basin development and syntectonic sedimentation associated with kinematically coupled strike slip and detachment faulting southern nevada a previously unrecognized 12 10 ma clastic sequence is distributed widely south of the las vegas valley shear zone and north of lake mead in southern nevada structural and stratigraphic evidence from these sedimentary and associated volcanic rocks suggests that basin development was kinematically related to movement along the las vegas valley shear zone major movement along the nearby saddle island detachment also occurred within this time interval we suggest that spatially and temporally related basin development sedimentation and stratal tilting reflect kinematically coupled movement along a combined las vegas valley shear zone saddle island detachment fault system

central zagros fold thrust belt iran new insights from seismic data field observation and sandbox modeling 1 we present five generalized cross sections across the central zagros fold and thrust belt iran these sections show that the fold geometry varies significantly both horizontally and vertically the style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and in particular to the presence of intermediate decollements within the sedimentary pile restoration of the sections shows amounts of shortening of the same order from one section to the other however it appears to be unequally distributed suggesting variations in basal decollement shear strength analogue modeling has been performed to systematically investigate the effect of an intermediate decollement level at different depths on the style of folding the models demonstrate that the position of intermediate decollements is an important factor controlling both structural style and fold wavelength models with shallow intermediate decollement show regularly and widely spaced anticlines in these models the fold wavelength depends directly on the thickness of the dominant competent layer and short wavelength superficial structures mask broad anticlines at depth models with deep intermediate decollement are characterized by the rapid propagation of deformation with small rate of shortening along this decollement influencing localization of forthcoming anticlines in the upper levels such propagation favors the development of duplexes and multiwavelength folds on this basis fold kinematics in central zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages some of these faults branched on decollement levels express the progression of folding whereas others are linked to late basement faults cutting through early structures in general the decollement levels are activated sequentially from deeper horizons to shallower ones however in one case gachsaran decollement a shallow decollement is activated during the early stages of folding and then abandoned during the subsequent evolution

formation of interior basins associated with curved faults in alaska the positions of certain nonmarine sedimentary basins in central and southern alaska are spatially related to the geometry of adjacent curved faults these interior basins occur along the northern convex side of these fault systems which change trend from northwest in canada and eastern alaska to east west in central alaska and to northeast in western alaska the basins probably initiated in early to middle tertiary time and deposition within all basins continued through the quaternary broadly synchronous with tertiary strike slip displacements along the tintina denali and border ranges fault systems we examine the spatial and temporal relationship between basins and faults by using a mechanical model of curved strike slip faults based on boundary elements we relate slip along the curved faults to tertiary pacific north american plate motions by using principal stress directions inferred from the plate motion directions locations of the predicted mean stress reductions around the fault bends caused by fault slip correlate well with positions of the interior basins our results suggest that basin subsidence and location were controlled primarily by the geometry of adjacent curved fault systems and the state of stress in alaska during the tertiary mechanical interaction between curved alaskan fault systems increases the tendency for basin subsidence stresses inferred from early tertiary plate motion vectors are not oriented correctly to drive right lateral slip along kaltag farewell and parallel faults in western alaska furthermore these stress states would have produced left lateral displacements for which there is no evidence along these western faults in their present orientations we find that a combination of slightly rotated fault geometry and low friction along the faults appears to facilitate right lateral slip along the faults in western alaska our results show that deformation well inside the continent can be explained in terms of the pacific north american plate motions thus tertiary plate motions have resulted in a broad zone of fault slip uplift and subsidence in the nonrigid north american plate producing several large basins

strike slip faulting and block rotation in the lake mead fault system strike slip faults in the basin and range province have often been considered passive boundaries between differentially extended domains of tilted normal faults and are thus considered secondary in accommodating regional horizontal deformation paleomagnotic investigation of late miocene age volcanic rocks displaced by the left lateral fault system of lake mead nevada shows 1 that these rocks have not been affected by significant structural tilt the difference between observed and expected inclinations being only 0 6 14 9 and 2 a significant horizontal counterclockwise rotation of 29 4 8 5 about a vertical axis this rotation was accommodated by slip on northwest trending right lateral strike slip faults this implies significant west northwest elongation results of the investigation indicate that strike slip faulting is the primary process accommodating crustal deformation along the lake mead fault system and that tilting in response to normal faulting is secondary

shear fracture patterns and connectivity at geometric complexities along strike slip faults shear fracture patterns and connectivity at geometric complexities such as echelon fault steps and fault bends along strike slip faults are investigated by simulating shear fracture propagation paths using a displacement discontinuity boundary element method together with a maximum distortional strain energy density criterion it is shown that shear fracture patterns and connectivity depend on the specific geometric configurations the applied stress orientations and the coefficient of friction for a given initial configuration of the major faults the subsequent patterns of the associated shear fractures and their linkage can be predicted if the remote state of stress and the coefficient of friction are known the analyses of fault geometries commonly encountered in nature have important implications for evaluating the effect of faults on fluid flow and earthquake hazards associated with the geometric complexities along strike slip faults in the upper crust

tertiary uplift and shortening in the basin and range the echo hills southeastern nevada the echo hills is a distinctive area of tectonic uplift and shortening located at a right step in the left lateral bitter spring valley fault of the late tertiary lake mead fault system nevada the fundamental internal structure of the echo hills is an asymmetric anticline disrupted by reverse and oblique faulting an analysis of the stress distribution within the stepover indicates that the interaction between the two segments of the bitter spring valley fault is responsible for the compressive deformation and structural uplift in the echo hills given the number of strike slip faults in the basin and range similar examples of tertiary uplift and shortening probably occur elsewhere within the province

new tectonic configuration in ne iran active strike slip faulting between the kopeh dagh and binalud mountains in this paper a combined approach of geomorphic analyses detailed geological mapping on spot 5 satellite images and field surveys complemented by radiometric dating ar 40 ar 39 allows proposing a new and consistent tectonic configuration for the northeastern arabia eurasia collision zone it favors a simple strike slip faulting mechanism in ne iran accommodating the northward motion of central iran with respect to eurasia between the binalud and kopeh dagh mountains our results demonstrate that similar to 2 mm a similar to 25 of this northward motion has been transferred from the binalud to the kopeh dagh through the meshkan transfer zone since similar to 5 ma the modern state of stress deduced from fault kinematics analyses shows n30 degrees e trending maximum stress axis and confirms a dominant strike slip faulting mechanism combining our geological data with other available data we conclude that kinematics of deformation can be appropriately described by rigid block faulting in ne iran instead the continuous deformation as it has been thought during the last 3 decades

