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

imaging topographic growth by long lived postseismic afterslip at sefidabeh east iran this paper describes observations and models of the postseismic deformation following the 1994 sefidabeh earthquake sequence in east iran which shed light on the nature of the earthquake cycle and the mechanisms of topographic growth in the region interferometric synthetic aperture radar observations show creeping fault motion postseismic afterslip on an array of faults some of these faults probably represent the extensions of those that ruptured in the blind thrust faulting earthquakes in 1994 and cut through the entire seismogenic layer while others are shallow and break up the hanging walls of the coseismic faults the postseismic slip accommodates at least part of the vertical displacement gradient resulting from the buried coseismic slip which was concentrated at depths of greater than 5 km the postseismic afterslip is visible for over 16 years following the earthquakes agreement between the areas of postseismic uplift and indications of long term motion preserved in the geomorphology suggest that shallow fault slip during seismic cycles similar to the one we have observed governs the development of the landscape in the region slip on an array of shallow faults provides a mechanism for the development of short wavelength topography and geological structures above active thrust faults and has important implications for the interpretation of shallow geological features produced in regions experiencing similar seismic cycles to that at sefidabeh

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

kinematics of fault related folding derived from a sandbox experiment we analyze the kinematics of fault tip folding at the front of a fold and thrust wedge using a sandbox experiment the analog model consists of sand layers intercalated with low friction glass bead layers deposited in a glass sided experimental device and with a total thickness h 4 8 cm a computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation active deformation at the tip of the forward propagating basal decollement is monitored along the cross section with a high resolution ccd camera and the displacement field between pairs of images is measured from the optical flow technique in the early stage when cumulative shortening is less than about h 10 slip along the decollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium in this stage of detachment tip folding horizontal displacements decrease linearly with distance toward the foreland vertical displacements reflect a nearly symmetrical mode of folding with displacements varying linearly between relatively well defined axial surfaces when the cumulative slip on the decollement exceeds about h 10 deformation tends to localize on a few discrete shear bands at the front of the system until shortening exceeds h 8 and deformation gets fully localized on a single emergent frontal ramp the fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system as long as strain localization is not fully established the sand layers experience a combination of thickening and horizontal shortening which induces gradual limb rotation the observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds relate finite deformation to incremental folding and derive shortening rates from deformed geomorphic markers or growth strata

a high resolution stable isotopic record from the junggar basin nw china implications for the paleotopographic evolution of the tianshan mountains this study presents high resolution oxygen and carbon isotopic records of paleosol carbonates from fluvial sediments and lacustrine carbonates sampled from the jingou he and kuitun he stratigraphic sections located in the northern tianshan piedmont these sections expose remarkable outcrops of junggar foreland basin sediments that have been previously dated by high resolution magnetostratigraphy to between 23 6 and 1 ma and 10 5 and 3 1 ma a total of 216 samples of fluvio lacustrine sediments were collected from which isotopic analyses yield 18o smow values that range from 13 7 to 29 9 in the jingou he section and 16 3 to 21 0 in the kuitun he section 13c pdb values range from 12 9 to 3 0 in the jingou he section and from 7 8 to 4 0 in the kuitun he section 18o values decrease between 25 and 23 ma and then remain relatively steady with the exception of one period that contains samples with higher oxygen isotope values at 16 ma during the periods when there are samples that overlap in time from the kuitun he and jingou he sections we observe a difference of 1 7 between values from the two locales the 13c values also decrease between 25 and 23 ma and then remain relatively steady until 10 ma with again one short period of higher values at 16 ma then between 10 and 3 1 ma carbon isotope values progressively increase we interpret that 18o and 13c isotopic values during lacustrine periods 25 23 ma and 16 ma as largely controlled by evaporation and opening closing of the lake to external inputs we interpret the 18o values of paleosol carbonate in the junggar basin to be influenced by the hypsometry of the high tianshan range while the 13c values may record the uplift history of the depositional area in the foreland basin itself as well as the isotopic composition of plants consequently we conclude that the jingou he and kuitun he drainage basins in the central tianshan have remained at relatively unchanged elevations for the past 20 ma we also suggest that the elevation of the southern part of the foreland basin increased between 10 and 3 1 ma probably as a result of tectonic deformation in the piedmont and sedimentary filling of the sedimentary basin the carbon isotope record remains relatively stable through time and isotopic values suggest that there was little or no expansion of c4 plants in this region in the late miocene

