release fault a variety of cross fault in linked extensional fault systems in the sergipe alagoas basin ne brazil abstract two types of cross faults are herein recognized transfer faults and the newly termed release faults transfer faults form where cross faults connect distinct normal faults and horizontal displacements predominate over vertical ones in contrast release faults form where cross faults associated with individual normal faults die out within the hangingwall before connecting to other normal faults and have predominantly vertical displacements release faults are geometrically required to accommodate variable displacements along the strike of a normal fault thus they form to release the bending stresses in the hangingwall and do not cut normal fault planes nor detachment surfaces at depth release faults have maximum throws adjacent to normal faults and may be nearly perpendicular or obliquely oriented to the strike of the latter such geometry appears not to depend upon pre existing weaknesses but such variable orientation to normal faults is an inherent property of release faults release faults commonly appear as simple normal faults in seismic sections without implying extension along the strike of rift and basins three dimensional strain deformation occurs in the hangingwall only between the terminations of an individual normal fault but regionally release faulting is associated with plane strain deformation in linked extensional fault systems

the subsidence history of conoco well 15 30 1 central north sea abstract the depth of deposition of the sediments from north sea well conoco 15 30 1 is determined using faunal and sedimentary evidence the effects of sedimentary load corrected for compaction and variations in water depth and sea level are removed to obtain the subsidence of the basement when covered by water only a crustal stretching and lithospheric thinning of 25 35 1 35 can account for both the initial fault controlled subsidence and the later uniform subsidence

orthorhombic fault fracture patterns and non plane strain in a synthetic transfer zone during rifting lennard shelf canning basin western australia abstract a complex series of faults occur within transfer zones normal to the wnw trending rifted northern margin of the canning basin western australia these zones controlled basinal fluid flow and the formation of some carbonate hosted mississippi valley type zn pb deposits along the basin margin during devonian to carboniferous rifting the study area has a regional fault geometry similar to a synthetic overlapping transfer zone surface and underground mapping in this transfer zone combined with 3d modelling indicate the faults and related extension fractures have an orthorhombic geometry the orthorhombic fault fracture mesh developed in response to three dimensional non plane strain in which the intermediate finite extension magnitude was non zero pre mineralisation marine calcite fill in the fault fracture mesh indicates that it formed early in the deformation history later deformation that overprints the zn pb mineralisation and fault fracture mesh was associated with a different maximum extension direction and this modified and reactivated the faults with both dip slip and oblique slip movement and tilting of earlier structures the orthorhombic geometry is not observed at a regional scale 10 10 km indicating probable scale dependant behaviour this study indicates that this transfer zone developed either by 1 strain partitioning with synchronous strike slip structures and adjacent zones of non plane extension or 2 by a component of non plane extension sub parallel to the basin margin followed by subsequent transtensional overprint of the system preferred model synthetic overlapping transfer zones are inferred to be key regions where orthorhombic fault geometries may develop

working in complex areas new restoration workflow based on quality control 2d and 3d restorations when working in complex areas the explorationist needs to construct 3d models and to check their coherency coherence can be analyzed on the current geometry but could also be quantified through restoration to achieve this restoration i e the search for an initial geometry with a realistic deformation pathway between the initial and the final geometries appropriate tools are necessary these include classical cross section balancing surface unfolding and volumetric restoration in this paper we will describe a workflow to do quantitative structural geology in complex areas this includes the construction and quality control of the surfacic model the line balancing the cross section surface and multi surface restoration and the volumic restoration in addition to the quality control of the geometries the restoration allows us to compute strain tensors this can be done in the three types of restoration and visualized through ellipses and ellipsoids resp 2d and 3d that represent the main strain or stress vectors we shall discuss the relationship between these strain tensors and the expected fracture network in density as in direction

the calculation of bulk strain in oblique and inclined balanced sections abstract the calculation of bulk strain from balanced sections is a technique commonly used in the study of orogenic belts the validity of a balanced section is often enhanced by controls such as seismic and or borehole data the construction of a conventional vertical section perpendicular to orogenic strike i e in the transport direction may not allow control data to be directly incorporated into the section the control data can be projected into the plane of the section or alternatively the section may be constructed in an orientation such that it contains the available control data in the case of a vertical section constructed at an oblique angle to the transport direction the bulk strain value obtained is a minimum and can be corrected to the true value of bulk strain in the perpendicular vertical section by a simple trigonometric calculation if the section is perpendicular to strike but inclined at an angle to the vertical the correction of the bulk strain values is mathematically unique to the section this problem can be overcome by using a digitizing table in conjunction with a simple computer program the general case of a section both oblique to the strike direction and inclined to the vertical can be resolved by removing the effects of the inclination to produce a vertical oblique section from which the bulk strain can be obtained and corrected in realistic geological problems the oblique section will be a more common problem than the inclined section in both cases deviations of 10 and less introduce such small errors in the estimates of bulk strain that their effects can be ignored

