structural attributes and paleostress analysis of quaternary landforms along the vigodi fault vf in western kachchh region abstract in this paper we elucidated deformational and kinematic characteristics of the nw se trending vigodi fault vf and its associated subsidiary faults in the western kachchh basin we applied paleostress inversion technique to understand the past stress regime from the acquired fault slip data the subsidiary faults strike nw se and ne sw and slickensided surfaces are well developed on the fault planes we present slip analysis and changes in the stress reorientation using the plane solutions to identify the principal stress axis 1 position regionally to obtain pressure tension and null axis pbt stress ratio and principal 1 axis we used the right dihedron method using the win tensor and t tecto software s respectively geomorphologically the vf zone comprises of bedrock strath terraces towards the upthrown block and fill terraces on the downthrown block of the fault development of fault scarps warped quaternary sediments slit canyons within quaternary sediments river nick points and deflected rivers are the major striking features observed along the strike length of the vigodi fault the analyses indicate that ne sw compressional stress dominates the regional area and the local area is affected by transpressional stress exhibiting oblique slip motion the combined observations made from the present investigation can be used to estimate seismic hazard and mitigation planning of the study area

experiments simulating surface deformation induced by pluton emplacement abstract we present centrifuge experiments to study the surface deformation induced by shallow pluton emplacement in a rheologically stratified crust sand simulates the topmost brittle crust plastilina and denser silicone represent more and less competent crustal portions respectively lighter silicone simulates a buoyant intrusion in the models density differences affect the rate of intrusion but not their evolution or shape whereas viscosity and strength stratifications control both the shape and rate of the intrusions with a higher viscosity contrast 10 2 4 between the intrusion and the embedding media the rise of the lighter silicone induces a laccolith like intrusion responsible for doming and thinning of the overburden an apical depression may form inducing silicone extrusion conversely with a lower 10 1 viscosity contrast the overburden and the intrusion exhibit a lens shaped form with a broad central depression bordered by an upward flexure towards the periphery a sag in the floor of the intrusion is commonly observed no silicone extrusion occurred the intrusion is a hybrid between a laccolith and a lopolith the comparison with nature 1 confirms roof uplift as an important means of accommodating space during pluton emplacement and 2 suggests that where roof uplift plays a major role pluton emplacement can induce a well correlated sequence of events at surface doming the development of a depression and extrusion

the eastern jura relations between thin skinned and basement tectonics local and regional the thesis area of hans cloos in the eastern jura straddles the boundary between the paleogene structures of the tabular jura a part of the southeastern end of the rhine graben and the neogene folds and thrusts of the folded jura a recent reflection seismic survey in the area adjacent to the east provides new information on the subsurface structure and the relation between three superposed tectonic events the main boundary fault zones of a deep and complexly faulted late paleozoic trough trending ene were reactivated in the early tertiary faulted flexures and small folds rooted in the basement and paleozoic with an amplitude of usually 100 to 300 m were produced rather than the normal faults typical for the extensional fields of the rhine bresse graben system in the west and the bavarian molasse basin in the east this suggests their being part of a transform zone between these extensional fields during jura decollement in the neogene these inherited deeply rooted sub decollement structures remained passive their small size is kinematically incompatible with the intense subsequent thrusting and folding of the thin mesozoic tertiary skin however thrust ramps were apparently nucleated at the respective southern foot of these paleogene flexures and folds the best defined and simplest of these composite structures is the mandach structure within the tabular jura a south facing flexure of about 300 m relief developed in the paleogene by reactivation of the northern border fault zone of the paleozoic trough in the neogene a north vergent decollement thrust which is connected with the regional jura decollement in the middle triassic evaporites was initiated at its site

structural evolution of a salt cored domed reactivated fault complex jebel madar oman abstract fault and fracture patterns associated with domal structures are observed around the world both at outcrop and in the subsurface however the structural evolution of domes and the influence of previous fault and fracture sets are not yet fully understood this study provides the first structural evolution analysis of jebel madar a domal outcrop in the adam foothills of northern oman and evaluates the role of multiple local tectonic events and the associated salt diapirism on fracture and fault distribution pattern development of a salt cored domal outcrop analyses at jebel madar suggest that three local tectonic events with different stress regimes that are tentatively linked to three regional tectonic events resulted in a salt cored domed reactivated fault complex 1 initial dome formation and ne sw oriented mode 1 opening fractures and subsequent grabens 2 e w oriented dextral strike slip faulting and 3 reactivation and inversion of faults and final dome formation salt emplacement is associated with the first and last tectonic events this integrated study highlights the complicated evolution of fault and fracture distribution patterns at a salt cored dome caution is therefore required in interpretation of similar structural patterns on top of and around salt cored domes

fault patterns within sediment layers overlying rising salt structures a numerical modelling approach abstract faulting of sediments overlying structures caused by salt movement is a widespread phenomenon and important for hydrocarbon production because the faults facilitate hydrocarbon migration to and from the reservoir or may compartmentalize the reservoir a major problem in mapping the intensity of deformation is that many faults and fractures are below the seismic resolution and that the seismic data may appear dimmed and distorted owing to escaping gas another major problem is that the salt displacement causing the deformation is often only reflected in the overlying fracture patterns and hence not directly observable this study uses a numerical spring slider model including vertical as well as horizontal movements of the substrata the salt the model demonstrates how the fracture patterns in the sediments above salt structures are controlled by the salt kinematics the modelling experiments show that concentric faults develop when only vertical salt movements are involved whereas radial faulting dominates when even small levels of horizontal movements are included a case study from the southern danish central graben illustrates that the fault structures in the cover sediments characterizes the salt movement the analysis and prediction of the systematics of these small scale faults which are too small to be recognized on seismic data is important when the fluid migration and hence hydrocarbon production from fields related to salt structures is to be optimized

novae on venus geology classification and evolution 1 novae are radially fractured centers 100 300 km in diameter and 64 have been identified on venus dense radial fracturing and upraised topography are common and massive amounts of volcanism are seen in some novae are interpreted to be the result of updoming and fracturing of the surface due to interaction of mantle diapirs with the lithosphere and radial fracturing caused by dike emplacement we analyzed the topography and character of deformational and morphological structures of all 64 novae leading to a better understanding of their evolution and relation to diapir dynamics and their age we subdivided novae into four topographic classes 1 upraised 2 annular 3 flat and negative and 4 plateau like novae are located mostly in areas of regional rises and rift zones with a small number in the lowlands about one half the novae studied show association with rifts in some of these the rift troughs surround nova rises and form plateau like novae plateau like novae may predate postdate or form simultaneously with rifts our analysis generally confirms and updates previous models of novae evolution with the following geological factors being important 1 depth of the neutral buoyancy level of the rising mantle diapir 2 rheological characteristics of the overlying lithosphere 3 whether or not the visco plastic material above the diapir undergoes spreading and 4 the nature and influence of regional stress and rift structures these combined factors exert control on the direction of nova evolution and appear to determine the primary characteristics of nova such as topography tectonics and volcanism we found clear evidence for 1 the important role of dike swarm emplacement in the formation of radial patterns of novae and 2 the formation of concentric tectonic features during the relaxation stage of novae novae have multiple evolutionary stages and are long lived structures stratigraphic analysis of all 64 local areas showed a similarity in the sequence of regional geologic units we found that 40 3 of the novae population started to form before emplacement of regional plains with wrinkle ridges and that 11 3 completed their activity before this time 88 7 of the population of novae was active after regional plains formation in contrast to novae coronae activity was greatest before formation of regional plains which may be due to thickening of the lithosphere with time detailed structural analysis shows that novae evolution does not always lead to the formation of corona like features

estimation of magma depth for resurgent domes an experimental approach post collapse resurgence is a phenomenon affecting many calderas attributed to a renewed magma rise the process is still poorly understood and the associated source parameters remain poorly constrained a set of experiments has been conducted to gain insight into the structural evolution of caldera resurgent domes a sand plaster mixture was chosen as an analogue for the brittle pile of volcanic rocks and silicone putty simulates the ductile behavior of the intruding magma resurgence is driven by the vertical uplift of the silicone with variable shape and depth similarity conditions are achieved through eight dimensionless numbers which are of the same order of magnitude in both nature and experiments results show that extension due to doming is in many cases accommodated by one axial graben opposite master faults of this graben intersect at depth at the junction with the rising viscous silicone the simplicity of the geometry of the whole analogue system provides equations which allow the estimation of the silicone depth from surface parameters these equations are then used in some field examples to assess the magma depth beneath natural resurgent domes

fault related domes insights from sedimentary outcrops at the northern tip of the gulf of suez rift egypt abstract domes may develop with various mechanisms in different types of rocks knowing the geometries and occurrences of domes is an important concern in classifying different types of domes a number of fault related domal structures are outcropped at the northern gulf of suez rift egypt and they are easily visualized on satellite imagery detailed surface geological field mapping is carried out at several localities to assess types and origins of these domes three main subdivisions of fault related domes are suggested in the present study these are 1 domes formed in strike slip zones d sz 2 domes formed by drag along normal fault arrays d df and 3 domes formed at transfer zones of normal faults d tz structural analysis of the studied domes reveals that each dome type has its own geometric parameters structural style and tectonic setting the obtained results are without doubt interesting for the analysis of similar domes at the subsurface and other exposures worldwide

