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

late cenozoic tectonic evolution of the northwestern tien shan new age estimates for the initiation of mountain building the tien shan are the quintessential intracontinental range situated more than 1000 km north of the suture between india and asia their initiation and growth in the cenozoic however remain poorly understood in this study we present stratigraphic detrital fission track and magnetostratigraphic results that provide a basis for reconstructing the cenozoic tectonic evolution of the kyrgyz range and adjacent chu basin in the northwestern tien shan detrital fission track thermochronology indicates that the northwestern tien shan was tectonically quiescent for much of the cenozoic prior to uplift and exhumation in the late miocene the kyrgyz range was buried by sediments shed from highlands to the south and or east paired bedrock fission track and u th he ages from a sampling transect of 2 4 km relief demonstrate that rapid exhumation commenced at ca 11 ma initial thrusting in the hinterland was followed by evaporite accumulation 0 4 km m y which coincided with erosion of the pre 11 ma strata that mantled the kyrgyz range between 10 and 3 ma bedrockexhumation rates decreased to 0 3 km m y while sedimentation rates decelerated initially to 0 25 km m y before accelerating to 0 4 km m y at 4 5 ma detrital fission track results indicate that by 4 5 ma

plate tectonic history basin development and petroleum source rock deposition onshore china abstract china comprises a mosaic of distinct continental fragments separated by fold belts these fold belts are suture zones resulting from the accretion of various fragments formerly separated by intervening areas of oceanic crust the major sedimentary basins onshore china can be classified into four groups those in western china are flexural developing as a result of north south compression in contrast those in the east are extensional and related to development of the pacific oceanic margin in central china basins have a more problematic origin those of north central china ordos sichuan are flexural basins controlled by eastward directed thrusting along their western margin in contrast basins further south chuxiong shiwandashan are predominantly extensional and related to major strike slip movements by synthesizing basin stratigraphies across china in tectonostratigraphic terms and in particular comparing the nature and timing of unconformities it is possible to formulate a coherent model for the palaeoreconstruction of china we identify five major tectonostratigraphic breaks which equate with the collision of the following continental fragments tarim north china carboniferous permian south china block permian triassic qiantang late triassic early jurassic lhasa block late jurassic early cretaceous and india early tertiary prior to permian times the southern margin of eurasia ran approximately along the northern border of modern china the late carboniferous collision of tarim north china with eurasia resulted in the development of a flexural basin junggar and deposition of non marine clastics to the south of the suture shallow marine deposition continued in the late permian early triassic the progressive collision from east to west of the south china block with the north china block resulted in a change to fluvial lacutrine sedimentation across the entire north china tarim block open marine carbonate deposition in the north of the south china block passed southward into a deeper marine clastic sequence deposited in a backarc basin further south a subduction zone existed along the southeastern margin of the south china block in western china northward subduction throughout the triassic resulted in the development of the songban ganzi accretionary prism with retroarc thrusting resulting in flexure and the first development of the tarim basin oblique collision of the qiantang block in the late triassic along the east of the south china block resulted in east west directed thrusting which initiated the suchuan and ordos basins continued strike slip deformation along the south western margin of the south china block resulted in the development of basins with a significant extensional component such as chuxiong the collision of the qiantang block with the southern edge of the tarim basin early jurassic resulted in a renewed clastic influx in both the tarim and junggar basins along the eastern pacific margin a compressional arc and retroarc basin in the south passed northwards into an extensional arc system subduction rollback of the extensional arc initiated rifting in the late jurassic in the eren and songliao basins the late jurassic early cretaceous collision of the lhasa block in the west rejuvenated the thrust systems bordering the western basin and resulted in a renewed clastic influx in the southeast the compressional arc phase culminated in widespread thrusting and folding of early cretaceous age in the northeast extension continued with the progressive migration of the rift system southward with time the arrival of the indian block in the early tertiary rejuvenated the bounding thrust belts of all the western basins in the east the change in convergence of the pacific plate to a more westerly direction is marked by extension and widespread rifting along the entire length of eastern china throughout most of china mesozoic and cenozoic deposition occurred in predominantly non marine environments source rocks in such settings comprise principally mudstones deposited in lakes organic rich mudstones these can accumulate in both deep and shallow lakes in order to accumulate substantial volumes the lake must be significant in space and time in china lacustrine orms occur in both rift and flexural basins lacustrine orms deposited under humid climatic conditions are restricted to the period of maximum tectonic subsidence in the flexural basins of western china source rock deposition follows basin initiation by 20 30 ma in the extensional basins of eastern china source rock deposition takes place 5 15 ma after basin initiation by contrast semi arid and arid climate lacustrine orms whilst being best developed during the period of maximum tectonic subsidence occur at all stages in the basin history

