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

slip rate measurements on the karakorum fault may imply secular variations in fault motion beryllium 10 surface exposure dating of offset moraines on one branch of the karakorum fault west of the gar basin yields a long term 140 to 20 thousand year right lateral slip rate of 10 7 0 7 millimeters per year this rate is 10 times larger than that inferred from recent insar analyses 1 3 millimeters per year that span 8 years and sample all branches of the fault the difference in slip rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales such fluctuations would be consistent with mechanical coupling between the seismogenic brittle creep and ductile shear sections of faults that reach deep into the crust

new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault 1 zircons and monazites from 6 samples of the north ayilari dextral shear zone nasz part of the karakorum fault zone kfz have been dated with the u th pb method using both id tims and sims techniques the ages reveal 1 inheritance from several events spanning a long period between the late archean and the jurassic 2 an eocene oligocene magmatic event similar to 35 32 ma 3 an oligo miocene magmatic event similar to 25 22 ma at least partly synkinematic to the right lateral deformation and 4 a period of metamorphism metasomatism similar to 22 14 ma interpreted as thermal and fluid advection in the shear zone the labhar kangri granite located similar to 375 km farther southeast along the kfz is dated at 21 1 0 3 ma such occurrence of several oligo miocene granites along the kfz some of which show evidence for synkinematic emplacement suggests that the fault zone played an important role in the genesis and or collection of crustal melts we discuss several scenarios for the onset and propagation of the kfz and offset estimates based on the main sutures zones our preferred scenario is an oligo miocene initiation of the fault close to the na range and propagation along most of its length prior to similar to 19 ma in its southern half the averaged long term fault rate of the kfz is greater than 8 to 10 mm a in good agreement with some shorter term estimates based on the indus river course or quaternary moraines and geodesy our results show the kfz cannot be considered as a small transient fault but played a major role in the collision history

significant late neogene east west extension in northern tibet field mapping in northern tibet reveals that the normal slip along late cenozoic northsouth trending faults is comparable to that estimated for equivalent structures in southern tibet the orientation of fault striations in two north south trending rifts suggests an eastnortheast west northwest direction of extension in northern tibet which in turn implies that northeast striking active faults in northern tibet have significant left slip components initiation of rifting in northern tibet postdates the early oligocene and possibly occurred after 4 ma the broad similarities in the magnitude of slip and the direction of extension for normal faults in both northern and southern tibet imply that the entire plateau has been extending this precludes significant eastward extrusion of north tibet relative to south tibet and requires a regional boundary condition as the cause of east west extension for the entire tibet plateau

kinematic evolution of the ama drime detachment insights into orogen parallel extension and exhumation of the ama drime massif tibet nepal abstract the ama drime massif is a north south trending antiformal structure located on the southern margin of the tibetan plateau that is bound by the ama drime and nyonno ri detachments on the western and eastern sides respectively detailed kinematic and vorticity analyses were combined with deformation temperature estimates on rocks from the ama drime detachment to document spatial and temporal patterns of deformation deformation temperatures estimated from quartz and feldspar microstructures quartz c axis fabrics and two feldspar geothermometry of asymmetric strain induced myrmekite range between 400 and 650 c micro and macro kinematic indicators suggest west directed displacement dominated over this temperature range mean kinematic vorticity estimates record early pure shear dominated flow 49 66 pure shear overprinted by later simple shear 1 57 pure shear high strain 36 50 shortening and 57 99 down dip extension dominated flow during the later increments of ductile deformation exhumation of the massif was accommodated by at least 21 42 km of displacement on the ama drime detachment samples from the nyonno ri detachment were exhumed from similar depths we propose that exhumation on the nyonno ri detachment during initiation of orogen parallel extension 11 13 ma resulted in a west dipping structural weakness in the footwall that reactivated as the ama drime detachment

comment on slip rate measurements on the karakorum fault may imply secular variations in fault motion chevalier et al 1 1 presented cosmic ray exposure dates for glacial deposits offset by movement along the karakorum fault they inferred a late quaternary slip rate on this fault 10 7 0 7 mm year that is higher than rates reported in recent field studies 2 2 the reported rate

age of initiation of the india asia collision in the east central himalaya abstract we document the stratigraphy and provenance of the lower tertiary terrigenous sections in the zhepure shan region of the tethyan himalaya southern tibet using petrographic and geochemical whole rock and single grain techniques the cretaceous early tertiary shelf deposits of shallow marine carbonates and siliciclastics of the former indian passive margin near the western end of the zhepure shan are conformably overlain by lower tertiary clastic rocks sandstones in the jidula formation paleocene mostly contain monocrystalline quartz grains of cratonic origin in contrast significant amounts of immature framework grains with a distinct ophiolitic and volcanic arc influence are present in the youxia early eocene and shenkeza post early eocene formations major trace and rare earth element concentrations in both sandstones and shales complement the petrographic data and indicate that the source of the jidula formation consisted primarily of quartzose basement rocks probably of indian con

reply to comment on block rotations and continental extension in the central aegean sea palaeomagnetic and structural evidence from tinos and mykonos cyclades greece by d avigad et al