predicting patterns of strain from three dimensional fold geometries neutral surface folds and forced folds the geometries and densities of fractures associated with fold structures can be predicted by assuming that the strains accommodated by fractures mimic the bulk strains induced in the strata during folding this paper examines from a theoretical standpoint the distributions of bedding plane strains expected in folds formed by various folding mechanisms the relationship between the state of bedding plane strain and fold surface geometry is found to vary according to different fold types distinguished on the basis of their curvature properties the first type are developable fold surfaces which have gaussian curvature equal to zero folding mechanisms which are dominated by the mechanical strength of the layering such as buckling produce surfaces of this type folds of this type allow the possibility of estimating the bedding plane strains from the geometrical features of the folded layer neutral surface folds and flexural slip folds are discussed as examples the other main class of folds have non developable surfaces which have non zero gaussian curvature folded surfaces with this form arise predominantly from mechanisms that involve the passive deflection of the layering in response to displacement gradients originating outside of the layer e g drape folding although the geometry of these surfaces implies the presence of bedding plane strains the quantification of these strains cannot be made from the fold geometry but requires additional information on these displacement patterns

post miocene rifting and diapirism in the northern red sea abstract rifts and diapirs are the dominant structures in the bathyal zone of the northern red sea where commonly the diapirs ascend along normal faults associated with the rifts in this manner the diapirs form elongated features sometimes exceeding lengths of 30 km and widths of 4 km they also penetrate a sedimentary sequence about 1000 m thickness or less thicknesses generally considered to be barely adequate for the gravity conversion required to initiate diapiric motion we suggest that development of diapirs under these minimal overburden conditions was made possible by the high thermal gradients in the area resulting from the underlying attenuated continental crust and ascending mantle that prevail in the rift system of the northern red sea diapiric evolution was also dependent on the extensional tectonic regime with its numerous normal faults forming weaknesses along which the diapirs could move upwards

origins of oblique slip faulting during caldera subsidence 1 although conventionally described as purely dip slip faults at caldera volcanoes may have a strike slip displacement component examples occur in the calderas of olympus mons mars miyakejima japan and dolomieu la reunion to investigate this phenomenon we use numerical and analog simulations of caldera subsidence caused by magma reservoir deflation the numerical models constrain mechanical causes of oblique slip faulting from the three dimensional stress field in the initial elastic phase of subsidence the analog experiments directly characterize the development of oblique slip faulting especially in the later non elastic phases of subsidence the combined results of both approaches can account for the orientation mode and location of oblique slip faulting at natural calderas kinematically oblique slip faulting originates to resolve the following 1 horizontal components of displacement that are directed radially toward the caldera center and 2 horizontal translation arising from off centered or asymmetric subsidence we informally call these two origins the camera iris and sliding trapdoor effects respectively our findings emphasize the fundamentally three dimensional nature of deformation during caldera subsidence they hence provide an improved basis for analyzing structural geodetic and geophysical data from calderas as well as analogous systems such as mines and producing hydrocarbon reservoirs

triassic evaporites and plio quaternary diapirism in western greece wide triassic evaporite outcrops run parallel to the strike of hellenide thrust faults in western greece they crop out along the leading edges of thrust sheets emplaced as part of the foreland migrating fold and thrust belt the evaporites acted as the plane of decollement for thrust sheet emplacement over much of the external hellenides plio quaternary diapirs occur locally within the broad outcrops of triassic evaporite they are the result of local mobilization of evaporite after its emplacement their rise may have been initially triggered by hellenide thrust sheet loading and subsequently accentuated by plio quaternary subsidence geophysical records and onland exposures show that diapiric rise controlled local sedimentation patterns above the sites of earlier hellenide thrusts the subsequent intrusion of diapirs into these cover sediments caused localized extensional structures to develop this is best seen in se zakinthos where strain hardened conjugate faults developed in friable pliocene sandstones early in the intrusion history principal strains calculated from these sets demonstrate patterns of extension sub orthogonal to intrusion margins they are comparable with patterns known from other field and experimental examples but contrast with some recent studies on diapir related strains

radial clastic dykes formed by a salt diapir in the dead sea rift israel fanning structures radiating from a central perturbation are known in various geological environments where different processes have produced similar geometry the present contribution describes and analyses fanning clastic dykes in the dead sea rift a new example of diapir related deformation the dykes are opening mode fractures exposed in lacustrine varved marl of the lisan formation deposited 70 15 ka they are arranged mainly in a radial and tangential geometry the radial traces converge at the black hill structural dome the geometry of the fractures is consistent with stresses exerted by the rise of a salt diapir located underneath the black hill the estimated extension of the radial fractures is in good agreement with the present topographic elevation of the hill the absence of fractures in the overlying holocene alluvium probably indicates that either the rise of the black hill salt diapir paused or is associated now with a different style of deformation

the problem of the deep structure of the southern alps 3 d material balance considerations and regional consequences abstract the lombardic southern alps are a typical thin skinned frontal fold and thrust belt although this recent reassessment is widely accepted figures for shortening and schemes for transfer of shortening at their eastern end in the giudicarie vary exact section balancing is not feasible because of insufficient information but approximate shortening is on an order probably exceeding 100 km with about 80 100 km attributable to the middle to late miocene milan belt acceptance of this quantitative conclusion has farreaching consequences transfer of the milan belt shortening in the east follows the lateral edge of the allochthon which is sinistrally transpressive the giudicarie line with its sedimentary decollement zone the giudicarie belt the pre existing adamello intrusions and the jorio tonale line are part of the thrust masses and consequently allochthonous transfer of shortening across the insubric line into the tauern antiform and associated structures of neo alpine compression in the eastern alps resulted in the sinistral dissection of the insubric line at the giudicarie line superposition of this compression on pannonian stretching east of and transtensive motion at the brenner line west of the tauern produced a confusing structural pattern whose quantitative kinematics have not been worked out another sinistral probably compressive transfer zone is postulated at the western end of the milan belt retrodeformation leads simultaneously to both a straightening of the insubric line and the connection of the canavese line with the villalvernia varzi levanto line to define the boundary of the adriatic block at the beginning of neo alpine deformation

neotectonics in central mexico regional neotectonic activity in central mexico was mapped through analysis of eleven landsat thematic mapper images the study area stretches from mexico city on the east to the gulf of california on the west between 17 and 21 n latitude fault scarps of plio quaternary age define several large scale tectonic features within the mexican volcanic belt dominated by rifting transtension and shear with probable sinistral components three large crustal blocks south of the mexican volcanic belt are separated from the north american plate and from each other by zones of neotectonic activity that express the relative motions between the adjacent blocks a simple vector diagram for plates and crustal blocks in central mexico has been constructed using information from the literature combined with the orientations of fault zones as mapped in this study the relative motion between the blocks varies from about 2 5 to 8 mm year 1 which is comparable to motions of crustal blocks in areas of active rifting in other parts of the world in the mexican volcanic belt there is a clear relationship between volcanism and neotectonic activity fault zones that traverse nearly the entire region have the same location and orientation as the volcanic belt this may indicate that deformation within the crust of the overriding slab plays a significant role in determining the unusual orientation of the mexican volcanic belt relative to the trench the ultimate factor controlling the location of plio quaternary volcanism and tectonism in central mexico may be large zones of crustal weakness formed during major mesozoic and cenozoic tectonic events

the southern rhine graben a new view of the initial phase one of the puzzling features of the southern end of the rhine graben is the dinkelberg tabular jura block on the eastern shoulder of the graben it is dissected by a large number of faults the most notable ones forming a field of narrow little grabens and half grabens whose bordering faults converge at the level of the middle triassic evaporites which points to decollement at that horizon the little grabens were traditionally considered to be of oligocene age coeval with the main taphrogenesis of the rhine graben two hypotheses were offered for their formation one ascribing them to extension on the extrados of large basement folds the other to gravity sliding on paleoslopes recent field work uncovered overwhelming evidence for an eocene age of the little grabens the time of the initial phase of rhine graben formation at that time there were neither large basement folds nor paleoslopes of any significance and therefore the two hypotheses offered until now do not work however the map view pattern of the field of faults offers a somewhat unusual way out of the dilemma this pattern is most prominently displayed in the dinkelberg area north of the rhine there a lane of narrow decollement grabens with a mean nne strike is confined within the nw striking dinkelberg graben which is much wider and rooted in the basement it is also very shallow with a subsidence on the order of 100 m the lane of decollement grabens forms a dextral en echelon pattern with respect to the dinkelberg graben suggesting stretching of the post evaporite sequence above a basement essentially extended by strike slip this model though not as clearly expressed is also compatible with the data in the rest of the dinkelberg tabular jura block it also fits surprisingly well a theoretical model by withjack and scheiner 1982 that predicts a dominance of strike slip in the marginal area of a system consisting of extension superimposed on doming