jurassic deep water fans in the neo tethys ocean the kashafrud formation of the kopet dagh basin iran abstract the middle jurassic kashafrud formation of northeast iran was deposited in the kopet dagh basin linked to the neo tethys ocean the 2 km thick succession commences with fluvio marine boulder conglomerates that occupy bedrock valleys but the bulk of the formation comprises a deep water succession of interbedded sandstone and mudstone packages with trace fossils and sparse ammonites neogene collisional events deformed the strata to create the kopet dagh mountains the deep water succession represents channel lobe systems and associated levees and overbank areas on slope to basin floor fans northward paleoflow suggests that rivers drained uplands along the paleo tethys suture zone forming fan deltas on a narrow shelf with associated sediment transport to deeper water coarse sands extrabasinal pebbles and plant fragments are present throughout the formation and a thick boulder conglomerate unit lies within the turbidite succession these observations suggest proximity to terrestrial sources throughout deposition sandstone packages are mainly less than 10 m thick maximum 84 m and numerous lensoid packages of thick bedded sandstone tens of meters thick and up to 200 m wide represent submarine channel fills thick bedded lenses and sheets show a relatively narrow range of paleoflow direction and represent major submarine conduits whereas the more varied paleoflow direction of thin bedded packages suggests that many were deposited on levees the presence in the kashafrud formation of potential source rocks in the form of organic rich mudstones and abundant plant fragments suggests that the formation may have contributed to hydrocarbon fields within overlying formations sandstone sheets and channel fills could form local reservoirs

tectonic inheritance crustal architecture and contrasting structural styles in the venezuela andes surface and subsurface data image contrasting structural styles for the two flanks of the venezuela andes in the north a flexural basin developed in neogene times between the andes and the lake maracaibo north verging thrusts are mainly detached in the pre cretaceous substratum and form a deeply buried antiformal stack secondary decollement levels occur both in the upper cretaceous and tertiary strata accounting for the passive roof thrust of a conventional frontal triangle zone in the south the barinas basin hardly compares with a flexural basin it is largely dominated by both north and south verging basement involving structures paleogene normal faults are locally inverted and caribbean nappes are frequently reactivated or refolded by younger oblique neogene andean structures seismic profiles in this area also attest to the strong neogene structural inversion of upper jurassic lower cretaceous grabens hercynian or more likely early paleozoic structures account for local preexisting crustal heterogeneities reactivated during both the tethyan rifting and the andean deformations two trans andean regional profiles have been balanced and constrained by an inversion of the gravimetric data they imply a progressive deepening of the northern moho and a south dipping subduction of the infracontinental lithospheric mantle of the maracaibo block the shortening for both sections averages 60 km palinspastic restorations assume a relative cylindricity for the deep crustal architecture of the andes and minimize the possible effects of a progressive right lateral escape of the maracaibo block with respect to stable south america along the bocono fault strain partitioning during neogene oblique convergence induced surficial thrust fronts parallel to the plate boundary strike slip motion in the allochthon along the bocono fault and an asymmetric subduction wedging at depth

vertical axis rotations in the las vegas valley shear zone southern nevada paleomagnetic constraints on kinematics and dynamics of block rotations paleomagnetic study of vertical axis rotations at 23 localities along the right lateral las vegas valley shear zone lvvsz in southern nevada indicates that clockwise rotations generally increase with proximity to the lvvsz reaching 100 at the closest localities rates of rotation determined at four localities range from l m y to 12 m y the maximum characteristic size of rotating blocks is 2 4 km considerably smaller than the dimensions of the zone of deformation associated with the shear zone 100 km in length 15 km in half width thus the deformation does not accord with kinematic models of block rotations that assume uniform rotations within domains having dimensions of the order of the width of the deforming zone instead the deformation appears to be quasi continuous when considered on a scale of 10 km we suggest that it is consistent with the deformation of a highly plastic layer of upper crustal material mechanically decoupled from deeper parts of the crust and that the across strike distribution of rotations is controlled by the rheological properties of the upper crust the length of the shear zone and the total amount of offset across the shear zone

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

deformation pattern around the conjoining strike slip fault systems in the basin and range southeast nevada the role of strike slip faulting in basin formation and inversion within the extensional regime of the basin and range strike slip faults create a regional pattern of opposing sense of fault systems the relationship between these faults and other deformational features nearby is enigmatic this paper addresses a diverse assemblage of contractional and extensional structures reflecting local uplift and subsidence respectively at the junction of two large neogene strike slip faults in southeastern nevada the right lateral las vegas valley shear zone and the left lateral bitter spring valley fault of the lake mead fault system first a middle miocene lacustrine carbonate basin the bitter ridge lovell wash carbonate basin formed north of the strike slip faults second the lacustrine basin inverted locally while sediments accumulated south of the strike slip faults third the study area was deformed by north northeast trending high angle oblique faults with normal and left slip components the results both from field observations and numerical modeling of the intersecting strike slip faults show that the las vegas valley shear zone and the bitter spring valley fault may have produced the basin in the north and its intense contractional deformation as well as the southward shift of deposition during the inversion event we conclude that conjoining strike slip fault systems can promote localized vertical tectonics and lead to basin formation and uplift right next to each other subsequent inversion of the earlier basinal deposits however requires a reversal in the sense of slip across the las vegas valley shear zone and a change in the regional stress system

