distribution and mechanisms of strain within rocks on the northwest ramp of pine mountain block southern appalachian foreland a field test of theory fractures faults stylolites and strain determined from an analysis of twinning in calcite in the mississippian newman limestone at the base of the pine mountain block show that deformation was accomplished primarily by a combination of bedding plane slip and layer parallel shortening poles to joints are either parallel to strike of the thrust sheet or are in the transport plane small slip surfaces with syntaxial calcite fibers lie either parallel to bedding or parallel to the strike of the pine mountain block and dip steeply movement along the former is in the direction of transport of the block whereas movement on the latter is approximately along strike tectonic stylolites are rare but appear to be controlled by subtle changes in lithology wackestones contain more stylolites than do packstones strains in calcite from closely spaced samples show the converse relationship they are highest in units without stylolites maximum shortening strain e 1 10 4 and lowest in units with stylolites or small faults e 1 2 0 the maximum principal shortening strain directions however are identical within the error and are parallel to both bedding and the transport direction a sequence of events in this portion of the pine mountain block is 1 layer parallel shortening producing tectonic stylolites and a strong preferred orientation of compression axes 2 development of fractures parallel to the strike of the block on the lower hinge of the ramp to accommodate stretching parallel to the transport direction these strike parallel fractures can also be interpreted as having occurred quite late 3 during 2 above and continuing the start of bedding plane slip marked by syntaxial calcite fibers which trend in the direction of transport and 4 complications such as shear parallel to the strike of the pine mountain fault as a result of motion of the entire block between bounding tear faults events 2 through 4 most likely overlapped in time these data suggest that the acquisition of dip of the rocks on the ramp was primarily accomplished by bedding plane slip on the slip surfaces which experienced a shear stress of

fracture abundance and strain in folded cardium formation red deer river anticline alberta foothills canada abstract the folded and thrusted mesozoic clastic sequence of the canadian rocky mountain foothills forms important hydrocarbon reservoirs however the generation of fractures and their timing relative to folding and thrusting have remained unclear understanding the distribution and evolution of natural fractures especially their timing of formation relative to the evolution of the fold and thrust system could potentially improve exploration and development outcomes in these otherwise tight low permeability reservoirs we investigated the relation between folding and fracture formation in the upper cretaceous cardium formation by combining field structural observations and kinematic modeling of the fold and thrust belt evolution we evaluated the effects of structural position and strain on the formation of predominantly opening mode fractures by analyzing fracture intensity and aperture in the backlimb the shallow forelimb close to the crest and the steep forelimb away from the crest of a reservoir scale anticline the red deer river anticline fracture strain determined from both outcrop and microscanlines varies little across the three structural domains of the fold although somewhat lower fracture strain was measured in the forelimb close to the crest these fracture strain measurements are qualitatively consistent with calculated horizontal strain in the tectonic transport direction obtained from kinematic numerical models that simulate fold development associated with slip along the underlying burnt timber thrust the kinematic models predict similar magnitudes of horizontal extension in both the back and forelimbs and somewhat lower extension in the upper forelimb during early development of the red deer river anticline predicted early fracture formation during fold development is consistent with field structural observations of shear reactivation during later stages of folding this combined kinematic modeling and field structural study demonstrates that deforming fold and thrust belts can undergo a complex evolution of bed parallel extension in both space and time resulting in spatially variable fracture formation in structurally complex subsurface reservoirs

modelling growth stratal architectures associated with double edge fault propagation folding abstract fault related folds in fold and thrust belts and accretionary prisms are commonly simulated by three end member classes of geometric models decollement folding fault propagation folding and fault bend folding a given model produces a fold shape that depends on the amount of shortening the fault shape and eventually the fault propagation history the great variety of geometric solutions implies that the final fold shape is adequate to distinguish among different folding mechanisms only in a limited suite of cases additional information to better constrain fold kinematics is provided by the analysis of growth strata patterns which passively register the progressive evolution of deformation in the substratum availability of growth strata pattern templates associated with different geometric and kinematic solutions provides a useful tool for inferring the dominant kinematic pathways of natural thrust related structures in this paper we present growth strata patterns associated with double edge fault propagation folding the influence of the sedimentation rate the fault shape and the fault s p ratio i e slip versus ramp propagation rate on growth strata architectures are investigated geometrical modelling and application to natural examples indicate that double edge fault propagation anticlines are characterised by growth triangles on both limbs their position and geometry relate to the ramp shape and propagation history and on the sedimentation rate

geometric analysis of fold development in overthrust terranes abstract fault bend folding fault propagation folding and detachment or decollement folding are three distinct scenarios for fold thrust interaction in overthrust terranes simple kink hinge models are used to determine the geometric associations implicit in each scenario bedding maintains constant thickness in the models except in the forelimb of the fold the forelimb is allowed to thicken or thin without limit the models address individual folds and the calculated fold geometries are balanced structures each mode of fold thrust interaction has a distinct set of geometric relationships final fold geometry is adequate in itself to discern many fault bend folds this is not the case for fault propagation and detachment folds these two fold forms have very similar geometric relationships some knowledge of the nature of the underlying thrust or decollement zone is usually needed to distinguish between them the geometry of a fold is altered in a predictable fashion by transport through an upper ramp hinge and by fault parallel shearing of the structure the shearing results in a tighter fold whereas transport through the ramp hinge produces a broader fold the viability of the geometric analysis technique is demonstrated through its application to a pair of detachment folds from the canadian cordillera the geometric analysis is also used to evaluate cross sections through subsurface structures in an example from the turner valley oil field the analysis indicates how the interpretation should be altered so as to balance the cross section the analysis reveals hidden assumptions and specific inconsistencies in structural interpretations

structures and mechanisms associated with development of a fold in the cantabrian zone thrust belt nw spain a detailed history of progressive fold development based on mesostructural analysis is provided for a metre scale fold in the cantabrian fold and thrust belt of northwestern spain the well exposed asymmetric syncline displays a wide variety of structures including extensional faults thrusts veins tectonic stylolites bedding plane faults drag folds and a main limb thrust that transects the entire fold important constraints on fold development are provided by the spatial distribution and style of deformation angular relations and cross cutting relations among the structures fold mechanisms varied as a function of structural position while the northwest limb was subjected to pure shear shortening in the form of contractional faults the southeast limb was bent under tangential longitudinal strain resulting in a combination of outer arc extensional faulting in

reconstruction of continental margin architecture deformed by the contraction of the lagonegro basin southern apennines italy thrust propagation through previously rifted continental margins may result in fold and thrust belts whose structure is strongly controlled by the inherited basin architecture as it occurs in southern italy the lagonegro units of the southern apennines comprise a deformed pelagic basin succession showing variable stratigraphic characteristics mainly lateral variations in both facies and thickness interpreted to be due to a complex basin topography related to a triassic rifting event in contrast to previous studies cross section balancing and restoration indicate that the lagonegro units exposed in the high agri valley area suffered relatively limited internal shortening 8 km i e 35 early deformation of these rocks later incorporated into a large displacement thrust sheet was dominated by folding around present day roughly north south trending axes the attainment of a regional decollement level was favoured by an early mild inversion of the basin producing a roughly similar structural elevation of both hanging wall and footwall successions to mesozoic faults most of the contractional deformation was accommodated by buckling of the mesozoic syn rift strata between synsedimentary faults which represented major mechanical interfaces early strain localization in the lagonegro basin ahead of the active thrust front was most probably mechanically controlled by a faulted crustal segment which originally lay within the continental margin between two massive carbonate platforms