miocene to recent cariaco basin offshore venezuela structure tectonosequences and basin forming mechanisms abstract the cariaco basin located 40 km off the central part of the coast of venezuela is the largest 4000 km 2 and bathymetrically deepest 1400 m bsl neogene fault bounded basin within the right lateral strike slip plate boundary zone that separates the caribbean and south american plates using subsurface geophysical data we test two previously proposed tectonic models for the age distribution and nature of east west striking strike slip faults and basin forming mechanism for the two main depocenters of the cariaco basin the earliest interpretation for the opening of the twin cariaco depocenters by schubert 1982 proposes that both depocenters formed synchronously by extension along transverse north south normal faults at a 30 km wide rhomboidally shaped pull apart basin between the right lateral east west striking and parallel san sebastian and el pilar fault zones a later model by ben avraham and zoback 1992 proposes that both depocenters formed synchronously by a process of transform normal parallel extension or rifting in a north south direction orthogonal to the east west striking and parallel strike slip faults we use more than 4000 km of 2d single and multi channel seismic data tied to 11 wells to map 5 tectono stratigraphic sequences and to produce a series of structural and isopach maps showing how the faults that controlled both cariaco depocenters evolved from paleogene to the present comparison of fault and isopach maps for dated horizons from paleogene to late neogene in age show three main phases in basin development 1 from middle miocene to pliocene the west cariaco basin formed as a rhomboidally shaped pull apart at a 30 km wide stepover between the northern branch of the san sebastian fault and the el pilar fault zone 2 during the early pliocene a new strike slip fault transected the west cariaco basin southern branch of the san sebastian fault and caused extension to cease and 3 during the early pliocene to recent a lazy z shaped pull apart formed along the curving connection between the southern branch of the san sebastian and el pilar fault zones

the relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls abstract we derive an analytical expression that relates the shape of a fault in cross section to the shape of the bedding horizons in its hanging wall block the expression assumes that the hanging wall deforms by simple shear and that the footwall remains undeformed throughout although this paper concentrates on normal faults the expression is equally valid and applicable to thrust faults the direction of simple shear in the hanging wall block is arbitrary and has a dramatic effect on the predicted fault or bedding geometry there is no reason to believe that the simple shear occurs on vertical planes as is commonly assumed in graphical approaches to this problem and ignoring the presence of inclined simple shear is likely to lead to considerable underestimates of the amount of extension across normal faults and in the amount of shortening across thrusts similar though more complicated expressions can be obtained when compaction within the hanging wall block is taken into account for a planar normal fault such compaction may result in the development of a hanging wall syncline

mechanics of wedge shaped fault blocks 2 an elastic solution for extensional wedges listric planar low angle and high angle normal faults are common in hanging walls of detachment faults an elastic model has been developed to evaluate the role of basal friction wedge geometry pore fluid pressure within the wedge and boundary conditions applied along the wedge rear in controlling the stress distribution in an extensional fault wedge this model assumes a stress free condition on the top and fractional sliding on the base of the wedge respectively a linear variation of stress components as a function of depth along the wedge rear and a uniform horizontal stress applied on the wedge toe the model predicts that 1 for the surface slope equal to zero a thin wedge favors development of high angle and planar faults whereas a thick wedge favors development of low angle and listric normal faults variation of pore fluid pressures along the basal detachment fault hardly affects the predicted fault geometry pore fluid pressure within the wedge is critical in controlling the state of stress in the wedge higher values of the internal pore fluid pressure promote low angle normal faulting and locally high angle reverse faulting 2 variation of surface slope and the uniform horizontal normal stress applied at the wedge toe does not affect the predicted fault geometry appreciably although the distribution of deviatoric stress magnitude changes for different cases and 3 listric normal faults are predicted in all computations and the fault curvature increases as the vertical gradient of the horizontal normal stress along the wedge rear the wedge angle surface slope dip angle and the internal pore fluid pressure increase the model provides a simple conceptual guide to deciphering the formation of complex fault geometries and cross cutting relationships as a function of mechanical parameters related to geologic processes and settings for example it provides an explanation for why low angle normal faults cut high angle normal faults in hanging walls of some detachment fault systems in the u s cordillera

a systematic technique for the sequential restoration of salt structures abstract a method is described for the sequential restoration of cross sections in areas of salt tectonics where deformation is confined to the salt and higher layers the subsurface geometry evolves with time through the interaction of various processes sedimentation compaction isostatic adjustment thermal subsidence if present faulting and salt withdrawal diapirism the technique systematically calculates and removes the effects of each of these processes during specified time intervals defined by the interpreted horizons it makes no assumptions about salt kinematics and generally results in the area of the salt layer changing through time the method is described for restoration of extensional terranes but it is also suitable for areas of contractional salt tectonics with only minor modifications after converting an interpreted seismic profile to depth the top layer is stripped off and the underlying section is decompacted according to standard porosity depth functions a deep baseline unaffected by compaction or deformation is used to restore any isostatic compensation or thermal subsidence isostasy is calculated according to the airy model and differential sedimentary loading across a section is shown to be approximately balanced by changes in salt thickness so that the load is evenly distributed after these processes have been reversed the resulting geometry and the seismic data are used to create the sea floor template for structural restoration fault offsets are removed and the layers down to the top salt are restored to this template while the base salt remains fixed the resulting space between the restored top salt and the fixed base salt defines the restored salt geometry in addition the difference between the sea floor template and a fixed sea level provides a measure of the change in water depth ignoring eustatic changes in sea level the technique is applied to an interpreted seismic profile from the eastern green canyon ewing bank area of offshore louisiana the section is characterized by a variety of salt structures including salt rollers a diapiric massif a remnant salt sheet and a salt weld which are shown to have derived from an originally continuous salt sheet which has been modified by sedimentary loading early loading created vertical basin growth that was accommodated primarily by salt withdrawal and associated diapiric rise through the process of downbuilding once the salt weld formed continued sedimentation was accommodated by a lateral increase in basin size caused by down dip extension on listric growth faults