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

transtensional deformation in the central himalaya and its role in accommodating growth of the himalayan orogen 1 field mapping structural analysis and geochronologic data from northwestern nepal reveal major normal right slip motion along a previously unrecognized west northwest striking system of shear zones that we term the gurla mandhata humla fault system gmh the gmh obliquely cuts across the greater himalayan crystalline sequence and into the lesser himalayan imbricate thrust belt via two right step over structures the average slip direction on the gmh parallels the strike of the himalayan orogen motion along this fault system has resulted in an apparent left separation of the south tibet detachment main central thrust zone and lesser himalayan imbricate thrust belt along a north striking segment of the fault system we estimate a minimum of 21 km of net slip on the southern branch of the gmh by restoring the trace of the main central thrust zone parallel to the average slip direction on the fault taking into account slip estimates from the northern branch of the gmh yields a minimum net slip estimate of 24 4 to 32 4 km for the gmh the 232th 208pb ion microprobe monazite ages from leucogranite bodies indicate that motion on the gmh occurred after 15 ma its initiation immediately followed crustal thickening between the main central thrust zone and indus yalu suture zone motion on the gmh is contemporaneous with arc normal contraction in the southernmost himalayan orogen these observations can be explained by a model that involves foreland propagating structural systems facilitating arc normal contraction in the foreland and arc parallel extension in the hinterland that work together to maintain the arcuate shape of the himalayan orogen

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

spatially variable extension in southern tibet based on gps measurements 1 we use global positioning system gps data and kinematic block models to study the present day deformation of southern tibet gps data from 33 sites in southern tibet and nepal surveyed between 1991 and 2000 reveal 13 2 mm yr of n110 e extension between lhasa and shiquanhe 80 e 91 e of which 9 7 3 0 mm yr represents permanent extension of the tibetan crust the remaining 3 mm yr results from elastic deformation from the locked curving main himalayan thrust fault this extension is spatially nonuniform one half to two thirds of the permanent extension is concentrated across the yadong gulu rift with an opening rate of 6 5 1 5 mm yr most of the remainder occurs on or near the thakkola graben with little extension across the rifts between them differential velocities of sites north and south of the yarlung zangbo suture in western tibet imply that the suture or an adjacent structure may be active as a strike slip fault a numerical model suggests that right lateral strike slip on the yarlung zangbo suture may extend from the karakorum fault zone in the west at least to the yadong gulu rift in the east with 3 mm yr slip rate accommodating part of the eastward extrusion of tibet the convergence directions inferred from gps are consistent with slip vectors of earthquakes however the rate of slip of india beneath tibet along the himalaya is lower than those previously estimated we estimate a slip rate of 12 4 0 4 mm yr between longitudes 83 e and 88 e and 17 1 and 19 1 mm yr in the western and eastern himalaya respectively the variable slip rate correlates with the variable extension rate in southern tibet and we suggest that it results from variation in the deformation rate of the overriding tibetan crust we infer that the slower convergence rate in the central himalaya is significant

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

topographic advection on fault bend folds inheritance of valley positions and the formation of wind gaps drainage basins formed along the flanks of any individual linear mountain range or fault block are commonly observed to be self similar in planform uniformly spaced and in some cases aligned with drainage basins on the opposing flank data from the siwalik hills nepal illustrate this organization where drainage basins and valleys are aligned across the main divide we suggest that valley alignment is a consequence of advection of topography across the divide to explore this hypothesis numerical experiments were conducted using a landscape evolution model of a fault bend fold that simulates detachment limited stream incision and linear hillslope diffusion results show that the presence of incised valleys and a lateral component of bedrock motion are necessary and sufficient conditions for advection of relief across the divide a mechanism by which wind gaps form and valley spacing on the far side of a ridge is inherited from that on the near side this topographic inheritance is promoted by low rock erodibility low precipitation rates fast bedrock velocities and or intermediate fault dips

thermochronologic constraints on the late cenozoic exhumation history of the gurla mandhata metamorphic core complex southwestern tibet how the tibetan plateau is geodynamically linked to the himalayas is a topic receiving considerable attention the karakoram fault plays key roles in describing the structural relationship between southern tibet and the himalayas in particular considerable debate exists at the southeastern end of the karakoram fault where its role is interpreted in two different ways one interpretation states that slip along the dextral karakoram fault extends eastward along the indus yalu suture zone bypassing the himalayas the other interprets that fault slip is fed southward into the himalayan thrust belt along the gurla mandhata detachment gmd to evaluate these competing models the late miocene history of the gmd was reconstructed from thermokinematic modeling of zircon u th he data three east west transects reveal rapid cooling of the gmd footwall from 8 0 1 3 ma to 2 6 0 7 ma model simulations show a southward decrease in slip magnitude and rate along the gmd in the north initiation of the gmd range between 14 and 11 ma with a mean fault slip rate of 5 0 0 9 mm yr the central transect shows an initiation age from 14 to 11 ma with a mean fault slip rate of 3 3 0 6 mm yr in the south initiation began between 15 and 8 ma with a mean fault slip rate of 3 2 1 6 mm yr the initiation ages and slip rates match the karakoram fault across several timescales supporting the idea that the two are kinematically linked specifically the data are consistent with the gmd acting as an extensional stepover with slip transferred southward into the himalayas of western nepal

