crustal reworking at nanga parbat pakistan metamorphic consequences of thermal mechanical coupling facilitated by erosion within the syntaxial bends of the india asia collision the himalaya terminate abruptly in a pair of metamorphic massifs nanga parbat in the west and namche barwa in the east are actively deforming antiformal domes which expose quaternary metamorphic rocks and granites the massifs are transected by major himalayan rivers indus and tsangpo and are loci of deep and rapid exhumation on the basis of velocity and attenuation tomography and microseismic magnetotelluric geochronological petrological structural and geomorphic data we have collected at nanga parbat we propose a model in which this intense metamorphic and structural reworking of crustal lithosphere is a consequence of strain focusing caused by significant erosion within deep gorges cut by the indus and tsangpo as these rivers turn sharply toward the foreland and exit their host syntaxes the localization of this phenomenon at the terminations of the himalayan arc owes its origin to both regional and local feedbacks between erosion and tectonics

evolution of the great river systems of southern asia during the cenozoic india asia collision rivers draining north from the pamir syntaxis abstract during uplift of the tibetan plateau and surrounding ranges tectonic processes have interacted with climatic change and with local random effects such as landslides to determine the development of the major river systems of asia rivers draining northward from the pamir syntaxis have three distinctive patterns that are controlled by different tectonic and climatic regimes west of the pamir the rivers have moderate but irregular gradients and drain northwards to disappear into arid depressions relatively steady uplift of the hindu kush in northern afghanistan allowed rivers to cut across the rising ranges modified by the shear along the harirud fault zone local faulting and by increasing rain shadow effects from the rising makran in the transition to the pamir the rivers have steeper but more even gradients suggesting more even flow and downcutting during uplift possibly related to larger glacial sources in the central pamir only one antecedent river the pyandzh appears to have kept its northward course with compression and uplift of the indenter and its course strangely corresponds with a major geophysical boundary a distorted subducted slab but not a geological boundary the other rivers are subsequent rivers developed along deformation fronts during development and northward displacements of the pamir structural units the above areas have sources north of the cretaceous karakorum south pamir andean margin on the eastern flank of the pamir in the kunlun and northern tibetan plateau the rivers rise similarly north of the cretaceous andean margin of southern tibet but then flow with low gradients across the plateau before cutting and plunging steeply down across the kunlun to disappear into the arid tarim these steep profiles are the result of late neogene uplift of the northern tibetan plateau and kunlun possibly modified by glacial diversion and river capture the drainage history of the pamir indenter can be reconstructed by restoring the gross movements of the plates and the tectonic displacements uplift and erosion of individual tectonic units most important changes in drainage took place in the last 10 million years late miocene to quaternary times as the pamir syntaxis developed

building the pamirs the view from the underside the pamir mountains are an outstanding example of extreme crustal shortening during continental collision that may have been accommodated by formation of a thick crust much thicker than is currently thought and or by continental subduction we pre sent new petrologic data and radiometric ages from xenoliths in miocene volcanic rocks in the southeastern pamir mountains that suggest that gondwanan igneous and sedimentary assemblages were underthrust northward buried to 50 80 km during the ear ly stage of the india asia collision and then heated and partly melted during subsequent thermal relaxation before finally being blasted to the surface these xenoliths the deepest crustal samples recovered from under any active collisional belt provide direct evidence for early cenozoic thickening of the pamirs and lower crustal melting during collision the xenoliths also suggest that the present mountain range was a steady state elevated plateau for most of the cenozoic

thermochronometry reveals headward propagation of erosion in an alpine landscape glacial erosion of mountain ranges produces spectacular alpine landscapes and by linking climate with tectonics influences a broad array of geophysical phenomena although the resultant landforms are easily identified the timing and spatial pattern of topographic adjustment to pleistocene glaciations remain poorly known we investigated topographic evolution in the archetypal glacial landscape of fiordland new zealand using u th he thermochronometry we find that erosion during the past 2 million years removed the entire pre pleistocene landscape and fundamentally reshaped the topography erosion focused on steep valley segments and propagated from trunk valleys toward the heads of drainage basins a behavior expected if subglacial erosion rate depends on ice sliding velocity the fiordland landscape illustrates complex effects of climate on earth s surface morphology

quaternary tectonic response to intensified glacial erosion in an orogenic wedge active orogens are thought to behave as internally deforming critical taper wedges that are in rough long term equilibrium with tectonic influx and erosional outflux spatial and temporal variations in climate are therefore hypothesized to have a significant influence on denudation topography and deformation of orogens thereby affecting wedge taper however the impact of the most severe transition in northern hemisphere climate during the cenozoic era the onset of glaciation has hitherto not been empirically documented here we analyse the spatial patterns of denudation and deformation and their temporal variations in the heavily glaciated st elias orogen in southern alaska low temperature thermochronometry thermokinematic modelling and offshore seismic reflection and borehole data suggest that the global scale intensification of glaciation in the middle pleistocene epoch enhanced glacier growth and caused ice streams to advance to the edge of the continental shelf this led to focused denudation across the subaerial reaches of the orogen and burial of the actively deforming wedge toe by the eroded sediment we propose that this climatically driven mass redistribution forced a structural reorganization of the orogen to maintain critical taper our empirical results thus support decades of numerical model predictions of orogenesis and provide compelling field evidence for the significant impact of climate change on tectonics intense glaciation during the middle pleistocene epoch led to focused denudation and mass redistribution within the st elias orogen in southern alaska and resulted in structural reorganization of the orogen the tectonic response of this orogen to climate change is consistent with predictions of numerical models

intense localized rock uplift and erosion in the st elias orogen of alaska the st elias orogen in alaska is one of the world s highest coastal mountain ranges an age analysis of detrital material in active sediment systems in the inaccessible ice covered valley bottoms reveals localized exhumation that is driven by coupling between erosion and active tectonic rock uplift

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

cenozoic crustal shortening between the pamir and tien shan and a reconstruction of the pamir tien shan transition zone for the cretaceous and palaeogene the magnitude of the late cenozoic crustal shortening during convergence of the pamir and tien shan was determined using a contemporary pattern consisting of facies zones palaeomagnetic data regarding the rotation of tectonic units and data on the structure of the tadjik depression by late cenozoic cretaceous and palaeogene facies zones were cut by the vakhsh trans alay overthrust and darvaz strike slip faults and a significant part of the cretaceous palaeogene tadjik basin was overthrust by the pamir massif the sediments of easternmost part of the basin are preserved in the tarim depression the facies zones of the southern slope of the afghan tadjik basin were deformed and moved northward a pattern of facies zones indicates a convergence between the pamir and tien shan over a distance of 300 400 km a number of cross sections through the tadjik depression were used to establish the structure before folding a rotation of tectonic units indicated by structural data conforms to the angles of rotation as determined in palaeomagnetic studies the data suggest 300 km of convergence between the pamir and tien shan stratigraphic lithological structural and palaeomagnetic data formed the basis for the construction of the palinspastically restored palaeogeographic and sedimentologic environments for the tadjik shallow sea basin which was situated between the pamir and tien shan before their convergence in the late cenozoic the maps were constructed for the eight stratigraphic levels of the cretaceous and palaeogene the tadjik sea was a bay in the enormous turan sea in the early aptian this bay was located in what is now the afghan tadjik basin in late cretaceous the eastern shore of the bay lay 600 700 km further eastward and in the eocene marine environments extended even further eastward but after the rupelian continental environments occupied all of this region 2000 elsevier science b v all rights reserved