kinematic analysis of a large scale leading edge fold lost river range idaho abstract the mahogany creek buck creek structure within the lost river range idaho is a large scale leading edge fold which developed in late paleozoic outer shelf stratigraphy during the sevier orogeny incremental strain histories determined from antitaxial fibrous pressure shadows are used to quantify temporal variations in the magnitude and orientation of elongation as a function of structural position around the leading edge of this northward and eastward propagating blind thrust plane strain is indicated by coaxial up dip extension on cleavage planes on the backlimb of the structure the bluebird mountain formation a calcareous sandstone has deformed by flexural flow whereas the forelimb of the structure records spin through a fixed steeply plunging incremental extension direction the flat limb ahead of the anticline exhibits top to the foreland simple shear in contrast the underlying surrett canyon formation a thick bedded limestone has experienced flexural flow localized within thin zones on both limbs of the anticline samples from the anticlinal hinge zone suggests kinematic partitioning with pin lines which were variably distributed within each unit and which were temporally transient finite elongations are greatest in the hinge and above the foreland flat in the bluebird mountain formation but are negligible in the surrett canyon formation except within the mechanically active interbeds of the hanging wall and within the footwall adjacent to the fault along the northernmost exposures strain histories in the hanging wall do not vary significantly along strike while the footwall varies from undeformed in the south to penetratively deformed in the north thus the strain data are consistent with self similar along strike fold development in the hanging wall during strike parallel ramp propagation forward thrust propagation may have been blunted by a combination of fold accommodated shortening and footwall deformation to the north once the fold had tightened and fold shortening required greater differential stress forward fault propagation resumed transporting the anticline onto the upper flat with little change in hanging wall fold geometry or strain distribution

geometry of fault propagation folds method and application abstract a new geometrical model to simulate the evolution of fault propagation folds beyond the stage referred to here as first generation represented by the models of suppe 1985 and jamison 1987 is presented according to this model based on fixed axis theory suppe and medwedeff 1990 a second generation fold develops when the tip line at the top of the ramp retreats to the base of the mechanically weak anticlinal axial plane and then propagates upwards along this plane two types of second generation fold geometry are possible depending on the ratio of cumulative thickness of the deformed layers to the ramp height the first type possesses a residual triangle from the crestal part of the first generation fold the whole of its forelimb is thinned the second type has no residual part and its forelimb is partially thinned this type can develop higher generations of fault propagation folds as its backlimb is long enough to be redeformed some second generation folds are comparable to breakthrough structures but they possess a higher interlimbs angle

styles of folding within thrust sheets examples from the appalachian and rocky mountains of the u s a and canada abstract folds in a single thrust sheet can be classified as trailing edge formed over footwall ramps intraplate due to shortening within the body of the sheet and leading edge leading edge folds are usually removed by erosion at the front of a thrust sheet but their unfaulted equivalents can be examined at the lateral termination of the thrusts most folds of these various classes possess a kink band geometry with sharp hinges and long planar limbs the orderly nature of kink band folds breaks down when thin incompetent units separate thicker competent members the resulting fold geometry ranging from simple disharmonic to hinge collapse is controlled by the thickness of interbedded incompetent materials the appalachian and rocky mountain thrust belts provide examples of these various classes and styles of folds

how do horizontal frictional discontinuities affect reverse fault propagation folding abstract the development of new reverse faults and related folds is strongly controlled by the mechanical characteristics of the host rocks in this study we analyze the impact of a specific kind of anisotropy i e thin mechanical and frictional discontinuities in affecting the development of reverse faults and of the associated folds using physical scaled models we perform analog modeling introducing one or two initially horizontal thin discontinuities above an initially blind fault dipping at 30 in one case and 45 in another and then compare the results with those obtained from a fully isotropic model the experimental results show that the occurrence of thin discontinuities affects both the development and the propagation of new faults and the shape of the associated folds new faults 1 accelerate or decelerate their propagation depending on the location of the tips with respect to the discontinuities 2 cross the discontinuities at a characteristic angle 90 and 3 produce folds with different shapes resulting not only from the dip of the new faults but also from their non linear propagation history our results may have direct impact on future kinematic models especially those aimed to reconstruct the tectonic history of faults that developed in layered rocks or in regions affected by pre existing faults

fold generated imbricates examples from the caledonides of southern norway abstract the cambro silurian sequence of the oslo region contains fold trains and closely spaced imbricate thrust faults the imbricates could be interpreted as having ramped off the sole detachment and generated fault propagation folds several imbricate thrusts however appear to die out both downwards and upwards into folds this suggests that the thrusts were generated within the cambro silurian sequence and propagated down to the sole thrust rather than propagating upwards from the sole thrust the mechanical stratigraphy is apparently responsible for this style where during folding relatively brittle limestone members faulted in the highly strained fold forelimbs prior to through going faulting developing in the shales understanding the origin of such imbricates is important when choosing a method of section restoration

bedding plane slip in initial stages of fault related folding abstract frictional slip along bedding planes contributes to fault related folding of layered rocks we use numerical experiments to investigate the deformation of frictional bedding planes near dipping faults under layerparallel contraction and extension within the numerical experiments contraction boundary conditions produce asymmetric anticlines and extension produces asymmetric synclines the fold shape may be used to infer dip of the underlying fault in situations where the fault may not be observable additionally sense of slip along bedding planes may indicate proximity to the fault tip under uniform remote tectonic strain fault slip induces deformation in both the hangingwall and the footwall at depths as shallow as 1 km there is no significant difference between fold amplitudes in the hangingwall and the footwall this result is contrary to many kinematic models currently in use kinematic models of fault related folds commonly include the development of flat ramp and flat ramp flat fault geometries which may be attributed to initial ramp thrusting and later flat development our mechanical models show that fault flats may be produced from fault ramps due to slip along frictional bedding planes near the thrust fault tips our numerical experiments also evaluate joint initiation joints perpendicular to bedding are promoted in extensional environments we compare the results of the mechanical model to kinematic models of fault propagation folds and conclude that mechanical models offer important insights to better understand the folding process

estimating the detachment depth in cross sections involving detachment folds this paper evaluates four different methods that have been proposed for the estimation of the detachment depth beneath detachment folds guidelines are presented in order to use the most suitable method in a particular region deformed by detachment folds these guidelines are constructed considering the assumptions of each method the influence of different parameters on the estimation of the detachment depth folding mechanisms cross sectional area variations position and orientation of the regional datum number of stratigraphic horizons bed length and thickness dip and position of the bounding lines initial thickness of the ductile unit single anticlines or fold trains and the available data ductile unit thickness regional datum detachment depth moreover a new simple method based on two previous methods is presented the advantages of this new method are that the calculations are extremely simple and it uses information from more than one stratigraphic horizon therefore it does not depend strongly on the accuracy of the data at one level the precision of the proposed methods is tested by their application to a number of natural and experimental single anticlines and fold trains it appears that better predictions are obtained when analysing a complete detachment fold train than when dealing with a single detachment anticline the reason might be that ductile material flow beneath the folds along the cross sectional plane is taken into account when dealing with a long enough cross section we also suggest some hypotheses concerning what the shape and dimensions of the detachment folds indicate about the detachment depth in those cases where insufficient data are available to apply the methods proposed

