pb diffusion in monazite constraints from a high t contact aureole setting abstract we report measurements of pb diffusion in natural monazite that was subjected to a static anhydrous high temperature overprint in the contact aureole of the makhavinekh lake pluton mlp northern labrador canada the 1850 ma monazite grains we studied were reheated to temperatures of 900 25 c during intrusion of mlp at 1322 ma ion microprobe depth profiling reveals the outermost 0 3 m of these grains to contain pb u gradients that can be modeled as a result of one dimensional concentration independent diffusion i e an error function profile at 1322 ma these gradients are combined with temperature time histories predicted by a numerical model of conductive heat flow in the contact aureole to calculate pb diffusion coefficients between 3 2 10 28 and 1 3 10 27 m2 s this range overlaps with the down temperature extrapolation of experimental pb diffusion data obtained under dry conditions confirming the slow diffusivity of pb in monazite at crustal temperatures and timescales

disturbance versus preservation of u th pb ages in monazite during fluid rock interaction textural chemical and isotopic in situ study in microgranites velay dome france monazite is extensively used to date crustal processes and is usually considered to be resistant to diffusive pb loss nevertheless fluid assisted recrystallisation is known to be capable of resetting the monazite chronometer this study focuses on chemical and isotopic disturbances in monazite grains from two microgranite intrusions in the french central massif charron and montasset petrologic data and oxygen isotopes suggest that both intrusions have interacted with alkali bearing hydrothermal magmatic fluids in the charron intrusion regardless of their textural location monazite grains are sub euhedral and cover a large domain of compositions u pb chronometers yield a lower intercept age of 297 4 ma an inherited component at 320 ma is responsible for the scattering of the u th pb ages the montasset intrusion was later affected by an additional f rich crustal fluid with crystallisation of ca ree fluorocarbonates fluorite calcite and chloritisation pristine monazite is chemically homogeneous and displays 208pb 232th and 206pb 238u concordant ages at 307 2 ma by contrast groundmass monazite shows dissolution recrystallisation features associated with apatite and thorite precipitation th silicate and strong chemical reequilibration 208pb 232th ages are disturbed and range between 270 and 690 ma showing that the th pb ratio is highly fractionated during the interaction with fluids apparent u pb ages are older due to common pb incorporation yielding a lower intercept age at 312 10 ma the age of the pristine monazite these results show that f rich fluids are responsible for th mobility and incorporation of excess pb which thus strongly disturbed the u th pb chronometers in the monazite

syn to post rift fault evolution in a failed rift a reflection seismic study in central cambay basin gujarat india the barmer and cambay basins india formed as rifts during the cretaceous to paleocene prior to seychelles india separation during late cretaceous both of the rifts failed subsequently and the seychelles separated from india along the current saurashtra mumbai continental margin we study the fault kinematics i e fault growth and linkages in the cambay tarapur block and comment on the fault evolution from syn to post rift stages we use fault plane topography throw length and throw depth plots to understand the kinematics of the fault planes throw length plots show the along strike linkage of faults the throw depth plots are used to understand the down and up dip linkage of the fault planes faults originating at the deccan traps level and faults confined only to post rift progressed as single fault planes along strike throughout their deformation history faults initiating within the syn rift started as multiple along strike segments and joined together as they grew along dip faults can be classified as i faults originating at deccan traps and reaching post rift ii faults originating within syn rift sediments and reaching post rift iii faults confined only within syn rift and iv faults confined only within post rift some of the syn rift faults also show spatially and temporally limited compression indicating their possible oblique slip nature the faults were normal slip or oblique slip during syn rift and thereafter they propagated as normal dip slip faults as analysed from fault plane topography showing strike perpendicular ridges such ridges may indicate only the last movement on the fault plane due to the presence of thick shale horizons in the syn rift many faults show soft linked segments along dip hydrocarbon occurrences in the shallow 1200 1600 m miocene sands can possibly be attributed to the normal faults controlling fluid flow into the reservoirs 282 words

tentative engineering approach to scour around breakwaters in random waves an approach by which the scour depth and protection layer width around the head of vertical wall breakwaters the scour and deposition depths as well as the protection layer widths at the round head of rubble mound breakwaters in random waves can be derived is presented here the formulas for scour depth by sumer and fredsoe 1997 for vertical wall breakwaters for regular waves and fredsoe and sumer 1997 for rubble mound breakwaters for irregular waves are used they are combined with describing the waves as a stationary gaussian narrow band random process to derive the scour and deposition depths as well as protection layer widths in random waves comparisons are made between the present approach and the fredsoe and sumer 1997 random wave scour data for rubble mound breakwaters

estimation of deformation temperatures flow stresses and strain rates from an intra continental shear zone the main boundary thrust nw himalaya uttarakhand india abstract this work generates thermal and tectonic data from the mylonitized rocks of the main boundary thrust mbt south and north to this major thrust the siwalik range and the lesser himalaya respectively have been receiving a renewed interest amongst the petroleum geoscientists understanding temperature flow stress and strain rates related to a major thrust is crucial in thermal mechanical modelling of the terrains adjacent to it strongly sheared proterozoic chandpur phyllites and abundant syntectonic quartz veins occur along the mbt zone one of the major foreland verging thrusts in the himalayan orogen near the sahenshahi temple at dehradun uttarakhand state india microstructure analyses show intense ductile top to s shear in terms of s c fabric and xrd analyses indicate presence of clays e g illite and clinochlore these clays not only bear the signatures of the intense fluid activity but also enhance the fault movement by reducing the mechanical strength of the fault zone rocks thermometry based on qualitative quartz grain boundary mobility 300 550 c and quantitative laser raman spectroscopy for carbonaceous materials 340 370 c reveal the maximum estimates of the deformation temperature and metamorphic temperature respectively the higher temperature microstructures can be found in lower temperature domains under the presence of fluids hence the quartz thermometry estimates a broader temperature range than the raman thermometry previous works report that the phyllites present at the base of a thrust sheet experiences deformation at

geochemical and isotopic investigation of the aquifer system in the djerid nefzaoua basin southern tunisia in the djerid nefzaoua region southern tunisia about 80 of agricultural and domestic water supply is provided by the complex terminal ct aquifer however 20 of this demand is provided by other hydraulically connected aquifers namely the continental intercalaire ci and the plio quaternary pq overexploitation of the ct aquifer for agricultural practices has contributed to the loss of the artesian condition and the decline of groundwater level which largely increased the downward leakage from the shallow pq aquifer excess irrigation water concentrates at different rates in the irrigation channels and in the pq aquifer itself then it returns to the ct aquifer and mixes with water from the regional flow system which contributes to the salinization of the ct groundwater a geochemical and isotopic study had been undertaken over a 2 years period in order to investigate the origin of waters pumped from the ct aquifer with an emphasis on its hydraulic relationships with the underlying and the overlying ci and pq aquifers geochemistry indicates that groundwater samples collected from different wells show an evolution of the water types from na cl to ca so4 cl dissolution of halite gypsum and anhydrite bearing rocks is the main mechanism that leads to the salinization of the groundwater isotopic data indicate the old origin of all groundwater in the aquifer system mixing and evaporation effects characterizing the ct and the pq aquifers were identified using 2h and 18o relationship and confirmed by the conjunction of 2h with chloride concentration

an early pliocene thermal disturbance of the main central thrust central nepal implications for himalayan tectonics since the beginning of the collision between india and asia at about 50 ma the convergence in the himalaya has largely been taken up along major thrust zones in this study samples of the lesser himalaya formations up to 10 km below the main central thrust mct and the greater himalaya sequence up to 12 km above the mct have been analyzed by the 40ar 39ar and u pb methods to investigate the thermal history of the mct the ages can be summarized as follows 1 the youngest ages from muscovites 3 1 ma biotites 3 4 ma and hornblendes 4 1 ma all come from within 1 km of the mct 2 there is a marked asymmetry of ages between the footwall and the hanging wall of the mct the maximum mica age in the hanging wall greater himalaya sequence is 13 ma whereas a muscovite 5 km below the mct in the footwall has an age spectrum with a gradient from 400 to 1400 ma 3 five k feldspars from 6 2 to 11 9 km above the mct all give minimum ages in the range 3 0 6 4 ma and 4 a 206pb 238u age on a brannerite from the greater himalayan sequence is 4 8 ma structural and petrologic observations preclude the possibility that this age distance distribution reflects faulting within the greater himalaya sequence and production of the necessary thermal energy by shear heating requires unrealistically high shear stresses infiltration of hot fluids through the mct zone appears to be the best hypothesis to explain these data simple numerical simulations which account for heat transfer by advection within the fluid flow zone and by conduction outside it indicate that the observed age distribution could have been produced by infiltration of hot fluids through the mct zone at circa 5 to 4 ma within the following range of conditions the fluids heated rocks to temperatures in the range 470 to 510 c for less than 1 million years in a region narrower than the entire mct zone the temperature of the thermal disturbance inferred from the 40ar 39ar data is consistent with petrologic data from albitic alteration assemblages in the greater himalaya sequence and the u pb age of the brannerite is similar to the youngest 40ar 39ar hornblende age this scenario hydrothermal heating culminating at about 4 ma is similar to the model of le fort 1981 for the generation of the high himalayan leucogranites in the late oligocene early miocene by dehydration of the footwall rocks of an active thrust in the younger instance we interpret that fluids derived from the footwall rocks of the main boundary thrust migrated upward through the lesser himalaya formations and were subsequently channeled along the mct producing the thermal disturbance

