deformation metamorphism and imbrication of the indian plate south of the main mantle thrust north pakistan south of the main mantle thrust in north pakistan rocks of the northern edge of the indian plate were deformed and metamorphosed during the main southward thrusting phase of the himalayan orogeny in the hazara region between the indus and kaghan valleys metamorphic grade increases northwards from chlorite zone to sillimanite zone rocks in a typically barrovian sequence metamorphism was largely synchronous with early phases of the deformation the metamorphic rocks were subsequently imbricated by late north dipping thrusts each with higher grade rocks in the hanging wall than in the footwall such that the metamorphic profile shows an overall tectonic inversion the rocks of the hazara region form one of a number of internally imbricated metamorphic blocks stacked after the metamorphic peak on top of each other during the late thrusting this imbrication and stacking represents an early period of post himalayan uplift

mechanics of fold and thrust belts and accretionary wedges cohesive coulomb theory a critically tapered fold and thrust belt or submarine accretionary wedge is one that is on the verge of coulomb failure everywhere including its base where frictional sliding along a decollement is assumed to be occurring cohesion within a wedge can add significantly to the overall strength near the toe the effect of this is to decrease the near toe taper leading to a critical topographic profile that is concave upward if the decollement is planar we obtain an approximate self consistent solution for the state of stress within a thin skinned cohesive critical coulomb wedge and determine the relationship between the wedge taper and its strength and basal friction the theory is then applied to the presently deforming fold and thrust belt of western taiwan fitting of theoretical critical wedge shapes to topographic profiles and measurements of the step up angles of thrust faults from the basal decollement are used to constrain the taiwan wedge strength parameters an attractive assertion fully consistent with all the observations is that the mechanics of fold and thrust belts and accretionary wedges is governed by normal frictional and fracture strengths of rocks measured in the laboratory in particular if byerlee s law b 0 85 is adopted as the coefficient of sliding friction on the base we find a coefficient of internal friction 0 9 1 0 in the wedge and a wedge cohesion so 5 20 mpa other solutions having strengths and ambient stresses up to 4 times lower than this can also however satisfy the data

polyphase metamorphism and the development of the main central thrust along a cross section through the lesser and higher himalayan units at the kishtwar window area north west india a polyphase barrovian type metamorphism has been delineated in relation to the development of the main central thrust mct in the metapelitic mineral assemblages three metamorphic phases have been distinguished a conditions up to amphibolite grade at moderate to high pressures alm rut ilm kya qtz characterize the m1 phase b pressure release and or temperature increase as a result of movement along the mct and the formation of gneiss domes in the higher himalaya as expressed by oriented n70 100 e fibrolite defines the m2 phase and c finally during uplift of the kishtwar window area a retrogressive m3 phase is characterized by the assemblage quartz muscovite chlorite both optically zoned and single stage garnets have been examined with the electron microprobe to determine their element partitioning normal zoning has been found in samples below the mct in the lesser himalaya indicating prograde growth during the m2 phase whereas tectonically above in the higher himalaya unit the garnets reveal double stage growth with a complex zoning pattern due to reaction partitioning during m1 and m2 and reverse zoning at their rims during the retrogressive m3 phase geothermometry on metapelites along a cross section through the mct zone and the higher himalaya imply distinct readjustments of garnet biotite exchange equilibria and indicate isothermal conditions 500 600 c throughout the section during the m3 retrogression pressure calculations gro an kya qtz and alm rut ilm kya qtz suggest a decrease in pressure towards the top of the section 6 7 5 to 4 5 5 kbar as corroborated by fibrolite replacing kyanite the spatially inverse metamorphism exposed within the lesser himalaya of the kishtwar window is regarded as a product of polyphase metamorphism combined with ongoing thrusting and shearing and is reflected by condensed m2 isograds around the kishtwar window