centrifuge modelling of fold thrust structures in a tripartite stratigraphic succession abstract analog models measuring 127 76 mm in plan were deformed at 2500 4000 g in a centrifuge scaled stratigraphic sequences were constructed of anisotropic multilayers with individual layers of plasticine and silicone putty as thin as 40 m the plasticine silicone putty multilayers are analogs for interbedded competent carbonates and clastics and incompetent pelites given the model ratios of acceleration 2500 g length 5 10 6 specific gravity 0 6 time 10 10 modelling of fold thrust tectonics emphasizes the influence of stratigraphic succession on structural evolution the models are constructed with a tripartite stratigraphic succession comprising basal and upper well laminated and incompetent units and a middle somewhat more isotropic and competent unit the models deform by three mechanisms layer parallel shortening folding and thrust faulting they reproduce a number of fold thrust relationships that have been observed in nature folds are typically periclinal in en echelon arrays folds and thrusts are arcuate in plan reflecting differential shortening fold attitudes grade from upright at high levels to overturned at deeper levels within a structural panel reflecting drag against the basal decollement fold axial surfaces and thrust faults are listric while competent units may be offset by localized displacement on thrust faults the discrete faults may die out both upwards and downwards into regions of ductile strain in less competent units thrust faults appear to follow staircase trajectories through the strata transecting incompetent units at shallow angles to bedding and competent units at steeper angles however the apparent staircase pattern results from propagation of a fault along a relatively straight trajectory through previously folded strata foreland verging thrusts are more common than back thrusts the latter have steeper dips the models suggest a mechanism of thrust ramp nucleation following detachment folding long wavelength buckling of a competent unit can initiate localized strain folding and layer parallel shear in an underlying incompetent unit beneath the anticlines of the competent unit thrust faults propagate up section from these high strain zones through the foreland dipping limbs of buckle folds in the competent unit this mechanism may explain the commonly observed spatial periodicity of thrust ramps the model results bear similarities to natural fold thrust belts in which the stratigraphic succession consists of three mechanical units for example the asiak foreland and bear creek hills fold thrust belts of the slave province northwest territories canada

kinematics of fault related folding in a duplex lost river range idaho u s a abstract the doublespring duplex located in the lost river range of idaho is a sevier age fault related fold complex in massive limestones of the upper mississippian scott peak formation folds within the duplex closely resemble fault bend fold geometrics with open interlimb angles and low angle bed cut offs narrow widely spaced bedding parallel shear zones with well developed pressure solution cleavage alternate with massive relatively undeformed layers on fold limbs shear zones are developed only on the limbs of anticlines and have similar but unique morphologies in each of three different folds incremental strain histories reconstructed from antitaxial fibrous overgrowths and veins within the shear zones constrain the kinematics of folding shear zones experienced distributed bedding parallel simple shear flexural flow towards pins near axial surfaces while adjacent massive layers experienced rotation through an externally fixed extension direction the absence of footwall synclines and morphological differences in shear zones from adjacent folds suggest that faulting preceded folding kinematic histories of folds that have experienced different translational histories are identical and are not compatible with strain histories predicted from previous kinematic models of fault bend folding shear zone development and fiber growth is instead interpreted to have occurred during low amplitude fixed hinge buckling in response to initial resistance to translation of the thrust sheet fault bend folding with mobile axial surfaces occurred with translation of the thrust sheets once the initial resistance to translation was overcome and resulted in no penetrative strain

3 d deformation pattern analysis and evolution of the anisclo anticline southern pyrenees understanding the genetic relationships of folding related deformation structures is of importance for both academic and industrial purposes we analysed the three dimensional deformation pattern of the anisclo anticline in the southern pyrenees the specifically designed statistical method includes sequential steps of statistical and spatial data analysis and classification our results indicate that pressure solution cleavage frequency exhibits a spatial distribution that depends on the position within the fold conversely such a dependence does not occur in joints and veins consequently our data suggest that pressure solution cleavage is the most appropriate deformation structure for unravelling fault fold kinematics in carbonate multilayer in particular we found that the spacing of solution cleavages s is related to the corresponding bed thickness h this supports the use of h s value for deformation intensity quantification instead of spacing in the anisclo anticline analysis of h s indicates the occurrence of three main deformation panels whose restoration suggests that fold evolution progressed from layer parallel shortening to decollement folding up to thrust breakthrough and fault propagation folding comparison of h s values with finite strain data indicates that line length was not preserved during fold evolution this evidence has important implications for the kinematic interpretation of layer parallel shortening and cross section balancing

fingerprinting stress stylolite and calcite twinning paleopiezometry revealing the complexity of progressive stress patterns during folding the case of the monte nero anticline in the apennines italy in this study we show for the first time how quantitative stress estimates can be derived by combining calcite twinning and stylolite roughness stress fingerprinting techniques in a fold and thrust belt first we present a new method that gives access to stress inversion using tectonic stylolites without access to the stylolite surface and compare results with calcite twin inversion second we use our new approach to present a high resolution deformation and stress history that affected meso cenozoic limestone strata in the monte nero anticline during its late miocene pliocene growth in the umbria marche arcuate ridge northern apennines italy in this area an extensive stylolite joint vein network developed during layer parallel shortening lps as well as during and after folding stress fingerprinting illustrates how stress in the sedimentary strata did build up prior to folding during lps the stress regime oscillated between strike slip and compressional during lps before ultimately becoming strike slip again during late stage fold tightening our case study shows that high resolution stress fingerprinting is possible and that this novel method can be used to unravel temporal relationships that relate to local variations of regional orogenic stresses beyond regional implications this study validates our approach as a new powerful toolbox to high resolution stress fingerprinting in basins and orogens combining joint and vein analysis with sedimentary and tectonic stylolite and calcite twin inversion techniques

tectonic geomorphological investigations of antiforms using differential geometry permam anticline northern iraq modern differential geometric methods are applied to compute and analyze curvature quantities of the permam anticline which is part of the zagros fold and thrust belt in northern iraq northeast of the city of erbil because this particular anticline is composed of among others weathering resistant limestones the surface topography strongly resembles the antiformal fold shape this makes it an ideal area where numerical curvature analysis applied to shuttle radar topography mission digital elevation models dems allows drawing not only geomorphological but also tectonic conclusions the curvature analysis is based on the computation of the gaussian and mean curvatures and is used to classify the folded surface into eight geologically relevant shapes antiform synform plane dome basin and three types of saddles the performed curvature analysis investigates in detail the effects of two adaptable parameters the cutoff wavelength of the low pass filter that is applied to the dem before curvature calculation and the curvature threshold that is applied to the principal curvature values before the calculation of the gaussian and mean curvatures the analysis demonstrates that these two parameters strongly influence each other and that they together determine the information content and interpretability of the results by choosing appropriate parameter combinations geomorphological oriented studies and tectonic oriented studies are viable using the same dem how tectonic oriented studies can be used to determine fracture patterns or densities in folded layers is discussed further suggestions are made to combine curvature analysis of dems with similar studies applied to seismically mapped surfaces in three dimensional seismic data sets where erosion is absent