reply to comments on drainage from a uniform soil layer on a hillslope by f stagnitti m b parlange t s steenhuis and j y parlange

neogene cooling and exhumation of upper amphibolite facies whiteschists in the southwest pamir mountains tajikistan abstract the pamir mountains of central asia are the product of accretion events during the paleozoic and mesozoic and have been further impacted by the continental collision between india and asia during the cenozoic deformation continues today in what is now a mountain belt within a continental interior the geology of the pamir is characterized by several arcuate shaped structurally bound regions with a general east west trend the southwest pamirs are noteworthy for the extensive development of whiteschists talc kyanite rocks and other ultramagnesian metamorphic assemblages in the goran series our interpretation of the goran series is that upper amphibolite facies metamorphism at temperatures above 650 c and pressures near 700 mpa kyanite talc kyanite potassium feldspar was followed by decompression to below 400 mpa sillimanite cordierite late stage andalusite is found only at kuhi lal available u pb k ar and rb sr data gave 2130 ma as a minimum age for the amphibolite facies metamorphism our 40ar 39ar cooling ages for biotite phlogopite and hornblende from kuhi lal darai stazh and mulvoj indicate miocene cooling for the goran series biotites from mica schist gave good plateau ages of 8 9 0 3 10 2 0 3 and 18 3 0 2 ma and phlogopite associated with sapphirine forsterite and enstatite gave a 16 9 0 3 ma plateau hornblende from amphibolite gave a plateau age of 22 2 1 3 ma and an age of 17 ma from a saddle shaped release spectrum our 17 22 ma ages are comparable to previously reported 18 23 ma rb sr isochron ages on the pamir shugnan complex of gneissic granite exposed 15 km northeast of the northernmost locality kuhi lal and thus could be related to heating associated with this plutonism our preferred interpretation is that the ages represent regional cooling due to exhumation related to tectonic activity in the miocene

post 4 ma initiation of normal faulting in southern tibet constraints from the kung co half graben the timing of e w extension of the tibetan plateau provides a test of mechanical models of the geodynamic evolution of the india asia convergence zone in this work we focus on the kung co half graben southern tibet china bounded by an active n s normal fault with a minimum vertical offset of 1600 m to estimate the onset of normal faulting we combined high and medium temperature u pb ar ar and low temperature u th he thermochronometry of the kung co pluton a two mica granite of the northern himalayan granitic belt that outcrop in the footwall of the fault biotite and muscovite ar ar ages are close from each other 16 ma 0 2 ms and 15 0 4 ma bt which is typical of fast cooling the zircon and apatite u th he ages range from 11 3 to 9 6 ma and 9 9 to 3 7 ma respectively these he ages are indicative of 1 fast initial cooling from 11 3 to 9 ma gradually decreasing with time and 2 a high geothermal gradient 400 c km close to the surface at 10 ma the kung co pluton was emplaced at about 22 ma u pb on zircon at less than 10 km depth and 520 545 c subsequent to its shallow emplacement the pluton underwent fast thermal re equilibration ending around 7 5 ma followed by a period of slow cooling caused either by the end of the thermal re equilibration or by very slow exhumation 0 02 0 03 mm yr from 7 5 ma to at least 4 ma in either case the data suggest that the exhumation rate increased after 4 ma we infer this increase to be related to the initiation of the kung co normal fault a critical examination of previously published data show that most n s tibetan normal faults may have formed less than 5 ma ago rather than in the miocene as assumed by several authors such a young age implies that e w extension is not related to the neogene south tibetan magmatism 25 to 8 ma consequently models relating e w extension to magmatism such as convective removal of the lower lithosphere may be inappropriate we rather think that this extension is related with local accommodation of boundary forces and displacements 2007 elsevier b v all rights reserved

southward propagation of the karakoram fault system southwest tibet timing and magnitude of slip the net slip on the southern portion of the karakoram fault system in southwest tibet is estimated by restoring a piercing line defined by two key surfaces in the south kailas thrust system a regional counter thrust along the indus yalu suture assuming that the thrust system is planar across the karakoram fault we calculate 66 5 5 km of normal right slip documentation of the south kailas thrust active at 13 ma implies that the karakoram fault in southwest tibet did not initiate until after the cessation of motion on the thrust however field investigations of the central portion of the karakoram fault system document the fault to have been active at 17 ma and to have accumulated a maximum of 150 km of right slip we suggest that these along strike variations in the magnitude of slip and timing constraints are best explained by southward propagation of the karakoram fault system this is inconsistent with major right lateral slip on the fault system which was used in support of extrusion models for tibet

cenozoic evolution of the eastern pamir implications for strain accommodation mechanisms at the western end of the himalayan tibetan orogen detailed field mapping geochronologic and thermochronologic analyses and petrologic investigations conducted along the southern segment of the late cenozoic kongur shan extensional system provide new information on the cenozoic tectonic evolution of the eastern pamir at the western end of the himalayan tibetan orogen field relations and cooling age patterns in the hanging wall and footwall of the active faults show a southward decrease in the magnitude of east west extension along the southern kongur shan extensional system from 20 km or less along the muztaghata massif in the north to l3 km along the tashkorgan fault in the south these results in conjunction with previously published work on the northern segment of the kongur shan extensional system show a general southward decrease in east west extension along the entire length of the extensional system consistent with models of extension primarily driven by oroclinal bending or radial thrusting of the pamir petrologic data 40 ar 39 ar cooling ages and monazite th pb ages from schists and gneisses in the footwall of the southern kongur shan normal fault along the muztaghata massif record two tectonic events that immediately preceded late miocene initiation of east west extension 1 high grade schists and gneisses experienced upper amphibolite facies metamorphic conditions 9 10 kbar 700 750 c dated as late oligocene to middle miocene by in situ ion microprobe analyses of monazite inclusions in garnet and 2 high grade schists and gneisses were subsequently rapidly exhumed to shallow crustal levels in the late miocene with 40 ar 39 ar biotite cooling ages of 7 5 9 ma rapid exhumation was accommodated in part by the east west striking south dipping shenti normal fault field relations and regional geologic correlations indicate that this exhumation event was related to the formation of the central pamir gneiss domes and the antiformal muztaghata massif is the eastward continuation of the sares dome of the central pamir these observations suggest that the antiformal gneiss domes of the central pamir have not been offset across the karakorum right slip fault from the qiangtang anticlinorium in tibet instead we propose that the development of the central pamir gneiss domes may have been related to oligocene miocene northward underthrusting and thickening of crust beneath the pamir