the ascent of felsic magmas in dykes abstract the results of a thermal and fluid dynamical analysis are presented that allow geologists to estimate the critical dyke or fracture width w c necessary for the transport of felsic magma through the crust without control by solidification the principal geological variables required to estimate w c are the magmatic viscosity the density and temperature contrasts and t between magma and country rock and the height of ascent h the results show that for typical values of and and for transport distances of 20 to 30 km the critical dyke width is constrained to lie between about 2 and 20 m

comment on appropriate boundary condition for dupuit boussinesq theory on the steady groundwater flow in an unconfined sloping aquifer with uniform recharge by wu et al

ductile shearing to brittle thrusting along the nepal himalaya linking miocene channel flow and critical wedge tectonics to 25th april 2015 gorkha earthquake the 25th april 2015 magnitude 7 8 gorkha earthquake in nepal ruptured the main himalayan thrust mht for 140 km east west and 50 km across strike the earthquake nucleated at a depth of 15 18 km approximating to the brittle ductile transition and propagated east along the mht but did not rupture to the surface leaving half of the fault extent still locked beneath the siwalik hills coseismic slip shows that motion is confined to the ramp flat geometry of the mht and there was no out of sequence movement along the main central thrust mct below 20 km depth the mht is a creeping aseismic ductile shear zone cumulated deformation over geological time has exhumed the deeper part of the himalayan orogen which is now exposed in the greater himalaya revealing a tectonic history quite different from presently active tectonics there early miocene structures including the mct are almost entirely ductile with deformation occurring at temperatures higher than 400 c and were active between 22 16 ma kyanite and sillimanite grade gneisses and migmatites approximately 5 20 km thick in the core of the greater himalayan sequence ghs together with leucogranite intrusions along the top of the ghs were extruded southward between 22 15 ma concomitant with ages of partial melting thermobarometric constraints show that ductile extrusion of the ghs during the miocene occurred at muscovite dehydration temperatures 650 775 c and thus brittle thrusting and critical taper models for ghs deformation are unrealistic as partial melting and channel flow ceased at 15 ma brittle thrusting and underplating associated with duplex formation occurred along the lesser himalaya passively uplifting the ghs

storage dependent drainable porosity for complex hillslopes 1 in hydraulic groundwater theory the parameter drainable porosity f a storage coefficient that accounts for the effect of the unsaturated zone on water table dynamics is usually treated as a constant for shallow unconfined aquifers the value of this parameter however depends on the depth to the water table and the water retention characteristics of the soil in this study an analytical expression for f as a function of water table depth is derived under the assumption of quasi steady state hydraulic equilibrium in this way accounting in part for the effects of the unsaturated zone on groundwater dynamics the derived expression is implemented in the nonlinear hillslope storage boussinesq hsb model troch et al 2003 to simulate the drainage response of complex hillslopes the model s behavior is analyzed by comparison to 1 the hsb model with a constant value for f and 2 measurements of water tables and outflow hydrographs on a 6 0 2 5 0 5 m laboratory hillslope experiment the comparison is conducted for a pure drainage case on two different hillslope shapes linearly convergent and divergent and for three different slope inclinations 5 10 and 15 comparison 1 is run in an uncalibrated and a fully calibrated mode and it enables us to evaluate the effect of a dynamic state dependent value for f on model output comparison 2 allows us to test the hsb model on several hillslope configurations and to analyze whether the concept of a storage dependent f enhances the model performance the comparison of the hsb models to the measurements from the laboratory hillslopes shows that it is possible to capture the general features of the outflow hydrograph during a drainage experiment using either one of the hsb models overall the original constant f hsb model with one fitting parameter more than the revised hsb model shows a slightly better fit on the hydrographs when compared to the revised variable f hsb model however the peak outflow values the first few minutes after initiation of the experiments are better captured by the revised hsb model the revised hsb model s performance in simulating water table movements is much more accurate than that of the original hsb model the improved match of the revised hsb model to piezometric measurements is worth stressing because the ability to model water tables is a key attribute of the model making it possible to investigate phenomena such as saturation excess runoff also noteworthy is the good match between the revised hsb model and the outflow measurements without any calibration for the divergent slopes the changing values of the calibrated drainable porosity parameter for the original hsb model as different configurations are simulated slope angle plan shape initial conditions together with the ability of the revised hsb model to more accurately simulate water table dynamics clearly demonstrates the importance of regarding drainable porosity as a dynamic storage dependent parameter

