brittle tectonic reconstruction of palaeo extension inherited from mesozoic rifting in west zagros kermanshah iran abstract the present day zagros mountain belt of sw iran corresponds to the former arabian passive continental margin of the southern neo tethyan basin which existed since a permian triassic rifting episode and underwent later collisional deformation in mid to late cenozoic time in west zagros the kermanshah radiolarian trough separated from the neo tethyan basin by the narrow continental platform of the bisotun limestone resulted from the triassic jurassic rifting of the passive margin brittle tectonic analyses of syndepositional normal fault slip data have been undertaken to study the extensional history of the passive margin in terms of palaeostress reconstruction dominant east west trends of the inherited rift related normal faults in west zagros indicate an approximately north south trend of extension that prevailed during the entire mesozoic syn to post rift evolution of the radiolarian trough this extension characterizes a stretched continental margin similar to the present day passive margin of the british isles considering the structural pattern of the inherited basement faults as revealed by the present day earthquake focal mechanisms an oblique crustal stretching model is proposed for the rifting process

tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

sediment yield exceeds sediment production in arid region drainage basins we use 10 be and 26 al to determine long term sediment generation rates identify significant sediment sources and test for landscape steady state in nahal yael an extensively studied hyperarid drainage basin in southern israel comparing a 33 yr sediment budget with 33 paired 10 be and 26 al analyses indicates that short term sediment yield 113 138 t km 2 yr 1 exceeds long term sediment production 74 16 t km 2 yr 1 by 53 86 the difference suggests that the basin is not in steady state but is currently evacuating sediment accumulated during periods of more rapid sediment generation and lower sediment yield nuclide data indicate that 1 sediment leaving the basin is derived primarily from hillslope colluvium 2 bedrock weathers more rapidly beneath a cover of colluvium than when exposed and 3 long term erosion rates of granite schist and amphibolite are similar

salt tectonics and tear faulting in the central part of the zagros fold thrust belt iran abstract the central part of the zagros fold thrust belt is characterized by a series of right lateral and left lateral transverse tear fault systems some of them being ornamented by salt diapirs of the late precambrian early cambrian hormuz evaporitic series many deep seated extensional faults mainly along n s and few along nw se and ne sw were formed or reactivated during the late precambrian early cambrian and generated horsts and grabens the extensional faults controlled deposition distribution and thickness of the hormuz series salt walls and diapirs initiated by the early paleozoic especially along the extensional faults long term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks they created weak zones in the sedimentary cover located approximately above the former and inactive deep seated extensional faults the n s to nne ssw direction of tectonic shortening during the neogene zagros folding was sub parallel with the strikes of the salt walls and rows of diapirs variations in thickness of the hormuz series prepared differences in the basal friction on both sides of the precambrian cambrian extensional faults which facilitated the zagros deformation front to advance faster wherever the salt layer was thicker consequently a series of tear fault systems developed along the rows of salt diapirs approximately above the precambrian cambrian extensional faults therefore the present surface expressions of the tear fault systems developed within the sedimentary cover during the zagros orogeny although the direction of the zagros shortening could also potentially reactivate the basement faults as strike slip structures subsurface data and majority of the moderate large earthquakes do not support basement involvement this suggests that the tear fault systems are detached on top of the hormuz series from the deep seated precambrian cambrian extensional faults in the basement

a sediment budget for a grazed semi arid catchment in the burdekin basin australia abstract in catchments adjacent to the great barrier reef world heritage area in queensland australia there is a growing concern that sediments and nutrients being exported from the land are having a detrimental effect on coral reef communities there is a need to determine the processes and rates of erosion from the major land use types so that management intervention can be initiated to reduce sediment yields where required this paper presents a sediment budget for weany creek a 13 5 km 2 grazed semi arid sub catchment of the burdekin river catchment australia a range of field methods was used to measure erosion from hillslopes gullies and stream banks as well as identify the amount of sediment being deposited and remobilised on the bed of gullies and the stream network the data suggests that at least during drought conditions the primary erosion source in this catchment is gully erosion however the largest source of sediment in the budget is actually associated with the remobilisation of in channel sediment stores overall the sediment budget is comprised of 81 coarse material and 19 fine sediment and an agreement between the fine sediment yield estimated in the sediment budget and the yield measured at the catchment outlet is within 10 the total sediment yield estimated for this catchment is 4205 t yr 1 and is much lower than expected for a catchment of this size this may reflect the drought conditions during the measurement period however there is also the possibility that the primary erosion sources have been exhausted and the rates of sediment loss may be much lower now than they may have been in the past nonetheless the results show that stored sediment which may have been deposited in the channel many decades ago is an important contributor to end of catchment sediment yields and warrants further investigation

gaw khuni basin an active stepover structure in the sanandaj sirjan zone iran the gaw khuni basin is located in the central part of the sanandaj sirjan zone on the northeastern margin of the zagros orogen this basin is one of the continuous zones of sanandaj sirjan zone basins that is filled by pliocene holocene sediments the gaw khuni basin is surrounded by an en echelon to parallel arrangement of active faults in dextral strike slip fault zones that indicate a right step dilational stepover structure the boundary faults of this basin are the eastern and western gaw khuni ramsheh and nain dehshir faults earthquake distribution determined along the faults dissection and displacement of holocene sediments and also the development of pull apart basins filled with holocene deposits along the faults confirm that these faults are active the gaw khuni stepover was formed during transtensional movements produced between two dextral strike slip faults nain dehshir and ramsheh also the gaw khuni pull apart basin and the eastern and western gaw khuni faults developed in a releasing step between the faults and grew in two directions during the time of their formation

inversion of field data in fault tectonics to obtain the regional stress iii a new rapid direct inversion method by analytical means summary a new method for determining the reduced stress tensor with four degrees of freedom the orientations of the three principal stress axes as well as the ratio of principal stress differences using fault slip data or focal mechanisms of earthquakes is presented from a computational point of view the inversion of fault slip data is made in a direct way by purely analytical means as a result the determination process is extremely fast and adaptable on small microcomputers from a physical point of view the method aims at simultaneously i minimizing the angles between theoretical shear stress and actual slip vector and ii having relative magnitudes of shear stress large enough to induce slip despite rock cohesion and friction examples of application to actual fault slip data sets with good or poor variety of fault slip orientations are shown the double significance of the basic criterion adopted results in a more realistic solution of the inverse problem than the single minimization of the shear stria angle