mantle flow tectonics the influence of a ductile lower crust and implications for the formation of topographic uplands on venus convective flow within the interiors of terrestrial planets is a primary source of large scale topographic and tectonic features we treat the crust and mantle as a layered viscous half space and find solutions for flow driven by a buoyancy force distribution within the mantle and by relief at the surface and crust mantle boundary the crust initially responds to mantle upwelling with uplift but continued flow causes significant crustal thinning and subsidence downwelling leads to initial subsidence and subsequent crustal thickening and surface uplift changes in crustal thickness are driven by 1 vertical normal stresses due to mantle flow and 2 shear coupling of horizontal mantle flow into the crust the degree and time scale of crustal deformation are sensitive to crustal thickness and viscosity and the presence of elastic layers in the upper crust and mantle deformation can occur on time scales less than several hundred million years for reasonable values of these parameters strong or elastic upper crustal layers enhance crustal thinning or thickening while large viscosity contrasts between the lower crust and upper mantle or elastic mantle layers tend to diminish deformation for time dependent mantle flow due to a rising or sinking diapiric body crustal deformation depends upon the ratio of diapir radius to crustal thickness and the ratio of crustal to mantle viscosity a sinking diapir can lead to crustal thickening elevated topography and a specific sequence of time varying deformation while regions such as beta regio have long been suggested to result from convective upwelling in the venus mantle we suggest that a mantle downwelling origin is consistent with many of the characteristics of the compressional mountain ranges of western ishtar terra

stress pattern at campi flegrei from focal mechanisms of the 1982 1984 earthquakes southern italy abstract campi flegrei is a holocene volcanic area in the campanian plain southern italy within the apennine chain a neogenic thrust belt built up since the middle miocene the volcanic complex consists of a c 12 km diameter caldera containing several monogenetic volcanoes the youngest of which monte nuovo erupted in 1538 since at least roman times the area has also been affected by slow vertical movements bradiseismic activity between 1982 and 1985 this slow motion was interrupted by a period of more rapid displacement which caused a maximum uplift of 180 cm in the town of pozzuoli to model the local stress field associated with the uplift the angelier inversion technique has been applied using the focal mechanisms of forty nine earthquakes which occurred between april 1982 and december 1984 the results show that doming coupled with a regional extensional strain can account for the seismic phenomena that affected the area

calderas and caldera structures a review abstract calderas are important features in all volcanic environments and are commonly the sites of geothermal activity and mineralisation yet it is only in the last 25 years that a thorough three dimensional study of calderas has been carried out utilising studies of eroded calderas geophysical analysis of their structures and analogue modelling of caldera formation as more data has become available on calderas their individuality has become apparent a distinction between caldera caldera complex cauldron and ring structure is necessary and new definitions are given in this paper descriptions of calderas based on dominant composition of eruptives basaltic peralkaline andesitic dacitic rhyolitic can be used and characteristics of each broad group are given styles of eruption may be effusive or explosive with the former dominant in basaltic calderas and the latter dominant in andesitic dacitic rhyolitic and peralkaline calderas four end member collapse styles occur plate or piston piecemeal trapdoor and downsag but many calderas have multiple styles features of so called funnel and chaotic calderas proposed in the literature can be explained by other collapse styles and the terms are considered unnecessary ground deformation comprises subsidence or collapse essential characteristics of a caldera and uplifting doming and fracturing due to tumescence and or resurgence frequent but not essential collapse may occur on pre existing structures such as regional faults or on faults created during the caldera formation and the shape of the collapse area will be influenced by depth size and shape of the magma chamber the final morphology of a caldera will depend on how the caldera floor breaks up whether collapse takes place in one event or multiple events whether vertical movement is spasmodic or continuous throughout the eruptive sequence and whether blocks subside uniformly or chaotically at one or more collapse centres a meaningful description of any caldera should therefore include number of collapse events presence or absence of resurgence caldera floor coherency caldera floor collapse geometry and dominant composition of eruptives

middle triassic strike slip tectonics and igneous activity of the dolomites southern alps abstract strike slip faults and south vergent thrusts deformed a rhomb shaped area measuring about 20 20 km in the dolomites during the late ladinian deformation was caused by a right stepover of a nne ssw trending sinistral strike slip fault strike slip displacement amounted to more than 10 km thrusting caused a relief shortening of more than 3 km and can be demonstrated by the matching of particular ladinian carbonate facies boundaries these tectonic movements may account for the termination of a transgressive depositional megacycle which had begun in permian times rupture of the crust of the deformed terrain caused the emplacement of a magma chamber beneath its evacuation in the latest ladinian and early carnian was associated with the collapse of its roof and the extrusion of shoshonitic lavas they filled a volcano tectonic depression which overlaps with the deformed and eroded area the orientation of volcanic dikes suggests the absence of tectonic strain during igneous activity provided that they formed contemporaneously

three dimensional 3 d seismic imaging of conduits and radial faults associated with hydrothermal vent complexes voring basin offshore norway abstract here we document a suite of radial faults associated with hydrothermal vent complexes in the voring basin offshore norway these complexes have pyramid shaped cylindrical and conical shaped conduits with a dome or eye shaped morphology at their summit intruding on paleogene sedimentary rocks hydrothermal vents are intimate with the tips of magmatic sills that were emplaced at depths ranging between 1800 and 5800 ms two way travel time twtt at shallower depths of 1800 to 3000 ms twtt and intermediate depths of 3000 to 5000 ms twwt magmatic sills regularly intersect the lower parts of the vent conduits which are characterized here as pipes an important parameter that is used to characterize the morphology of a hydrothermal vent conduit is the width of the conduit which is defined as the longest axis marking the extent of the vents conduit within the surrounding host rock strata our findings reveal that radial faults are commonly associated with the summits of hydrothermal vents implying the existence of local stress fields around the vents where the maximum compressive stress is radial and minimum stress is circumferential which overrides the regional stress field and indicate variable stress regimes as opposed to tectonic faults importantly circumferential stretching due to catastrophic plumbing of hydrothermal fluids differential compaction and intensive fracturing enabled the polygonal faults to realign in a radial pattern resulting in the formation of radial faults at the vent summit as a corollary of this work we hypothesize that pyramid shaped hydrothermal conduits are possibly markers of protracted sill emplacement in sedimentary basins

discrete element modelling of hanging wall deformation along the d 1 fault system danish north sea with implications for gas chimney interpretations abstract this study uses 3d seismic mapping nncc attribute analysis and 2d sdem modelling of soft sediment deformation to analyse hanging wall deformation related to faulting across a listric fault detaching along the top of a major salt roller the computational model experiments used the overall fault and salt structure evolution as boundary conditions to predict the distribution of faults within the hanging wall the modelling successfully reproduced geometries similar to the syn and antithetic faults that are visible on seismics but it also showed the presence of well defined vertical deformation zones both in the hanging wall and the foot wall of the listric fault in the model salt movement controls the formation of the deformation zones the similarity of nncc inferred vertical chimneys and the modelled deformation zones suggests that the subtle vertical chimneys identified in the 3d seismic data might actually be related to vertical to sub vertical deformation zones caused by the presence and movement of the salt structure

flexure and faulting of sedimentary host rocks during growth of igneous domes henry mountains utah abstract a sequence of sedimentary rocks about 4 km thick was bent stretched and uplifted during the growth of three igneous domes in the southern henry mountains mount holmes mount ellsworth and mount hillers are all about 12 km in diameter but the amplitudes of their domes are about 1 2 1 85 and 3 0 km respectively these mountains record successive stages in the inflation of near surface diorite intrusions that are probably laccolithic in origin the host rocks deformed along networks of outcrop scale faults or deformation bands marked by crushed grains consolidation of the porous sandstone and small displacements of sedimentary beds zones of deformation bands oriented parallel to the beds and formation contacts subdivided the overburden into thin mechanical layers that slipped over one another during doming measurements of outcrop scale fault populations at the three mountains reveal a network of faults that strikes at high angles to sedimentary beds which themselves strike tangentially about the domes these faults have normal and reverse components of slip that accommodated bending and stretching strains within the strata an early stage of this deformation is displayed at mount holmes where states of stress computed from three fault samples correlate with the theoretical distribution of stresses resulting from bending of thin circular elastic plates field observations and analysis of frictional driving stresses acting on horizontal planes above an opening mode dislocation as well as the paleostress analysis of faulting indicate that bedding plane slip and layer flexure were important components of the early deformation as the amplitude of doming increased radial and circumferential stretching of the strata and rotation of the older faults in the steepening limbs of the domes increased the complexity of the fault patterns steeply dipping map scale faults with dip slip displacements indicate a late stage jostling of major blocks over the central magma chamber radial dikes pierced the dome and accommodated some of the circumferential stretching