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

zanskar shear zone northeast southwest extension within the higher himalayas ladakh india a complete geologic section through the northwestern himalayas is well exposed in ladakh india the collision between the indian shield and the tibetan platform caused large scale intracrustal thrusting and piling up of the himalayan nappes this compressional event was accompanied by prograde regional metamorphism the metamorphism ranges from low grade anchimetamorphism in the indus suture zone in the northeast to upper amphibolite grade in the higher himalaya tectonic unit in the southwest in the zanskar area a well exposed and morphologically prominent shear zone 2 25 to 6 75 km wide can be followed from the northwest to the southeast for at least 80 km in contrast to the main compressional tectonics this shear zone indicates an extensional event within the higher himalaya tectonic unit the zanskar shear zone involves granitic rocks leucogranites of miocene age and various metasediments and in general separates the late precambrian early cambrian sedimentary sequence phe formation from the underlying crystalline basement zanskar crystalline unit a normal sense of shear has been determined by using asymmetric macroscopic and microscopic structures such as pegmatite boudins feldspar augen and crystallographic fabrics the metamorphic isograds are very close within this shear zone as a result of shear deformation a gradual transition from upper amphibolite to lower greenschist facies occurs within 200 m movement in this zone occurred late in the metamorphic history under greenschist or lower metamorphic conditions the minimum horizontal extension and vertical displacement are on the order of 16 and 19 km respectively

ductile thrusting in the himalayas shear sense criteria and stretching lineations the most useful criteria used for the determination of the sense of shear can be found in the huge himalayan ductile shear zone known as m c t they allow the determination of the sense of shear in relation with an unequivocal southward directed intracontinental thrust the various criteria analyzed at different scales of observation show the permanence of the shear flow regime throughout the metamorphic evolution however most of the observed shear criteria are due to late nappe emplacement postdating the climax of the metamorphism the most striking feature is the stretching lineation which is roughly normal to the thrust trace all along the belt it parallels everywhere the shear direction and thus indicates the transport direction of the nappes the observed radial pattern of stretch trajectories implies that the local motion does not correspond to the average plate convergence

reply to comment by kong et al on appropriate boundary condition for dupuit boussinesq theory on the steady groundwater flow in an unconfined sloping aquifer with uniform recharge

thermal model for the zanskar himalaya abstract crustal thickening along the northern margin of the indian plate following the 50 ma collision along the indus suture zone in ladakh caused widespread high temperature medium pressure barrovian facies series metamorphism and anatexis in the zanskar himalaya metamorphic isograds are inverted and structurally telescoped along the main central thrust mct zone at the base of the high himalayan slab along the zanskar valley at the top of the slab isograds are the right way up and are also telescoped along northeast dipping normal faults of the zanskar shear zone zsz which are related to culmination collapse behind the miocene himalayan thrust front between the mct and the zsz a metamorphic anatectic core within sillimanite grade rocks contains abundant leucogranite granite crustal melts of probable himalayan age a thermal model based on a crustal scale cross section across the zanskar himalaya suggests that m1 isograds developed during early himalayan barrovian metamorphism were overprinted during high grade mct related anatexis and folded around a large scale recumbent fold developed in the hanging wall of the mct

