active flexural slip faulting a study from the pamir tian shan convergent zone nw china the flexural slip fault fsf a type of secondary fault generated by bed parallel slip occurs commonly and plays an important role in accommodating fold growth although the kinematics and mechanics of fsfs are well studied relatively few field observations or geometric models explore its geomorphic expression in the pamir tian shan convergent zone nw china suites of well preserved fsf scarps displace fluvial terraces in the mingyaole and wulagen folds integrating interpretations of google earth images detailed geologic and geomorphic mapping and differential gps measurements of terrace surfaces we summarize geomorphic features that typify these faults and create kinematic models of active flexural slip faulting our study indicates the following i fsf scarps commonly occur near synclinal hinges irrespective of whether a the dip direction of beds on either side of the hinge is unidirectional or in opposite directions b the hinge is migrating or fixed or c the hinge shape is narrow and angular or wide and curved ii active fsfs are likely to produce higher scarps on steeper beds whereas lower or no topographic scarps typify gentler beds iii tilt angles of the terrace surface displaced above fsfs progressively decrease farther away from the hinge with abrupt changes in slope coinciding with fsf scarps the changes in tilt angle and scarp height have a predictable geometric relationship iv active fsfs can accommodate a significant fraction of total slip and play a significant role in folding deformation v active fsfs may be used to assess seismic hazards associated with active folds and associated blind thrusts

structural analysis and interpretation of the surface deformations of the el asnam earthquake of october 10 1980 the el asnam earthquake of october 10 1980 represents the major seismotectonic event of these last decades in the west mediterranean area it has induced a large amount of surface breaks this earthquake reveals the importance of compressional phenomena that characterize nowadays the tectonics of north africa the tectonic analysis of surface rupture shows the complexity of the deformation mechanism the principal mechanism consists of the activation of a nw se trending thrust fault accompanied with a left lateral motion and with an intense deformation of the northwestern overthrusting block an accurate description of these deformations shows that for a large part the breaks geometry depends closely on the substratum structure finally the analysis of the dislocations on irrigation ducts just above the fault traces allowed a quantitative study of the deformation

kinematic models of fluvial terraces over active detachment folds constraints on the growth mechanism of the kashi atushi fold system chinese tian shan during detachment folding the relationship between differential uplift and shortening depends on the mechanism of fold growth such as limb rotation or hinge migration and may vary over the lifetime of a fold thus neither long term shortening rates nor the present fold geometry unambiguously constrain the kinematics of fold growth where rivers cut through growing anticlines flights of abandoned fluvial terraces act as passive kinematic markers as shortening progresses the terraces become deformed and thereby preserve critical information about the kinematics and evolution of active fold growth to constrain recent fold growth across three detachment folds in the kashi atushi fold system in the sw tian shan china we surveyed flights of deformed terraces and compared them with geometric models of successively emplaced horizontal unconformities terraces across pregrowth strata deformed by hinge migration limb rotation and a combination of the two migration of angular hinges and curved hinge zones were also compared each kinematic model predicts both a distinct geometry for the deformed terraces and contrasting angular relationships between the terraces and the pregrowth strata notably limb rotation and migration of curved hinge zones result in progressively rotated terraces that cut across pregrowth strata whereas all limb lengthening models result in parallelism between pregrowth strata and terrace straths across much of the fold the kashi atushi terraces show clear evidence of abandoned axial surfaces concentrated deformation near the core of the folds and progressive tilting with age when compared to the model predictions the folds are likely growing by a combination of limb rotation in the tight cores of the folds and hinge zone migration of pregrowth strata across the flanks of the folds

detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

an audiofrequency magnetotelluric traverse across the mana pools basin northern zimbabwe summary audiofrequency magnetotelluric soundings in the frequency range 0 016 128 hz have been conducted to investigate the structure of the mana pools basin in northern zimbabwe a karoo sedimentary basin in the zambezi valley data from nine tensorial soundings along a 40 km n s traverse from the river zambezi to the zimbabwe craton and a further sounding on the escarpment have been processed giving the sounding curves required for preliminary modelling studies a variety of l d inversion algorithms have subsequently been applied to these processed data sets to yield interpretive models an approximate 2 d geoelectrical section has been derived by collating the 1 d models a marked and rapid contrast in subsurface resistivity distribution between the escarpment and the basin is apparent within the basin the results show the presence of a top sequence of variable thickness up to 10 km overlying a more resistive 0 1 s m 1 unit that may represent the geoelectrical basement these top sequences which have tentatively been interpreted as sedimentary formations with different stratigraphic units consist of highly conducting 0 3 s m 1 to 1 s m 1 materials overlain by a slightly more resistive typically 0 2 s m 1 unit in some cases with another good conductor adjacent to the surface the data also suggest a rapid thinning of the top sequences close to the escarpment in contrast to the more gradual decrease of the sediments in previous geophysical models for the area on the escarpment the resistivity is higher at all depths the mana pools basin thus appears to be a continuation of the good conductor running from namibia into western zimbabwe identified by de beer 1982a and provides a link to another beneath the lower zambezi basin to the east of mana pools discovered magnetotellurically by losecke knodel muller 1988 comparisons between the geoelectrical model and other available results for the region are presented

earthquakes generated from bedding plane parallel reverse faults above an active wedge thrust seattle fault zone a key question in earthquake hazard analysis is whether individual faults within fault zones represent independent seismic sources for the seattle fault zone an upper plate structure within the cascadia convergent margin evaluating seismic hazard requires understanding how north side up bedding plane reverse faults which generate late holocene fault scarps interact with the north vergent master ramp thrust and overlying backthrust of the fault zone a regional uplift at a d 900 930 involved an earthquake that nucleated at depth and included slip on both the master ramp thrust and the backthrust this earthquake also included slip on some of the 6 km deep north side up bedding plane reverse faults at locales where the north side up reverse faults intersect the puget sound coast an earthquake a few centuries earlier than the a d 900 930 regional uplift only uplifted areas within hundreds of meters north of the reverse faults we infer that the bedding plane reverse faults are seismogenic because shore platforms near the reverse faults have been abruptly uplifted during earthquakes when other shorelines in the seattle fault zone were unaffected faults of the seattle fault zone therefore can both produce regional uplift earthquakes with or without surface displacement on the reverse faults and produce earthquakes that rupture the bedding plane reverse faults causing fault scarps and uplift localized to hundreds of meters north of these faults this latter type of earthquake has occurred at least twice and perhaps three times in the late holocene and all these earthquakes preceded the regional coseismic uplift of a d 900 930 to account for the paleoseismic observations we propose that the seattle fault zone is a wedge thrust with the leading edge being a fault bend wedge thrust fold the active axial surface of the wedge thrust fold is pinned at the tip of the wedge and a steeply north dipping sequence of tertiary sediment forms the south limb of the wedge thrust fold some of these steeply north dipping bedding plane surfaces are seismogenic reverse faults that produce scarps earthquakes on the wedge thrust produce the regional coseismic uplift events and earthquakes within the faultbend fold cause the local uplift earthquakes thus bedding plane faults can rupture during earthquakes when the wedge thrust does not rupture but instead continues to accumulate seismic energy