late miocene pleistocene aridification of asian inland revealed by geochemical records of lacustrine fan delta sediments from the western tarim basin nw china abstract continuous cenozoic deposits have accumulated in the tarim basin northwestern china and are crucial to investigating the aridification history of the asian interior which has long been thought to be linked with the growth of the tibetan plateau retreat of the para tethys sea and global cooling however less and poor climatic records from the region hinder our understanding of the questions above here we report continuous lithologic sedimentary color and geochemical caco3 and salt ions records from precisely dated late miocene early pleistocene sedimentary sequence from western tarim basin nw china they indicate that arid climate had prevailed within the basin at latest at ca 5 7 ma and gradually increased in degree until ca 3 7 ma between ca 3 7 and 2 1 ma a hydrologic event occurred which supplied more water from the tien shan after ca 2 1 ma the climate in the basin turned to hyper arid we attribute the stepwise drying of the asian inland since ca 5 7 ma to the late miocene pliocene episodic uplift of the tibetan plateau pamir and the tien shan and the connection of the pamir with the tien shan in remote response to the collision of india with asia

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

quaternary climate change and the formation of river terraces across growing anticlines on the north flank of the tien shan china nested stream terraces warped upward over actively growing anticlines along the north flank of the tien shan in western china appear to record alternating phases of valley widening and incision differences of relative heights between remnants of four separate strath terraces along one river and between two such terraces along another reach 100 to 120 m over the crests of the anticlines we infer that this spacing is due to alternating stages of valley widening and rapid incision associated with climate changes with a periodicity of 100 kyr the crests of the anticlines appear to emerge from the aggrading flanks of the anticlines at an average rate of about 1 mm a the maximum heights of 25 and 35 10 m for the lowest terraces above their projected initial profiles imply ages of roughly 25 kyr and 35 kyr 10 kyr hence they suggest that flood plains which were abandoned to form the terraces developed adjacent to active stream beds during the last glacial period when climates were relatively

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

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

exhumation of basement cored uplifts example of the kyrgyz range quantified with apatite fission track thermochronology 1 the kyrgyz range the northernmost portion of the kyrgyzstan tien shan displays topographic evidence for lateral propagation of surface uplift and exhumation the highest most deeply dissected segment lies in the center of the range to the east topography and relief decrease and preserved remnants of a cretaceous regional erosion surface imply minimal amounts of bedrock exhumation the timing of exhumation of range segments defines the lateral propagation rate of the range bounding reverse fault and quantifies the time and erosion depth needed to transform a mountain range from a juvenile to a mature morphology new multicompositional apatite fission track aft data from three transects from the eastern kyrgyz range combined with published aft data demonstrate that the range has propagated over 110 km eastward over the last 7 11 myr on the basis of the thermal and topographic evolutionary history we present a model for a time varying exhumation rate driven by rock uplift and changes in erodability and the timescale of geomorphic adjustment to surface uplift easily eroded cenozoic sedimentary rocks overlying resistant basement control early rapid exhumation and exhibit slow surface uplift rates as increasing amounts of resistant basement are exposed exhumation rates decrease while surface uplift rates are sustained or increase thereby growing topography as the range becomes high enough to cause ice accumulation and to develop steep river valleys fluvial and glacial erosion becomes more powerful and exhumation rates once again increase independently determined range normal shortening rates also varied over time suggesting a feedback between erosional efficiency and shortening rate

