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

provenance and tectonic settings of permian turbidites from the beishan mountains nw china implications for the late paleozoic accretionary tectonics of the southern altaids the beishan orogenic belt which connects the tianshan suture on the west and solonker suture on the east contains key evidence for the termination time of the southern altaids critical for evaluating different controversial tectonic models are permian marine volcaniclastic arenites in the liuyuan and heishankou areas which are dominated by greywackes and lenticular pebbly litharenites that contain grading groove marks and erosional bases which provide evidence of turbidity action sandstones from the liuyuan section are dominated by angular basaltic andesitic and feldspar fragments but sandstones from the heishankou section mainly consist of andesitic and felsic volcanic fragments these relations suggest derivation from two different sources major element compositions suggest that the source rocks of the heishankou litharenites were more sio2 rich than those at liuyuan sandstones at heishankou are characterized by lower ni co cr v and slightly higher th and la contents than those at liuyuan this indicates that the litharenites in the liuyuan and heishankou areas were derived from intermediate mafic and intermediate felsic source rocks respectively tectonic setting discrimination plots suggest that the liuyuan sandstones were deposited as detritus from an oceanic island arc but the heishankou sediments from an andean continental margin our petrological and geochemical data from these two types of permian turbidites suggest that an arc continent collision took place in the early permian and this is consistent with the permian termination of the southern altaids

the chamberlin 1910 balanced section context contribution and critical reassessment abstract chamberlin 1910 was the first to quantitatively predict the shape and position of a basal detachment from detailed surface observations his predicted detachment beneath the appalachian valley and ridge fold thrust belt of central pennsylvania is substantially deeper and differs in geometry from the current interpretation the modern profile by faill and nickelsen 1999 across the same area shows a much shallower planar lower detachment and the presence of a duplex below the surface folds a significant conceptual difference from the chamberlin profile two assumptions prove to be critical in causing the discrepancies the width of the segments used as the unit of analysis and the assumption of constant bed length the segmentation scheme led to an erroneous conjugate fault detachment geometry the depth discrepancy is primarily due to ignoring the layer parallel strain the duplex is of the coupled roof style and not responsible for the differences a result supported by an experimental model we use the modern profile and the area depth relationship to quantify the effects of uncertainty on profile geometry and estimates of orogenic shortening small differences in the assumptions inference error lead to significant differences in displacement detachment location and layer parallel strain our best area balanced interpretation is a slightly modified version of the faill and nickelsen profile

a tale of amalgamation of three permo triassic collage systems in central asia oroclines sutures and terminal accretion the central asian orogenic belt records the accretion and convergence of three collage systems that were finally rotated into two major oroclines the mongolia collage system was a long n s oriented composite ribbon that was rotated to its current orientation when the mongol okhotsk orocline was formed the components of the kazakhstan collage system were welded together into a long single composite arc that was bent to form the kazakhstan orocline the cratons of tarim and north china were united and sutured by the beishan orogen which terminated with formation of the solonker suture in northern china all components of the three collage systems were generated by the neoproterozoic and were amalgamated in the permo triassic the central asian orogenic belt evolved by multiple convergence and accretion of many orogenic components during multiple phases of amalgamation followed by two phases of orocline rotation

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

cenozoic tectonics in the urumgi korla region of the chinese tien shan cenozoic deformation within the tien shan of central asia has accommodated part of the post collisional indentation of the indian plate into asia within the urumgi korla region of the chinese tien shan this occurred dominantly on thrusts with secondary strike slip faulting the gross pattern of deformation is of moderate to steeply dipping thrusts that have overthrust foreland basins to the north and south of the range the junggar and tarim basins respectively smaller foreland basins lie within the margins of the range itself turfan chai wo pu korla and qumishi basins these lie in the footwalls of local thrust systems both the turfan and the korla basins contain major thrusts within them they are complex foreland basins deformation has progressively affected regions further into the interior of the junggar basin and propagated into the interiors of the intermontane basins no unidirectional deformation front has passed across the tien shan in the neogene and quaternary an oligocene unconformity may indicate the time of the onset of the cenozoic deformation but most of the cenozoic molasse has been deposited after the palaeogene the rate of deposition in basins next to the uplifted ranges has increased since the onset of deformation there has been at least about 80 km of cenozoic shortening across this part of the tien shan cenozoic shortening is greater in sections of the range further west these are nearer to the northern margin of the indian indenter cenozoic compression has reactivated structures created by the two late palaeozoic collisions that created the ancestral tien shan these palaeozoic structures have exerted a strong control over the style and location of the cenozoic deformation

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

a unified kinematic model for the evolution of detachment folds abstract detachment folds represent a major structural element in a number of fold belts they are common in the jura mountains the zagros fold belt the central appalachian fold belt the wyoming fold belt the brooks range the parry islands fold belt and parts of the subandean belt these structures form in stratigraphic packages with high competency contrasts among units the competent upper units exhibit parallel fold geometries whereas the weak lower unit displays disharmonic folding and significant penetrative deformation two distinct geometric types disharmonic detachment folds and lift off folds have been recognized however these structures commonly represent different stages in the progressive evolution of detachment folds the structures first form by symmetric or asymmetric folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require sinking of units in the synclines and movement of the ductile unit from the synclines to the anticlines continuing deformation results in increasing fold amplitudes and tighter geometries resulting from both limb segment rotation and hinge migration initially limb rotation occurs primarily by flexural slip folding but in the late stages of deformation the rotation may involve significant internal deformation of units between locked hinges the folds eventually assume tight isoclinal geometries resembling lift off folds variations in the geometry of detachment fold geometry such as fold asymmetry significant faulting and fold associated with multiple detachments are related to variations in the mechanical stratigraphy and pre existing structure

