the scheelite skarn deposit of salau ariege french pyrenees between 1971 and 1986 the scheelite deposit of salau located in the french hercynian pyrenees produced 930 000 metric tons of ore with 1 50 percent wo 3 13 950 metric tons of wo 3 the skarn deposit is hosted in a devonian carbonate and partly detrital series intruded by a late carboniferous stock in the devonian series the lithostratigraphy and geochemistry of which is described in some detail a unit of so called barregiennes i e rythmic alternations of limestones and silts appears to be very favorable for extensive development of skarns and overprinted ores the hercynian orogeny involved polyphase deformation regional metamorphism of greenschist facies and late intrusions of granite granodiorite deformation included two coaxial stages of tight isoclinal folding and one important later stage which partly controlled the intrusion of the granodiorite stock followed by three stages of brittle deformation ore deposition is related to faulting stages 0 and 1 and orebodies are cut into slices by stage 2 reverse faults the salau intrusion includes various rock types belonging to two slightly different calcalkaline trends one of these trends characterized by its low k contents is unusual in the pyrenees the local shapes of the intrusion apophyses and embayments are important controls of the orebodies after isochemical contact metamorphism the skarns and ores developed in two main stages related to the infiltration of two quite different types of fluids during the first stage 540 degrees 450 degrees c anhydrous skarn formation was followed by an intergranular development of pyrrhotite scheelite quartz calcite in equilibrium with the earlier hedenbergite the resulting tungsten grade is uneconomic the associated fluids probably of magmatic origin had a high salinity in the second stage 450 degrees 350 degrees c no new skarn formed transformations of the silicate rocks are observed a first substage of epidotization was followed by the development of intermediate grossularite almandine spessartite garnet and finally by the main ore stage with scheelite pyrrhotite arsenopyrite and other sulfides with some gold two types of fluid inclusions are found in this stage one is similar in composition to the first stage the other is characterized by low salinity and high co 2 and ch 4 contents

grain size dependent concentration of cosmogenic 10be and erosion dynamics in a landslide dominated himalayan watershed for documenting recent or late quaternary erosion rates at the scale of a small watershed or even an entire mountain range the use of in situ terrestrial cosmogenic nuclides tcn such as 10be in river sediments has become widespread over the last decade in mountainous settings however landslides may induce a two fold complication in the cosmogenic nuclide budget first they may episodically deliver large amounts of sediment with low tcn concentrations to the river channel second they may generate a grain size concentration dependence in these sediments however studies that have explored grain size dependence in landslide dominated areas have reached differing conclusions and the underlying mechanisms remain poorly understood the present study focuses on the khudi khola river basin a small drainage basin in the central himalayas the area is characterized by steep slopes heavy rainfall and high sediment production rates importantly the watershed contains a large area of active landsliding in situ 10be was analyzed in sediments of grain sizes ranging from 75 m to 4 cm collected from five locations upstream downstream and in the small tributaries which drain the landslides in all sampling locations including those situated upstream of the landslides the finest grains 75 250 m are two to four times more concentrated in 10be than the largest clasts 4 7 mm we developed a numerical slope model which includes a low level of background soil erosion and episodic denudation from large mass wasting events we then introduced a coarsening of average grain size with soil depth to the model our simulation shows that the data available for this valley are compatible with a scenario in which landslides deliver coarse grains to the channel that are less concentrated in tcn and have deeper provenance best fit estimates of the model parameters suggest recurrence times of 3000 to 9000 years for a major landslide on the same slope and mean long term landslide denudation rates of 1 7 to 4 7 mm yr 1 a negative correlation between tcn concentration and grain size is also observed directly upstream and 5 km downstream of the landsliding area suggesting that nearly all of the sediment carried by the river is derived from ancient landslides while almost no sediment is supplied by erosion of soil mantled slopes despite these complications apparent denudation rates directly derived from the tcn concentrations and from previously published data in the region are all on the same order of magnitude around 2 mm yr 1 however a factor of three variability remains between the different studies depending on the location the year of sampling and the analyzed grain size fraction thus although tcn derived average denudation rates provide a useful first order estimate even in fast eroding terrains dominated by landslides caution should be applied when using quantitative results in such settings

