strain heating as a mechanism for partial melting and ultrahigh temperature metamorphism in convergent orogens implications of temperature dependent thermal diffusivity and rheology 1 we explore the importance of strain heating in ductile shear zones for production of leucogranites and high temperature metamorphism in collisional orogens with temperature dependent thermal diffusivity d and rock rheology new measurements on metamorphic rocks from the bohemian massif show that d is 1 3 mm2 s at 25 c and decreases exponentially to as low as 0 4 mm2 s at 600 c this temperature dependence causes model lithospheric geotherms to be straighter compared to geotherms calculated with a constant d using power law parameters for rheology we show that deformation of quartzite at strain rate of 3 10 13 s 1 produces 100 w m3 at 550 c and 7 w m3 at 800 c deformation of stronger clinopyroxenite at this strain rate produces 8 w m3 even at 1050 c when strain heating is introduced by a 3 km thick ductile shear zone with quartz rheology at the depth of 35 km in a lithosphere that has 70 km thick crust and 60 km thick lithospheric mantle the schist solidus is reached by 8 myr in the vicinity of the shear zone deforming at the strain rate of 3 10 13 s 1 for clinopyroxenite rheology ultrahigh temperature uht metamorphic conditions are reached in 40 myr after initiation of strain heating two dimensional models that replicate the exhumation of the greater himalaya crystalline rocks above the main central thrust produce extensive partial melting and an inverted metamorphic field gradient occurrences of leucogranites within crustal shear zone systems may be evidence of the coupling between deformation and heat production in the crust

increased late pleistocene erosion rates during fluvial aggradation in the garhwal himalaya northern india the response of surface processes to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution in the himalaya most large rivers feature prominent fill terraces that record an imbalance between sediment supply and transport capacity presumably due to past fluctuations in monsoon precipitation and or effects of glaciation at high elevation here we present volume estimates chronological constraints and 10 be derived paleo erosion rates from a prominent valley fill in the yamuna catchment garhwal himalaya to elucidate the coupled response of rivers and hillslopes to pleistocene climate change although precise age control is complicated due to methodological problems the new data support formation of the valley fill during the late pleistocene and its incision during the holocene we interpret this timing to indicate that changes in discharge and river transport capacity were major controls compared to the present day late pleistocene hillslope erosion rates were higher by a factor of 2 4 but appear to have decreased during valley aggradation the higher late pleistocene erosion rates are largely unrelated to glacial erosion and could be explained by enhanced sediment production on steep hillslopes due to increased periglacial activity that declined as temperatures increased alternatively erosion rates that decrease during valley aggradation are also consistent with reduced landsliding from threshold hillslopes as a result of rising base levels in that case the similarity of paleo erosion rates near the end of the aggradation period with modern erosion rates might imply that channels and hillslopes are not yet fully coupled everywhere and that present day hillslope erosion rates may underrepresent long term incision rates

the thermal structure of collisional orogens as a response to accretion erosion and radiogenic heating thermal models of collisional orogens generally predict temperature structures that are much cooler than those recovered by thermobarometric studies here we demonstrate that high temperature low pressure metamorphism and the development of inverted geotherms within collisional belts may be the result of accretion and erosion acting on crust enriched with heat producing elements a new two dimensional finite difference model described here incorporates the subduction of lithosphere with heat producing material in the upper crust accretion of crustal material from the subducting plate to the upper plate and surface erosion of the upper plate these processes result in the development of a wedge of heat producing material within the upper plate the rate of heat production within the wedge and maximum depth of the wedge are the most important parameters controlling the magnitude of upper plate temperatures our model yields inverted upper plate geotherms when heat production rates exceed 0 75 w m3 and the heat producing wedge extends to a depth greater than 35 km temperatures in excess of 500 c at depths of 20 30 km are computed when heat production rates are greater than 1 75 w m3 and the wedge extends to a depth 50 km other processes such as shear heating fluid flow or mantle delamination need not be invoked to explain geologic evidence of high temperatures or inverted thermal gradients in collisional systems

hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 2 intercomparison with a three dimensional richards equation model 1 the boussinesq equation for subsurface flow in an idealized sloping aquifer of unit width has recently been extended to hillslopes of arbitrary geometry by incorporating the hillslope width function w x into the governing equation where x is the flow distance along the length of the hillslope troch et al 2003 introduction of a source sink term n allows simulation of storm interstorm sequences in addition to drainage processes while a function sc x representing the maximum subsurface water storage can be used to account for surface saturation response in variable source areas activated by the saturation excess mechanism of runoff generation the model can thus simulate subsurface flow and storage dynamics for nonidealized more realistic hillslope configurations in this paper we assess the behavior of this relatively simple one dimensional model in a series of intercomparison tests with a fully three dimensional richards equation model special attention is given to the discretization and setup of the boundary and initial conditions for seven representative hillslopes of uniform convergent and divergent plan shape drainage and recharge experiments are conducted on these hillslopes for both gentle 5 and steep 30 bedrock slope angles the treatment and influence of the drainable porosity parameter are also considered and for the uniform idealized hillslope case the impact of the unsaturated zone is examined by running simulations for different capillary fringe heights in general terms the intercomparison results show that the hillslope storage boussinesq model is able to capture the broad shapes of the storage and outflow profiles for all of the hillslope configurations in specific terms agreement with the richards equation results varies according to the scenario being simulated the best matches in outflow hydrographs were obtained for the drainage experiments suggesting a greater influence of the unsaturated zone under recharge conditions due to transmission of water throughout the hillslope in the spatiotemporal water table response a better match was observed for convergent than divergent hillslopes and the bedrock slope angle was not found to greatly influence the quality of the agreement between the two models on the basis of the intercomparison experiments we make some suggestions for further development and testing of the hillslope storage model

a late quaternary catastrophic flood in the lahul himalayas impressive flood deposits are described resulting from a catastrophic lake outburst in the upper chandra valley in the lahul himalaya northern india reconstructions of the former glacial lake glacial lake batal and the discharges were undertaken using landforms and sediment data the glacial dam burst released 1 496 km3 of water in 0 72 days with peak discharges of between 21 000 and 27000 m3 s at batal dating by osl suggests the flood occurred ca 36 9 if 8 4 to 43 4 2 10 3 ka ago this cataclysmic flood was responsible for major resedimentation and landscape modification within the chandra valley journal of quaternary suence

role of horizontal thermal conduction and finite time thrust emplacement in simulation of pressure temperature time paths abstract comparison of metamorphic thermal histories produced by 1 one vs two dimensional conductive models and 2 instantaneous vs finite emplacement time thrusting indicates that the simple 1d or instantaneous models applied by many petrologists generally produce pressure temperature pt paths with topologies similiar to those generated by 2d time transitive models however maximum temperatures attained by footwall rocks are significantly lower in 1d than in 2d conductive models leading us to recommend that 2d thermal effects be incorporated into models whenever possible pt paths produced by instantaneous and finite duration thrust emplacement differ significantly during the synthrusting period but the peak metamorphic conditions t max and pressure at t max eventually attained by footwall rocks during erosional unroofing are the same within minimum analytical uncertainties 50 k 100 mpa on geothermobarometric data thus if erosion begins only after the end of the thrusting event instantaneous thrusting is a reasonable simplifying assumption that introduces relatively little inaccuracy into pt models devised to examine peak metamorphic conditions

physics controlled thickness of shear zones caused by viscous heating implications for crustal shear localization we evaluate the parameters that control the thickness of ductile shear zones that are generated by viscous heating we employ two dimensional thermomechanical numerical models to simulate shear zone development under compression results show that the shear zone thickness is essentially independent on the numerical resolution and the initial size of a weak inclusion that triggers shear localization a simple scaling law is derived which predicts the thickness with six physical parameters far field stress and strain rate thermal conductivity both constant and temperature dependent initial temperature activation energy and stress exponent the scaling law is confirmed by numerical simulations for a wide range of parameters for crustal deformation conditions typical temperature increase ranges between 50 c and 200 c and the predicted thickness is between 1 km and 7 km these thicknesses agree with natural crustal and lithospheric shear zones suggesting that shear heating is a process controlling crustal shear zone formation