cenozoic right slip faulting along the eastern margin of the pamir salient northwestern china the pamir salient defines the western end of the himalayan tibetan orogen and has overthrust the tarim tajik basin to the north by 300 km along a late cenozoic south dipping intracontinental subduction zone field mapping structural measurements and analysis of mesoscale structures along a 32 km long reach of the yarkand river document the tectonic evolution of the east flank of this salient between the north pamir to the west and the western kunlun shan to the east the study area is cut by a set of four north northwest striking steeply dipping brittle faults microstructures and asymmetric outcrop to map scale folds indicate right slip along these faults between these structures fault bounded panels of phanerozoic strata are deformed by en echelon folds with axes that trend more westerly than the adjacent faults consistent with dextral transpression the fault system described here extends for 350 km along the eastern flank of the pamir salient transpressional right slip along this set of faults here called the kashgar yecheng transfer system appears to have accommodated late cenozoic separation of the north pamir from the western kunlun shan during south directed intracontinental subduction beneath the leading edge of the pamir salient correlation of major faults suggests total slip along the kashgar yecheng transfer system is likely on the order of 280 km this offset estimate implies long term slip rates of 7 15 mm a along the kashgar yecheng transfer system when combined with previous sedimentologic stratigraphic and thermochronologic data that indicate deformation along the east flank of the pamir started between the late eocene and early miocene these results imply that the first order structures on the western and eastern flanks of the pamir are asymmetric previous work has shown that deformation in the west was accommodated by anticlockwise vertical axis rotation of the pamir over the eastern margin of the tajik basin this rotation is generally interpreted to reflect northwest directed radial thrusting in contrast to the transpressional right slip transfer faulting on the east side reported here

rapid glacial erosion at 1 8 ma revealed by 4he 3he thermochronometry alpine glaciation and river incision control the topography of mountain ranges but their relative contributions have been debated for years apatite 4 he 3 he thermochronometry tightly constrains the timing and rate of glacial erosion within one of the largest valleys in the southern coast mountains of british columbia canada five proximate samples require accelerated denudation of the klinaklini valley initiating 1 8 0 2 million years ago ma at least 2 kilometers of overlying rock were removed from the valley at 5 millimeters per year indicating that glacial valley deepening proceeded 6 times as fast as erosion rates before 1 8 ma this intense erosion may be related to a global transition to enhanced climate instability 1 9 ma

tectonic evolution of the northeastern pamir constraints from the northern portion of the cenozoic kongur shan extensional system western china the late cenozoic kongur shan extensional system lies along the northeastern margin of the pamir at the western end of the himalayan tibetan orogen accommodating east west extension in the pamir at the northern end of the extensional system the kongur shan normal fault juxtaposes medium to high grade metamorphic rocks in both its hanging wall and footwall which record several mesozoic to cenozoic tectonic events schists within the hanging wall preserve a buchan metamorphic sequence dated as late triassic to early jurassic 230 200 ma from monazite inclusions in garnet metamorphic ages overlap with u pb zircon ages from local granite bodies and are interpreted to be the result of regional arc magmatism created by subduction of the paleo tethys ocean the northern portion of the footwall of the extensional system exposes an upper amphibolite facies unit 650 c 8 kbar which structurally overlies a lowgrade metagraywacke unit the high grade unit records late early cretaceous crustal thickening at ca 125 110 ma followed by emplacement over the low grade metagraywacke along a north northeast directed thrust prior to ca 100 ma together these results indicate signifi cant middle cretaceous crustal thickening and shortening in the northern pamir prior to the indo asian collision a third late miocene ca 9 ma amphibolite facies metamorphic event 650 700 c 8 kbar is recorded in footwall gneisses of the kongur shan massif north of the kongur shan massif rapid cooling in the footwall beginning at 7 8 ma is interpreted to date the initiation of exhumation along the kongur shan normal fault a minimum of 34 km of east west extension is inferred along the kongur shan massif based on the magnitude of exhumation since the late miocene 29 km and the present dip of the kongur shan normal fault 40 field observations and interpretation of satellite images along the southernmost segment of the kongur shan extensional system indicate that the magnitude of late cenozoic east west extension decreases signifi cantly toward the south this observation is inconsistent with models in which east west extension in the pamir is driven by northward propagation of the right slip karakoram fault suggesting instead that extension is driven by vertical extrusion due to topographic collapse radial thrusting along the main pamir thrust or oroclinal bending of the entire pamir region

a note on alongshore sediment transport on weakly curvilinear coasts and its implications abstract this paper presents a simple approximation for assessment of the alongshore sediment transport rate on dissipative weakly curvilinear coasts the approximation considers spatial variations in the wave angle and energy sediment size beach slope and type of wave breaking inside the surf zone similar approaches were employed in the past for coasts forced by high oblique waves where shoreline undulations frequently develop with our approach we can analyze more realistic situations i e alongshore relations between the sediment size and the beach slope the general expression for alongshore sediment transport is made explicit using a simple model for wave propagation the solution is used to examine the implications of the behavior of alongshore sediment transport on shoreline evolution after the analysis of the effects of variations in the wave conditions the alongshore beach slope distribution and the shoreline geometry three different shoreline tendencies were obtained for undulating shorelines migration for changes in deep water wave angle amplitude growth for increases in wave height or period and changes in shoreline geometry and wavelength changes and asymmetries for coasts with alongshore changes in beach slope our results also indicate that wave setup may enhance the formation of undulating shoreline features

modeling the evolution of continental subduction processes in the pamir hindu kush region several geological and geophysical studies suggest the presence of two converging subduction zones in the western syntaxis of the india eurasia collision zone with steep northward subduction of indian lithosphere beneath the hindu kush and southward subduction of asian lithosphere under the pamir we investigate the geometry and the timing of these subduction processes seismic tomography images are used to constrain the geometry of the two slabs under the pamir and the hindu kush by measuring the tomographically inferred length of the indian slab under the hindu kush region and by comparison with paleomagnetic reconstructions we estimate that the process of indian slab break off most likely occurred at the early stage of the collision at ca 44 48 ma we infer that after slab break off western india continued its northward motion until its northern boundary reached the present hindu kush region where it began to subduct we estimate an age for the initiation of subduction in this region of about 8 ma we apply 2d thermo kinematic and rheological numerical modeling to compute the temperature distribution and brittle field along two vertical sections across the hindu kush and pamir regions for the hindu kush we introduce parameters reproducing fast and near vertical subduction whereas in the pamir region we use the results from published studies to reproduce slower subduction modeling results indicate that faster subduction under the hindu kush results in a deeper brittle region which is consistent with observed deeper seismicity than in the pamir region

wave setup and setdown generated by obliquely incident waves an analytical theory is developed for the wave setup and setdown induced by obliquely incident waves on an impermeable swell built beach profile the wave setup and setdown are found to decrease as wave obliquity increases the incorporation of wave obliquity in wave setup and setdown formulation offers the physical reality in engineering applications the general solutions presented in this paper yield the limiting case of normal wave incidence and the result is consistent with the classical theories published the present theory is primarily applicable to the spilling and plunging breaker across the surf zone within which wave amplitude is assumed to be linearly related to the local water depth experiments were conducted in a large scale wave basin to compare with theoretical results and especially to investigate the applicability of this assumption to the case of obliquely incident waves the dimensionless setup versus the distance offshore within the surf zone is found to depend on wave breaking angle and the shape of the beach profile and it has a non zero value at the original shoreline position this implies that the original shoreline will advance landwards and that the extent of this movement can be related to wave angle at breaking and the beach profile under consideration the results of the present theory are in good agreement with experimental data and field measurements available