a review of brittle compressional wedge models abstract fold and thrust belts and accretionary wedges form by compression of sedimentary sequences and basement rocks into forward and backward thrusts folds nappes and duplexes for over a century models have been used to investigate the essential characteristics of such brittle wedges here i review model studies of brittle thrust wedges in orthogonal compression focussing on critical taper theory analogue and numerical techniques for modelling brittle behaviour and the most commonly investigated variations in wedge model studies those in basal dip basal strength internal strength and surface processes many model results can be placed in the context of critical taper theory which provides analytical solutions for wedge taper angle and slip line orientations for a homogeneous material on the verge of failure throughout dynamic forward models have confirmed critical taper predictions of decreasing surface dip for increasing basal dip wider wedges with steeper forward thrusts and shallower backward thrusts for decreasing basal strength narrower wedges and enhanced exhumation for surface erosion and decreasing surface dip for increasing internal strength but analogue and numerical models have been able to take these results a step further by investigating the evolution of non critical thrust wedges and the effects of non homogeneous materials with decollement layers and strain weakening shear zones these results have highlighted the strong impact of heterogeneous materials on the internal structures of thrust wedges and raise the question whether the complexity of structures that are observed in many natural fold and thrust belts requires that lithological layering inherited faults or a wide range of rheologies need to be included in forward models of brittle thrust wedges

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

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

automatic bayesian polarity determination this work was funded under a natural environment research council nerc studentship as a case award with schlumberger seismometers were borrowed from the nerc seis uk loan 842 who also archive the data

late quaternary slip rates across the central tien shan kyrgyzstan central asia 1 slip rates across active faults and folds show that late quaternary faulting is distributed across the central tien shan not concentrated at its margins nearly every intermontane basin contains neogene and quaternary syntectonic strata deformed by holocene north south shortening on thrust or reverse faults in a region that spans two thirds of the north south width of the central tien shan slip rates on eight faults in five basins range from 0 1 to 3 mm yr fault slip rates are derived from faulted and folded river terraces and from trenches radiocarbon optically stimulated luminescence and thermoluminescence ages limit ages of terraces and aid in their regional correlation monte carlo simulations that sample from normally distributed and discrete probability distributions for each variable in the slip rate calculations generate most likely slip rate values and 95 confidence limits faults in basins appear to merge at relatively shallow depths with crustal scale ramps that underlie mountain ranges composed of pre cenozoic rocks the sum and overall pattern of late quaternary rates of shortening are similar to current rates of north south shortening measured using global positioning system geodesy this similarity suggests that deformation is concentrated along major fault zones near range basin margins such faults separated by rigid blocks accommodate most of the shortening in the upper crust index terms 8107 tectonophysics continental neotectonics 9320 information related to geographic region asia 8010 structural geology fractures and faults

late cenozoic tectonic evolution of the southern chinese tian shan structural sedimentological magnetostratigraphic and 40ar 39ar thermochronological investigations were conducted in the southern chinese tian shan on the basis of our own mapping and earlier investigations in the area the late cenozoic southern tian shan thrust belt may be divided into four segments based on their style of deformation from west to east they are 1 kashi aksu imbricate thrust system 2 the baicheng kuche fold and thrust system 3 the korla right slip transfer system and 4 the lop nor thrust system the westernmost kashi aksu system is characterized by the occurrence of evenly spaced 12 15 km imbricate thrusts the baicheng kuche and korla systems are expressed by a major north dipping thrust the kuche thrust that changes its strike eastward to become a nw striking oblique thrust ramp the korla transfer zone the lop nor system in the eastern most part of the southern chinese tian shan consists of widely spaced thrusts all involved with basement rocks geologic mapping and cross section construction suggest that at least 20 40 km of crustal shortening with a horizontal shortening strain of 20 30 has occurred in the southern chinese tian shan during the late cenozoic these estimates are minimum because of both conservative extrapolation of the thrust geometries and partial coverage of the thrust belt by the cross sections the timing of initial thrusting is best constrained in the kuche basin where crustal shortening may have occurred at 21 24 ma the time of a major facies transition between lacustrine and braided fluvial sequences constrained in general by biostratigraphy and in detail by magnetostratigraphy this estimate represents only a minimum age as development of thrusts in the southern chinese tian shan may have propagated southward toward the foreland thus the sedimentary record only represents the southernmost and therefore youngest phase of thrusting if our estimate of timing for the thrust initiation 21 24 ma is correct using the estimated magnitude of shortening 20 40 km and shortening strain 20 30 the averaged rates of late cenozoic horizontal slip and shortening strain are 1 1 9 mm yr 1 and 2 9 4 5 10 16 s 1 respectively our reconnaissance 40ar 39ar thermochronological analysis in conjunction with earlier published results of apatite fission track analysis by other workers in the chinese tian shan suggests that the magnitude of cenozoic denudation is no more than 10 km most likely less than 5 km we demonstrate via a simple airy isostasy model that when the thermal effect on changes in surface elevation is negligible determination of the spatial distribution and temporal variation of both horizontal shortening strain and denudation becomes a key to reconstructing the elevation history of the tian shan using this simple model the loosely constrained magnitude of crustal shortening strain and denudation in the southern chinese tian shan implies that it may have been elevated 1 0 2 0 km since the onset of cenozoic thrusting

stratigraphic controls on eformation patterns in fault related folds a detachment fold example from the sierra madre oriental northeast mexico abstract deformation patterns are described by the style intensity and distribution of structures throughout a volume of rock in fault related folds presently observed deformation patterns are controlled by structural factors like kinematic history environmental factors like burial history and stratigraphic factors like layer thickness and competence to demonstrate the role of stratigraphy in controlling fold related deformation patterns we document the stratigraphic variability of mesostructures at one structural position on a map scale detachment fold unique assemblages of faults fractures and cleavages in certain stratigraphic intervals define a mechanical stratigraphy comprised of several units each exhibiting a characteristic deformation response to the folding process the varying response of each mechanical unit suggests that folding mechanisms such as orthogonal flexure flexural slip or flexural flow were sequentially or coevally operative in each of the units using the simple theoretical strain distributions associated with each folding mechanism and the fact that each mechanical unit accommodates fold related strain by developing a characteristic set of mesostructures we are able to predict general deformation patterns elsewhere in the fold the significance of this approach is that it recognizes that even in a single structure fold kinematics and deformation response may be dramatically different in various parts of a stratigraphic section because of this the quality and character of reservoir rocks in anticlinal traps may change markedly over short stratigraphic distances predictions of fold related deformation based solely on fold kinematics are unlikely to resolve these variations