coronae of mnemosyne regio morphology and origin abstract coronae are circular to elliptical structures 150 600 km across characterized in venera 15 16 and arecibo radar images by an annulus of concentric ridges the interiors of the structures are geologically complex displaying volcanic flows domes and radial concentric and or obliquely trending ridges and are generally distinct from the exterior the mnemosyne regio area to the west of ishtar terra contains seven coronae the largest cluster of coronae identified on venus on the basis of the morphologic and topographic characteristics of the coronae in the mnemosyne region we assess several possible models of corona origin using cross cutting and stratigraphic relationships we have been able to identify a sequence of features and events for this group of coronae and have determined that a variety of processes contribute to the origin and evolution of coronae we find that several processes associated with diapirism or hotspots and gravitational relaxation of high topography are most consistent with observed corona topography and morphology and are thus likely to have been significant in the formation and evolution of coronae on the basis of these observations and stratigraphic relationships the following sequence of events is outlined for the formation and evolution of coronae in this region 1 regional volcanic and tectonic activity 2 localized uplift and volcanism caused by diapirism or hotspots 3 annulus and trough formation related to gravitational relaxation accompanied by further volcanic activity 4 continued local volcanic flooding of the corona annulus and trough differences in morphology between coronae reflect variations in amount and significance of these geologic processes coronae in other regions exhibit the same overall characteristics as the mnemosyne coronae and support a similar origin for the majority of coronae

experiments on cauldron formation a polygonal cauldron and ring fractures abstract the sequence of formation of the motojuku type cauldron fujita et al 1970 is summarized as follows 1 doming due to ascent of a magma body 2 development of normal faults which produce a polygonal cauldron and 3 eruption of acidic to intermediate pyroclastic material model experiments on a scale of 1 200 000 reveal that ascent of the magma body which was imitated by a ball of hardened putty produced a polygonal cauldron composed of radial and concentrically arranged short fractures on the roof of a dome no ring fractures were formed this type of cauldron develops near the surface on the other hand emission of magma which was imitated by evaporation of a ball of dry ice in brittle powdered material caused ring faults dipping outward and a circular cauldron without up or downwarping this type of cauldron develops upward from the magma body the former model is equated to the motojuku type cauldron and the latter model to the other types of cauldrons with ring fractures

development of crestal normal faults associated with deepwater fold growth deepwater anticlines during their early stages of development approximately between interlimb angles of 180 and 140 grow and accumulate weak fine grained and poorly lithified sediment on their crests growth of the anticlines induced gravitational instability within the syn kinematic sediments and development of a range of shallow gravity driven failure mechanisms in addition to shallow tens of metres depth to detachment rotational landslides deeper seated normal fault swarms also affect the fold crests and upper fold limbs these faults tend to penetrate to depths between 200 and 800 m are 100s of metres to a few kilometres long planar to weakly curved in cross section and display throws in the order of tens of metres the faults do not sole out into a detachment but die out downwards they can occur as single sets or tiers of faults that have developed at different times in map view the fault patterns range from straight to anastamosing to highly curved with complex cross cutting relationships the number and orientation of faults corresponds to the maximum slope dip and direction and consequently the faults are inferred to be mainly the product of gravity induced deformation although tangential stresses arising from outer arc bending of a fold or crestal collapse in response to a mobile sedimentary unit may contribute to some extent

tectonic and volcanic evolution of dark terrain and its implications for the internal structure and evolution of ganymede furrows in ancient dark terrain on ganymede form three systems that are each hemispheric or greater in scale the oldest of the systems designated system iii is dominated by approximately concentric troughs centered on about 60 n 50 w system i in the anti jovian hemisphere contains concentric and subradial furrows arrayed around a large degraded palimpsest centered at 15 s 165 w furrows in each system formed on and locally are buried by dark volcanic materials that embay and infill preexisting topographic features they crosscut extremely few well preserved older craters and they occur on surfaces having significantly different relative crater ages system ii also in the anti jovian hemisphere contains widely spaced radially arrayed furrows commonly 500 2000 km in length which are organized around a large area of dark smooth resurfacing material intense dark terrain fracturing and some of the globally oldest light material the total thickness of dark terrain resurfacing estimated using the stratigraphy of different dark material deposits and the rim heights of the largest crater size class whose density was depleted by each deposit is probably in the range of 3 8 km multiple models of the origin of each furrow system were tested using observed geologic features and patterns systems i and iii were found to be most consistent with reactivation of impact generated multiringed structures by endogenic global extension during a period of widespread dark material volcanism that obliterated a dense ancient crater population system ii was found to be most consistent with fracturing of a single circular isostatic uplift covering an entire hemisphere on the basis of geologic observations and interpretations and theoretical models of convection in spheres it is hypothesized that the uplift developed by long term warming of the upwelling current of a single axisymmetric convection cell in an initially cooler undifferentiated interior such wanning would also have created global expansion and supplied the tensional stress inferred to have formed systems i and iii this hypothesis is supported by the concentration around the center of system ii of intense fracturing and relatively young dark volcanic deposits suggestive of high lithospheric heat flow lithospheric thinning and stress concentration an observed long term decrease in the width of extensional tectonic features interpreted to be of endogenic origin is also consistent with lithospheric thinning due to warming of a cool interior

fault patterns associated with domes an experimental and analytical study experimental clay and analytical models suggest that regional strain either extension or compression significantly affects the fault patterns produced by doming our models specifically simulate the shallow deformation produced by gentle doming of a homogeneous material with and without a simultaneously applied regional horizontal strain the models of circular domes show that without regional strain normal faults develop on the crests and flanks on the flanks the normal faults have radial trends with regional extension normal faults on the crests of circular domes trend perpendicularly to the regional extension direction whereas many normal faults on the flanks trend obliquely to it strike slip faults trending 60 from the regional extension direction fo m near the peripheries with regional compression many normal faults on the crests and flanks of circular domes strike parallel with the regional compression direction strike slip faults trending 30 from the regional compression direction also form on the flanks and reverse faults striking perpendicularly to the regional compression direction develop on the peripheries our models show that regional strain affects the fault patterns produced by elliptical doming similarly the fault patterns of our models resemble fault patterns of domed strata above salt diapirs and above uplifted blocks of basement

mechanics of active salt diapirism abstract an active diapir forcefully intrudes its overburden driven by diapir pressure that overcomes the resistance of the overburden strength possible causes for the driving pressure are differential loading of the source layer and a density contrast with the overburden possible resisting forces derive from the mass of the roof block and resistance to the faulting and folding that accommodate the intrusion for a typical density contrast between salt and a sedimentary overburden a simple force balance demonstrates that the diapir height must be more than two thirds to three quarters the thickness of the surrounding overburden to initiate substantial active diapirism narrow diapirs must be even taller physical and numerical modeling show that typical structures of active diapirism are a central crestal graben flanked by relatively unstrained flaps that rotate upward and outward curved reverse faults can separate the flaps from the regional overburden normal faults in the crestal graben propagate downward with new faults created farther outward as the roof arches over the rising diapir thin wide roofs develop multiple grabens separating a relatively flat roof from the rotating flaps in cases leading to emergence the piercing diapir evolves from a pointed crest to a progressively rounded and widening crest as the flaps rotate outward the numerical models show that overburden flexure contributes to early formation of active diapir structures but piercement does not continue to emergence unless the diapir is very wide or tall relative to the overburden thickness active diapirism becomes progressively more difficult for diapir crests ranging from a rectangle a round cornered rectangle a semicircle to a triangle with a pointed crest

tectonics of nisyros island greece by field and offshore data and analogue modelling abstract we use new on land and offshore structural data and scaled analogue models to analyse the fault tectonic pattern at nisyros island greece which has an active caldera that shows a complicated network of faults fractures and volcano tectonic structures we measured 157 faults that show dominant dip slip normal motions along planes mainly striking ne sw nne ssw and nnw sse inside the caldera dykes necks and morphometric parameters of volcanic domes explosion craters and fumarole pits indicate the control by ne striking discontinuities on magma and gas paths the nnw and ne striking faults bound a major block that underwent repeated downthrow and uplift movements during the late pleistocene holocene experiments with scaled models of caldera resurgence and two magma chambers indicate the formation of an hourglass shaped fault pattern as seen in plan view with an asymmetric increase in the fault offset and a widening of the fault divergence towards the volcano flank all these data suggest that regional fault tectonics and stress state strongly guided magma upwelling and the emplacement of volcanic centres whereas periodical bulging due to the overpressure of a second magma chamber located northwest of the caldera combined with faulting due to tectonic stresses can account for the overall deformation field

in situ stress orientations in the uk southern north sea regional trends deviations and detachment of the post zechstein stress field the orientation of the maximum horizontal compressive stress shmax in the uk southern north sea has been determined using data derived from borehole breakout analysis of four arm caliper logs the results agree with existing stress models for nw europe confirming that horizontal stresses in the region have an approximately nw se orientation of shmax this is interpreted as being a result of plate boundary convergence local deviations in the shmax orientations are observed spatially and also vertically within some wells some of these deviations are attributed to rotations of the stress field adjacent to faults or between different fault blocks the data also suggest detachment of the stress regime in the post permian cover rocks caused by the presence of a thick underlying permian aged evaporite sequence and associated halokinesis analyses of borehole resistivity image logs have been used to verify the shmax orientations in some wells these image logs validate some of the stress indicators whilst highlighting a number of deficiencies in the use of four arm caliper data to characterise borehole breakouts from the available data it is difficult to unambiguously define the nature of variations from the mean shmax orientations observed further analyses of image log data over greater depth ranges are therefore required in order to investigate more fully the effects of stress rotations near faults and apparent stress detachment above salt cored anticlinal structures