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

new space geodetic constraints on the distribution of deformation in central asia abstract results from repeated measurements across a 90 sites global positioning system network in central asia provide direct evidence of current high rates of tectonic deformation far north of the india eurasia suture zone the data help to quantify both the partitioning of deformation within the seismically active tien shan and northern pamirs as well as the ongoing rotation of virtually undeformed blocks such as the tarim with respect to stable eurasia the nnw to sse shortening rates derived from the computations reach values of 23 3 mm yr 1 over the ranges studied suggesting that regional deformation rates have increased considerably within the study area since the onset of cenozoic shortening 20 25 myr ago

cenozoic ostracoda and palaeoenvironments of the northeastern tarim basin western china abstract the paleogene rocks of the northeastern tarim basin in western china are composed mainly of reddish gypsum bearing coarse grained sediments and fossils are rare within these clastic facies however since the onset of the himalayan orogeny in the miocene continuous uplift of the tianshan mountains resulted in the rapid subsidence and appearance of a shallow lake environment as a result of this ostracods are widespread in the late cenozoic rocks of the tarim basin the brackish water ostracod cyprideis thrived from the mid to late miocene gypsum bearing sand and mud sediments were also deposited widely in the shallow brackish water lake environments this situation is similar to that of the qaidam basin which lies to the south of the altun mountains from the pliocene onwards the rates of subsidence and sedimentation increased the resulting regression of the lake led to disappearance of ostracods from a large part of the basin to the north of the kuqa depression the tianshan mountains underwent continuous uplift during the late himalayan orogeny as a result the quaternary lake deposits have a much greater extent than those of the pliocene and extend even further southward than those of the miocene consequently the brackish water ostracod cyprideis became dominant again during the quaternary from the end of the early pleistocene to present in this area an abundant and high diversity fauna of fresh to brackish water ostracods appeared alongside abundant cyprideis this situation is similar to that of the southern qaidam basin to the north of kunlun mountains the quaternary assemblages mainly consist of cyprideis torosa candoniella lactea candona neglecta candona arcina cypridopsis vidua limnocythere inopinata cypris subglobosa ilyocypris gibba ilyocypris biplicata eucypris inflata candoniella albicans darwinula sp and stenocypris sp under the extremely arid climate in the tarim basin freshwater originated mainly from snow melt this suggests that the tianshan mountains to the north were uplifted rapidly to above the snow line during the last million years the evolution of the ostracod assemblages indicates that the late himalayan orogeny not only controlled the deposition of biota assemblages but also took an important role in the hydrocarbon accumulation and migration

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

the age of the taklimakan desert the taklimakan desert is located in the foreland basin of the tibetan plateau we report here the results of stratigraphic investigations of a 1626 meter thick sequence with interbedded wind blown silt from the southern marginal taklimakan desert because the studied section is located downwind of the desert the eolian silt accumulation is closely linked to desert formation our new evidence indicates that shifting sand dunes prevailed in the tarim basin by at least 5 3 million years ago as they do today we attribute this event to late cenozoic climatic deterioration as well as to changes in atmospheric circulation induced by tibetan plateau uplift

late cenozoic transpression in southwestern mongolia and the gobi altai tien shan connection the gobi altai region of southwestern mongolia is a natural laboratory for studying processes of active transpressional intracontinental mountain building at different stages of development the region is structurally dominated by several major e w left lateral strike slip fault systems the north gobi altai fault system is a seismically active right stepping left lateral strike slip fault system that can be traced along the surface for over 350 km the eastern two thirds of the fault system ruptured during a major earthquake m 8 3 in 1957 whereas degraded fault scarps cutting alluvial deposits along the western third of the system indicate that this segment did not rupture during the 1957 event but has been active during the quaternary the highest mountains in the gobi altai are restraining bend uplifts along the length of the fault system detailed transects across two of the restraining bends indicate that they have asymmetric flower structure cross sectional geometries with thrust faults rooting into oblique slip and strike slip master faults continued ne directed convergence across the fault system coupled with left lateral strike slip displacements will lead to growth and coalescence of the restraining bends into a continuous sublinear range possibly obscuring the original strike slip fault system this may be a common mountain building process the largely unknown gobi tien shan fault system is a major left lateral strike slip fault system 1200 km long that links the southern ranges of the gobi altai with the barkol tagh and bogda shan of the easternmost tien shan in china active scarps cutting alluvial deposits are visible on satellite imagery along much of its central section indicating quaternary activity the total displacement is unknown but small parallel splays have apparent offsets of 20 km suggesting that the main fault zone has experienced significantly more displacement field investigations conducted at two locations in southwestern mongolia indicate that late cenozoic transpressional uplift is still active along the fault system the spatial relationship between topography and active faults in the barkol tagh and bogda shan strongly suggests that these ranges are large coalescing restraining bends that have accommodated the fault s left lateral motion by thrusting oblique slip displacement and uplift thus from a mongolian perspective the easternmost tien shan formed where it is because it lies at the western termination zone of the gobi tien shan fault system the gobi tien shan fault system is one of the longest fault systems in central asia and together with the north gobi altai and other smaller subparallel fault systems is accommodating the eastward translation of south mongolia relative to the hangay dome and siberia these displacements are interpreted to be due to eastward viscous flow of uppermost mantle material in the topographically low e w trending corridor between the northern edge of the tibetan plateau and the hangay dome presumably in response to the indo eurasian collision 2500 km to the south