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

folding kinematics expressed in fracture patterns an example from the anti atlas fold belt morocco the anti atlas fold belt morocco formed during the same variscan collisional event that produced the valley and ridge fold thrust belt of the appalachian mountains both are external belts of the appalachian ouachita mauritanides chain and at the map scale have very similar topographic expressions the anti atlas however consists of map scale folds that are buckle related detachment folds whereas the valley and ridge folds developed in response to imbricate thrusting for this reason the anti atlas is referred to as a fold belt rather than a fold thrust belt this paper examines variscan folding processes in the anti atlas mountains folding in some layers occurred by sliding along a penetrative network of mesoscale fractures i e cataclastic flow during buckling layer parallel shortening fractures were reactivated in the later stages of folding to accommodate limb rotation although boutonnieres i e basement uplifts punctuate the fold belt the fracture patterns indicate that the uplifts failed to provide any bending component folding is also interpreted to occur under low to moderate confining pressures because the fracture network includes conjugate shear fractures with very small 20 dihedral angles

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

syntectonic sedimentation effects on the growth of fold and thrust belts we use two dimensional mechanical models to investigate the effects of syntectonic sedimentation on fold and thrust belt development testing variable syntectonic wedge top and foredeep sediment thicknesses and flexural rigidities model results indicate a first order control of syntectonic sedimentation on thrust sheet length and thrust spacing thrust sheets are longer when syntectonic sediment thickness and or flexural rigidity increase comparison with observations from several fold and thrust belts confirms this first order control of syntectonic sedimentation

coseismic and blind fault of the 2015 pishan mw 6 5 earthquake implications for the sedimentary tectonic framework of the western kunlun mountains northern tibetan plateau on 3 july 2015 the mw 6 5 pishan earthquake occurred in the western kunlun mountains front at the northern margin of the tibetan plateau to reveal the sedimentary tectonic framework of the seismically active structure three high resolution seismic reflection profiles and well drilling data were collected for seismic interpretation the western kunlun mountains and tarim basin have two gypseous detachments and one basement detachment that control the tectonic framework and structural deformation the upper gypseous detachment d1 is in the lower paleocene and the middle gypseous detachment d2 is in the middle to lower cambrian a neogene shallow thrust system is developing above d1 and includes the zepu fault f2 and mazar tagh fault f3 a deep thrust system is developing between d1 and d2 and forms a large scale structural wedge beneath the western kunlun mountains front the pishan mw 6 5 earthquake was triggered on a frontal blind fault of this deep thrust system the lower detachment is in the proterozoic basement d3 which extends into the tarim basin and develops another deep thrust f4 beneath the f3 belt d1 d2 d3 and the tiekelike fault f1 merge together at depth crustal shortening of the western kunlun mountains front continues for approximately 54 km two tectonic evolutionary stages have occurred since the miocene according to sedimentary unconformity axial analysis and fault interpretation the results of this study indicate a regime of episodic growth of the western kunlun mountains and tarim basin during the cenozoic

oceanic style subduction controls late cenozoic deformation of the northern pamir orogen abstract the northern part of the pamir orogen is the preeminent example of an active intracontinental subduction zone in the early stages of continent continent collision such zones are the least understood type of plate boundaries because modern examples are few and of limited access and ancient analogs have been extensively overprinted by subsequent tectonic and erosion processes in the pamir it has been assumed that most of the plate convergence was accommodated by overthrusting along the plate bounding main pamir thrust mpt which forms the principal northern mountain and deformation front of the pamir however the synopsis of our new and previously published thermochronologic data from this region shows that the hanging wall of the mpt experienced relatively minor amounts of late cenozoic exhumation the pamir orogen as a whole is an integral part of the overriding plate in a subduction system while the remnant basin to the north constitutes the downgoing plate with the bulk of the convergence accommodated by underthrusting herein we demonstrate that the observed deformation of the upper and lower plates within the pamir alai convergence zone resembles highly arcuate oceanic subduction systems characterized by slab rollback subduction erosion subduction accretion and marginal slab tear faults we suggest that the curvature of the north pamir is genetically linked to the short width and rollback of the south dipping alai slab northward motion indentation of the pamir is accommodated by crustal processes related to this rollback the onset of south dipping subduction is tentatively linked to intense pamir contraction following break off of the north dipping indian slab beneath the karakoram

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

active tectonics in southern xinjiang china analysis of terrace riser and normal fault scarp degradation along the hotan qira fault system the northern piedmont of the western kunlun mountains xinjiang china is marked at its easternmost extremity south of the hotan qira oases by a set of normal faults trending n50e for nearly 70 km conspicuous on landsat and spot images these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the tarim platform loaded by the western kunlun northward overthrust the hotan qira normal fault system vertically offsets the piedmont slope by 70 m highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high successive stream entrenchments in uplifted footwalls have formed inset terraces we have leveled topographic profiles across fault scarps and transverse abandoned terrace risers the state of degradation of each terrace edge has been characterized by a degradation coefficient derived by comparison with analytical erosion models edges of highest abandoned terraces yield a degradation coefficient of 33 4 m 2 profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model the analysis shows that 1 rate of fault slip remained essentially constant since the aggradation of the piedmont surface and 2 the occurrence of inset terraces was synchronous at all studied sites suggesting a climate driven terrace formation observation of glacial and periglacial geomorphic features along the northern front of the western kunlun range indicates that the qira glaciofluvial fan emplaced after the last glacial maximum during the retreat of the kunlun glaciers 12 22 ka the age of the most developed inset terrace in uplifted valleys is inferred to be 10 3 ka coeval with humid climate pulses of the last deglaciation the mass diffusivity constant k t being time b p in the hotan region is determined to be 3 3 1 4 m 2 10 3 years consistent with other estimates in similar climatic and geologic environments of western china these results imply a minimum rate for the tarim subsidence of 3 5 2 mm yr if western kunlun overthrusts the tarim platform on a crustal ramp dipping 40 45 to the south it would absorb at least 4 5 3 mm yr of convergence between western tibet and tarim