numerical modeling of fold initiation at thrust ramps abstract the movement of the hangingwall over the footwall at thrust ramps produces a variety of structures found commonly at different scales in fold and thrust belts the nature of the structure depends on the relative rigidity of the hangingwall and footwall friction along the fault fault dip fault displacement and the boundary conditions of the deformation structures include fault bend style folds fault propagation style folds and wedge folds we investigate the initial stages of development of such structures using the finite difference code flac the rock layers are represented as continua with elastic plastic mohr coulomb constitutive relations and the fault and bounding bedding planes are assigned normal and shear stiffnesses and coefficients of friction under conditions with all layers compressed antisymmetric fault propagation style folds develop in both the hangingwall and footwall with rigid footwall and restricted far field slip in the hangingwall a single fault propagation style fold develops with far field displacement of the hangingwall allowed broader antisymmetric wedge folds develop if hangingwall and footwall are deformable and a single fault bend style fold develops if the footwall is rigid all structures become accentuated with increasing slip on the fault where both hangingwall and footwall are deformable the deformation reduces the ramp angle and tends to minimize distortion of the rock adjacent to the fault fault propagation style folds paired wedge folds and fault bend style folds are common in nature and small scale examples can be found in various stages of development continued slip on thrust faults may lead to the mature structures commonly seen in fold and thrust belts

influence of deflection on a fold to fault progression field evidence from near marietta south carolina abstract four periods of deformation d1 d4 are recognized in the lion park road borrow pit near marietta south carolina although each period is characterized by distinct structures d3 produced two structural styles d3a d3b resulting from layer parallel shortening d3a is characterized by detachment folding at the tip of an underlying thrust d3b is a fold to fault progression that was localized by east dipping quartz filled gash fractures the fold to fault progression demonstrates the influence of a mechanical anisotropy on ramp development the early stages of d3b were formed by deflection of northwest directed layer parallel shortening and active down section propagation of folds and thrusts following connection with a splay of basal detachment later d3b stages resulted from up section movement that produced kink folding and a throughgoing thrust this up section movement deformed and modified the geometries of older down section structures detailed mesoscopic field observations integrated with a combination of current thrust fault models are used to interpret the d3b fold to fault progression

origin of kinkbands and shear band cleavage in shear zones an experimental study specimens of artificial kcl mica schist have been deformed in simple shear with different initial orientations 10 intervals between 0 and 170 of the mica schistosity s1 relative to the imposed simple shear plane for most experiments the angular shear strain was 30 the strain rate 4 8 10 4s 1 and the stress normal to the imposed shear plane 20 mpa all experiments were conducted at room temperature deformation of the specimens is achieved largely by slip parallel to the s1 mica foliation however two new types of slip surfaces also develop as either a single orientation set or as a pair of conjugate sets these new slip surfaces are kinkbands and a shear band cleavage the type and number of sets of new slip surfaces which develop depends on the orientation of s1 relative to the shortening and extension fields of the instantaneous strain ellipsoid our experiments indicate that kinkbands or shear band cleavage form in shear zones in which s1 is inclined to the margin of the zone which structure forms and whether it occurs as a single set of structures or as a conjugate pair depends on the initial orientation of s1 in situations where s1 is parallel to the margins of the zone neither structure develops if the deformation is a simple shear the presence of kinkbands or shear band cleavage in such zones where s1 is parallel to the margins is an indication that the zones were transtensional or transpressional respectively we conclude that shear band cleavage is not only an excellent indicator of shear sense but also a qualitative indicator of the ratio of s1 normal shortening to s1 parallel shear conjugate shear bands indicate that s1 normal shortening was relatively strong and single shear band sets indicate that s1 parallel shear was relatively strong

3d geometry of growth strata in a fault propagation fold insights into space time evolution of the crevillente fault abanilla alicante sector betic cordillera spain this work presents a 3d geometric model of growth strata cropping out in a fault propagation fold associated with the crevillente fault abanilla alicante sector from the bajo segura basin eastern betic cordillera southern spain the analysis of this 3d model enables us to unravel the along strike and along section variations of the growth strata providing constraints to assess the fold development and hence the fault kinematic evolution in space and time we postulate that the observed along strike dip variations are related to lateral variation in fault displacement along section variations of the progressive unconformity opening angles indicate greater fault slip in the upper tortonian messinian time span from the messinian on quantitative analysis of the unconformity indicate a constant or lower tectonic activity of the crevillente fault abanilla alicante sector the minor abundance of striated pebbles in the pliocene quaternary units could be interpreted as a decrease in the stress magnitude and consequently in the tectonic activity of the fault at a regional scale comparison of the growth successions cropping out in the northern and southern limits of the bajo segura basin points to a southward migration of deformation in the basin this means that the bajo segura fault became active after the crevillente fault abanilla alicante sector for which activity on the latter was probably decreasing according to our data consequently we propose that the seismic hazard at the northern limit of the bajo segura basin should be lower than at the southern limit

methodology for a regional tidal model evaluation with application to central california abstract observations from disparate observational assets including tide gauges moorings and high frequency hf radars were used to depict the tidal variability and to evaluate model tidal simulations for a region off central california including the monterey bay for this study the hydrodynamic model was forced only with tides derived from a large scale model for the northeast pacific ocean homogeneous density and initially horizontally uniform density stratification cases were considered the model successfully reproduced tidal sea surface height variations within the model domain as determined by comparisons with sea level or bottom pressure measured at six locations to achieve tidal currents with realistic amplitudes as determined from hf radar and moored measurements it was found that barotropic velocity as well as sea level from the large scale regional tidal model must be included in specifying the open boundary condition however even with such forcing the model with homogeneous density field under predicted the semidiurnal and diurnal barotropic currents as estimated from depth averaged currents measured at 11 locations in the diurnal frequency band the observed surface and nearshore depth averaged currents are likely influenced by meteorological forcing which was not included in the model the hf radar measured surface tidal currents both semidiurnal and diurnal are consistent from year to year and between the winter season and the entire year semidiurnal surface tidal currents derived from year long hf radar measurements do not resemble either the modeled or measured barotropic current fields rather they exhibit amplitudes and small scale spatial variability indicative of the presence of internal tides thus indicating that model derived barotropic tidal currents cannot be validated over large spatial extents using long time series of hf radar derived surface currents with initially horizontally uniform vertical density stratification the model produced surface currents with spatial variability and amplitude range comparable to what was derived from hf radar surface current measurements but the point by point comparisons are not impressive for this region of complex topography likewise the subsurface current comparisons performed at four deepwater locations show considerable model data differences possible reasons for these disparities include the effects of atmospheric forcing spatially and temporally varying stratification remotely generated coastally trapped waves and remotely generated internal tides

low amplitude evolution of break thrust folding abstract this paper proposes a mechanistic explanation for fault related flexural slip folds that form predominantly by fixed hinge folding i e break thrust folds it also presents a stepwise evolutionary history for these folds which contrasts with the model suggested for self similar migrating hinge fault propagation fold models both mechanical folding theory and rock fabric evidence suggest that folding in advance of a growing thrust fault can evolve in a five step process 1 initial sinusoidal buckling instability