petrologic and structural controls on geomorphology of prehistoric tsergo ri slope failure langtang himal nepal high relief h up to 2600 m and spatial orientation of discontinuities such as leucogranitic intrusions mylonitic and pseudotachylitic horizons and related ore structures were the preparatory causal factors for the giant prehistoric tsergo ri landslide high himalayan crystalline langtang himal nepal other controlling factors include overthrusting detachment faulting and paleoseismics related to the main central thrust mct and southern tibet detachment system stds neotectonically generated structures and predesigned form of the scarp broken crest and the direction of movement towards the wsw coherently displacement of several 109 m3 materials caused frictional fusion landslide dynamics and specific morphologic conditions created four different types of sliding surfaces in chronological sequence i primary at the basement ii secondary parallel or subparallel to i iii tertiary vertical to i and ii and iv quarternary sliding surfaces local variety of iii note ordinal numeric terms are not in time stratigraphic sense these planes represented the main discontinuities conducting different syn event stresses in the sliding mass and for further landslide dynamics spatial difference and widespread distribution of sliding planes and sets of discontinuities all over the landslide area caused different classes of rock quality which subsequently determined specific erosional processes within the landslide accumulation area the subsequent glacial and fluvial erosional processes were controlled by the correlating preexisting lithotectonic patterns the hyalomylonitic and or breccious sliding planes and the recent morphologic features or shapes of tsergo ri i the se part is gradationally brecciated to the top and includes tsergo ri itself the residual mass of the bulk has been eroded almost isometrically as far as the primary sliding plane crops out along the intact gneissic basement differences in rock quality along a horizon of secondary sliding planes indicate a steplike break in the relief after the last main glaciation ii the earlier halted nw part still preserved micromountainous shape of compact sliding blocks phushung i and ii kyimoshung separated by landslide dynamic triggered faults tertiary and quarternary sliding planes primary and secondary sliding planes almost covered by holocene sediments produced an insignificant morphology iii the highest brecciated strike slip fault generated during collision with the obstacle of pangshungtramo peak in the southwest is the deeply eroded dranglung chu valley which has been kept morphologically active in a major way until recent times iv except for the collision obstacle of pangshungtramo peak with recent semi active erosion and a small secondary rockslide block of tsangbu north of it all surrounding parts show typical features of high altitude erosion

crustal structure of the himalayan orogen at 90 east longitude from project indepth deep reflection profiles international deep profiling of tibet and the himalaya indepth deep seismic reflection profiles show that the indian lithosphere is underthrusting the central himalaya along a gently north dipping decollement that is traceable northward beneath the tethyan belt to 28 6 n and to a depth of about 45 km the decollement carries in its hanging wall a near crustal thickness slice of internally deformed indian continental basement and cover represented in outcrop by the greater himalayan belt and structurally overlying tethyan belt geometric relationships suggest that the decollement probably ramps downward beneath the northern tethyan belt to near the base of the crust and that the hanging wall crustal slice was detached from indian mantle lithosphere that presently underlies southern tibet to the north the north himalayan anticlinorium kangmar dome appears to be a large duplex ramp anticline in the hanging wall of the decollement the south tibetan detachment appears to have been imaged in two areas in the wagye la area it appears to follow the tethyan belt greater himalayan belt contact northward in the subsurface and to have been folded over the kangmar dome in the zherger la area it appears to have been active relatively recently as a 30 north dipping normal fault that cuts deeply into the greater himalayan belt allochthon palinspastic reconstruction indicates a minimum of about 326 km of shortening of the indian basement across the himalaya since the initiation of the main central thrust hence indian continental lithosphere largely stripped of its overlying crust can extend northward beneath the tibetan plateau to at least 32 n where earthquake seismological observations show that the properties of the upper mantle change markedly e g mcnamara et al 1995 taken together the seismic reflection and earthquake seismological observations lend support for the view that the indian mantle lid mechanically underplates roughly the southern half of the tibetan plateau the indepth reflection data do not show that indian crust attached to this lithosphere extends north of southernmost tibet kangmar dome nor do they negate this possibility similarly the reflection data do not yield direct evidence for or against lower crustal subduction beneath the himalaya