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

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

geometry of fault propagation folds method and application abstract a new geometrical model to simulate the evolution of fault propagation folds beyond the stage referred to here as first generation represented by the models of suppe 1985 and jamison 1987 is presented according to this model based on fixed axis theory suppe and medwedeff 1990 a second generation fold develops when the tip line at the top of the ramp retreats to the base of the mechanically weak anticlinal axial plane and then propagates upwards along this plane two types of second generation fold geometry are possible depending on the ratio of cumulative thickness of the deformed layers to the ramp height the first type possesses a residual triangle from the crestal part of the first generation fold the whole of its forelimb is thinned the second type has no residual part and its forelimb is partially thinned this type can develop higher generations of fault propagation folds as its backlimb is long enough to be redeformed some second generation folds are comparable to breakthrough structures but they possess a higher interlimbs angle

geodynamics of the tarim basin and the tian shan in central asia the india asia collision has caused crustal thickening in tibet by at least a factor of 2 in the last 20 30 myr of this collision the tian shan mountain range has also been reactivated the tarim basin however shows little internal deformation we describe a series of numerical experiments which constrain the effective lithospheric strength parameters of the tarim basin and the tian shan in the context of a thin viscous sheet model we use a finite element representation of the thin viscous sheet model to approximate the deformation field in the india asia collision and compare model crustal thickness distributions with that inferred from a local isostatic model of topography the experiments show that a strong tarim basin while undergoing little internal deformation transfers strain to the tian shan producing significant crustal thickening in the tian shan region based only on diagnostic parameters such as the maximum thickening in the tian shan and the minimum in the tarim basin the principal features of the topography can be approximately reproduced using models in which either the tarim basin is strong or the tian shan is weak or both for a rheological model in which the stress versus strain rate exponent is n 3 the strength coefficient for the strong tarim basin model vtarim is between about 1 7 and 2 for the weak tian shan model the relative strength coefficient vtian is between about 0 65 and 0 75 if both strong tarim and weak tian shan are included there is a trade off between the required values of vtarim and vtian and the shape of the predicted crustal thickness profiles better matches the observed profiles the steep topographic slope on the southern margin of the tarim basin requires that it is anomalously strong while the rapid decrease of topographic height to the north of the tian shan requires that it is anomalously weak similar conclusions are obtained with a rheological model based on n 10 simplified rheological models of the lithosphere show that the variations in lithospheric strength may be explained by changes to the moho temperature of the order of 10 to 30 c

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

velocity field in asia inferred from quaternary fault slip rates and global positioning system observations we perform a joint inversion of quaternary strain rates and 238 global positioning system gps velocities in asia for a self consistent velocity field the reference frames for all geodetic velocity observations are determined in our inversion procedure india in moves relative to eurasia eu about a pole of rotation at 29 78 n 7 51 e 0 353 myr 1 which yields a velocity along the himalaya within india that is 73 76 of the magnitude of the in eu nuvel 1a velocity and a vector azimuth that is 8 10 clockwise of nuvel 1a in eu vector azimuth relative to eurasia south china moves at 9 11 mm yr in the direction 110 120 with a pole position 64 84 n 156 74 e 0 12 myr 1 amurian block motion has a pole position in a similar location but at a slower rate 64 61 n 158 23 e 0 077 myr 1 and most of the amurian eurasia motion is accommodated by extension across lake baikal tarim basin moves relative to eurasia about a pole of rotation at 39 24 n 98 2 e 0 539 myr 1 and 16 18 mm yr of shortening is accommodated across the west central tien shan there is distributed e w extension throughout both southern and north central tibet within southern tibet between the longitudes of 77 e to 92 e the deformation field accommodates 16 19 mm yr of e w extension we compare predicted seismic moment rates with those observed in this century in asia total observed seismic moment rates within the entire area of central and east asia 2 2 107 km2 in this century are 2 26 0 7 1020 n m yr 1 as compared with a predicted total rate of 2 03 0 066 1020 n m yr 1 comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long term seismic moment rates from a catalog of limited duration 94 years an observation period of 10 000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates inferred from the joint inversion of gps and quaternary rates of strain we show that in general a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude mb 5 0 for the period january 1 1965 to january 1 1999