major temporal variations in shortening rate absorbed along a large active fold of the southeastern tianshan piedmont china the investigation of deformation rates on a mountain piedmont can provide key information for improving our understanding of the overall dynamics of a mountain range here we estimate the shortening rate absorbed by a quaternary emergent detachment fold on the southeastern piedmont of the tianshan china our work is primarily based on new 10be cosmogenic exposure dating of deformed alluvial surfaces the method we have developed combines depth profiling with sampling of surface cobbles thereby allowing exposure time erosion rate and inheritance to be simultaneously constrained the exposure ages of the uppermost uplifted alluvial surfaces are around 140 17 ka140 17 ka 130 9 ka130 9 ka and 47 9 ka47 9 ka from west to east a terrace lying below the 140 ka surface is dated at 65 5 ka65 5 ka the ages of the uplifted and folded alluvial surfaces were then combined with estimates of shortening obtained using two distinct methods 1 the excess area method where sedimentation rates extracted from magnetostratigraphic studies are used to determine the amount of sedimentation after the abandonment of the river and 2 a folding model derived from sandbox experiments the late pleistocene shortening rates are shown to be between 0 4 0 1 mm yr0 4 0 1 mm yr and 0 8 0 5 mm yr0 8 0 5 mm yr on the western part of the fold and 2 1 0 4 mm yr2 1 0 4 mm yr along its central part the central part of the frontal yakeng anticline therefore accommodates up to 25 of the total shortening currently absorbed across the whole eastern tianshan range 8 mm yr however this situation seems to have prevailed for only the last 150 ka as the shortening rate absorbed by this nascent fold was previously ten times slower while the initiation of folding of the yakeng anticline can be traced back to 5 5 ma ago the basinward migration of the active deformation front onto the yakeng fold is a relatively recent phenomenon and appears to be diachronous from west to east probably in relation to the tectonic activity of the folds in the hinterland

late cenozoic tectonics of the kepingtage thrust zone interactions of the tien shan and tarim basin northwest china the kepingtage kalpin thrust zone northwest china is an actively deforming part of the india asia collision system it lies south of the tien shan has an area of 16 000 km2 and consists of arcuate emergent imbricates overall vergence is toward the interior of the tarim basin to the south thrust sheets typically expose upper cambrian to permian platformal strata thrusting is largely thin skinned thin upper cambrian evaporites are likely to be the main decollement horizon the kepingtage thrust zone is the only margin of the tarim basin to deform in this style in the cenozoic it is replaced to the east and west by thrust zones which have propagated shorter distances into the interior of the tarim basin thick up to 10 km mesozoic and cenozoic clastic successions are present and deformed in these regions such successions are not present in the kepingtage thrust zone or the adjacent bachu uplift within the tarim basin because of episodic activity on steep northwest southeast trending thrusts which define the margins of the bachu uplift these mesozoic cenozoic strata may have suppressed the ability of regions along strike from the kepingtage thrust zone to deform by thin skinned thrusting utilizing the upper cambrian decollement the along strike variation in active thrusting at the southern margin of the tien shan is an example of syntectonic sedimentation controlling thrust belt deformation style a balanced section across the thrust zone indicates 28 shortening equivalent to 35 km this is equivalent to an average slip rate of 1 8 mm yr 1 and a strain rate of 4 4 10 16 s 1 assuming deformation began at circa 20 ma active deformation is focused along the frontal thrust the kepingtage fault the northern boundary of the kepingtage thrust zone is formed by the south tien shan fault this major north dipping thrust is seismically active with published earthquake focal depths at midcrustal levels 14 and 18 km it juxtaposes upper carboniferous sedimentary rocks of different facies and different paleozoic deformation histories speculatively it represents a reactivation of a late paleozoic thrust which originated at the boundary between the platformal interior of the tarim block and a deeper water foreland basin to its north

late oligocene early miocene initiation of shortening in the southwestern chinese tian shan implications for neogene shortening rate variations abstract the cenozoic tian shan is one of the preeminent examples of an intracontinental orogen however there remains a significant controversy over when deformation related to the india asia collision commenced and therefore how shortening within the mountains has been partitioned over time one approach has been to look at the modern shortening rate as measured by geodetic studies combined with estimates of the total shortening across the range and extrapolate backwards this approach suggests that the onset of range construction was ca 10 ma k y abdrakhmatov s a aldazhanov b h hager m w hamburger t a herring k b kalabaev k b kalabayev v i makarov p molnar s v panasyuk m t prilepin r e reilinger i s sadybakasov b j souter y a trapeznikov v y tsurkov a v zubovich relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates nature 384 6608 1996 450 453 an alternate method is to determine the age of the onset of exhumation using thermochronology we present 19 new apatite fission track aft results from the southwestern chinese portion of the belt this region represents the first area exhumed during the late tertiary along a transect at ca 76 e exhumation commenced at the oligocene miocene boundary 24 ma along the maidan and muziduke thrusts which bound the southern side of the kokshaal range subsequently deformation propagated ca 20 km south to the kashi basin bounding thrust kbt which was exhumed by no earlier than 18 9 3 3 ma three detrital aft samples from plio pleistocene strata deposited ca 20 km farther south contain fission track grain age peaks that young monotonically upwards from 20 9 7 0 5 3 ma to 15 9 5 4 4 0 ma with a fairly constant lag time of 16 to 18 ma these ages combined with structural data suggest that both the hanging wall and the footwall of the kbt experienced a renewed episode of exhumation during the latest cenozoic the discrepancy between the late oligocene miocene initiation of significant exhumation shown herein and the 10 ma initiation estimate from geodesy suggests that the tian shan has undergone a complex late cenozoic shortening history assuming that the present shortening rate could account for the total amount of cenozoic shortening in 10 ma and realizing that shortening initiated at least 15 myr earlier we conclude that the shortening rate must have varied over time possibly in pulsed southward migrating events and that the present rate may not reflect the average rate since initiation of range uplift

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

gps velocity field for the tien shan and surrounding regions 1 measurements at 400 campaign style gps points and another 14 continuously recording stations in central asia define variations in their velocities both along and across the kyrgyz and neighboring parts of tien shan they show that at the longitude of kyrgyzstan the tarim basin converges with eurasia at 20 2 mm yr nearly two thirds of the total convergence rate between india and eurasia at this longitude this high rate suggests that the tien shan has grown into a major mountain range only late in the evolution of the india eurasia collision most of the convergence between tarim and eurasia within the upper crust of the tien shan presumably occurs by slip on faults on the edges of and within the belt but 1 3 mm yr of convergence is absorbed farther north at the dzungarian alatau and at a lower rate with the kazakh platform to the west the tarim basin is thrust beneath the tien shan at 4 7 mm yr with respect to eurasia the ferghana valley rotates counterclockwise at 0 7 myr 1 about an axis at the southwest end of the valley thus gps data place a bound of 4 mm yr on the rate of crustal shortening across the chatkal and neighboring ranges on the northwest margin of the ferghana valley and they limit the present day slip rate on the right lateral talas ferghana fault to less than 2 mm yr gps measurements corroborate geologic evidence indicating that the northern margin of the pamir overthrusts the alay valley and require a rate of at least 10 and possibly 15 mm yr