rheological stratification of the lithosphere abstract the rheology of the lithosphere is estimated on the basis of pore pressure dependent frictional failure in the brittle regime and power law steady state creep in the ductile regime different petrological models of the continental and oceanic lithosphere combined with different geotherms and thicknesses are used to generate models covering a variety of geodynamic situations results show that the depth dependence of lithospheric rheology varies with the tectonic province and that in many instances the continental lithosphere has one at the bottom of the crust or two the previous one plus another at mid crustal levels soft ductile layers sandwiched between brittle layers the depth distribution of geophysical parameters seismicity seismic wave velocity and electrical conductivity matches the theological predictions well the lithospheric rheological profiles are used to analyze observed variations in the structural style of deformed continental margin and oceanic terranes in the southeastern canadian cordillera the large scale characteristics of the system show a satisfactory agreement with the inferred rheological structure sub horizontal decollements should be the rule rather than the exception where the lithospheric rheology is strongly stratified

uplift and convergence along the himalayan frontal thrust of india along the himalayan thrust front in northwestern india terrace deposits exposed 20 to 30 m above modern stream level are interpreted to have been uplifted by displacement on the underlying himalayan frontal thrust a radiocarbon age limits the age of the terrace to 1665 215 calendar bc 3663 215 radiocarbon years before present yielding a vertical uplift rate of 6 9 1 8 mm yr in combination with published studies constraining the dip of the himalayan frontal thrust fault to about 30 in the study area the observed uplift rate equates to horizontal shortening across the himalayan frontal thrust of 11 9 3 1 mm yr and the slip rate of the himalayan frontal thrust of 13 8 3 6 mm yr this is similar to previously reported rate estimates along the himalayan arc based on displacement of older plio miocene age rocks or the much shorter records of geodesy and historical seismicity the similarity is consistent with the idea that convergence across the himalayan front has occurred at a relatively steady rate through time the seismic expression of this deformation includes several great m 8 historical earthquakes which due to lack of surface rupture during those events have been attributed to their occurrence on blind thrusts yet the occurrence of a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismic scarps these observations suggest a potential for earthquakes along the himalayan frontal thrust larger than those observed historically

infiltration on sloping terrain and its role on runoff generation and slope stability abstract a modified green and ampt model is formulated to quantify infiltration on sloping terrain underlain by homogeneous soil wetted by surficial water application this paper s theory for quantifying infiltration relies on the mathematical statement of the coupled partial differential equations pdes governing infiltration and runoff these pdes are solved by employing an explicit finite difference numerical method that yields the infiltration the infiltration rate the depth to the wetting front the rate of runoff and the depth of runoff everywhere on the slope during external wetting data inputs consist of a water application rate or the rainfall hyetograph of a storm of arbitrary duration soil hydraulic characteristics and antecedent moisture and the slope s hydraulic and geometric characteristics the presented theory predicts the effect an advancing wetting front has on slope stability with respect to translational sliding this paper s theory also develops the 1d pde governing suspended sediment transport and slope degradation caused by runoff influenced by infiltration three examples illustrate the application of the developed theory to calculate infiltration and runoff on a slope and their role on the stability of cohesive and cohesionless soils forming sloping terrain

on the meaning of peak temperature profiles in inverted metamorphic sequences inverted metamorphic sequences ims are common features of main thrust systems on earth they exhibit an upwards continuous increase in peak temperature conditions and thereby constitute evidence of the close relationship between the thermal field evolution and tectonic processes heat advection and shear heating are known to allow the formation of such metamorphic signatures heat diffusion also plays an important role in temperature distribution on both sides of the thrust other advection processes such as erosion or accretion may also cause a local peak temperature inversion each one of these processes therefore affects the thermal field around the thrust however despite the crucial importance of all these processes for the interpretation of the inverted peak temperature signatures their respective influences have never been quantified and compared all together to address this issue we propose an innovative coupled approach i we use two dimensional numerical models that simulate various thrust systems allowing for a wide diversity of setups to illustrate this study we focus on intracontinental thrust systems for which all processes listed are likely to play a key role in the thermal evolution we perform a parametric study including kinematic settings i e convergence erosion and accretion thermal properties mechanical strength and heat sources ii dimensionless numbers based on parameters are used to quantify the relative contributions of each process to the thermal budget evolution hence the three thermal processes i e heat diffusion heat advection and shear heating are compared with each other via three dimensionless combinations of the peclet and brinkman numbers rdif radv and rpro respectively erosion and accretion are compared separately based on a fourth dimensionless number rea iii we analytically examine the inverted peak temperature recorded along profiles that are perpendicular to the thrust zone defined in our numerical experiments each peak temperature profile presenting an inversion can then be characterized by a function of approximation involving six meaningful parameters the location ff and width ff of the maximum peak temperature inversion the characteristic peak temperature tcte and gradient glb beneath the inversion zone and the inversion related contrasts in the peak temperature t and gradient g this coupled approach linking numerical modelling and analytical treatment allows to quantitatively interpret ims in terms of the processes involved the application of our method to intracontinental thrust systems demonstrates that shear heating and erosion support significant inversions but that the relative contributions of each process have meaningful consequences our results reveal that competition between shear heating and heat diffusion on the one hand and between erosion and accretion on the other hand have a high impact in particular the variability in the rock s mechanical strength strongly influences the features of peak temperature inversions consequently none of these processes can be ignored our results highlight the major importance of the rheology of rocks in the thermal evolution of shear zones finally our methodology is not only restricted to the analysis of numerical data but also constitutes a way of broad interest to analyse peak temperature signatures around any shear zone

contrasting patterns of early twenty first century glacier mass change in the himalayas glaciers are among the best terrestrial climate indicators an important water resource in mountains1 2 and a major contributor to global sea level rise3 4 in the hindu kush karakoram himalaya region hkkh a paucity of appropriate glacier data has prevented a comprehensive assessment of current regional mass balance5 however there are indirect evidences of a complex pattern of glacial responses5 8 in reaction to heterogeneous climate change signals9 here we provide the first coherent data set of detailed glacier thickness changes over the hkkh during 2003 2009 by combining satellite laser altimetry and a global elevation model in the eastern central and south western parts of the hkkh glacier wastage is widespread with regional thinning rates up to 0 66 0 09 m a 1 in the jammu kashmir region conversely in the karakoram glaciers are close to balance with only a slight thinning of 0 07 0 04 m a 1 regionally averaged thinning rates under debris mantled ice are similar to those of clean ice despite insulation by debris covers the 2003 2008 specific mass balance for our hkkh study region is 0 21 0 05 m a 1 water equivalent we significantly less negative than the global average of 0 7 m a 1 we for glaciers and ice caps4 10 this difference is mainly an effect of the balanced glacier mass budget in the karakoram the corresponding hkkh sea level contribution is 0 035 0 009 mm a 1 amounting to 1 of the present day sea level rise11 our 2003 2008 mass budget of 12 8 3 5 gt a 1 is more negative than recent satellite gravimetry based estimates of 5 6 gt a 1 over 2003 2010 ref 12 for the mountain catchments of the indus and ganges basins13 the glacier imbalance contributes 3 5 and 2 0 respectively to the annual average river discharge13 and up to 10 for the upper indus basin14