convergence across the northwest himalaya from gps measurements 1 horizontal velocities of 26 global positioning system gps stations in the northwest himalayan region provide new constraints on the partitioning of india eurasia convergence and elastic strain accumulation about the locked main frontal thrust mft the northwest striking karakorum fault slips at 11 4 mm yr and contributes to east west extension of southern tibet and westward motion of the northwest himalaya towards nanga parbat rather than playing a role in eastward extrusion of tibet crustal shortening across the himalaya occurs within a zone centered about 100 km north of the siwalik foothills and the mft model inversions of the gps data indicate that the mft is locked over a width of 100 km comparison with geologic mft slip rate estimates suggests that this zone is building up a slip deficit at a rate of 14 1 mm yr and will eventually fail in future great earthquakes

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

spatially constant slip rate along the southern segment of the karakorum fault since 200 ka abstract determining the slip rate history along the right lateral karakorum fault kf is fundamental to understanding its present day kinematic role in the deformation of tibet geodetic and geologic studies suggest slip rates of 0 11 mm yr along this structure whether slip rate variability exists along strike and or time or simply results from different measuring techniques timescales remains unknown in order to constrain slip rates within a timescale of 200 ka we studied fluvial and glacial geomorphic features that are right laterally or vertically offset by the fault by varying amounts from 7 1 m to 430 30 m and up to 53 5 m respectively we constrained their ages using 10be surface exposure dating on 141 quartz rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the kf menshi kailas basin and along the gurla mandhata detachment fault in the pulan graben from the 30 fault bend at baer 80 5 e to mount kailas area the slip rate along the kf is 7 1 3 2 1 7 mm yr at menshi and 7 9 3 2 2 5 mm yr at kailas slip on two parallel fault strands in the pulan graben the normal fault slip rate is 1 6 0 4 0 3 mm yr our data suggest that the quaternary slip rate along the southern kf does not decrease eastward but is constant along strike for at least 200 km from 5 11 mm yr in the gar basin further north to 7 8 mm yr in the menshi kailas basin because no expected along strike slip rate gradient is observed it implies that the kf does not end at the kailas but must extend where the slip rate decreases i e eastward along the yarlung zangbo suture and southward along the gurla mandhata humla fault system

shear wave birefringence and current configuration of converging lithosphere under tibet article i nfo new data from west central tibet show that birefringence of s waves has two pronounced increases in magnitude toward the hinterland null birefringence persists to about 75 km north of the indus yarlung suture iys between the indian shield and the lhasa terrane of southern tibet a second rapid increase occurs about 100 km farther north of the bangong nujiang sutures between the lhasa terrane and the qiangtang terrane in central tibet the latter feature is consistently observed along three long transects that collectively span a lateral orogen parallel distance of about 600 km and is likely to mark the northern leading edge of sub horizontally advancing mantle lithosphere of the indian shield the greater india an interpretation consistent with the latest results of finite frequency tomography using both p and s wave travel times previous results of modeling gravity anomalies and a host of other seismic observations similarly complementary constraints indicate that the sudden onset of significant birefringence north of the iys is likely to be the southern termination of eurasian mantle lithosphere curiously the shortest of three transects showed null birefringence through much of the lhasa terrane a pattern inconsistent with those of he isotopes and gravity

middle to late miocene extremely rapid exhumation and thermal reequilibration in the kung co rift southern tibet 1 the kung co rift is an approximately nnw striking wsw dipping normal fault exposed in southern tibet and is part of an extensive network of active approximately ns striking normal faults exposed across the tibetan plateau detailed new and published u th he zircon and apatite thermochronometric data from the footwall of the early miocene kung co granite provide constraints on the middle miocene to present day exhumation history of the footwall to the kung co fault inverse modeling of thermochronometric data yield age patterns that are interpreted as indicating 1 initiation of normal fault slip at 12 13 ma and rapid exhumation of the footwall between 13 and 10 ma 2 acceleration of normal fault slip at rates of 21 9 6 9 mm yr at 10 ma 3 rapid thermal reequilibration between 10 and 9 ma and 4 slow exhumation and or quiescence from 9 ma to the present day hanging glacial valleys in the footwall and fault scarps that cut late quaternary till and moraine deposits indicate that fault slip continues today middle to late miocene initiation of extension across the kung co rift is broadly the same as the documented initiation of ew extension across the south central tibetan plateau eastward flow of middle or lower crust from beneath tibet accommodated by northward underthrusting of indian crust beneath tibet provides a plausible explanation for the onset of ew extension across the tibetan plateau

reply to comment on displacement along the karakoram fault nw himalaya estimated from la icpms u pb dating of offset geologic markers published by leloup et al in epsl 2013