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

tessera terrain and crustal plateaus venus many workers assume that tessera terrain marked by multiple tectonic lineaments and exposed in crustal plateaus comprises a global onion skin on venus a growing body of structural mechanical magmatic gravitational topographic and geologic evidence indicates that tesserae record the local interaction of individual deep mantle plumes with an ancient globally thin venusian lithosphere resulting in local regions of thickened crust

activation of diffuse discontinuities and folding of sedimentary layers 1 folding of sedimentary layers is often accommodated by the opening or sliding of inherited and new discontinuities which are assumed here to be diffuse so that a continuum description applies at the fold scale the rock rheology is then described with an elastoplasticity model for which the permanent deformation is of simple shear sliding or dilation opening with respect to specific orientations of the new or inherited diffuse discontinuities to illustrate the relation between folding and activation of diffuse discontinuities a three dimensional layer under compression in the two horizontal directions and sustaining the overburden lithostatic pressure is studied cylindrical buckling occurs either before elastic or after the diffuse discontinuities have been activated if buckling is elastic inherited vertical discontinuities striking obliquely to the fold geometrical axes are activated in a sliding mode in the outer arc leading to a rotation of the principal stress directions opening is then detected across new vertical planes striking obliquely to the fold axis the activation of inherited or new vertical discontinuities can be suppressed if sliding takes place along weak bedding interfaces alternatively early and homogeneous layer parallel shortening marked by a reverse fault mode drastically reduces the critical buckling load compared to the euler load and modifies the final geometry of buckling which is then more of a circular dome shape the switching in buckling mode results in the fold limbs in a change from the early reverse fault to a strike slip fault sliding and to opening across diffuse planes oriented consistently with the final circular structure

karst system developed in salt layers of the lisan peninsula dead sea jordan the lisan peninsula jordan is a massive salt layer accumulated in the inner part of the dead sea s precursory lakes this tongue shaped emergent land results in a salt diapir uplifted in the dead sea strike slip regional stress field and modified by the water level fluctuations of the last lake during the holocene these two elements associated with dissolution caused by rainfall and groundwater circulation resulted in an authentic karst system since the 1960s the dead sea lowering of 80 cm to 1 m per year caused costly damages to the industrial plant set up on the peninsula the lisan karst system is described in this article and the components of the present dynamic setting clarified

microfractures in chalks of albuskjell field norwegian sector north sea possible origin and distribution production data from many north sea chalk fields have indicated moderate to considerable contribution to production from natural fractures this paper illustrates a detailed study of natural fracturing in the albuskjell field where gas condensate hydrocarbons are contained in upper cretaceous maastrichtian and lower tertiary danian chalks the field is a large halokinetically induced dome located on the northern limits of the productive chalk region known as the greater ekofisk area examination of core material from wells 1 6 3 2 4 f10 and 1 6a 10 albuskjell has revealed the presence of two types of fractures the first appear to be early are commonly compacted predominantly healed and resemble conjugate shear fractures the second type is related mainly to the tips of stylolites these are vertical preferentially open and are interpreted as tension fractures tension fractures form when the minimum effective stress is reduced to the tensile strength of the chalk as a result of increased pore fluid pressure and or decreased total confining stress due to relative extension construction of effective stress versus progressive burial depth profiles using three models of overpressure generation suggests that high pore fluid pressures alone could not have formed the tension fractures in albuskjell measurements and calculations from depth converted seismic sections have shown that halokinesis occurred throughout chalk deposition and continued in a series of pulses until early miocene time incremental stress values associated with halokinesis predict optimum conditions for tension fracture formation at 4 500 ft 1 370 m burial owing to a combination of halokinetic doming and overpressuring with an important contribution from source rock maturation these fractures possibly formed therefore post hydrocarbon emplacement 3 000 ft 1 000 m burial identity mid oligocene and have been preserved by hydrocarbon invasion the healed shear fractures formed prior to significant pressure solution and hydrocarbon emplacement and are thought to be associated with extra dome processes possibly involving graben tectonics or halokinetic reactivation of earlier northwest southeast trending major faults their distribution is expected to be fairly uniform over the field with broadly northwest southeast orientations shear fracture density is moderately constant between the danian and maastrichtian chalk sequences but is significantly reduced to absent in the argillaceous base danian model studies predict that tension fractures should be concentrated in crestal areas of the field where near random orientations may occur preferentially radial with some concentric orientations relative to the structural dome may occur off the crest with radial fractures persisting farther downflank predicted tension fracture orientations agree well with those measured from the oriented cores of well 1 6 a10 open tension fractures are preferentially absent from tight early cemented or argillaceous chalks they are also poorly developed in soft lithologies and predominantly occur in chalks with moderate to high porosities with stylolites the spacing of open tension fractures is assumed to be constant over the field whereas fracture width decreases from crest to flank this is in line with the concept of lower horizontal stresses in the structural crest a plot of optimum fracture spacing versus fracture width has been constructed using strain values calculated from the halokinetic models analysis of production data supports the proposed model and agrees well with a strong halokinetic influence on fracture development although significant halokinesis ceased during the early miocene residual strain may still exist in albuskjell with larger horizontal effective stresses occurring in the flanks of the structure calculations suggest that tension fractures are probably open under initial field conditions to a potentia depth of 11 500 ft 3 500 m

experimental fracture strain and subsidence patterns over en echelon strike slip faults implications for the structural evolution of pull apart basins abstract claybox experiments show that with progressive left lateral displacement on basal left stepping en echelon strike slip faults an extremely complicated zone of evolving fracture strain and subsidence patterns develops in the overlying clay the fracture pattern is more complex than predicted by theoretical models and consists of a progressively widening array of riedel shears conjugate riedel shears and tension gashes above basal master faults conjugate riedel shears rotate anticlockwise and lengthen forming s shaped fractures riedel shears rotate both anticlockwise and clockwise those that rotate anticlockwise eventually open as tension gashes other tension gashes open where the ends of riedel and conjugate riedel shears link strain contours in the deformed clay show an asymmetrical z shaped pattern over the stepover area between basal en echelon faults in the early stages of displacement strain is distributed penetratively over a progressively broadening zone in later stages of displacement strain is partitioned into a narrow middle zone maximum strain is sustained always in the middle of the sheared zone and increases exponentially with progressive displacement subsidence is accommodated in the stepover area by oblique slip on many riedel and conjugate riedel shears distributed throughout the stepover area subsidence y exhibits a linear relationship with master fault displacement x described by y 0 36 x 1 4 the experimental fracture strain and subsidence patterns in clay over en echelon faults can be used as interpretive and predictive tools with which to constrain interpretations of static field examples especially in pull apart basins on the crustal scale where many similarities with the models exist

analog modeling of normal faulting above middle east domes during regional extension we study the effects of planform dome shape on fault patterns developing with and without concurrent regional extension oriented oblique to the long axis of the dome the motivation was the need to understand fault and fracture patterns in two adjacent mature hydrocarbon fields in the middle east one an elliptical dome and one an irregularly shaped dome the largest faults have throws of approximately 30 m 98 ft which is close to the resolution limit of older two dimensional seismic reflection data the known fault trends are not parallel to the highest transmissivity direction but could form compartment boundaries fault and fracture patterns developed over the modeled domes provide insight into the populations of faults and fractures that are likely to exist in the reservoirs but have been undetected because they are at or below the resolution limit of reflection seismic data major domal structural elements crestal fault systems end splay systems and radial faults are observed in modeled domes rising both with and without concurrent regional extension experimental results indicate that fault and fracture patterns are influenced by the effects of dome shape regional extension and relative timing of uplift with respect to regional extension the expression of particular sets of faults and fractures associated with concurrent doming and regional extension depends on the interaction among regional extension outer arc extension over the dome and tangential extension around the dome margins our results also indicate that the two adjacent natural domes possibly experienced different kinematic histories from those previously interpreted

significance of the 1982 2014 campi flegrei seismicity preexisting structures hydrothermal processes and hazard assessment we find that the double difference relocated seismicity which occurred over the last 30 years at campi flegrei was triggered by the uprising of fluids preferentially concentrated along onshore and offshore nw striking preexisting caldera faults focal volumes of the 2005 2014 seismicity do not overlap that of the 1982 1984 period when a major uplift of 1 8 m occurred in the central sector of the caldera this indicates a transition from an elastic to a plastic behavior due to fluid saturation and heating of the rocks in the hydrothermal reservoir the 2012 2014 deeper earthquakes are located in a low vp vs zone at the western boundary of the hydrothermal reservoir where a volume increase from a magmatic body at 3 5 km depth has been recognized the progressive rheological change from elastic to plastic in the upper 4 km of the crust implies that a slow upward migration of magma may not necessarily be preceded by earthquakes or swarms