quaternary folding of the eastern tian shan northwest china abstract the tian shan east west trending more than 2000 km is one of most active intracontinental mountain building belts that resulted from india eurasia collision during cenozoic in this study quaternary folding related to intracontinental mountain building of the tian shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images landsat thematic mapper tm enhanced thematic mapper etm and india remote sensing irs pan combined with field geologic and geomorphic observations and seismic reflection profiles analyses of spatial temporal features of quaternary folded structure indicate that the early quaternary folds are widely distributed in both piedmont and intermontane basins whereas the late quaternary active folds are mainly concentrated on the northern range fronts field observations indicate that quaternary folds are mainly characterized by fault related folding the formation and migration of quaternary folding are likely related to decollement surfaces beneath the fold and fault zone as revealed by seismic reflection profiles moreover analysis of growth strata indicates that the quaternary folding began in late stage of early pleistocene 2 1 1 2 ma finally tectonic evolution model of the quaternary deformation in the tian shan is presented this model shows that the quaternary folding and faulting gradually migrate toward the range fronts due to the continuous compression related to india eurasia collision during quaternary time as a result the high topographic relief of the tian shan was formed

excess area and depth to detachment a plot of the excess area in cross section vs the depth to a reference level for several stratigraphic horizons in a compressional fold produces a curve that gives the depth to detachment the curve is a straight line for detachment folds the slope of the line is the displacement on the lower detachment and the depth intercept where excess area zero is the depth to detachment for a fault bend fold the result is a line that abruptly changes slope at the position corresponding to the upper detachment the difference in slope between the two parts of the line is the displacement on the upper detachment added layer parallel shear produces a curve on the graph tested on detachment folds from the jura mountains the method accurately predicts the depth to detachment he tip top field anticline in the wyoming thrust belt is found to be interpretable as either a detachment anticline with a basal detachment close to the top of the basement or as a fault bend fold with a basal detachment at the base of the triassic the excess area diagram is useful for testing a cross section for balance determining the structural style detachment anticline vs fault bend fold and for examining alternatives in the construction of cross sections

active intracontinental transpressional mountain building in the mongolian altai defining a new class of orogen abstract mountain ranges that are actively forming around the western and northern perimeter of the indo eurasia collisional deformational field such as the mongolian altai comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens late cenozoic uplift and mountain building in the mongolian altai is dominated by regional scale dextral strike slip faults that link with thrust and oblique slip faults within a 300 km wide deforming belt sandwiched between the more rigid junggar basin block and hangay precambrian craton dominant orogenic elements in the mongolian altai include double restraining bends terminal restraining bends partial restraining bends single thrust ridges thrust ridges linked by strike slip faults and triangular block uplifts in areas of conjugate strike slip faults the overall pattern is similar to a regional strike slip duplex array however the significant amount of contractional and oblique slip displacement within the range and large number of historical oblique slip seismic events renders the term transpressional duplex more accurate intramontane and range flanking basins can be classified as ramp basins half ramp basins open sided thrust basins pull apart basins and strike slip basins neither a classic fold and thrust orogenic wedge geometry nor a bounding foredeep exists the manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown however crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late cenozoic regional epeirogenic uplift in the russian altai and sayan regions

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

closing history of the southern tianshan oceanic basin western china an oblique collisional orogeny abstract the tianshan tien shan range is an important paleozoic collisional orogenic belt and the key to understand the central asia tectonic evolution this paper integrates our research results with the existing chinese and international literature on sedimentology geochemistry isotopic geochronology paleontonology and paleomagnetism of the tianshan and tarim regions to propose that the oblique collision may have played an important role in the late paleozoic closing of the southern tianshan oceanic basin as a result of the sinian latest proterozoic younger than 800 ma continental extension and rifting process the tarim and yili blocks separated from their parent continent in the late cambrian ordovician the southern tianshan oceanic crusts between the two blocks subducted northward beneath the southern margin of the yili block in the silurian during the devonian early carboniferous the tarim block rapidly drifted to the north and rotated about 46 clockwise this process induced the collision of the yili micro continent with the eastern segment present geographical position of the tarim continent in the late devonian and the southern tianshan oceanic crust evolved to be a west facing remnant oceanic basin during the late carboniferous early permian the tarim block located within an almost constant latitude range rotated about 26 clockwise with respect to the yili micro continent which ultimately closed the remnant oceanic basin in a scissors like manner from east to west and completed the tarim yili collision subsequent a type subduction of the tarim continental crust and lithosphere scale sinistral shearing generated a magmatic arc on the southern margin of the tarim yili suture zone the late permian early triassic clastics deposited in a peripheral foreland basin developed above the arc