holocene hydrological changes inferred from alluvial stream entrenchment in north tian shan northwestern china abstract we analyze the possible contribution of climate change or tectonics on fluvial incision from the study of a case example along the northern flank of tian shan the rivers that exit the high range fed large alluvial fans by the end of the last glacial period they have since deeply entrenched the piedmont by as much as 300 m we have surveyed several terraces that were cut and abandoned during river entrenchment providing information on intermediate positions of the riverbed during downcutting they suggest a gradual decline in river slope during a major phase of incision throughout the holocene tectonic uplift affects only a zone about 5 km wide corresponding to a growing anticline and is shown to account for about 10 of total incision incision was therefore most probably driven by climate change from observed fluvial incision we estimate the water discharge in excess of that needed to carry the sediments supplied by hillslope erosion in the headwaters we used a model based on a transpor

tectono stratigraphic history of the southern junggar basin seismic profiling evidences the modern tianshan is an active intracontinental range in central asia its initial timing is poorly known and still hotly debated as the subsidence of foreland basins is intrinsically coupled with the uplift of orogenic wedges the foreland sedimentary records may accurately constrain the tianshan uplifting history to better address the question we analyse a seismic profile across the southern junggar foreland basin to decipher its tectonic and stratigraphic history four structural layers can be identified in an ascending order the permian lower jurassic transtension related layer the jurassic cretaceous thermal subsistence layer the palaeogene layer and the miocene quaternary foreland sedimentary layer the oldest sedimentary sequence in the foreland succession is of the shawan formation deposited at 24 ma based on magnetostratigraphic constraints this indicates that foreland deformation in the northern tianshan and uplifting of the modern tianshan probably initiated at the beginning of the miocene

rate of active shortening across the southern thrust front of the greater caucasus in western georgia from kinematic modeling of folded river terraces above a listric thrust abstract although the greater caucasus gc mountains accommodate a significant fraction of orogen perpendicular arabia eurasia convergence at their longitude the locations and slip rates of the active structures absorbing this shortening are poorly known here we report the first late quaternary shortening rate for an active thrust in the gc determined from dating and reconstructing a deformed landform in the rioni basin along the southwestern flank of the gc terraces along the enguri river have been folded by the south vergent tsaishi anticline and record quaternary shortening along the southernmost exposed frontal structure terrace surfaces are well preserved and together with underlying mesozoic to neogene strata clearly record folding we use high resolution topographic data from differential gps surveys and bedding attitudes across the fold to construct a kinematic model that describes both the terrace deformation and finite shortening across the anticline recorded by the folded strata we calculate that a deformed terrace records 106 1 38 7 36 4 m of slip since abandonment optically stimulated luminescence dating of quartz in a loess cap on this terrace indicates it was abandoned before 94 1 12 8 ka implying a geologic shortening rate of 1 09 0 62 0 43 mm yr since 100 ka this work confirms that the frontal structure of the rioni fold thrust belt is quaternary active but has a rate that falls short of the regional geodetic shortening rate of 3 5 mm yr we infer that the missing late quaternary shortening is accommodated by additional structures within the gc to the north folding of late quaternary terraces and a possible coseismic scarp along the frontal structure of the gc together imply that structures in the western gc may be capable of coseismic rupture within and beneath the adjacent basin in addition to blind ruptures within the main range such as the 1991 racha earthquake thus the gc system appears to be broadly analogous to the himalaya where the foreland fold thrust belt connects by a shallow seismogenic detachment to structures beneath the main range the geometry of this detachment may influence earthquake rupture initiation and propagation potentially playing a significant role in the seismic hazard of the gc