tectonic underplating versus out of sequence thrusting beneath the lesser himalaya insights from the analogue modeling of the nepal himalaya fold and thrust belt abstract the nepal himalaya fold and thrust belt is a classical two decollement thrust fold system the belt has been extensively studied by analogue and numerical modeling but the formation mechanism of the mid crustal duplex structure beneath the northern part of the lesser himalaya remains debated the formation of this thrust duplex has been attributed either to tectonic underplating along new ramps in response to the subducting indian plate or to out of sequence thrusting along preexisting ramps we conducted a series of experiments using analogue models employing a model setup that was faithful to the geological setting of the nepal himalaya we used industrial computed tomography ct and particle image velocimetry piv to generate detailed deformation maps the analogue models successfully reproduce the main structure of the nepal himalaya fold and thrust belt showing that the two competing processes i e underplating along new ramps and out of sequence thrusting along preexisting ramps operate alternately to form the duplex structure the models also show that underplating is associated with extensive foreland sedimentation analogous to the foreland molassic sedimentation in the sub himalaya which leads to a systematic recession of the deformation front and a smaller horse finally the recognition that out of sequence thrusting occurs in the interval between major underplating events provides important insights into the origin of the 2015 m w 7 8 gorkha earthquake

earthquake hazard assessment for dehradun uttarakhand india including a characteristic earthquake recurrence model for the himalaya frontal fault hff the seismic hazard has been computed for the city of dehradun uttarakhand india the city lies in the himalayan foothills between two faults the main boundary thrust mbt and the himalayan frontal fault hff the contributions from these two faults have been modelled differently in a probabilistic model while the mbt has been modelled with a poissonian earthquake distribution the hff has been modelled both with a characteristic earthquake recurrence model and a poissonian model the hazard scenarios reveal different patterns depending on the classical approaches and the characteristic models applied and the obtained results indicate that dehradun may experience pga shaking around 2 2 m s2 for 225 years return period and around 4 6 m s2 for a 2 500 years return period

estimation of strain distribution using gps measurements in the kumaun region of lesser himalaya abstract the continuous process of continent continent collision between the indian and the eurasian plates has led to the formation of the himalayan range and continuously caused earthquakes in the region large earthquakes with magnitudes of 8 and above occur in this region infrequently releasing the elastic strain accumulated over years around the plate boundary geodetic measurements can help estimate the strain distribution along the fault system these measurements provide information on active deformations and associated potential seismic hazards along the himalayan arc in order to understand the present deformation around the plate boundary we collected gps data during three campaigns in the years of 2005 2007 at 16 sites in the kumaun region of the lesser himalaya horizontal velocity vectors estimated in itrf2000 are found to be in the range of 41 50 mm yr with an uncertainty level of the order of 1 mm yr the velocity field indicates that the present convergence of around 15 mm yr takes place in the kumaun himalaya further we estimate the strain components in the study area for understanding the currently active tectonic process in the region the estimated dilatational strain indicates that the northern part near the main central thrust mct is more compressional than the southern part maximum shear strain is mostly accommodated in the northern part too the maximum shear and dilatational strain rates are about 1 0 and 0 5 strain yr it is seen that the distribution of high shear strain spatially correlates with seismicity the maximum of extensional and compressional strains due to the force acting along the main central thrust mct in the nw se direction are found to be 0 4 and 0 1 strain yr respectively the maximum shear strain in the northern part of the himalaya appears to be associated with the convergence of the region proposed by other geophysical studies

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

on the growth of normal faults and the existence of flats and ramps along the el asnam active fold and thrust system the combination of detailed topographic leveling on the southwest segment of the el asnam thrust fault with existing seismic and geologic data implies that the geometry of this fault involves shallow dipping flats and steep ramps the fault appears to be growing along strike toward the southwest end where the main shock initiated in 1980 from a depth of about 10 km the main thrust appears to ramp to the basement cenozoic cover interface on a plane striking n40 e and dipping 50 55 to the northwest along the southwest segment where folding has not yet developed the thrust continues steeply through the cenozoic cover to the near surface where it flattens causing normal faulting along the central and northeast segments which display a more evolved fold structure the deep thrust probably flattens at a depth of 5 6 km into a decollement along the cenozoic jurassic interface before ramping to the surface the sara el marouf and kef el mes anticlines have thus formed as fault propagation folds normal faults at beni rached probably branch with the thrust to maintain kinematic compatibility between the deep ramp and decollement the greater separation 7 km between the normal faults at beni rached and the thrust where it crosses oued cheliff than along the southwest segment 1 km reflects the greater depth of the ramp to flat bend we infer that the september 9 1954 earthquake activated only the central deep segment of the main thrust together with the beni rached normal faults while that of october 10 1980 activated the whole system of flat decollements ramp thrusts and compatibility normal faults further complexities of the faulting in map view are related to changes of strike of the thrust in particular north of oued cheliff