structural models of faulted detachment folds faulted detachment folds represent a common structural style in several hydrocarbon producing fold and thrust belts including the zagros idaho wyoming utah carpathian and albanide belts and several deep water fold belts including the mississippi fan and per dido belts these structures form in units with high competency contrasts and display a transition in deformational behavior from detachment folding to progressive fault propagation with increasing shortening the structures first form by symmetric or asymmetric detachment folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require the movement of material from the synclines to the anticlines contin ued shortening results in tighter folds with limb rotation by hinge migration limb segment rotation and internal shear rotation of limb segments between locked hinges results in thrust faults which propagate through deformation zones on the frontlimb and possibly the backlimb the faults may terminate both up and down section within brittle or ductile deformation zones eventually a through going fault connects one of the major faults with the basal detach ment variations in the structural geometry are related to the rela tive thickness and competency of the units and the mechanisms of deformation because faulted detachment folds superficially resem ble fault propagation folds their geometry can be misinterpreted in areas of poor data quality characteristic features for distinguish ing these structures include 1 smaller variations in anticlinal length during fold evolution 2 a more open and rounded fold geometry 3 complex and nonuniform variations in fault slip 4 a significant variation in deformational behavior among different units and 5 fold fault relationships indicating transition from folding to faulting such as footwall synclines and decapitated fold geometries

superposed buckle folding in the eastern iberian chain spain abstract the aliaga area eastern iberian chain shows large scale examples of buckle superposition developed during tertiary folding in most cases ene trending folds overprint earlier nnw sse trending ones the resulting structures are mapped analysed and genetically classified by comparison with analogue models described by several authors the following types are found standard type 1 1a dome and basin structure 1b unequal wavelength overprinted folds modified type 1 1c t shaped joined folds 1d t shaped abutting folds 1e l shaped folds 1f snake like folds standard type 2 2a non cylindrical buckling of earlier axial surfaces involving hinge replacement different superposed sets of flexural slip striations record successive folding episodes in snake like folds and hinge replacement in the case of type 2a superpositions types 1 and 2 apparently develop where the earlier folds have interlimb angles over and below 90 respectively which fits the results of analogue modelling and theoretical analysis by previous authors types 1b and 1d are associated with higher w1 w2 wavelength ratios than types 1a and 1c other controlling factors are viscosity contrast and erosion processes specifically erosion of competent limestone beds in the hinge zone of a nnw sse trending anticline allowed the near vertical eastern limb to be refolded into snake like folds

lithospheric structure and dynamic processes of the tianshan orogenic belt and the junggar basin abstract located at the center of the eurasian continent and accommodating as much as 44 of the present crustal shortening between india and siberia the tianshan orogenic belt tob is one of the youngest 7000 m orogenic belts in the world it provides a natural laboratory for examining the processes of intracontinental deformation in recent years wide angle seismic reflection refraction profiling and magnetotelluric sounding surveys have been carried out along a geoscience transect which extends northeastward from xayar at the northern margin of the tarim basin tb through the tianshan orogenic belt and the junggar basin jb to burjing at the southern piedmont of the altay mountain we have also obtained the 2d density structure of the crust and upper mantle of this area by using the bouguer anomaly data of northwestern xinjiang with these surveys we attempt to image the 2d velocity and the 2d electric structure of the crust and upper mantle beneath the tianshan orogenic belt and the junggar basin in order to obtain the small scale structure of the crust mantle transitional zone of the study area the wavelet transform method is applied to the seismic wide angle reflection refraction data combining our survey results with heat flow and other geological data we propose a model that interprets the deep processes beneath the tianshan orogenic belt and the junggar basin located between the tarim basin and the junggar basin the tianshan orogenic belt is a block with relatively low velocity low density and partially high resistivity it is tectonically a shortening zone under lateral compression a detachment exists in the upper crust at the northern margin of the tarim basin its lower part of the upper crust intruded into the lower part of the upper and the middle crust of the tianshan near the korla fault its middle crust intruded into the lower crust of the tianshan and its lower crust and lithospheric mantle subducted into the upper mantle of the tianshan in these processes the mass of the lower crust of the tarim basin was carried down to the upper mantle beneath the tianshan forming a 20 km thick complex crust mantle transitional zone composed of seven thin layers with a lower than average velocity the thrusting and folding of the sedimentary cover the intrusive layer in the upper and middle crust and the mass added by the subduction of the tarim basin into the upper mantle of the tianshan are probably responsible for the crustal thickening of the tianshan due to the important mass deficiency in the crust and the upper mantle of the tianshan buoyancy must occur and lead to rapid ascent of the tianshan the episodic tectonic uplift of the tianshan and tectonic subsidence of the junggar basin are closely related to the evolution of the paleozoic mesozoic and cenozoic tethys