active deformation within the zagros mountains deduced from gps measurements we present and interpret the results of global positioning system gps measurements at 35 stations in and beside the zagros mountain belt sw iran for three campaigns ending march 1998 december 1999 and june 2001 preliminary motion estimates show clearly the change in character along the strike of the belt stations to the se move at 13 22 3 mm a 1 towards n 7 5 e with respect to eurasia most of the shortening indicated by the gps velocities seems to occur in the se zagros along two major seismic zones and along the zagros front to the nw stations move oblique to the trend of the belt towards n 12 8 w at 14 19 3 mm a 1 most of the shortening in the nw zagros seems to occur along the mountain front fault with its major earthquakes as well as along the zagros front the change in direction and magnitude of the velocity vectors across the north south trending kazerun and karebas faults involves extension of up to 4 mm a 1 along the strike of the zagros belt

fault tectonics and deformation a method of quantification using field data abstract a new method for analysing fault populations in terms of infinitesimal strain is discussed a fractured rock volume taken as a whole can be considered to be affected by continuous deformation provided fault offsets are small compared to its size each fault then acts as a penetrative simple shear we combinen simple shears to define an average deformation ellipsoid for the given faulted volume the method has been tested using accurate fault slip data collected in two superposed levels of coal mines of the lorraine basin the studied rock volume has been affected by extensional phenomena during permo triassic results show that within a major tilted block the average deformation corresponds to e w extension with a total factor of extension of 1 03 this result is in good agreement with independent estimates

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

spatial and temporal analysis of hillslope channel coupling and implications for the longitudinal profile in a dryland basin author s michaelides katerina hollings rory singer michael bliss nichols mary h nearing mark a

from orientation to magnitudes in paleostress determinations using fault slip data abstract determinations of reduced stress tensors using fault slip data yield the orientation of principal stress axes and the ratio of the differences between principal stress magnitudes the use of rupture and friction laws allows determination of the two remaining unknowns that is the reconstruction of the complete stress tensor taking into account the depth of overburden brings an additional constraint the method is applied and discussed in the case of the hoover dam site western u s a where large data sets and rock mechanics information are available differences between intact sample and rock mass properties account for apparent disagreements between paleostress levels determined in similar tectonic environments pore pressure plays an important role where information about pore pressure is absent zero and hydrostatic pore pressure cases should be considered as limits

a sediment budget for a small semiarid watershed in southeastern arizona usa article i nfo article history a sediment budget was developed for a 43 7 ha and a nested 3 7 ha semiarid shrub dominated watershed based on hydrologic geomorphic erosion and sediment data collected from 1963 through 2006 on the usda ars walnut gulch experimental watershed in the southwestern us sediment budgets based on such extensive and intensive field campaigns over several decades are rare the sediment budget was bal anced with a high degree of confidence because the study watershed is controlled by an earth dam at the out let although the channel network is well developed and incising in the steeper reaches of the watershed hillslopes are the dominant source of sediment contributing 85 of the overall total sediment yield erosion and sediment redistribution were driven by highly variable rainfall and runoff during july august and september sediment transfers are influenced by channel abstractions and the presence of the outlet dam which created conditions for deposition in the pond approach reach although earth dams are ubiquitous throughout the southwestern us and they can provide a measure of outlet sediment yield these outlet mea surements may be insufficient to interpret temporal and spatial variability in watershed sediment dynamics identification of dominant processes and sediment sources is critical for determining management actions that will improve rangeland conditions published by elsevier b v

stress state reconstruction of oblique collision and evolution of deformation partitioning in w zagros iran kermanshah summary the w zagros of iran is characterized by a deformation partitioning pattern with a right lateral strike slip motion along the main recent fault and a shortening component across the zagros simple fold belt under the late cenozoic n s oblique collision between the arabian and iranian continental plates in this study we examined the brittle structures that developed during the mountain building process in the high zagros belt of kermanshah province which is structurally located between the two partitioned components of deformation to decipher the history of polyphase deformation and variations in stress fields within the sedimentary cover since the onset of collision the earthquake focal mechanisms of w zagros were analysed to evaluate the recent stress fields within the basement analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of the corresponding stress tensor with reference to folding our stress reconstruction indicates a major change in stress state from a miocene pliocene syn folding compressional regime to a pliocene recent post folding strike slip system with a significant anticlockwise reorientation of the horizontal 1 stress axis from ne sw to n s the results of the recent stress states indicate that the stress trends are similar throughout the basement and sedimentary cover the differences between stress and strain axes suggest different possible degrees in partitioning of seismic and aseismic deformation as revealed by earthquake focal mechanisms in the basement and geodetic surveys at the surface of the sedimentary cover the integrated palaeostress results on the regional tectonic framework suggest that the late cenozoic brittle tectonic evolution of the w zagros was achieved through the transition from thin to thick skinned deformation under the oblique plate convergence highlighting a southwestward shift of the deformation partitioning during the final pliocene collisional reorganization

cenozoic post collisional brittle tectonic history and stress reorientation in the high zagros belt iran fars province abstract the zagros fold and thrust belt of sw iran is among the youngest continental collision zones on earth collision is thought to have occurred in the late oligocene early miocene followed by continental shortening the high zagros belt hzb presents a neogene imbricate structure that has affected the thick sedimentary cover of the former arabian continental passive margin the hzb of interior fars marks the innermost part of se zagros trending nw se that is characterised by higher elevation lack of seismicity and no evident active crustal shortening with respect to the outer sw parts this study examines the brittle structures that developed during the mountain building process to decipher the history of polyphase deformation and variations in compressive tectonic fields since the onset of collision analytic inversion techniques enabled us to determine and separate different brittle tectonic regimes in terms of stress tensors various strike slip compressional and tensional stress regimes are thus identified with different stress fields brittle tectonic analyses were carried out to reconstruct possible geometrical relationships between different structures and to establish relative chronologies of corresponding stress fields considering the folding process results indicate that in the studied area the main fold and thrust structure developed in a general compressional stress regime with an average n032 direction of 1 stress axis during the miocene strike slip structures were generated under three successive strike slip stress regimes with different 1 directions in the early miocene n053 late miocene early pliocene n026 and post pliocene n002 evolving from pre fold to post fold faulting tensional structures also developed as a function of the evolving stress regimes our reconstruction of stress fields suggests an anticlockwise reorientation of the horizontal 1 axis since the onset of collision and a significant change in vertical stress from 3 to 2 since the late stage of folding and thrusting a late right lateral reactivation was also observed on some pre existing belt parallel brittle structures especially along the reverse fault systems consistent with the recent n s plate convergence however this feature was not reflected by large structures in the hzb of interior fars the results should not be extrapolated to the entire zagros belt where the deformation front has propagated from inner to outer zones during the younger events