tectonic evolution of the northumberland basin the effects of renewed extension upon an inverted extensional basin the northumberland sedimentary basin has a history of repeated extensional and contractional tectonic phases and a study of the deformation interference pattern and sedimentary record allows the identification of the tectonic state through time initial rifting is represented by a thick dinantian sedimentary fill but carboniferous extension is thought to have ceased by the early namurian in order to explain the development of certain facies patterns during the westphalian thermal subsidence phase of the evolution of the northumberland basin some syn depositional extensional fault movements are required at other times in the westphalian compaction induced subsidence was the dominant control on facies distribution a single phase of e w to se nw variscan compression commenced during or after late westphalian times and ceased prior to the intrusion of the whin sills and dykes subsequent permo mesozoic extension with a right lateral shear component re activated pre existing normal fault lines these later structures may be interpreted as being listric in form shallowing onto decollement surfaces within the carboniferous basin fill and overlie the buried faulted margin at the southern side of the basin

internal structure of uppermost oceanic crust along the western blanco transform scarp implications for subaxial accretion and deformation at the juan de fuca ridge 1 the uppermost 2 km of oceanic crust created near the southern end of the juan de fuca ridge 60 mm yr full spreading rate is exposed in a tectonic window created along the north wall of the blanco transform fault a total of 27 submersible dives transect this escarpment over a distance of 30 km corresponding to 1 m y of spreading history in this exposure weakly deformed basaltic lavas grade downward into much more intensely fractured lavas cut by basaltic dikes lava flow surfaces dip persistently to the northwest toward the spreading center and the dikes dip southeast away from the spreading center the underlying sheeted dike complex is composed of subparallel dikes that dip moderately to the southeast discrete faults and more distributed cataclastic deformation zones separate the panels of sheeted dikes from one another disruption of the lava and dike units are interpreted as a result of dramatic subaxial vertical mass transport that created the accommodation space for the accumulation of a thickness of 1000 1500 m of basaltic lava the observed patterns of tilting of lavas and dikes imply subsidence beneath the region of active volcanism 3 km wide that is most rapid near the axis and diminishes quickly off axis deformation that accommodates this subsidence has generated extensive fracture porosity in the subaxial region that could strongly influence upper crustal hydrothermal pathways alteration history seismic properties and the distribution of subsurface biological communities

palinspastic reconstruction of structure maps an automated finite element approach with heterogeneous strain existing methods for the palinspastic reconstruction of structure maps do not adequately account for heterogeneous rock strain and hence cannot accurately treat features such as fault terminations and non cylindrical folds we propose a new finite element formulation of the map reconstruction problem that treats such features explicitly in this approach a model of the map surface with internal openings that honor the topology of the fault gap network is constructed of triangular finite elements both model building and reconstruction algorithms are guided by rules relating fault gap topology to the kinematics of fault motion and are fully automated we represent the total strain as the sum of a prescribed component of locally homogeneous simple shear and a minimum amount of heterogeneous residual strain the region within which a particular orientation of simple shear is treated as homogenous can be as small as an individual element or as large as the entire map for residual strain calculations we treat the map surface as a hyperelastic membrane a globally optimum reconstruction is found that unfolds the map while faithfully honoring assigned strain mechanisms closes fault gaps without overlap or gap and imparts the least possible residual strain in the restored surface the amount and distribution of the residual strain serves as a diagnostic tool for identifying mapping errors the method can be used to reconstruct maps offset by any number of faults that terminate branch and offset each other in arbitrarily complex ways

the ardeche palaeomargin of the south east basin of france mesozoic evolution of a part of the tethyan continental margin geologie profonde de la france programme abstract this paper incorporates the results of seismic and gravity investigations borehole data and studies of sedimentology biostratigraphy sequence stratigraphy and structural geology carried out in the framework of the deep geology of france programme the main purpose of the paper is to define the structure and to reconstruct the evolution of the ardeche palaeomargin of the south east basin of france from the stephanian to the end of the mesozoic the acquisition and processing of three seismic reflection profiles the drilling of two scientific boreholes ba1 and mm1 and subsequent structural modelling with the use of cross section balancing techniques applied to both the depth migrated seismic and geological sections provide new geometrical constraints which lead to the following hypothesis of the geodynamic evolution of the margin 1 1 late palaeozoic extension with the development of high angle basement faults asymmetrical permian half grabens pre extension sedimentary cover 2 2 during the middle triassic a pre rift stage with the creation of small fault blocks and in the late triassic the formation of an e w flexure 3 3 end lias early jurassic to middle jurassic formation of a major detachment in the carboniferous coal measures leading to complete decoupling of the mesozoic sedimentary cover from the basement this episode of extension coeval with the opening of tethys can be related to a phase of episodic rifting between the late sinemurian and the late bathonian i e during 30 ma 4 4 late jurassic to early cretaceous thermal subsidence with regional downwarping of the basement towards the east 5 5 after the late cretaceous the period of maximum burial pyrenean and alpine deformation in the south and east causing progressive uplift of the ardeche palaeomargin as much as two kilometres of mesozoic deposits subsequently being eroded from the section during the tertiary