gravity anomalies the deep structure and dynamic processes beneath the tien shan bouguer gravity anomalies over the tien shan and pamir are large and negative and therefore consistent with crustal thickening beneath both mountain ranges gravity anomalies over the western tien shan are within about 10 mgal of those expected for local airy isostatic equilibrium but those over the eastern tien shan are up to 50 mgal too large and negative thus they require static or dynamic support of an uncompensated mass deficit these gravity anomalies cannot be matched using regional compensation of the weight of the range on a continuous elastic plate a simple model of two separate elastic plates extending north and south from the axis of the tien shan can allow an adequate fit of observed and calculated anomalies the flexural rigidity of the northern plate must be quite small d 1023 n m corresponding to an equivalent effective elastic thicknesste 25 km but that of the southern plate must be larger d 1024 n m te 50 60 km the data for the eastern tien shan cannot be fit without a force per unit length of roughly 1 4 1012 n or by a bending moment applied to the end of the southern plate thus either a deep mass per unit length of about 1 4 1011 kg m must underlie the eastern part of the range or dynamic deviatoric tensional normal stresses of up to about 5 mpa due to flow in the asthenosphere must pull the tien shan down probably a combination of them resulting from the formation and sinking of a thickened lithospheric root causes the deflection of the moho and the deviations from local isostatic equilibrium

late cenozoic slip on the talas ferghana fault the tien shan central asia although cenozoic crustal shortening and thickening by thrust faulting have built the present tien shan active right lateral shear on the northwest trending talas ferghana fault appears to be the most rapid localized deformation in the belt ephemeral stream valleys have been offset right laterally tens of metres new and published radiocarbon dates of organic material deposited in depressions blocked by offset ridges place upper bounds on the average holocene slip rate at 18 localities uncertainties allow 14 upper bounds to overlap the range of 8 16 mm yr and 95 confidence limits on such bounds at 11 sites are entirely within this range we infer that the rate of 10 mm yr is not simply an upper bound but applies to the late holocene epoch although the bounds on rates permit more rapid slip in the northwest than the southeast they do not place a useful constraint on variations in slip rate along the fault offsets of paleozoic facies boundaries imply a total right lateral shear of 180 250 km but early cretaceous sedimentary rock appears to have been offset only 60 10 km published paleomagnetic declinations of cretaceous miocene rock demonstrate 20 30 of counterclockwise rotation of the ferghana valley which lies just west of the talas ferghana fault with respect to stable parts of eurasia and 20 11 with respect to the central tien shan east of the fault these declinations are consistent with a maximum northwestward translation of 70 210 km of the ferghana valley at the talas ferghana fault and therefore with a similar maximum horizontal shortening across the chatkal ranges which lie between the ferghana valley and the kazakh platform estimates of crustal thickness beneath the chatkal ranges however permit only 60 100 km of cenozoic shortening if 100 km of slip on the talas ferghana fault accumulated at a constant rate of 10 mm yr it would imply an initiation of slip more recently than ca 10 ma long after india collided with the rest of eurasia