late quaternary drainage evolution in response to fold growth in the northern chinese tian shan foreland abstract alluvial units are important in understanding the interactions of antecedent drainage evolution with fold growth along the flanks of active orogenic belts this is demonstrated by the anjihai river in the northern chinese tian shan foreland which at present flows northward cutting sequentially through the nananjihai anticline the huoerguos anticline and the anjihai anticline three episodes of alluviation designated as fans fa fb and fc are identified for the anjihai river these three alluvial terrain features comprise a series of terraces where the topographic characteristics geomorphologic structure and up warped longitudinal profiles indicate continuous uplift and lateral propagation of the halaande anticline and the anjihai anticline over the past 50 ky shortly after 3 6 ka when the oldest terrace during the period of the fan fb sedimentation was formed significant rock uplift at the overlapping zone of the anjihai anticline and the halaande anticline led to the eastward deflection of the antecedent anjihai river a series of local terraces with elevation decreasing eastward indicate the gradual eastward migration of the channel of the anjihai river during the period of the fan fc sedimentation finally the anjihai river occupied the previous course of the jingou river when the latter was deflected eastward in response to rock uplift of the anjihai anticline presently flowing across the eastern tip of the anjihai anticline

evolution of the cenozoic tarim basin by flexural subsidence and sediment ponding insights from quantitative basin modelling abstract the tarim basin became a closed continental sedimentary basin in the cenozoic due to uplift of the western kunlun tian shan and the altyn tagh ranges in the context of the indian asia collision a north northeast trending seismic profile across the basin reveals that cenozoic strata comprise a wedge of sediments in the southern and northern regions generated by flexural subsidence overlain by a more uniform regional sediment drape we obtain the subsidence profiles across the basin at 26 ma 13 ma 5 ma and the present day using backstripping based on the sedimentary architecture shown in the seismic profile we use a numerical finite elastic plate to model these subsidence profiles our modelling indicates that the southern and northern flexural depressions started to interfere to form a single flexural bulge within the basin since late paleogene times the flexural bulge migrated 52 km toward the western kunlun range since 26 ma reflecting a decrease in the ratio of loads of the western kunlun range versus the tian shan we separate the sediment drape from the flexural subsidence according to the preceding modelling results our separating demonstrates that the thickness of the drape increased from 230 30 m at 26 ma to 1910 200 m at present occupying 30 of cenozoic strata in the profile the rise in the base level since the paleogene is estimated as 356 80 m by correcting for sediment loading of the drape we adopt a decreasing basin width to model the evolution of the flexural subsidence suggesting significant uplifting of the western kunlun range and the tian shan from 26 ma to 13 ma relative stable elevations in these ranges from 13 ma to 5 ma and their rapid uplifts since 5 ma

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

quaternary activity of the range front thrust system in the longmen shan piedmont china revealed by seismic imaging and growth strata reliable estimates of quaternary or cenozoic upper crustal shortening in the longmen shan fold and thrust belt are rare in this paper we report on our use of high resolution 2 d and 3 d seismic reflection profiles at various scales together with borehole data to investigate the structural geometry of the longmen shan piedmont the results reveal a thrust system beneath the longmen shan termed the range front thrust system which consists of the range front blind thrust and its upward splay faults moreover on these faults we identified growth strata that provide an excellent opportunity for assessing the activity of this thrust system analyses of the growth strata reveal early to late pleistocene activity on the range front blind thrust with minimum dip slip and horizontal shortening rates of 1 1 0 2 mm yr and 1 mm yr accordingly the maximum accumulated slip on the range front blind thrust is calculated to be 7 5 0 3 km in the longmen shan using the new horizontal shortening rate and other published data we also estimated that the long term shortening rate across the longmen shan fold and thrust belt is 1 3 mm yr which is comparable to the short term gps rate the similarity of these rates suggests that the longmen shan attained a steady state condition over the past 2 myr an additional highlight of our results is that we show quaternary activity around the tibetan plateau to have been nearly synchronous in different regions including in the longmen shan the himalayas the western kunlun shan and the northern qilian shan