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

fault slip inversions their importance in terms of strain heterogeneity and kinematics of brittle deformation abstract heterogeneous deformation is intrinsic in natural deformation but often underestimated in the analysis and interpretation of mesoscopic brittle shear faults based on the analysis of 11 222 faults from two distinct tectonic settings the central andes in argentina and the sudbury area in canada interpolation of principal strain directions and scaled analogue modelling we revisit controversial issues of fault slip inversions collectively adhering to heterogeneous deformation these issues include the significance of inversion solutions in terms of 1 strain or paleo stress 2 displacement notably plate convergence 3 local versus far field deformation 4 strain perturbations and 5 spacing between stations of fault slip data acquisition furthermore we highlight the value of inversions for identifying the kinematics of master fault zones in the absence of displaced geological markers a key result of our assessment is that fault slip inversions relate to local strain not paleo stress and thus can aid in inferring the kinematics of master faults moreover strain perturbations caused by mechanical anomalies of the deforming upper crust significantly influence local principal strain directions thus differently oriented principal strain axes inferred from fault slip inversions in a given region may not point to regional deformation caused by successive and distinct deformation regimes this outcome calls into question the common practice of separating heterogeneous fault slip data sets into apparently homogeneous subsets finally the fact that displacement vectors and principal strains are rarely co linear defies the use of brittle fault data as proxy for estimating directions of plate scale motions

the origin of changes in structural style across the bandar abbas syntaxis se zagros iran abstract the bandar abbas syntaxis marks the transition between the zagros collisional belt and the makran subduction related prism and constitutes a major structural feature within the alpine himalayan mountain belt within the foreland part of the zagros the zagros fold thrust belt zftb the transition is marked by a sudden change in structural trends and style and a rapid decrease in seismicity and salt diapirism from west to east of the syntaxis the depth to decollement and lithology affect the geometry and size of the folds on each side of the syntaxis while different mechanical coupling along the basal decollement affects the degree of internal rock deformation thus the short and broad folds of the western side of the syntaxis are decoupled along the 8 km deep hormuz evaporites visible at surface in numerous salt diapirs strong seismicity in this area suggests that the basement is involved in the deformation by contrast the long and narrow folds of the eastern side of the syntaxis appear to be controlled by frictional slip along a 6 km deep detachment the absence of seismicity suggests that the basement is not involved in the deformation in this area we propose that the basal decollement for these structures corresponds to the eroded top of the nne ssw trending oman mesozoic nappes resulting from late cretaceous obduction of tethys on the arabian margin these structures are visible onshore in the northern tip of the oman peninsula and seen in offshore seismic profiles continuing northward beneath the strait of hormuz finally map view observations show that the main zagros thrust and the zendan fault separating the zftb from the internal zones of the orogen are shallow low angle thrust faults rather than steeply dipping faults

headcut retreat in a semiarid watershed in the southwestern united states since 1935 abstract headcuts are prominent features in the southwestern united states within the walnut gulch experimental watershed wgew survey data was available to quantify the retreat of the three most prominent headcuts in sub watershed 63 011 from 1935 to 2006 the headcuts serve as major sediment sources and were investigated to identify and understand factors controlling retreat rate in this watershed the data was incorporated and analyzed in a geographical information system gis the headcuts have retreated persistently since 1935 a power relationship was fitted by regression r 2 0 89 correlating the retreat rate with the product of contributing drainage area and areal precipitation for precipitation exceeding a threshold intensity i30 25 mm hr 1 this site specific relationship may not apply universally in other regions headcut retreat was not induced by external forcing the autocyclic behavior of headcut retreat was found typical for the southwestern united states the data did not allow timing or identification of initial causes for headcut retreat data suggests that all three headcuts will continue to retreat in the future even though the retreat rate of one headcut was severely inhibited by exhumation a layer of cemented material acting as local base level control most of the sediment eroded at the active headcut scarp was not transported very far indicating that headcutting in this area results in local reworking rather than removal of material from the watershed

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

structural evidence for superposition of transtension on transpression in the zagros collision zone main recent fault piranshahr area nw iran abstract the main recent fault of the zagros orogen is an active major dextral strike slip fault along the zagros collision zone generated by oblique continent continent collision of the arabian plate with iranian micro continent two different fault styles are observed along the piranshahr fault segment of the main recent fault in nw iran the first style is a sw dipping oblique reverse fault with dextral strike slip displacement and the second style consists of cross cutting ne dipping oblique normal fault dipping to the ne with the same dextral strike slip displacement a fault propagation anticline is generated sw of the oblique reverse fault an active pull apart basin has been produced to the ne of the piranshahr oblique normal fault and is associated with other sub parallel ne dipping normal faults cutting the reverse oblique fault another cross cutting set of ne sw trending normal faults are also exist in the pull apart area we conclude that the ne verging major dextral oblique reverse fault initiated as a sw verging thrust system due to dextral transpression tectonic of the zagros collision zone and later it has been overprinted by the ne dipping oblique normal fault producing dextral strike slip displacement reflecting progressive change of transpression into transtension in the collision zone the active piranshahr pull apart basin has been generated due to a releasing damage zone along the nw segment of the main recent fault in this area at an overlap of piranshahr oblique normal fault segment of the main recent fault and the serow fault the continuation of the main recent fault to the n

cenozoic faults and faulting phases in the western tarim basin nw china effects of the collisions on the southern margin of the eurasian plate abstract the bachu rise in the western tarim basin is the fore bulge of the kunlun late cenozoic intra continental foreland basin system formed under the far field effect of india asia collision cenozoic faults and faulting are abnormally developed in the bachu rise and its adjacent area taking the niaoshan gudongshan area on the southern boundary of the bachu rise as the key study area 5 cenozoic faulting phases were identified in the bachu rise and its adjacent area after careful seismic interpretation they are end cretaceous beginning paleogene ca 65 ma decollement thrusting end paleogene beginning neogene ca 23 ma decollement thrusting end miocene beginning pliocene ca 5 ma basement involved thrusting late pliocene early pleistocene ca 3 2 ma normal faulting middle pleistocene holocene ca

variability of sediment removal in a semiarid watershed field and documentary data from walnut gulch watershed an instrumented semiarid drainage basin of approximately 150 km 2 57 mi 2 in southeastern arizona show that 83 of the alluvium removed from the basin during a 15 year erosion episode beginning about 1930 was excavated from the highest order stream the amount of alluvium removed in the erosion episode would have been equal to a covering of about 4 cm 1 6 in over the entire basin the rate of sediment removal during the erosion episode was 18 times greater than the rate of present channel sediment transport production of sediment from slopes and channel throughput at present rates are approximately equal and refilling will not occur under present conditions the channel forms left by the massive evacuation of sediment impose controls on the spatial distribution of tractive force and total stream power that make renewed storage of sediment likely in only a few restricted locations modern instrumented records of a decade or more provide an inadequate perspective on long term sediment movement