sedimentary record of late paleozoic to recent tectonism in central asia analysis of subsurface data from the turan and south kazak domains abstract the turan and south kazak domains tsk are in central asia between the caspian sea and the tien shan the area is covered by sediments deposited since the late permian during a series of tectonic events closely related to the history of two oceanic domains paleotethys and neotethys sedimentary basins on the tsk therefore provide constraints on the tectonic development of the southern margin of eurasia since the late permian our study is based on structure contour maps and isopach maps of five key stratigraphic markers of late permian to tertiary age isopach maps help locate major faults and delimit sedimentary basins providing information on vertical motions and in some instances horizontal motions subsidence associated with extension appears to have dominated the tsk from the late permian to the eocene the extension may have been of back arc type in southern eurasia next to the active margin where the paleotethys and neotethys successively subducted toward the north here sedimentary basins are both wide and deep up to 15 km during the mesozoic two compressional events of regional significance occurred in association with accretion of continental blocks at the southern margin of eurasia the first one at the end of the triassic led to strong selective inversion of basins over the turan domain the second one during the late jurassic early cretaceous had weaker effects since the oligocene following collision of both india and arabia with eurasia inversion has become more generalized and compressional basins have formed on the tsk throughout the entire history of development of the tsk from the late permian to the tertiary structures of paleozoic and early mesozoic age have exerted a strong control on sedimentation and especially on the location of depocenters the south kazak domain has registered little subsidence in comparison with the turan domain where some basins have become very deep

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

kinematics and timing of tertiary extension in the western lake mead region nevada explanation of the origin of the complex array of structures in some extensional terranes including folds and normal strike slip and reverse faults includes many models that implicitly assume kinematic compatibility between and contemporaneous operation of these structures we present new stratigraphic and age data from the highly extended western lake mead region nevada together with an analysis of fault kinematics technique of marrett and allmendinger 1990 to test the assumptions of kinematic compatibility and contemporaneity of structures in an area of excellent exposure and superb stratigraphic control our analysis indicates an overlapping but clearly distinct chronology of deformation early regional extension 18 13 5 ma is marked by development of a basin into which the middle miocene lower horse spring formation was deposited in the western lake mead region this basin was disrupted by more areally restricted post 13 ma normal and kinematically coupled right slip faulting along the las vegas valley shear zone kinematic analysis of faults indicates an average regional extension direction of nearly due west for the middle and late miocene extension and right slip faulting was followed by development of dominantly southvergent contractional structures including tight east plunging folds and east striking reverse faults these structures deform the post 8 5 ma muddy creek formation the muddy creek formation is not cut by the las vegas valley shear zone older faults including the eastern las vegas valley shear zone reactivated as south vergent reverse faults northeast striking left slip faults cut folds and reverse faults these observations show that north south shortening and left slip faulting postdate the major phase of extension and right slip faulting in the western lake mead area dynamic models that invoke either a single stress field or rotating stress fields to explain development of structures in the western lake mead area are inconsistent with the kinematic and age data similarly kinematic models that view all structures in the context of a single strain field are precluded by systematic cross cutting relationships that demonstrate at least partial diachroneity of deformational styles large magnitude extension south of the las vegas valley and lake mead fault zones appears to have been followed by north south contraction that was highly localized near the region of greatest extension we suggest that lateral pressure gradients arising from differential crustal thinning at the northern end of the colorado river extensional corridor may have provided the driving mechanism for localized contractional deformation

composition porosity and reservoir potential of the middle jurassic kashafrud formation northeast iran abstract in the kopet dagh basin of iran deep sea sandstones and shales of the middle jurassic kashafrud formation are disconformably overlain by hydrocarbon bearing carbonates of upper jurassic and cretaceous age to explore the reservoir potential of the sandstones we studied their burial history using more than 500 thin sections supplemented by heavy mineral analysis microprobe analysis porosity and permeability determination and vitrinite reflectance the sandstones are arkosic and lithic arenites rich in sedimentary and volcanic rock fragments quartz overgrowths and pore filling carbonate cements calcite dolomite siderite and ankerite occluded most of the porosity during early to deep burial assisted by early compaction that improved packing and fractured quartz grains iron oxides are prominent as alteration products of framework grains probably reflecting source area weathering prior to deposition and locally as pore fills minor cements include pore filling clays pyrite authigenic albite and k feldspar and barite existing porosity is secondary resulting largely from dissolution of feldspars micas and rock fragments with some fracture porosity porosity and permeability of six samples averages 3 2 and 0 0023 md respectively and 150 thin section point counts averaged 2 7 porosity reflectance of vitrinite in eight sandstone samples yielded values of 0 64 0 83 in the early mature to mature stage of hydrocarbon generation within the oil window kashafrud formation petrographic trends were compared with trends from first cycle basins elsewhere in the world inferred burial conditions accord with the maturation data suggesting only a moderate thermal regime during burial some fractures iron oxide cements and dissolution may reflect cenozoic tectonism and uplift that created the kopet dagh mountains the low porosity and permeability levels of kashafrud formation sandstones suggest only a modest reservoir potential for such tight sandstones fractures may enhance the reservoir potential

late cenozoic deformation in the south caspian region effects of a rigid basement block within a collision zone abstract active deformation in the south caspian region demonstrates the enormous variation in kinematics and structural style generated where a rigid basement block lies within a collision zone rigid basement to the south caspian basin moves with a westward component relative both to stable eurasia and iran and is beginning to subduct at its northern and western margins this motion is oblique to the approximately north south arabia eurasia convergence and causes oblique shortening to the south and northeast of the south caspian basin thrusting in the alborz and kopet dagh is accompanied by range parallel strike slip faults which are respectively left and right lateral there are also arcuate fold and thrust belts in the region for two principal reasons firstly weaker regions deform and wrap around the rigid block this occurs at the curved transition zone between the alborz and talysh ranges where thrust traces are concave towards the foreland secondly a curved fold and thrust belt can link a deformation zone created by movement of the basement block to one created by the regional convergence west to east thrusts in the eastern talysh represent underthrusting of the south caspian basement but pass via an arcuate fan of fold trains into ssw directed thrusts in the eastern greater caucasus which accommodates part of the arabia eurasia convergence each part of the south caspian region contains one or more detachment levels which vary dependent on the pre pliocene geology buckle folds in the south caspian basin are detached from older rocks on thick mid tertiary mudrocks whereas thrust sheets in the eastern greater caucasus detach on mesozoic horizons in the future the south caspian basement may be largely eliminated by subduction leading to a situation similar to archaean greenstone belts of interthrust mafic and sedimentary slices surrounded by the roots of mountain ranges constructed from continental crust