paleozoic accretionary and collisional tectonics of the eastern tianshan china implications for the continental growth of central asia this paper deals with the various tectonic units in the chinese eastern tianshan orogenic collage in the central asian orogenic belt and discusses the paleozoic geological history of the several periods of accretion and collision of archipelago systems lying between the tarim and southern angaran continental margins the late ordovician silurian to early devonian eastern tianshan archipelago was characterized by a the harlik dananhu subduction system with a s dipping polarity in the north b a southerly n dipping subduction system beneath the central tianshan arc in the middle and c the south tianshan ocean against tarim in the south during the devonian to early carboniferous n dipping subduction led to the harlik dananhu arc and the kanggurtag forearc basin accretionary complex in the early to mid carboniferous the magmatic front associated with the n dipping subduction beneath the dananhu harlik arc migrated southwards forming the yamansu arc constructed upon the kanggurtag accretionary forearc by the late carboniferous the dananhu harlik arc was attached northwards to the angaran margin resulting in lateral enlargement of the angaran continent in the latest carboniferous to early permian a multiple soft collision left wide suture zones in the south that include the ophiolite strewn aqikkuduk shaquanzi and kumishi accretion collision complexes which were stitched by early permian post collisional plutons by re defining and re interpreting the various tectonic terranes this paper presents a new improved model for the paleozoic evolution of this part of central asia

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

syntectonic growth strata and implications for late cenozoic tectonic uplift in the northern tian shan china abstract propagation of faults and folds in the foreland basins of tian shan is an important process accommodating cenozoic crustal shortening and mountain building but little is known about the accurate time of the cenozoic tectonic deformation based on growth strata and age determination we show that syntectonic growth strata began to develop in the middle part of tian shan since 6 ma ago geometry analysis indicates that formation of the growth strata is associated with progressive fold limb rotation formation of the growth strata is contemporaneous with the tectonic deformation in the thrusting and folding zones together with the remarkable increase of sedimentation rate as well as the accumulation of coarse molasse deposits we conclude that the late cenozoic crustal shortening and mountain building in the region initiated since about 6 ma and lasted to the early pleistocene as a consequence of intracontinental deformation within the india eurasia convergent system

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

geometric constraints derived from the law of conservation of volume and applied to evolutionary models for detachment folding geologic note 1 this paper presents geometric arguments for modifying the conventional concept for the evolution of concentric fold trains above nonductile detachment zones the common geometric model for concentric folding above a detachment invokes a wave train with fixed fold axes regularly spaced along the fold panel limb lengths from crest to trough remain constant as the limb dips increase to uplift the anticlinal crests while the synclinal troughs slide parallel to the detachment plane the basic depth to detachment calculation which derives from the law of conservation of volume requires that the area of uplift above regional for a concentric anticline be equal to the arithmetic product of the shortening and the depth to detachment this imposes a geometric constraint with whi h a constant limb length anticline growing by increasing limb dip above a fixed detachment plane cannot comply unless in the early stages mobile material in the detachment zone flows from the synclinal troughs to the anticlinal crests and then in the later stages the flow direction reverses relatively few detachment zones contain a significant amount of mobile salt or shale therefore in most concentric detachment fold trains a basic geometric incompatibility exists between the conventional geometric model and the law of conservation of volume the conflict can be resolved by an evolutionary fold model wherein the anticlinal fold limbs are short at the inception of folding and grow longer as dips increase and the fold grows in this model the anticlinal axes generally are fixed and the synclinal axes active which has structural and economic implications for the distribution of permeability and syntectonic sediments as well as for the migration and entrapment of hydrocarbons

triassic deformation of permian early triassic arc related sediments in the beishan nw china last pulse of the accretionary orogenesis in the southernmost altaids abstract the beishan orogenic collage boc in the southernmost altaids provides evidence of the final stage of evolution of the paleo asian ocean however the closure time of the paleo asian ocean in the boc is controversial from field mapping and structural analysis of mesoscale superposed folds in early triassic sediments in the hongyanjing basin in the central boc we define at least two phases of deformation which we can bracket in age as end permian to early late triassic the sandstones in the basin are poorly sorted with angular clasts which indicates immaturity characteristic of proximal and rapid deposition geochemical data indicate that the hongyanjing basin probably developed in an arc related setting near an active continental margin or mature island arc combined with published regional geological data we interpret the hongyanjing basin as a permian early triassic inter arc basin between the carboniferous mazongshan arc to the north and the ordovician to permian huaniushan dundunshan arc to the south in addition the age distribution of our sediments shows that the active continental margin or continental arc on which the hongyanjing arc related basin sat was somehow independently distributed in the paleo asian ocean without any major contribution of provenance from the tarim craton and dunhuang block to the south and southern mongolia accretionary system to the north deformation of the superposed folds began in the end permian continued in the early triassic and ended before the middle late triassic 219 ma therefore the accretionary orogenesis in the beishan part of the southernmost altaids was still ongoing in the early to middle triassic and it finished in the late triassic which might have been the last pulse of the accretionary orogenesis in the southernmost altaids we correlate this terminal event with tectonic developments in the kunlun and qinling orogens in the tethyan domain