relationships between early paleozoic facies patterns and structural trends in the saltville thrust family tennessee valley and ridge southern appalachians structural style variations across the tennessee segment of the valley and ridge thrust belt are correlated with two facies changes in important structural stratigraphic units the middle and upper cambrian conasauga group and the middle ordovician chickamauga group change their internal stratigraphy regionally at oblique angles to the trend of this segment of the thrust belt these stratigraphic variations correlate geographically with structural style changes within individual thrust sheets whereas other variables such as temperature pressure and magnitude of tectonic transport do not in the conasauga the east to west limestone to shale facies transition coincides with areas where structural styles change along thrusts at the conasauga level the shale dominated and carbonate dominated facies show simple frontal imbricate thrusts whereas in the shale carbonate zone of interlayering duplexes occur in the chickamauga an east west change from basinal shale to shelfal limestone controlled the regional presence of a middle level glide zone in the paths of eastern thrusts and its absence to the west this stratigraphic inhomogeneity also controlled a change in the knoxville area from surficial folding in the northeast to surficial thrusting in the southwest the terminology of structural lithic units and their subsidiary predominant and conforming members is applied in dividing the stratigraphic section into structurally significant packages

displacement transfer at thrust terminations the saltville thrust and sinking creek anticline virginia u s a abstract the saltville thrust terminates in the core of the sinking creek anticline changes in the amplitude of the anticline may preserve profile shortening as the thrust displacement decreases towards the fault termination consequently thrust displacement would be transferred into the fold we combine newly published maps and new strain and mesostructural data from the tuscarora sandstone to argue that the sinking creek anticline did perform this kinematic role we propose that the anticline developed as a fault propagation fold that experienced both decollement and anticlinal breakthrough by the saltville thrust thrust displacement was accommodated by the development of the modified fault propagation fold and by transfer to a roof flat from the decollement breakthrough new strain and mesostructural data indicate no fixed pin lines in either the hinge or backlimb throughout folding consequently layer slip occurred through the hinge during folding and the forelimb deformed internally during breakthrough towards the plungeout of the sinking creek anticline the displacement on the saltville thrust is transferred to a floor thrust we apply this interpretation to the termination of the st clair thrust which has a similar surface geometry where the thrust terminates into an anticline a testable implication of this proposed interpretation for the st clair thrust is that the appalachian plateau must absorb over 20 km of thrust displacement as horizontal shortening

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

the kinematics of break thrust folds abstract the kinematics of asymmetric open to close often overturned thrust related folds are commonly explained with fault propagation or detachment fold models field observations of thrust related folds exposed in tennessee virginia wyoming and montana that exhibit this geometry indicate that models of fault propagation and detachment folds do not adequately describe the kinematics of these structures existing models of fault propagation and detachment folding employ migrating kink shaped hinges and relate fold geometry entirely to fault geometry slip and to the thickness of the basal detachment layers the models exclude the relation between fold shape and amplitude and they do not predict a correlation between competent layer thickness and fold wavelength as expected from buckling theory thrust related folds examined in this study exhibit unique distributions of fabrics in the hinges and forelimbs which demonstrate a lack of hinge migration furthermore the ratios of dominant member thickness to fold wavelenght agree with those expected for folds controlled by a single layer and they are within the expected range for folds with multiple evenly spaced harmonically deforming layers our analyses suggest these folds evolved from an initial brief stage of sinusoidal buckling to a later stage of fixed hinge kinking and thrusting thrust related folds which exhibit a geometry and mesofabric distribution suggesting this type of evolution are defined as break thrust folds

detachment folds with fixed hinges and variable detachment depth northeastern brooks range alaska abstract detachment anticlines in the northeastern brooks range accommodated displacement above a detachment by buckling of a competent unit over an incompetent unit meso and microstructures in hinges and a lack of relict hinge structures in limbs suggest that these folds grew with fixed hinges the structural thickness of the incompetent unit beneath the folds detachment depth varies from less than to greater than the stratigraphic thickness a model in which incompetent unit thickness varies with fold area better approximates the geometry of the folds than does a more conventional constant depth model additional discrepancies between modelled and observed incompetent unit thickness and field observations suggest non plane strain and or transport of material through the boundaries of the fold in the plane of the cross section the results of this study suggest a typical evolutionary sequence for detachment folds in the northeastern brooks range which may be applicable elsewhere anticlines initiate as fixed hinge buckle folds rapid initial increase in anticlinal cross sectional area results in a decrease in incompetent unit thickness fold area begins to decrease with tightening beyond an interlimb angle of 90 dg decreasing fold area is accommodated through some combination of structural thickening of the incompetent unit transport of solid or dissolved material out of the plane of section transport of material through the boundaries of the fold in the plane of the cross section and or truncation by thrust faults

geometry amount and sequence of thrusting in the subalpine molasse of western austria and southern germany european alps in this paper we review the structure of the most external thrust belt of the alps between the rhein valley and salzburg based on a new tectonic map and the re interpretation of seismic sections specifically we address the correlation between deformation in the subalpine molasse and the alpine thrust belt in general and focus on the control of sedimentary facies on the structural style a dramatic change in architecture from a ramp flat structure to buckle folding is related to a change from coarse grained fans to fine grained deposits within the subalpine molasse additionally the interaction of escape tectonics with postcollisional shortening controls the decrease of late early miocene and younger shortening within the subalpine molasse from 50 km near the rhine valley to almost zero near salzburg transfer of shortening into the hinterland which is the zone of lateral escape ended foreland propagation of the alpine thrusts and initiated a general break back sequence of thrusting throughout this time the thrusts remained active in such a scenario tectonic units on top of the subalpine molasse are expected to undergo clockwise rotation around vertical axes as thrusting in the subalpine molasse is closely related to contemporaneous transport and shortening within the tectonically higher helvetic thrust sheets amounts of miocene differential shortening and related clockwise vertical axis rotation are minimum amounts true clockwise vertical axis rotation is probably larger than the 12 deduced from the subalpine molasse thrust belt

superposed deformation fabrics in the precambrian metabasic rocks of the iron ore group singhbhum craton eastern india evidences from anisotropy of magnetic susceptibility studies abstract anisotropy of magnetic susceptibility ams data have been utilized to build up the multiple deformation sequences and strain variation from an apparently undeformed metabasic lava sequence of the basal part of the paleo mesoarchean greenstone succession of the iron ore group rocks in the western iron ore basin singhbhum craton eastern india the basal lava crops out bordering the regional horseshoe shaped outcrop the horseshoe synclinorium structure of the overlying bif rocks ams data of 892 cylindrical specimens drilled from 83 samples collected from different structural domains within the synclinorium structure are presented in the analysis ams orientation data have been analyzed in the light of superposed fold type 1 interference fabrics developed within bif as a result of successive deformation episodes d1 and d2 it is found that the lava samples ubiquitously present two consistent magnetic fabrics homogeneous over smaller sub areas which have been successfully correlated with the d1 and d2 deformation fabrics from the bif rocks moreover a regional scale variation in intensity and nature of strain is noticed from the ams data which have been utilized to decipher folding mechanism as well as the changing deformation pattern during successive folding events