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

magnetostratigraphy of the yaha section tarim basin china 11 ma acceleration in erosion and uplift of the tian shan mountains we report a magnetostratigraphic and rock magnetic study of the yaha section located on the southern flank of the central tian shan mountains asia our results show a two fold increase in sedimentation rate as well as marked changes in rock magnetic characteristics ca 11 ma after 11 ma sedimentation rate remained remarkably constant until at least 5 2 ma these findings are consistent with sedimentary records from other sections surrounding the tian shan we conclude that uplift and erosion of the tian shan accelerated ca 11 ma long after the onset of the collision between india and asia and that the range rapidly evolved toward a steady state geometry via a balance between tectonic and erosion processes

oxygen isotopes of an early archaean layered ultramafic body southern west greenland implications for magma source and post intrusion history a large number of metamorphosed ultramafic bodies are found in the region sw of the isua greenstone belt in southern west greenland enclosed in archaean banded tonalitic gneisses these enclaves of dunite and harzburgite range in size from a few to several hundred meters the ujarassuit nunat layered body occurs as a large enclave 800 m 100 m entrained within tonalitic gneisses and preserves primary igneous layering and textures this enclave has been subjected to amphibolite grade metamorphism but for the most part the magmatic mineralogy remains intact separated minerals have been analysed for 18o by co2 laser fluorination 18o values range from 4 49 to 4 89 for olivine and from 5 70 to 5 86 for orthopyroxene all chromite values are 2 5 closure temperatures recorded for olivine orthopyroxene pairs vary from 700 to 900 c much lower than expected for an ultramafic magma widespread late magmatic re equilibration has resulted in significant decreases in 18o for chromites and small changes of 0 3 in olivine but orthopyroxene values show little variation from typical magmatic signatures the lowering of 18o in chromite is associated with significant fe enrichment thermometry suggests that the re equilibration took place at 680 750 c with equilibration between plagioclase and amphibole in residual gabbro anorthosite melt around 700 c hydration possibly associated with this late melt stage resulted in further changes to chromite chemistry formation of secondary amphibole phlogopite and chlorite and may have further enhanced 18o depletion in disseminated chromites all these events are related to late magmatic processes only the later metamorphic mineral ruby corundum present in amphibole harzburgite adjacent to an intrusive gneiss vein clearly indicates an external oxygen input to this system olivines from an unlayered dunite body 3 5 km away from ujarassuit nunat have higher 18o values around 5 25 typical of more recent high temperature mantle peridotite nodules and suggesting that mantle oxygen composition at 3 8 ga was already similar to the present composition

spatiotemporal patterns of the late quaternary deformation across the northern chinese tian shan foreland abstract the investigations of active deformation across a mountain foreland can provide important insights into the pattern and dynamics of deformation of an active orogenic belt here we focus on the spatiotemporal patterns of the late quaternary deformation along the north piedmont of the chinese tian shan a mountain range formed by the ongoing india asia collision by using a terrace as the reference and applying the area conservation method the holocene shortening rate of the halaande anticline a fold of the distal structure belt iii in the foreland is estimated to 2 14 0 24 mm yr for the first time similarly we re calculate the holocene shortening rates of the other anticlines of belt ii iii using the magnitude of shortening documented by river terraces and the terrace formation ages published previously the summed holocene 103 year timescale shortening rates of individual anticlines along n s transects are 2 4 mm yr consistent with the late pleistocene 104 year timescale shortening rate but about 2 6 times higher than the long term 106 year timescale average shortening rate of 1 mm yr during the past several million years together with the shortening rates of individual anticlines at the 103 year 104 year and 106 year scales these observations imply that the deformation across the northern chinese tian shan foreland has accelerated since at least late pleistocene by summing the late quaternary rates of shortening in the southern chinese tian shan foreland 4 5 mm yr and the intermontane basins in the hinterland of the tian shan 2 mm yr the late quaternary rate of shortening across the tian shan range between longitude 83 e and 87 e amounts to 9 0 1 0 mm yr approximately matching the modern shortening rate of 8 mm yr derived from the gps measurements these results imply i that the deformation across the tian shan range and its foreland basins between longitude 83 e and 87 e could have not been changed significantly since at least late pleistocene ii that in the northern chinese tian shan foreland the recurrence interval of paleoseismic events during the past tens of thousands of years may be determined by a linear extrapolation of the holocene or even geodetic rate of deformation