shisha pangma leucogranite south tibetan himalaya field relations geochemistry age origin and emplacement the shisha pangma pluton forming most of the xixabangma 8027 m massif in south tibet is one of the 20 larger leucogranite intrusives that mark the highest structural levels of the himalayan metamorphic core the pluton occurs immediately below the shisha pangma detachment a strand of the south tibetan detachment std system a low angle 30 north dipping normal fault placing paleozoic black slates atop sillimanite grade pelites and calc silicate rocks k feldspar augen gneisses containing fibrolite and sillimanite paragneisses along the footwall show strong internal s c fabrics indicative of down to the north extension the shisha pangma leucogranite is a heterogeneous polyphase intrusion with an earlier foliated biotite rich phase and a later tourmaline muscovite rich phase typically containing the assemblage kfs pl qtz ms tur gt bt sil ap the highly peraluminous granites have high 87sr 86sr ratios 0 738 0 750 typical of pelite derived anatectites nd depleted mantle model

partial high grade alteration of monazite using alkali bearing fluids experiment and nature recent advances in the dating of monazite using the electron microprobe indicate that thsio 4 and or cath po 4 2 enriched intergrowths in monazite can give ages younger than the original monazite the morphology of the intergrowths suggests that the original monazite grain has been partly altered by a fluid in which th si and ca are mobile this hypothesis has been tested in the piston cylinder apparatus at 1000 mpa and 900 c utilizing a natural unzoned th and pb bearing monazite ce and na 2 si 2 o 5 h 2 o during the experiment a subset of the monazite grains acquired thsi0 4 enriched areas with sharp compositional boundaries devoid of pb and show evidence of being a pseudomorphic partial replacement of the monazite rather than an overgrowth of the monazite these experiments support the hypothesis that similar th enriched or th depleted patches with sharp compositional boundaries observed in natural monazite could be the result of fluid induced alteration via coupled dissolution reprecipitation if so such altered regions would yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of single or multiple metasomatic events assuming that all pre existing radiogenic pb is removed during alteration

growth of lithosphere scale fault system in ne tibet numerical modeling constrained by high resolution seismic reflection data abstract the east kunlun fault is an important strike slip shear zone to understand continental deformation in ne tibet the recent high resolution deep seismic reflection profiling across the kunlun fault reveals a thrust fault system and two decollements in the crust along with another thrust fault system which reaches to the depth of upper mantle and cuts off the moho the mechanism of the growth of these shear zones at lithosphere scale which reveals the type of deep deformation is investigated using the finite element method with an elastic plastic constitutive relationship the results show that the thrust fault system in the crust may be explained by the conjugated plastic deformation belts under compression from the indian plate the pre existing fault in the depth may develop to cut the moho toward two new directions rather than along the original direction the vertical and lateral heterogeneity of material frictional property and geometry of the models all affect the feature of the fault growth the growth of the thrust fault system on both sides of the kunlun fault is only located in the crust it means that the kunlun fault does not reach to the moho depth

orogen parallel ductile extension and extrusion of the greater himalaya in the late oligocene and miocene 1 predominant stretching structures in the greater himalayan crystalline complex ghc trend perpendicular to the belt and are linked to the southward exhumation or emplacement of the ghc between the south tibet detachment std and the main central thrust however our field investigations in southern tibet reveal the widespread presence of gently dipping shear zones with a penetrative orogen parallel stretching lineation which separates the tethyan himalayan sequence and the underlying ghc the shear zones are well preserved in the upper part of the ghc south to and structurally lower than the std field criteria microstructures and quartz fabrics indicate top to the east shearing in the yadong shear zone eastern ghc coexistence of top to the east and top to the west shearing in the nyalam shear zone central ghc but top to the west shearing in the pulan shear zone western ghc characteristic microstructures and slip systems of quartz in the high grade ghc rocks resulted from the lateral flow under upper amphibolite up to 650 700 c to greenschist facies conditions u pb ages of metamorphic zircon rims by sensitive high resolution ion microprobe shrimp and laser ablation multi collector inductively coupled plasma mass spectrometry la mc icp ms analyses yield 28 26 ma for the initiation of the yadong and nyalam shear zones and 22 15 ma for the activation of the pulan shear zone in addition 40ar 39ar cooling ages of biotite and muscovite suggest cessation of ductile sharing at 13 11 ma on the yadong shear zone which is coeval with the activation of the std combined with previous studies we propose that initiation of orogen parallel extension marks the transition from burial crustal thickening to exhumation of the ghc due to lateral crustal thickness gradients in a thickened crust orogen parallel gravitational collapse occurred within the convergent himalayan orogen in the late oligocene miocene this tectonic denudation triggered and enhanced partial melting and ductile extrusion of the ghc in the miocene

study on the hydrochemical characteristics of groundwater along the taklimakan desert highway groundwater is the only water source of the shelterbelt along the taklimakan desert highway in northwestern china understanding the hydrochemical zoning characteristics material source and hydrochemical processes of this desert groundwater is important for rational groundwater exploitation meanwhile determining the location of the dividing boundary which divides the influence ranges of the tarim river and the kunlun mountain river system on the desert groundwater is meaningful for the local desert hydrogeological study for these objectives 105 groundwater samples were investigated to obtain analytical data of groundwater chemistry and ionic relations methods including ratio graphs and gibbs plots were applied in the chemical analysis for these data chemical analysis shows that desert groundwater is characterized by cl so4 na mg and cl so4 na types with total dissolved solid tds of 2 80 29 77 g l spatial variation patterns of major ions tds and so42 cl molar ratio reveal clear four hydrochemical zones along the groundwater flow direction on one hand on the other hand these variation patterns also indicate that the boundary dividing the influence ranges of the tarim river and the kunlun mountain river system is the approximate location of well 030 ratio graphs show that the average molar ratios na k cl 1 05 and ca2 mg2 so42 0 93 are approximately equal to 1 and there is an approximately linear correlation between na k and so42 these results reveal that the groundwater composition is mainly influenced by dissolution of evaporate halite gypsum and mirabilite moreover ionic relations demonstrate that the dominating hydrochemical processes in the groundwater evolution are evaporation and cations exchange

muscovite 40ar 39ar ages help reveal the neogene tectonic evolution of the southern annapurna range central nepal we present new muscovite 40 ar 39 ar ages from thirteen greater himalayan rocks and one lesser himalayan rock collected from four north trending transects across the southern annapurna range combining the new data with previously published ages leads to the following new insight into the tectonic development of the southern annapurna muscovite cooling ages from greater himalayan rocks are c 16 10 ma in the western annapurna and c 6 2 ma in the eastern annapurna revealing a decrease of 4 14 ma from west to east similarly the muscovite cooling age from one lesser himalayan rock in the west is c 7 ma and ages from several samples in the east are c 5 2 ma indicating a decline of 2 5 ma towards the east earlier cooling in the western annapurna can be explained by along strike differences in the geometry of the frontal ramp on the underlying thrust that carries these greater and lesser himalayan rocks and or by a ne striking fault that cut these rocks in greater himalayan rocks from the modi river valley one sample yielded muscovite 40 ar 39 ar ages of 18 0 0 7 and 16 2 0 5 ma for grain sizes of approximately 750 and 200 m respectively in contrast a sample collected 200 m structurally lower produced ages of 12 6 0 2 and 9 9 0 1 ma for these two grain sizes the north dipping bhanuwa fault has been proposed between these samples with different authors arguing for normal or thrust sense motion our newfound pattern of an older muscovite 40 ar 39 ar age pair in the hanging wall supports arguments for the existence of the bhanuwa fault and suggests normal sense motion

records of the evolution of the himalayan orogen from in situ th pb ion microprobe dating of monazite eastern nepal and western garhwal abstract in situ th pb monazite ages from rocks collected along two transects the dudh kosi everest eastern nepal and the bhagirathi river garhwal himalaya india perpendicular to the main central thrust mct suggest a striking continuity of tectonic events across the himalaya the youngest age reported in this study 5 9 0 2 ma mswd 0 4 from matrix monazite grains collected beneath the mct in the garhwal region is consistent with several age data from rocks at similar structural levels in central nepal providing support for widespread late miocene mct activity the lateral parallelism of orogenic events is further manifested by the 20 7 0 1 ma age of a high himalayan leucogranite from an injection complex that outcrops along the dudh kosi everest transect resembling ages of these bodies reported elsewhere the youngest monazite grain analyzed along the dudh kosi everest transect is 10 3 0 8 ma the absence of 7 3 ma monazite ages in eastern nepal may reflect a different nappe structure which obscures the reactivated ramp equivalent exposed in the garhwal and central nepal garnets from the mct hanging wall greater himalayan crystallines and footwall lesser himalaya display different major element zoning and the patterns are useful for constraining the location of the thrust system that separates the two lithologies pressure temperature paths for two upper lesser himalayan garnets that contain monazite inclusions indicate the utility of an in situ methodology to constrain the metamorphic evolution of the shear zone along the dudh kosi everest transect upper lesser himalayan monazite grains from three rocks record a clear signal at 14 5 0 1 ma mswd 8 4 and the 23 ma age that characterizes the hanging wall is notably absent monazites collected within a large scale greater himalayan crystallines fold yield the 14 ma age consistent with the structure forming due to mct related compression paleo mesoproterozoic 1407 35 ma matrix monazite grains are found within an augen gneiss unit located beneath the mct whereas cambro ordovician 436 8 548 17 ma inclusions are preserved within garnets of the greater himalayan crystallines the presence of 45 2 2 1 ma grains from lower structural levels of the greater himalayan crystallines indicates the unit realized conditions conducive for monazite growth during the eocene