no late quaternary strike slip motion along the northern karakoram fault abstract models that treat long term evolution of the tibetan orogen in terms of interactions between rigid blocks require the right slip karakoram fault that bounds the western margin of the tibetan plateau to be a long lived stable high slip rate feature while the southern portion of the fault clearly remains active recent work has proposed that the northern half of the karakoram fault is currently inactive new field observations and geochronologic results from the northern end of the karakoram fault system confirm this interpretation and provide the first quantitative data on the minimum age for the termination of slip in the southeast pamir gravel that yields a u series age of 198 5 ka on secondary carbonate caps a non deformed strath terrace that extends across the main strand of the karakoram fault the secondary achiehkopai fault strand is overlain by undisturbed hangdi glacial stage 24 6 ka deposits and dabudar glacial stage penultimate glacial cycle 150 ka or older deposits which lack observable lateral displacement or deformation together these observations show that the northern portion of the karakoram fault system has not accommodated any detectable strike slip deformation since at least 24 6 ka and most likely since 200 ka or more these results show that the karakoram fault system no longer forms a continuous discrete kinematic boundary at the western margin of the tibetan plateau this suggests that even long 500 km strike slip faults within orogenic belts are inherently unstable features consistent with models of continental collision zones involving relatively weak crust and distributed deformation

relationships between right lateral shear along the karakoram fault and metamorphism magmatism exhumation and uplift evidence from the k2 gasherbrum pangong ranges north pakistan and ladakh the karakoram fault is a major nw se aligned dextral strike slip fault that has accommodated minor extrusion of thickened tibetan crust since the mid miocene controversy exists as to whether the fault is lithospheric in scale resulting in synkinematic metamorphism and granite melting or whether it is an upper crustal fault cutting through earlier metamorphic and granitic rocks structural metamorphic and geochronological data from the karakoram fault show that 1 metamorphism and granite genesis occurred prior to strike slip shearing meaning that u pb zircon and monazite ages from deformed granites cannot be used as proxies for dating strike slip shearing only as a maximum age constraint on initiation of ductile shearing 2 sheared miocene leucogranites along the fault are equivalent to the baltoro granite batholith offset 40 150 km along the fault and show a strain gradient from high ductile strain to undeformed away from the fault 3 40 ar 39 ar and fission track ages of k2 orthogneisses and gasherbrum diorite show that rocks adjacent to the fault cooled during cretaceous to mid tertiary time and were not reset during shearing indicating that shear heating was not important 4 the gasherbrum diorite adjacent to the fault has never been at depths greater than 6 km since the early cretaceous and less than 3 km of material has been eroded off since then we conclude that the karakoram fault has had no significant influence on regional metamorphism or melting at least at levels exposed today and is restricted to the upper middle crust

exhumation and incision history of the lahul himalaya northern india based on u th he thermochronometry and terrestrial cosmogenic nuclide methods abstract low temperature apatite u th he ahe thermochronology on vertical transects of leucogranite stocks and 10 be terrestrial cosmogenic nuclide tcn surface exposure dating on strath terraces in the lahul himalaya provide a first approximation of long term 10 4 10 6 years exhumation rates for the high himalayan crystalline series hhcs for northern india the ahe ages show that exhumation of the hhcs in lahul from shallow crustal levels to the surface was 1 2 mm a and occurred during the past 2 5 ma bedrock exhumation in lahul fits into a regional pattern in the hhcs of low temperature thermochronometers yielding plio pleistocene ages surface exposure ages of strath terraces along the chandra river range from 3 5 to 0 2 ka two sites along the chandra river show a correlation between tcn age and height above the river level yielding maximum incision rates of 12 and 5 5 mm a comparison of our ahe and surface exposure ages from lahul with thermochronometry data from the fastest uplifting region at the western end of the himalaya the nanga parbat syntaxis illustrates that there are contrasting regions in the high himalaya where longer term 10 5 10 7 years erosion and exhumation of bedrock substantially differ even though holocene rates of fluvial incision are comparable these data imply that the orogen s indenting corners are regions where focused denudation has been stable since the mid pliocene however away from these localized areas where there is a potent coupling of tectonic and surface processes that produce rapid uplift and denudation plio pleistocene erosion and exhumation can be characterized by disequilibrium where longer term rates are relatively slower and shorter term fluvial erosion is highly variable over time and distance the surface exposure age data reflect differential incision along the length of the chandra river over millennial time frames illustrate the variances that are possible in himalayan river incision and highlight the complexity of himalayan environments

shear heating not a cause of inverted metamorphism an archetypal example of inverted metamorphism purportedly resulting from shear heating is found in the pelona schist of southern california united states recent studies demonstrate that the pelona schist was subducted and accreted at the onset of laramide fl at subduction under thermal and kinematic conditions not considered in earlier numerical models to test the shear heating hypothesis under these conditions we constructed a thermokinematic model of fl subduction initiation involving continuous accretion of the schist a neighborhood algorithm inversion demonstrates that available metamorphic and thermochronologic constraints in the sierra pelona mountains are satisfi ed only if accretion rates were 0 2 3 6 km m y and shear heating was minimal shear stress 0 19 mpa minimal shear heating is also consistent with an inversion of models constrained by thermochronology of the east fork of the san gabriel river exposure of the schist shear heating inhibits the formation of modeled inverted gradients during accretion and should not be considered an important factor in their generation

a dimensional analysis to quantify the thermal budget around lithospheric scale shear zones the thermal evolution around shear zones is controlled by three major thermal processes diffusion advection and shear heating we present a dimensional analysis to quantify to first order the relative contributions of these three processes to the thermal evolution around lithospheric scale shear zones we consider 11 parameters that control the kinematics the three dimensional 3 d geometry the initial thermal structure and the average strength of the shear zone three dimensionless parameters are presented to quantify the relative contributions of the three thermal processes we validate the dimensional analysis with 2 d thermo kinematic numerical models the applicability of the dimensional analysis to any kind of shear zone i e thrust normal slip and strike slip shear zones makes it a useful tool that is complementary to previous numerical and analytical studies finally thrust type shear zones are used to illustrate how the three thermal processes control the thermal evolution

a method for computing infiltration and redistribution in a discretized moisture content domain 1 a new one dimensional infiltration and redistribution method is proposed as an alternative to the richards equation re for coupled surface and subsurface models the proposed method discretizes soil water content into hypothetical hydraulically interacting bins the entry and propagation of displacement fronts in each bin are simulated by means of explicit infiltration and drainage approximations based on capillary and gravitational driving forces wetting front advances within bins create water deficits that are satisfied by capillary driven interbin flow the method inherently provides numerical stability by precluding the need to directly estimate nonlinear gradients through numerical schemes comparisons of the performance of this method against re solutions for theoretical laboratory and field data in both well drained and high water table conditions are presented the new method produces infiltration flux estimates with errors less than 10 compared to a widely used re solution in tests on multiple soil textures with and without high water table conditions while providing unconditionally guaranteed conservation of mass

thermal effects of thrust faulting abstract calculations based on simple models of overthrust sheets in crystalline basement rocks show that significant thermal effects may result from their movements if rates are sufficiently high e g plate tectonic rates the thrust sheets sufficiently thick 5 10 and 15 km are modelled here the distances moved sufficiently large and for reasonable values of the coefficient of friction along the thrust plane overthrusting can cause metamorphic mineral zonations and heat flow anomalies observable in the field regions where large scale overthrusting has occurred should be characterized by a decrease with depth of grade of metamorphic mineral assemblages and anomalously low heat flow the theoretical effects are presented as a series of maximum temperature vs depth and heat flow vs time plots