magnetostratigraphy of the kelasu section in the baicheng depression southern tian shan northwestern china abstract in order to better constrain chronology of the cenozoic sediments in the foreland basin of the southern tian shan we carried out a magnetostratigraphic study along the kelasu river in the baicheng depression northwestern china this is the basis for future studies of the tectonic shortening history and paleoclimatic changes stepwise thermal demagnetization was used to isolate the high temperature characteristic component chrm from 1521 oriented samples collected along two overlapped sections the chrm directions are interpreted to be acquired at or close to the time of rock formation a composite magnetostratigraphic column composed of 86 45 normal and 41 reversed polarity chrons can correlate with gpts ck95 from 54 ma to 7 6 ma the basal ages of the kumugeliemu suweiyi jidike and the kangcun formations are 54 ma 46 ma 34 ma and 9 7 ma respectively the changes of anisotropy of magnetic susceptibility ams parameters p j and t cannot be used to reflect the cenozoic uplift of the southern chinese tian shan due to the parameters have a significant linear positive correlation with the bulk magnetic susceptibility k m suggesting a sedimentary provenance control based on the alignments of the ams we concluded that the paleo river channel flowed from north to south being similar to the present river flowing direction suggesting that there was still a residue relief of the tian shan orogen after the long term mesozoic denudation or the reactivation of the tian shan may have been initiated as early as 54 ma

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

improving temporal resolution in ambient noise monitoring of seismic wave speed 1 the use of ambient seismic noise has been intensively investigated to perform passive tomography at various scales besides passive tomography passive monitoring is another application of seismic noise correlation as was shown by the recent observation of postseismic velocity changes around the san andreas fault in parkfield california one of the drawbacks of using ambient noise correlation for passive monitoring is the need to average the correlations over a long time period in order to obtain a sufficient signal to noise ratio snr for the phase fluctuations to be measured accurately for the application to passive monitoring one wants the possibility of following short term velocity variations 1 day or less using noise correlation functions calculated on short time windows another difficulty may then appear when the spatial distribution of noise sources also evolves with time the aim of this paper is to introduce an adaptive filter to the parkfield data set in order to improve the snr output of the ambient noise correlation functions when applied to passive monitoring the temporal resolution can be increased from 30 days up to 1 day with this improved temporal resolution the velocity drop observed at parkfield is shown to be cosesimic with the 24 september 2004 mw 6 0 event the relationship between the measured velocity fluctuations and the time evolution of the spatial distribution of the noise wavefield is also investigated finally the error bar in the amplitudes of the velocity variations is compared with a theoretical expectation

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

modeling the shortening history of a fault tip fold using structural and geomorphic records of deformation 1 we present a methodology to derive the growth history of a fault tip fold above a basal detachment our approach is based on modeling the stratigraphic and geomorphic records of deformation as well as the finite structure of the fold constrained from seismic profiles we parameterize the spatial deformation pattern using a simple formulation of the displacement field derived from sandbox experiments assuming a stationary spatial pattern of deformation we simulate the gradual warping and uplift of stratigraphic and geomorphic markers which provides an estimate of the cumulative amounts of shortening they have recorded this approach allows modeling of isolated terraces or growth strata we apply this method to the study of two fault tip folds in the tien shan the yakeng and anjihai anticlines documenting their deformation history over the past 6 7 myr we show that the modern shortening rates can be estimated from the width of the fold topography provided that the sedimentation rate is known yielding respective rates of 2 15 and 1 12 mm yr across yakeng and anjihai consistent with the deformation recorded by fluvial and alluvial terraces this study demonstrates that the shortening rates across both folds accelerated significantly since the onset of folding it also illustrates the usefulness of a simple geometric folding model and highlights the importance of considering local interactions between tectonic deformation sedimentation and erosion

cenozoic tectonic deformation and uplift of the south tian shan implications from magnetostratigraphy and balanced cross section restoration of the kuqa depression abstract the collision of india with eurasia has caused rejuvenated deformation and uplift of the remote tian shan intracontinental orogenic range and has led to deposition of thick cenozoic sediments in its flank depressions however our knowledge when and how the range was deformed and uplifted is still limited we carried out detailed tectonic investigations seismostratigraphic analysis and paleomagnetic dating of the thrust fold belt in the kuqa depression at the southern tian shan flank combined with re interpretation of other magnetostratigraphic results in the depression we determined ages of major stratigraphic boundaries and constructed and restored the balanced cross section across the depression the results show that the total cenozoic shortening along the cross section in the depression is 13 95 km significant shortening began at 36 ma accelerated since 13 ma and further increased two to three fold since 6 5 ma especially since 2 6 ma this shortening process caused the development of the kuqa thrust fold system associated with the variation of the sedimentation rate upward coarsening of sediments and a progressive development of growth strata we therefore argue that significant deformation and uplift of the south tian shan began at 36 ma becoming more evident since 13 ma and culminating since 6 5 ma reaching its peak after 2 6 ma

timing of the tianshan mountains uplift constrained by magnetostratigraphic analysis of molasse deposits abstract the tianshan mountains lie in the actively deforming part of the india asia collision zone the thrust faulting and folding of the neogene and quaternary sediments forming linear roughly east west anticlines at the northern and southern borders of the orogenic belts indicate crustal shortening and thickening in late cenozoic time detailed magnetostratigraphic studies of the molasse deposits of the folded neogene and quaternary strata in the northern edge of the tianshan mountains indicate that the onset of uplift occurred at 7 ma deposition of the thick conglomerates between 7 and 2 58 ma in the studied region was mainly in response to the tectonic uplift while the accumulation of the early pleistocene conglomerates xiyu formation was mostly controlled by both tectonics and climatic cooling our results indicate that the present high relief of the tianshan mountains is the result of two dominant phases of uplift occurring at about 7 2 58 ma and the early pleistocene