higher himalayan shear zone sutlej section structural geology and extrusion mechanism by various combinations of simple shear pure shear and channel flow in shifting modes the higher himalayan shear zone hhsz in the sutlej section reveals 1 top to sw ductile shearing 2 top to ne ductile shearing in the upper and the lower strands of the south tibetan detachment system stdsu stdsl and 3 top to sw brittle shearing corroborated by trapezoid shaped minerals in micro scale in the proposed extrusion model of the hhsz the e1 phase during 25 19 ma is marked by simple shearing of the upper sub channel defined by the upper strand of the main central thrust mctu and the top of stdsu as the lower and the upper boundaries respectively subsequently the e2a pulse during 15 14 ma was characterized by simple shear pure shear and channel flow of the entire hhsz finally the e2b pulse during 14 12 ma observed simple shearing and channel flow of the lower sub channel defined by the lower strand of the main central thrust mctl and the top of the stdsl as the lower and the upper boundaries respectively the model explains the constraints of thicknesses of the stdsu and the stdsl along with spatially variable extrusion rate and the inverted metamorphism of the hhsz the model predicts 1 shear strain after ductile extrusion to be maximum at the boundaries of the hhsz which crudely matches with the existing data the other speculations that cannot be checked are 2 uniform shear strain from the mctu to the top of the hhsz in the e1 phase 3 fastest rates of extrusion of the lower boundaries of the stdsu and the stdsl during the e2a and e2b pulses respectively and 4 variable thickness of the stdsl and rare absence of the stdsu non parabolic shear fabrics of the hhsz possibly indicate heterogeneous strain the top to sw brittle shearing around 12 ma augmented the ductile extruded rocks to arrive a shallower depth the brittle ductile extension leading to boudinage possibly did not enhance the extrusion

tectonics of the himalaya an introduction soumyajit mukherjee1 rodolfo carosi2 peter van der beek3 barun kumar mukherjee4 delores m robinson5 department of earth sciences indian institute of technology bombay powai mumbai 400 076 maharashtra india dipartimento di scienze della terra v valperga caluso 35 10125 torino italy universite grenoble alpes institut des sciences de la terre 38041 grenoble france petrology and geochemistry group wadia institute of himalayan geology 33 gms road dehra dun 248001 india department of geological sciences university of alabama 201 7th ave room 2003 bevill building tuscaloosa al 35487 usa

stable isotopic and geochemical characteristics of groundwater in kherlen river basin a semi arid region in eastern mongolia summary inorganic solute ion concentrations and stable isotopes of oxygen and hydrogen in groundwater river water and precipitation were investigated to gain insight into the groundwater recharge process in the kherlen river basin a semi arid region in eastern mongolia the solute constituents in the river water main stream were of ca hco3 type spatially invariant and low in concentration groundwater in the upstream region was also characterized by a ca hco3 type though all ion concentrations were higher than in the river water on the other hand the chemical composition of the groundwater in the midstream region southern and eastern was spatially variable and the na mg2 cl and hco 3 concentrations were considerably higher than in the river water and upstream groundwater the stable isotopic compositions showed an evaporation effect on the groundwater and river water as well as an altitude effect in the precipitation and river water preferential recharge by relatively large rainfall events is thought to have caused the depleted isotopic ratio in the groundwater in the dry regions the stable isotope chemical and hydrological data suggest that the main stream water of the kherlen river is recharged by precipitation that falls in a headwater region at an altitude of more than 1650 m and that the interaction between the groundwater and river water is not dominant in the midstream and downstream regions of the river basin

need for re apprehension of basin tectono depositional set up during initial stage of himalayan orogeny from pedogenic evidences abstract the collision and suturing of indian and eurasian plates about 50 ma ago closed the tethys ocean initiated himalayan orogen and a foreland basin developed towards its south the last phase of marine sedimentation in indian sub continent during paleocene eocene is represented by subathu formation overlain by continental dagshai sediments and nature of this transition named as passage beds sensu bhatia and mathur 1965 is controversial further it is poorly understood both in terms of depositional environment and age surprisingly these beds show evidences of pedogenesis but no such palaeopedological studies have been reported so far the degree and nature of pedogenesis is widely used in solving diverse geological problems in complex geological settings therefore pedogenesis of these beds exposed in the shimla hills of subathu sub basin has been worked out morphological and micromorphological studies divide them into older green greenish grey pedofacies gp and younger red reddish brown pedofacies rp units pedons are up to tens of centimeters thick structure largely comprises sub angular to sub rounded blocky peds a suite of pedogenic features include burrows root traces infillings mottling cutans segregations and nodules which vary in dominance from gp to rp unit greenish grey pedons are characterized by mottles fe mn oxide segregations whereas reddish brown pedons by root traces commonly filled with carbonates presence of carbonate segregations and cutans detailed field and laboratory studies at various local and regional exposures can reveal the nature and extent of pedogenesis which will be significant to enact depositional environment as well as stratigraphic position of passage beds co relatable at different localities throughout length of the himalaya from pakistan to nepal because of their distinctive lithology and stratigraphic position such studies bear global significance in demonstrating the use of palaeosols as a geologic archive in complex geological settings

peridotitic minerals of the nidar ophiolite in the nw himalaya sourced from the depth of the mantle transition zone and above the nidar ophiolite complex noc consists of a c 10 km thick ophiolite suite in the nw himalaya india the c 7 km thick lower ultramafic part of the ophiolite body terminates against the tso morari crystallines which represent the leading edge of the indian continental margin mineral inclusions from the peridotites in the lower ultramafic part of the noc were studied including c 2 c clinoenstatite disordered coesite and high pressure mg 2 sio 4 probably mg 2 sio 4 these minerals found in two lherzolite bodies from the ophiolite s mantle section were characterized by laser raman spectroscopy and electron micro probe analysis textural evidence supporting decompression from an ultra high pressure condition was also observed such as cr spinel exsolution needles in olivine crystals the systematic mineral phase transitions of coesite quartz high pressure clinoenstatite orthoenstatite and mg 2 sio 4 cr spinel exsolution needles in olivine suggest that the mantle section of the nidar ophiolite evolved from the deep mantle beneath a palaeo spreading centre the phase stabilities of these high pressure minerals require derivation from the depth of the mantle transition zone 410 660 km a transport mechanism for these minerals is suggested via dunite channels along a mantle adiabat in the focused convective flow below the spreading centre this mechanism brought these deep mantle phases into the ultramafic part of the noc these observations suggest that some part of the mantle section of the noc in the nw himalaya originated in a mid ocean ridge setting

channel flow extrusion model to constrain dynamic viscosity and prandtl number of the higher himalayan shear zone constraining magnitudes of mechanical and thermo mechanical parameters of rocks and shear zones are the important goals in structural geology and tectonics talbot in j struct geol 21 949 957 1999 such parameters aid dynamic scaling of analogue tectonic models ramberg in gravity deformation and the earth s crust in theory experiments and geological applications 2nd edn academic press london 1981 which are useful to unravel tectonics in further details schultz ela and walsh in j struct geol 24 247 275 2002 the channel flow extrusion of the higher himalayan shear zone hhsz higher himalaya can be explained by a top to s sw simple shear i e the d2 deformation in combination with a pressure gradient induced flow against gravity presuming its newtonian incompressible rheology with parallel inclined boundaries the viscosity of this shear zone along a part of the himalayan chain through india nepal and bhutan is estimated to vary widely between 1016 and 1023 pa s and its prandtl number pr within 1021 1028 the estimates utilized ranges of known thickness 6 58 km of the hhsz that of its top subzone of ductile shear of normal shear sense stdsu 0 35 9 4 km total rate of slip of its two boundaries 0 7 131 mm year 1 pressure gradient 0 02 6 kb km 1 density 2 2 3 1 g cm 3 and thermal diffusivity 0 5 10 6 2 1 10 6 m s 2 along the orogenic trend considering most of the parameters specifically for the sutlej section india the calculated viscosity and the prandtl number pr of the hhsz are deduced to be 1017 1023 pa s and pr 1022 1028 the upper limits of the estimated viscosity ranges are broadly in conformity with a strong tibetan mid crust from where a part of the hhsz rocks extruded on the other hand their complete ranges match with those for its constituent main rock types and partly with those for the superstructure and the infrastructure the estimated mechanical and thermo mechanical parameters of the hhsz will help to build dynamically scaled analogue models for the himalayan deformation of the d2 phase