irregular earthquake cycle along the southern tianshan front aksu area china 1 a long deformation record 16 5 ka showing nonsteady earthquake recurrence is established for the aksu thrust tianshan china on the basis of cosmogenic 10be dating of faulted surfaces topographic leveling across the aksu fault scarp indicates up to 10 m uplift across a moraine abandoned 16 5 ka and similar uplift of 6 m across two inset surfaces yielding ages of 12 5 and 5 ka successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period these data show that the aksu thrust fault was quiet for at least 7500 years and active in the last 5000 years and probably in the interval 16 5 12 5 ka the seismic cycle along the aksu thrust fault over the last 16 500 years was thus strongly irregular showing long quiescence and clustering which is a challenge for paleoseismology and hazard assessment this irregularity also makes it more difficult to estimate long term shortening rates nevertheless we are able to constrain a minimum total shortening rate 7 mm yr across the southern tianshan front for the last 12 500 years that is about a third of the total geodetic rate for the western tianshan 20 mm yr

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

subsidenz und tektonik des saar nahe beckens sw deutschland the saar nahe basin in sw germany is one of the largest permo carboniferous basins in the internal zone of the variscides its evolution is closely related to movements along the hunsruck boundary fault which separates the rhenohercynian and the saxothuringian zones recent deep seismic surveys indicate that the saar nahe basin formed in the hanging wall of a major detachment which soles out at lower crustal levels at about 16 km depth oblique extension along an inverted variscan thrust resulted in the formation of a half graben within more than 8 km of entirely continental strata accumulated the structural style within the basin is characterized by normal faults parallel to the basin axis and orthogonal transfer fault zones balanced cross section construction and subsidence analysis indicate extension of the orogenically thickened lithosphere by 35 subsidence modeling shows discontinuous depth dependent extension with laterally varying extension factors for crust and mantle lithosphere thus the offset between maximum rift and thermal subsidence can be explained by a zone of mantle extension shifted laterally with respect to the zone of maximum crustal extension

a mechanism for decoupling within the oceanic lithosphere revealed in the troodos ophiolite contrasting kinematic histories recorded in the sheeted dykes and underlying plutonic rocks of the troodos ophiolite provide a new perspective on the mechanical evolution of oceanic spreading centres the kinematic framework of the decoupling zone that partitions deformation between the sheeted dykes and plutonics contrasts with low angle detachment models for slow spreading ridges based on continental rift analogues a model for the generation of multiple horizontal decoupling horizons linked by planar normal faults demonstrates new possibilities for the kinematic and rheological significance of seismic reflectors in oceanic lithosphere

restoration in plan view of faulted upper cretaceous and oligocene horizons and its bearing on the history of salt tectonics in the campos basin brazil abstract in the campos basin atlantic margin of brazil cretaceous and tertiary sediments show abundant evidence for thin skinned deformation above a layer of aptian salt near the coast there is a domain of downslope extension further offshore a domain of donwslope contraction thus we attribute the domainal pattern to gravitational gliding on the salt layer gravitational gliding appears to be driven primarily by surface slopes each material particle tends to move in the direction of steepest slope if topography is irregular particle paths diverge or converge deformation then differs from a plane strain and vertical cross sections cannot be individually balanced or restored we have therefore developed a method for restoring non plane deformation in extensional domains assuming that blocks between faults are rigid we restore stratigraphic horizons in plan view by least squares minimization of distances across fault separations cut off lenses obtaining fields of finite horizontal displacements for selected areas in the extensional domain of the campos basin where divergent gravitational gliding has led to extension in various horizontal directions we have restored two stratigraphie markers an upper cretaceous and an oligocene horizon for each horizon displacement vectors diverge seawards forming a fanlike pattern with a degree of mirror symmetry nevertheless there are major differences between the upper cretaceous and oligocene patterns both for faults and for displacements we infer that this resulted from the development during the tertiary of a propagating deltaic front whose sediment load drove the divergent gravitational gliding and induced a new fault pattern