natural and human induced landsliding in the garhwal himalaya of northern india after the march 28 1999 garhwal earthquake 338 active landslides including 56 earthquake induced landslides were mapped in a 226 km 2 study area in the garhwal himalaya northern india these landslides mainly comprised shallow failures in regolith and highly weathered bedrock involving avalanches slides and flows the total volume of active 33 landslide debris in the region was estimated to be 1 3 million m including 0 02 million m 2 of the total volume moved during and within a few days of the earthquake the denudation produced by the active landsliding within the study area is equivalent to a maximum landscape lowering of 5 7 mm if active landsliding persists for a duration of between 1 and 10 years then denudation due to landsliding is in the order of 0 6 6 mm a y1 approximately two thirds of the landslides in this region were initiated or accelerated by human activity mostly by the removal of slope toes at road cuts suggesting that human activity is accelerating denudation in this region three ancient catastrophic landslides each involving 1 million m 3 of debris were identified and two were dated to the early middle holocene using cosmogenic radionuclide 10 be and 26 al cosmogenic radionuclide 10 be and 26 al were also used to date strath terraces along the alaknanda river in lower garhwal himalaya to provide an estimate of 4m m a y1 for the rate of regional denudation throughout the holocene natural landsliding therefore contributes 5 50 of the overall denudation in this region and is important as a formative process in shaping the landscape q 2001 elsevier science b v all rights reserved

ponded infiltration into soils bounded by a water table a simple model of ponded infiltration into homogenous soils bounded by and at steady state equilibrium with a water table is presented the model parameterizes the wetting front profile as a tension saturated zone above a zone in which the moisture content decreases linearly with depth application of the model requires numerical evaluation of an integral relating the time since the onset of ponding to the infiltration rate or wetting front position wetting fronts predicted by the simplified model compare favorably with laboratory measurements of vachaud and thony 1971 and for a wide range of soil types with those predicted by finite element integration of the governing flow equations the presence of a shallow water table causes the infiltration rate to decrease faster than it would under semi infinite conditions with uniform initial moisture content infiltration equations for soils bounded by water table may be used in distributed hydrologie models and other applications where the shallow position of the water table significantly affects the partitioning of precipitation forcing during storms

viscous heating allows thrusting to overcome crustal scale buckling numerical investigation with application to the himalayan syntaxes article i nfo the eastern and western himalayan syntaxes are crustal scale antiforms whose metamorphic evolution is coeval in the india asia collisional history finite element modelling of lithospheric shortening and the resultingcrustal scale folds havepreviously been used todebate the structuralconditions for the development of such structures however numerical models could not account for the metamorphic evolution associated with folding in continuation of previous work we present two dimensional finite element modelling of lithospheric shortening inwhich thermal effects are implemented the new models are consistent with earlier interpretations that crustal folding is the plausible mechanism that shaped the two himalayan syntaxes they further lend support to the concept that lithospheric buckling is a basic response to large scale continental shorteningandan efficientmountainbuilding process introducingviscous shearheating shows however that the buckling mode shifts to a thrusting mode within few shortening depending on the initial thermal rheological structure of the deforming lithosphere the change to the thrusting mode prohibits further fold amplification and lateral fold propagation this mayexplainwhy in continental lithosphere crustal scale folds are isolated whereas regular periodic crustal fold trains are rare focusing deformation on through limbs thrust zones accompanies the establishment of inverted metamorphic gradients these results offer new working hypotheseson howlargethrusts like thehimalayamain centralthrustnucleate results further show that the thermal structure of the lithosphere strongly controls three fundamental deformation and metamorphic modes 1 a cold lithosphere mainly deforms by thermally activated thrusting and exhibits large areas with significant tectonic overpressures twice lithostatic 2 a warm lithosphere is essentially buckled and significant tectonic overpressure builds up in the upper crust and 3 a hot lithosphere tends to thicken homogenously and mainly records lithostatic pressures below the upper crust

timing and climatic drivers for glaciation across semi arid western himalayan tibetan orogen abstract mapping and forty seven new 10 be ages help define the timing of glaciation in the ladakh and pangong ranges in northwest india five new local glacial stages are defined for the ladakh range from oldest to youngest these include the ladakh 4 glacial stage at 81 20 ka the ladakh 3 glacial stage not dated the ladakh 2 glacial stage at 22 3 ka the ladakh 1 glacial stage not dated and the ladakh cirque glacial stage at 1 8 0 4 ka three local glacial stages are defined for the pangong range which include the pangong 2 glacial stage at 85 15 ka the pangong 1 glacial stage at 40 3 ka and the pangong cirque glacial stage at 0 4 0 3 ka the new 10 be ages are combined with 645 recalculated 10 be ages from previous studies to develop the first regional framework of glaciation across the dryland regions of the greater himalaya transhimalaya pamir and tian shan at the western end of the himalayan tibetan orogen nineteen regional glacial stages are recognized that are termed semi arid western himalayan tibetan stages swhts these include swhts 9 at 311 32 ka swhts 7 at 234 44 ka tentative swhts 6 at 146 18 ka swhts 5e at 121 11 ka swhts 5a at 80 5 ka swhts 5a at 72 8 ka swhts 4 at 61 5 ka swhts 3 at 46 4 ka swhts 2f at 30 3 ka swhts 2e at 20 2 ka swhts 2d at 16 9 0 7 ka swhts 2c at 14 9 0 8 ka swhts 2b at 13 9 0 5 ka swhts 2a at 12 2 0 8 ka swhts 1e at 8 8 0 3 ka tentative swhts 1d at 6 9 0 2 ka tentative swhts 1c at 3 8 0 6 ka swhts 1b at 1 7 0 2 ka and swhts 1a at 0 4 0 1 ka regional glacial stages older than 21 ka are broadly correlated with strong monsoons swhts that are 21 ka or younger have smaller uncertainties and broadly correlate with global ice volume given by marine oxygen isotope stages and northern hemisphere climatic events oldest dryas older dryas younger dryas roman humid period and little ice age

quaternary lacustrine deposits in a high energy semi arid mountain environment karakoram mountains northern pakistan impressive quaternary lacustrine deposits are present as terrace remnants through out the karakoram mountains northern pakistan they are mainly the result of damming of drainage systems during glacial advances or by catastrophic mass movement deposits the longevity of most lakes is relatively short in the order of years to tens of yeaa but sedimentation rates are extremely high as a consequence of the high sediment loads within the rivers this results in deposits that frequently exceed 10 rn in thickness the sediments comprise dominantly planar bedded massive and less commonly planar laminated silts comprising detrital quartz brml of qwtermry science feldspar mica calcite chlorite and illite a facies model for lacustrine sedimentation in a high energy semi arid high mountain region is presented using case studies from a glacially dammed palaeolake glacial lake gilgit and a debris flow dammed palaeolake lake serat the rapid deposition and absence of organic material restricts the usefulness of these lacustrine sediments as proxies for palaeoenvironmental reconstruction but they are helpful in reconstructing the former extent of glaciers and illustrating the importance of high magnitude low frequency events such as landsliding as formative processes contributing to the evolution of the karakoram land scape

hillslope glacier coupling the interplay of topography and glacial dynamics in high asia 1 high asian glacial landscapes have large variations in topographic relief and the size and steepness of snow accumulation areas associated differences in glacial cover and dynamics allow a first order determination of the dominant processes shaping these landscapes here we provide a regional synthesis of the topography and flow characteristics of 287 glaciers across high asia using digital elevation analysis and remotely sensed glacier surface velocities glaciers situated in low relief areas on the tibetan plateau are mainly nourished by direct snowfall have little or no debris cover and have a relatively symmetrical distribution of velocities along their length in contrast avalanche fed glaciers with steep accumulation areas which occur at the deeply incised edges of the tibetan plateau are heavily covered with supraglacial debris and flow velocities are highest along short segments near their headwalls but greatly reduced along their debris mantled lower parts the downstream distribution of flow velocities suggests that the glacial erosion potential is progressively shifted upstream as accumulation areas get steeper and hillslope debris fluxes increase our data suggest that the coupling of hillslopes and glacial dynamics increases with topographic steepness and debris cover the melt lowering effect of thick debris cover allows the existence of glaciers even when they are located entirely below the snow line however slow velocities limit the erosion potential of such glaciers and their main landscape shaping contribution may simply be the evacuation of debris from the base of glacial headwalls which inhibits the formation of scree slopes and thereby allows ongoing headwall retreat by periglacial hillslope processes we propose a conceptual model in which glacially influenced plateau margins evolve from low relief to high relief landscapes with distinctive contributions of hillslope processes and glaciers to relief production and decay