higher himalayan shear zone zanskar indian himalaya microstructural studies and extrusion mechanism by a combination of simple shear and channel flow thin section studies of the zanskar shear zone zsz rocks reveal a top to sw and subsequent primary and secondary top to ne ductile shearing brittle ductile and brittle extensions top to sw brittle shear steep normal faulting and fracturing in the proposed two phase model of ductile extrusion of the higher himalayan shear zone hhsz a top to sw simple shearing during 22 18 ma was followed by a combination of top to sw simple shear and channel flow at 18 16 ma the second phase simulates a thin zsz characterized by a top to ne shearing the channel flow component ceased around 16 ma the extruding hhsz entered the brittle regime but the top to sw shearing continued until perturbed by faults and fractures variation in the extrusion parameters led to variable thickness of the zsz shear strain after the extrusion is presumably maximum at the boundaries of the hhsz and falls towards the base of the zsz which crudely matches with the existing data the other predictions 1 spatially uniform shear strain after the first stage 2 fastest extrusion rate at the base of the zsz and 3 a lack of continuation of the zsz along the himalayan trend are not possible to validate due to paucity of suitable data non parabolic shear fabrics of the zsz indicate their heterogeneous deformation

ion probe u th pb zircon dating of polymetamorphic orthogneisses from northern labrador canada rounded zircons included within igneous zircons from the uivak i gneisses northern labrador have ages of up to 3863 12 ma 2 showing the former existence of rocks that predate the uivak gneisses by more than 100 ma the igneous zircons themselves have experienced varying amounts of early pb loss but age estimates based on maximum 207pb 206pb from three separate gneiss samples agree to within error at 3732 6 ma 2 which is taken as the age of emplacement of the igneous precursor to the dominant component of the uivak gneisses a new generation of zircons was formed during migmatization at ca 3620 ma the volumetrically less important lister gneiss was emplaced at 3235 8 ma 2 in the late archaean different parts of the gneiss complex were subjected to different grades of metamorphic overprinting the zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events with simultaneous recrystallization of old zircons and growth of new u poor zi

deformation and kinematic evolution of the subsurface structures zagros foreland fold and thrust belt northern dezful embayment iran the dezful embayment is located in the foreland part of the zagros fold and thrust belt structural style of folding and thrusting vary in the dezful embayment in this study balanced cross sections and subsurface data including 2d seismic profiles and wells data decoded structural style of the subsurface structures in the northern dezful embayment presence of the multiple decollement horizons is the main controlling factor of the structural style in this area the subsurface anticlines have been formed between two main decollement horizons which include the miocene gachsaran formation as upper decollement and permian dashtak evaporites and lower cretaceous garau shales as the middle decollement horizons geometry of the subsurface anticlines differs much vertically and horizontally growth strata indicate folding is started in middle miocene time in this region anticlines formed as open wide and disharmonic structures active processes in the evolution of anticlines are limb rotation and hinge migration which was resulted in increase of inhomogeneous shortening rate more shortening rate indicates more structural relief in anticlines these anticlines are formed as a detachment folds in initiation and then during their evolution converted to fault propagation fold and fault bend fold final geometric shape of these anticlines depends on the geometry of thrusts propagation that formed in the forelimb

synkinematic magmatism heterogeneous deformation and progressive strain localization in a strike slip shear zone the case of the right lateral karakorum fault 1 new structural observations coupled with 15 u pb and 24 ar ar new ages from the karakorum shear zone ksz constrain the timing and slip rate of the right lateral karakorum fault zone kfz one of the great continental asian strike slip faults in the tangtse darbuk area the tangtse sw and muglib ne mylonitic strands of the ksz frame the less deformed pangong range inherited u pb ages show that granitic protoliths are mostly from the karakorum and ladakh batoliths with a major miocene melting event lasting from 21 5 to 13 5 ma some of the miocene granitic bodies show structural evidence for intrusion synkinematic to the ksz the oldest of these granitoids is 18 8 0 4 ma old implying that deformation started prior to 19 ma microstructural data show that right lateral deformation pursued during cooling ar ar data show that ductile deformation stopped earlier in the tangtse 11 ma than in the muglib strand 7 ma deformation ended at 11 ma in the tangtse strand while it is still active in the muglib strand suggesting a progressive localization of deformation when merged with published observations along the kfz these data suggest that the kfz nucleated in the north ayilari range at least 22 ma ago the long term fault rate is 0 84 to 1 3 cm yr considering a total offset of 200 to 240 km the ksz collected magma produced within the shear zone and or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow

scour below marine pipelines in shoaling conditions for random waves abstract this paper provides an approach by which the scour depth below pipelines in shoaling conditions beneath non breaking and breaking random waves can be derived here the scour depth formula in shoaling conditions for regular non breaking and breaking waves with normal incidence to the pipeline presented by cevik and yuksel cevik e and yuksel y 1999 scour under submarine pipelines in waves in shoaling conditions asce j waterw port coast ocean eng 125 1 9 19 combined with the wave height distribution including shoaling and breaking waves presented by mendez et al mendez f j losada i j and medina r 2004 transformation model of wave height distribution on planar beaches coast eng 50 3 97 115 are used moreover the approach is based on describing the wave motion as a stationary gaussian narrow band random process an example of calculation is also presented

north south extension within the convergent himalayan region recent work by burg et al 1984 indicates the presence of east west striking gently north dipping normal faults in the higher himalayas and southern tibet that formed during postcollisional convergence of india and tibet these faults extend for at least 800 km along strike we interpret these normal faults as probable late miocene extensional features with perhaps several tens of kilometres of down to the north displacement a simple elastic model suggests that these normal faults may have formed during gravitational collapse of the miocene topographic front between india and tibet in this interpretation gravitational collapse occurred by southward motion relative to india and tibet of a wedge of crustal rocks bounded above by gently north dipping normal faults and below by thrust faults that probably dip north north south extension produced in this way is probably confined to upper crustal levels only and does not reflect regional extension of the entire lithosphere

two mica and tourmaline leucogranites from the everest makalu region nepal tibet himalayan leucogranite genesis by isobaric heating in the higher himalaya of the region from cho oyu to the arun valley northeast of makalu the miocene leucogranites are not hosted only in the upper high himalayan crystallines hhc a network of dykes also cuts the lower hhc and the lesser himalayan crystallines lhc the plutons and dykes are mainly composed of two mica muscovite biotite tourmaline cordierite andalusite sillimanite leucogranite with tourmaline 2 6 and biotite 1 5 modal and tourmaline muscovite tourmaline biotite sillimanite garnet kyanite andalusite spinel corundum leucogranite with tourmaline 2 2 and biotite 1 5 modal both leucogranite types were produced by partial melting in the andalusite sillimanite facies series under lp ht conditions constrained by the occurrence of peritectic andalusite and cordierite the geochemical features of the leucogranites suggest that tourmaline leucogranite was produced by muscovite dehydration melting in muscovite rich metapelites at p 350 mpa and t 640 c whereas two mica leucogranite was produced by biotite dehydration melting in biotite rich metapelites at p 300 mpa and t 660 710 c melting in fertile muscovite rich metapelites of the top of both the hhc and lhc produced magmas which were emplaced at the same structural level in which they had been generated melting in the biotite rich gneiss of both the hhc and lhc produced hotter magmas which were transported upwards by dyking and eventually coalesced in the plutons of the upper hhc a similar process also produced a network of two mica granite at the top of the lhc in the ama drime nyonno ri range northeast of makalu the prograde character of leucogranite melt producing reactions in the everest makalu area suggests that here the generation of miocene leucogranites took place in a regime of nearly isobaric heating following nearly adiabatic decompression

crustal structure and variability of the himalayan border of tibet reversed critical wide angle reflection profiles of the crust mantle boundary south of the yarlung zangbo suture in tibet reveal a deep 70 km moho extending north from the high himalayas whilst to the south the moho is 15 km higher even further south reflections from 35 km depth may correspond to the moho of peninsular india

leucogranite intruding the south tibetan detachment in western nepal implications for exhumation models in the himalayas the most popular models regarding the exhumation of the greater himalayan sequence ghs such as extrusion channel flow critical taper and wedge extrusion require prolonged activity of the two bounding shear zones and faults the main central thrust mct and the south tibetan detachment std we present the crystallization age of an undeformed leucogranite that intrudes both the ghs and the tethyan himalaya sequence ths zircon and monazite u pb ages in the leucogranite give ages between 23 and 25 ma constraining at that time the end of shearing along the std our results limit the contemporaneous activity of the mct and std to a short period of time 1 2 ma and thus argue against exhumation models requiring prolonged contemporaneous activity of the mct and std