mechanical response to stratigraphic inhomogeneity during extension and surface expression of buried structures gulf of suez egypt abstract mechanical response of the stratigraphic succession to rifting in the gulf of suez egypt varies depending on the degree of competence of the rock units this mechanical stratigraphy has been documented by observational evidence from field surveys in the northern esh el mallaha and in the ras issaran area in conjunction with seismic reflection data complex response patterns to basement rooted block faulting is seen on several scales in both the prerift and synrift rocks the prerift section is divided into three major units based on mechanical response precambrian basement pre cenomanian nubian sandstone and cenomanian through eocene stable platform marine rocks brittle faulting in the basement propagates into the nubian sandstone by densely fracturing the latter parallel to the fault planes the overlying inhomogeneous cenomanian eocene section drapes and folds over underlying structural elements these rocks contain complicated structures due to the interlayering of thin brittle and ductile beds the incompetent units allow bedding parallel detachment and also flow into voids created during faulting or folding of the competent units the synrift section comprises three major stratigraphic units each of which reacts differently to block faulting these are the early miocene carbonate clastic section the middle late miocene evaporite section and the onshore pliocene recent clastic passive cover sequence in general the lower synrift rocks respond to deformation much like the cenomanian eocene units draping and folding due to interlayered brittle and ductile beds seismic reflection data indicate that the evaporite section is a major detachment zone with faults in underlying units dying out upwards as the ductile salts or anhydrites drape and flow structural response in this section is varied and complex the deformation of the evaporites breaks the overlying passive cover rocks with faults in the latter soling into the underlying ductile strate on gravel plains flanking the gulf of suez the neotectonic fault pattern and resulting topographic and drainage changes reflect underlying structures the faults breaking the passive cover sequence at the surface initially form en echelon traces with continued movement these coalesce into straight or curved often splaying fault traces where the evaporite section reaches a significant thickness the structures seen at the surface may be entirely decoupled from those of the prerift and early synrift sequences

reverse drag revisited why footwall deformation may be the key to inferring listric fault geometry abstract although reverse drag the down warping of hanging wall strata toward a normal fault is widely accepted as an indicator of listric fault geometry previous studies have shown that similar folding may form in response to slip on faults of finite vertical extent with listric or planar geometry in this study we therefore seek more general criteria for inferring subsurface fault geometry from observations of near surface deformation by directly comparing patterns of displacement stress and strain around planar and listric faults as predicted by elastic boundary element models in agreement with previous work we find that models with finite planar planar detached and listric detached faults all develop hanging wall reverse drag folds all of these model geometries also predict a region of tension and elevated maximum coulomb stress in the hanging wall suggesting that the distribution and orientation of near surface joints and secondary faults may also be of limited utility in predicting subsurface fault geometry the most notable difference between the three models however is the magnitude of footwall uplift footwall uplift decreases slightly with introduction of a detachment and more significantly with the addition of a listric fault shape a parametric investigation of faults with constant slip ranging from nearly planar to strongly listric over depths from 1 to 15 km reveals that footwall fold width is sensitive to fault geometry while hanging wall fold width largely reflects fault depth application of a graphical approach based on these results as well as more complete inverse modeling illustrates how patterns of combined hanging wall and footwall deformation may be used to constrain subsurface fault geometry

chronologic modeling of faulted and fractured reservoirs using geomechanically based restoration technique and industry applications we have developed a geomechanically based restoration method to model reservoir deformation the approach founded on the finite element method simulates the physical behavior of the rock mass and considers heterogeneous material properties bedding slip and the mechanical interaction of faults to demonstrate the method s potential we analyze the deformation and fault growth in the hanging wall of a synsedimentary listric normal fault from a sand box model which provides an analog for evaluating complex faulted reservoirs the numerical model results are then analyzed to investigate the chronology of faulting the numerical model corresponds well to the physical model and provides additional insights about reservoir evolution and deformation the approach is also tested on a natural example of folding using outcrop data to study contractional deformation these examples illustrate how undetected faults and fractures reservoir compartmentalization hydrocarbon migration pathways and hydrocarbon traps can be understood in the context of tectonic processes and how this understanding can be exploited in decision making and reducing risk we conclude that the geomechanically based restoration of faulted and fractured reservoirs has significant potential for industry applications compared to common geometric restoration techniques which lack a mechanical basis

a new 3d geological model and interpretation of structural evolution of the world class rio tinto vms deposit iberian pyrite belt spain abstract a new 3d geological model and interpretation of structural evolution of the rio tinto world class vms deposit are presented in this work the rio tinto volcanogenic massive sulfide vms deposit is located in the spanish segment of the iberian pyrite belt and is hosted by felsic porphyritic volcanic rocks and tuffs computer generated 3d modeling of the different orebodies and host rocks has been carried out using data from around 3000 drill core logs allowing us to build 93 cross sections and 6 plants both 50 m spacing this has enabled us to recognize the geometry and relationships between the mineralization and the earliest carboniferous transtensional tectonics through the development of an extensional pull apart basin with two sub basins separated by the nw se trending eduardo fault the sub basins cerro colorado and san dionisio were limited by two e w strike slip faults the northern and southern faults and bounded in the east and west by the nw se trending nerva and western faults respectively the generated pull apart basin was first filled by a basaltic magmatism of mantle origin and later following the deposition of the intermediate complex sedimentary unit by rhyodacitic volcanic rocks of crustal origin the evolution of the subsiding basins caused the development of an e w oriented rollover anticline that affected these filling rocks as a result of a counterclockwise rotation of the stress axes the primitive pull apart basin evolved into a basin affected by e w transtensional sinistral shearing its northern and southern limits were favorable areas for increased hydrothermal fluid flow which gave way to the huge concentration of vms mineralization located near the limits the northern and to a lesser degree the southern extensional faults thus become channel areas for feeding and discharging of the vms and stockwork ores the main mineralizing period was related to this stage subsequently during the variscan transpressional phase the e w extensional faults were reactivated as inverse faults affecting the volcanic sequence of mafic to felsic composition and the intermediate complex sedimentary unit fault propagation folds developed above these faults affecting the massive sulfides the transition series and the culm flysch sediments with buttressing playing a significant role in the geometry of tectonically inverted structures the vms mineralization and cupriferous stockworks were folded and dismembered from the original conduits in the volcanic series and a dextral reactivation of the nw se trending faults also developed finally it should be emphasized that this new 3d geological model is an approach to provide a better insight into the 3d structure of the world class vms rio tinto deposit and could be a key point for further studies providing a new tool to increase knowledge of the vms mineralizations and exploration guidelines elsewhere in the ipb