slip vectors and stretching of the sumatran fore arc slip vectors from thrust earthquakes at the java trench southwest of sumatra demonstrate that the sumatran fore arc is not a single rigid plate that is translated to the northwest by oblique plate convergence instead they indicate arc parallel stretching of the fore arc at a uniform strain rate of 3 4 x 10 8 yr the northwestward motion of the fore arc relative to the upper plate southeast asia increases from near zero at the sunda strait to 45 60 mm yr in northwest sumatra and should result in variable slip rates on the sumatran fault

coarse bed material patch evolution in low order ephemeral channels abstract in river channel beds composed of a wide range of grain sizes the bed material is often arranged in discrete patches discernable by relative texture these bed material patches are the primary source of entrainable coarse sediment within the channel system and their composition and size have been found to influence the composition and rate of sediment transport twelve coarse gravel cobble sediment patches distributed throughout the channel network within a 4 53 ha watershed in southeastern arizona were monitored for 2 years changes in patch area and grain size were measured and painted patch grains were monitored to confirm that patch grains were mobilized during flow individual coarse bed material patches exhibited variable persistence during flows with return frequencies ranging from approximately 1 year to 4 6 years while no patch fully dispersed during the study period two new patches formed most coarse patches remained relatively stable in area and grain size distribution despite the entrainment of patch grains as lost grains were sufficiently replaced with sediment from upstream because of the grain replacement process and the effect of other sediment supply dynamics the changes in patch area and grain size distribution display a complex relationship with the magnitude of predicted grain mobilization within each patch results indicate that relative stability varies from patch to patch influenced by the balance of patch grains transported out of the patch and the deposition of new grains into the patch predictive models of coarse sediment transport and yield that assume the channel bed is a fixed source of sediment supply may not adequately capture the sediment dynamics within patchy channel beds and should be used with caution when applied to these environments due to the possibility of patch instability as documented in this study

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

the post eocene evolution of the doruneh fault region central iran the intraplate response to the reorganization of the arabia eurasia collision zone

strain rate and stress fields in the west and south lut block iran insights from the inversion of focal mechanism and geodetic data abstract the active tectonic deformation and hazardous earthquakes in the south and west of the lut block have been investigated for a long time in this study we compute the geodetic and seismic strain rates using focal mechanism data from the harvard cmt catalogue and various other sources including the published gps velocities moreover we also perform focal mechanism stress inversion fmsi to deduce a stress model for the region our study shows an expected correlation between the stress orientations seismic and geodetic strain rates our results show that the south and west of the lut block is generally exposed as a compressional strike slip tectonic regime the tectonic convergence in this area is taken up not only by motions along and across the faults but also by the rotation of those blocks which bounded by these faults the maximum amount of rotation rate is observed where there are the main right lateral strike slip fault systems such as sabzevaran gowk nayband bam kuhbanan and kahurak the orientation of the mean stress direction obtained from the fmsi results in the west and south of the lut block is approximated n19 e in this area faults are almost oblique relative to the tectonic motion direction moreover there are right lateral and left lateral shears in addition to the dip movements in different parts of the south and west of the lut block our analyses show three main categories of the stress regimes including strike slip faulting 43 2 thrust faulting 38 6 and unknown or oblique faulting 18 2 we also calculated seismic and geodetic moment rates for this area which indicate the seismic moment rate is relatively high between bam and shahdad where there are some segments of the gowk fault

control of folding and faulting on fracturing in the zagros iran the kuh e sarbalesh anticline abstract the kuh e sarbalesh anticline fars region shows a strong and poorly studied curvature in the vicinity of the kazerun transfer zone here we investigated this structure by analyzing the orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system and paleo burial conditions far away from the kazerun fault the orientation of fractures is similar to that observed in other folds in the zagros two tensional fracture sets f1 and f2 develop respectively parallel and perpendicular to the fold axis whereas two shear fracture sets dextral f3 and sinistral f4 develop at 30 from f2 closer to the kazerun fault f1 and f2 become less abundant whereas f3 fractures do prevail f3 dextral shear fractures are associated with dextral shear zones sz3 within sz3 sets of tensional fractures f5 occur f4 shear planes are less abundant than f3 sets and are sometimes associated with sinistral shear zones sz4 within sz4 sets of tensional fractures f6 occur the frequency of f3 and sz3 structures increases from south to north suggesting a control by dextral shear along the kazerun fault average fracture spacing is around 20 cm and fracturing saturation values is larger than 0 7 at 20 km distance from the kazerun fault whilst spacing is smaller than 1 cm and saturation is as low as 0 32 typical of well developed fracture systems close to the fault highlighting a strong strain gradient from south to north the orientation of f1 and f2 fracture sets changes from south to north according to the clockwise rotation of the northern part of the fold with respect to the southern part inorganic thermal parameters derived from x ray diffraction analysis of clay minerals indicate that the asmari formation was deformed at burial depths of 3 km assuming a geothermal gradient of 20 c km we suggest that the progressive differential advancement of the thrust front produced the curved shape of the kuh e sarbalesh anticline with associated rotation of the pre early folding f1 and f2 fracture sets observed in the field consistently with a dextral shear associated with the kazerun transfer fault

tectonic analysis and the evolution of a curved collision belt the hsuehshan range northern taiwan abstract detailed studies of fracture patterns and paleostress reconstructions based on analyses of fault slip data sets allow identification of four main patterns of compressional paleostress orientations in the cenozoic rocks of northern taiwan these patterns correspond to five successive tectonic events dominated by 1 n s 2 wsw ene 3 wnw ese 4 nw se and 5 wnw ese directions of compression the first two events are characterized by relatively minor structures in the foreland fold and thrust belt the first event probably reflects major left lateral shear along nne ssw trends which occurred in the adjacent eastern metamorphic belt during the middle late miocene these first two events do not affect the plio pleistocene in the localities studied in contrast the last three events created the major compressional structures of the foreland belt during the plio pleistocene collision in taiwan preliminary studies suggest that the magnetic fabric of the rocks has been significantly influenced by compressional deformation along wnw ese and nw se trends especially in the slate belt thus confirming the importance of these last three events on the basis of paleomagnetic work in progress the northernmost segment of the taiwan belt has been affected by a clockwise rotation of about 20 taking into account the distribution of successive compressional paleostress patterns we conclude that of the 55 angle of the sharply curved belt of northern taiwan about 20 probably correspond to actual clockwise rotation during the plio pleistocene whereas the remaining 35 reflect the initial shape of the curved plio quaternary belt the paleostress history of northern taiwan is examined in terms of geodynamic evolution and kinematic reconstructions the plio quaternary development of the collision between the luzon arc and eurasia followed a late miocene predominantly transform motion from south to north of the philippine sea plate relative to eurasia the succession of plio pleistocene paleostress patterns in northern taiwan is found to be consistent with the longitudinal shift from northeast to southwest and the transverse migration from the inner to the outer zones of compressional phenomena related to the evolution of oblique collision some major changes in compressional trends are also accounted for by variations in the kinematics of plate convergence the most recent charge comprises a counterclockwise change in the direction of philippine sea plate eurasia convergence