deformation of leucogranites of the crystalline main central sheet in southern tibet china abstract towards the top of the main central sheet in southern tibet china leucogranites intrude metamorphic rocks related to rocks of the main central thrust in the himalayas our study shows that the leucogranites suffered a northward shear deformation the significance of this event is discussed in terms of gravity driven decollement of the 10 000 m thick tethyan sedimentary pile over its crystalline basement

tectonothermal evolution of the high himalayan crystalline sequence langtang valley northern nepal the high himalayan crystalline sequence in north central nepal is a 15 km thick pile of metasediments that is bound by the main central thrust to the south and a normal fault to the north the langtang section through the metasediments shows an apparent inversion of metamorphic isograds with high p kyanite grade rocks exposed beneath low p sillimanite grade rocks textural evidence confirms that the observed inversion is a result of a polyphase metamorphic history and phase equilibria studies indicate that thermal decoupling has occurred within a mechanically coherent section of crust rocks now exposed at the base of the high himalayan thrust sheet underwent barrovian regional metamorphism m1 prior to 34 ma in the early stages of the himalayan orogeny recording metamorphic conditions of t 710 30 c p 9 1 kbar after the activation of the main central thrust which emplaced these metapelites southwards onto the lower grade lesser himalayan formations the upper part of the thrust sheet was overprinted by a second heating event m2 resulting in sillimanite grade metamorphism and anatexis of metapelites at t 760 30 c p 5 8 0 4 kbar between 17 and 20 ma crustally derived leucogranite magmas have been emplaced into low grade tethyan sediments on the hangingwall of the normal fault that bounds the northern limit of the metapelitic sequence the cause of the selective heating of the upper section of the metasediments during m2 cannot be reconciled with either post thrusting thermal relaxation or advection models the cause of m2 remains problematical but it is suggested that heat focusing has occurred at the top of the high himalayan crystalline sequence as a result of movement on the normal fault blanketing metapelites of high heat productivity with low grade sediments of low thermal conductivity this model implies that the normal fault was active before m2 consistent with decompression textures that formed during or shortly after sillimanite grade metamorphism

effects of unsaturated flow on hillslope recession characteristics recession flow analysis is usually conducted to infer hydraulic parameters of hillslope aquifers various boussinesq equation based models both linear and nonlinear have been used to analyze the recession curves for sloping aquifers with a focus on the long time recession behavior based on a modified boussinesq equation with capillarity incorporated we demonstrate the significant effect of unsaturated flow on the recession curve which result in three instead of two power law regimes with two transition points instead of one corresponding to the formation of a fully unsaturated zone at the adjacent area of the upslope boundary and across the whole domain respectively the results show that the power of the second and third recession regime is variable depending on the slope angles soil types and hillslope geometries the unsaturated flow effects also lead to the absence of drastic drop of formula presented at the transition between the first and second regime which was predicted by previous numerical models but has not been observed in the field or laboratory experiments these findings have important implications for recession flow analysis in studies of hillslope aquifers