updating martin s global extinction model australia has been cited as a weak link in anthropogenic models of megafauna extinction but recent work suggests instead that the evidence for rapid extinction shortly after human arrival is robust the global model is revisited based on the contention that late pleistocene megafauna extinctions took place rapidly on islands and some islands such as australia and the americas are much larger than others modern dating methods are increasingly able to refine chronologies and careful scrutiny suggests that hundreds of dates should be deleted from archives an updated summary of results from new zealand north america and australia is presented with a brief discussion on why temperate refugia offering protection from climate change ultimately did not work strongly supporting the global extinction hypothesis pioneered by paul martin

magnetostratigraphic record of the early evolution of the southwestern tian shan foreland basin ulugqat area interactions with pamir indentation and india asia collision the tian shan range is an inherited intracontinental structure reactivated by the far field effects of the india asia collision a growing body of thermochronology and magnetostratigraphy datasets shows that the range grew through several tectonic pulses since 25 ma however the early cenozoic history remains poorly constrained the time lag between the eocene india asia collision and the miocene onset of tian shan exhumation is particularly enigmatic this peculiar period is potentially recorded along the southwestern tian shan piedmont there late eocene marine deposits of the proto paratethys epicontinental sea transition to continental foreland basin sediments of unknown age were recently dated we provide magnetostratigraphic dating of these continental sediments from the 1700 m thick mine section integrated with previously published detrital apatite fission track and u pb zircon ages the most likely correlation to the geomagnetic polarity time scale indicates an age span from 20 8 to 13 3 ma with a marked increase in accumulation rates at 19 18 ma this implies that the entire oligocene period is missing between the last marine and first continental sediments as suggested by previous southwestern tian shan results this differs from the southwestern tarim basin where eocene marine deposits are continuously overlain by late eocene oligocene continental sediments this supports a simple evolution model of the western tarim basin with eocene oligocene foreland basin activation to the south related to northward thrusting of the kunlun shan followed by early miocene activation of northern foreland basin related to overthrusting of the south tian shan our data also support southward propagation of the tian shan piedmont from 20 to 18 ma that may relate to motion on the talas fergana fault the coeval activation of a major right lateral strike slip system allowing indentation of the pamir salient into the tarim basin suggests far field deformation from the india asia collision zone affected the tian shan and the talas fergana fault by early miocene

cenozoic detachment folding in the southern tianshan foreland nw china shortening distances and rates abstract intracontinental foreland basins with fold and thrust belts on the southern periphery of the tianshan orogenic belt in china resulted from still active contractional deformation ultimately cased by the india asia collision to quantify the amounts of shortening distance and the rates of deformation and to decipher the architectural framework we mapped the stratigraphy and structure of four anticlines in the kuqa and baicheng foreland thrust belts in the central southern tianshan in the baicheng foreland thrust belts lower cretaceous baxigai and bashijiqike formations located in the core of the kumugeliemu anticline are overlain by the paleocene to eocene kumugeliemu formation above which are conformable oligocene through pleistocene sediments a disharmonic transition from parallel to unconformable bedding at the boundary of the miocene kangcun and pliocene kuqa formations suggests a change from pre detachment folded strata to beds deposited on top of a growing anticline most of the anticlines have steep limbs 70 90 and are box to isoclinal folds suggestive of detachment folding or faulted detachment folding faults that transect a fold core or limb shortening estimates calculated from the cross sections by the excess area method indicate that the total shortening for the kelasu kuchetawu kezile and yaken sections are 6 3 km 6 4 km 5 8 km and 0 6 km respectively and the respective depths of the detachment zones are 2 3 km and 6 9 km 2 3 km 2 5 km and 3 4 km time estimates derived from a paleomagnetic study indicate that the transition to syn folding strata occurred at 6 5 ma at the kuchetawu section along the kuqa river in addition according to our field observations and previous sedimentary rate studies the initial time of folding of the yaken anticline was at 0 15 0 21 ma therefore the average shortening rate that began at 6 ma was 2 mm a for the kelasu kuchetawu and kezile sections at 0 15 0 21 ma the average shortening rate increased to 3 4 mm a in the yaken section combined with the recent gps data the shortening rate in the central southern tianshan area increased to 4 7 1 5 mm a at present we suggest that there was a linear increase in shortening rate in the southern tianshan foreland basin which also indicates that the far field stress increased considerably from the late miocene to present in response to the india asia collision