plate tectonic evolution of the southern margin of eurasia in the mesozoic and cenozoic abstract thirteen time interval maps were constructed which depict the triassic to neogene plate tectonic configuration paleogeography and general lithofacies of the southern margin of eurasia the aim of this paper is to provide an outline of the geodynamic evolution and position of the major tectonic elements of the area within a global framework the hercynian orogeny was completed by the collision of gondwana and laurussia whereas the tethys ocean formed the embayment between the eurasian and gondwanian branches of pangea during late triassic early jurassic times several microplates were sutured to the eurasian margin closing the paleotethys ocean a jurassic cretaceous north dipping subduction boundary was developed along this new continental margin south of the pontides transcaucasus and iranian plates the subduction zone trench pulling effect caused rifting creating the back arc basin of the greater caucasus proto south caspian sea which achieved its maximum width during the late cretaceous in the western tethys separation of eurasia from gondwana resulted in the formation of the ligurian penninic pieniny magura ocean alpine tethys as an extension of middle atlantic system and a part of the pangean breakup tectonic system during late jurassic early cretaceous times the outer carpathian rift developed the opening of the western black sea occurred by rifting and drifting of the western central pontides away from the moesian and scythian platforms of eurasia during the early cretaceous cenomanian the latest cretaceous paleogene was the time of the closure of the ligurian pieniny ocean adria alcapa terranes continued their northward movement during eocene early miocene times their oblique collision with the north european plate led to the development of the accretionary wedge of the outer carpathians and its foreland basin the formation of the west carpathian thrusts was completed by the miocene the thrust front was still propagating eastwards in the eastern carpathians during the late cretaceous the lesser caucasus sanandaj sirjan and makran plates were sutured to the iranian afghanistan plates in the caucasus caspian sea area a north dipping subduction zone jumped during paleogene to the scythian turan platform the shatski terrane moved northward closing the greater caucasus basin and opening the eastern black sea the south caspian underwent reorganization during oligocene neogene times the southwestern part of the south caspian basin was reopened while the northwestern part was gradually reduced in size the collision of india and the lut plate with eurasia caused the deformation of central asia and created a system of nw se wrench faults the remnants of jurassic cretaceous back arc systems oceanic and attenuated crust as well as tertiary oceanic and attenuated crust were locked between adjacent continental plates and orogenic systems

aspects of three dimensional strain at the margin of the extensional orogen virgin river depression area nevada utah and arizona the virgin river depression and surrounding mountains are neogene features that are partly contiguous with the little strained rocks of the structural transition to the colorado plateau province this contiguity makes the area ideally suited for evaluating the sense magnitude and kinematics of neogene deformation analysis along the strain boundary shows that compared to the adjacent little strained area large magnitude vertical deformation both uplift and depression locally exceeding 10 km greatly exceeds extensional deformation and that significant amounts of lateral displacement approximately parallel the province boundary extensional kinematics the directions of lateral displacements and the position and orientation of uplifts and one major depression are such that isostatic rebound following tectonic denudation is an unlikely direct cause of the strong vertical structural relief adjacent to the strain boundary instead the observed structures are first order features defining a three dimensional strain field produced by approximately east west extension vertical structural attenuation and extension normal shortening all major structural elements of the strain boundary strain field are also found in the adjacent basin and range especially evident is a discontinuous and inhomogeneous distribution of vertical structural relief resulting from uplift and tilting of the footwalls on convex upward normal faults combined with formation of extension parallel folds deformation resulted in a bewilderingly complex mixture of coeval folds normal faults strike slip faults and in some areas reverse faults thrust faults and thrust faults reactivated as extensional detachment faults these complexly mixed structures exhibit a tectonically important aspect of scale independence ranging from micro structures to mountain range scale many intensely extended domains appear to reflect a process of surface relief minimization above uplifted and tilted blocks some intensely extended zones are depth limited by relatively undeformed rocks above and intact tilted blocks below and are best viewed as subhorizontal zones of accommodation for the uplift and tilt of subjacent blocks whether or not the intense deformation extends to the surface its depth distribution commonly reflects lithologic or paleostructural controls whatever the cause for the concentration of extensional strain many gently dipping zones are more accurately viewed as local features recording small to moderate extension parallel translations than a regionally interconnected detachment faults recording enormous extension parallel translations although the total neogene strain field in the nevada utah arizona tricorner area has unique aspects other parts of the basin and range contain generally similar structures that presumably formed from similar processes these processes include lateral mass transfer probably by viscoelastic flow of the material needed to inflate areas of strong uplift and to translate blocks laterally by tectonic rafting directions of mass transfer vary but are commonly both parallel and normal to the direction of extension or parallel to the boundaries of extended areas much of the strong vertical structural relief probably reflects boundary condition or localized perturbations in the form of restraints or releases of the lateral flow system these conclusions are consistent with modern concepts of the flexural strength and rheological stratification of the crust in regions undergoing extension

neogene paleostress changes in the basin and range a case study at hoover dam nevada arizona at hoover dam 40 km southeast of las vegas nevada well exposed highly faulted miocene rocks provide an excellent opportunity to study the paleostress history of a very small area within a region where previous geologic studies indicate clockwise rotation of paleostress and a nearness to a major strike slip fault zone boundary within 0 5 km3 of rock the sense of slip was determined on almost 500 separate faults the fault slip data show internal consistency with respect to lithology size of faults and location within the small area with respect to fault slip however the data represent an in homogeneous mixture of primarily strike slip and dip slip motions from this mixture it is possible to resolve two distinct stress fields with directions of extension that differ by 60 each stress field corresponds to a mixture of strike slip and dip slip faults and thus the orientations of 1 and 2 are not tightly constrained if however the data are first separated into strike slip and dip slip faulting modes and subsequently searched for sub populations that correspond to contrasting paleostress orientations the computations yield tightly constrained tensors that illustrate two distinct stress fields with subhorizontal 3 axes that trend n50 e and n75 w the 1 and 2 axes permutate in two vertical planes that strike n40 w and n15 e because 1 and 2 are close in value relative to 3 these relationships suggest that strike slip and dip slip faulting belong to the same tectonic regime qualitative observations of polyphase slip fault fault offsets and fault bedding geometric relationships when evaluated in the context of changes in 3 orientation and permutations of 1 and 2 provide a basis for a two stage late cenozoic structural evolution at hoover dam these stages are 1 strike slip faulting partly pre tilt and dip slip faulting and associated stratal tilting and 2 mostly post tilt complexly interrelated strike slip oblique slip and dip slip faulting the qualitative evaluations indicate that strike slip and dip slip faulting alternated in time during the second stage of deformation and may have done so during the first these mixed mode movements probably represent stress oscillations in time and space rather than discrete stress reorganizations in contrast the two different orientations of 3 either represent a major clockwise rotation of the stress field or a major counterclockwise rotation of the rocks during the faulting history each alternative is consistent with regional geologic relationships and the choice of which is correct cannot be made within the small area that was studied