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

the role of footwall deformation and denudation in controlling cooling age patterns of detachment systems an application to the kongur shan extensional system in the eastern pamir china abstract determining the relationship between deformation and exhumation history in the footwall rocks of major low angle normal faults i e detachment faults provides a way to quantify different models of continental extension although pressure temperature time p t t datasets are commonly used to infer magnitude and rates of slip across detachment faults correct use of these datasets requires a sound understanding of coupling effects between footwall deformation and advection of isotherms on the distribution of cooling ages in this study we present thermo kinematic modeling results which examine the relationship between different footwall kinematic models erosion and the spatial distribution of muscovite and biotite 40 ar 39 ar cooling ages our results show that large magnitudes of footwall erosion during normal faulting significantly affect cooling age patterns as footwall rocks at different distances from the fault surface pass through different thermal gradients we apply our modeling results to simulating muscovite and biotite cooling age patterns from the footwall of the cenozoic kongur shan normal fault system in the pamir previous studies had interpreted a documented 5 fold increase in cooling rate at 2 ma to indicate an increase in exhumation rate during the quaternary however our results show that the observed cooling age patterns and increase in cooling rate can be produced by a constant exhumation rate over the last 7 ma due to the effect of changes in the rate of isotherm advection during exhumation

cenozoic thermo tectonic evolution of the northeastern pamir revealed by zircon and apatite fission track thermochronology abstract the northeastern pamir is a key location to explore asian intracontinental tectonic processes during the cenozoic new zircon fission track zft data show a 20 to 50 km wide region of partially reset ages on the northeastern margin of the pamir salient interpreted as an exhumed and tilted partial annealing zone paz widespread zft age peaks at 50 ma within the zft paz likely date early motion of the kashgar yecheng transfer system kyts but suggest this fault system was narrower in the early cenozoic than it is today apatite fission track aft ages of 10 6 ma combined with field observations across the kyts hint at an episode of strong thrusting related exhumational cooling which indicates that the modern fault system probably formed at this time to the southwest of the kyts the combination of new fission track and existing thermochronology data allows establishing temperature time trajectories that present diachronous rapid cooling from 450 to 120 c in the sares 13 10 ma muztagata 10 7 ma and kongur shan 3 1 ma domes rapid cooling in the eastern sares and southern muztagata massifs is driven by doming as supported by kinematic analyses of the shen ti fault successive rapid cooling of these massifs confirms eastward propagation of doming processes shortly postdating magma emplacement at 11 ma we propose that the synchronicity of regional tectonism magmatism and metamorphism implies that strong crustal thickening and contraction occurred beneath the northeastern pamir during the middle late miocene possibly associated with initial collision between the pamir and tian shan

late cenozoic extension and crustal doming in the india eurasia collision zone new thermochronologic constraints from the ne chinese pamir 1 the northward motion of the pamir indenter with respect to eurasia has resulted in coeval thrusting strike slip faulting and normal faulting the eastern pamir is currently deformed by east west oriented extension accompanied by uplift and exhumation of the kongur shan 7719 m and muztagh ata 7546 m gneiss domes both domes are an integral part of the footwall of the kongur shan extensional fault system kes a 250 km long north south oriented graben why active normal faulting within the pamir is primarily localized along the kes and not distributed more widely throughout the orogen has remained unclear in addition relatively little is known about how deformation has evolved throughout the cenozoic despite refined estimates on present day crustal deformation rates and microseismicity which indicate where crustal deformation is presently being accommodated to better constrain the spatiotemporal evolution of faulting along the kes we present 39 new apatite fission track zircon u th sm he and 40ar 39ar cooling ages from a series of footwall transects along the kes graben shoulder combining these data with present day topographic relief 1 d thermokinematic and exhumational modeling documents successive stages rather than synchronous deformation and gneiss dome exhumation while the exhumation of the kongur shan commenced during the late miocene extensional processes in the muztagh ata massif began earlier and have slowed down since the late miocene we present a new model of synorogenic extension suggesting that thermal and density effects associated with a lithospheric tear fault along the eastern margin of the subducting alai slab localize extensional upper plate deformation along the kes and decouple crustal motion between the central western pamir and eastern pamir tarim basin

a zero damage model for fission track annealing in zircon a zircon fission track annealing model is calculated on the basis of annealing experiments from the literature with induced tracks in decay event damage free zircon samples empirically derived parallel and fanning equations for this zero damage model yield an excellent fit to the data with the fanning model providing slightly better statistical parameters a comparison between annealing models with fanning iso annealing lines but different decay event damage densities reveals that annealing temperatures and closure temperatures for the estimated partial annealing zone are highest for the zero damage model compilations of existing geologic constraints on the zircon partial annealing zone on one hand and the zircon closure temperature on the other show that these constraints do not or only partly overlap with curves of proposed models for the zircon partial annealing zone and closure temperature this finding is consistent with the fact that the annealing behavior of zircon from long duration temperature evolutions is increasingly influenced by the accumulated decay event damage zircon samples of young age or low u content show a behavior closest to the predictions of the zero damage model and are in the predicted range of published models with low decay event damage density for thermal events of more than 10 myr duration however constraints from field studies show marked differences from proposed partial annealing zone boundaries of the zero or low damage models the applicability of the zero damage model is threefold 1 it predicts correct closure temperatures in the case of very rapid cooling across the partial annealing zone where basically no decay event damage is accumulated 2 it predicts an uppermost boundary for complete annealing of a mixture of zircon components of different age as found in sedimentary samples and in this case may be used as a thermometer 3 it represents an important reference for the establishment of a more comprehensive model of zircon fission track annealing that also includes the influence of decay event damage for such a model two different equations are discussed however additional detailed experimental and field data are needed for a more robust annealing model that includes the influence of decay event damage annealing

focused pliocene quaternary exhumation of the eastern pamir domes western china abstract the kongur shan and muztagata domes are the most prominent topographic features in the eastern pamir indenter corner in spite of several previous bedrock thermochronology studies the extent processes and mechanisms of dome exhumation remain unclear we present 1158 detrital zircon fission track dzft ages from modern glacier and river sediments along the domes to better constrain the spatial distribution of exhumation our thermochronologic dataset from the chakragil massif shows a sharp increase in the proportion of dzft ages 10 ma from basins that drain the peak region to those further to the north which suggests that the kalagile fault forms the northern boundary of the rapidly exhuming dome structure a cluster of middle miocene dzft ages in these samples documents pre doming cooling possibly associated with motion on the main pamir thrust and or oytag fault large fractions of dzft grain ages

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

postglacial slip rate increase on the teton normal fault northern basin and range province caused by melting of the yellowstone ice cap and deglaciation of the teton range along the eastern front of the teton range wyoming prominent fault scarps offset pinedale deposits by up to 30 m and document that multiple earthquakes ruptured the range bounding teton normal fault after the last glacial period paleoseismological data suggest that 70 of the postglacial slip on the southern teton fault accumulated during or shortly after deglaciation before 8 ka here we use a three dimensional fi nite element model to show that melting of the yellowstone ice cap and the valley glaciers in the teton range may have caused the postglacial slip rate increase on the teton fault during deglaciation slip on our model fault accelerates by a factor of 6 with respect to the long term rate our model further shows that the impact of the melting yellowstone ice cap on fault slip increases along strike of the fault from south to north and is everywhere larger than the effect of the former valley glaciers in the teton range the results demonstrate that postglacial slip on faults in glaciated regions may not have been uniform through time rather a signifi cant fraction of slip may have accumulated within a few thousand years after the last glaciation we hypothesize that the rebound caused by the yellowstone ice cap has also triggered clusters of earthquakes on other normal faults in the surrounding basin and range province