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

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

new evidence on the age of the taklimakan desert the taklimakan desert is the world s second largest shifting sand desert located in the rain shadow of the tibetan plateau the initiation of desert formation in the asian interior is one of the most prominent climate changes in the northern hemisphere during the cenozoic era dating the earliest formation of this desert is important for understanding the climatic effects of the uplifted tibetan plateau here we report 1071 m thick neogene deposits with inter calated eolian dune sands from the only outcrop in the central taklimakan desert based on paleo magnetic measurements biostratigraphic age control and previous electron spin resonance dating results the oldest in situ eolian dune sands were confi rmed to be ca 7 ma much older than the previous reported wind blown siltstone from the southern edge of the taklimakan desert this new result indicates that desert conditions initiated ca 7 ma in the center of the tarim basin we attribute this event to the late cenozoic climatic deterioration and or to the rain shadow effect caused by late miocene uplift of the northern tibetan margin

late cenozoic magnetochronology and paleoenvironmental changes in the northern foreland basin of the tian shan mountains 1 the folded neogene deposits in the northern foreland basin of the tian shan mountains provide important information about tectonic history and environmental changes of northwestern china on the basis of lithostratigraphic and magnetostratigraphic evidence we develop a new chronology for the previous studied kuitun he section our palynological study on the late miocene pliocene sediment of the dushanzi section yields new information about vegetation and climate change during the period of 8 7 2 58 ma the results indicate that steppe taxa artemisia and chenopodiaceae were generally dominant in the studied areas between 8 7 and 2 58 ma implying that a dry climate has occurred in the inland basins of northwestern china at least since 8 7 ma ago although the general climate pattern indicated by our palynological results displays to some extent of drought a warm and humid phase occurred at 5 8 3 9 ma ago this climatic optimum is comparable with the other records from the chinese loess plateau central japan the sub himalayan zone and the marine eustatic sea level rise implying this seems to be at least a regional climatic optimum

late cenozoic tectonic development of the intramontane alai valley pamir tien shan region central asia an example of intracontinental deformation due to the indo eurasia collision 1 the pamir indentor of the northwestern himalayan syntaxis is a first order feature demonstrating partly the northward extent of deformation due to the cenozoic indo eurasia collision the alai valley of kyrgyzstan at the northern end of the indentor is a strategically positioned e w trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone to quantify the convergence accommodated across the alai valley during the late cenozoic we collected structural and stratigraphic field data reviewed existing soviet literature and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin our study suggests that the development progressive closure and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events 1 distributed north south contraction took place during the late oligocene early miocene accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface and 2 n s shortening resumed in the mid miocene and continues today during this second episode the thrust front migrated southward localized along the trans alai ranges and failed to reactivate earlier neogene structures horizontal shortening of about 35 across the alai valley implies relatively low strain rates and displacement rates of about 4 18 4 69 10 16 s 1 and 0 66 0 78 mm yr 1 respectively for the last 25 myr our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the asian continent as early as the late oligocene

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen

relatively recent construction of the tien shan inferred from gps measurements of present day crustal deformation rates the tien shan a high seismically active intracontinental mountain belt 1 000 2 000 km north of the himalaya has grown as a result of india s collision with asia1 the crustal shortening 200 50 km refs 2 3 and thickening that gave rise to the tien shan accommodates only a small fraction of india s total penetration into asia 2 000 3 000km and the temporal relationship of deformation in this belt to the india asia collision remains unclear here we report geodetic measurements of the tien shan using the global positioning system gps that indicate that the current crustal shortening rate is nearly half of india s convergence rate with eurasia in this area4 we infer a total shortening rate for the tien shan of 20 mm yr 1 which is approximately twice that inferred previously from the extrapolation of slip rates in the holocene3 and earthquake induced displacements during this century5 suggesting that the rate of mountain building in this region has accelerated several fold since the onset of collision 50 55 myr ago6 7 if as we argue the current shortening rate can be extrapolated to geological timescales then our results suggest that most of the tien shan has been constructed during the past 10 myr perhaps in response to an increased horizontal force following an abrupt rise of the tibetan plateau8 9

eocene seawater retreat from the southwest tarim basin and implications for early cenozoic tectonic evolution in the pamir plateau article i nfo the pamir plateau lies in the western end of the india eurasia collision zone being an unusual example for studying crustal shortening and evolution of the neotethys ocean here we present new results from the southwestern margin of the tarim basin for discussing tectonic history in the northern pamir plateau as well as for providing precise dates of the final seawater retreat from the studied region our results indicate that early uplift of the northern edge of the pamir plateau occurred at about 55 ma but this uplift preceded the closure of the link between the neotethys and the tarim basin five marine transgression and regression cycles occurred during the early eocene mostly in response to global eustatic sea level fluctuations and the final seawater retreat from the southwest tarim basin occurred at about 47 ma another uplift episode started 34 ma supported by the accumulation of coarse molasse deposits as well as our palynological evi dence suggesting that the convergence between the pamir plateau and the tian shan ranges accelerated since the beginning of the early oligocene

magnetostratigraphic data on neogene growth folding in the foreland basin of the southern tianshan mountains the tianshan range is one of the longest and highest mountain belts in central asia stretching east west for 2500 km uplift of this late paleozoic orogenic belt resulted from intracontinental deformation caused by the collision of the indian and eurasian plates during the cenozoic era to constrain the timing of cenozoic tectonic deformation of the tianshan range we analyzed the magnetostratigraphy of 3780 m thick neogene deposits from the kuqa foreland basin of southern tianshan the geometry measurements and magnetic fabric data show that syntectonic growth strata began to accumulate at 6 5 ma ago indicating that crustal shortening initiated in the latest miocene the increase in sedimentation rate and an abrupt change of the magnetic fabric parameters also occurred at 6 5 ma accompanied by onset of syntectonic growth strata the latest miocene crustal shortening is a signifi cant tectonic event in the foreland basin of the southern tianshan range in response to the india eurasia collision