role of oblique convergence in the active deformation of the himalayas and southern tibet plateau noting similarities with subduction along curved oceanic trenches and using a simple block model we show that radial vergence evident in earthquake slip vectors along the himalayan deformation front east west extension on north trending normal faults in the himalayas and southern tibet and right lateral strike slip on the karakorum jiali fault zone can all result from basal shear caused by the indian plate sliding obliquely beneath tibet along a gently dipping arcuate plate boundary within the framework of this mechanism the normal faults in the himalayas and southern tibet are not proxies for the uplift history of tibet the distribution and style of the faults in the himalayas and southern tibet suggest that the basal drag from the underthrusting indian lithosphere extends northward beneath most of southern tibet

the present day deformation of the central zagros from gps measurements 1 in 1997 and in 2000 we measured the distances between 14 geodetic benchmarks across the central zagros mountain belt the results show that about 10 mm yr of shortening in the central zagros is distributed across the mountain belt this shortening corresponds to roughly 50 of the total convergence between arabia and eurasia and is consistent in direction the persian gulf does not deform significantly the main zagros reverse fault is not an active kinematic boundary the internal deformation of the folded belt is rather homogeneous at the scale of our survey which does not allow us to detect any individual active blind fault however the strain pattern suggests that n s dextral strike slip faults may accommodate part of the deformation

an investigation into the fault patterns in the chadegan region west iran evidence for dextral brittle transpressional tectonics in the sanandaj sirjan zone the nw se trending sanandaj sirjan zone ssz is the internal part of the zagros continental collision zone which mainly consists of metamorphic rocks deformed in a dextral transpressional zone this dextral transpression is attributed to brittle deformation related to late cenozoic arabia eurasia oblique continental collision major nw trending faults including the dalan garmdareh yasechah sheida and ben faults are reverse faults with a dextral strike slip component these faults were displaced by nw trending synthetic and ne trending antithetic faults there are also e trending thrusts and n trending normal faults developing in directions that are respectively almost normal and parallel to the major shortening direction the nw trending ben yasechah and sheida faults are ne dipping faults and the dalan and garmdareh faults are sw dipping faults these faults indicate the presence of a transpressive flower structure zone that probably led to the exhumation of jurassic high grade metamorphic rocks such as eclogite in the central part of the study area

the hydrological setting occurrence and significance of gypsum in late quaternary salt lakes in south australia well exposed often laminated gypsum sequences occur in many quarternary salt lakes in southern south australia the gypsum in the salt lakes is classified by increasing grain size into gypsite gypsarenite and selenite the salt lakes are classified by age and hydrological setting into coastal salinas which are holocene sea water fed groundwater lakes and continental playas which are late pleistocene endorheic basins a study of the relationships between coastal salina hydrology and the associated gypsum deposition has shown the different types of gypsum form under distinct hydrological regimes as the hydrology above a coastal salina depositional surface changes through time so does the type of gypsum deposited application of a gypsum depositional model derived from a study of the coastal salina gypsum to those portions of a continental playa gypsum unit where deposition is no longer occurring confirms the applicability of the model to non salina gypsum deposits

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

impact of coarse sediment supply from hillslopes to the channel in runoff dominated dryland fluvial systems sediment supply from hillslopes to channels is an important control on basin functioning and evolution however current theoretical frameworks do not adequately consider processes of runoff driven hillslope sediment supply which affect river channels spatially and temporally mountainous dryland basins exhibit an important manifestation of these processes because their debris mantled hillslopes produce coarse sediment and because rainfall is delivered as infrequent high intensity short duration rainstorms this paper combines field measurements and modeling to explore runoff driven coarse sediment supply from hillslopes to the channel and assesses a range of plausible storms on the longitudinal patterns of sediment load and its caliber over a dryland basin reach our results show that modeled sediment load and its grain size distribution are determined by the nonlinear interaction between rainfall characteristics and hillslope attributes resulting in longitudinal fluctuations in sediment supply the relative magnitude and location of which varies between storms results suggest that long hillslopes are most sensitive to rainfall and they exhibit large variations in supplied sediment load and grain size for different runoff characteristics short and steep hillslopes are less sensitive to rainfall variations as gradient effects dominate over the role of length in modulating runoff accumulation furthermore the signal of the median fraction d50 of modeled sediment supplied by the hillslope is preserved in the coarse fraction of the measured in channel grain sizes d90 finally we propose a simple index which provides new insights into the effectiveness of different rainstorms in terms of the impact of hillslope sediment supply on the channel

in situ experimental research on water scouring of loess slopes frequent occurrence of landslides in the chinese loess plateau has been influenced by the changes of water conditions this paper based on in situ water scouring experiments under various slope gradients cross sectional discharge shapes and flow quantities analyzed the rill flow information characteristics on a loess slope and its driving factors for anti scourability of the loess stratum the results show that the critical erosion slope gradient for the loess stratum q3 is about 24 and the mean erosion rate under half round cross sectional discharge is smaller than that under rectangular discharge the relationship between flow quantity and mean erosion rate is linear and is positively correlated mechanical subsurface erosion was the primary condition responsible for water scouring on loess slopes because of stronger runoff channels such as vertical joints and large amounts of macro void caused by plants and animals loess anti scourability is a significant issue to advance the research for soil and water conservation in the loess plateau of china