a fluvial terrace record of late quaternary folding rate of the anjihai anticline in the northern piedmont of tian shan china abstract crustal shortening of the tian shan range in northwest china has largely been accommodated by fold and thrust belts that mark the northern and southern mountain boundaries which were formed during the basinward propagation of the deformation front of tian shan investigating the deformation rates of active folds anticlines in the mountain piedmonts within different timescales is important for understanding the mountain building and front propagation processes of the tian shan in this study we investigate the late quaternary folding rate of the anjihai anticline one of the major anticlines in the northern piedmont of tian shan our study is based on optically stimulated luminescence osl dating and topographic measurements of folded river terraces three well preserved fluvial terraces across the anjihai anticline were identified and dated to be 3 6 0 1 ka 9 0 0 6 ka and 53 3 2 2 ka respectively these terrace ages are combined with shortening and uplift of the terraces estimated using an area conservation method and the terrace height profiles to evaluate the average shortening and uplift rates our results show that the minimum shortening rate of the anjihai anticline is 0 4 mm a between 53 ka and 9 ka and 1 1 mm a over the past 9 ka and the corresponding minimum uplift rates are 0 5 mm a and 1 4 mm a respectively if a local sedimentation rate of 0 3 mm a is taken into consideration the shortening rate is 0 7 mm a between 53 ka and 9 ka and 1 3 mm a since 9 ka and the corresponding uplift rates are 0 8 mm a and 1 5 mm a respectively these data suggest that the anjihai anticline has accommodated 20 25 of the total shortening across the whole eastern tian shan 5 mm a in the holocene our results suggest that the holocene is a relatively tectonically active time interval since the late pleistocene the late quaternary shortening rate of the anjihai anticline is much higher than its long term average shortening rate 0 2 mm a since its formation at 7 4 ma a similar situation has also been observed for other active folds in the northern and southern piedmonts of tian shan the higher late quaternary folding rate is possibly attributed to the gradual propagation of the tian shan towards its northern and southern foreland basins in the quaternary

miocene to present kinematics of fault bend folding across the huerguosi anticline northern tianshan china derived from structural seismic and magnetostratigraphic data we combine surface structural measurements subsurface seismic imaging and magnetostratigraphic dating to retrieve through geometric modeling the detailed history of fold growth and sedimentation across the huerguosi anticline on the northern tianshan piedmont taking advantage of a beautifully exposed section of growth strata the model assumes a fault bend folding mechanism consistent with subsurface fold geometry the shortening history is obtained by least squares fi tting of the measured dip angles of the growth strata the shortening rate across the anticline is shown to have been remarkably constant it increased only slightly from 0 84 0 04 mm yr between 10 and 4 ma to 1 14 0 02 mm yr over the past 4 m y this approach also allows correcting syntectonic sedimentation rates for the effect of the fold growth and shows that the sedimentation rates in the piggyback basin increased abruptly from 0 4 to 0 7 mm yr ca 4 ma

investigation of field installation effects of horizontal twin jet grouting in shanghai soft soil deposits this paper presents a case study of an investigation into the responses of the surrounding ground to the horizontal twin jet grouting method htjgm in soft soil deposits of shanghai during the fi

finite element analysis of mixed in place mip columns supporting excavations in slopes considering tension softening the use of mixed in place mip columns can be considered as an attractive alternative to sheet pile diaphragm or bored pile walls for supporting deep excavations even in difficult ground conditi

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

deciphering cumulative fault slip vectors from fold scarps relationships between long term and coseismic deformations in central western taiwan we document the 30 ka cumulative slip history and long term slip vector azimuth on the northern chelungpu fault based on a series of fault bend folded alluvial terraces and draw quantitative relationships between geological structure deformation observed from the geomorphology and coseismic displacements during the 1999 mw 7 6 chi chi earthquake in our study area three main terrace levels show progressive folding by kink band migration in relation to the underlying fault geometry forming a main n s fold scarp up to 193 m high and secondary e w scarps detailed analysis using 5 m resolution digital elevation model allows us to characterize the scarp morphology and quantify the deformation parameters namely terrace heights fold scarp relief and fold limb width and slope angle the 3 d deformation of the highest terrace dated by optically stimulated luminescence at 30 2 4 0 ka enables to simultaneously determine amplitude and azimuth of the long term slip vector based on scarp relief the long term slip vector oriented n338 6 is found to parallel the chi chi coseismic displacements in this area cumulative slip and dating results yield a constant slip rate of 17 7 2 2 mm a in the direction n338 6 late quaternary shortening rates observed at four sites vary along strike in a similar way to chi chi coseismic displacements together with the collinearity of long term and coseismic slip vectors at our study site this suggests that chi chi earthquake is a characteristic earthquake for the chelungpu thrust with recurrence interval 470 years we also discuss implications for the regional and long term distribution of shortening in the central western foothills