thermal evolution of the greater himalaya garhwal india the hanging wall of the main central thrust mct in garhwal india roughly 79 n 80 e 30 n 31 n exhibits an inverted metamorphic gradient sillimanite potassium feldspar assemblages near the top of the hanging wall or greater himalayan sequence are underlain by kyanite grade rocks near the fault textural relationships in pelitic samples from the alaknanda and dhauli river valleys indicate that the inversion is the product of two distinct metamorphic events an early harrovian event m1 which affected the entire greater himalayan sequence and a later buchan event m2 the effects of which are most obvious in the upper part of the sequence rim thermobarometry garnet inclusion thermobarometry and thermodynamic modeling of garnet zoning reveal that the basal portions of the metamorphic sequence experienced peak m1 conditions of 900 k and 960 mpa roughly 36 km depth before following an erosion controlled uplift path e g england and richardson 1977 m2 metamorphic temperatures in the upper part of the sequence also exceeded 900 k but maximum pressures 317 523 mpa indicate paleodepths of only 12 19 km calculated pressure temperature paths indicate that m2 was characterized by temperature increases of 80 k and roughly 5 km of tectonic burial we attribute m1 to tectonic burial of the greater himalayan sequence during the early stages of india eurasia collision we believe that the uplift and cooling path of the sequence was interrupted in late oligocene miocene time by a second burial and heating event m2 related to thrust imbrications in southern tibet this burial was coincident with the generation of leucogranites which are abundant near the top of the greater himalayan sequence but are virtually absent near the mct field relations do not constrain whether the leucogranites were derived from some presently unexposed portion of the greater himalayan sequence and were injected at their present structural level or were melted in situ if the granites were injected then they may have provided some of the heat necessary for m2 metamorphism although our data suggest no direct relationship between the main central thrust as mapped in garhwal and metamorphism in the greater himalaya anatectic melting of an unexposed portion of the greater himalayan sequence could have been associated with movement along a blind thrust with characteristics similar to the mapped mct in central nepal cf le fort 1981 if the granites were produced by in situ m2 melting then we must appeal to a heat source within the upper part of the greater himalayan sequence such as locally high concentrations of heat producing elements cf pinet and jaupart 1987

the contact between the higher himalaya crystallines and the tibetan sedimentary series miocene large scale dextral shearing space and time evolution of the synmetamorphic structures across the metamorphic pile have been studied in several areas along the himalayan belt east and central nepal garhwal zanskar from one area to the other the evolution is very similar 1 at the base of the pile in the main central thrust mct shear zone the stretching lineation penetrative and regularly oriented n0 e to n30 e indicates the mct transport direction very constant all along the belt from the eohimalayan main metamorphic development up to the late metamorphic movements 2 at the top of the pile at the contact between the crystalline unit and its sedimentary cover gravity driven structures are confirmed north vergent folds ductile normal faulting however there are numerous local indications of late miocene syn to late emplacement of the leucogranitic plutons dextral shearing 3 in between across the medium part of the pile the stretching lineation shows a conspicuous progressive regional clockwise rotation clearly indicated by the strain trajectories mapped in nepal and garhwal points 1 and 2 show that the crystalline sedimentary boundary despite its apparent structural and metamorphic continuity is not only a normal fault but also an important dextral shear zone which has acted since the upper miocene as the main southern limit of the eastward extruding tibetan block

pressure temperature and time constraints on himalayan metamorphism from eastern kashmir and western zanskar himalayan metamorphism in the kashmir and zanskar sector of the high himalaya resulted from thrust and fold related crustal thickening within the indian plate following the collision of india and asia at c 50 ma interbanded metapelites marbles calcareous schists amphibolites and quartzites represent metamorphosed equivalents of the palaeozoic lower mesozoic continental margin rocks granitic rocks include pre collision k feldspar megacrystic and biotite granites and post collision two mica garnet tourmaline granites average pressure temperature conditions of equilibration using the self consistent thermodynamic data set of holland powell 1990 are presented across a 45 km traverse of the eastern kashmir western zanskar high himalaya kyanite is the stable aluminosilicate phase across 35 km outcrop width in the middle of the slab complex microstructures indicate that prograde metamorphism up to kyanite grade and fabric development in the upper structural nappes is early and unrelated to the main central thrust diachronous metamorphism propagated southwards with the overall structural evolution early isograds and thrust fold structures were carried passively in the hanging wall of the main central thrust peak metamorphism based on 40 ar 39 ar hornblende ages occurred pre 30 7 2 0 ma at the top of the slab and in the middle of the slab was pre 22 1 0 ma probably 25 28 ma the lower structural levels in zanskar record peak metamorphic conditions around 700 750 c and 8 kbar reflecting depths of burial of 28 30 km a new younger schistosity which is not present in the higher structural levels was developed under kyanite grade conditions the regional distribution of high temperatures recorded by thermo barometry does not support the concept of additional heat being supplied by frictional heating along the main central thrust or magmatic heat resulting from anatexis exhumation of the himalayan metamorphic rocks was achieved by three major processes erosion as a result of crustal thickening uplift of the rocks along the hangingwall of the main central thrust above a major frontal ramp in the kishtwar window area and extensional unroofing along the footwall of a large scale ne dipping normal fault at upper crustal levels probably synchronous with compression at depth