monitoring channel head erosion processes in response to an artificially induced abrupt base level change using time lapse photography abstract gullies that terminate at a vertical wall are ubiquitous throughout arid and semiarid regions multi year assessments of gully evolution and headcut advance are typically accomplished using traditional ground surveys and aerial photographs with much recent research focused on integrating data collected at very high spatial resolutions using new techniques such as aerial surveys with blimps or kites and ground surveys with lidar scanners however knowledge of specific processes that drive headcut advance is limited due to inadequate observation and documentation of flash floods and subsequent erosion that can occur at temporal resolutions not captured through repeat surveys this paper presents a method for using very high temporal resolution ground based time lapse photography to capture short duration flash floods and gully head evolution in response in 2004 a base level controlling concrete weir was removed from the outlet of a 1 29 ha semiarid headwater drainage on the walnut gulch experimental watershed in southeastern arizona usa during the ten year period from 2004 to 2014 the headcut migrated upchannel a total of 14 5 m reducing the contributing area at the headwall by 9 5 beginning in july 2012 time lapse photography was employed to observe event scale channel evolution dynamics the most frequent erosion processes observed during three seasons of time lapse photography were plunge pool erosion and mass wasting through sidewall or channel headwall slumping that occurred during summer months geomorphic change during the ten year period was dominated by a single piping event in august 2014 that advanced the channel head 7 4 m 51 of the overall advance and removed 11 3 m 3 of sediment high temporal resolution time lapse photography was critical for identifying subsurface erosion processes in the absence of time lapse images piping would not have been identified as an erosion mechanism responsible for advancing the gully headwall at this site

late cenozoic and modern stress fields in the western fars iran implications for the tectonic and kinematic evolution of central zagros 1 the zagros iran developed during mio pliocene times in response to arabia eurasia convergence the western fars highlights a major bend of the deformation front and displays a remarkable set of nearly n s right lateral strike slip faults the kazerun borazjan karebass sabz pushan sarvestan faults oblique at high angle to the belt the region likely plays a major kinematic role by accommodating the change in shortening modes from partitioned in the western central zagros to nonpartitioned in the eastern zagros the inversion of focal mechanisms from small and moderate earthquakes shows a consistent n020 030 compression with a low ratio between differential stresses this regime accounts for the combination of strike slip and thrust type mechanisms through likely 2 3 permutations fault slip analysis reveals two successive late cenozoic regional compressional trends ne sw then n020 the latter is in good agreement with the present day stress the significance of the ne sw compression is discussed alternatively in terms of stress deviations or block rotations in relation to the strike slip fault system fieldwork and satellite imagery suggest that these faults behave first as transfer faults during folding of the cover and later as strike slip faults in agreement with the succession of stress regimes and the evolution of the dominant deformation style from thin skinned to thick skinned the first order stability of the collision related state of stress since 5 ma supports that the arabia eurasia convergence did not give rise to partitioning in the western fars but rather was and is still accommodated by distributed deformation involving both shortening and strike slip motion throughout the cover and the basement

crustal stress map of iran insight from seismic and geodetic computations we used the focal mechanisms of crustal earthquakes depth 40 km in the period 1909 2012 and the available gps velocities derived from the data collected between 1999 to 2011 to estimate the magnitude and directions of maximum principal stress and strain rates in iran the pearson product moment correlation was used to find the correlation between the stress field obtained from the focal mechanism stress inversion and that obtained using the seismic and geodetic strain rates our assumption is that stresses in a continuum are produced by tectonic forces and the consequent deformation on the crustal scale therefore the direction of the stress and strain or strain rate are ideally to be the same our results show a strong correlation between the directions of the principal components of stress and strain rate obtained using the different data methods using weighted average analysis we present a new stress map for iran

thick and thin skinned deformation rates in the central zagros simple folded zone iran indicated by displacement of geomorphic surfaces although the geology and structure of the zagros fold and thrust belt iran have been studied extensively the distribution of active deformation across the belt and its seismotectonic behaviour remain controversial we have mapped deformed fluvial terraces along the dalaki and mand rivers in the central zagros as well as marine terraces along the persian gulf in order to unravel the spatial pattern of vertical displacements and to analyse active deformation and its implications for seismicity using appropriate fold models based on structural data allows interpreting such vertical displacements in terms of horizontal shortening across the fold structures obtaining well constrained rates of deformation depends on reliably dating deformed geomorphic markers by combining different dating techniques and correlations to sea level history we propose an internally consistent set of ages which allow the first geomorphic estimates of shortening rates absorbed by individual structures in the central zagros our results show that shortening on late pleistocene timescales is concentrated in the frontal part of the belt consistent with recent gps data three or four frontal structures appear to absorb practically all of the active shortening across the zagros broadly consistent with a normal forward propagating deformation sequence but with local out of sequence activation of structures behind the forward most folds the localization rate and direction of surface shortening across individual structures appear decoupled from basement deformation as indicated by structural cross sections and the distribution of seismicity such independent behaviour suggests that the sedimentary cover of the frontal zagros is decoupled from the basement most probably at the level of the hormuz salt this weak basal detachment level together with several intermediate decollement levels appears to be responsible for the overwhelmingly aseismic deformation of the zagros sedimentary cover and also to control the development of a large panel of fold structures from detachment to fault propagation folds with varying wavelength and rooting depth

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

structural evidence for slip partitioning and inclined dextral transpression along the se sanandaj sirjan zone iran the structural evolution of the sanandaj sirjan zone is the result of the convergence of the iranian microcontinent and the afro arabian continent the study area at khabr in the se sanandaj sirjan zone in the hinterland of the zagros orogen consists of paleozoic mesozoic and cenozoic rocks in this area deformation phases were distinguished in different rock units based on structural and stratigraphical evidence and the deformational events are divided into two stages 1 a late triassic event and 2 a late cretaceous to miocene event the late triassic deformation event caused regional metamorphism in the paleozoic units these units are overlain by unmetamorphosed jurassic clastic sequences fabrics and structural evidence confirm that the f1 folding recumbent and refolded folds were synchronous with the metamorphism of the paleozoic units and terminated in the early jurassic the time table of the orogenic phases shows that this deformation event is related to the cimmerian orogenic phase from a geodynamic point of view the early cimmerian deformation in the southeastern iranian margin suggests that the se sanandaj sirjan zone was an active margin at that time the early cimmerian discordance recorded the onset of a contractional component related to the oblique subduction of neo tethys beneath the central iranian microcontinent structures related to the late cretaceous to miocene deformation phase are observed in jurassic to oligocene units which contain moderately inclined and plunging folds comparing these folds with domains of deformation generated in models of transpression shows that the folding was caused by a combination of contractional and dip slip components of movement eventually resulting in the formation of a thrust system the khabr thrust systems consist of five sheets of oblique thrusts duplex structures and shear zones the shear zones generally strike e w and dip moderately n 30 40 the occurrence of asymmetric folds with hinges that are either parallel to strike or plunge down dip demonstrates an oblique slip component in these thrust shear zones the stretching lineation in the mylonites within the shear zones is defined by the long axes of ellipsoidal grains of quartz calcite plagioclase and garnet in general stretching lineations trend from n40 w to n80 w with an intermediate 35 plunge the geometry of foliation and lineation within these shear zones shows the effect of dip and oblique slip shearing deformation continued with strike slip faulting becoming important during the last stages of deformation from the miocene to the present day the results of this study demonstrate that the evolution of the se sanandaj sirjan zone from late triassic to miocene is compatible with an inclined dextral transpression along this zone