roles of plutonism midcrustal flow tectonic rafting and horizontal collapse in shaping the miocene strain field of the lake mead area nevada and arizona the lake mead area contains a well exposed record of highly contrasting neogene structural development that includes major magmatism and extension in its southern part and large magnitude lateral translations to 65 km of amagmatic structural blocks in its northern part these highly contrasting parts are joined at the hamblin bay fault a major crustal boundary that forms the south margin of the lake mead fault system and the north margin of the lower colorado river extensional corridor intrusive rocks adjacent to this crustal boundary on the south record major crustal rifting normal to an 350 axis they also display steep axis disharmonic folds that formed by post magmatic extension related horizontal collapse of highly weakened crust the rocks directly north of the crustal boundary not only display large lateral translations but they also are cut by fault systems suggestive of diverse paleostress conditions and formed into diversely oriented coeval folds collectively producing a complex neogene deformation field that defies interpretation in terms of a uniform system of remote stresses because structures forming this complex deformation field range from outcrop scale to 65 km of lateral displacement and can not be uniformly partitioned according to relative age we prefer tectonic models based on a protracted uniform dynamic process or super posed dynamic processes to models based on time varying states of stress we suggest that the large lateral displacements and extreme structural complexity record synextensional rafting of structural blocks atop a flowing undermass and concomitant contraction of the zone of flowage structural blocks north of the main zone of flowage the great basin sector of the basin and range moved southward and occluded to the block south of the zone the colorado river extensional corridor as a large west ward widening wedge of upper crust was carried to the west southwest toward california on the flowing undermass where occlusion is almost complete in the northern black mountains north south shortening is estimated at 55 km the narrow zone of strong rifting plutonism crustal softening and horizontal collapse that developed at the north margin of the colorado river extensional corridor is interpreted to result from contact with the zone of crustal flowage

oroclinal bending distributed thrust and strike slip faulting and the accommodation of arabia eurasia convergence in ne iran since the oligocene regional shortening is accommodated across ne iran in response to the collision of arabia with eurasia we examine how n s shortening is achieved on major thrust systems bounding the eastern branch of the alborz east of 57 e sabzevar and kuh e sorkh mountain ranges which lie south of the kopeh dagh mountains in ne iran although these ranges have experienced relatively few large earthquakes over the last 50 yr they have been subject to a number of devastating historical events at neyshabur esfarayen and sabzevar a significant change in the tectonics of the eastern alborz occurs directly south of the central kopeh dagh near 57 e to the east shortening occurs on major thrust faults which bound the southern margin of the range resulting in significant crustal thickening and forming peaks up to 3000 m high active shortening dies out eastward into afghanistan which is thought to belong to stable eurasia the rate of shortening across thrust faults bounding the south side of the eastern alborz north of neyshabur is determined using optically stimulated luminescence dating of displaced river deposits and is likely to be 0 4 1 7 mm yr 1 shortening across the sabzevar range 150 km west of neyshabur has previously been determined at 0 4 0 6 mm yr 1 although reassessment of the rate here suggests it may be as high as 1 mm yr 1 migration of thrust faulting into foreland basins is common across ne iran especially in the esfarayen region near 57 e where the northward deflection of the east alborz range reaches a maximum of 200 20 km from its presumed linear e w strike at the beginning of the oligocene west of 57 e the tectonics of the alborz are affected by the westward motion of the south caspian region which results in the partitioning of shortening onto separate thrust and left lateral strike slip faults north and south of the range at the longitude of 59 e published gps velocities indicate that 50 per cent of the overall shortening across ne iran is accommodated in the kopeh dagh the remaining 50 per cent regional shortening must therefore be accommodated south of the kopeh dagh in the eastern alborz and kuh e sorkh ranges assuming present day rates of slip and the fault kinematics are representative of the late cenozoic deformation in ne iran the total 200 20 km n s shortening across the eastern alborz and kopeh dagh mountains since the beginning of uplift of the kopeh dagh basin would be accommodated in 30 8 ma although this extrapolation may be inappropriate over such a long timescale the age is nevertheless consistent with geological estimates of post early to middle oligocene 30 ma for the onset of kopeh dagh uplift