artemis surface expression of a deep mantle plume on venus artemis a unique 2600 km diameter circular feature on venus defies geomorphic classification as a corona crustal plateau or volcanic rise artemis is similar in size to plateaus and rises yet topographically resembles a corona geologic mapping using correlated digital remote data sets including nasa magellan c1 c2 and f scale synthetic aperture radar sar imagery altimetry and synthetic stereo has led to a determination of the geologic history of artemis artemis comprises a large topographic welt that includes a paired circular 1 km deep trough artemis chasma and 1 km high outer rise thus artemis is divisible into chasma trough interior region and exterior region the chasma hosts trough normal faults and folds the interior includes five 350 km diameter coronae quasi circular features marked by radial and or concentric fractures that record rich tectono volcanic histories radial extension fractures and trough concentric wrinkle ridges dominate the exterior tectonic fabric artemis formed as a coherent entity the coronae chasma chasma structures radial fractures and wrinkle ridges are all consistent with a deep plume model for artemis formation rising and flattening of the plume head led to early uplift doming and radial fracturing as the plume head collapsed vertically and spread laterally likely causing outward migration of the trough as well as fracturing and wrinkle ridge formation outboard of the trough within the trough material was pulled downward forming normal faults and folds the plume continued to spread laterally outboard of the trough resulting in continued radial fracturing and wrinkle ridge formation small scale interior convection cells or compositional diapirs resulted in coronae with radial fractures and or concentric fractures and or folds and associated volcanism artemis is akin in its formation to crustal plateaus and volcanic rises and likely formed during the transition from globally thin to thick lithosphere

paleostress pattern and salt tectonics within a developing foreland basin north western subhercynian basin northern germany analysing the paleostress field in sedimentary basins is important for understanding tectonic processes and the planning of drilling campaigns the subhercynian basin of northern germany is a perfect natural laboratory to study the paleostress field in a developing foreland basin the simple layer cake geometry of the basin fill is dominated by several piercing and non piercing salt structures we derived the paleostress field from the orientation of fracture sets faults slickensides and stylolites on a regional scale the basin fill is characterized by a horizontal compressional paleostress vector that is mainly nne ssw oriented which reflects the late cretaceous inversion phase in central europe we show that the local paleostress field is distinctly perturbated due to the salt structures along the edge of the salt pillows the maximum horizontal paleostress vector is deflected by up to 90 from the regional trend in the case of the elm salt pillow it forms a radial pattern restoration of balanced cross sections demonstrates at least 9 of the shortening of the north western part of the subhercynian basin was achieved by folding the salt structures in the north western subhercynian basin are the result of varying stress conditions initial extension in the triassic caused first salt movements that prevailed during the jurassic and early cretaceous most important is the late cretaceous contractional phase that shortened the diapirs and led to the formation of the salt pillows between diapirs due to detachment folding we derive four main controlling factors for such salt dominated contractional basins 1 the wedge shape basin fill is the product of the dynamic load at the southern margin of the basin 2 a basal salt layer fed the diapirs and acted as a detachment horizon during the later shortening 3 detachment folding was the dominating deformation mechanism during contraction and 4 the pre existing diapirs controlled the position of the detachment folds

fracture pattern analysis as a tool for constraining the interaction between regional and diapir related stress fields poza de la sal diapir basque pyrenees spain during diapir evolution the local stress field results from the interaction between diapirrelated and remote regional stress fields the fracture pattern hosted in the overburden can register this evolving interaction providing significant insights for the unravelling of the diapir kinematics in this work we present the example of the poza de la sal diapir which is a salt diapir that pierces the synorogenic deposits of the basque pyrenees the integrated analysis of mesostructural data which includes field collected faults joints and fracture traces digitalized on high resolution orthophotos allowed us to establish an evolutionary model for the stress field around diapirs the presented data support the idea that during diapir evolution stress fields evolve from mostly regional related to mostly diapir related contrasting with other geological data seismic data geological map and cross section we observe that different methods provide complementary information coherent with the proposed evolutionary model of the poza de la sal diapir the study of fracture development associated with the growth of salt diapirs is of interest for both academic and industrial purposes in fact fractures play an important role in fluid flow and its accumulation in salt diapir related reservoirs johnson bredeson 1971 koestler ehrmann 1987 davison et al 2000a b on the other hand the analysis of fracture patterns is useful to constrain the host structure evolution thorbjornsen dunne 1997 tavani et al 2008 and accordingly can provide useful information for understanding diapir kinematics alsop 1996 stewart 2006 yin groshong 2007 yin et al 2009 the fracture pattern associated with salt diapirs and in general with doming structures is characterized by two classes of elements radial and concentric fig 1a b e g parker mcdowell 1955 withjack 1979 squyres et al 1992 branney 1995 malthe sorenssen et al 1999 rowan et al 1999 2003 davison et al 2000a b freed et al 2001 stewart 2006 this pattern is documented in simple structures where the remote stress field is negligible in relation to the diapir related stress fields when such a condition is not verified the interaction of these two stress fields leads to the development of more complex patterns ode 1957 withjack scheiner 1982 studies of interacting regional and punctual stress fields e g ode 1957 indicate that the influence of diapir induced stress progressively reduces away from the dome i e the punctual structure as a consequence far from the diapir the fracture pattern responds to the remote stress field and approaching the diapir the fracture pattern tends to be radial and concentric fig 1c although these patterns have been observed by several authors in different structures withjack scheiner 1982 mege masson 1996 ernst et al 2003 there are no detailed field studies focusing on this topic in this work we present a simple 2d theoretical stress field model where the stress tensor resulting from the interaction between remote and diapirrelated stress fields is assumed to be for a fixed distance from the diapir centre a 2 2 matrix provided by the sum of the horizontal components of the two stress tensors the eigenvectors associated with this matrix are assumed to be the principal axes of the local stress field the working hypothesis is that if the stress field changes the azimuth of fractures joints developed under these stress fields also change by understanding interactions between diapir related and regional stress fields we can predict the azimuth of the developed fractures to test the validity of this theoretical model we have applied it to a well exposed salt diapir located at the western pyrenees poza de la sal diapir this is a near circular diapir with a mainly carbonate overburden affected by a complex pattern of fractures results of this comparison indicate that despite its simplicity the provided stress model is a useful tool for understanding the kinematics of salt diapirs accordingly in this paper we provide from alsop g i archer s g hartley a j grant n t hodgkinson r eds 2012 salt tectonics sediments and prospectivity geological society london special publications 363 521 532 http dx doi org 10 1144 sp363 25 the geological society of london 2012 publishing disclaimer www geolsoc org uk pub ethics guidelines to obtain a fracture pattern using the theoretical model presented to complement other techniques of investigation such as field work or 3d seismic interpretations

the role of pre existing tectonic structures and magma chamber shape on the geometry of resurgent blocks analogue models abstract a set of analogue models has been carried out to understand the role of an asymmetric magma chamber on the resurgence related deformation of a previously deformed crustal sector the results are then compared with those of similar experiments previously performed using a symmetric magma chamber two lines of experiments were performed to simulate resurgence in an area with a simple graben like structure and resurgence in a caldera that collapsed within the previously generated graben like structure on the basis of commonly accepted scaling laws we used dry quartz sand to simulate the brittle behaviour of the crust and newtonian silicone to simulate the ductile behaviour of the intruding magma an asymmetric shape of the magma chamber was simulated by moulding the upper surface of the silicone the resulting empty space was then filled with sand the results of the asymmetric resurgence experiments are similar to those obtained with symmetrically shaped silicone in the sample with a simple graben like structure resurgence occurs through the formation of a discrete number of differentially displaced blocks the most uplifted portion of the deformed depression floor is affected by newly formed high angle inward dipping reverse ring faults the least uplifted portion of the caldera is affected by normal faults with similar orientation either newly formed or resulting from reactivation of the pre existing graben faults this asymmetric block resurgence is also observed in experiments performed with a previous caldera collapse in this case the caldera collapse related reverse ring fault is completely erased along the shortened side and enhances the effect of the extensional faults on the opposite side so facilitating the intrusion of the silicone the most uplifted sector due to an asymmetrically shaped intrusion is always in correspondence of the thickest overburden these results suggest that the stress field induced by resurgence is likely dictated by the geometry of the intruding magma body and the related deformation is partially controlled by pre existing tectonic and or volcano tectonic structures

restoration of cross sections above intrusive salt domes the applicability of bed length restoration to the sequence above a vertical intrusion of salt was tested on an experimental model that included deposition of units during uplift restoration of the model resulted in an apparently unbalanced cross section due to excess bed length in the pre growth interval the excess bed length was due to significant internal strain for a correct restoration it is thus important to distinguish between the growth and pre growth sequences the thinning index which quantifies the thinning onto the uplift aids in making this distinction a thinning index vs depth curve has a sharp inflection at the top of the pre growth sequence the pre growth sequence is restored by area balancing the growth sequence deforms mainly by formation of a restal graben with little other strain sequential restoration of growth intervals shows the growth history of the dome when applied to the pool creek salt dome from the mississippi interior salt basin the methods developed for the model served to separate the pre growth from the growth sequence and to indicate a growth history of vertical intrusion changing through time to vertical intrusion plus regional extension