detrital zircon fission track ages for the hoh formation implications for late cenozoic evolution of the cascadia subduction wedge we report new fission track ft ages for detrital zircons for 34 sandstone samples and 2 volcanic ash beds from the hoh formation exposed along the western side of the olympic mountains of western washington state the hoh formation is now formally known as the coastal unit of the olympic structural complex or coastal osc for short about 35 zircons were dated per sample the fission track grain age ftga distributions are all strongly discordant grain ages range from 10 to older than 100 ma low vitrinite reflectance values short etch times for the zircons and a broad range of grain ages indicate that the zircon ft ages are unreset and thus preserve information about cooling events in the source region for these sedimentary rocks five areas were sampled repeatedly and yield similar ftga distributions demonstrating that sampling errors are not a problem we show that almost all of the samples contain a well defined young component that was probably derived from a contemporaneous active volcanic source presumably the adjacent cascadia arc binomial peak fitting was used to estimate the ft minimum age which is the age of the youngest concordant fraction of zircon ft grain ages in a ftga distribution in most cases minimum ages are similar to fossil ages where available this result supports our contention that zircon ft minimum ages from volcaniclastic sandstones commonly can be used as a proxy for depositional age our zircon ft minimum ages indicate that the coastal osc is made up mainly of lower miocene ca 24 to 16 ma sedimentary rocks we use these age data together with other geologic constraints to reconstruct a tectonic history sedimentary rocks of the coastal osc were derived from a mixed source region that included an active volcanic arc and also older units including cretaceous metamorphic rocks probably located in the omineca crystalline belt in the canadian rockies the upper part of the clallam formation located on the northern side of the olympic peninsula appears to be a remnant of the sedimentary system that fed the coastal osc the sediments that formed the coastal osc were initially deposited seaward of the cascadia trench at water depths of 2000 m this debris was deposited seaward of the cascadia trench at water depths of 2000 m and subsequently accreted beneath the frontal 50 to 100 km of the wedge owing to continued accretion at the front of the wedge and erosion of the forearc high in back of the wedge these lower miocene sediments were moved rearward within the cascadia subduction wedge a simple relationship based on the cross sectional area of the wedge and a steady accretion flux indicates that it would have taken 22 m y for the coastal osc to reach its present position 140 km landward of the toe of the wedge this estimate is in good agreement with the unit9s early miocene age

tectonic history of the altyn tagh fault system in northern tibet inferred from cenozoic sedimentation the active left slip altyn tagh fault defines the northern edge of the tibetan plateau to determine its deformation history we conducted integrated research on cenozoic stratigraphic sections in the southern part of the tarim basin fission track ages of detrital apatites existing biostratigraphic data and magnetostratigraphic analysis were used to establish chronostratigraphy whereas composition of sandstone and coarse clastic sedimentary rocks was used to determine the unroofing history of the source region much of the detrital grains in our measured sections can be correlated with uplifted sides of major thrusts or transpressional faults implying a temporal link between sedimentation and deformation the results of our studies together with existing stratigraphic data from the qaidam basin and the hexi corridor suggest that crustal thickening in northern tibet began prior to 46 ma for the western kunlun shan thrust belt at ca 49 ma for the qimen tagh and north qaidam thrust systems bounding the north and south margins of the qaidam basin and prior to ca 33 ma for the nan shan thrust belt these ages suggest that deformation front reached northern tibet only 10 5 m y after the initial collision of india with asia at 65 55 ma because the aforementioned thrust systems are either termination structures or branching faults of the altyn tagh left slip system the altyn tagh fault must have been active since ca 49 ma the altyn tagh range between the tarim basin and the altyn tagh fault has been a long lived topographic high since at least the early oligocene or possibly late eocene this range has shed sediments into both the tarim and qaidam basins while being offset by the altyn tagh fault its continuous motion has made the range act as a sliding door which eventually closed the outlets of westward flowing drainages in the qaidam basin this process has caused large amounts of oligocene miocene sediments to be trapped in the qaidam basin the estimated total slip of 470 70 km and the initiation age of 49 ma yield an average slip rate along the altyn tagh fault of 9 2 mm yr remarkably similar to the rates determined by gps global positioning system surveys this result implies that geologic deformation rates are steady state over millions of years during continental collision

erosional processes as a control on the structural evolution of an actively deforming fold and thrust belt an example from the pamir tien shan region central asia the foreland of the pamir mountains displays an unusual orogenic topography in which an active north vergent thin skinned fold and thrust belt shows no topographic foredeep in advance of the thrust sheets instead the thrusts are impinging on a topographic barrier formed by the southern edge of the tien shan the deformation front of this thrust belt is coincident with a deeply incised river valley occupied by a large river the surkhob we suggest that this river played a key role in the evolution of this orogenic system by acting as a lateral conveyor belt for the transport of mass delivered to the deformation front by thrusting on the basis of reconnaissance geologic mapping it is clear that the present system developed in the late miocene or pliocene when the tien shan were uplifted within an existing foreland basin as the tien shan highland developed a longitudinal river within the foreland basin was trapped between the north directed thrusts and the tien shan highland with continued deformation the river was squeezed into a narrow canyon and since that time the system has been in an unusual equilibrium where thrusting acts to push the deformation front northward toward the tien shan but fluvial erosion and transport act to keep it in a constant position geologic relationships indicate that the vakhsh thrust the frontal thrust of the north directed system is now emerging on an erosion surface beneath a thin quaternary cover throughout the canyon suggesting that the river has been unable to keep pace with the tectonic mass flux and the thrust front as well as the river have been pushed northward across the beveled edge of what was originally the southern edge of the tien shan we suggest that the original deformation front of the tien shan now lies 10 km south of the present day topographic front of the tien shan beneath the north vergent vakhsh thrust as indicated by 1 a near vertical zone of intense basement seismicity the petrovsky seismic zone 2 an en echelon array of backthrusts along the south flank of the peter the first range and 3 footwall cutoff relationships of the vakhsh thrust system order of magnitude mass balance considerations based on sediment budgets support this conclusion but suggest that the mass imbalance may be small thus large volumes of material may have passed through the thrust fron and been carried out of the system by erosion a relationship that may account for the narrow 30 50 km wide band of deformed sedimentary rock between the pamir salient and the tien shan the present near equilibrium is maintained by long term tectonic transport rates and fluvial transport rates the latter closely linked to climate particularly precipitation thus although there is apparently a mass pile up within this system other systems of this type might show grossly different structural and stratigraphic relationships depending on the amount of rainfall and corresponding variations in rates of fluvial sediment transport similar settings can be recognized in the active thick skinned thrust systems of the tien shan and ancient systems like the laramide belt of western north america

kongur shan normal fault type example of mountain building assisted by extension karakoram fault eastern pamir the northernmost segment of the karakoram fault is an active normal dextral wrench fault that bounds the muji tashgurgan pliocene quaternary basin eastern pamir the kongurshan 7719 m and mustaghata 7546 m mountains are interpreted as twin crustal ramp anticlines formed en echelon on the eastern side of the karakoram fault by subduction of the tarim lithosphere under the pamir west dipping s c mylonitic gneisses that have downdip stretching lineations form the western flank of kongur mountain kinematic criteria consistently indicate a top to the west sense of shear the mylonitic foliation is cut by a steeper active normal fault which is marked by prominent triangular facets on west facing spurs the ductile normal shearing deformation occurred during the interval 5 1 ma therefore like the himalayas the pamir mountain range shows the coeval development of frontal thrusting and rear normal faulting the kongur fault thus appears to be an excellent example of synorogenic extension where normal faulting contributes to relief