denudation outpaced by crustal thickening in the eastern tianshan the modern high topography of the tianshan resulted from the reactivation of a paleozoic orogenic belt by the india asia collision today the range exhibits tectonically active forelands and intermontane basins based on quantitative morphotectonic observations and age constraints derived from cosmogenic 10be dating single grain post infrared infrared stimulated luminescence p ir irsl dating and modeling of fault scarp degradation we quantify the deformation in the nalati and bayanbulak intermontane basins in the central eastern tianshan our results indicate that at least 1 4 mm yr of horizontal crustal shortening is accommodated within these two basins this shortening represents over 15 of the 8 5 0 5 mm yr total shortening rate across the entire range at this longitude this shortening rate implies that the eastern central tianshan is thickening at a mean rate of 1 4 mm yr a rate that is significantly higher than the average denudation rate of 0 14 mm yr derived from our cosmogenic analysis this discrepancy suggests that the tianshan range has not yet reached a steady state topography and remains in a transient state of topographic growth most likely due to limited denudation rates driven by the arid climate of central asia

a field trial of jet grouting in marine clay the basement excavation of the singapore post center involved extensive jet grouting to improve the soft marine clay present within the excavation the treated soil mass with much improved strength and deformation characteristics was intended to act as an internal strut below the bottom of the excavation level reducing movements caused by the basement excavation this paper presents the performance of a well instrumented field jet grouting trial during the construction of the building basement results of monitoring suggest that the jet grouting trial caused the retaining diaphragm walls and the adjacent soils immediately behind and at some distance away from the walls to move away from the jet grouted area the maximum free field lateral soil movements in the excavation side of the jet grouted mass were much larger than the corresponding lateral movements behind the wall the results suggest that the diaphragm wall provided considerable restraint thereby reducing the lateral movements of the soil beh

basin width control of faulting in the naryn basin south central kyrgyzstan 1 in central asia s tien shan deformation is distributed across the wide orogen a characteristic of intracontinental mountain building active faults are commonly found within intramontane basins that separate its constituent ranges in order to explore the controls on this intramontane basin deformation we study the naryn basin of south central kyrgyzstan a series of five balanced cross sections reveals a transition in patterns of faulting from faults confined to basin margins to faults focused within the basin center the 20 km wide eastern naryn basin displays deformation attributed to low angle splays of the northern basin bounding fault in the 40 km wide western naryn basin the pattern of deformation linked to the northern range remains but is accompanied by steeper faults that dip both south and north without being directly linked to the basin bounding fault we compare these cross sections to synthetic aperture radar interferometry insar measurements of surface deformation profiles of insar derived surface deformation rates across the naryn basin reveal that in the west deformation is distributed across the broad basin interior whereas in the east rapid uplift is concentrated at the margin of the narrower basin from the geodetic and structural data we infer that in the western naryn basin deformation has migrated away from the northern basin margin and into the interior deformation of the eastern basin interior however remains linked to the basin bounding fault a simple mechanical model demonstrates that basin width may control basin deformation whereby basin interior faulting in the narrow eastern naryn basin is inhibited by the overburden of adjacent ranges citation goode j k d w burbank and b bookhagen 2011 basin width control of faulting in the naryn basin south central kyrgyzstan tectonics 30 tc6009 doi 10 1029 2011tc002910