three dimensional architecture of growth strata associated to fault bend fault propagation and decollement anticlines in non erosional environments abstract the evolution of surficial structures at the toes of orogens arises from the complex interplay between tectonic and surface processes the internal architecture of syntectonic sediments has been shown to provide useful insights on the kinematic mechanism of folding two dimensional templates of growth strata patterns associated to thrust related anticlines are available in the literature in this paper we show the results of three dimensional numerical modelling of growth fault bend folds fault propagation folds fixed limb length decollement folds and fixed limb dip decollement folds we point out that total thickness contour maps single syntectonic layer contour maps and above all the computation of their directional first derivative maps provide useful templates for inferring the kinematic mechanism of folding when compared with similar maps from natural examples application of these three dimensional numerical models includes the comparison and supervised best fit with three dimensional seismic reflection data sets numerical results are contrasted with the growth strata map patterns of the mediano oliana and pico del aguila anticlines in the spanish pyrenees

late paleozoic tectonic amalgamation of northwestern china sedimentary record of the northern tarim northwestern turpan and southern junggar basins sedimentary rocks contained in basins adjacent to the tian shan provide a long and complex record of the late paleozoic continental amalgamation of northwestern china complementing that provided by rocks preserved within the range this record which comprises dramatic changes in sedimentary facies sediment dispersal patterns sandstone provenance and basin subsidence rates broadly supports previous interpretations of a two part evolution of the tian shan late devonian to early carboniferous collision of the tarim continental block with the central tian shan followed by collision of this combined block with island arcs in the north tian shan and bogda shan in late carboniferous early permian times the first collision resulted in widespread angular unconformities within the tarim basin continued convergence following the collision created a long lived flexural foredeep along the northern margin of the tarim block which received at least 2000 m of lower carboniferous through lower permian fluvial and marine sediment derived from the interior of tarim subsequent early permian continental extension of the northern tarim basin resulted in the deposition of interbedded nonmarine siliciclastic sedimentary rocks and mafic to felsicvolcanic rocks sandstone within this interval was derived from the paleo tian shan and is composed predominantly of lithic volcanic grains similar to the rhyolite in contrast to the tarim basin calc alkaline volcanic rocks and volcanogenic sedimentary rocks dominated carboniferous and permian sedimentation in the northern turpan and northwestern junggar basins volcanic arcs remained active in the north tian shan and bogda shan through the early late carboniferous depositing a kilometers thick interval of deep marine sediment gravity flows in the northwestern junggar basin major arc magmatism ceased in the late carboniferous in response to closure of the oceanic basin between the combined tarim central tian shan block and the north tian shan bogda shan arcs upper carboniferous through lower permian rocks in the northwestern junggar basin compose the sedimentary fill of a bathymetric basin of oceanic depth on the northern side of the volcanic arcs culminating in a 1000 m thick marine regressive sequence middle to upper permian sandstones were derived from the uplifted paleo tian shan and bear the distinctive provenance imprint of granitic rocks presently exposed within the range late permian subsidence of the junggar basin accommodated 5 km of nonmarine sediments however the cause of this subsidence and its relationship to regional tectonic events remain controversial

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

basin analysis of the jurassic lower cretaceous southwest tarim basin northwest china the jurassic through cretaceous southwest tarim basin northwest china contains more than 6 km of fluvial and lacustrine strata deposited in a foreland setting during the successive collisions with eurasia of the changtang block during late triassic early jurassic time and with the mega lhasa block during late jurassic early cretaceous time this tectonism is chronologically linked with the creation of a narrow lower middle jurassic transtensional basin with thick sedimentary infill succeeded by a broader upper jurassic lower cretaceous compressional basin with thinner sedimentary infill the older basin formed between a north northwest striking dextral fault on the eastern side of the southwest tarim basin in the tian shan and a postulated strike slip or normal fault on the western margin of the basin along the kunlun shan the former fault is now the talas ferghana fault the latter may be a predecessor to the main pamir thrust subsidence analysis of the thickest sedimentary section suggests thermal subsidence interpreted as the result of transtension between the two basin bounding faults the younger basin extends farther east and west and does not preserve evidence of activity along the talas ferghana fault the change in basin style between these two episodes of basin development likely reflects either a small counterclockwise rotation of basin bounding structures during the first episode or a small clockwise rotation of the maximum compressive stress between the two episodes