unroofing history of late paleozoic magmatic arcs within the turan plate tuarkyr turkmenistan abstract stratigraphic sedimentologic and petrographic data collected on the kizilkaya sedimentary succession western turkmenistan demonstrate that the turan plate consists in fact of an amalgamation of late paleozoic to triassic continental microblocks separated by ocean sutures in the kizilkaya area an ophiolitic sequence including pyroxenite gabbro pillow basalt and chert interpreted as the oceanic crust of a back arc or intra arc basin is tectonically juxtaposed against volcaniclastic redbeds documenting penecontemporaneous felsic arc magmatism amanbulak group a collisional event took place around mid carboniferous times when oceanic rocks underwent greenschist facies metamorphism and a thick volcaniclastic wedge with pyroclastic rocks interbedded in the lower part accumulated kizilkaya formation the climax of orogenic activity is testified by arid fanglomerates shed from the rapid unroofing of a continental arc sequence including middle upper devonian back reef carbonates and cherts and the underlying metamorphic and granitoid basement rocks yashmu formation after a short period of relative quiescence renewed tectonic activity is indicated by a conglomeratic sequence documenting erosion of a sedimentary and metasedimentary succession including chert sandstone slate and a few carbonates a final stage of rhyolitic magmatism took place during rapid unroofing of granitoid basement rocks kizildag formation such a complex sequence of events recorded by the kizilkaya episutural basin succession documents the stepwise assemblage of magmatic arcs and continental fragments to form the turan microblock collage during the late paleozoic evolution of detrital modes is compatible with that predicted for juvenile to accreted and unroofed crustal blocks the deposition of braidplain lithic arkoses in earliest triassic time indicates that strong subsidence continued after the end of the volcanic activity possibly in retroarc foreland basin settings the occurrence of transgressive coquinas yielding endemic ammonoids dorikranites characteristic of the whole caspian area suggests proximity to the southern margin of the newly formed eurasian continent in the late early triassic the late triassic eo cimmerian orogeny caused only mild tilting and rejuvenation of the underlying succession in the study area only at this time were the turan blocks a series of indonesian type terranes comprised between the mashad paleo tethys suture in the south and the mangyshlak belt in the north finally incorporated into the eurasian landmass

chapter 3 structural development of a major extensional accommodation zone in the basin and range province northwestern arizona and southern nevada implications for kinematic models of continental extension

structural and geochemical constraints on the reassembly of disrupted mid miocene volcanoes in the lake mead eldorado valley area of southern nevada in the lake mead eldorado valley lmev area of southern nevada mid tertiary volcanic and plutonic rocks in the river mccullough and eldorado mountains lie in the upper plate of a regional detachment structure the detachment structure and strike slip faults of the lake mead fault zone are temporally and kinematically related strike slip systems and normal faults eldorado valley fault serve as boundaries between regions of variable extension in the upper plate of this detachment geochemical correlation and geometric reconstructions suggest that prior to extension the lmev area was characterized by three stratovolcano complexes each above or adjacent to a chemically correlative pluton geochemical correlation techniques are useful tools that may have general application in reconstructing structurally disrupted volcanic plutonic terranes

diverse pliocene quaternary tectonics in a transform environment san francisco bay region california the san francisco bay region occupies part of the diffuse transform boundary zone between the pacific and north american plates although dextral strike slip faulting is dominant the plate motion is expressed in a variety of ways some strike slip faults are parallel with the plate boundary but some are slightly oblique the major strike slip faults are zones in which an interplay occurs between strands some of which are en echelon this interplay may be responsible for some apparent pull apart basins and presumed normal faults along the calaveras fault zone in extensive areas between strike slip fault zones there are many compressional structures folds and reverse faults that are pliocene quaternary in age hence largely coeval with the strike slip faults some of the compressional structures are oblique to and others are parallel with the major strike slip faults we have divided the san francisco bay region into domains on the basis of the types orientations and relationships of structures or in one case lack of strong deformation each domain has responded in its own way to the regional northwest southeast dextral shear imposed by the relative plate motion in an attempt to understand the origin of various structures and the interrelationships among them we compared established models with our observations some observed geometric relationships agree quite well with classical coulomb anderson and simple shear models but others require further explanation models based on fault interaction seem to apply to certain cases for example the east bay hills domain which is between the left stepping calaveras and hayward rodgers creek fault zones is under compression resulting from interaction between the two strike slip zones

elastic stress relaxation a mechanism for opposite sense of secondary faulting with respect to a major fault abstract the motion along a major fault perturbs the local stress field and produces numerous secondary fractures among these the secondary fractures that have the opposite sense of motion with respect to the main fault are particularly intriguing for example the right lateral reverse motion of the ms 7 1 loma prieta earthquake of 18 october 1989 produced a series of left lateral normal fractures located in a narrow zone about 1 km in widt subparallel to the trace of the san andreas fault through a rigorous inversion of geodetic data associated with the earthquake that allowed the slip to vary on the rupture surface we studied the origin of the left lateral normal fractures by comparing the location orientation and slip sense of the observed fractures with the perturbed elastic stress field calculated from the estimated slip distribution of the earthquake the perturbed state of stress at the earth s surface is complex and the greatest principal stress changes from horizontal to vertical the area of left lateral tensile state of stress coincides with that of the observed left lateral normal fractures the magnitudes of the induced fault normal tensile stresses of 60 120 bars and left lateral fault parallel shear stresses of 0 4 bars in the area are large enough to produce the ground failures thus the observed left lateral normal fractures adjacent to the san andreas fault are interpreted to be related to coseismic elastic stress relaxation the same mechanism can also be used to explain the normal faulting in the upthrown blocks of the thrust faults which produced the 1980 el asnam algeria and the 1968 tokachi oki japan earthquakes

variation in fracture patterns in damage zones related to strike slip faults interfering with pre existing fractures in sandstone calcione area southern tuscany italy abstract this paper deals with the effects of pre existing fractures on the development of damage zones related to meter and decameter strike slip faults which affected late oligocene early miocene sandstone in the calcione area southern tuscany italy strike slip faults dissected rock masses locally affected by pervasive pre existing fractures related to previous deformational events two different domains were identified rock masses affected and unaffected or relatively unaffected by pre existing fractures strike slip faults affecting the two domains made it possible to compare the different configurations of fracture patterns related to isolated or interacting fault segments new data is provided on scaling relations between i fault length and the length of related fractures ii mean step length and width for overstepping fault segments iii angular values at the intersection of the fault plane and related fractures scaling relations obeyed a positive power law for faults dissecting sandstone unaffected by pre existing fractures on the contrary no scaling relations were recognized for faults dissecting sandstone affected by pre existing fractures the development of strike slip faults on rock masses affected by pre existing fractures can simulate splays apparently related to faulting three main points were categorized for detecting deceptive cases there is a real chance of a deceptive fracture pattern if i the angular values at the intersection of the fault and its fractures mode i opening fracture exceed 50 in the wall damage zone ii the scaling relation between fault length and maximum fracture length does not fit a power law iii fractures acted as shear fractures the resulting framework provides additional data for understanding the development and architecture of strike slip faults