uplift in the nepal himalaya revealed by spirit leveling a 250 km long first order leveling line linking the geodetic surveys of tibet and india through the kingdom of nepal has been measured twice in the past 15 years changes in relative bench mark elevation projected along a 200 km line orthogonal to the mean structural trend in the himalaya indicate a pattern of uplift with wavelengths of 30 50 km not related to earthquake occurrence relative vertical velocities of bench marks of up to 4 mm year show no evident correlation with level line slope an absence of microearthquake data prevents localized uplift from being attributed to slip on mapped or buried faults although circumstantial evidence suggests this is likely in the north in line with the high himalayan peaks relative uplift rates of 4 1 mm yr and a wavelength of 50 km are coincident with a steepening in the main boundary thrust and the moho proposed by lyon caen and molnar 1985 in the south uplift rates of 2 0 3 mm yr with a wavelength of 30 km correspond to active folding of an anticline on the southern flank of the lesser himalaya observed tilt rates of 0 06 rad year are similar to the long term tilt rates needed to produce the 40 70 flanks of the anticline a range of detachment geometries and slip velocities can generate the observed deformation field but geologically realistic models fall into a group of horizontal to shallow dipping sub horizontal faults between 12 and 6 km in depth no unique solution exists although the wavelength of the observed deformation field permits models with significant slip closer than 4 km to the surface to be excluded

imaging the moho and the main himalayan thrust in western nepal with receiver functions the crustal structure of western nepal is studied for the first time by performing receiver function analysis on teleseismic waveforms recorded at 16 seismic stations the moho geometry is imaged as it deepens from 40 km depth beneath the foothills and the lesser himalaya to 58 km depth beneath the higher himalayan range a midcrustal low velocity zone is detected at 15 km depth along 55 km horizontal distance and is interpreted as the signature of fluids expelled from rocks descending in the footwall of the main himalayan thrust our new image allows structural comparison of the moho and of the main himalayan thrust geometry along strike of the himalayas and documents long wavelength lateral variations the general crustal architecture observed on our images resembles that of central nepal therefore western nepal is also expected to be able to host large m w 8 megathrust earthquakes as the 1505 ce event plain language summary we investigate the earth s crust in western nepal we use 16 stations to detect waves from faraway earthquakes and using these we make an image of the structure of the crust we find that the crust is getting thicker beneath the himalaya and that fluids are locally present in the upper part of the crust as this image is similar to the one we know in central nepal where major earthquakes happened it is possible that major earthquakes will also happen in western nepal in the future without knowing when

duplex in the main himalayan thrust illuminated by aftershocks of the 2015 m w 7 8 gorkha earthquake in april 2015 the lower locked portion of the main himalayan thrust ruptured beneath nepal causing the disastrous mw 7 8 gorkha earthquake elucidating the enigmatic geometry of this plate boundary fault is important for understanding the nucleation and arrest of large earthquake ruptures as well as the seismic hazard topography and tectonics of the himalaya here we interpret the geometry of the main himalayan thrust from the spatial distribution and rupture patterns of a dynamic sequence of aftershocks following the gorkha earthquake which were recorded by a rapidly deployed dense seismic network we find that the thrust comprises two north dipping subhorizontal planes that are connected by a system of bounded imbricate thrust faults this structure is known as a duplex we propose that this duplex acts as an impediment to plate convergence and accommodates tectonic stress along its complex system of faults such a prominent structure to the main himalayan thrust is consistent with surface geological studies but challenges geophysically derived conventional models with simpler geometries the main himalayan thrust comprises two fault planes connected by imbricated faults a structure that impedes convergence according to an analysis of the distribution and orientation of aftershocks of the 2015 gorkha earthquake in nepal