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

flow exchange between the deep and shallow groundwaters in the sbeϊtla synclinal basin tunisia an isotopic approach stable 18o 2 h and radiogenic 3h 14c isotopes of water have been used to constrain the source origin age migration pathway and mixing processes in the sbeitla tunisia system the system is composed of an upper unconfined middle miocene aquifer with a variable thickness from 10 300 m an intermediate confined unconfined lower miocene aquifer about 100 m thick and a deeper confined lower cretaceous aquifer about 150 m thick separated by a thin clay layer a total of 53 groundwater samples from the three aquifers and spring samples were collected during february and march 2000 and isotopically analysed using conventional methods the stable isotopes composition of waters establishes that the deep groundwater depleted as compared to present corresponding local rainfall is ancient water recharged probably during the late pleistocene and the early holocene periods the relatively recent water in the superficial aquifer is composed of mixed waters resulting presumably from upward leakage from the deeper groundwater the radiogenic 3h 14c isotopes data confirm that the recent water with a tritium content between 6 5 and 19 tu represents post nuclear recharge and the ancient groundwater with low carbon 14 contents between 7 and 26 pmc infiltrated between 8 000 to 20 000 years ago when used in conjunction with the stable isotopes data the mixing process can be clearly identified especially in the sbeitla sill area groundwater of the upper aquifer exhibits isotopic signatures of both the old and recent waters by using isotopic mass balance the computed contribution of the deep groundwater in recharging the upper aquifer is up to 94

spatial characteristics and controlling factors of chemical weathering of loess in the dry season in the middle loess plateau china hydrochemistry methods were used to decipher the weathering and geochemical processes controlling solute acquisition of river waters in the dry season in the middle loess plateau mlp one of the most severely eroded areas and turbid riverine systems in the world river waters were neutral to slightly alkaline with ph varying from 7 6 to 9 6 the total dissolved solids decreased from northwest to southeast with a mean value of 804 mg l much higher than the global average and other large rivers in china ternary diagram showed that river waters were dominated by na hco3 and cl with the main water type of hco3 cl na saturation index values mg2 ca2 and hco3 analyses indicated the preferential ca2 removal by calcite precipitation gibbs plots and stoichiometry plots indicated that the dissolved solutes were mainly derived from rock weathering with minor anthropogenic and atmospheric inputs samples in the northwestern basin are also influenced by evaporation a forward model of mass budget calculation showed that owing to high soluble characteristics evaporite dissolution was a major feature of river waters and contributed 41 to the total dissolved cations on average while carbonate and silicate weathering contributed 28 and 25 on average respectively besides evaporite dissolution cation exchange is also responsible for the high concentrations of na in river water spatial variations showed that evaporite dissolution and silicate weathering were higher in the northern basin whereas carbonate weathering was higher in the southern basin different from most rivers in the world the physical erosion rates varying from 117 7 to 4116 6 t km2y are much higher than the chemical weathering rates varying from 3 54 to 6 76 t km2y in the mlp because of the loose structure of loess and poor vegetation in the basin in the future studies on comparison of water geochemistry in different seasons and on influence of different types of land use and soil salinization on water geochemistry denudation rates and water quality should be strengthened in the mlp these results shed some lights on processes responsible for modern loess weathering and also indicate the importance of time series sampling strategy for river water chemistry copyright 2016 john wiley sons ltd

heat capacities and entropies of sillimanite fibrolite andalusite kyanite and quartz and the al2sio5 phase diagram low temperature heat capacities for sillimanite fibrolite and both fine grained and coarse grained quartz have been measured superambient heat capacities have been measured for four sillimanite two andalusite one kyanite and two fibrolite samples the following equations are recommended for the temperature dependence of the heat capacities of kyanite andalusite sillimanite and fibrolite

microstructures and strain variation evidence of multiple splays in the north almora thrust zone kumaun lesser himalaya uttarakhand india abstract the north almora thrust zone natz marks the boundary of the almora crystalline complex acc against the lesser himalayan sedimentary sequence lhs in the north its southern counterpart the south almora thrust sat is a sharply marked contact between the acc and the lhs in the south published studies argue various contradictory emplacement modes of the north almora thrust recent studies have implied splays of smaller back thrusts in the natz the present study investigates meso and microstructures and strain distribution in the natz and compares it with strain distribution across the sat in the natz field evidence reveals repeated sequence of 10 500 m thick slices of proto to ultra mylonite thrust over the lesser himalayan rautgara quartzite in accordance with the field evidence the strain analysis reveals effects of splays of smaller thrust in the natz the study therefore argues that contrary to popular nomenclature the northern contact of the acc with the lhs is not a single thrust plane but a thrust zone marked by numerous thrust splays

review on symmetric structures in ductile shear zones symmetric structures in ductile shear zones range widely in shapes and geneses matrix rheology its flow pattern its competency contrast with the clast degree of slip of the clast shear intensity and its variation across shear zone and deformation temperature and degree of confinement of clast in shear zones affects independently the degree of symmetry of objects kinematic vorticity number is one of the parameters that govern tail geometry across clasts for example symmetric and nearly straight tails develop if the clast matrix system underwent dominantly a pure shear compression prolonged deformation and concomitant recrystallization can significantly change the degree of symmetry of clasts angular relation between two shear zones or between a shear zone and anisotropy determines fundamentally the degree of symmetry of lozenges symmetry of boudinaged clasts too depends on competency contrast between the matrix and clast in some cases and on the degrees of slip of inter boudin surfaces and pure shear parasitic folds and post tectonic veins are usually symmetric

fluid induced disturbance of the monazite th pb chronometer in situ dating and element mapping in pegmatites from the rhodope greece bulgaria abstract the monazite th pb chronometer is widely used in a variety of geological contexts but may be affected by interaction with fluids in the central part of the rhodope massif greece bulgaria synfolial pegmatite veins were emplaced within two major synmetamorphic shear zones in the chepelare shear zone czs which displays no evidence of post metamorphic fluid flow consistent monazite th pb ages of 36 ma are interpreted as dating vein emplacement higher in the metamorphic pile zircon and monazite give u th pb ages of 42 ma for vein emplacement in the nestos shear zone nsz pegmatites show evidence of post emplacement interaction with fluids during greenschist facies ductile deformation evidence for this includes the precipitation of calcite in microscale tension gashes within feldspar porphyroclasts and the oxygen isotope disequilibrium between quartz and feldspar aqueous carbonic fluids deriving from carbonate lithologies in the footwall of the nsz are identifiable in the pegmatites by the high 18 o value of quartz up to 21 8 and the presence of calcium in calcite veinlets in these samples some of the monazite grains show large intragrain scattering of th pb age spanning up to 12 ma with intergrain scattering reaching 16 ma from 39 to 55 ma within individual grains age domains correlate with chemical heterogeneities and some show a characteristic ca excess these chemical and isotopic alterations are interpreted to be caused by interaction with fluids derived from carbonate lithologies complementary u pb data on zircons from the nsz pegmatites yield mostly mesozoic ages related to an older metamorphic cycle and an age of 48 ma for one grain with typical magmatic zoning the th pb ages of 49 3 1 6 to 54 9 1 7 ma probably relate to the emplacement of the pegmatites the spread of younger th pb ages from 38 6 1 1 to 46 2 1 6 ma probably reflects the period of fluid circulation during progressive cooling to greenschist facies conditions or variable perturbations of the monazite isotope system during fluid assisted greenschist facies deformation this is consistent with 39 ar 40 ar mica ages of 32 to 34 ma interpreted as a tighter constraint for the timing of the greenschist facies metamorphism this study illustrates the capacity of monazite to record distinct events in a single rock and highlights the need for identifying the potential involvement of fluids in order to interpret monazite ages

role of grain size in phyllonitisation insights from mineralogy microstructures strain analyses and numerical modeling abstract brittle y and p planes exist in an exposure of greywacke in the garhwal lesser himalaya india although y planes are well developed throughout the p planes are prominent only in some parts domain a and not elsewhere domain b to investigate why the p planes developed selectively the following studies were undertaken 1 clay separated xrd analyses clinochlore and illite are present in both the domains 2 strain analyses by rf method it deduces strain magnitudes of 1 8 for the ductile deformed quartz grains from both the domains a and b 3 grain size analyses of quartz clasts domain a is mostly composed of finer grains area up to 40 000 m2 whereas domain b consists of a population of coarser grains area 45 000 m2 a 2d finite element modeling of linear elastic material was performed using comsol software to investigate the control of grain size variation on the generation brittle shear planes the results of numerical modeling corroborate the known fact that an increase in grain size reduces the elastic strain energy density a broader grain size distribution increases the effects of diffusion creep and resists the onset of dislocation creep thus rocks with coarser grain population domain b tend to resist the generation of shear fractures unlike their fine grained counterpart domain a

hydrochemical characteristics controlling factors and solute sources of groundwater within the tarim river basin in the extreme arid region nw tibetan plateau abstract in the extreme arid region of the tarim river basin trb groundwater is the most valuable resource for people s lives and regional ecology major ion concentrations of groundwater were analyzed to decipher hydrochemistry temporal and spatial variations solute sources and controlling factors of the groundwater within the trb groundwaters in this area were neutral to alkaline in nature and most of them were hard brackish waters dominated by na ca mg cl and so4 ions the total dissolved solid tds varied over two orders of magnitude with a mean value of 2044 mg l in wet season and 3091 mg l in dry season about 1 2 times higher than those in river water in this area hydrochemical types and chemical compositions of groundwaters showed zonal distribution mineral dissolution and evaporation were the main processes responsible for high solutes in groundwater ion exchange between na on clay minerals and ca mg in groundwater increased na concentrations groundwater was oversaturated with respect to dolomite calcite and aragonite and under saturated with respect to gypsum and halite a forward model of mass budget calculation showed that evaporite dissolution carbonate weathering silicate weathering and atmospheric input contributed 58 14 25 12 13 2 and 4 2 of the total dissolved cations on average in wet season and 68 13 20 12 10 2 and 2 1 in dry season for the whole basin respectively spatial variations of rock weathering were significant with higher evaporite dissolution in the southern basin and higher carbonate weathering in the northern basin although anthropogenic inputs were minor the majority of samples were not suitable for drinking with reference to tds f and or so 4 2 these results can enhance the understanding of hydrochemical characteristics in desert environments and provide information for the material sources of lop nor