coexistent pre existing extensional and subsequent compressional tectonic deformation in the kashmir basin nw himalaya abstract this paper presents a new interpretation of overlapping differential deformations and likely causes of the structural heterogeneity within the kashmir basin representing a prominent and distinctive strain feature in nw himalaya the broad geomorphic expression of the kashmir as an elongated nw se trending sedimentary trough is inconsistent with general compression governing structural trend and deformation pattern of 2500 km long himalayan frontal thrust zone in addition to the general extensional geometry there are prominent anomalous deformation features at varied spatial scales in the basins that imply dominance of extensional tectonics we infer that contrary to the overall compression dominant mechanism of the himalaya the apparent extensional geometry of the basin connotes orogen parallel extensional deformation pull apart triggered by oblique convergence in the nw himalaya moreover we construe that the comparatively younger contractile positive features in form of the geomorphic convexity push up accompanied by out of sequence reverse faulting balapur fault hereafter called as bf within the basin which is generally believed to be associated with the uplift along ne dipping southern thrust complex mbt mct possibly resulted due to the tectonic reversal positive inversion the presence of the compressional features within the locally predominant extensional setting is suggestive of the basin s hybrid character where variable tectonic regimes earlier extension and subsequent compression seem to be coexistent

structural evolution of the kopeh dagh fold and thrust belt ne iran and interactions with the south caspian sea basin and amu darya basin abstract we present a detailed stratigraphic and structural study of the kopeh dagh fold and thrust belt in ne iran which is an investigation of the complex polyphased tectonic history of this belt and its links with the adjacent south caspian sea and amu darya basins based on numerous field surveys a large amount of 2d and 3d seismic data borehole data and more than 150 new biostratigaphic datings a new detailed biostratigraphic chart and 4 main regional cross sections illustrate the importance of lateral facies variations and structural inheritance in the present day structure of the belt after the cimmerian orogeny corresponding to the closure of the paleotethys ocean in late triassic early jurassic times a middle jurassic post collisional rifting event was associated with the deposition of one of the main source rocks of the kopeh dagh and the amu darya basin kashafrud formation following this rifting event over 7 km of sediments were accumulated until the tertiary above a regional post triassic unconformity the occurrence of local uplifts during the late cretaceous early paleocene is interpreted as a consequence of regional scale modification of plate slab coupling in the neotethys subduction zone the main inversion of the kopeh dagh occurred at late eocene times when the far field deformation developed in eurasia as a consequence of the locking of the neo tethys subduction this folding phase is sealed in the western part of the belt by a major eocene oligocene unconformity at the base of the thick sedimentary series belonging to the south caspian sea basin the bulk of sedimentary infill in the south caspian sea basin is oligocene and younger and it is probably related to syn compressional downward flexure of the resistant basement basin at the onset of the alpine phase in the eastern part of the kopeh dagh this deformation is characterized by middle jurassic graben inversion with evidence of forced folding short cuts and as well by larger scale basement uplifts in contrast the northwestern part of the belt shows thrust faults involving basement and fault propagation folds within the sedimentary sequence the kopeh dagh presents tectonic structures that are parallel to the paleotethys suture zone which emphasizes the importance of the structural inheritance and inversion processes during the structural evolution of the belt finally a change from a mostly dip slip to a mostly strike slip tectonics occurred during the pliocene within the kopeh dagh as a consequence of a major tectonic reorganization in north east iran

inversion tectonics in central alborz iran abstract structural analyses carried out in the southern central alborz iran have shown that the evolution of this belt has been strongly conditioned by the inversion of pre existent extensional faults inversion tectonics has been identified especially in the southern part of the belt and it is related to the reactivation of grabens formed in the foreland of the late triassic eo cimmerian orogen resulting from the accretion of the iranian block to eurasia three main associations of structures active during the late cenozoic have been distinguished 1 e w thrust faults and folds followed by the activation of 2 e w right lateral strike slip faults associated to large ene wsw trending en echelon folds and finally 3 ese wnw to se nw thrust faults and left lateral strike slip faults inverting in some cases previous e w right lateral faults central alborz is strongly controlled by the geometry of pre existing tectonic discontinuities which are responsible for strain partitioning between strike slip and reverse faults during convergence these results provide new insights on the style and evolution of this complex intracontinental belt which can be considered a significant example of transpressive tectonics

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

kinematic role of transverse structures in continental extension an example from the las vegas valley shear zone nevada analysis of the slip budget of the las vegas valley shear zone southern nevada leads to a model that explains many of the kinematic complexities that characterize transverse structures in continental extensional settings including 1 abrupt terminations of these structures along strike 2 large lateral translations across relatively short faults 3 apparent lack of strike slip offset or contradictory evidence of shear sense along some transverse structures 4 significant variation in slip magnitude along strike and 5 juxtaposition of differentially extended terranes on opposite sides of faults many major transverse structures may function largely as transfer faults that either link or form passive boundaries between differentially extended terranes

basin genesis associated with strike slip faulting in the basin and range southeastern nevada the structural nature of two prominent basin and range strike slip systems the lake mead fault system and the las vegas valley shear zone are examined using both geological field mapping and geophysical surveys at various scales the intent of this study is to document deformation directly attributable to strike slip faulting with an emphasis on basin genesis our field study of the lake mead fault system reveals a major left step in the system the stepover results in the genesis of a 2 km deep pull apart the overton arm basin consistent with the kinematics and mechanics of strike slip faulting having established the origin of the overton arm basin as a strike slip related pull apart basin the geometry of poorly exposed strike slip systems can be revealed by understanding the related basins along their length one such system the las vegas valley shear zone is shown with the aid of geophysical data to be geographically related to three distinct en echelon basins when these basins are interpreted as pull apart basins the geometry of the las vegas valley shear zone becomes apparent for the first time we assert that strike slip faulting in southeastern nevada is a deformational mechanism that contributes locally to the regional extensional tectonics such an interpretation modifies extant models that treat strike slip faults in rifted terrains as passive lateral boundaries that simply accommodate extension without contributing to the process