estimation and applicability of attenuation characteristics for source parameters and scaling relations in the garhwal kumaun himalaya region india abstract source parameters of the small to moderate earthquakes are significant for understanding the dynamic rupture process the scaling relations of the earthquakes and for assessment of seismic hazard potential of a region in this study the source parameters were determined for 58 small to moderate size earthquakes 3 0 m w 5 0 occurred during 2007 2015 in the garhwal kumaun region the estimated shear wave quality factor q f values for each station at different frequencies have been applied to eliminate any bias in the determination of source parameters the q f values have been estimated by using coda wave normalization method in the frequency range 1 5 16 hz a frequency dependent s wave quality factor relation is obtained as q f 152 9 7 f 0 82 0 005 by fitting a power law frequency dependence model for the estimated values over the whole study region the spectral low frequency spectral level and corner frequency and source static stress drop seismic moment apparent stress and radiated energy parameters are obtained assuming 2 source model the displacement spectra are corrected for estimated frequency dependent attenuation site effect using spectral decay parameter kappa the frequency resolution limit was resolved by quantifying the bias in corner frequencies stress drop and radiated energy estimates due to finite bandwidth effect the data of the region shows shallow focused earthquakes with low stress drop the estimation of zuniga parameter e suggests the partial stress drop mechanism in the region the observed low stress drop and apparent stress can be explained by partial stress drop and low effective stress model presence of subsurface fluid at seismogenic depth certainly manipulates the dynamics of the region however the limited event selection may strongly bias the scaling relation even after taking as much as possible precaution in considering effects of finite bandwidth attenuation and site corrections although the scaling can be improved further with the integration of large dataset of microearthquakes and use of a stable and robust approach

convergence rate across the nepal himalaya and interseismic coupling on the main himalayan thrust implications for seismic hazard we document geodetic strain across the nepal himalaya using gps times series from 30 stations in nepal and southern tibet in addition to previously published campaign gps points and leveling data and determine the pattern of interseismic coupling on the main himalayan thrust fault mht the noise on the daily gps positions is modeled as a combination of white and colored noise in order to infer secular velocities at the stations with consistent uncertainties we then locate the pole of rotation of the indian plate in the itrf 2005 reference frame at longitude 1 34 3 31 latitude 51 4 0 3 with an angular velocity of 0 5029 0 0072 myr the pattern of coupling on the mht is computed on a fault dipping 10 to the north and whose strike roughly follows the arcuate shape of the himalaya the model indicates that the mht is locked from the surface to a distance of approximately 100 km down dip corresponding to a depth of 15 to 20 km in map view the transition zone between the locked portion of the mht and the portion which is creeping at the long term slip rate seems to be at the most a few tens of kilometers wide and coincides with the belt of midcrustal microseismicity underneath the himalaya according to a previous study based on thermokinematic modeling of thermochronological and thermobarometric data this transition seems to happen in a zone where the temperature reaches 350 c the convergence between india and south tibet proceeds at a rate of 17 8 0 5 mm yr in central and eastern nepal and 20 5 1 mm yr in western nepal the moment deficit due to locking of the mht in the interseismic period accrues at a rate of 6 6 0 4 10 19 nm yr on the mht underneath nepal for comparison the moment released by the seismicity over the past 500 years including 14 m w 7 earthquakes with moment magnitudes up to 8 5 amounts to only 0 9 10 19 nm yr indicating a large deficit of seismic slip over that period or very infrequent large slow slip events no large slow slip event has been observed however over the 20 years covered by geodetic measurements in the nepal himalaya we discuss the magnitude and return period of m 8 earthquakes required to balance the long term slip budget on the mht

interseismic strain accumulation on the himalayan crustal ramp nepal the departement of mines and geology has been monitoring the seismicity of the central himalayas of nepal since 1985 intense microseismicity and frequent medium size earthquakes ml 4 tend to cluster beneath the topographic front of the higher himalaya this 10 20km deep seismicity also correlates with a zone of localized uplift that has been evidenced from geodetic data both microseismic and geodetic data indicate strain accumulation on a mid crustal ramp that had been previously inferred from geological and geophysical evidence this ramp connects a flat decollement under the lesser and sub himalaya with a deeper decollement under the higher himalaya and probably acts as a geometric asperity where strain and stress build up during the interseismic period the large himalayan earthquakes could nucleate there and probably activate the whole flat and ramp system up to the blind thrusts of the sub himalaya