temporal constraints and pulsed late cenozoic deformation during the structural disruption of the active kashi foreland northwest china 1 in response to the ongoing indo asian collision structural deformation has encroached into the tian shan foreland in western china since the early miocene in order to reconstruct a detailed history of foreland deformation along the southern margin of the tian shan we have synthesized extensive mapping analysis of seismic sections magnetostratigraphy of the foreland fill and associated growth strata apatite fission track dating changes in sediment accumulation rates and geodetic surveys of deformed fluvial terraces across an area exceeding 6500 km2 that spans the kashi foreland in the northwestern tarim basin we use these data to place temporal constraints on individual structures that delineate at least 4 distinct stages of deformation stage 1 involved initial uplift of hinterland structures beginning at 20 25 ma stage 2 began at 16 3 ma when the basement involved deformation front stepped south to the kashi basin thrust that bounds the foredeep strata stage 3 occurred from 13 5 to 4 ma as the deformation front migrated south in episodic steps above thin skinned detachment and ramp flat folding finally stage 4 began after 4 ma with growth of the keketamu anticline followed by rapid southward migration of the deformation front to the atushi and then kashi detachment anticlines on the basis of the deformed tertiary strata and available seismic data calculations of the minimum magnitude of shortening yield totals ranging from 10 to 32 km since the early miocene of which 7 12 km occurred since 4 ma although average shortening rates since 16 3 ma were 0 8 1 3 mm a rates were faster from 16 3 to 13 5 ma 1 1 3 2 mm a after which they decreased to 0 5 mm a between 13 5 and 4 ma before increasing to 2 2 2 7 mm a after 4 ma similarly the rate of southward propagation of the deformation front was initially 3 7 mm a for the first 10 ma of basin development slowed to 1 5 mm a between 13 5 and 4 ma and increased to more than 10 mm a since 4 ma these changes in shortening and structural migration rates over time suggest that the loci of orogenic deformation shifted in and out of the foreland during the neogene surveyed stream terraces suggest that although most current deformation is located along the southern front of the foreland modest deformation and shortening continue in the hinterland structural style within the foreland has also changed over time from imbricate thrust faults with hanging wall folds along the northern margin to ramp flat faults and detachment folds along the southern margin where the basement rocks are previously deformed such as in the hinterland of the kashi foreland thick skinned fault ramps and related fault propagation folds dominate the structural style as syntectonic sedimentation within the foreland produced thick subhorizontal stratigraphy the structural style evolved to detachment and fault bend folding above these footwall flats within the neogene strata

pliocene pleistocene initiation style and sequencing of deformation in the central tien shan in response to the indo asian collision deformation of the tien shan initiated at 25 ma along the northwestern margin of the tarim basin 300 km north the kyrgyz range began deforming 15 ma later although multiple intervening structures across the tien shan are currently active the sequencing of initial deformation across the orogen s entire width remains poorly known to determine whether deformation migrated sequentially northward or developed less predictably we documented deformation patterns within the naryn basin in south central kyrgyzstan detailed mapping and a published balanced cross section across the naryn basin suggest that deep seated relatively steeply dipping thrust faults have disrupted the basin during late cenozoic deformation dating of deformed fluvial terraces with ages between 10 and 250 ka constrains the rate of deformation across relatively young structures in the tien shan interior based on geodetic surveys of dated terraces local rates of relative rock uplift span from 0 3 to 3 5 mm yr folding rates and patterns are temporally persistent at a given site moreover they mimic modern geodetic rates measured from interferometric synthetic aperture radar extrapolating these rates into the past suggests that structures within the interior of the naryn basin formed in the last 1 myr whereas the ranges surrounding the basin initiated at least 1 4 myr earlier hence within the naryn basin itself deformation has migrated from margins to interior similarly these new chronologies indicate that at least some deformation in the interior of the tien shan initiated millions of years later than along either orogenic margin 2014 american geophysical union all rights reserved

mechanisms of active folding of the landscape southern tian shan china 1 we explore the kinematic mechanisms of active large scale folding based on analysis of two adjacent major anticlines in tian shan central asia that share an acceleration of shortening rate leading to topographic emergence and folded geomorphic surfaces their folding mechanisms are fundamentally different yakeng anticline is a gentle pure shear detachment fold with 1200 m of shortening and a well constrained history of growth beginning at 5 5 ma with an order of magnitude increase in shortening rate from 0 16 to 1 2 1 6 mm yr at 0 16 0 21 ma the shape of the deformed topographic surface and of subsurface horizons deposited during deformation is a linearly proportional image at reduced amplitude of the deeper structure which shows that instantaneous uplift rates have been pointwise linearly proportional to the current finite fold amplitude in contrast quilitak anticline is a complex fault bend fold with uplift rates proportional to the sine of the fault dip showing discontinuities in uplift rate across active axial surfaces the 10 to 20 km wide anticline is topographically emergent only in a central 5 to 7 km wide mountainous uplift the abrupt southern edge of which is marked by 600 to 700 m high triangular facets that result from active folding of a pediment across an active axial surface the giant facets are shown to form by kink band migration and record postemergence deformation since an order of magnitude acceleration in shortening rate from 0 6 to 4 5 mm yr apparently contemporaneous with yakeng sections logged across the active 115 m wide hinge zone show that recent strata provide a bed by bed record of fold scarp growth which is quantitatively deciphered by fitting bed shapes to a finite width kink band migration model

quantification of growth and lateral propagation of the kashi anticline southwest chinese tian shan received 11 february 2006 revised 16 january 2007 accepted 2 february 2007 published 28 march 2007 1 the kashi anticline is a north vergent asymmetric doubly plunging detachment fold located in the sw tian shan foreland we combine structural magnetostratigraphic and topographic data to define the fold s lateral propagation surface uplift and concomitant exhumation two new magnetostratigraphic sections indicate that the fold began growing at 1 4 ma and by 1 07 ma deformation had propagated eastward 13 km at an average rate of 40 km myr subsequently propagation rates increased at least twofold until the fold reached 60 km in length by 0 8 0 3 ma since then eastward fold propagation slowed to 15 km myr and the eastern 15 25 of the fold remains buried in the rapidly aggrading foreland the structure and topography of the emergent fold support interpretations of fold growth in three stages initial symmetric lateral growth both east and west to a total length of 30 km followed by first rapid and then slower eastward lengthening to 72 10 km total length shortening rates as high as 1 9 0 2 0 3 mm yr characterize the western part of the fold but decrease toward the east significant dissection of the emergent fold does not occur until topographic relief is sufficient 200 m to permit stripping of protective conglomerates from across the fold s upper surface as differential rock uplift continues following breaching of the conglomerate 75 of the rock raised above local base level is subsequently eroded at rates as high as 2 4 km myr despite extensive erosion the modern fold topography mimics spatial patterns of both long term shortening and variations in rock uplift