the metamorphism in the central himalaya all along the himalayan chain an axis of crystalline rocks has been preserved made of the higher himalaya crystalline and the crystalline nappes of the lesser himalaya the salient points of the metamorphism as deduced from data collected in central himalaya central nepal and kumaun are 1 the higher himalaya crystalline also called the tibetan slab displays a polymetamorphic history with a first stage of barrovian type overprinted by a lower pressure and or higher temperature type metamorphism the metamorphism is due to quick and quasi adiabatic uplift of the tibetan slab by transport along an mct ramp accompanied by thermal refraction effects in the contact zone between the gneisses and their sedimentary cover the resulting metamorphic pattern is an apparent diachronic inverse zonation with the sillimanite zone above the kyanite zone 2 conversely the famous inverted zonation of the lesser himalaya is basically a primary pattern acquired during a one stage prograde metamorphism its origin must be related to the thrusting along the mct with heat supplied from the overlying hot tibetan slab as shown by synmetamorphic microstructures and the close geometrical relationships between the metamorphic isograds and the thrust 3 thermal equilibrium is reached between units above and below the mct far behind the thrust tip there is good agreement between the maximum temperature attained in the hanging wall and the temperature of the tibetan slab during the second metamorphic stage but closer to the mct front the thermal accordance between both sides of the thrust is due to a retrogressive metamorphic episode in the basal part of the tibetan slab

dynamics of orogenic wedges and the uplift of high pressure metamorphic rocks subduction accretion complexes can be approximated as wedge shaped continua with a rigid buttress behind and a subducting litho spheric slab beneath thick wedges undergoing prograde metamorphism have a negligible long term yield strength and are likely to exhibit a complex nonlinear viscous rheology such a wedge will tend to deform internally until it reaches a stable configuration in which the gravitational forces generated by the wedge geometry balance the traction exerted on its underside by the subducting slab accretion of material at the wedge front will lengthen the wedge and cause it to shorten internally to regain the stable geometry this shortening will be expressed as late out of sequence thrusting backthrusting and folding conversely underplating of sediment or crustal slices will thicken the wedge which may need to extend internally to regain stability extension will cause listric normal faults that may merge downward into zones of ductile extension continued underplating at depth and compensating extension above provides a mechanism for bringing high p low t metamorphic rocks to upper levels in the rear of the wedge where they are commonly observed many major tectonic boundaries in convergent orogens such as the coast range thrust in the franciscan complex major nappe contacts in the alps and the contact between the nevado filabride and higher betic nappe complexes in the betic cordillera show abrupt increases in metamorphic grade downward across them this is consistent with their origin or reactivation as uplift related extensional structures

metamorphic evolution of the high himalayan crystallines in se zanskar india the high himalayan crystallines hhc of se zanskar consist of biotite paragneisses of orthogneisses that derive from early palaeozoic granitoids of minor metabasics and of post metamorphic leucogranites of miocene age two main metamorphic events have been documented in the hhc the first event occurred at p 12 0 0 5 kbar and t 750 50 c in rare metabasics intruded by early palaeozoic granitoids in the biotite paragneisses thermobarometric estimates of the first event point to comparable t at p 4 5 kbar lower the first event is followed by a pervasive syn tectonic crystallization characterized by lower p and t on the basis of the cooling ages of the metamorphic minerals and on the geological evidence the second event is referred to the tertiary himalayan crystallization further petrological and geochronological studies are necessary to prove whether a few mineral relics ascribed to the first event define a polyphase himalayan evolution or if they record the incomplete obliteration of an older history during the himalayan event the hhc of se zanskar show a decrease in metamorphic grade from the middle structural levels upward close to the kade unit and downward close to the lesser himalaya from sillimanite k feldspar biotite bearing assemblages to kyanite staurolite muscovite bearing assemblages this metamorphic zonation is probably a consequence of the polyphase history of intracontinental thrusts and of the tectonic emplacement of hot crustal slabs within shallower and colder thrust sheets at relatively late stages of the continental collision between india and eurasia