major role of shear heating in intracontinental inverted metamorphism inference from a thermo kinematic parametric study abstract inverted metamorphism corresponds to the stacking of high temperature metamorphic units structurally on top of lower temperature units and is commonly observed along main thrusts in major orogens yet in spite of many existing models the origin and preservation of the metamorphic inversion in intracontinental collision belts are still debated in this study we use a crustal scale 2d thermo kinematic model in order to investigate the key parameters controlling the inversion of the geothermal gradient at crustal scale our results confirm that the kinematic framework strongly impacts the thermal evolution around the thrust erosion velocity and thermal conductivity of rocks are two parameters that control the spatial location of the thermal perturbation and the intensity of inversion respectively however even in extreme kinematic configurations i e convergence velocities 3 cm yr 1 and relatively high thrust dip angles 30 the thermal inversion is fleeting and thrust temperatures cannot reach the high temperature peak values characteristic of natural occurrences 600 c if shear heating is not taken into account conversion of mechanical energy into heat represents a main contribution to the thermal budget along main crustal shear zones it leads to high temperature conditions in the thrust zone and our results attest that it is the only process that allows the preservation through time of an intense thermal inversion our quantification shows that shear heating is much more efficient than other processes such as accretion and surface denudation and is compatible with the observations of inverted metamorphism in the himalayan or variscan belts for example this comparison with natural occurrences suggests that the formation and preservation of intracontinental inverted metamorphism require shear zone viscosity values of the order of 10 20 10 21 pa s for convergence velocities between 1 and 3 cm yr 1

growth and drainage of supraglacial lakes on debris mantled ngozumpa glacier khumbu himal nepal ablation of debris mantled glaciers in nepal has resulted in the formation of several potentially unstable moraine dammed lakes some of which constitute serious hazards ngozumpa glacier khumbu himal has undergone significant downwasting in recent decades and is believed to lie close to the threshold for moraine dammed lake formation the debris mantled ablation area of the glacier is studded with numerous supraglacial lakes the majority of which occupy closed basins with no perennial connections to the englacial drainage system perched lakes perched lakes can undergo rapid growth by subaerial and water line melting of exposed ice faces and calving subaerial and subaqueous melting beneath thick 1 m debris mantles is comparatively insignificant although lake expansion can contribute substantially to ablation of the glacier perched lakes cannot continue to grow indefinitely but are subject to rapid drainage once a connection is made to englacial conduits the level of one of the lakes on the ngozumpa however is controlled by the altitude of a spillway through the lateral moraine of the glacier this lake underwent only limited growth in the period 1998 2000 but is likely to experience monotonic growth if glacier mass balance continues to be negative

shear zone and nappe formation by thermal softening related stress and temperature evolution and application to the alps we present the results of two dimensional thermo mechanical numerical simulations of the formation of kilometre scale shear zones and tectonic nappes which are generated by thermal softening during horizontal shortening this model is thermo mechanically coupled and conserves energy by converting mechanical work into heat the results show that in homogeneous material the temperature increase in shear zones caused by viscous heating can be 100 c the characteristic width of the thermally perturbed part of the deforming zone is three times larger than the width of the corresponding shear zone because of diffusive heating of the wall rock therefore temperature variations initiated by shear heating may be difficult to identify based on petrological inferences of field data during lithospheric shortening with a bulk rate of 2 5 10 15 s 1 a nappe forms in the crust at a depth of 45 km peak temperatures in the nappe reach 600 c 100 c increase due to shear heating significant shear heating occurs only locally and is not active continuously in time along the entire crustal shear zone peak values of the maximal principal stress locally reach 2 5 gpa in the nappe peak values of temperature and maximal principal stress increase locally to 770 c 300 c increase due to shear heating and 3 8 gpa respectively if the applied bulk shortening rate is 5 10 15 s 1 and if higher effective viscosities for the crust are applied in the model lithosphere high differential stresses 500 mpa and significant stress deviations from the lithostatic pressure 50 occur only locally and are transient the highest average effective viscosity of the model lithosphere is 2 1022 pa s which is in agreement with the estimates for the continental lithosphere a characteristic feature of the presented dynamic nappe model is a significant stress decrease and cooling within a hundred thousand to 2 million years these rates of decompression and cooling are discussed in the context of microstructural and metamorphic observations the results also show that differential stresses in mature shear zones can be several hundred mpa smaller than at the onset of shear zone formation which suggests that estimates based on microstructural analysis of rocks in ductile shear zones provide minimum values the presented model could explain the formation of coherent alpine nappes with inferred high pressure 1 5 2 5 gpa and ultrahigh pressure 3 gpa conditions in 40 60 km depth at the base of an orogenic wedge

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

thermal evolution of the scandian hinterland naver nappe northern scotland the northern highlands terrane of scotland hosts several thrust nappes that were deformed and metamorphosed during the silurian scandian orogeny quantitative petrological analysis of metamorphic assemblages indicates that the hinterland positioned naver nappe experienced decompression heating from 8 9 kbar and 600 c to 6 7 kbar and 700 c monazite xenotime thermometry and geochronology delineate a detailed temperature time history for the naver nappe monazite often exhibits compositional zoning which is used to establish multiple temperature time points in several samples these data indicate that the naver nappe experienced relatively fast heating c 50 c myr 1 and relatively slow cooling 15 20 c myr 1 with peak temperatures occurring at c 425 ma this temperature time evolution is compatible with the early emsian 407 403 ma deposition of unmetamorphosed conglomerates that rest on high grade metamorphic rocks in the naver nappe but requires an acceleration in the cooling rate to 40 50 c myr 1 at 420 410 ma geochronological constraints from this study and previous work suggest that deformation and metamorphism in the hinterland of the scandian orogen in northern mainland scotland are younger than the c 430 ma deformation in the foreland positioned moine thrust zone we postulate that heat from pervasive granitic intrusions in the naver nappe weakened the crust allowing deformation to retreat to the hinterland of the orogen supplementary material a description of our analytical methods all u pb trace element data additional figures explaining our petrological analysis and other relevant data are available at https doi org 10 6084 m9 figshare c 4458041

glacier and landslide feedbacks to topographic relief in the himalayan syntaxes despite longstanding research on the age and formation of the tibetan plateau the controls on the erosional decay of its margins remain controversial pronounced aridity and highly localized rock uplift have traditionally been viewed as limits to the dissection of the plateau by bedrock rivers recently however glacier dynamics and landsliding have been argued to retard headward fluvial erosion into the plateau interior by forming dams and protective alluvial fill here we report a conspicuous clustering of hundreds of natural dams along the indus and the tsangpo rivers where these cross the himalayan syntaxes the indus is riddled by hundreds of dams composed of debris from catastrophic rock avalanches forming the largest concentration of giant landslide dams known worldwide whereas the tsangpo seems devoid of comparable landslide dams in contrast glacial dams such as river blocking moraines in the headwaters of both rivers are limited to where isolated mountain ranges intersect the regional snowline we find that to first order high local topographic relief along both rivers corresponds to conspicuously different knickzones and differences in the type and potential longevity of these dams in both syntaxes glacier and landslide dams act as a negative feedback in response to fluvial dissection of the plateau margins natural damming protects bedrock from river incision and delays headward knickpoint migration thereby helping stabilize the southwestern and southeastern margins of the tibetan plateau in concert with the effects of upstream aridity and localized rock uplift