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

geometry and kinematics of single layer detachment folds detachment folds form above below or above and below bed parallel thrusts where thrust displacement is transferred into folding geometric and kinematic models are developed for individual single layer detachment folds formed above the tip line of a thrust we analyze three different detachment fold shapes kink bands chevron and box detachment folds and consider three principal detachment fold models 1 constant limb dip where the detachment fold grows by limb lengthening 2 constant limb length where the detachment fold grows by limb rotation and 3 variable limb length and variable limb dip where the detachment fold grows by both limb rotation and limb lengthening the allowance for variable forelimb thickness and excess layer parallel shear enables us to de elop a wide range of possible detachment fold geometry the geometric validity fields for folds with excess parallel shear are reduced when forelimb thinning takes place folds formed with constant limb length are likely to lock up in the initial amplification stages whereas larger amounts of shortening can be taken up by folds formed with variable limb length the manner in which a fold evolves affects the fracture and porosity features of the folded strata therefore determining which mechanism operated to form a specific detachment fold is of particular importance in hydrocarbon exploration the models we present are aimed at permitting more accurate geometric and kinematic interpretations of individual detachment folds examples of detachment folds are analyzed to illustrate the po ential benefits and limitations of the geometric model presented

seismotectonic range front segmentation and mountain belt growth in the pamir alai region kyrgyzstan india eurasia collision zone the trans alai range along the northern perimeter of the pamir region of kyrgyzstan is at the northern edge of the india eurasia collision zone the range defines a section of main pamir thrust which is divided into eastern central and western segments that record differential absorption of plate convergence the 50 km long east west striking central fault segment of the main pamir thrust has dip slip thrust fault offsets with a minimum holocene dip slip rate of 6 mm yr and is linked to the other segments via northwest striking dextral transfer the western transfer faults are well characterized geomorphically and the westernmost records the predominant transition to north vergent thrusting along the western segment via north vergent low angle thrust faults rooted in a steeply south dipping dextral shear zone in contrast the eastern segment deformation is widely distributed and geomorphically less evident but the transfer also takes place in a structurally complex zone asymmetric offset of a regionally correlated terrace geomorphic zonation and the distribution of historic earthquakes suggest that the central segment is mechanically linked with the western segment but not with the eastern segment the progressive closure of the alai valley by the northward advance of thrusting exemplifies the annihilation of an intramontane basin if the high surface uplift rates implied by these geologic observations have been maintained for the last few million years they attest to the high level of tectonic activity and the recency of construction of the trans alai range

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

halogens and trace metal emissions from the ongoing 2008 summit eruption of kīlauea volcano hawai i volcanic plume samples taken in 2008 and 2009 from the halema uma u eruption at k lauea provide new insights into k lauea s degassing behaviour the cl f and s gas systematics are consistent with syn eruptive east rift zone measurements suggesting that the new halema uma u activity is fed by a convecting magma reservoir shallower than the main summit storage area comparison with degassing models suggests that plume halogen and s composition is controlled by very shallow 77 as gaseous elemental mercury at the point of emission sulphate is an important aerosol component modal particle diameter 0 44 m aerosol halide ion concentrations are low compared to other systems consistent with the lower proportion of gaseous hydrogen halides plume concentrations of many metallic elements rb cs be b cr ni cu mo cd w re ge as in sn sb te tl pb mg sr sc ti v mn fe co y zr hf ta al p ga th u la ce pr nd sm eu gd tb dy er tm are elevated above background air there is considerable variability in metal to so2 ratios but our ratios generally at the lower end of the range previously measured at k lauea support assertions that k lauea s emissions are metal poor compared to other volcanic settings our aerosol re and cd measurements are complementary to degassing trends observed in hawaiian rock suites although measured aerosol metal s ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry plume enrichment factors with respect to hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed i e lithophile elements having lower volatility and chalcophile elements having higher volatility the proportion of metal associated with the largest particle size mode collected 2 5 m and that bound to silicate is significantly higher for lithophiles than chalcophiles many metals show higher solubility in ph 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility nonetheless many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog however metal levels in grass samples showed no clear enrichment downwind of the active vents

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