tectonometamorphic discontinuities within the greater himalayan sequence in western nepal central himalaya insights on the exhumation of crystalline rocks abstract the core of the greater himalayan sequence in the mugu karnali area western nepal is affected by a thick shear zone with development of nearly 4 km of mylonites mangri shear zone it is a contractional shear zone showing a top to the sw and wsw sense of shear the shear zone developed during the decompression in the sillimanite stability field of rocks that previously underwent relatively high pressure metamorphism deformed under the kyanite stability field p t conditions indicate that the footwall experienced higher pressure 1 0 0 9 gpa than the hanging wall 0 7 gpa and similar temperatures 675 700 c u pb in situ dating of monazites indicate a continuous activity of the shear zone between 25 and 18 ma samples from the lower part of the greater himalayan sequence underwent similar ductile shearing at 17 13 ma these ages and the associated p t t paths revealed that peak metamorphic conditions were reached 5 7 ma later in the footwall of the shear zone with respect to the hanging wall pointing to a diachroneity in the metamorphism triggered by the shear zone itself mangri shear zone with the other recently documented tectonic and metamorphic discontinuities within the greater himalayan sequence point to the occurrence of a regional tectonic feature the high himalayan discontinuity running for more than 500 km along the strike of the central himalayas it was responsible of the exhumation of the upper part of the greater himalayan sequence starting from 28 ma well before the activation of the main central thrust and the south tibetan detachment our data point out that exhumation of the greater himalayan sequence was partitioned in space and time and different slices were exhumed in different times starting from the older in the upper part to the younger in the lower one

high resolution 5 μm u th pb isotope dating of monazite with excimer laser ablation ela icpms abstract monazite lree po 4 a common accessory mineral in magmatic and metamorphic rocks is complementary to zircon in u th pb geochronology because the mineral can record successive growth phases it is useful for unravelling complex geological histories a high spatial resolution is required to identify contrasted age domains that may occur at the crystal scale bulk mineral techniques such as id tims applied to single monazite grains recording multiple overgrowths or isotope resetting can result in partly scattered discordant analytical points that produce inaccurate intercept ages laser ablation la icpms has been demonstrated to be a useful technique for u th pb dating of zircons and this study tests its analytical capabilities for dating monazite a sector field high resolution icpms coupled with a 193 nm arf excimer laser ablation microprobe is capable of achieving a high spatial resolution and producing stable and reliable isotope measurements the u th pb systematic was applied to monazite grains from several samples a lower palaeozoic lens from high grade terrains in southern madagascar neogene hydrothermal crystals from the western alps a palaeoproterozoic very high temperature granulite from central madagascar and a variscan leucogranite from spain directly on a polished thin section the major aim was to compare and or reproduce tims and emp ages of monazite from a variety of settings and ages the three independent 206 pb 238 u 207 pb 235 u and 208 pb 232 th ratios and ages were calculated isotope fractionation effects mass bias laser induced fractionation were corrected using a chemically homogeneous and u pb concordant monazite as external standard this study demonstrates that excimer laser ablation ela icpms allows u th pb dating of monazite with a high level of repeatability accuracy and precision as well as rapidity of analysis a spatial resolution almost comparable to that of emp in terms of crater width 5 m produced precise 208 pb 232 th 206 pb 238 u and 207 pb 235 u ratios for dating palaeozoic to precambrian monazites the advantages of ela icpms isotope dating are precision accuracy and the ability to detect discordance in the case of late miocene hydrothermal monazites from the alps a larger spot size of 25 m diameter is required and precise and accurate ages were obtained only for 208 pb 232 th systematics results from the variscan granite show that in situ u th pb dating of monazites with ela icpms is possible using a 5 m spot directly on thin sections so that age data can be placed in a textural context

quartz fabric transition in a cooling syntectonic granite hermitage massif france abstract the hermitage granite situated in the northwest massif central france is a syntectonic hercynian leucogranite emplaced along an active transcurrent shear zone during emplacement and cooling the progressive deformation is marked by the development of a primary homogeneous foliation gradually affected by ductile shear bands c s mylonites increase in strain heterogeneity during cooling corresponds to a change of dominant deformation mechanism of the quartz phase from grain growth and migration recrystallization to intracrystalline a slip and rotation recrystallization migration recrystallization is characterized by preferred orientations of c axes close to the principal extension direction we discuss relevant deformation mechanisms and rheological implications for syntectonic plutons in particular we argue that the transitions between homogeneous and heterogeneous accumulation of strain cannot generally be correlated with transition between magmatic and solid state flow

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

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

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

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

post collisional deposits in the zagros foreland basin implications for diachronous underthrusting detailed sedimentology of the neogene foreland basin deposits is investigated and classified into 11 lithofacies associations with respect to their paleo sedimentary environments the foreland deposits reveal a single coarsening upward mega sequence with continuous passage from back bulge to forebulge foredeep and wedge top sedimentary environments the gachsaran deposits form the base of the foreland strata and consist mainly of three different lithofacies associations including fluvial marine and sabkha deposits in the eastern zagros in fars and are typically dominated with evaporites toward the west in the dezful and kirkuk embayments the mishan formation has three different shallow marine lithofacies associations in a vertical succession representing foredeep deposits in the eastern zagros which tapers toward the dezful embayment and disappears in iraq the agha jari distal wedge top deposits also contain three different lithofacies associations including delta deposits mostly in the fars tidal flat deposits in dezful and mesopotamia basin and continental fluvial deposits across the entire zagros the uppermost synorogenic bakhtiari formation represents proximal wedge top deposits and consists mainly of two main lithofacies associations including shallow marine and fluvial deposits within which the fluvial succession is divided into three sub lithofacies associations with respect to distance from the mountain front and hydraulic power of the river networks synthetizing sedimentary facies association with age constraints of the old foreland deposits near the zagros suture in the high zagros area suggests that a considerable part of the arabian plate has been removed at the northern edge by underthrusting and erosion moreover preservation of the young distal foreland deposits near the suture in the western zagros implies that the magnitude and rate of removal of the proximal foreland deposits have been inconstant along strike the belt and decreases toward the east

anhydrite and the sr isotope evolution of groundwater in a carbonate aquifer major element concentrations and 87 sr 86 sr ratios were measured in groundwaters and bedrock from the madison aquifer in western south dakota in this region the madison aquifer is primarily comprised of dolomite belonging to the madison limestone group the purpose of the study was to investigate controls on the downgradient evolution of dissolved sr 2 in a carbonate groundwater system that is recharged by waters with high 87 sr 86 sr ratios draining precambrian basement rocks and to establish the sources of sr 2 added to the waters by reaction with the aquifer lithology a mass balance model following previous workers was used to calculate amounts and effective rates of mineral dissolution and precipitation during groundwater transport along a 240 km flow path both the calculated reaction rates and data for the sr isotope geochemistry of the reacting phases were then used to develop a self consistent and quantitative description of the concentration and isotopic composition of dissolved sr 2 in the aquifer waters the major ion chemistry of madison aquifer groundwater is known to evolve according to dolomite dissolution anhydrite dissolution calcite precipitation and ion exchange with clay minerals dissolved 87 sr 86 sr ratios in the madison aquifer decrease downgradient input waters draining the igneous black hills have 87 sr 86 sr ratios of 0 723 while highly evolved waters in the aquifer have 87 sr 86 sr ratios of 0 708 dissolved sr 2 concentrations undergo a concurrent increase from 1200 to 66 000 nmol l model results indicate that dolomite dissolution exerts a critical control on the major ion chemistry but is not the primary source of nonradiogenic sr 2 as both the dissolution rate and sr concentration of dolomite are very low anhydrite is readily soluble in water has a low 87 sr 86 sr ratio 0 708 and a very high sr concentration 50 000 nmol g anhydrite is also greatly undersaturated in the groundwaters and the downgradient evolution of sr 2 accompanies an 80 fold increase in dissolved so 4 2 while anhydrite has a very low abundance in the aquifer rocks the flow model indicates that anhydrite dissolution provides 300 times more sr 2 per liter of water relative to dolomite dissolution these findings suggest that anhydrite dissolution governs the sr 2 geochemistry of madison aquifer groundwaters whereas dolomite dissolution and calcite precipitation control the bulk chemistry lastly it is shown that the calculation of net mineral masses transferred to solution requires very high relative proportions of anhydrite and clay to dolomite mineral masses obtained by this approach actually represent bulk contributions without consideration of the intrinsic reaction rates of the phases or their modal abundances in the aquifer rocks however consideration of these parameters in a transport equation for flow through porous media shows that the high apparent abundances are not a real requirement this latter approach is consistent with laboratory experiments and indicates that as little as 0 04 wt of very soluble anhydrite and 0 3 wt of exchangeable clay in the aquifer rock are sufficient to produce the observed groundwater chemistry in most of the flow path

burial and scour of short cylinders under combined random waves and currents including effects of second order wave asymmetry abstract this paper provides an approach by which the burial and scour of short cylinders under combined second order random waves and currents can be derived here the formulas for burial and scour for regular waves plus currents presented by catano lopera and garcia catano lopera y a and garcia m h 2006 burial of short cylinders induced by scour under combined waves and currents asce j waterway port coastal and ocean eng 132 6 439 449 catano lopera y a and garcia m h 2007 geometry of scour hole around and the influence of the angle of attack on the burial of finite cylinders under combined flows ocean eng 34 5 6 856 869 are used together with stokes second order wave theory by assuming the basic harmonic wave motion to be a stationary gaussian narrow band random process an example of calculation is also presented