erosion and exhumation in the himalaya from cosmogenic isotope inventories of river sediments the outward erosional flux is a key factor in the tectonic evolution of mountain belts and there is much debate about the feedbacks between tectonics erosion and climate here we use cosmogenic nuclides 10be and 26al analysed in quartz from river sediments from the upper ganges catchment to make the first direct measurements of large scale erosion rates in a rapidly uplifting mountain belt the erosion rates are highest in the high himalaya at 2 7 0 3 mm yr 1 errors fall to 1 2 0 1 mm yr on the southern edge of the tibetan plateau and are 0 8 0 3 to 0 6 mm yr in the foothills to the south of the high mountains these relative estimates are corroborated by the nd isotopic mass balance of the river sediment analysis of sediment from an abandoned terrace suggests that similar erosion rates have been maintained for at least the last few thousand years the data presented here along with data recently published for european river catchments demonstrate that a log linear relationship between relief and erosion rate holds over three orders of magnitude variation in erosion rate and between very different climatic and tectonic regimes the erosion rate estimates from cosmogenic nuclides correlate well with exhumation rates calculated from previously published apatite fission track ages in the indian himalaya this confirms that much of the exhumation in the himalayan mountain chain is now balanced by erosion however exhumation rates calculated from high blocking temperature systems such as 40ar 39ar in muscovite imply lower exhumation rates rocks presently at the surface must have undergone a three to six fold increase in exhumation rate within the last few million years we show how this could be explained either by climatic forcing of erosion rate changes or by tectonics published evidence for equally rapid changes of exhumation rate in the past and the probable diachroneity in the time at which the present exhumation rates accelerated imply that tectonics has moderated at least some of the change in exhumation rates

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

downstream changes of alpine zircon fission track ages in the rhone and rhine rivers zircons from 13 sediment samples from the rhone and rhine drainages were dated by the fission track method to study downstream changes in detrital fissiontrack grain age distributions in large river systems draining the european alps the orogen parallel rhone river shows a zircon fission track grain age distribution similar to that in its alpine source areas this signal is well preserved because there are alpine sources along its full length and input from non alpine sources is small in contrast only the headwaters of the north flowing rhine river are located in the alps as a consequence alpine derived zircons which are distinguished by young fission track ages become progressively diluted downstream by older ages from zircon sources external to the alps nevertheless the alpine component is persistent and can easily be detected in sediments more than 1000 km downstream at the rhine delta these results demonstrate that fission track dating of detrital zircons can provide useful information about orogenic processes even where sediments have been transported hundreds of kilometers from the orogenic source crossing ephemeral lakes and subsiding basins deposits along the lower reaches of the river appear to have a short residence time 1 myr and thus many of these deposits serve to smooth out variations in the supply of sediment from fast eroding heterogeneous sources in the alpine headwaters of these drainages for the rhone and the rhine rivers we show that fast erosion in the alps accounts for most of the sediment load this finding supports a widespread observation that the sediment in most large continental drainages is usually derived from a small part of the drainage where uplift relief and erosion rates are greatest

high cooling and denudation rates at kongur shan eastern pamir xinjiang china revealed by 40ar 39ar alkali feldspar thermochronology orthogneiss samples taken from the kongur antiform show ages varying from 2 ma to 1 ma for 40ar 39ar ages of biotites and muscovites and fission tracks on apatites leading to cooling rates of 150 c m y modeling of k feldspars highlights the effect of a range of diffusion domains with contrasting diffusion characteristics yielding closure temperatures from 400 to 150 c the feldspar data document the cooling history since 5 ma and indicate a sudden change in cooling rates of the antiform at 2 ma at that time cooling increases by a factor of 5 from an average of 20 c m y to a minimum of 150 c m y consideration of the regional thermal history ongoing uplift and erosional history of the antiform during the quaternary suggests that denudation rates have been of the order of 5 7 km m y since 2 m y ago and could be associated with significant upward surface movement triggered by major normal faulting the antiform is interpreted to have formed during thrusting at the pamir front as a result of the development of thrust ramps and normal faulting at the crustal scale ramp stacking is an important process of mountain building and normal faulting in this context must be regarded as a very efficient way of building high relief

slip rate variations on normal faults during glacial interglacial changes in surface loads geologic and palaeoseismological data document a marked increase in the slip rates of the wasatch fault and three adjacent normal faults in the basin and range province during the late pleistocene early holocene epochs the cause of this synchronous acceleration of fault slip and the subsequent clustering of earthquakes during the holocene has remained enigmatic although it has been suggested that the coincidence between the acceleration of slip and the shrinkage of lake bonneville after the last glacial maximum may indicate a causal relationship here we use finite element models of a discrete normal fault within a rheologically layered lithosphere to evaluate the relative importance of two competing processes that affect fault slip postglacial unloading the removal of mass which decreases the slip rate and lithospheric rebound which promotes faster slip we show that lithospheric rebound caused by regression of lake bonneville and deglaciation of adjacent mountain ranges provides a feasible mechanism for the high holocene rates of faulting in the wasatch region our analysis implies that climate controlled changes in loads applied to earth s surface may exert a fundamental control on the slip history of individual normal faults

using tracer thermochronology to measure modern relief change in the sierra nevada california abstract we examine relief change in two major sierra nevada drainages the kings and the san joaquin the modern distribution of bedrock cooling ages is derived by fitting isochrones to a dense distribution of existing cooling ages this analysis indicates southwest tilting of the range by 3 4 0 8 which is consistent with other geologic evidence for tilting after 5 ma the detrital cooling ages from the kings show an excess of young ages relative to what would be expected from uniform erosion whereas the san joaquin drainage shows excess old ages these results indicate increasing relief in the kings the results in the san joaquin are more difficult to interpret due to the dense network of dams which trap sediment however we analyze the effect of storage behind the dams and suggest steady or declining relief in the san joaquin the residence time of sediment in these drainages indicates that these relief estimates are averaged over the last 100 to 10 ka we suggest that relief change is related to localized surface uplift in the southern sierra nevada including the kings drainage caused by ongoing lower lithosphere removal the san joaquin drainage may be north of the lithospheric anomaly which is consistent with stagnating or decaying relief there

paleo erosion rates in central asia since 9 ma a transient increase at the onset of quaternary glaciations erosion is a fundamental player of the interactions existing between internal geodynamics and climate in particular through its influence on the carbon dioxide budget however long term 1 ma erosion rates estimated indirectly from sediment budget remain poorly constrained while some studies suggest that worldwide erosion rates increased at the plio pleistocene climatic transition 4 2 ma the validity of this observation and its significance is a matter of debate due to potential biases of the sedimentary record and to the influence of sea level fall on the global sedimentary flux to marginal basins in the present study we estimate erosion rates over the last 9 ma using in situ produced cosmogenic 10be concentrations measured in magnetostratigraphically dated continental sediments we focus on an intracontinental endorheic watershed draining the northern tianshan in central asia a key region regarding the ongoing debate while erosion rates between 0 1 and 1 mm yr 1 are derived from most of our record they reach values as high as 2 5 mm yr 1 from 2 5 to 1 7 ma then after 1 7 ma recent and modern erosion rates fell below 1 mm yr 1 this temporary increase is correlated with the onset of quaternary ice ages and suggests that global climate had a significant and transient impact on erosion