kinematics of large scale tip line folds from the high atlas thrust belt morocco abstract the kinematics of several tip line folds situated along the south atlas front near goulmima morocco is established using both forward modelling and analysis of syn folding deformation from the sahara foreland to the atlas the two successive major structures forming the mountain front in this area fit geometrically with a generalised fault propagation fold model and a model of fault propagation fold altered by late transport on the upper flat respectively field evidence shows that the two folds are developed more or less synchronously the analysis of minor structures helps address the question of migrating hinges vs fixed hinges during the fold s growth

kink detachment fold in the southwest montana fold and thrust belt the hossfeldt anticline in the southwest montana thrust belt is characterized by a kink geometry and probably overlies a thrust detachment at depth the mesofabric distribution in the limbs documents that the eastern overturned limb has undergone most of the rotation and internal deformation during folding leaving the gently dipping western limb virtually undeformed the anticline exhibits unique mesofabrics in its hinge region that require a pinned anticlinal hinge during its evolution the half wavelength of the hossfeldt anticline eustis syncline pair coincides with that predicted from buckling theory if one considers the massive carbonates of the paleozoic section as a competent beam although the geometry and mesofabric distribution of the hossfeldt anticline satisfy the geometric requirements of either a fault propagation fold or a detachment kink fold the buckling wavelength strongly suggests that its origin was as a kink buckle fold above a flat detachment rather than as a fault propagation fold above a thrust ramp

influence of heterogeneous lithostructural layering on orogenic deformation in the variscan front zone eastern belgium the ramp flat thrust model and other classical models based on rocky ountains or appalachians structures allow a better understanding of ault and fold interaction in a sequence dominated by competent rocks n which in most cases thrusts propagate forward in sequence this attern however fails to explain the deformation history of rock uccessions with low proportions of competent rocks in such ithologies out of sequence faults are more common features the ariscan front zone in eastern belgium serves as a case study for this on classical deformation model cross sections are well constrained by urface data covering a large area the devono carboniferous sequence esting unconformably on caledonian basement has shortened drastically nd the tectonic history can best be explained by a composite structural odel continuous and discontinuous deformations took place in uccessive steps a lame anticline developed first it evolved ubsequently into either break thrust or translated fault propagation olds out of sequence thrusting by the theux tunnel fault formed the esdre nappe the latter is the northern part of the ardenne allochthon he main discrepancies with the ramp flat thrust model are emphasized articularly the vesdre nappe which is the highest thrust sheet is ot the youngest event of deformation common elements of the variscan ront zone between northern france and western germany are discussed he theux tunnel fault has the same kinematics significance as the idi aachen fault the footwall of the vesdre nappe is the eastward rolongation of the brabant foreland the complex structure of the theux indow reflects imbrications under the allochthon and can be compared ith other wedges and thrust sheets c 1999 elsevier science b v all ights reserved

distribution of fault slip in outcrop scale fault related folds appalachian mountains abstract current kinematic models of ramp related folds predict a direct relationship between ramp angle and fold shape and imply specific sequences of deformation analyses of outcrop scale structures in the valley and ridge province of the appalachians reveal configurations that depart from model predictions the models fail to account for the presence of footwall synclines and are inconsistent with measured displacement distributions on some natural faults observations support the interpretation that faults can grow by propagation both up and down dip from a nucleation point fault propagation in either direction may result in the formation of folds primarily on the side of the fault that is displaced in the direction of fault propagation

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

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

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

kinematics of decollement folding in the lost river range idaho decollement folding of massive 2 m thick carbonate beds of the scott peak formation within the willow creek anticline northern lost river range idaho was associated with the development of thin 0 25 m widely spaced deformation zones incremental strain histories determined from fibrous overgrowths in strain fringes from the deformation zones provide a basis for kinematic analysis of the anticline plane strain is indicated by coaxial up dip extension on cleavage xy planes and a lack of extension in the y direction in xz sections coaxial incremental strain histories characterize fold hinges and document pinned hinges during folding the sense of rotation on opposing limbs indicates that the fiber curvature records primarily the spin of layers through fixed moderately steep 66 12 dg l diverging extension directions the magnitude of the external rotation for each sample is typically less than the bedding dip suggesting that the external rotation also includes a component of internal rotation related to layer parallel shear toward the upper flat panel or the hinge pin line the magnitude of this internal rotation varies within and between layers

kinematics of foreland vergent crustal accretion inferences from the dinarides evolution one of the most common observation in mediterranean areas is the migration of contractional deformation and associated slabs through time towards external orogenic areas associated with lower plate crustal accretion the dinarides orogen of central europe is an optimal place to study such a sequence of contractional deformation compared with other areas contraction in the dinarides was less overprinted by subsequent extension while a remnant of the subducted slab is observed in a far external orogenic position understanding the deformational evolution of the dinarides is hampered by the reduced availability of kinematic studies therefore we have performed a surface kinematic study in the external parts of the dinarides by correlating with available geophysical and evolutionary constraints we constructed two large scale kinematically controlled regional transects the results demonstrate a long lived evolution of shortening that affected the dinarides lower orogenic plate while the late jurassic earliest cretaceous deformation was associated with an earlier obduction moment the latest cretaceous onset of continental collision has gradually focused deformation at inherited rheological weakness zones we show that shortening was interrupted by a period of miocene extension that affected all orogenic areas and created the dinarides lake system the extension was followed by renewed shortening that started during the latest miocene and remains presently active whose kinematics in the central and se part of the dinarides is revealed for the first time by our study these results indicate a lower plate crustal accretion mechanism that was spatially and temporally connected with gradual slab retreat in the dinarides

the pleistocene holocene transition and human occupation in the central andes of argentina agua de la cueva locality in the central andes of argentina evidences of early human occupations come from the precordillera a low mountain system which was under periglacial conditions prior to 14 000 14c yr bp when the cordillera principal and cordillera frontal were glaciated the corridors for human migration across the andes may have opened before 13 000 14c yr bp the pleistocene holocene transition gave rise to a substantial variability of environments and consequently of natural resources for early people who found in the precordillera new ecosystems with suitable conditions for living the first human groups arrived ca 11 000 14c yr bp at agua de la cueva rockshelter located at 2900 m above sea level in the western flank of the precordillera the occurrence of raw material outcrops close to the site and the archaeofaunistic record indicate a local and likely seasonal exploitation of mountain resources these early people lived in a shrub steppe environment under cooler and probably wetter conditions in which camelids were the most important food resource since 9000 14c yr bp warmer and drier conditions were dominant except for a lower intensity of human occupations the site function of agua de la cueva seems to have remained the same

uplift rates of marine terraces as a constraint on fault propagation fold kinematics examples from the hawkswood and kate anticlines north canterbury new zealand abstract marine terraces on growing fault propagation folds provide valuable insight into the relationship between fold kinematics and uplift rates providing a means to distinguish among otherwise non unique kinematic model solutions here we investigate this relationship at two locations in north canterbury new zealand the kate anticline and haumuri bluff at the northern end of the hawkswood anticline at both locations we calculate uplift rates of previously dated marine terraces using dgps surveys to estimate terrace inner edge elevations we then use markov chain monte carlo methods to fit fault propagation fold kinematic models to structural geologic data and we incorporate marine terrace uplift into the models as an additional constraint at haumuri bluff we find that marine terraces when restored to originally horizontal surfaces can help to eliminate certain trishear models that would fit the geologic data alone at kate anticline we compare uplift rates at different structural positions and find that the spatial pattern of uplift rates is more consistent with trishear than with a parallel fault propagation fold kink band model finally we use our model results to compute new estimates for fault slip rates 1 2 m ka at kate anticline and 1 4 m ka at haumuri bluff and ages of the folds 1 ma which are consistent with previous estimates for the onset of folding in this region these results are consistent with previous work on the age of onset of folding in this region provide revised estimates of fault slip rates necessary to understand the seismic hazard posed by these faults and demonstrate the value of incorporating marine terraces in inverse fold kinematic models as a means to distinguish among non unique solutions