late cenozoic reorganization of the arabia eurasia collision and the comparison of short term and long term deformation rates the arabia eurasia collision deforms an area of 3 000 000 km2 of continental crust making it one of the largest regions of convergent deformation on earth there are now estimates for the active slip rates total convergence and timing of collision related deformation of regions from western turkey to eastern iran this paper shows that extrapolating the present day slip rates of many active fault systems for 3 7 million years accounts for their total displacement this result means that the present kinematics of the arabia eurasia collision are unlikely be the same as at its start which was probably in the early miocene 16 23 ma or earlier in some but not all active fault systems short term 10 year and long term 5 million year average deformation rates are consistent there is little active thickening across the turkish iranian plateau and possibly the interior of the greater caucasus these are two areas where present shortening rates would need more than 7 million years to account for the total crustal thickening and where there are structural and or stratigraphic data for pre late miocene deformation we suggest that once thick crust up to 60 km built up in the turkish iranian plateau and the greater caucasus convergence took place more easily by crustal shortening in less elevated regions such as the zagros simple folded zone the south caspian region and foothills of the greater caucasus or in other ways such as westward transport of turkey between the north and east anatolian faults the time and duration of this changeover are not known for certain and are likely be diachronous although deformation started or intensified in many of the currently active fault systems at 5 2 ma

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

active tectonics of the turkish iranian plateau 1 this paper examines how active faulting in the turkey iran caucasus region accommodates the arabia eurasia collision and the velocity field observed by gps the overall shortening across the zone is in general spatially separated partitioned into right lateral strike slip in the turkish iranian plateau and thrusting in the greater caucasus a band of counterclockwise rotating nw se right lateral strike slip faults accommodates a nw se gradient in ne directed velocity relative to eurasia between the black and caspian seas a nnw sse band of previously unrecognized oblique normal faults is present on the turkey iran border we estimate the offsets on faults from geomorphological features and show that these offsets can be achieved in 5 2 ma at present rates this implies a reorganization of deformation in the collision zone at that time after the initial collision at 12 ma probably in response to mantle induced dynamic uplift

gps constraints on continental deformation in the africa arabia eurasia continental collision zone and implications for the dynamics of plate interactions 1 the gps derived velocity field 1988 2005 for the zone of interaction of the arabian african nubian somalian and eurasian plates indicates counterclockwise rotation of a broad area of the earth s surface including the arabian plate adjacent parts of the zagros and central iran turkey and the aegean peloponnesus relative to eurasia at rates in the range of 20 30 mm yr this relatively rapid motion occurs within the framework of the slow moving 5 mm yr relative motions eurasian nubian and somalian plates the circulatory pattern of motion increases in rate toward the hellenic trench system we develop an elastic block model to constrain present day plate motions relative euler vectors regional deformation within the interplate zone and slip rates for major faults substantial areas of continental lithosphere within the region of plate interaction show coherent motion with internal deformations below 1 2 mm yr including central and eastern anatolia turkey the southwestern aegean peloponnesus the lesser caucasus and central iran geodetic slip rates for major block bounding structures are mostly comparable to geologic rates estimated for the most recent geological period 3 5 myr we find that the convergence of arabia with eurasia is accommodated in large part by lateral transport within the interior part of the collision zone and lithospheric shortening along the caucasus and zagros mountain belts around the periphery of the collision zone in addition we find that the principal boundary between the westerly moving anatolian plate and arabia east anatolian fault is presently characterized by pure left lateral strike slip with no fault normal convergence this implies that extrusion is not presently inducing westward motion of anatolia on the basis of the observed kinematics we hypothesize that deformation in the africa arabia eurasia collision zone is driven in large part by rollback of the subducting african lithosphere beneath the hellenic and cyprus trenches aided by slab pull on the southeastern side of the subducting arabian plate along the makran subduction zone we further suggest that the separation of arabia from africa is a response to plate motions induced by active subduction

tertiary extension north of the las vegas valley shear zone sheep and desert ranges clark county nevada detailed mapping reveals the presence of high angle extensional faults and low angle gravity slides on the west side of the sheep range three major high angle faulting events each account for 20 of eastward rotation and accommodate extension between the las vegas range and the desert range low angle faults represent surficial slides in response to topography produced by extension on the high angle faults faulting took place during the miocene synchronously with deposition of the horse spring formation and with displacement on the las vegas valley shear zone the extension in the sheep range took place without volcanism intrusion or metamorphism of the paleozoic sedimentary rocks offset thrust faults suggest that the area west of the sheep range extended almost 100 during the miocene while the corresponding area south of the las vegas valley shear zone did not extend significantly the shear zone bounded the extending terrane on the south acting as a transform fault this extension west of the sheep range may in part balance that mapped by anderson 1971 in the eldorado mountains the las vegas valley shear zone and the lake mead fault system may have acted together to compensate for areas of localized extension between the colorado plateau and the vicinity of the specter range

the binalud mountains a key piece for the geodynamic puzzle of ne iran 1 we applied a combined approach of morphotectonic analyzes of spot 5 satellite images and field surveys complemented by in situ produced10be exposure dating to determine the kinematics and rate of active faulting in the binalud mountains bounded by the neyshabur fault system to the southwest and the mashhad fault zone to the northeast three regional episodes of alluvial surface abandonment were dated at 4 8 ka q1 105 ka q3 and 255 ka s3 along the neyshabur fault system cumulative offsets recorded by q3fan surfaces yield slip rates of 2 4 0 5 and 2 8 0 6 mm yr for right lateral and reverse components of active faulting corresponding to an oblique slip rate of 3 6 1 0 mm yr respectively reconstructing the cumulative right lateral offset recorded by s3surfaces a maximum slip rate of 1 3 0 1 mm yr is suggested for the mashhad fault zone these imply an overall rate of 3 7 0 6 mm yr for the range parallel displacement and an uplift rate of 2 8 mm yr due to the range normal shortening 1 6 2 2 mm yr during late quaternary the binalud mountains are deformed as a soft linked restraining relay zone taking up the motion between central iran and eurasia at a rate of 4 0 1 3 mm yr this translates central iran in the n340 e direction our data favor localized faulting instead of distributed deformation at the northeastern boundary of the arabia eurasia collision zone