a note on wave induced set up by obliquely incident waves abstract water level variations due to obliquely incident shoaling and breaking waves on a plane sloping beach were discussed recently by hsu et al coastal engineering 53 865 877 2006 an inconsistency in this work with respect to the set down and its implications to circulation offshore of the breakpoint was pointed out by shi and kirby coastal engineering 55 1246 1249 2008 here we extend that discussion to include the surfzone momentum balance and wave induced set up we discuss some remaining inconsistencies in the approximation of the surfzone momentum balance derive and present a consistent approximation and validate the new approximation through numerical comparison to a more exact model

cenozoic evolution of the pamir plateau based on stratigraphy zircon provenance and stable isotopes of foreland basin sediments at oytag wuyitake in the tarim basin west china abstract the pamir salient is the western expression of mountain growth related to indo eurasian convergence though a rough framework has emerged describing the tectonic evolution of the pamir detailed knowledge of the spatial and temporal evolution of cenozoic deformation is necessary to determine how strain progressed through the orogenic belt here we present new stratigraphic zircon provenance and stable isotope data from jurassic to miocene strata along the pamir s northeastern margin near the town of oytag wuyitake in the tarim basin west china prominent 40 ma peaks in oligocene to early miocene detrital zircon grains record the erosion of an eocene belt of shoshonitic rocks in the central to southeastern pamir this is roughly coincident with an 4 shift in the oxygen isotopic composition 18o of carbonates during the eocene and or oligocene from an average of 8 7 to 12 6 suggesting a reorganization of atmospheric circulation during that time this could have been caused by uplift of tarim basin bounding ranges and or retreat of the paratethys sea a subsequent change from eocene to jurassic aged detrital zircon grains in the early to middle miocene indicates provenance shifted from source rocks in the central and or se pamir to the hanging wall of the main pamir thrust mpt coincident with prograding facies at that time this suggests deformation progressed outward toward the northeast margin of the pamir plateau in the early to middle miocene our results corroborate outward advancement of himalayan deformation affecting all margins of the tarim basin by the middle miocene

influence of a glacial buzzsaw on the height and morphology of the cascade range in central washington state usa abstract analysis of climatic and topographic evidence from the cascade range of washington state indicates that glacial erosion limits the height and controls the morphology of this range glacial erosion linked to long term spatial gradients in the ela created a tilted planar zone of 373 cirques across the central part of the range peaks and ridges now rise 600 m above this zone hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply and mean slopes 30 indicate that the areas above the cirques may be at or near threshold steepness the mean plus 1 relief of individual cirque basins 570 m corresponds to the 600 m envelope above which peaks rarely rise the summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ela and enhanced hillslope processes due to the creation of steep topography on the high precipitation western flank of the cascades the dominance of glacial and hillslope erosion at altitudes at and above the ela may explain the lack of a correspondence between stream power erosion models and measured exhumation rates from apatite u th he thermochronometry

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

apatite u th he signal of large magnitude accelerated glacial erosion southwest british columbia alpine glaciers are efficient agents of erosion and capable of significantly modifying topography despite recent advances in theoretical and field studies that quantify glacial erosion processes few studies have documented glacial erosion rates over long 10 6 yr or large more than tens of kilometers scales we use apatite u th he ahe and apatite fission track aft cooling ages to address the late miocene to holocene erosion history across two 60 km long transects of the heavily glaciated southern coast mountains british columbia observed ahe cooling ages from equal elevation samples range between 1 5 and 8 ma and suggest that thick alpine glaciers resulted in a 16 km shift of the highest point in the topography in the past 1 5 4 0 m y we evaluated temporal and spatial variations in erosion rates using a three dimensional thermal kinematic model that predicted ahe and aft ages at the surface for different erosion histories comparison of model predicted and observed cooling ages suggests an increase in erosion rates of as much as 300 over the past 1 5 7 m y coincident with the onset of glaciation of this range

the initiation of northern hemisphere glaciation for well over a century scientists have speculated that variations in the atmospheric concentration of radiatively important trace gases such as carbon dioxide could control the earth s climate e g arrhenius 1 896 recent observations of significant glacial interglacial variation in atmo spheric co2 in ice cores put this idea on a firm observational as well as theoretical footing e g barnola et ai1 987 in this century as atmospheric co2 levels creep steadily upwards in response to the burning of fossil fuels and forests the specter of manmade global climate change looms before us ipcc 1990 a possibility that has heightened interest in the natural variability of climate in the past in particular the 3 c warming pre dicted for the next century has stimulated interest in past warm climates such as the middle pliocene around 3 0 million years ma ago an interval that has often been invoked as a greenhouse world budyko et al 1985 in this paper the climate transition from the warm mid pliocene around 3 2 ma to the onset of northern hemisphere ice ages around 2 4 ma is examined evidence for the initiation of significant northern hemisphere glaciation is examined as well as how this event affected climate around the globe while the cause of individual glacial interglacial oscillations is tied to milankovitch variations in the earth s orbit around the sun e g imbrie et ai 1 992 these insolation changes cannot account for the long term cooling trend which culminated in northern hemisphere glaciation in the final section of this paper mechanisms of long term climate change

cenozoic depositional sequences in the piedmont of the west kunlun and their paleogeographic and tectonic implications abstract the west kunlun forms the northwestern margin of the qinghai tibet plateau well developed cenozoic depositional sequences in the piedmont along the margins of the tarim basin record changes in sedimentary environment and the uplift of the west kunlun during the cenozoic during latest cretaceous to oligocene deposition in the west kunlun occurred in a marine environment the tarim bay during the paleogene gypsum beds bivalve shell limestones and variegated clastics were deposited rapid sedimentation during the late miocene resulted in the deposition of molasse sediments 2000 3000 m thick indicating a relatively high depositional rate the upper miocene sequences show a coarsening up tendency indicating a rapid and accelerated uplift of the west kunlun from late miocene to early pleistocene times molasse deposition was interrupted in the early pleistocene by a tectonic pulse which resulted in tilting of the molasse and underlying sediments at high angle towards the tarim basin undeformed middle to late pleistocene coarse fluvial and pluvial deposits overlie the steeply dipping molasse and older rocks unconformably and represent the resumption of rapid deposition a continual high rate of uplift during the holocene is presumed on the basis of an incised drainage system that flows from west kunlun into the tarim basin and cuts middle to late pleistocene gravels and older sediments to a depth from 50 m to more than 100 m although climatic changes may also have played a part