hillslope storage boussinesq model for subsurface flow and variable source areas along complex hillslopes 1 formulation and characteristic response 1 hillslope response to rainfall remains one of the central problems of catchment hydrology flow processes in a one dimensional sloping aquifer can be described by boussinesq s hydraulic groundwater theory most hillslopes however have complex three dimensional shapes that are characterized by their plan shape profile curvature of surface and bedrock and the soil depth field studies and numerical simulation have shown that these attributes are the most significant topographic controls on subsurface flow and saturation along hillslopes in this paper the boussinesq equation is reformulated in terms of soil water storage rather than water table height the continuity and darcy equations formulated in terms of storage along the hillslope lead to the hillslope storage boussinesq hsb equation for subsurface flow solutions of the hsb equation account explicitly for plan shape of the hillslope by introducing the hillslope width function and for profile curvature through the bedrock slope angle and the hillslope soil depth function we investigate the behavior of the hsb model for different hillslope types uniform convergent and divergent and different slope angles under free drainage conditions after partial initial saturation drainage scenario and under constant rainfall recharge conditions recharge scenario the hsb equation is solved by means of numerical integration of the partial differential equation we find that convergent hillslopes drain much more slowly compared to divergent hillslopes the accumulation of moisture storage near the outlet of convergent hillslopes results in bell shaped hydrographs in contrast the fast draining divergent hillslopes produce highly peaked hydrographs in order to investigate the relative importance of the different terms in the hsb equation several simplified nonlinear and linearized versions are derived for instance by recognizing that the width function of a hillslope generally shows smooth transition along the flow direction or by introducing a fitting parameter to account for average storage along the hillslope the dynamic response of these reduced versions of the hsb equation under free drainage conditions depend strongly on hillslope shape and bedrock slope angle for flat slopes of the order of 5 only the simplified nonlinear hsb equation is able to capture the dynamics of subsurface flow along complex hillslopes in contrast for steep slopes of the order of 30 we see that all the reduced versions show very similar results compared to the full version it can be concluded that the complex derivative terms of width with respect to flow distance play a less dominant role with increasing slope angle comparison with the hillslope storage kinematic wave model of troch et al 2002 shows that the diffusive drainage terms of the hsb model become less important for the fast draining divergent hillslopes these results have important implications for the use of simplified versions of the hsb equation in landscapes and for the development of appropriate analytical solutions for subsurface flow along complex hillslopes

improvement of the hillslope storage boussinesq model by considering lateral flow in the unsaturated zone unsaturated flow is an important factor that affects groundwater motion among various drainage models the nonlinear hillslope storage boussinesq hsb model has been commonly used to predict water flux along a slope in this study we improved this model by considering lateral flow in the unsaturated zone using modified van genuchten functions we analytically expressed the concept of equivalent propagation thickness in the vadose zone this analytical expression was then incorporated into the hsb model to reflect two different stages of the drainage process and to simulate the hillslope drainage process more accurately the model results indicated that lateral flow has significant effects in the unsaturated zone during the hillslope drainage process even in sandy aquifers the amount of water contributed by the unsaturated zone is a key factor that enables a decrease in the water table during the middle and late stages of the process a comparison between the measured and simulated results based on both convergent type and divergent type hillslope drainage processes revealed that the thickness of the saturated zone decreases as the unsaturated flow increases this study emphasizes the necessity of considering unsaturated flow in the hsb model to improve the accuracy of predicting groundwater outflow rates and develop more accurate hydrographs the concept of equivalent propagation thickness also provides a criterion for assessing the importance of unsaturated lateral flow for future drainage research