implications of passive salt diapir kinematics for reservoir segmentation by radial and concentric faults abstract reservoirs associated with salt diapirs that are circular or elliptical in plan view can be segmented by radial faults concentric faults both or neither explanations for this variation are offered based on integration of fault kinematics published studies and seismic examples strata around diapirs can be divided into three structural domains with characteristic fault styles 1 roof zone between the present day depositional surface and crest of a buried inactive diapir this zone is characterised by doming radial faults and occasionally conic graben doming is usually caused by differential compaction and increases with depth 2 a steeply dipping sheath of strata surrounds the diapir out to a distance of less than one diapir radius recording near surface diapir growth in poorly lithified sediments these contain early gravity slumps and late concentric extensional faults regional layer bound polygonal fault systems form radial faults within approximately one diapir radius the only significant radial faulting mechanism below the roof zone 3 diapir root zone of strata whose structural architecture records the diapirs initiating mechanism typically rim synclines or graben that detach on the salt source layer concentric faults at radial distances of a kilometre or more have been found only in root zone rim synclines and sheared sheath strata these models and observations can assist seismic interpretation and structural model building in areas of poor geophysical imaging for instance below overhanging salt

experimental formation of brittle structural assemblages in oblique divergence abstract a series of experiments is reported in which brittle minor structures are initiated in narrow deformation zones in clay under conditions of kinematically controlled oblique divergent displacement nineteen settings of boundary displacement angle were used from pure wrench to pure divergence under conditions favouring either faults dry experiments or extension fractures wet experiments pure wrench produced the well known assemblage of riedel strike slip faults whereas experiments in pure divergence produced conjugate arrays of normal faults and extension fractures with a dihedral angle of 30 bisected by the direction of the zone as has been described in rift zones experiments with boundary displacements at intermediate settings show a continuum of structural orientations and dihedral angles between these two extremes a boundary between assemblages dominated by strike slip faults and extensional faults was found at a displacement angle of 45 from the deformation zone these results are interpreted kinematically in terms of 1 principal axes of infinitesimal incremental strain 2 material dilatancy control on shear structure dihedral angles and 3 whether the vertical strain in divergent wrench settings is a thickening strike slip assemblage or a thinning normal fault assemblage

the role of extensional structures on experimental calderas and resurgence the structure and shape of collapses and resurgences is often controlled by pre existing discontinuities such as normal faults in rift zones in order to study the role of extensional structures on collapse and resurgence we used analogue models dry sand simulated the brittle crust silicone located at the base of the sand pack simulated magma in the experiments regional extension pre dated collapse or resurgence forming normal faults in a graben like structure the graben was filled with additional sand simulating post rift deposits a piston then moved the silicone downward or upward inducing collapse or resurgence within the previously deformed sand the collapses showed an ellipticity length of minor axis length of major axis between 0 8 and 0 9 with the major axis parallel to the extension direction the partial reactivation of the pre existing normal faults was observed during the development of the caldera reverse faults which conversely to what was expected from experiments without pre existing extension became partly inward dipping resurgence showed an elongation of the uplifted part with the main axis perpendicular to the extension direction at depth pre existing normal faults were partly reactivated by the reverse faults formed during resurgence these locally became outward dipping normal faults a total reactivation of pre existing faults was also observed during resurgence the experiments suggest that the observed elongation of calderas and resurgences is the result of the reactivation of pre existing structures during differential uplift such a reactivation is mainly related to the loss in the coefficient of friction of the sand the results suggest that elliptic calderas and resurgences in nature may develop even from circular magma chambers

a structural outline of the yenkahe volcanic resurgent dome tanna island vanuatu arc south pacific abstract a structural study has been conducted on the resurgent yenkahe dome 5 km long by 3 km wide located in the heart of the siwi caldera of tanna island vanuatu arc south pacific this spectacular resurgent dome hosts a small caldera and a very active strombolian cinder cone the yasur volcano in the west and exhibits an intriguing graben in its central part detailed mapping and structural observations make it possible to unravel the volcano tectonic history of the dome it is shown that following the early formation of a resurgent dome in the west a complex collapse caldera plus graben occurred and this was associated with the recent uplift of the eastern part of the present dome eastward migration of the underlying magma related to regional tectonics is proposed to explain this evolution

simulation of subseismic joint and fault networks using a heuristic mechanical model author s gillespie p casini g iben h o brien jf abstract 2018 the author s flow simulations of fractured and faulted reservoirs require representation of subseismic structures about which subsurface data are limited we describe a method for simulating fracture growth that is mechanically based but heuristic allowing for realistic modelling of fracture networks with reasonable run times the method takes a triangulated meshed surface as input together with an initial stress field fractures initiate and grow based on the stress field and the growing fractures relieve the stress in the mesh we show that a wide range of bedding plane joint networks can be modelled simply by varying the distribution and anisotropy of the initial stress field the results are in good qualitative agreement with natural joint patterns we then apply the method to a set of parallel veins and demonstrate how the variations in thickness of the veins can be represented lastly we apply the method to the simulation of normal fault patterns on salt domes we derive the stress field on the bedding surface using the horizon curvature the modelled fault network shows both radial and concentric faults the new method provides an effective means of modelling joint and fault networks that can be imported to the flow simulator

physical modeling of structures formed by salt withdrawal implications for deformation caused by salt dissolution by creating 15 physical models we investigated deformation above subsiding tabular salt salt walls and salt stocks dry quartz sand simulated a brittle sedimentary roof above viscous silicone representing salt the modeled diapiric walls had linear planforms and rectangular semicircular triangular or leaning cross sectional shapes the stock was cylindrical in models where the source layer or allochthonous salt sheet was initially tabular a gentle flat bottomed syncline bounded by monoclinal flexures formed above a linear zone where the silicone was locally removed above all subsiding diapirs the deformed roof was bounded by an inner zone of steep convex upward reverse faults and an outer zone of normal faults above subsiding diapiric walls extensional and contractional zones were balanced above the subsiding salt stock conical concentric fault zones comprised inner reverse faults and outer normal faults sediments were added both before prekinematic and during synkinematic salt withdrawal in entirely prekinematic roofs reverse fault zones and normal fault zones both widened with time reverse faults propagated upward from the corners of the withdrawing diapirs new reverse faults formed in the footwalls of reverse faults each nearer the center of the deepening roof trough conversely new normal faults formed successively outward from the sagging trough synkinematic deposition retarded faulting but the pattern of inner reverse and outer normal faults was repeated however reverse faults formed successively outward whereas normal faults formed inward new conceptual models suggest that salt dissolution forms similar structures to those physically modeled for salt withdrawal the appropriate physical models resemble natural dissolution structures above tabular salt extension alone above diapirs is not caused merely by salt withdrawal or dissolution but by regional extension or active diapirism

the interaction between regional and local tectonics during resurgent doming the case of the island of ischia italy abstract the volcanic island of ischia is located on the tyrrhenian margin of central italy characterized by plio quaternary nw se and ne sw trending extensional fractures ischia displays a resurgent dome uplifted by at least 800 m in the last 33 ka remote sensing and field data have been collected to study the structural setting of the island the deformation pattern associated with resurgence and the superimposition of the regional and the resurgence induced stress fields nw se and ne sw extensional fracture systems predominate throughout the island and around the resurgent block suggesting a relationship with the regional extensional structures these systems were formed before resurgence and were partly reactivated during resurgence the reactivation of pre existing regional systems during resurgence confined the extent of the uplifted area n s and e w trending systems have been found exclusively at the borders of the dome and are interpreted as being induced by resurgence the topmost resurgent block shows an octagonal shape in map view and is tilted at an angle of 15 around a ne sw trending horizontal axis the block is partly bordered by high angle inward dipping regional faults more than 90 in volume of the volcanic products coeval with resurgence on ischia have been erupted outside the resurgent block area suggesting that the resurgence process locally replaced volcanic activity in the last 33 ka

uplift induced residual strain release and late thrusting extension in the anaran mountain front anticline zagros iran abstract in this work we present and discuss the pattern of extensional faults of the anaran anticline lurestan province of the zagros iran one of the most aesthetically appealing mountain front anticlines of the zaros this 100 km long structure is affected by extensional faults occurring in different along strike sectors of the anticline running parallel and oblique to the local trend of the fold hinge line and having displacements of hundreds of metres relationships between fold growth and extensional deformation are investigated by quantitatively analysing the attributes i e curvature elevation and throw across faults of a 3d surface representing the top of the ilam formation results indicate that the main stage of extensional deformation occurred during folding in particular we deduce that extensional faulting was associated with the erosional uplift of the crestal sector of the anticline where exhumation of previously shortened strata implied release of residual compressive strain with consequent annihilation of the horizontal stress component paralleling the tectonic transport direction this determined the onset of a large scale extensional regime at the shallower structural levels of the growing anticline