isotopic characteristics of the gurla mandhata metamorphic core complex implications for the architecture of the himalayan orogen isotopic data from the gurla mandhata metamorphic core complex provide insight on the character of rocks exposed within it and permit possible correlations of these rocks to those exposed in the himalayan thrust belt whole rock sr and nd isotopic analyses show that rock units in the metamorphic core have isotopic signatures that correlate to those of greater and lesser himalayan rocks exposed in the foreland these data are the first to document lesser himalayan rocks north of the higher himalayan physiographic zone when combined with previously published structural reconstructions of the himalayan orogen these data reveal a crustal architecture that requires significant uplift of lesser himalayan rocks in the hinterland with respect to their position in the foreland a greater amount of underthrusting of the lesser himalayan rocks and more shortening in the hinterland within the tethyan himalaya physiographic zone than currently estimated

role of oblique convergence in the active deformation of the himalayas and southern tibet plateau noting similarities with subduction along curved oceanic trenches and using a simple block model we show that radial vergence evident in earthquake slip vectors along the himalayan deformation front east west extension on north trending normal faults in the himalayas and southern tibet and right lateral strike slip on the karakorum jiali fault zone can all result from basal shear caused by the indian plate sliding obliquely beneath tibet along a gently dipping arcuate plate boundary within the framework of this mechanism the normal faults in the himalayas and southern tibet are not proxies for the uplift history of tibet the distribution and style of the faults in the himalayas and southern tibet suggest that the basal drag from the underthrusting indian lithosphere extends northward beneath most of southern tibet

palaeomagnetic estimates of crustal shortening in the himalayan thrusts and zangbo suture this article reports new palaeomagnetic results from precisely dated late palaeocene limestones from the former northern margin of the indian subcontinent now in tibet between the major himalayan thrusts and the india tibet suture zone convergence in the suture and intracontinental thrusting can be estimated separately and are respectively found to be of the order of 550 km 650 km and 400 km 400 km comparison with kinematic models derived from magnetic anomalies constrains the age of the collision at about 50 myr

the himalayan arc large scale continental subduction oroclinal bending and back arc spreading abstract palaeomagnetic results from the himalayan arc and southern tibet compared with simulated apparent polar wander paths for the indian plate show a consistent pattern of rotations of the himalayan arc relative to the indian shield varying gradually from 45 clockwise in the northwestern himalaya to slightly counterclockwise in the lhasa region this pattern is consistent with continental underthrusting of greater india beneath the tibetan plateau since the early miocene over at least 650 km at the longitude of western nepal and oroclinal bending since the latest miocene available palaeomagnetic observations support the steady state model for the formation of the himalayan arc with refinements as follows 1 collision between greater india s northern boundary and southern asia occurred at equatorial latitudes with progressive suturing from palaeocene in the northwestern himalaya until early eocene in the eastern himalaya 2 continuing convergence and indentation of greater india into southern asia over about 2000 km up to the early miocene resulted in southeastward extrusion of indochina and 3 neogene counterclockwise rotational underthrusting of greater india along the main central thrust with pliocene quaternary oroclinal bending of the himalayan arc

displacement along the karakoram fault nw himalaya estimated from la icp ms u pb dating of offset geologic markers abstract the magnitude of fault offset a key parameter of fault geometry and kinematics provides critical information on the role of the karakoram fault kkf in accommodating deformation of the tibetan crust geologic markers used for estimating the magnitude of offset along the kkf include 1 geomorphologic features 2 correlative stratigraphic sequences 3 ophiolite melange belts 4 igneous bodies and 5 regional fault systems the debated offsets of the kkf range from 40 km to as much as 1000 km conflicting offsets may result from a lack of available offset correlations based on quantitative measurements the kunsha granite and the ayilari granite provide another set of potential markers for estimating the offset along the kkf u pb zircon ages and textural observations provide the basis for correlating these granites zircon u pb ages show that both the kunsha granite and the south ayilari granite crystallized around 50 ma ago whereas the north ayilari granite formed mostly around 20 ma ago reconstruction of batholiths on two sides of the namru menshi basin as well as the yalung zangbo suture and the trace of the south kailas thrust show the offset along the kkf to be about 52 2 km the chronologic data appear to preclude a 100 km offset based on the correlation between the north ayilari granite and the kunsha granite our data further disproves the conjecture that the north ayilari granite is synkinematic granite of the kkf and thus contradicts a 280 400 km ophiolite melange belt offset since it is based on the an incorrect fault initiation time we calculate a slip rate of 4 5 0 1 mm yr since 12 ma which implies that the average long term slip rate is low this does not support the lateral extrusion model which predicts a high slip rate it does support the concept that the collision between india and eurasia proceeded by distributed deformation rather than lateral extrusion along faults that bound a rigid tibet