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

tectonic analysis of fault slip data sets using data that include the direction and the sense of motion on individual fault surfaces determined by slickenside lineations it is possible to reconstruct reduced stress tensors that correspond to the orientation of stress axes and to the ratio 2 3 1 3 between principal stress values 1 2 3 compression being positive no assumption is made concerning the orientation of fault planes relative to stress axes so that reactived faults are taken into account as well as newly created ones qualitative and quantitative methods for analysis of fault slip data were developed during the last 10 years the practical limitation of the methods and the necessity for critical field observations are emphasized these methods can be applied to focal mechanisms of earthquakes a more complex analysis of heterogeneous data sets involving an iterative separation of different stress systems is also discussed this analysis enables one to distinguish successive faulting events careful qualitative study in the field is in all cases essential

offset on the main recent fault of nw iran and implications for the late cenozoic tectonics of the arabia eurasia collision zone summary we use drainage patterns geological markers and geomorphological features to determine a right lateral offset of 50 km and possibly as much as 70 km on the main recent fault in nw iran this fault trends nw se and forms the ne border of the zagros mountains it accommodates the strike slip component of the n s convergence between arabia and eurasia with the ne sw shortening component being accommodated in the zagros fold belt its 50 km strike slip offset implies a shortening of 50 km in the fold belt and 70 km total n s convergence accommodated in the nw zagros this is a substantial fraction of the 85 140 km overall arabia eurasia convergence expected over the last 3 5 ma if the main recent fault initiated at that time as seems likely from geological arguments it has a horizontal slip rate of at least 10 17 mm yr 1 and should be the source of frequent earthquakes of ms 6 7 as has been seen in the 20th century and the earlier historical record the similarity of the offsets and probable ages of the north anatolian and main recent faults suggests that they have been active as an almost continuous zone of right lateral shear on the north edge of the arabian and anatolian plates since the early pliocene

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

new magnetic fabric data and their comparison with palaeostress markers in the western fars arc zagros iran tectonic implications the zagros simply folded belt zsfb is an active fold and thrust belt resulting from the still continuing continental collision between the arabian plate and the iranian plate which probably started in the oligocene the present day shortening n25 is well documented by focal mechanisms of earthquakes and global positioning system gps surveys we propose in this study a comparison of published palaeostress markers including magnetic fabric brittle deformation and calcite twinning data in addition we describe the magnetic fabric from palaeocene carbonates 10 sites and mio pliocene clastic deposits 15 sites the magnetic fabrics are intermediate with magnetic foliation parallel to the bedding and a magnetic lineation mostly at right angles to the shortening direction this suggests that the magnetic fabric retains the record of an early layer parallel shortening lps that occurred prior to folding the record of lps allows the identification of originally oblique folds such as the mand fold which have developed in front of the kazerun fault the shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the zsfb the palaeostress datasets covering the palaeocene to pleistocene time interval support several folding episodes accompanied by a counter clockwise rotation of the stress field direction the palaeocene carbonates in the zsfb record a n47 lps during early to middle miocene detachment folding in the high zagros belt hzb the mio pliocene clastic deposits recorded a n38 lps prior to and during detachment folding within the zsfb at the end of the miocene pliocene similarly fault slip and calcite twin data from the zsfb also support a counter clockwise rotation from ne to n20 between the pre folding stage and the late rejuvenation of folds this counter clockwise trend of palaeostress data agrees with fault slip data from the hzb during the late stage of folding in the zsfb the plio quaternary palaeostress trends are consistently parallel to the present day shortening direction

characterization and impact on reservoir quality of fractures in the cretaceous qamchuqa formation zagros folded belt abstract reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties the tectonic origin of fractures the relationship of fractures to other sedimentary features within the rockmass and diagenesis in this study fracture analysis porosity and permeability of the qamchuqa formation in the miran west block of the zagros folded belt in kurdistan has been studied this was undertaken using core analysis micro resistivity image logs drill stem tests dst mud logging data repeat formation test rft drilled cutting samples and wireline log data the integrated analysis shows that the qamchuqa formation is characterized by heterogeneous sedimentary and tectonic features the sedimentary features include burial stylolites dissolution seams and some fractures which formed at early stages of burial and diagenesis phase 1 open fractures partially open mineralized fractures veins and tectonic stylolites were formed by later tectonic activity phase 2 the finding of this study highlight that the fracture properties including aperture length frequency and origin play an important role in controlling the reservoir s quality the open fractures and partially open mineralized fractures enhance permeability providing an inter connected fracture network leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock the fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix in contrast structures including stylolites dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow this work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs

progressive unconformities within an evolving foreland fold thrust belt zagros mountains a major angular unconformity between the bakhtyari conglomerates and the underlying agha jari formation has long been interpreted as indicating that orogeny in the zagros simply folded zone took place in plio pleistocene times this study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the zagros simply folded zone has propagated in time and space these unconformities indicate that deformation started as early as end eocene in the northeast of the simply folded zone and propagated progressively to the southwest where unconformable contacts are only seen between younger units as shortening continued the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the persian gulf and mesopotamia the climax of orogeny took place at end pliocene time when the most extensive unconformity in the zagros simply folded zone developed between the upper bakhtyari formation and older units active seismicity and documented present uplift imply that the simply folded zone is still propagating southwestward