analogue models of collapse calderas and resurgent domes collapse calderas and resurgent domes are a common association related to inflation deflation processes in volcanic systems the structure of calderas and domes depends upon the permitted relative movements of crustal volumes at depth the so called space problem in order to study the structures of collapse calderas and resurgent domes and to take the space problem into account several analogue models were made dry quartz sand was used to simulate the rheology of the brittle crust while newtonian silicone putty located at the base of the sand pack simulated the ductile behaviour of the magma a piston moved the silicone putty downward or upward inducing collapse and doming within the sand three separate sets of experiments simulated 1 caldera collapse 2 resurgence and 3 superimposition of resurgence on collapse and vice versa collapse experiments are characterized by the development of two concentric depressions the first formed depression is bordered by outward dipping reverse ring faults the subsequent outer concentric depression is bordered by inward dipping normal ring faults the deformation pattern during resurgence is a function of the overburden thickness t and the dome diameter d for higher t d ratios a dome forms bordered by inward dipping high angle reverse ring faults outward dipping normal ring faults develop at late stages for lower t d ratios the dome shows at late stages a crestal depression accompanied by radial fractures subsequently an apical extrusion of silicone occurs the superimposition of resurgence over collapse and vice versa is characterized by the complete reactivation with opposite kinematics of all the pre existing ring faults during inversion both in caldera and resurgence reverse ring faults form in the early stages due to differential uplift extensional structures subsequently form to accommodate gravitational collapse during the activity of the reverse faults the experiments and the overall similarities with nature suggest that the activity of both reverse and normal faults constitutes a possible solution to the space problem during major collapses or resurgences

fault slip analysis and late exhumation of the tauern window eastern alps exhumation of the eastern alps from the early tertiary to the late miocene was localized mainly in the tauern window a thermal and structural dome located in front of the dolomites indenter stress inversions based on new structural investigations over the entire tauern window indicate a regional zoning of the paleostress field with a predominance of strike slip states of stress in the core of the investigated area and dominant extensional regimes in the eastern and western borders of the dome few inverse fault structures have been highlighted we propose a two stage deformation history in order to explain the different types of structures that characterise the ductile and the brittle domains during the first stage of exhumation of the tauern window corresponding to the folding event the brittle crust was probably dominated by n s shortening and compression the second stage of exhumation was marked by normal faulting at the borders of the dome and strike slip faulting in the core during the second stage the brittle part of the crust that was previously affected by compressive structures belonging to the first stage was eroded normal faulting associated to e w extension along the eastern and western borders of the tauern window was accommodated by strike slip faulting located in the core of the tauern window yielding e w extension and n s shortening the orientation of the extensional axes and the nature of the stress tensors are similar to the ones inferred for the late stage brittle overprint of the internal basement massifs of the central alps pointing to a possible common large scale state of stress acting well beyond the area of the eastern alps

effects of changing stress states on the development of caldera bounding faults geological evidence from kumano caldera japan abstract collapse of a large caldera can cause spatial and temporal perturbations of stress and formation of caldera faults the stress variations influence the direction of slip vectors on the fault planes hence stress estimation is important for the study of caldera forming processes in our paleostress estimation the stress variations in the collapse of the ca 14 ma kumano caldera in japan have been revealed a stress inversion method based on the wallace bott hypothesis was used to compute the orientation of the principal stress axes 1 2 3 and the stress ratio 2 3 1 3 where 0 1 the caldera faults formed simultaneously with the caldera forming ash flow tuff eruption therefore paleostress solutions obtained from slip data measured on such faults show the spatial and temporal changes of the stress at the time of the caldera collapse the computed stress ratio characterizes a pair of stress fields in the early stage the stress field with 1 0 shows a semi radial trajectory of stress 2 and an eastern concentric trajectory of stress 3 this stress regime resulting from pre collapse tumescence counteracts the gravitational force and thus produces smaller net vertical stress the regional tumescence above an inflated magma chamber is the most plausible source of the stress field and it is consistent with the timing of the caldera formation in the late stage the stress field with 0 5 shows the semi radial trajectory of stress 2 and the west convex and concentric trajectory of stress 3 change of the stress ratio from 1 0 to 0 5 implies that increase in the relative magnitude of the stress 1 caused the deeper subsidence of the caldera floor stress variations may be of significant value for reconstructing the structural history of the caldera

experimental models of extensional forced folds we have used single layer and multilayer clay models to study the development of forced folds above normal faults our modeling results show that the deformation patterns associated with extensional forced folding depend on the dip of the underlying normal fault and the presence of layer parallel detachments in single layer clay models extensional forced folds are upward widening monoclines anticlinal axial surfaces dip in the same direction as underlying master normal faults and synclinal axial surfaces dip in the opposite direction of master normal faults most secondary faults are upward steepening normal faults if master normal faults are steeply dipping however many secondary normal faults become high angle reverse faults at shallow depths the propagation and linkage of secondary faults into through going normal faults terminates the development of extensional forced folds more folding occurs prior to fault linkage if the master normal fault is steeply dipping rather than gently dipping most dipping beds and secondary faults are preserved in the hanging walls of the through oing normal faults in multilayer clay models with layer parallel detachments extensional forced folds are also upward widening monoclines slip on the lowest detachment laterally transfers extension induced by normal faulting and forced folding from the master normal fault to the detachment edge slip on overlying detachments accommodates minor thickness changes associated with upward widening of the fold secondary faults include low angle normal faults near the anticlinal axial surface minor thrust faults near the synclinal axial surface and high angle normal faults above the detachment edge the model predicted deformation patterns are similar to those of extensional forced folds from the gulf of suez and offshore norway this similarity suggests that our modeling results apply to extensional forced folds and can provide guidelines for interpreting field well and seismic data

discrete element modeling of the faulting in the sedimentary cover above an active salt diapir geological mapping seismic analyses and analogue experiments show that active salt diapirism results in significant faulting in the overburden strata faults associated with active diapirism generally develop over the crest of the dome and form a radial pattern in this study we have created a 3 d discrete element model and used this model to investigate the fault system over active diapirs the model reproduces some common features observed in physical experiments and natural examples the discrete element results show that most faults initiate near the model surface and have displacement decreasing downward in addition model results indicate that the earliest fault working as the master fault has a strong influence on the subsequent fault pattern the footwall of the master fault is mainly deformed by arc parallel stretching and develops a subradial fault pattern whereas the hanging wall is deformed by both arc parallel stretching and gliding along the master fault and top of salt and hence develops both parallel and oblique faults model results replicate the fault pattern and deformation mechanism of the reitbrook dome germany

physical modelling of overburden deformation around salt diapirs abstract salt diapirs produce highly complex deformation patterns in the surrounding overburden which are difficult to image seismically or model numerically to further the understanding of deformation around salt structures we have used physical models with brittle granular overburdens and simulated sedimentation accompanying diapiric rise rigid linear indentors produce a crestal horst above the indentor with two flanking graben large amounts of indentation produce predominantly reverse faults along the margins of the diapir and extensional faults over the crest in contrast hemispherical indentors produced inward dipping concentric reverse faults forefully intruded polymer diapirs produce a narrow crestal graben above the diapir crest downbuilt polymer diapirs produce extensional faults on the flanks of the diapirs which offset the diapir walls no clear secondary rim synclines were developed as polymer is withdrawn evenly from the whole of the polymer layer across the model strong and anisotropic layered overburden were simulated using cohesive clay and mica respectively detachments were formed along mica layers which suppressed faults with large throws cohesive layer deformation began with tensile fractures permitting rotation of fractured rafts around the sides of the diapir these progressively slip off the crest and create large gaps in the stratigraphy

crustal domains in the northern kaapvaal craton as defined by magnetic lineaments abstract the northern part of the kaapvaal craton and limpopo belt can be subdivided into domains on the basis of aeromagnetic lineament patterns these subdivisions reflect portions of the lithosphere with different tectonic histories and many of these domains correlate with known metamorphic tectonic provinces the dykes causing the lineation pattern intruded intermittently over a very long period of time and within a domain the trend of the intruded dykes is determined not only by the stress field operative at the time of intrusion but also by an inherited fracture pattern in that domain the event that introduced the fracture pattern has to be older than 2456 78 ma and younger than 2603 129 ma the magnetic lineation data show that a 15 anticlockwise rotation of the central zone of the limpopo belt with respect to the southern marginal zone will restore parallelism in the fracture pattern of the two domains the presence of the greenstone belts has no effect on the dyke pattern and domain boundaries cut across these structures

structural evolution of salt influenced fold and thrust belts a synthesis and new insights from basins containing isolated salt diapirs abstract lateral shortening is expressed in unique ways in salt basins especially if pre shortening diapirs are present we present an overview of previously published and new physical models and present new 3 d conceptual models that capture the evolution of shortening structures in salt provinces dominated by precursor isolated diapirs termed isolated diapir provinces in such provinces isolated diapirs form only a minor volumetric component of a sedimentary basin however due to the relative weakness of rock salt and their ability to localize strain during shortening they have a disproportionately large influence on structural development we find three key mechanical principles govern the processes and structural styles developed during shortening of isolated diapir provinces first salt diapirs shorten before surrounding sedimentary rocks due to their relative weakness and so form salients in the thrust front during early shortening second diapirs tend to nucleate folds and faults which radiate out from the diapirs third as diapir walls converge the roof must shorten extrusive salt sheets are expelled through thin roofs but thicker roofs resist piercement and so tend to undergo complex folding and faulting as a result of these principles the first order controls on the structural styles expressed across a shortened isolated diapir province are the configuration the diapir array prior to shortening the connectivity of these diapirs prior to shortening total strain magnitude and diapir roof thickness second order controls include the initial cross sectional and map view geometry of diapirs diapir size and diapir orientation with respect to the shortening direction