thrust fault geometry of the snake river range idaho and wyoming the snake river range is located at the north end of the absaroka fault system in the idaho wyoming utah thrust belt and it adjoins the teton mountains nine imbricate sheets of the absaroka system form a shingled array of overlapping thrusts most fault nomenclature in the range dates from early discontinuous reconnaissance studies wherein names were applied from the top thrust down whether or not the thrust sheets separated by this method are or ever were connected as mechanical blocks fault names are revised here to consider the lateral continuity of sheets as the major criteria for defining the block to which a name should be applied the absaroka thrust and st john thrust are recognized to be equivalent different parts of a major transfer zone using the continuity of sheets as the main criteria the map pattern of the range is dominated by major re entrants to the west in the traces of the st john and absaroka thrusts the re entrants in both major faults are caused by folding in their foot walls related to lateral ramping of each thrust upward to the southeast the folding of the st john thrust above the indian creek culmination also folds the thrust sheets above it helping to mark the emplacement of the imbricate sheets as being from top to bottom and west to east the absaroka system thrusts formed from 20 to 40 km west of their present position they are folded by underlying faults of the jackson or farther south the darby system indicating that the absaroka system was emplaced into its present position by motion on these underlying faults discussions concerning mechanical interaction between the thrust belt and a foreland buttress ancestral teton or targhee uplift concentrate on intensities of deformation and changes in geometry adjacent to the proposed buttress the individual imbricate geometries and regional changes in trend are more related to a changing stratigraphic package and the lateral thrust ramps than to geographic proximity to any proposed buttress

a reappraisal of the structure of the spanish segment of the iberian pyrite belt the major structural features of the iberian pyrite belt are described in terms of geometry deformation mechanisms scale timing kinematics and the mutual relationships among the various architectural elements the result of such an analysis allows this zone to be considered as a s verging thin skinned fold and thrust belt propagating southwards over a mid crustal basal detachment this was the response in the footwall of the suture to the major phase of hercynian oblique collision between the south portuguese plate and the ossa morena zone of the iberian autochthon this thin skinned event inverted a previous extensional structure acquired during the initial stages of the collisional process and intimately linked to the formation of the ore deposits that make this region a world class metallogenic province

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

inclined transpression in the neka valley eastern alborz iran three major nappes in the neka valley in the eastern alborz mountains of iran allow the cimmerian to present convergence following the oblique collision between iran and the southern margin of eurasia this work reports the identification of an inclined transpression zone recognized by field investigations and strain analyses of the geometries of formations and detailed mesoscopic structural analyses of multiple faults folds and a cleavage the main structures encountered include refolded recumbent asymmetric fold nappes highly curved fold hinges in a transpression zone that dips 37 to the nw between boundaries thrusts striking from n050 to n060 the angle the angle between the zone boundary and direction of horizontal far field shortening is about 80 the north west and south east boundaries of this zone coincide with the haji abad thrust and the shah kuh thrust respectively fold axes generally trend ne sw and step to both right and left as a result of strike slip components of fault displacements strain analyses using fry s method on macroscopic ooids and fusulina deformed into oblate ellipsoids indicate that the natural strain varies between 2 1 and 3 14 the estimated angle between the maximum instantaneous strain axis isamax and the transpression zone boundary is between 6 and 20 the estimated oblique convergence angle therefore ranges between 31 and 43 the average kinematic vorticity number wk is 0 6 in a zone of sinistral pure shear dominated inclined triclinic transpression these results support the applicability of kinematic models of triclinic transpression to natural brittle ductile shear zones

structural and microstructural evolution of the rattlesnake mountain anticline wyoming usa new insights into the sevier and laramide orogenic stress build up in the bighorn basin the rocky mountains in western us provide among the best examples of thick skinned tectonics following a period of thin skinned tectonics related to the sevier orogeny the compressional reactivation of basement faults gave birth to the so called laramide uplifts arches the bighorn basin located in wyoming is therefore a key place to study the transition from thin to thick skinned tectonics in orogenic forelands especially in terms of microstructural and stress strain evolution our study focuses on a classic laramide structure the rattlesnake mountain anticline rma wyoming usa a basement cored anticline located in the western part of the bighorn basin stress and strain evolution analysis in folded sedimentary layers and underlying faulted basement rocks were performed on the basis of combined analyses of fractures fault slip data and calcite twinning paleopiezometry most of the fractures are related to three main tectonic events the sevier thin skinned contraction the laramide thick skinned contraction and the basin and range extension serial balanced cross sections of rma and displacement profiles suggest that all thrust faults were coeval evidencing strain distribution in the basement during faulting the comparison of rma with another structure located in the eastern edge of the bighorn basin i e the sheep mountain anticline sma allows to propose a conceptual model for the geometric and kinematic evolution of laramide related basement cored anticlines finally the stress evolution is reconstructed at both the fold scale and the basin scale we show that the evolution of stress trends and magnitudes was quite similar in both structures rma and sma during laramide times thick skinned tectonics in spite of different stress regimes during sevier thin skinned tectonics and post laramide times stress trends and fracture patterns were different in these two structures these results suggest that the distance to the orogenic front influenced the fracture patterns but not the foreland stress magnitudes which were likely controlled by the structural style

kinematic model of detachment folding including limb rotation fixed hinges and layer parallel strain abstract detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will in general require layer parallel shortening a kinematic model for detachment folds is presented that has planar limbs and is area balanced but requires bed length changes that can be expressed as layer parallel strain the fold grows primarily by limb rotation not by limb lengthening at constant dip the kinematic evolution of the geometry and strain is examined fold geometry is well predicted and the strain estimated in applications of the model to two map scale detachment folds a triangle zone from the front of the wyoming thrust belt and a duplex cored anticline from the appalachian plateau