structure of uppermost fast spread oceanic crust exposed at the hess deep rift implications for subaxial processes at the east pacific rise the uppermost 2 km of the oceanic crust created at the fast spreading 135 mm yr 1 full rate equatorial east pacific rise epr is exposed for tens of kilometers along escarpments bounding the hess deep rift mosaics of large scale digital images from the remotely operated vehicle rov argo ii and direct observations from the submersible alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units these rock units are characterized by extensive faulting fine scale fracturing and rotations of coherent crustal blocks meters to tens of meters across the uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces through most of the basaltic lava unit however lava flow contacts dip 20 70 w toward the epr and generally increase in dip downward in the section dikes cutting the lavas and in the underlying sheeted dike unit generally dip 90 40 e away from the epr deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units we interpret this upper crustal structure as the result of subaxial subsidence within 1 2 km of the epr that accommodated the thickening of the basaltic lava unit to 500 m variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply these results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the hess deep rift if this type of structure is typical of uppermost oceanic crust generated at the epr these processes may be common along fast spreading mid ocean ridges

balanced cross section construction from seismic sections in areas of extensional tectonics abstract the application of the technique of balanced section construction initially developed for areas of compressional folding and faulting is reviewed with reference to extensional tectonics a number of examples are discussed where these techniques have been successfully applied in the north sea the interpretation of geoseismic sections is considered to be greatly assisted by careful application of geometrical balance and a consideration of strain even in areas of low crustal extensions the nature of seismic sections however places limitations on the validity of balancing which must be borne in mind with such interpretations and wherever possible the balancing of a geoseismic section should be confirmed by complete depth conversion the rapid testing of the integrity of the geoseismic section by attempting to balance the section at the interpretational phase can eliminate many problems as well as allowing the fullest use to be made of the geophysical information

a method for automatically determining normal fault geometry at depth a large number of methods have been described which relate the shape of a normal fault at depth to the shape of a sedimentary horizon in its hanging wall unfortunately the calculated fault geometry is strongly dependent upon the method used here arguments are put forward in favor of a general two dimensional kinematic model which assumes that the hanging wall deforms by a combination of arbitrarily inclined simple shear and differential compaction the method should be applicable to areas where it can be assumed that the fault plane does not change shape as deformation proceeds this assumption may not always be valid especially in the case of large scale basement extending normal faults fault geometry the inclination of simple shear and compaction parameters may all be determined from n beds using a simple inversion scheme based on the general method throughout it is assumed that hanging wall and footwall stratigraphies are accurately known though uncertainty in either could be included as a bounded variable within a formal inversion scheme the most important feature of the model is that it is testable it has first been tested on synthetic data using a range of fault geometries the results of such modeling are encouraging and imply that all unknown parameters including fault geometry can in general be uniquely determined provided that the geometries of two or more beds within the hanging wall are known the greater the number of beds used the greater the degree of confidence in the solution the method has also been applied to published sand box models with surprisingly good results ultimately it is hoped that the method can be applied routinely to depth converted seismic reflection data the preliminary applications presented here suggest that bulk antithetically inclined simple shear combined with differential compaction provide a good approximation for hanging wall deformation in the future the scheme will be generalized to allow for deformation in three dimensions other complexities such as horizontal and vertical variation in the degree of compaction could also be included although at this stage the data do not appear to justify them

numerical simulation of rifting in the northern viking graben the mutual effect of modelling parameters numerous basin modelling studies have been performed on the viking graben in the northern north sea during the past decades in order to understand the driving mechanisms for basin evolution and palaeo temperature estimations in such modelling it is important to include lithospheric flexure the values derived for the lithospheric strength by these studies vary considerably i e up to a factor of 30 in this study which is based on new interpretation of a regional transect we show that both the estimated value of the effective elastic thickness and the derived b profile are dependent on the assumed value of the depth of necking the use of models that implicitly set the level of necking at a depth of 0 km generally leads to an underestimation of the lithospheric strength and an overestimation of the thinning factors in the northern viking graben a necking depth at intermediate crustal levels gives results comparable to the observations extension by faulting is modelled to be a significant factor in conclusion rifting in the northern viking graben can be explained with various models of effective elastic thicknesses eet varying from 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking it is also shown that the development of the basin during the post rift phase cannot be explained by pure shear simple shear extension two mechanisms are proposed here to explain the post rift subsidence pattern namely intra plate stress and phase boundary migration the two extreme models for eet mentioned above 1 km for a zero necking depth to the depth of the 450 jc isotherm for an intermediate level of necking give very different responses to compressional stress the latter gives basically no response for realistic intra plate stress d 2004 elsevier b v all rights reserved