late miocene topographic inversion in southwest tibet based on integrated paleoelevation reconstructions and structural history article investigations of the deformation history of the himalayan orogen support interpretations of rapid and striking changes in the landscape of the tibetan himalaya and high himalaya we examine this issue by integrating oxygen isotope based paleoelevation reconstructions of the zada basin in southwestern tibet with information on the structural evolution of the high and tibetan himalaya between 79 e and 84 30 e 18 opsw values were calculated from 18 occ values from pristine fluvial miocene gastropod shells analyses comparing the most negative 18 osw and reconstructed 18 opsw values to 18 osw versus elevation relationships based on both thermodynamic models and an empirical data set suggest a decrease in the mean watershed elevation of 1 to 1 5 km since the late miocene geologic mapping and structural data from crustal scale fault systems in the zada region and regions to its east indicate a phase of arc normal shortening and vertical thickening since the middle miocene followed by ongoing arc parallel extension and vertical thinning these results suggest that regions in this part of the orogen transitioned from undergoing arc normal shortening to arc parallel extension in the late miocene and that arc parallel extensional structures root deeply within the himalayan thrust wedge when combined with data on the distribution age and provenance of sedimentary basins our geologic mapping structural data and paleoelevation results suggest that this transition from shortening to extension was accompanied by a topographic inversion from mountains to basins in b4 m y these observations can be explained by a foreland propagating fault system that accommodates outward radial expansion of the himalayan orogen

orogen parallel active left slip faults in the eastern himalaya implications for the growth mechanism of the himalayan arc abstract one of the key issues about the evolution of the himalayan orogen is how its map view curvature has changed with time some researchers propose that the arc curvature has decreased due to arc perpendicular rifting while others suggest that it has increased due to arc parallel strike slip faulting to quantify this problem we conducted field mapping geomorphologic analysis of active structures and dating of pliocene quaternary sedimentary units in southeastern tibet this study reveals the existence of a 100 km wide and 500 km long east striking left slip fault zone in the eastern himalaya the left slip faults initiated prior to 3 4 ma and have a total left slip rate of 4 8 mm yr across the fault zone although the left slip rate in the eastern himalaya is broadly comparable to the right slip rate across the western himalayan arc the distributed and short segmented geometry of left slip faulting in the eastern himalaya contrasts sharply to the discrete geometry of right slip faulting in the western himalaya the different geometry may have resulted from an earlier initiation and a greater magnitude of fault motion on the right slip faults which implies that asymmetric eastward extrusion of western tibet across the himalayan arc was a dominant process in the earlier himalayan history this was replaced by oroclinal bending since 4 ma producing symmetric right slip and left slip faulting in the western and eastern himalaya respectively

some elements of continental subduction along the himalayan front abstract detachment tectonics in which the subducting basement is not internally affected by thrusting and a steady state system in which the pattern of deformation and topography are invariant uplift is balanced by erosion and the material can experience subsequent phases of deformation by migrating through the system are proposed to be the fundamental mechanisms of convergence at the himalayan arc both surface and subsurface data are more consistent with these concepts than with more familiar concepts widely used in current models intracrustal thrusting and evolutionary tectonics where superimposed phases of deformation are interpreted as distinct phases the belt of intermediate magnitude thrust earthquakes the topographic front at the high himalaya and the main central thrust mct are associated with the same fundamental element the basement thrust front btf which traces a small circle in the central portion of the himalayan arc fault plane solutions indicate thrusting in the radial direction of this arc this radial convergence at the btf implies that tibet is extending laterally at a rate similar to the rate of convergence across the btf this extension cannot be unidirectional and must be parallel to the btf if the circular shape of the btf is invariant

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

gps derived deformation rates in northwestern himalaya and ladakh deformation rates derived from gps measurements made at two continuously operating stations at leh 34 1 n 77 6 e and hanle 32 7 n 78 9 e and eight campaign sites in the trans himalayan ladakh spanning 11 years 1997 2008 provide a clear picture of the kinematics of this region as well as the convergence rate across northwestern himalaya all the ladakh sites move 32 34 mm year ne in the itrf2005 reference frame and their relative velocities are 13 16 mm year sw in the indian reference frame and 19 mm year w with reference to the lhasa igs station in southeastern tibet the results indicate that there is no statistically significant deformation in the 200 km stretch between the continuous sites leh and hanle as well as between leh and nubra valley sites along the karakoram fault whereas the sites in and around the splayed karakoram fault region indicate surface deformation of 2 5 mm year campaign sites along the karakoram fault zone indicate a fault parallel surface motion of 1 4 2 5 mm year in the tangste and western panamik segment of the karakoram fault which quantifies the best possible gps derived dextral slip rate of 3 mm year along this fault during this 11 year period baselines of ladakh sites show convergence rates of 15 18 mm year with respect to south india and 12 15 mm year with respect to delhi in north india and almora in the himalaya 400 km north northeast of delhi these constitute an arc normal convergence of 12 15 mm year across the western himalaya which is consistent with arc normal convergence all along the himalayan arc from west to east baseline extension rates of 14 16 mm year between lhasa and ladakh sites are consistent with the east west extension rate of tibetan plateau