late pleistocene shortening rate on the northern margin of the yanqi basin southeastern tian shan nw china abstract how strain is distributed and partitioned on individual faults and folds on the margins of intermontane basins remains poorly understood the haermodun ha anticline located along the northern margin of the intermontane yanqi basin on the southeastern flank of the tian shan preserves flights of passively deformed alluvial terraces these terraces cross the active anticline and can be used to constrain local crustal shortening and uplift rates geologic and geomorphic mapping in conjunction with high resolution dgps topographic surveys reveal that the terrace surfaces are perpendicular to the fold s strike and display increased rotation with age implying that the anticline has grown by progressive limb rotation combined with the open sinusoidal curve model and excess area method we calculated uplift and shortening values for each terrace since abandonment using the published exposure ages of each terrace we found the vertical uplift rate gradually decreased from 0 43 to 0 11 mm a whereas the shortening rate remained constant at 0 3 mm a since the anticline began to grow a fresh fault scarp 0 4 0 1 m high is visible along the southern portion of the ha anticline and is interpreted to be the most recent evidence of seismic activity using an estimated rupture area and the length of the fresh offset created by this earthquake we estimate that the main thrust underlying the ha anticline has generated moderate m

aspects and origins of fractured dip domain boundaries in folded carbonate rocks abstract we present comparative field studies in folded areas southern france moroccan western atlas and abruzzo italy giving new insights into fracture distribution within folded rocks of the shallow brittle crust we show that the curvature in folds formed in brittle mechanical units is usually accommodated by multiple dip domain boundaries appearing as curvature discontinuities at fold scale corresponding to relatively narrow and dense fracture zones striking parallel or slightly oblique to the fold axis they separate dip domains where curvature is absent or moderate it is shown that the dip domain boundaries which are obvious in the case of kink folds or box fold anticlines are currently present as multiple subtle hinges even when the curvature appears continuous at first sight the nature of dip domain boundaries is studied they often cut through the whole thickness of the mechanical units their internal structure varies and a non exhaustive typology is proposed for each type an interpretative kinematic scenario shows how the dip domain boundaries could initiate and develop we suggest two kinds of origins 1 they could correspond to the reactivation of inherited along strike fracture zones opening mode fracture concentrations such as big joints fracture corridors inherited faults etc 2 they could be created as mechanical instabilities during the fold formation syn folding origin in particular through small reverse faults in both cases early zones of weakness localize the dip domain boundaries and control the increase in curvature in association with increasing fracture density within the boundary because they represent well defined vertically and axially persistent sub seismic fracture zones generally limited to the thickness of the folded unit dip domain boundaries could enhance the axial permeability of folded and fractured reservoirs

exhumation history of the west kunlun mountains northwestern tibet evidence for a long lived rejuvenated orogen abstract how and when the northwestern tibetan plateau originated and developed upon pre existing crustal and topographic features is not well understood to address this question we present an integrated analysis of detrital zircon u pb and fission track double dating of cenozoic synorogenic sediments from the kekeya and sanju sections in the southwestern tarim basin these data help establishing a new chronostratigraphic framework for the sanju section and confirm a recent revision of the chronostratigraphy at kekeya detrital zircon fission track ages present prominent triassic early jurassic 250 170 ma and early cretaceous 130 100 ma static age peaks and paleocene early miocene 60 21 ma to eocene late miocene 39 7 ma moving age peaks representing source exhumation triassic early jurassic static peak ages document unroofing of the kunlun terrane probably related to the subduction of paleotethys oceanic lithosphere in combination with the occurrence of synorogenic sediments on both flanks of the kunlun terrane these data suggest that an ancient west kunlun range had emerged above sea level by triassic early jurassic times early cretaceous fission track peak ages are interpreted to document exhumation related to thrusting along the tam karaul fault kinematically correlated to the main pamir thrust further west widespread middle late mesozoic crustal shortening and thickening likely enhanced the early mesozoic topography paleocene early eocene fission track peak ages are presumably partially reset limited regional exhumation indicates that the early cenozoic topographic and crustal pattern of the west kunlun may be largely preserved from the middle late mesozoic the main pamir tam karaul thrust belt could be a first order tectonic feature bounding the northwestern margin of the middle late mesozoic to early cenozoic tibetan plateau toward the tarim basin late oligocene early miocene steady exhumation at a rate of 0 9 km myr is likely related to initial thrusting of the tiklik fault and reactivation of the tam karaul thrust thrusting together with upper crustal shortening in the mountain front indicates basinward expansion of the west kunlun orogen at this time this episode of exhumation and uplift associated with magmatism across western tibet is compatible with a double sided lithospheric wedge model primarily driven by breakoff of the indian crustal slab accelerated exhumation of the mountain front at a rate of 1 1 km myr since 15 ma supports active compressional deformation at the margins of the northwestern tibetan plateau we thus propose that the west kunlun mountains are a long lived topographic unit dating back to triassic early jurassic times and have experienced middle late mesozoic to early cenozoic rejuvenation and late oligocene miocene expansion

outward growth of the tibetan plateau during the cenozoic a review abstract the surface uplift history of the tibetan plateau tp offers a key testing ground for evaluating models of collisional tectonics and holds important implications for processes ranging from global cooling to the onset of the asian monsoon various models have been proposed to reveal the surface uplift history of the tp but controversies remain we evaluate these models using data from sedimentology and stratigraphy structural geology magmatism exhumation and paleoaltimetry studies structural analyses indicate that thrust belts which spread from the central tp outward toward its surrounding margins accommodated most of the india asia convergence and facilitated crustal shortening and thickening in the central tp eocene adakitic rocks located in the qiangtang and the lhasa blocks likely were generated by partial melting of an eclogitic source paleogene 50 30 ma potassic rocks only occur in the qiangtang block whereas late oligocene late miocene 26 8 ma potassic rocks occur both in the qiangtang and lhasa blocks low temperature thermochronologic ages in the central tp are older than 40 35 ma whereas those in the margins are younger than 20 ma mostly late miocene and pliocene pleistocene in age independent paleoaltimetry estimates suggest that the lhasa and qiangtang terranes attained their current elevations during the eocene most likely due to the initial collision between india and lhasa whereas the hoh xil basin area to the north and himalayas to the south were still low even below sea level in the latter case we argue for an inside out growth pattern for the tibetan plateau the tp grew southward and northward from a nucleus of high topography and is likely to continue expanding along the mazar tagh fault to the northwest the kuantai shan hei shan longshou shan to the northeast the longquan shan to the east and the shillong plateau to the south if the northward force of india would not diminished