timing and style of late quaternary glaciation in the eastern hindu kush chitral northern pakistan a review and revision of the glacial chronology based on new optically stimulated luminescence dating abstract glacial landforms and sediments provide evidence for two late quaternary major glaciations in the eastern hindu kush new optically stimulated luminescence osl dating was undertaken to define the timing of these glaciations and associated sediment deposition the drosh glacial was defined by osl dating to have occurred during marine isotopic stage 3 producing an extensive valley glaciation that extended to an altitude of 1300 m above sea level asl in the main valley with an equilibrium line altitude ela depression of 1200 m the pret glacial produced a valley glaciation that extended to an altitude of 1670 m asl in the main valley with an ela depression of 1000 m the new osl dating suggests that this glacial stage probably represents several glacial advances that occurred during the latter part of the last glacial moraines representing two minor glacial advances the shandur and barum glacial stages were also recognized near the contemporary glaciers these probably formed during the middle late holocene and little ice age respectively this study and comparisons with adjacent regions suggest that there was limited glaciation during the global last glacial maximum lgm in the hindu kush deglaciation in the mountain ranges of the himalayas and the consequent meltwater discharge into the adjacent seas was negligible immediately after the global lgm and it was therefore of minor importance as a forcing factor for global climate change during the end of the last glacial cycle however our studies show that glaciation and particularly deglaciation is important in controlling the deposition of thick valley fills and the landscape evolution of the high mountain environments

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

late quaternary holocene landscape evolution of a monsoon influenced high himalayan valley gori ganga nanda devi ne garhwal the garhwal himalaya provides an excellent natural laboratory in which to examine landscape evolution in a monsoon influenced high mountain environment geomorphic and sedimentological analysis and 10be cosmogenic radionuclide crn surface exposure dating of moraines fans and river and strath terraces in the gori ganga valley of nanda devi ne garhwal indicate that fans and river terraces developed rapidly by debris flow and flood processes during periods of deglaciation these phases of high sediment transfer occurred at 1 2 4 5 and 7 8 ka fan incision rates subsequent to major times of resedimentation after each glacial advance are between 19 and 57 mm year this contrasts with bedrock incision rates based on mid holocene strath terraces of 5 mm year these rates indicate that despite episodes of rapid denudation and resedimentation linked to glacial activity in this region the background rates of denudation are similar to those for other regions of the himalaya averaging several millimeters per year furthermore these data show the importance of climatic controls on landscape evolution and suggest a strong monsoonal control on the dynamics of earth surface processes in this region

chronology and climatic implications of late quaternary glaciations in the goriganga valley central himalaya india abstract goriganga valley which is located in the transition zone between the dry steppe of the tibetan plateau in the north and the sub humid himalayan climate in the south has preserved four events of glaciation with decreasing magnitude the oldest stage i glaciation is represented by a 12 5 km long discontinuous diamictite ridge which terminates north of rilkot 3100 m asl the stage ii glaciation is represented by sub rounded and partially eroded lateral moraines and terminates around martoli village 3240 m asl the stage iii and iv glacial moraines are sharp crested unstable and terminate proximal to the present day glacier at 3640 m asl and 3740 m asl respectively the stage ii moraines have been optically dated between 25 2 ka and 22 1 ka implying that glacier expanded during the global last glacial maximum lgm this is contrary to the suggestion that during last glacial maximum lgm glaciation was limited in extent due to weak indian summer monsoon ism in the monsoon dominated regions of the himalaya we ascribe the lgm glaciations to a combination of the lowered temperature and enhanced mid latitude westerlies following the lgm glaciation goriganga valley experienced two major pulses of deglaciation the older event is dated between 16 and 12 ka and is coeval with the initiation of the ism whereas the younger events 10 8 ka represent the early to mid holocene strengthened ism the stage iii and iv glaciations which terminated proximal to the modern glacier are speculated to occur during the mid holocene and little ice age lia respectively

the interpretation of inverted metamorphic isograds using simple physical calculations several zones of major thrust faulting exhibit a juxtaposition of rocks of higher metamorphic grade over rocks of lower grade this configuration may indicate but does not require that temperature gradients were temporarily inverted near the fault we examine the physical conditions under which such a temperature inversion could occur the overthrusting of hotter rock on colder rock can cause a temporarily inverted gradient both above and below the fault only if the time taken to underthrust rock from the land surface to a given depth z on the fault is less than times the characteristic time for diffusion of heat through the block above the fault where is thermal diffusivity an inverted gradient cannot form without heat generation in the fault zone unless v z sin 100 where v is the rate of underthrusting in millimeters per year z is in kilometers and is the dip of the fault this simple criterion is sufficient to demonstrate that several examples of inverted metamorphic gradients cannot be explained simply by the thrusting of hot on cold rock without heat sources in the fault zone dissipative heating accompanying deformation can cause an inverted temperature gradient within and beneath the thrust zone but whereas the overthrusting of hot upon cold rocks cools the fault zone dissipation heats it thus the overthrusting of hot on cold rock and dissipative heating affect the temperature gradient and the maximum temperatures differently we show that the magnitudes of the inverted temperature gradient and of the maximum temperature above the inverted gradient yield independent estimates of the rate of dissipative heating discrepancy between these estimates implies that some additional process must have occurred such as the post thrusting disruption of the isograds if there is such a discrepancy the maximum temperature probably provides the more reliable estimate of the rate of heating at the fault we illustrate this analysis by applying it to reported inverted metamorphic zonation in the pelona schist the st anthony complex the mt everest region of the main central thrust and the olympos thrust petrological inferences of maximum temperatures depths of metamorphism and magnitudes of apparent inverted gradients imply that shear stresses of about 100 mpa accompanied thrust faulting in some of these regions and that some zones of inverted metamorphism have been tectonically thinned after the metamorphism occured

kinematics and shear heat pattern of ductile simple shear zones with slip boundary condition extrusion by poiseuille flow and simple shear of hot lower crust has been deciphered from large hot orogens and partial slip boundary condition has been encountered in analogue models shear heat and velocity profiles are deduced from a simplified form of navier stokes equation for simple shear together with extrusive poiseuille flow and slip boundary condition for newtonian viscous rheology a higher velocity at the upper boundary of the shear zone promotes higher slip velocity at the lower boundary the other parameters that affect the slip are viscosity and thickness of the shear zone and the resultant pressure gradient that drives extrusion in the partial slip case depending on flow parameters resultant pressure gradient density and viscosity and thickness of the shear zone the velocity profiles can curve and indicate opposite shear senses the corresponding shear heat profiles can indicate temperature maximum inside shear zones near either boundaries of the shear zone or equidistant from them

crustal channel flows 2 numerical models with implications for metamorphism in the himalayan tibetan orogen 1 results from a thermal mechanical model ht1 that includes midcrustal channel flow are compatible with many features of the himalayan tibetan system radioactive self heating and rheological weakening of thickened model orogenic crust lead to the formation of a hot low viscosity midcrustal channel and a broad plateau channel material corresponding to the greater himalayan sequence ghs flows outward from beneath the plateau in response to topographically induced differential pressure at the plateau flank it is exhumed by focused surface denudation and juxtaposed with cooler newly accreted material corresponding to the lesser himalayan sequence lhs the model channel is bounded by coeval thrust and normal sense ductile shear zones interpreted to represent the main central thrust mct zone and south tibetan detachment system respectively inverted metamorphism associated with the model mct zone results from distributed ductile shear along the mct and extrusion of the hot channel a variety of model p t t path styles resembling those observed in the ghs and lhs are produced for points traveling through contrasting tectonic regimes that coexist in different parts of the model predicted times of peak metamorphism cooling and erosion of metamorphic facies are generally compatible with observations although model ghs cooling ages are too young the times of m1 and m2 metamorphic events observed in the ghs correspond to model times of maximum burial and maximum heating respectively the results highlight the need to integrate tectonics and metamorphism in continental collision models and demonstrate the importance of lateral transport of both heat and material in large hot orogens