twenty million years of continuous deformation along the karakorum fault western tibet a thermochronological analysis the role of the karakorum fault zone kfz is debated south of 33 n ongoing dextral oblique slip along the sw edge of the gar basin exhumes metamorphic and magmatic rocks of the ayilari range minerals have recorded a continuum of deformation from temperatures 600 400 c down to 20 ma of deformation along the fault greenschist facies deformation superimposed upon the medium to high grade deformation marks a kinematic change from pure dextral to dextral normal motion associated with the onset of rapid cooling at the regional scale the coexistence of transtension in the gar basin with transpression documented along the pangong range farther north suggests another example of the zipper tectonics model developed along the red river fault the kinematic shift induced the rise of the ayilari range starting at 16 12 ma and the incision of major river courses the indus river might have become captive of the relief at this time the river s 120 km of apparent offset implies dextral motion at a long term rate of ca 8 5 1 5 mm yr

miocene initiation and acceleration of extension in the south lunggar rift western tibet evolution of an active detachment system from structural mapping and u th he thermochronology 1 ongoing extension in tibet may have begun in the middle to late miocene but there are few robust estimates of the rates timing or magnitude of neogene deformation within the tibetan plateau we present a comprehensive study of the seismically active south lunggar rift in southwestern tibet incorporating mapping u pb geochronology and zircon u th he thermochronology the south lunggar rift is the southern continuation of the north lunggar rift and comprises a 50 km n s central horst bound by two major normal faults the west dipping south lunggar detachment and the east dipping palung co fault the sld dips at the rangefront 20 w and exhumes a well developed mylonite zone in its footwall displaying fabrics indicative of normal sense shear the range is composed of felsic orthogneiss mafic amphibolite and leucogranite intrusions dated at 16 and 63 ma zircon u th he cooling ages are oligocene through late pliocene with the youngest ages observed in the footwall of the sld we tested 25 000 unique thermokinematic forward models in pecube against the structural and u th he data to fully bracket the allowable ranges in fault initiations accelerations and slip rates we find that normal faulting in the slr began in the middle miocene with horizontal extension rates of 1 mm a 1 and in the north accelerated at 8 ma to 2 5 3 0 mm a 1 as faulting commenced on the sld cumulative horizontal extension across the slr ranges from 10 km in the south to 19 21 km in the north

underplating in the himalaya tibet collision zone revealed by the hi climb experiment we studied the formation of the himalayan mountain range and the tibetan plateau by investigating their lithospheric structure using an 800 kilometer long densely spaced seismic array we have constructed an image of the crust and upper mantle beneath the himalayas and the southern tibetan plateau the image reveals in a continuous fashion the main himalayan thrust fault as it extends from a shallow depth under nepal to the mid crust under southern tibet indian crust can be traced to 31 n the crust mantle interface beneath tibet is anisotropic indicating shearing during its formation the dipping mantle fabric suggests that the indian mantle is subducting in a diffuse fashion along several evolving subparallel structures

conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau this is the published version copyright 2002 american geophysical union all rights reserved

orogen parallel extension and exhumation enhanced by denudation in the trans himalayan arun river gorge ama drime massif tibet nepal focused denudation and mid crustal flow are coupled in many active tectonic settings including the himalaya where exhumation of mid crustal rocks accommodated by thrust faults and low angle detachment systems during crustal shortening is well documented new structural and u th he apatite data from the mount everest region demonstrate that the trans himalayan ama drime massif has been exhumed at a minimum rate of 1 mm yr between 1 5 and 3 0 ma during orogen parallel extension the ama drime massif offsets the south tibetan detachment system and therefore the south tibetan detachment system is no longer capable of accommodating south directed mid crustal flow or coupling it with focused denudation previous investigations interpreted the nne ssw striking shear zone on the west side of the ama drime massif as the main central thrust zone however our data show that the ama drime massif is bounded on either side by 100 300 m thick normal sense shear zone and detachment systems that are kinematically linked to young brittle faults that offset quaternary deposits and record active orogen parallel extension when combined with existing data these results suggest that the ama drime massif was exhumed during orogen parallel extension that was enhanced by or potentially coupled with denudation in the trans himalayan arun river gorge this model provides important insights into the mechanisms that exhumed trans himalayan antiformal structures during orogen parallel extension along the southern margin of the tibetan plateau