geologic structure of the uppermost oceanic crust created at fast to intermediate rate spreading centers abstract geological investigations of major fault scarps tectonic windows and dsdp odp drill holes provide direct views of the uppermost oceanic crust generated at fast to intermediate rate spreading centers these areas reveal a consistent upper crustal structural geometry with basaltic lava flows defining a pattern of downward increasing inward dip toward the spreading center at which they formed and dikes in the lavas and underlying sheeted dike complex showing a similar degree of outward dip widespread fracturing faulting and hydrothermal metamorphism accompanied magmatic construction these geological relationships can be interpreted in terms of dramatic asymmetrical subaxial subsidence of upper crustal rock units that diminishes across the very narrow few kilometers wide zone of lava accumulation and dike intrusion at the ridge axis this type of crustal structure is in accord with some existing models of spreading but augments these idealized views with more realistic geological

elucidating the geometry of the active shanchiao fault in the taipei metropolis northern taiwan and the reactivation relationship with preexisting orogen structures the shanchiao fault is an active normal fault with documented paleoearthquakes in the taipei metropolis taiwan while posing direct seismic threat on the multimillion population its crustal scale fault plane configuration has not been constrained this study presents the first attempt to resolve the fault plane dip changes of the shanchiao fault within the upper crust by forward modeling late quaternary deformation tectonic subsidence over the last 23 ka is estimated from vertical displacements of a rapidly formed alluvial fan horizon deformed into a dramatic rollover monocline a 2 d profile across the shanchiao fault is chosen for elastic half space dislocation modeling and the results suggest that the fault is listric in the shallow crust with an abrupt change from subvertical ramp 85 75 to near horizontal flat 10 15 at 3 4 km depth consistent with an origin from the inversion of an orogen related thrust detachment given the presence of rift related fabrics in the underthrust chinese continental margin basement beneath the taiwanese orogenic wedge listric ramp flat ramp models with a second deeper bend to 60 dip are also tested reasonable fits with the geological observations are produced when the lower ramp is located at greater than 8 km depth which correlates with the hypocentral location of a moderate earthquake in 2004 joint reactivation of preexisting thrust and rift faults by the shanchiao fault is therefore plausible with implications for seismic hazard in the taipei area

structure and stratigraphy of the rukwa rift abstract combining recently acquired multifold seismic data with well and gravity information and field mapping a comprehensive picture of the structure and stratigraphy of the rukwa rift has emerged the rukwa rift lies between the tanganyika and nyasa malawi rifts in the western branch of the east african rift system in southwest tanzania the rukwa rift is a nw trending half graben basin that is 350 km long and 40 km wide unlike the neighboring tanganyika and nyasa rifts there is no evidence of half graben polarity reversals in the rukwa rift the nw trending boundary fault system lies on the northeastern side of the basin and comprises a series of listric faults most internal faults also show listric forms and trend n s oblique to the boundary fault the basal sedimentary section is the permo triassic karroo sequence this is overlain by the red bed sandstone sequence in which both mesozoic and tertiary fauna have been found the cenozoic lake bed sequence is the highest unit and covers nearly all of the present basin sediment thicknesses commonly reach 7 km and attain a maximum of 12 km at the southeastern end of the basin the lake bed sequence is the thickest unit in the main depocentre but the karroo sequence is often the thickest unit on the shoaling side of the half graben the rukwa rift is here interpreted to have evolved as a strike to oblique slip pull apart basin based on numerous indications of nw trending strike slip faulting

spatiotemporal patterns of the late quaternary deformation across the northern chinese tian shan foreland abstract the investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt here we focus on the spatiotemporal patterns of the late quaternary deformation along the north piedmont of the chinese tian shan a mountain range formed by the ongoing india asia collision by using a terrace as the reference and applying the area conservation method the holocene shortening rate of the halaande anticline a fold of the distal structure belt iii in the foreland is estimated to 2 14 0 24 mm yr for the first time similarly we re calculate the holocene shortening rates of the other anticlines of belt ii iii using the magnitude of shortening documented by river terraces and the terrace formation ages published previously the summed holocene 103 year timescale shortening rates of individual anticlines along n s transects are 2 4 mm yr consistent with the late pleistocene 104 year timescale shortening rate but about 2 6 times higher than the long term 106 year timescale average shortening rate of 1 mm yr during the past several million years together with the shortening rates of individual anticlines at the 103 year 104 year and 106 year scales these observations imply that the deformation across the northern chinese tian shan foreland has accelerated since at least late pleistocene by summing the late quaternary rates of shortening in the southern chinese tian shan foreland 4 5 mm yr and the intermontane basins in the hinterland of the tian shan 2 mm yr the late quaternary rate of shortening across the tian shan range between longitude 83 e and 87 e amounts to 9 0 1 0 mm yr approximately matching the modern shortening rate of 8 mm yr derived from the gps measurements these results imply i that the deformation across the tian shan range and its foreland basins between longitude 83 e and 87 e could have not been changed significantly since at least late pleistocene ii that in the northern chinese tian shan foreland the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the holocene or even geodetic rate of deformation