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

stress states in the zagros fold and thrust belt from passive margin to collisional tectonic setting abstract the present day zagros fold and thrust belt of sw iran corresponds to the former arabian passive continental margin of the southern neo tethyan basin since the permian triassic rifting undergoing later collisional deformation in mid late cenozoic times in this paper an overview of brittle tectonics and palaeostress reconstructions of the zagros fold and thrust belt is presented based on direct stress tensor inversion of fault slip data the results indicate that during the neo tethyan oceanic opening an extensional tectonic regime affectedthe sedimentary cover in triassic jurassic times with an approximately n s trend of the 3 axis oblique to the margin which was followed by some local changes to a ne sw trend during jurassic cretaceous times the stress state significantly changed to thrust setting with a ne sw trend of the 1 axis and a compressional tectonic regime prevailed during the continental collision and folding of the sedimentary cover in oligocene miocene times this compression was then followed by a strike slip stress state with an approximately n s trend of the 1 axis oblique to the belt during inversion of the inherited extensional basement structures in pliocene recent times the brittle tectonic reconstructions therefore highlighted major changes of the stress state in conjunction with transitions between thin and thick skinned structures during different extensional and compressional stages of continental deformation within the oblique divergent and convergent settings respectively

sediment budget of high mountain stream channels in an arid zone high atlas mountains morocco abstract in an arid zone the sediment budget is predominantly dependent on runoff which is controlled mainly by the type of rainfall sediment budget calculation is one of the indirect methods of estimating channel morphodynamics this method is advised here since it is not possible to directly measure this important hydrological indicator of environmental dynamics this is because in small mountain catchments of an arid zone it is impossible to obtain flow rates due to factors such as the amount and size of transported rock debris as well as the episodic and sudden nature of precipitation events the research was conducted in 3 catchments 2 95 km2 7 39 km2 22 73 km2 situated within the boundaries of the basin of the upper dades on the southern slopes of the high atlas in morocco the rivers of these catchments tributaries to a trunk river dades are ephemeral and mostly bedrock depending on lithology of the geology three automatic weather stations were installed there precipitation events 10 mm 51 rains in 3 catchments were used in the analysis simple rainfall typology 3 types was devised for these events during the research period seasonally repeated 6 times measurements of topography were obtained from 21 cross section profiles of streams of different order these measurements formed a basis for calculating both the intensity of flow in ephemeral rivers max 69 6 m s and the sediment budget in 70 of analysed channel cross sections erosion was dominant the average change of the surface area of the cross section profile is 82 the maximum seasonal between measurements enlargement of the surface cross section erosion is as high as 128 the lower catchment which is predominantly composed of conglomerates distinctly shows the slightest changes of the cross section profile surfaces max 24 the average volume of channel material displaced at the measurement point is 1 07 m3 max 9 81 m3 there is evidence that not only high intensity rains but also less intense but longer lasting rains amounting to high precipitation totals type c may result in the highest channel sediment budgets differences between a catchment lithology composed of limestones and marlstones and that composed of conglomerates have only a minor impact on sediment budgets in the first and second order channels whereas in the channels of the third and fourth order this impact is much higher it was found that sediment budgets calculated for individual channels were higher for the catchments composed of limestones and marlstones than for those composed of conglomerates even though the catchments of different lithology may have had the same number of tributaries this suggests that the sediment supply from slopes is comparatively larger in the catchments dominated by limestones and marlstones

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

formation of intracontinental basins in the opposite corners of the tabas block as coeval structures controlled by transpressional faulting iran the interaction of strike slip faults in their restraining junctions allowed for the coeval formation of the tabas and abdoughi basins and led to their inversion during the late cenozoic the intracontinental basins filled with neogene and quaternary deposits were controlled by large scale dextral transpression along major faults that bounded the tabas block which is a part of the central iranian block the anastomosing strike slip fault pattern facilitated the development of both basins in opposite corners of the tabas block the subsided areas were formed as a result of interaction between the restraining junctions of strike slip faults and thrusts flexural loading caused by the uplifted series of thrust sheets resulted in the depression of the opposite fault slabs which permitted deposition of neogene sediments deformation according to the bookshelf mechanism can be considered as a consequence of accommodation of the shortening of the area north of the main zagros thrust and externally imposed shearing along the great kavir doruneh fault during the collision of the arabian and eurasian plates related processes of transpression and counterclockwise rotation of the tectonic blocks included in the central iranian block favored the interaction of strike slip faults the change of far field stress and continuous transpression caused inversion of the basins and formation of neogene folds in the northern and southern corners of the tabas block the geomorphic features observed along these strike slip faults and on the thrust surfaces bounding the folds display their recent activity consistent with present day seismicity and geodetic measurements within the central iranian block

analysis of the infiltrative metasomatic relationships controlling skarn mineralization at the abbas abad fe cu deposit isfahan north zefreh fault central iran abstract the abbas abad volcano sedimentary hosted fe cu skarn deposit ne isfahan is one of the most important skarns in the central urumieh dokhtar magmatic arc it was formed along the contact with the dorojin granitoid massif next to the zefreh fault the plutonic rocks are of i type volcanic arc affinity with normal k metaluminous calc alkaline to calcic quartz diorite tonalite and granodiorite similar to many other fe type skarn related granitoids worldwide the parent magma involved in this skarn system is high temperature and relatively oxidized amphibole geobarometery in quartz diorite yielded a crystallization pressure lower than 200 mpa 2 kb 7 km at 724 to 785 c granitoid compositions around the ore deposit are mainly granodiorite u pb zircon dating yields early miocene ages of 23 0 1 6 ma for a quartz dioritic rock and 21 3 1 5 ma for a tonalitic sample the injection and cooling of the granodiorite produced a hornblende hornfels aureole with endoskarn paragenetic relationships and microprobe data indicate that abbas abad calcic skarn evolution can be subdivided into three stages as follow i prograde skarn associated andradite rich garnet adr93 98grs0 4spe1 2 and pyroxene ii retrograde skarn starting with garnet adr53 69grs28 43spe2 4 magnetite and sulfide minerals associated with calcic alteration and iii post ore with pyrite chalcedony epidote quartz calcite and zeolite veinlets textural and compositional studies of garnet and magnetite from the garnet bearing exoskarn zone reveal the multiple events associated with skarn formation garnets are characterized by low tio2 and relatively high cao that are indicative of a calcareous wall rock among eocene volcaniclastic rocks they are grouped into garnet 1 low w r and garnet 2 inverse zoning at high w r with notable cu contents up to 743 ppm petrographically magnetite morphology is divided into fine grained granular needle like and polycrystalline aggregates mineral chemistry of needle like type reveals impure components al2o3 cao and sio2 this type formed from dissolution reprecipitation processes during a stage of reequilibration in the skarn system mixing with cooler external fluid rich in oxygen and poor in fe2 is reflected in individual features during infiltration metasomatism during garnet and magnetite growth such as oscillatory zoning and needle like textures thus we infer increasing ph decreasing acidity and decreasing t related to carbonate neutralization reactions affecting fe and cu chloride complexing as the main controls on mineralization the structural studies of the area show that movement of the dextral transtensional zefreh fault provide local zones for emplacement of dorojin granitoid during the early miocene consequently the dextral transtensional zefreh fault and dextral transpression associated with the marbin rangan fault uplifted the skarn and host units and dorojin body under the roughly n s directed maximum compression direction furthermore the interplay of zefreh and marbin rangan faults within the n s regional compressional regime formed an anticlinal structure that exposed the dorojin body within the core