partitioning of localized and diffuse deformation in the tibetan plateau from joint inversions of geologic and geodetic observations abstract the spatial complexity of continental deformation in the greater tibetan plateau region can be defined as the extent to which relative motion of the indian and asian plates is partitioned between localized slip on major faults and distributed deformation potency rates provide a quantitative metric for determining the magnitudes of diffuse and on fault crustal deformation which are proportional to strain rates within crustal micro plates and fault slip rates respectively we simultaneously estimate micro plate rotation rates interseismic elastic strain accumulation fault slip rates on major structures and strain rates within 24 tectonic micro plates inferred from active fault maps in the greater tibetan plateau region using quasi static block models constrained by interseismic surface velocities at 731 gps sites and 9 holocene late quaternary geologic fault slip rates the joint geodetic geologic inversion indicates that geologic slip rates are kinematically consistent with differential micro plate motions estimated left lateral slip rates on the altyn tagh west central kunlun and xianshuihe faults are relatively homogeneous along strike 11 5 10 5 and 11 mm yr respectively while segmentation of the eastern kunlun fault by the intersecting elashan and riyueshan faults results in a decreased slip rate consistent with geologic observations the fraction of total potency rate associated with intrablock strain uncorrected for observational noise ranges from 0 27 in the himalayan range block to 0 91 in the aksai chin block monte carlo simulations are used to quantify the likelihood that internal deformation is statistically distinguishable from the uncertainties in geodetic velocities these simulations indicate that internal block deformation is statistically significant only within the himalayan range front where internal deformation accounts for id 0 11 of block potency rate budget west central plateau id 0 68 ganzi yushu xianshuihe 0 58 burma 0 09 jiali 0 38 and aksai chin 0 68 blocks in the other 18 tectonic micro plates within the plateau region estimated internal block potency is not currently distinguishable from the expected contribution of observational noise to residual velocities of the total potency budget within the tibetan plateau 85 is taken up by slip on major faults with the remaining 15 accommodated by internal processes at sub block scale distinguishable from observational noise the localization of the majority of plate boundary activity is also supported by the spatial distribution of modern and historical crustal earthquakes sixty seven percent of the total moment released by earthquakes in the cmt catalog and 90 of historical moment since 1900 have been released within 25 km of the major faults included in the block model representing only 12 of the characteristic half block length scale of 215 km the localization of deformation inferred from geologic geodetic and seismic observations suggests that forces applied to tectonic micro plates drive fault system activity at the india asia collision zone over decadal to quaternary time scales

styles of post subduction collisional orogeny influence of convergence velocity crustal rheology and radiogenic heat production abstract a number of models of continental collision already exist but the role of foregoing oceanic plate subduction or variable coupling between plates still remains to be explored in addition heat generation by radioactive decay may be quite variable for example our geochemical data from low to high grade metamorphic rocks of the lesser and higher himalayan sequences reveal measured heat production values on the order 4 5 w m 3 which is considerably higher than normal inferred upper crustal values 3 therefore we performed 2d numerical experiments of oceanic continental subduction followed by continental collision for varying continental lower crustal strength convergence velocity and radiogenic heating rate oceanic subduction produces thinning and upwarping of the overriding lithospheric wedge such as is observed in andean type collisional settings cascadia and central andes after collision two main orogenic styles develop depending on the values of key parameters either a slow convergence rates weak shear heating and consequently strong rheological coupling between plates and or a weak lower crust generate a two sided thick and narrow symmetrical collisional zone or b high convergence rates strong shear heating and therefore weak rheological coupling between plates and a strong lower crust produce a one sided thin and broad asymmetrical collisional zone in this case a vertical lithospheric body divides two upper crustal wedges that develop distinct deformation patterns in both cases enhanced radiogenic heating favors the formation of midcrustal partially melted channels that propagate toward the surface and the pro foreland partial melting triggers lateral extrusion of metamorphic rocks from different depths 15 23 kbar 700 c on top of coherent lp lt units the geometry of metamorphic isograds inverted shapes of p t paths at different grades and exhumation rates are similar to those observed in parts of the himalayan chain indicating that the models capture the essence of real systems the model results demonstrate that internal heat production rate is a crucial parameter in determining the timing of slab breakoff polarity reversal and exhumation of the inverted metamorphic sequence with respect to the timing of partial melting late stages of some numerical experiments showed interesting geodynamical evolution of the collisional zone with the appearance of polarity reversal roll over of both plates and roll back of the subducting slab irrespective of these details hundreds of km of continental lithosphere are recycled into the mantle in all models supporting the idea that continental crustal consumption is indeed a common and considerable process during collision this affects inferences about extents of convergence and or shortening during orogenesis moreover crustal recycling into the deep mantle during collisional orogeny needs to be considered in models of crustal growth and evolution

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

response to comment on slip rate measurements on the karakorum fault may imply secular variations in fault motion brown et al 1 1 argue that the dispersion in the exposure ages we obtained from the manikala glacier moraines 2 2 is influenced by postdepositional processes and that only the oldest boulder age on each moraine group can be used to assess its abandonment age determining the

slip rates of the karakorum fault ladakh india determined using cosmic ray exposure dating of debris flows and moraines most recent major glacial advance occurred at 90 15 ka this is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with northern hemisphere continental ice sheets if features including lateral moraines that liu inferred to have been offset 300 350 m by the karakorum fault date from the same period they too imply a slip rate of 3 4 mm yr 1 this slip rate is comparable to rates of extension across grabens within tibet with recent evidence that slip along the altyn tagh fault occurs at 10 mm yr 1 our rate suggests that slip along the boundaries of tibet is not significantly more rapid than extension within the plateau hence plate tectonics in the strictest sense ought not be applied to tibet because tibet does not behave as a rigid plate index terms 1824 hydrology geomorphology 1625 1035 geochemistry geochronology 9320 information related to geographic region asia 8107 tectonophysics continental neotectonics keywords karakorum fault slip rate cosmic ray exposure age beryllium 10