geomorphological markers of faulting and neotectonic activity along the western andean margin northern chile in the atacama desert northern chile some ephemeral channels are developed in the plio quaternary alluvial sequence that caps the neogene atacama gravels formation geomorpho logical studies and high resolution digital elevation data gps along a structural transect in the cen tral depression are used to document modern growth history of subtle folding and faulting in the fore arc region outcrop data of the most recent deposits are combined with observations of warped and faulted late quaternary pediments alluvial fans and terrace surfaces to propose unsuspected neotec tonic processes on the western flank of the domeyko cordillera neotectonic process recognition is here based largely upon the interpretation of alluvial landforms drainage organisation and evolution as the intermittent river network shows systematic patterns of course deflections successive incisions or deposition processes as it encounters the fault scarps or folds in the superficial deposits this area presents both n s trending active vertical faults in the topographically higher pampas and n s trending active folding in the lower pampas these faults seem to accommodate e w extension and compression that could be related to uplift of the western andean margin within a compressive context uplift may have taken place unevenly over the past few million years after the deposition of the superficial alluvial surfaces that cap the neogene atacama gravels copyright 2003 john wiley sons ltd

uplift of the west kunlun range northern tibetan plateau dominated by brittle thickening of the upper crust high resolution seismic reflection data from the west kunlun range front show that crustal structures beneath the northwestern margin of the tibetan plateau are dominated by nappes of upper crustal rocks geological cross section balancing suggests an average of 24 6 54 km 38 52 of upper crustal shortening this horizontal shortening by brittle folding and faulting in the upper crust correlates positively with crustal thickening an increase in moho depth by 5 7 km and the topography our work suggests that upper crustal shortening is a chief factor for topographic uplift and crustal thickening at the northwestern margin of the tibetan plateau such a mechanism is different from that proposed for the plateau south of the karakax strike slip fault where crustal flow may have played a prominent role in plateau uplift

flexural slip folding in the meguma group nova scotia canada abstract flexural slip folding has been established for two anticlines in the meguma group nova scotia flexural slip postdates the main acadian episode of flexural flow fold growth and represents a late brittle ductile reactivation of the fold belt flexural slip structures are dominated by bedding parallel movement horizons but include a linked system of frontal and lateral ramps and conjugate movement horizons slip amount calculated from displacement of discordant quartz veins combined with vein spacing indicates an average local shear strain of approximately 0 5 however because flexural slip occurred when the fold limbs were steep the shear strain accounts for a small change in limb dip 4 8 variation of slip amount with spacing of movement horizons suggests progressive flexural slip was accommodated by continuous initiation of new movement horizons as well as continuing slip on existing movement horizons the presence of quartz veins along flexural slip structures together with evidence for ductile deformation coeval with flexural slip suggests that slip episodes were fluid assisted and intermittent separated by periods of ductile deformation and build up of fluid pressure flexural slip veins in the ovens anticline are auriferous and a flexural slip model may be appropriate for other similar meguma gold deposits thrust sheets up to 10 m thick occurring on a fold limb are interpreted to have originated in flat box fold hinges and to have been placed onto the steep limbs of the chevron folds during the flexural slip episode thrusting may have assisted the transformation of a box fold into a chevron

magnetochronology of the upper cenozoic strata in the southwestern chinese tian shan rates of pleistocene folding and thrusting abstract the southwestern chinese tian shan of central asia is an actively deforming part of the indian asian collision system paleomagnetic investigations of two plio pleistocene terrestrial successions provide the first detailed magnetostratigraphy for the upper cenozoic strata in this region paleomagnetic samples were collected from 358 sites within the atushi formation and xiyu formation across the atushi talanghe anticline near atushi thermal demagnetization behavior reversal and fold tests of paleomagnetic stability indicate that the characteristic remanence directions were acquired before tilting and folding of the strata a composite magnetostratigraphic section for this sequence correlates with the mammoth subchron to the jaramillo subchron between 3 3 and 1 07 myr of the geomagnetic polarity timescale of cande and kent j geophys res 100 1995 6093 6095 the mean declination 349 3 in the boguzihe section indicates a counterclockwise vertical axis rotation 11 2 during the past 1 4 myr the conglomeratic xiyu formation is time transgressive along its progradational contact with the underlying atushi formation across a map distance of 6 km the basal contact ranges from less than 1 0 myr in the ganhangou section to 1 9 myr in the boguzihe section to the southwest and to 2 8 myr on the northwest limb of the anticline northeastward lateral propagation and growth of the atushi talanghe anticline initiated at 1 4 myr in the boguzihe and 1 2 myr in the ganhangou the cross section in the boguzihe provides a conservative maximum estimate of shortening rate of 3 3 4 4 mm yr and uplift rate of 3 mm yr this rate represents about half of the geodetically determined shortening rate between the northern tarim basin and the kyrgyz tian shan wang et al acta seismol sin 22 2000 263 270 reiger et al earth planet sci lett 191 2001 157 165 during fold growth over the past 1 4 myr the crest of the atushi talanghe anticline eroded at an average rate of 2 6 2 7 mm yr

hinge migrated fold scarp model based on an analysis of bed geometry a study from the mingyaole anticline southern foreland of chinese tian shan 2015 american geophysical union all rights reserved fold scarps a type of geomorphic scarp formed by folding mechanisms of hinge migration or limb rotation serve to delineate both fault bend characteristics and folding histories which can in turn illuminate tectonic processes and seismic hazards associated with thrust systems because the subsurface geometry of folds is commonly difficult to determine existing fold scarp models which rely on both the fold type and its causative fault geometries remain uncertain with respect to the kinematic evolution of a given fold in this paper we develop a model to illustrate that irrespective of specific fold type and subsurface geometries fold scarp growth in the mechanism of hinge migration can be successfully reconstructed based on analyses of bed geometry this model reveals that the underlying bed dips and the ratio of hinge migration distance hinge width control the fold scarp shape and slope during initial growth ratio 1 the slope reaches a maximum which solely depends on underlying bed dips the scarp height however is independent of the hinge width and can be used to quantify folding magnitude application of our model to fold scarps in the mingyaole anticline in the southern foreland of chinese tian shan indicates that the modeled fold scarp geometry can roughly match with field observations the mingyaole shortening rate is estimated to be 5 0 mm a since 15ka such that this single fold has accommodated about half of the regional convergence during the holocene key points folding through curved hinges creates a distinctive fold scarp geometry scarp slope relies on ratio of hinge migration width but scarp height is not shortening rate of the mingyaole fold is estimated to be 5 0 mm a since 15 ka such that this single fold has accommodated about half of the regional convergence during the holocene