mesozoic intracontinental underthrust in the se margin of the north china block insights from the xu huai thrust and fold belt the xu huai thrust and fold belt located in the southeastern margin of the north china block consists mainly of thrust and folded pre mesozoic strata its geodynamic evolution and tectonic setting are topics of long debate this paper provides new evidence from geological mapping structural analysis and making balance cross sections with restoration of cross sections results suggest that this belt was subjected to two phase deformation including an early phase regional scale nw ward thrust and fold and a late phase extension followed by the emplacement of dioritic monzodioritic porphyrites dated at 131 135 ma and locally strike slip shearing according to the mapping field observations and drill hole data three structural units were distinguished namely 1 the pre neoproterozoic crystalline basement in the eastern segment 2 the nappe unit or the thrust and fold zone in the central segment which is composed of neoproterozoic to ordovician carbonate rocks and carboniferous permian coal bearing rocks about 2600 m thick and 3 the western frontal zone a major decollement fault has also been identified in the base of the nappe unit on which dozen meter to km scale thrust and fold bodies were commonly developed all pre mesozoic depositional sequences were involved into a widespread thrust and fold event six uncompetent rock layers with biostratigraphic ages nanjing university 1996 have been recognized and each uncompetent rock layer occurred mainly in the top of the footwall playing an important role in the development of the xu huai thrust and fold belt geometry of the major decollement fault suggests that the nappe unit of this belt was rooted in its eastern side near the tan lu fault zone two geological cross sections were chosen for structural balancing and restoration from the balanced cross sections ramp flat and imbricated faults as well as fault related folds were identified a shortening of 20 6 29 6 km was obtained from restoration of balanced sections corresponding to a shortening rate of 43 6 46 4 this shortening deformation was likely related to the se ward intracontinental underthrust of the north china block beneath the south china block during the mesozoic

effective porosity of a carbonate aquifer with bacterial contamination walkerton ontario canada summary preferential flow through solutionally enlarged fractures can be a significant influence on travel times and source area definition in carbonate aquifers however it has proven challenging to step beyond a conceptual model to implementing parameterizing and testing an appropriate numerical model of preferential flow here both porous medium and preferential flow models are developed with respect to a deadly contamination of the municipal groundwater supply at walkerton ontario canada the preferential flow model is based on simple orthogonal fracture aperture and spacing the models are parameterized from borehole gamma flow and video logs resulting in a two order of magnitude lower effective porosity for the preferential flow model the observed hydraulic conductivity and effective porosity are used to predict groundwater travel times using a porous medium model these model predictions are compared to a number of independent estimates of effective porosity including three forced gradient tracer tests the results show that the effective porosity and hydraulic conductivity values closely match the preferential flow predictions for an equivalent fracture network of 10 m spacing of 1 mm fractures three tracer tests resulted in groundwater velocities of hundreds of meters per day as predicted when an effective porosity of 0 05 was used in the groundwater model these velocities are consistent with a compilation of 185 tracer test velocities from regional paleozoic carbonate aquifers the implication is that carbonate aquifers in southern ontario are characterized by relatively low volume dissolutionally enlarged fracture networks that dominate flow and transport the porous matrix has large storage capacity but contributes little to transport numerical models based on much higher porosities risk significantly underestimating capture zones in such aquifers the hydraulic conductivity effective porosity prediction framework provides a general analytical framework for a preferential flow carbonate aquifer not only is the framework readily parameterized from borehole observations but also it can be implemented in a conventional porous medium model and critically tested using simple tracer tests

4 d evolution of rift systems insights from scaled physical models the four dimensional 4 d evolution of brittle fault systems in orthogonal oblique and offset rift systems has been simulated by scaled sandbox models using dry cohesionless fine grained quartz sand extensional deformation in the models was controlled by the orientation and geometry of a zone of stretching at the base of the model the results of these analog model studies are compared with natural examples of rift fault systems rift basins produced by orthogonal and oblique rifting are defined by segmented border fault systems parallel to the rift axes and by intrarift fault systems that are subperpendicular to the extension direction segmentation of the rift margin increases with increase in obliquity of the rift axis resulting in a consequent increase in displacement on intrarift fault systems offset rift models are characterized by highly segmented border faults and offset subbasins in the rift zone along strike displacement transfer in the model rifts occurred as a result of formation of two types of accommodation zones high relief extension parallel accommodation zones typically are found in 60 degrees rifts and above left steps in offset rift systems changes in fault polarities in these accommodation zones were achieved by interlocking arrays of conjugate extensional faults the second type of accommodation zone was generally oblique to the extension direction and consisted of conjugate fault arrays having rotated tips that bounded a low relief oblique slip zone or grabens these typically are found in highly oblique rift systems 45 degrees and above right steps in offset rift models