mountain building in the nepal himalaya thermal and kinematic model we model crustal deformation and the resulting thermal structure across the nepal himalaya assuming that since 20 ma shortening across the range has been primarily taken up by slip along a single thrust fault the main himalayan thrust mht fault and that the growth of the himalayan wedge has resulted mainly from underplating and to the development of a duplex at midcrustal depth we show that this process can account for the inverse thermal metamorphic gradient documented throughout the lesser himalaya lh the discontinuity of peak metamorphic temperatures across the mct as well as the distribution of age of exhumation across the range this study suggests that the metamorphic evolution of the range over about the last 20 million years is compatible with the kinematics of recent crustal deformation deduced from morphotectonic and geodetic studies

terrestrial cosmogenic nuclide surface exposure dating of the oldest glacial successions in the himalayan orogen ladakh range northern india terrestrial cosmogenic nuclide surface exposure dating of moraine boulders and alluvial fan sediments define the timing of five glacial advances over at least the last five glacial cycles in the ladakh range of the transhimalaya the glacial stages that have been identified are the indus valley glacial stage dated at older than 430 ka the leh glacial stage occurring in the penultimate glacial cycle or older the kar glacial stage occurring during the early part of the last glacial cycle the bazgo glacial stage at its maximum during the middle of the last glacial cycle and the early holocene khalling glacial stage the exposure ages of the indus valley moraines are the oldest observed to date throughout the himalayan orogen we observe a pattern of progressively more restricted glaciation during the last five glacial cycles likely indicating a progressive reduction in the moisture supply necessary to sustain glaciation a possible explanation is that uplift of himalayan ranges to the south and or of the karakoram mountains to the west of the region may have effectively blocked moisture supply by the south asian summer monsoon and mid latitude westerlies respectively alternatively this pattern of glaciation may reflect a trend of progressively less extensive glaciation in mountain regions that has been observed globally throughout the pleistocene

geomorphology how tibet might keep its edge the stability of the margins of the himalayan tibetan mountain belt constitutes a puzzle repeated damming of major tibetan rivers by glaciers so controlling river erosion is a possible explanation much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

earthquake recurrence and rupture dynamics of himalayan frontal thrust india the black mango fault is a structural discontinuity that transforms motion between two segments of the active himalayan frontal thrust hft in northwestern india the black mango fault displays evidence of two large surface rupture earthquakes during the past 650 years subsequent to 1294 a d and 1423 a d and possibly another rupture at about 260 a d displacement during the last two earthquakes was at minimum 4 6 meters and 2 4 to 4 0 meters respectively and possibly larger for the 260 a d event abandoned terraces of the adjacent markanda river record uplift due to slip on the underlying hft of 4 8 0 9 millimeters per year or greater since the mid holocene the uplift rate is equivalent to rates of fault slip and crustal shortening of 9 6 3 5 7 0 millimeters per year and 8 4 3 6 7 3 millimeters per year respectively when it is assumed that the hft dips 30 10

loessic silt deposits in the western himalayas their sedimentology genesis and age abstract loess is abundant in the foreland basins of the himalayas however it is poorly developed within the intermontane basins of the western himalayas and karaloram selected sections were studied from the swat himalaya and the karakoram mountains fieldwork and sedimentological analysis including grain size mineralogy and microfabric showed that the loessic sediments have been reworked and some have undergone weak pedogeneses these silts are not true loess rather a loessic colluvium thermoluminescence tl dates from the loessic sediments in sections from the swat valley provided younger ages than earlier workers had suggested this is consistent with reworking of the loess in these areas it is concluded that care must be taken when using loessic silts for tl in similar mountainous terranes

style and timing of glacial and paraglacial sedimentation in a monsoon influenced high himalayan environment the upper bhagirathi valley garhwal himalaya abstract the gangotri glacier at the source of the ganges river has fluctuated greatly throughout the late quaternary in response to climatic oscillations this has resulted in impressive moraines paraglacial debris flow fans and terraces along the upper stretches of the bhagirathi valley cosmogenic radionuclide crn dating of glacial and paraglacial landforms shows that fans terraces and associated moraines formed approximately synchronously as the landscape readjusted to changing environmental conditions this synchronicity suggests that fan and terrace formation is intimately related to glaciation and that fluctuations in glacial and associated environments during times of climatic instability cause rapid sediment transfer and resedimentation of glacial landforms the crn dates show that all existing glacial and paraglacial landforms in the upper bhagirathi valley formed during the late pleistocene and holocene this demonstrates that in this high mountain environment paraglacial and glacial landforms are eroded and resedimented within about 20 000 years furthermore this testifies to the dynamic nature of glacial environments in monsoon influenced high mountain regions

orographic barriers high resolution trmm rainfall and relief variations along the eastern andes 1 quantifying the degree to which tectonic and erosive processes shape landscapes is key to understanding the evolution of tectonically active mountain belts here we explore the interplay of these two processes along the humid eastern flank of the south american andes we use high resolution tropical rainfall measurement mission trmm and srtm data to characterize elevation relief and hillslope angle of peak rainfall at orographic barriers over a distance of more than 3500 km along the eastern flanks we find that peak rainfall 3 5 m yr occurs at a mean elevation of 1 3 0 17 km a mean relief of 0 95 0 08 km and at moderate mean hillslope angles of 18 3 1 7 we suggest that topographic relief is the best first order rainfall predictor and we demonstrate how relief changes along strike south of the andean orocline alter rainfall distribution changes in climatic sedimentary and tectonic processes prevent the formation of high relief amounts at the mountain front and these areas are not characterized by pronounced rainfall peak

gis based landslide susceptibility mapping for the 2005 kashmir earthquake region abstract the m w 7 6 october 8 2005 kashmir earthquake triggered several thousand landslides throughout the himalaya of northern pakistan and india these were concentrated in six different geomorphic geologic anthropogenic settings a spatial database which included 2252 landslides was developed and analyzed using aster satellite imagery and geographical information system gis technology a multi criterion evaluation was applied to determine the significance of event controlling parameters in triggering the landslides the parameters included lithology faults slope gradient slope aspect elevation land cover rivers and roads the results showed four classes of landslide susceptibility furthermore they indicated that lithology had the strongest influence on landsliding particularly when the rock is highly fractured such as in shale slate clastic sediments and limestone and dolomite moreover the proximity of the landslides to faults rivers and roads was also an important factor in helping to initiate failures in addition landslides occurred particularly in moderate elevations on south facing slopes shrub land grassland and also agricultural land were highly susceptible to failures while forested slopes had few landslides one third of the study area was highly or very highly susceptible to future landsliding and requires immediate mitigation action the rest of the region had a low or moderate susceptibility to landsliding and remains relatively stable this study supports the view that 1 earthquake triggered landslides are concentrated in specific zones associated with event controlling parameters and 2 in the western himalaya deforestation and road construction contributed significantly to landsliding during and shortly after earthquakes