new radiometric dating constrains the time for initiation of the karakorum fault zone kfz sw tibet abstract the karakorum fault zone kfz composed of strike slip faults has played an important role in intra continental deformation during the cenozoic convergence between the indian and eurasian plates however the spatial and temporal evolution of the kfz remains under debate this paper reports new zircon u pb sensitive high resolution ion microprobe shrimp and biotite 40ar 39ar ages for samples from the fault zone to clarify the timing of events the ages of zircon u pb fall mainly around 47 50 ma which corresponds to a period of important magmatic activity of the gangdese granitic belt also known as the trans himalayan magmatic belt a metamorphic event followed in the period around 32 ma and that was then followed by a medium temperature cooling event between about 12 and 7 7 ma biotite 40ar 39ar ages provide evidence that the 12 7 7 ma cooling event coincides with the initiation of the kfz cutting through the ayilari granite the ayilari granite pluton does not seem to have experienced the separate 25 23 ma cooling event as shown in previous studies 60 80 km west of the current study area lacassin r valli f arnaud n leloup p h paquette j l li h tapponnier p chevalier m l guillot s maheo g xu z 2004 large scale geometry offset and kinematic evolution of the karakorum fault tibet earth and planetary science letters 219 3 4 255 269 valli f arnaud n leloup h p sobel e r maheo g lacassin r guillot s li h tapponnier p xu z 2007 twenty million years of continuous deformation along the karakorum fault western tibet a thermochronological analysis tectonics 26 doi 10 1029 2005tc001913 valli f leloup p paquette j arnaud n li h tapponnier p lacassin r guillot s liu d deloule e xu z mahe o g 2008 new u th pb constraints on timing of shearing and long term slip rate on the karakorum fault tectonics 27 doi 10 1029 2007tc002184 we conclude that the 25 23 ma cooling event bears no relationship to the activity of the kfz but resulted from a local metamorphic event caused either by a regional tectonic event such as activity of the south kailas thrust fault or by magmatism around shiquanhe also known as gar the study of the kfz around namru supports the opinion that the kfz propagated along the fault strike to the gar menshi area around 12 ma

syncollisional extension along the india asia suture zone south central tibet implications for crustal deformation of tibet abstract crustal deformation models of the tibetan plateau are assessed by investigating the nature of neogene deformation along the india asia suture zone through geologic mapping in south central tibet 84 30 e our mapping shows that the suture zone is dominated by a system of 3 to 4 ene striking south dipping thrust faults rather than strike slip faults as predicted by models calling upon eastward extrusion of the tibetan plateau faults along the suture zone are not active as they are cut by a system of nnw striking oblique slip normal faults referred to herein as the lopukangri fault system fault slip data from the lopukangri fault system shows that the mean slip direction of its hanging wall is n36w we estimate the net slip on the lopukangri fault by restoring components of the thrust system we estimate that the fault has accommodated 7 km of right slip and 8 km of normal dip slip yielding a net slip of 10 5 km and 6 km of horizontal east west extension the lopukangri fault system is active and geomorphic offsets indicate right separations and westside down dip separation the mapview curviplanar geometry and geomorphic expression of the lopukangri fault system is similar to faults and rift basins to its east and west these extensional faults are en echelon in map view and encompass a region that is 200 km long east west and 95 km wide north south assuming our results for the lopukangri fault are applicable to the entire system we estimate a maximum of 18 extension across the zone all active faults in the system terminate southward adjacent to the india asia suture zone because the individual rift geometries are similar and suggest a common kinematic relationship we propose that the extensional system formed as a trailing extensional imbricate fan at the southern termination of the central tibet conjugate fault zone alternatively the extensional system may terminate to the north and represent a group of isolated crustal tears both kinematic interpretations imply a semi smooth north south variation in the magnitude of east west extension in southern tibet with higher magnitudes in the north along the bangong nujiang suture zone than in the south along the india asia suture zone our results from southern tibet show that deformation between southern tibet and the himalayas is broad 95 km wide and best described as a continuum possibly since the late miocene conversely the structural boundary between western tibet and the himalayas which is defined by the karakoram fault is presently a discrete boundary and probably has been since the middle miocene we think this variation in the displacement gradient and age of these structural boundaries within the interior of tibet is best explained by the fault patterns and strain history describing wholesale e w stretching and n s shortening of the tibetan crust

satellite geodetic imaging reveals internal deformation of western tibet 1 it is often assumed that the majority of the interseismic strain accumulates around the major mapped geological block boundaries however numerous recent earthquakes in the continents have occurred on faults that were previously unidentified existing deformation data from tibet are insufficiently dense to map the distribution of interseismic strain here we combine 265 interferograms formed from 166 radar images with gps data to constrain a high resolution velocity field covering 200 000 km2 of western tibet we confirm that the slip rate of the karakoram fault is low 6 mm yr but show that areas of focused strain do not coincide with the major fault structures some of this strain is due to postseismic relaxation after a mw 6 8 earthquake that occurred in 1996 on a structure that is difficult to identify in satellite imagery models of seismic hazard that rely on imperfect knowledge of the boundaries of crustal blocks can therefore underestimate hazard from unknown faults