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

folding of passive layers and forms of minor structures near terminations of blind thrust faults application to the central appalachian blind thrust abstract the existence of detachment surfaces or decollement zones beneath folded rocks of the valley and ridge and plateau provinces of the appalachians has been recognized as an important condition of folding large folds at the border between the two provinces resulted primarily from repetition of strata by thrusting of blocks over ramp faults that connect detachement surfaces at different horizons some investigators have suggested that folds in the plateau province of pennsylvania were produced by splay faults arising from detachment surfaces but field observations and theoretical analyses by sherwin and by wiltschko chapple suggest that the folds are a result of buckling of multilayered rocks above a decollement an exception may be the burning springs anticline in west virginia which appears to have formed at the termination of a detachment surface investigation of the translation of an homogenous viscous material above a flat detachment surface that terminates laterally indicates that the termination produces a broad low amplitude anticline in passive layering as a result of thickening induced by a gradient of shear stresses in the vertical direction this thickening above the termination of a detachment is a mechanism of folding if the viscous fluid contained mechanical layering the fold would become amplified by buckling computations of stresses in the material indicate that minor faults should be generated first near the termination of the flat detachment surface the burning springs anticline probably was initiated by termination of a detachment surface and subsequently amplified by buckling

evaluation analysis and prediction of geologic structures abstract balanced cross sections claim to be better because they apply a rigorous set of rules to develop the conceptual model of the structures present in an area balanced cross sections can be further improved and become more useful to understanding real physical problems by collection of additional data such as seismic reflection surveys collection of additional stratigraphic data or collection of rock fabric information the additional information validates the initial model and provides details on deformation conditions and on local rock responses to the deformation although individual cross sections are two dimensional the objective of evaluation and analysis of deformed regions should be three dimensional whenever possible to recognize the challenges of the real world subsurface system analysis derived from the hydrologic community emphasizes conceptual model development through model verification validation uncertainty quantification benchmarking and meta analysis their approach includes many steps informally used by the structural geology community but in a much more explicit way newer geological applications of structural geology would benefit from this more rigorous approach for designing and doing performance predictions as technological needs become more socially sensitive such as for carbon storage sites new areas of energy exploration in higher population density areas or for nuclear waste storage facilities

unfolding an inverse approach to fold kinematics preservedfoldshapesusuallyreveallittleabouttheirkinematicevolution syntectonic strata preserved in growth synclines in contact with a fold however can permit unfolding a sequential reconstruction of fold growth backward through time from a geometry observed at present to an initial undeformed state such reconstructions can define the kinematics of fold growth growth strata associated with anticlinal forelimbs in the ebro basin exhibit depositional tapering of beds on fold flanks and progressive limb rotation unfoldingawell dateddetachmentfolddefinesitskinematicevolutionandcoevallyvarying rates of shortening forelimb uplift and forelimb rotation interplay of these rates with sedimentation rates controls onlap and offlap relations

fracture patterns in the zagros simply folded belt fars iran constraints on early collisional tectonic history and role of basement faults pre early folding fracture patterns were recognized in several anticlines from three structural domains in the simply folded belt of the fars arc these fracture sets were characterized in terms of opening mode and relative chronology and used to reconstruct the main compressional trends related to the early zagros collisional history the palaeostress reconstructions based on these fracture sets were further refined by combination with newly collected or already available fault slip and calcite twin data as an alternative to previous models of rigid block rotations or regional stress rotation we propose that the complex pattern of pre folding fractures and the contrasting palaeostress orientations through time in the different domains investigated are related to the presence of basement faults with n s and wnw trends above which basement and cover were variably coupled during stress build up and early deformation of the arabian margin beyond regional implications this study draws attention to the need to carefully consider pre existing fractures possibly unrelated to folding to build more realistic conceptual fold fracture models

the role of fractures in the structural interpretation of sheep mountain anticline wyoming the development of fractures in the sedimentary layers of sheep mountain anticline a laramide asymmetric fault cored fold of the bighorn basin is documented and interpreted to constrain the kinematic evolution of the fold the fracture pattern is interpreted to identify five main fracture sets a fracture set striking 110 set i oblique to the future fold trend is interpreted as a regional fracture set that predates laramide compression a joint set set ii striking 045 and present in the hinge and backlimb is related to the ne oriented laramide compression just prior to and during initial anticline growth joints striking 135 set iii parallel to the fold trend are found within the hinge and are interpreted to have developed in response to the bending of layers the two youngest fracture sets are attributed to a late stage of fold growth a joint set set iv in the backlimb striking parallel to the set i fractures but vertical and a fracture set in the forelimb consisting of set i fractures reactivated as reverse faults the relative chronology mode of formation opening vs shearing and structural locations of these fractures suggest the following kinematics of folding at sheep mountain anticline little or no lateral fold propagation no hinge migration and limb rotation with only minor limb flexure and stretching

tectonic thickening of hanging wall units over a ramp in this article we use results of analogue models and published numerical models to study the elements that influence the amount of thickening of hanging wall units during their transport over a ramp the models consisting of granular layers were shortened over a single pass rigid ramp dipping at 15 30 or 45 and friction coefficient that was large 0 67 intermediate 0 42 or null model results show that the amount of thickening depends on the ramp angle and its friction thickening increases dramatically with increasing ramp friction and dip the maximum amount of thickening 80 is observed over steepest ramps 45 with largest ramp friction 0 67 whereas the minimum amount of thickening 2 5 occurs over frictionless ramps dipping 15 for the same friction coefficient along the ramp steeper ramps cause larger amounts of thickening the tectonic thickening demonstrated by our models was compared with thickening of hanging wall units of natural examples and other experimental and model studies this comparison shows that thickening occurs whether the material considered is brittle viscous or plastic it also confirms the importance to thickening of ramp angle and fault friction finally it reveals also that ramp shape round or sharp bend its changes due to footwall deformations and the topographic relief are additional boundary conditions for thickening more generally our model results and other published model results demonstrate that retardation during the transport of hanging wall units over a ramp results in hanging wall thickening

geometry of thin skinned tectonic systems in relation to detachment layer thickness in sedimentary basins characterizing features of both extensional and compressional thin skinned systems may be controlled by the thickness of the underlying mobile material within extensional fault arrays detachment layer thickness in conjunction with detachment dip controls variations in fault spacing and polarity because rigid fault blocks are only free to rotate as long as there is enough underlying mobile material to redistribute between the fault block keels different styles of extensional fault array range from single polarity arrays with closely spaced faults thin detachment to arrays where the fault blocks rotate until the fault blocks separate from one another thick detachment departure from this relationship depends on the amount of internal deformation that can be sustained by the domino fault blocks within contractional zones detachment folds occur where the amount of mobile material can fill the evolving fold core via redistribution thrusts occur where there is insufficient mobile material to sustain detachment fold growth the variations in extensional and contractional style that are described here in relation to mobile layer thickness can be combined to give an idealized model of regional variation in structural style in relation to regional variation in stratigraphy applying this model to a salt basin an allochthon in the area of thickest salt may be characterized by updip raft tectonics and downdip detachment fold belts this style would be laterally transitional toward areas of thinner or lower net salt to updip domino fault arrays and downdip thrust systems

deformation pattern and evolution of the structures in the penganga group the pranhita godavari valley india probable effects of grenvillian movement on a mesoproterozoic basin abstract recent studies reveal imprints of tectonic deformation in the mesoproterozoic rocks of the pranhita godavari p g valley india outcrop scale structures that record a progressive sequence of deformation can thus be used to clarify the kinematic evolution of the penganga group a mesoproterozoic succession in the northern and central parts along the sw marginal proterozoic belt of the pg valley overprinting relationships among the structures in the northern part indicate three distinct structural stages 1 layer parallel shortening 2 thrusting and folding in combination and 3 extensional joint and fracture opening the former two stages are explained in the framework of a progressive deformation model the extensional structures were produced during exhumation similar structures are also developed in the central part of the sw belt of the pg valley though the two areas slightly differ in the overall pattern of deformation the geometry of the progressive deformation structures from both regions of the belt suggests that they were produced under a regime of ne sw ene wsw directed regional compression the deformation in the proterozoic basin is possibly related to the grenvillian orogeny recorded in the eastern ghats mobile belt and may represent a small scale meso neoproterozoic convergence event