late quaternary valley infill and dissection in the indus river western tibetan plateau margin abstract the indus one of earth s major rivers drains large parts of the nw himalaya and the transhimalayan ranges that form part of the western tibetan plateau margin in the western himalayan syntaxis where local topographic relief exceeds 7 km the indus has incised a steep bedrock gorge at rates of several mm yr 1 upstream however the upper indus and its tributaries alternate between bedrock gorges and broad alluvial flats flanked by the ladakh and zanskar ranges we review the late quaternary valley history in this region with a focus on the confluence of the indus and zanskar rivers where vast alluvial terrace staircases and lake sediments record major episodes of aggradation and incision new absolute dating of high level fluvial terrace remnants using cosmogenic 10 be optically and infrared stimulated luminescence osl irsl indicates at least two phases of late quaternary valley infilling these phases commenced before 200 ka and 50 20 ka judging from terrace treads stranded 150 m and 30 40 m above modern river levels respectively numerous stacks of lacustrine sediments that straddle the indus river 200 km between the city of leh and the confluence with the shyok river share a distinct horizontal alignment constraints from irsl samples of lacustrine sequences from the leh spituk area reveal a protracted lake phase from 177 ka to 72 ka locally accumulating 50 m thick deposits in the absence of tectonic faulting major lithological differences and stream capture we attribute the formation of this and other large lakes in the region to natural damming by large landslides glaciers and alluvial fans the overall patchy landform age constraints from earlier studies can be reconciled by postulating a major deglacial control on sediment flux valley infilling and subsequent incision that has been modulated locally by backwater effects of natural damming while comparison with pleistocene monsoon proxies reveals no obvious correlation a late or post glacial sediment pulse seems a more likely source of this widespread sedimentation that has partly buried the dissected bedrock topography overall the long residence times of fluvial alluvial and lacustrine deposits in the region 500 ka support previous studies but remain striking given the dominantly steep slopes and deeply carved valleys that characterise this high altitude mountain desert recalculated late quaternary rates of fluvial bedrock incision in the indus and zanskar of 1 5 0 2 mm yr 1 are at odds with the longevity of juxtaposed valley fill deposits unless a lack of decisive lateral fluvial erosion helps to preserve these late pleistocene sedimentary archives we conclude that alternating 10 4 yr long phases of massive infilling and incision have dominated the late quaternary history of the indus valley below the western tibetan plateau margin

bayesian inference of plastosphere viscosities near the kunlun fault northern tibet 1 flow of the mid crust in the tibetan plateau may strongly influence the patterns of deformation and topography within this area this flow requires the lower crust to have low viscosity and so quantifying this viscosity may be used to test the idea of channel flow an application of bayesian methods to geologic and geodetic data from north central tibet yields lower crustal viscosities assumed newtonian of 1 1019 pa s and 2 1021 pa s 95 bounds the lower bound is larger than the value of 1016 1018 pa s required by models of flow of the lower crust of tibet unless the entire lower crust participates in channel flow

tibetan plateau river incision inhibited by glacial stabilization of the tsangpo gorge much attention has focused on how and when the tibetan plateau formed but far less research has been done on the controls on river incision into the plateau itself oliver korup and david montgomery address this issue which also relates to the question of why the tibetan plateau is still there at all despite hosting one of the deepest gorges on earth the plateau edge is extremely well defined and according to widely accepted stream power theory should be heavily dissected by one of asia s most powerful rivers the yarlung tsangp or yarlung zangbo korup and montgomery propose that the southeastern edge of the plateau was preserved in part by the presence of glaciers that were large enough during the holocene to stall aggressive river downcutting along the plateau margin a considerable amount of research has focused on how and when the tibetan plateau formed in the wake of tectonic convergence between india and asia1 although far less enquiry has addressed the controls on river incision into the plateau itself2 widely accepted theory3 predicts that steep fluvial knick points river reaches with very steep gradients in the eastern himalayan syntaxis at the southeastern plateau margin should erode rapidly4 driving a wave of incision back into the plateau preservation of the plateau edge thus presents something of a conundrum that may be resolved by invoking either differential rock uplift matching erosional decay5 6 7 or other mechanisms for retarding bedrock river incision8 9 in this region where high stream power excludes the potential for aridity as a simple limit to dissection of the plateau10 here we report morphologic evidence showing that quaternary depression of the regional equilibrium line altitude where long term glacier mass gain equals mass loss was sufficient to repeatedly form moraine dams on major rivers such damming substantially impeded river incision into the southeastern edge of the tibetan plateau through the coupled effects of upstream impoundment and interglacial aggradation such glacial stabilization of the resulting highly focused river incision centred on the tsangpo gorge could further contribute to initiating and accentuating a locus of rapid exhumation known as tectonic anaeurysm6

long recurrence interval of faulting beyond the 2005 kashmir earthquake around the northwestern margin of the indo asian collision zone the 2005 kashmir earthquake in pakistan occurred on a previously mapped active fault around the northwest margin of the indo asian collision zone to address the quantitative contribution of the earthquake to plate convergence we performed paleoseismological trench excavations at nisar camp site near muzaffarabad across the middle section of the 2005 surface rupture the fault strands exposed in the trench cut late holocene fluvial deposits and record evidence of both the 2005 and a penultimate event supported by the presence of colluvial deposits and a downdip increase in displacement along the fault strands the 2005 event produced a net slip of 5 4 m and the penultimate earthquake exhibits a similar amount of slip radiocarbon ages and historical accounts loosely constrain the timing of the penultimate event between 500 and 2200 yr b p however the exposed section encompasses 4 k y of stratigraphy suggesting an average interevent interval of 2 k y for the 2005 type events we thus conclude that the 2005 event did not occur on the plate boundary megathrusts but on intraplate active faults within the sub himalaya consequently the accumulated elastic strain around the complex northwestern margin of the indo asian collision zone has not been significantly released by the 2005 earthquake

shear heating in extensional detachments implications for the thermal history of the devonian basins of w norway article i nfo the supra detachment basins in western norway were formed during lower to middle devonian in the hangingwall of the extensional system of detachments known as the nordfjord sogn detachment zone nsdz the basins experienced elevated peak temperatures up to 345 c adjacent to the main detachment fault during the terminal stages of the extension in this study we show that the heat generated by the de formation of the rocks within the shear zone of the detachment also known as shear heating played a role in the thermal evolution of the entire region during the extension and could have induced the elevated peak temperatures of the supra detachment basins we numerically analyse the influence of the rheology and the deformation style within the shear zone the rate of exhumation of the footwall and the thickness of the sedimentary accumulation on the top of the system the model reproduces the elevated temperatures recorded in the supra detachment basins where locally 100 c and 25 of the total heat budget can be attrib uted to shear heating we show that this additional heat source may increase the peak temperatures of the hangingwall as far as 5 km away from the detachment

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

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

shear heating in continental strike slip shear zones model and field examples summary a two layer crust and upper mantle finite diverence steady state thermomechanical model of a long lived several million years lithospheric strike slip fault is presented and its predictions compared with field observations from various major fault zones in order to estimate the maximum amount of shear heating all mechanical energy is assumed to be dissipated in heat in ductile as well as in brittle layers deformation follows a friction law in the brittle layer s and a power flow law in the ductile one s variations of several independent parameters and their influence on the thermomechanical state of the fault zone and on shear heating are systematically explored shear heating is found to be more important in fault zones avecting an initially cold lithosphere and increases with slip rate friction coeycient and stivness of materials in extreme cases slip rate of 10 cm yr 1 stiv lithosphere shear heating could lead to temperature increases close to 590 c at the moho and 475 c at 20 km depth for more common cases shear heating leads to smaller temperature increases but can still explain high grade metamorphic conditions encountered in strike slip shear zones however modelled temperature conditions often fall short of those observed this could be due to heat transport by mechanisms more eycient than conduction common syntectonic emplacement of granitic melts in ductile strike slip shear zones can be explained by lower crust partial melting induced by shear heating in the upper mantle besides slip rate the possibility of such melting depends mostly on the upper mantle rheology and on the fertility of the lower crust for hard upper mantle and highly fertile lower crust partial melting could occur at rates of 1 cm yr 1 while in most cases it would result from the breakdown of micas for slip rates over 3 cm yr 1 as a result of shear heating partial melting of the upper mantle could occur in the presence of small amounts of fluids rise of magmas and or hot fluids in the shear zone will further enhance the temperature increase in shallower parts of the fault zone in nature shear heating would inevitably cause strain localization in the deeper parts of strike slip faults as is often observed in the field for crustal shear zones