the yenefrito pb zn mine spanish central pyrenees an example of superimposed metallogenetic events three types of base metal deposits occur in the devonian of the central pyrenees accompanying and post dating the hercynian orogeny since spatial and temporal relationships between mineralization can be recognized in the yenefrito area they have been incorporated into a metallogenetic model sedex like ore composed of sphalerite with minor galena pyrite arsenopyrite and magnetite is enclosed within a carbonate siltstone succession containing volcanic sills crust type mineralization is linked to an unconformity landscape and made up by quartz and minor sphalerite pyrite and galena finally vein deposit cross cutting these deposit types contains galena sphalerite and pyrite sedex like and crust type deposits are linked to hercynian extensional tectonics which favoured the development of an unstable depositional environment mainly controlled by synsedimentary faults being sedex mineralizations developed prior to crust type both mineralization types suffered diagenesis and deformation during the hercynian the vein type was generated by extensional movements related to early alpine rifting

focal depths and fault plane solutions of earthquakes and active tectonics of the himalaya synthetic seismograms were compared with long period body waves for nine earthquakes with epicenters in the himalayan arc to determine depths of foci and to improve fault plane solutions focal depths are shallow 10 20 km inferred slip vectors are locally perpendicular to the mountain range they plunge very gently about 10 deg in the eastern sections of the range and more steeply about 25 deg in western sections assuming india to be a rigid plate the radially oriented slip vectors imply that southern tibet extends at about half the rate of underthrusting in the himalaya and therefore probably at about 5 10 mm yr the shallow depths and gentle dips of the fault planes at least for the events in the eastern half of the range are consistent with coherent underthrusting of the indian plate beneath at least the lesser himalaya the steeper dips of fault planes in the western part of the arc might reflect deformation of the overriding thrust plate or simply a steepening of the main underthrusting zone beneath the greater himalaya

fault plane solutions of earthquakes and active tectonics of the tibetan plateau and its margins summary fault plane solutions of earthquakes within and on the margins of the tibetan plateau show diverse styles of faulting and deformation with thrust faulting and crustal shortening normal to the margins of the plateau and with normal and strike slip faulting resulting in roughly east west crustal extension within the plateau the direction of overthrusting of the himalaya onto the indian shield is radially outward varying from southwest in the western himalaya to south southeast in the east assuming that the indian shield behaves rigidly this requires a west northwest divergence of western tibet from southeastern tibet at a rate of 18 9 mm yr 1 comparable with the rate of convergence at the himalaya fault plane solutions of earthquakes in the southern portion of the tibet plateau consistently show large components of normal faulting on roughly north striking planes and corroborate such extension within the high plateau where elevations exceed 5000 m normal and strike slip faulting occur so that an overall east southeast west northwest extension of the region at about 10 mm yr 1 is partitioned into roughly equal parts of crustal thinning and north northeast south southwest crustal shortening about 5 mm yr 1 in general strike slip faulting characterizes solutions for earthquakes within eastern tibet where mean elevations drop below 4500 5000 m but the orientations of the strike slip faults vary across the region in central tibet left lateral slip occurs on planes trending roughly northeast but for earthquakes farther east the orientations of that plane become progressively east west and then southeast this variation in orientation implies a rotation of material along curved left lateral shear zones thus the eastward extrusion of tibet appears to be facilitated not only by rapid left lateral shear but also by large clockwise rotations of the material in eastern tibet the rate of eastward extrusion of material in eastern tibet relative to the tarim basin to its north is roughly 30 40 mm yr 1 fault plane solutions of earthquakes in the northern and eastern margins of tibet show large components of thrust faulting with the p axes oriented radially outward from the plateau and approximately perpendicular to the regional topographic contours of the plateau the orientation of this crustal shortening is northeast southwest on the northeastern margin east west on the eastern margin and northwest southeast in the longmenshan on the southeastern margin thus at least some of the extrusion of eastern tibet out of india s northward path into asia is absorbed by crustal shortening on the margins of the plateau the variation from normal faulting in the high tibetan plateau where elevations exceed 5000 m to dominantly strike slip faulting farther east where elevations are lower and then to thrust faulting on the margins of the plateau where elevations drop below 3000 m surely results at least in part from a decrease in the value of the vertical stress the magnitude of the east west compressive stress need not vary across the plateau

