing and igneous intrusion in the earth s crust geological society london special publications 367 51 69 http dx doi org 10 1144 sp367 5 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics by guest on august 9 2012 http sp lyellcollection org downloaded from

the denholm landslide saskatchewan canada an update the lower block of the denholm landslide has moved 370 m over alluvium deposited by the north saskatchewan spillway and river during the last 11 500 years at an average rate of 32 mm year these values must be considered minimal because erosion of the toe of the landslide is required for the formation of retrogressive landslides the shear strength for the bedrock clay shale of the lea park formation was back calculated to be assuming zero cohesion key words retrogressive landslide clay shale residual strength movement rates geological age inclinometer

calcite twins their geometry appearance and significance as stress strain markers and indicators of tectonic regime a review twin lamellae are a widespread feature in calcites of any type and origin twinning in calcite is an important intracrystalline deformation mechanism with low critical resolved shear stress and virtually no temperature dependence in contrast to most slip systems in rock forming minerals twinning therefore permits intracrystalline deformation at very low temperature and very little confining pressure twinning alone however cannot lead to large strains because only one independent slip system is effectively available twins lead to discontinuous shearing on the grain scale which gives rise to considerable strain incompatibilities at grain boundaries twinning consequently leads to strain hardening detailed observations of the geometry of twin lamellae show that incompatibilities at grain boundaries are eliminated by pressure solution on the grain scale at low temperature and dynamic recovery processes at higher temperatures twins are found in various tectonic environments and record very small strains in rocks deformed under very little cover different twinning strain and twinning stress methods and palaeopiezometers are critically reviewed all methods are limited to strains of less than 15 shortening or extension by twinning twinning nevertheless is an important although not directly measurable contribution to the total strain in highly strained calcite rocks at least up to middle greenschist facies under which conditions it is the most effective contributor to the formation of strong lattice preferred orientations in calcite tectonites the appearance of calcite twin lamellae changes systematically as a function of deformation temperature micro twins and straight narrow 1 5 m but fewer twins are developed above approximately 200 c curved twins twinned twins and completely twinned grains indicate the progressive importance of other slip systems and larger intracrystalline strains are possible at ca 250 c and above ancient straight twin lamellae are modified into irregular geometries by recrystallization and grain boundary migration the appearance of calcite twins is proposed as an approximate but rapid and easy to use geothermometer in low temperature environments

stress and fluid control on decollement within competent limestone abstract the larra thrust of the pyrenees is a bedding parallel decollement located within a competent limestone unit it forms the floor of a thrust system of hectometric scale imbrications developed beneath a synorogenic basin the fault rock at the decollement is a dense stack of mainly bedding parallel calcite veins with variable internal deformation by twinning and recrystallization veins developed as extension fractures parallel to a horizontal maximum compressive stress cemented by cavity type crystals conditions during vein formation are interpreted in terms of a compressional model where crack arrays develop at applied stresses approaching the shear strength of the rock and at fluid pressures equal to or less than the overburden pressure the cracks developed in response to high differential stress which was channelled in the strong limestone and high fluid pressure in or below the thrust plane ductile deformation although conspicuous cannot account for the kilometric displacement of the thrust which was mostly accommodated by slip on water sills constituted by open cracks a model of cyclic differential brittle contraction stress reorientation slip and ductile relaxation at a rheological step in the limestone is proposed as a mechanism for episodic decollement movement the model accounts for the peculiar microstructural character of the fault zone for alternating sequences of bedding parallel shortening leading to crack dilation and bedding parallel shear leading to decollement slip and for hanging wall imbrication consequent upon decollement slip

non coulomb wedges wrong way thrusting and natural hazards in cascadia landward vergence in accretionary wedges is an uncommon phenomenon not readily explained by classical mohr coulomb critical wedge theory predominantly landward vergent thrust faults are observed along the cascadia convergent margin from 45 n to 48 n we present depth migrated multichannel seismic images of the internal structure of the accretionary wedge offshore washington collected during the orwell project in 1996 these reveal a high p wave velocity 4 km s basal layer that thickens landward and serves as a decollement for a series of overlying landward vergent thrust faults analog modeling using a ductile basal layer consisting of silicone putty produces an array of trenchward propagating landward vergent thrusts and offers a plausible mechanical model for the evolution of these structures the rheological properties of a basal calcareous mudstone layer offshore cascadia are discussed in relation to the mechanics of landward vergence and to rapid loading due to the prograding nitinat and astoria deep sea fans a viscoelastic layer beneath the accretionary wedge is considered to be capable of rupturing during great interplate earthquakes and thus represents an increased risk for both the maximum size of such an event and for the generation of tsunamis

red deer hill a drumlinized glaciotectonic feature near prince albert saskatchewan canada red deer hill is 5 km long 3 km wide and 70 m high the hill is a glaciotectonic structure formed by a single 106 m thick thrust block presumably derived from the 80 m deep upglacier holmes depression the thrust block became dislodged by displacement along a presheared horizontal gouge zone where the shearing resistance of the clay was reduced to a residual state by the first mennon glaciation the hill depression structure was formed by the battleford glacier which drumlinized red deer hill before depositing a veneer of till over the structure the holmes depression was filled with glacial lake saskatchewan lacustrine and deltaic sediments horizontal displacement along a decollement in the direction of the activating force resulted in a stress environment changing from extension to compression in the zone of extension holmes depression an active rankine state developed and beds stretched and thinned in the zone of compression red deer hill conversely a passive rankine state developed an