numerical simulation of present day tectonic stress across the indian subcontinent in situ measurements of maximum horizontal stress shmax in the indian subcontinent are limited and do not present regional trends of intraplate stress orientation the observed orientations of shmax vary considerably and often differ from the plate velocity direction we have simulated orientation and magnitude of shmax through finite element modeling incorporating heterogeneities in elastic property of the indian continent and plain stress approximation to understand the variability of shmax four different scenarios are tested in simulation 1 homogeneous plate with fixed plate boundary 2 homogeneous plate with boundary forces 3 heterogeneous plate with fixed boundary 4 heterogeneous plate with boundary forces the estimated orientation and magnitude of shmax with a heterogeneous plate with boundary forces in the himalayan region and an eastern plate boundary comprising the indo burmese arc and andaman subduction zone are consistent with measured maximum horizontal stress this study suggests that plate boundary force varies along the northern indian plate margin and also provides a constraint on the intraplate stress field in the indian subcontinent

kashmir basin fault and its tectonic significance in nw himalaya jammu and kashmir india the kashmir basin fault is located in the jammu and kashmir region of kashmir basin in nw himalaya india it is a classic example of an out of sequence thrust faulting and is tectonically active as observed from multiple geological evidences its geomorphology structure and lateral extent indicate significant accommodation of stress since long which is further supported by the absence of a large earthquake in this region it seems this fault is actively accommodating some portion of the total india eurasia convergence apart from two well recognised active structures the medlicott wadia thrust and the main frontal thrust which are referred in vassallo et al earth planet sci lett 411 241 252 2015 this requires its quantification and inclusion into slip distribution scheme of nw himalaya therefore it should be explored extensively because this internal out of sequence thrust could serve major seismic hazard in kb repeating a situation similar to muzaffarabad earthquake of northern pakistan in 2005

groundwater evolution in the continental intercalaire aquifer of southern algeria and tunisia trace element and isotopic indicators abstract the geochemical processes taking place along an 800 km flow line in the non carbonate continental intercalaire aquifer ci aquifer in north africa are described using chemical major and trace element and isotopic indicators the aquifer is hydraulically continuous from the atlas mountains in algeria to the chotts of tunisia and the geochemical evidence corroborates this the highest discharge temperature is 73 c but silica geothermometry indicates a maximum temperature of 94 c at depth chloride concentrations increase from 200 to 800 mg l 1 and the br cl ratios confirm the dissolution of non marine evaporites or interstitial waters as the main source of salinity fluoride concentrations are low and are likely to be derived from rainfall recording oscillations in source radiocarbon ages except near outcrop are at or near detection limits and the 18o and 2h values indicate a cooler recharge regime with rainfall having lower primary evaporation than today this is shown by the fact that mean isotope ratios of ci waters are around 3 lighter than the present day weighted mean value for rain major ion ratios and most trace elements indicate that despite the complex structure and stratigraphy uniform evolution with continuous water rock interaction takes place along the flow lines which are only disturbed near the tunisian chotts by groundwater converging from additional flow lines the ageing of the water can also be followed by the smooth increase in several indicator elements such as li k and mn which are least affected by solubility controls similarly the influence of marine facies in the tunisian sector may be recognised by the changing mg ca and higher br cl as well as trace element indicators the groundwaters are oxidising up to 300 km from outcrop dissolved o2 has persisted for at least 20 ka and within this zone the concentrations of several elements forming oxy anions such as u and cr increase and no3 remains conservative beyond 300 km from outcrop the groundwaters are reducing and contain high fe concentrations the basin contains huge reserves of fresh brackish waters but these need careful development due to the limiting high salinity and scaling tendency resulting from the high temperatures and mineral super saturation caused during abstraction as well as high concentrations of some harmful elements such as cr in the oxidising section

can an earthquake of mw 9 occur in the himalayan region it has been suggested that all of the earth s subduction zones are capable of producing an m w 9 earthquake such a possibility has also been suggested for the himalayan collisional arc we examined recent and historical earthquakes in the himalayan region and suggest that in the past few hundred years only great earthquakes m w 8 have occurred in the region the largest being the 1950 assam earthquake with m w 8 6 several aseismic ridges segment the himalayan arc and these appear to have limited the extent of rupture in earthquakes of the past 200 years there is also evidence of distributed deformation and out of sequence thrusting where only part of the detachment participates in the accommodation of the convergence we concluded that although it is unlikely that an m w 9 earthquake could occur in the himalaya from the hazard point of view a great earthquake of m w 8 anywhere along the himalayan arc could kill about one million people in the himalaya and adjoining indo ganga plains as an example a scenario developed for a hypothetical m w 8 earthquake occurring in the middle of the night at mandi close to the epicentre of the 1905 kangra earthquake predicts an estimated loss of one million human lives

eocene partial melting recorded in peritectic garnets from kyanite gneiss greater himalayan sequence central nepal the himalayan mountain belt is characterized by the impressive continuity over 2500 km of tectonic units thrusts and normal faults as well as large volumes of high grade metamorphic rocks and granite exposed at the surface visona et al 2012 although there are many studies on metamorphism melt generation and deformation concentrated in the same time span as activity on the mct and std 23 17 ma godin et al 2006 much fewer data on deformation metamorphism melt generation and geochronology in the greater himalayan sequence ghs is available for the large time span 30 m y between collision at 55 ma and mct std activities carosi et al 2010 2013 montomoli et al 2013 melt generation and granite emplacement have been mainly related to the exhumation stage of the ghs during early miocene harris and massey 1994 very few evidences of partial melting during prograde metamorphism have been reported until now in the southern part of the belt godin et al 2001 imayama et al 2012 the ghs of eastern nepal and sikkim india shows the occurrence of melting at the bottom of the ghs barun gneiss at nearly 33 27 ma imayama et al 2012 ferrero et al 2012 rubatto et al 2012 anatectic melt inclusions nanogranites and nanotonalites have been found in garnet of kyanite gneiss at the bottom of the greater himalayan sequence fig 1 along kali gandaki valley central nepal nearly 1 km structurally above the main central thrust in situ u th pb dating of monazite included in garnets in the same structural positions as melt inclusions allowed to constrain partial melting starting at 36 41 ma carosi et al in press

the use of hydrochemical and environmental isotopic tracers to understand the functioning of the aquifer system in the bou hafna and haffouz regions central tunisia abstract major ions hydrochemistry and isotopic data 18o 2h 3h 14c have been used to improve the understanding of mineralisation processes origins and circulation patterns of groundwaters of the bou hafna and haffouz region in central tunisia hydrochemical investigation indicates that the salinity in groundwater which varies greatly from 0 2 to 1 3 g l results mainly from the dissolution of evaporates halite gypsum and anhydrite cation exchange and dedolomitization processes the use of stable isotopes tracers 18o 2h has classified groundwaters samples into two groups the non evaporated groundwaters are distinguished by relatively depleted isotope contents highlighting significant recharge at higher altitudes the evaporated groundwaters are characterized by enriched 18o and 2h contents reflecting the contribution of return flow of irrigation waters to the recharge of the studied aquifer system tritium contents varying from 0 03 to 1 23 ut provide evidence of the presence of two sources of recharge that correspond to pre nuclear recharge and to a mixture between pre nuclear water and the contemporaneous recharge the 14c activities ranging between 7 4 and 78 6 pmc identify two groundwater groups the first group is dominated by the direct infiltration of present day meteoric water at higher altitude the second group is formed by a mixture of recent and palaeoclimatic groundwaters

evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using ebsd and fabric analyser techniques quartz crystallographic preferred orientations cpo from three distinct orthogneisses using both the electron back scatter diffraction ebsd and fabric analyser fa techniques reveal a clear trend from basal and rhomb slip for high p t conditions 670 20 degrees c 9 kbar rhomb and basal slip for medium p t 590 15 degrees c 6 kbar and a dominance of prism slip for lower p t conditions 570 degrees c 4 5 kbar the textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences locally quartz cpus are different within one thin section and in comparison to bulk orientation measurements both ebsd and the fabric analyser techniques are ideal to determine such textural heterogeneities while the ebsd is a powerful technique to determine the full cpo measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the fa is an accurate tool to determine cpus of c axis orientations in uniaxial materials in a cpo focussed study the fa is a cheap alternative to ebsd as the analysis of whole thin section can be accomplished in a very short time with minimal sample preparation with the fa it is possible to evaluate the cpus of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity

paleohydrologie isotopique de l oued el akarit sud tunisie au pleistocene superieur et a l holocene previous data from gobert and howe coque and page on the upper quaternary deposits from wadi el akarit are expanded through radiocarbon and stable isotope measurements 18c and 13c from carbonates 18o and 34s from sulphates these new results report on detailed stratigraphic profiles and indicate fluviatile and palustrine environments during the late pleistocene vegetal dams linked to spring activity caused water stagnation fine grained sediments were deposited with appreciable amounts of organic matter which locally developed into some peaty levels in the upper part of the typical cross section located on the left bank about 100 m upstream of the railway bridge pleistocene deposits show a palustrine carbonate crust this formation is attributed to the drainage induced by the major marine regression at glacial maximum during the holocene stagnation periods still occurred interrupted by flood episodes marked by bottom transport and coarse deposits in the typical cross section deposits are well drained and oxidized however downstream a stagnation episode takes place with a rich malacofauna dominated by cerastoderma cardium the uneven distribution of rainfall is documented by the alternation of fine and coarse deposits and it is accentuated by the climatic evolution toward aridity which results in the formation of a gypsum crust after 4000 yr bp later exceptional floods removed sediments from the wadi channel cutting the upper quaternary deposits for about 13 m along the central course of the wadi radiocarbon ages on carbonates are discussed according to various possible origins of total dissolved carbon atmospheric co2 organic activity in the basins and aquifer supply a simple exchange mixing model between aquifer bicarbonate and atmospheric co2 is used for calculations of initial carbonate activities chemical isotopic and hydraulic steady states are assumed in this treatment present day 14c and 13c contents of aquifer bicarbonate are thus adopted for past values the model leads to acceptable corrected ages for pleistocene carbonate samples corrected ages are younger than apparent ages by a few thousands of years and become consistent with ages given by organic matter from nearby levels however holocene samples appear overcorrected their crystallization appears to be controlled by modern organogenic co2 holocene 14c ages are probably correct 18o contents of carbonate indicate a continental origin for environmental water nodules and carbonate concretions crystallized in bottom sediments through upward leakage of confined aquifers they show 18o contents compatible with present day stable isotope compositions of artesian springs this supports the concept of a good time constancy in stable isotope contents shell carbonate values indicate a variable evaporation rate from the same initial waters 18o and 34s contents of gypsums are also compatible with aqueous sulphates from springs the data set falls within the range of permo triassic sulphate and suggests deep hydraulic connections within aquifer systems the entire formation appears to be of continental origin the occurence of cardium rich basins can only be attributed to the initial salinity of springs waters 7 9 g 1 1 sightly increased by evaporation this signifies that one can not deduce any tectonic uplift from their location with respect to sea level

scour below pipelines and around vertical piles in random waves an approach by which the scour depth and scour width below a fixed pipeline and scour depth around a circular vertical pile in random waves can be derived is presented here the scour depth formulas by sumer and fredsoe asce j waterw port coastal ocean eng 116 1990 307 for pipelines and sumer et al asce j waterw port coastal ocean eng 114 1992 599 for vertical piles as well as the scour width formula by sumer and fredsoe the mechanics of scour in the marine environment world scientific singapore 2002 for pipelines combined with describing the waves as a stationary gaussian narrow band random process are used to derive the cumulative distribution functions of the scour depths and width comparisons are made between the present approach and random wave scour data tentative approaches to related random wave scour cases are also suggested

a structural analysis of the main central thrust zone langtang national park central nepal himalaya the main central thrust mct is one of the most tectonically significant structures in the himalayan orogen detailed geologic mapping and structural analysis of the mct in the langtang national park region of central nepal reveals that this segment of the fault zone experienced multiple episodes of south directed movement under both brittle and ductile conditions during the tertiary period early mid miocene movement resulted in the development of mylonitic fabrics synchronous with amphibolite facies metamorphism the mean orientation of the dominant mylonitic foliation is n28 w 38 ne an associated mineral stretching lineation plunges 40 to n40 e kinematic indicators suggest hanging wall movement to the southwest relative to the footwall along the north dipping fault it is not possible to constrain the magnitude of high temperature displacement on the mct at the longitude of langtang late stage structures in the mct zone at langtang include a series of imbricate brittle thrust faults that separate different lithostratigraphic units and correspond to metamorphic discontinuities we interpret this fault system as a duplex structure muscovite 40 ar 39 ar cooling ages from the mct zone range from 8 9 6 9 ma because the nominal closure temperature of ar diffusion in muscovite approximately 625 k is higher than the apparent temperature conditions under which late brittle deformation occurred we suggest that brittle deformation was a latest miocene pliocene phenomenon another major himalayan fault the main boundary thrust mbt was developing to the south of langtang at approximately the same time we speculate that brittle faulting within the mct zone may have initiated as the mct zone was transported over a ramp in the mbt

variable anelastic attenuation and site effect in estimating source parameters of various major earthquakes including m w 7 8 nepal and m w 7 5 hindu kush earthquake by using far field strong motion data strong motion records of recent gorkha nepal earthquake m w 7 8 its strong aftershocks and seismic events of hindu kush region have been analysed for estimation of source parameters the m w 7 8 gorkha nepal earthquake of 25 april 2015 and its six aftershocks of magnitude range 5 3 7 3 are recorded at multi parametric geophysical observatory ghuttu garhwal himalaya india 600 km west from the epicentre of main shock of gorkha earthquake the acceleration data of eight earthquakes occurred in the hindu kush region also recorded at this observatory which is located 1000 km east from the epicentre of m w 7 5 hindu kush earthquake on 26 october 2015 the shear wave spectra of acceleration record are corrected for the possible effects of anelastic attenuation at both source and recording site as well as for site amplification the strong motion data of six local earthquakes are used to estimate the site amplification and the shear wave quality factor q at recording site the frequency dependent q f 124f 0 98 is computed at ghuttu station by using inversion technique the corrected spectrum is compared with theoretical spectrum obtained from brune s circular model for the horizontal components using grid search algorithm computed seismic moment stress drop and source radius of the earthquakes used in this work range 8 20 1016 5 72 1020 nm 7 1 50 6 bars and 3 55 36 70 km respectively the results match with the available values obtained by other agencies

quaternary extensional and compressional tectonics revealed from quaternary landforms along kosi river valley outer kumaun lesser himalaya uttarakhand a portion of the kosi river in the outer kumaun lesser himalaya is characterized by wide river course situated south of the ramgarh thrust where huge thickness 200 m of the landslide deposits and two to three levels of unpaired fan terraces are present brittle normal faults suggesting extensional tectonics are recognized in the quaternary deposits and bedrocks as further supported by surface morphology trending e w these faults measure from 3 to 5 km in length and are traced as discontinuous linear mini horst and fault scarps sackungen exposed due to cutting across by streams active normal faults have displaced the coarsely laminated debris fan deposits at two sites located 550 m apart at one of the sites the faults look like bookshelf faulting with the maximum displacement of 2 m and rotation of the quaternary boulders along the fault plane is observed at another site the maximum displacement measures about 0 60 cm thick mud units deposited due to blocking of the streams by landslides are observed within and above the fan deposit landslide debris fans and terrace landforms are widely developed the highest level of fan is observed 1240 m above mean sea level at some places the reworking of the debris fans by streams is characterized by thick laminated sand body along the south almora thrust and ramgarh thrust zones the valleys are narrow and v shaped where quaternary deposits are sparse due to relatively rapid uplift across these thrusts along the south almora thrust zone three to four levels of fluvial terraces are observed and have been incised by river exposing the bedrocks due to recent movement along the rt and sat abandoned channel tilted mud deposits incised meandering deep cut v shaped valleys and strath terraces indicate rapid uplift of the area thick mud sequences in the quaternary columns indicate damming of streams a 10 km long north south trending transverse garampani fault has offset the ramgarh thrust producing tectonic landforms

stress regime changes in the main boundary thrust zone eastern himalaya decoded from fault slip analysis abstract the main boundary thrust mbt zone in the darjeeling foothills eastern himalaya exhibits northerly dipping fault splays named here as mbt 1 and mbt 2 with proterozoic daling group in the mbt 1 hanging wall upper paleozoic gondwana rocks between the mbt 1 and the mbt 2 and neogene siwalik group in the footwall of the mbt 2 on the basis of reduced stress tensors from fault slip analysis and their grouping relative to different stratigraphic units in the mbt zone that crops out over a strike length of 20 km the following successive stress regimes have been interpreted the earliest brittle deformation recorded only in the basal part of the gondwana succession was controlled by a pre himalayan nw se extensional regime the himalayan deformation under sustained n s compressive regime developed in three stages a thrust displacement along the mbt 1 juxtaposing folded daling rocks against the lower gondwana rocks b tilting and fracturing of lower gondwana succession and thrust transport over the siwalik rocks along the mbt 2 c strike slip regime with nw and ne trending faults affecting both the lower gondwana and siwalik strata developed possibly due to increased tectonic loading the tensor solutions under n s compressional regime are consistent with the modern plate convergence supporting a foreland propagating thrust system in the eastern himalaya in addition an e w extensional regime led to apparent orogen parallel extension

analogue modeling of the role of multi level decollement layers on the geometry of orogenic wedge an application to the zagros fold thrust belt sw iran the presence of evaporate and incompetent formations i e decollement horizons within the sedimentary sequence of fold thrust belts can control their structural style and deformation evolution in the present study the influence of the decollement layers e g basal and internal decollement layers on the deformation style of several segments of the zagros fold thrust belt zftb sw iran e g fars arc dezful embayment and izeh zone was investigated using a series of analogue models of accretionary wedges the study of seismic profiles to understand the structural evolution of these segments of the belt where several decollement intervals acted as basal and internal decollements is complemented by the analogue model results the experimental results reveal that the thickness of the internal decollement layers influences the creation of fold dominated or thrust dominated deformations respectively experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation in sequence and or out of sequence faults into overlying strata towards southwest by fore deformation and control the rate of deformation propagation in the zftb the presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the zftb in addition the geometry spacing activity and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low frictional decollements geophys j int 165 1 336 356 2006 geochem geophys geosyst 14 1131 1155 2013 the seismic profiles of the zftb showed that in addition to lithological contrasts the existence and activity of deep seated and basement faults had a big impact on the structural styles of the region