late miocene pliocene deceleration of dextral slip between pamir and tarim implications for pamir orogenesis abstract the timing of the late cenozoic collision between the pamir salient and the tien shan as well as changes in the relative motion between the pamir and tarim are poorly constrained the northern margin of the pamir salient indented northward by 300 km during the late cenozoic accommodated by south dipping intracontinental subduction along the main pamir thrust mpt coupled to strike slip faults on the eastern flank of the orogen and both strike slip and thrust faults on the western margin the kashgar yecheng transfer system kyts is the main dextral slip shear zone separating tarim from the eastern pamir with an estimated cumulative offset of 280 km at an average late cenozoic dextral slip rate of 11 15 mm a cowgill 2010 in order to better constrain the slip history of the kyts we collected thermochronologic samples along the eastward flowing deeply incised antecedent tashkorgan yarkand river which crosses the fault system on the eastern flank of the orogen we present 29 new biotite 40 ar 39 ar ages apatite and zircon u th sm he ages and apatite fission track aft analysis combined with published muscovite and biotite 40 ar 39 ar and aft data to create a unique thermochronologic dataset in this poorly studied and remote region we constrain the timing of four major n trending faults the latter three are strands of the kyts the westernmost the kuke fault experienced significant dip slip west side up displacement between 12 and 6 ma to the east within the kyts our new thermochronologic data and geomorphic observations suggest that the kumtag and kusilaf dextral slip faults have been inactive since at least 3 5 ma long term incision rates across the aertashi dextral slip fault the easternmost strand of the kyts are compatible with slow horizontal slip rates of 1 7 5 3 mm a over the past 3 to 5 ma in summary these data show that the slip rate of the kyts decreased substantially during the late miocene or pliocene furthermore miocene present regional kinematic reconstructions suggest that this deceleration reflects the substantial increase of northward motion of tarim rather than a significant decrease of the northward velocity of the pamir

a field based estimate of the zircon fission track closure temperature abstract a field based estimate of the zircon fission track closure temperature is proposed from 13 zircon fission track cooling ages of the gold butte block se nevada using previously published and new thermochronological data the thermal history of the gold butte block is re evaluated resulting in a geothermal gradient estimate of 20 3 c km and a slow cooling rate of 0 55 0 02 c m y from the late jurassic to the early miocene before onset of rapid miocene cooling the rapidly cooled part of the gold butte block provides a slip rate of 10 5 km m y of the hanging wall that caused the miocene exhumation of this crustal section assuming these thermal conditions are correct the closure temperature of the zircon fission track system is determined at 205 18 c which is in good agreement with previous field based estimates because of the variation in zircon fission track annealing behavior with radiation damage field studies are a suitable way to calibrate the closure temperature of the zircon fission track system

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

quaternary glaciation of muztag ata and kongur shan evidence for glacier response to rapid climate changes throughout the late glacial and holocene in westernmost tibet the glacial geology of two massifs muztag ata and kongur shan in western tibet was examined to help define the timing and style of glaciation in the semiarid regions of western tibet remote sensing geomorphic mapping and 10be terrestrial cosmogenic nuclide tcn surface exposure dating of boulders on the moraines and sediment in depth profiles show that glaciers advanced at least 12 times during at least the last two glacial cycles over this time the style of glaciation changed progressively from one that produced ice caps to one that produced less extensive and more deeply entrenched valley glaciers the timing of the two earliest glaciations is poorly defined but they likely occurred prior to the penultimate glacial cycle the karasu glacial stage and the early part of the last glacial cycle or during the penultimate glacial cycle the subaxh glacial stage in contrast the timing of later glacial advances the olimde glacial stage is relatively well defined showing quasiperiodical oscillations on millennial time scales 17 1 0 3 ka 13 7 0 5 ka 11 2 0 1 ka 10 2 0 3 ka 8 4 0 4 ka 6 7 0 2 ka 4 2 0 3 ka 3 3 0 6 ka 1 4 0 1 ka and a few hundred years before the present these data suggest that since the global last glacial maximum lgm the glaciers in western tibet likely responded to northern hemisphere climate oscillations rapid climate changes with minor influences from the south asian monsoon this study provides the first well defined glacial geologic evidence to suggest that glaciers in western tibet respond to rapid climate changes on millennial time scales throughout the late glacial and holocene

quaternary deformation in the eastern pamirs tadzhikistan and kyrgyzstan active deformation in the eastern pamir of central asia is concentrated on the margins of the orogen with minor deformation within the high terrain along the trans alai mountain front at the northern perimeter of the orogen quaternary thrusting is documented by uplifted pediments now at 500 m above the piedmont holocene fault scarps and large earthquakes with n to nw oriented p axes seismicity in the interior of the orogen outlines a n s belt that includes normal faulting events with e w oriented t axes n s striking active normal faults in the interior lake karakul region are compatible with these earthquakes they define an asymmetric graben with a master fault at the western basin margin in the southern pamirs dextral strike slip faults root in the dextral karakorum fault which bounds the pamirs to the east a mixture of dextral and reverse offsets totalling 135 m in pleistocene terraces and 8 m in late pleistocene holocene deposits demonstrates contemporary transpression indicating average displacement rates of 1 mm yr the concentration of young thrusts along the trans alai the northward migration of thrusting and the scarcity of other large scale shortening features within the eastern pamirs suggest that this part of the orogen moves northward en bloc and causes the progressive annihilation of the intermontane alai valley widespread dextral shear in the eastern pamirs both to the south and north of the extensional karakul depression and combined dextral strike slip and normal faulting in the muji tashgorgan graben of the chinese pamirs are interpreted as localized space accommodation phenomena formed during progressive transfer of compressional deformation along a dextral strike slip deformation zone with extensional stepovers

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

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

geomorphology of anomalously high glaciated mountains at the northwestern end of tibet muztag ata and kongur shan article i nfo muztag ata and kongur shan massifs represent a significant area of anomalously high topography at the northwestern end of the tibetan plateau rising to n7500 m above sea level asl from the plateau that has an average elevation of 3500 m asl these massifs provide an excellent opportunity to test geomorphic concepts such as the glacial buzz saw model using remote sensing digital elevation modeling field mapping and terrestrial cosmogenic nuclide tcn methods the massifs were examined to determine the relative importance of tectonics and geomorphic processes in shaping the regional landscape and to provide a framework for testing geomorphic models the gneiss domes that underlie the peaks are the result of exhumation along the kongur detachment fault that has unroofed the massifs at a rate of between 4 6 km ma over the last few million years this has resulted in rapid uplift and active seismicity which is exemplified by the numerous fresh fault scarps throughout the region and large historic earthquakes the geomorphic system is dominated by glaciation and the region contains extensive successions of moraines and paraglacial landforms including fans terraces and landslides glaciers have oscillated considerably throughout the latter part of the quaternary and three major glacier stages are recognized karasu oldest olimde and subaxh youngest glacial stage that include at least 10 smaller glacial advance the style of glaciation has changed over time from expanded ice caps to piedmont glaciers to valley and cirque glaciers this possibly reflects a change in climate and or topographic constraints as the massifs grew and became incised the topography and glaciers in the region vary across the massifs divided by a broadly n s trending high ridge and watershed the western portion situated upwind the stoss slopes of the mid latitude westerlies that bring moisture to the region has gentle high topography and small valley glaciers in contrast on the eastern leeward slopes gradients are higher and long debris covered valley glaciers are present the hypsometry of the region indicate two peaks in the distribution frequency of elevation 3600 4100 m and 4400 4800 m asl these two elevation zones are consistent in space with the former equilibrium line altitudes during the olimde and subaxh glacial stages and suggest that glacial erosion most effective at the ela has helped control topography this observation supports the glacial buzz saw hypothesis which argues that glaciers determine hypsometry by means of rapid surface erosion based on tcn methods basin wide rates of erosion range from 0 1 to 1 4 km ma and are five to ten times lower than the unroofing rate of both massifs the discrepancy over different time scales suggests that initial unroofing was produced by abrupt tectonic uplift and that the unroofing of the massifs has continued at a slower pace during the late quaternary