climatically controlled formation of river terraces in a tectonically active region along the southern piedmont of the tian shan nw china abstract combined tectonic uplift and quaternary climate variability control the deposition and abandonment of terraces along the southern tian shan in northwest china several preserved terraces have been deformed by an actively growing anticline within the uplifted frontal thrust system of the southern tian shan we combine geomorphic mapping topographic surveys of the deformed terrace surfaces 10be terrestrial cosmogenic nuclide tcn depth profile dating and optically stimulated luminescence osl dating to develop a new chronology for the terraces along the huangshui he since 550 ka our in situ 10be dating of fluvial gravels capping strath terraces suggests a relationship between the formation and abandonment of the terraces and glacial climate cycles since the middle late pleistocene these data indicate that the formation of the four terraces occurred at 550 430 350 and 60 ka we suggest that episodes of aggradation were facilitated by high sediment supply during glacial periods followed by subsequent incision that led to abandonment of these terraces during deglaciation we also estimate that tectonically induced river incision may account for about 60 70 of the total incision however during the intervening time between 350 ka and present only one terrace was formed and preserved we suggest that this record might be caused by a gradually decreasing uplift rate of the anticline through time and thus has influenced the preservation of terraces therefore our results demonstrate the utility of chronologic records from southern tian shan for deconvolving the effects of tectonics and climate on fluvial incision

can flexural slip faults related to evaporite dissolution generate hazardous earthquakes the case of the grand hogback monocline of west central colorado a paleoseismological investigation of flexural slip faults related to interstratal evaporite dissolution suggests that such gravitational structures might have the potential to generate earthquakes with damaging magnitude the carbondale collapse center in the southern rocky mountains of colorado is a morpho structural depression of 1200 km 2 where miocene volcanic rocks are downdropped as much as 1200 m due to interstratal dissolution of halite bearing evaporites on the western margin of the collapse center the debuttressing effect related to active evaporite dissolution drives unfolding of the steeply dipping late laramide grand hogback monocline accompanied by displacement on bedding parallel faults these flexural slip faults rupture unconformable miocene basalts and quaternary mantled pediments generating conspicuous half graben depressions bounded by antislope fault scarps parallel to the underlying strata of the monocline two trenches dug across flexural slip fault scarps developed in each stratigraphic marker basalt cap mantled pediment revealed unexpected evidence of multiple late quaternary faulting events e g faulted colluvial wedge sharp unconformities with displacement per event values of 1 m three faulting events were inferred from the trench dug in the pediment w around 6

tertiary evolution of the western tarim basin northwest china a tectono sedimentary response to northward indentation of the pamir salient 1 this paper deals with the tertiary tectonic and sedimentary evolution of the western tarim basin based on an integrated stratigraphic sedimentary structural and tectonic analyses basin evolution is divided into three stages paleogene miocene and pliocene the western tarim basin was the easternmost part of the tethyan realm from late cretaceous to paleogene and marine sedimentation continued into the early miocene miocene development of the western tarim basin was chiefly governed by west kunlun right slip faulting and the simultaneous northward thrusting of the pamir salient and tianshuihai terrane yecheng subbasin developed as a pull apart basin owing to synchronous activity of the west kunlun and the shache yangdaman right slip faults hotan foreland basin formed in response to northward displacement of the tianshuihai terrane and another might have developed in front of the advancing pamir salient in the miocene basinward thrusting became predominant in the orogenic belts adjacent to the western tarim basin in the pliocene north directed displacement and uplift of the tiklik thrust terrane fragmented the preexisting hotan foreland basin and collision of the pamir with the southern tian shan deformational fronts caused complete destruction of the miocene pamir foreland basin eastward displacement of the qimugen fold thrust system led to flexural subsidence of the yecheng subbasin in the pliocene kashi subbasin developed as part of the southern tian shan foreland basin and was controlled by the eastern pamir as well a tectonic scenario is proposed to illustrate complicated interplay of the western tarim basin with its peripheral orogens in the tertiary

pliocene uplift of the northern tibetan plateau neogene redbeds passing upward into upward coarsening conglomerate and debris flow deposits at the foot of the kunlun mountains record the change in paleoslope related to uplift of the surface of the northern tibetan plateau detailed magnetostratigraphy of a 4 5 km section near yecheng in the western kunlun mountains shows that the change from deposition on distal alluvial plains to proximal alluvial fans occurred during the gilbert reversed chron 4 5 3 5 ma the change in depositional facies was accompanied by an increase in sedimentation rate from an average 0 15 mm yr between the earliest oligocene and the earliest pliocene to 1 4 mm yr in the gauss normal chron 3 6 2 6 ma we interpret the change in depositional facies and increase in sedimentation rate as indicating that the main uplift of the northwestern tibetan plateau began ca 4 5 ma

late miocene northward propagation of the northeast pamir thrust system northwest china 2015 american geophysical union piggyback basins on the margins of growing orogens commonly serve as sensitive recorders of the onset of thrust deformation and changes in source areas the bieertuokuoyi piggyback basin located in the hanging wall of the pamir frontal thrust provides an unambiguous record of the outward growth of the northeast pamir margin in northwest china from the miocene through the quaternary to reconstruct the deformation along the margin we synthesized structural mapping stratigraphy magnetostratigraphy and cosmogenic burial dating of basin fill and growth strata the bieertuokuoyi basin records the initiation of the pamir frontal thrust and the takegai thrust 5 6ma as well as clast provenance and paleocurrent changes resulting from the pliocene to recent uplift and exhumation of the pamir to the south our results show that coeval deformation was accommodated on the major structures on the northeast pamir margin throughout the miocene to recent furthermore our data support a change in the regional kinematics around the miocene pliocene boundary 5 6ma rapid exhumation of ne pamir extensional domes coupled with cessation of the kashgar yecheng transfer system on the eastern margin of the pamir accelerated the outward propagation of the northeastern pamir margin and the southward propagation of the kashi atushi fold and thrust belt in the southern tian shan this coeval deformation signifies the coupling of the pamir and tarim blocks and the transfer of shortening north to the pamir frontal faults and across the quasi rigid tarim basin to the southern tian shan kashi atushi fold and thrust system

equivalency of geologic and geodetic rates in contractional orogens new insights from the pamir frontal thrust across contractional orogens the equivalency between decadal convergence rates from geodetic gps data and geologic shortening rates at time scales of thousands or millions of years has rarely been documented here we present an example from the northern margin of chinese pamir where the main pamir thrust is tectonically quiescent and recent deformation is concentrated on the pamir frontal thrust pft based on dated and faulted fluvial terraces magnetostratigraphy and mapping the horizontal shortening rate of the pft is 6 7 mm a at time scales of both 18 4 ka and 0 35 ma comparable to the geodetic rate of 6 9 mm a across the same zone implying that modern geodetic rates are a reasonable proxy for geologic rates since 0 35 ma comparing this example with studies in other contractional orogens we conjecture that a match or mismatch of geologic geodetic rates typically depends on the time scale of observation fault geometry and fault mechanics 2012 by the american geophysical union