depth varying rupture properties during the 2015 mw 7 8 gorkha nepal earthquake on april 25th 2015 the mw 7 8 gorkha nepal earthquake ruptured a portion of the main himalayan thrust underlying kathmandu and surrounding regions we develop kinematic slip models of the gorkha earthquake using both a regularized multi time window mtw approach and an unsmoothed bayesian formulation constrained by static and high rate gps observations synthetic aperture radar sar offset images interferometric sar insar and teleseismic body wave records these models indicate that kathmandu is located near the updip limit of fault slip and approximately 20 km south of the centroid of fault slip fault slip propagated unilaterally along strike in an ese direction for approximately 140 km with a 60 km cross strike extent the deeper portions of the fault are characterized by a larger ratio of high frequency 0 03 0 2 hz to low frequency slip than the shallower portions from both the mtw and bayesian results we can resolve depth variations in slip characteristics with higher slip roughness higher rupture velocity longer rise time and higher complexity of subfault source time functions in the deeper extents of the rupture the depth varying nature of rupture characteristics suggests that the up dip portions are characterized by relatively continuous rupture while the down dip portions may be better characterized by a cascaded rupture the rupture behavior and the tectonic setting indicate that the earthquake may have ruptured both fully seismically locked and a deeper transitional portions of the collision interface analogous to what has been seen in major subduction zone earthquakes

active lower crustal deformation and himalayan seismic hazard revealed by stream channels and regional geology abstract thick tibetan crust stores energy driving large earthquakes along its margins at its southern margin it is hypothesized that its lower crust is extruded between two shear zones such that strain in the ductile lower crust is fed into the higher seismogenic portions of the crust predicting rock uplift between these structures the upper shear zone is regionally referred to as the south tibetan detachment std and the lower shear zone as the main central thrust mct we use field mapping and ksn channel steepness analysis to test this hypothesis in northwestern nepal within a notable gap in historic seismicity here we show an 170 km 40 km swath of rapid rock uplift at the southern margin of the tibetan plateau that overlaps a regional anticline suggesting active folding the area of rapid uplift coincides with peak interseismic strain determined by gps and overlies the inferred locked to creeping transition along the india asia plate boundary the fold is cored by thick ductiley deformed crust and defined by a shear zone interpreted as the std because the std is folded it cannot facilitate active extrusion of a mid crustal channel a regional cross section across the fold shows that while the uppercrust has little post miocene shortening the lower middle crust is anomalously thick we explain this by duplexing whereby thrust sense shear zones stack ductile lower middle crust beneath the std north downdip of the locked to creeping transition the plate boundary here last ruptured during the mw 8 2 ad 1505 earthquake whose inferred rupture area encompasses the region of rapid rock uplift shown here predicting a high slip potential integrating the structural geology and ksn analysis with microseismicity patterns and the 1505 surface rupture suggests that in western nepal the locked to creeping transition is 40 km wide and lies 100 120 km north of the himalayan thrust front

stratigraphy structure and tectonic evolution of the himalayan fold thrust belt in western nepal regional mapping stratigraphic study and 40ar 39ar geochronology provide the basis for an incremental restoration of the himalayan fold thrust belt in western nepal tectonostratigraphic zonation developed in other regions of the himalaya is applicable with minor modifications in western nepal from south to north the major structural features are 1 the main frontal thrust system comprising the main frontal thrust and two to three thrust sheets of neogene foreland basin deposits 2 the main boundary thrust sheet which consists of proterozoic to early miocene lesser himalayan metasedimentary rocks 3 the ramgarh thrust sheet composed of paleoproterozoic low grade metasedimentary rocks 4 the dadeldhura thrust sheet which consists of medium grade metamorphic rocks cambrian ordovician granite and granitic mylonite and early paleozoic tethyan rocks 5 the lesser himalayan duplex which is a large composite antiformal stack and hinterland dipping duplex and 6 the main central thrust zone a broad ductile shear zone the major structures formed in a general southward progression beginning with the main central thrust in late early miocene time eocene oligocene thrusting in the tibetan himalaya north of the study area is inferred from the detrital unroofing record on the basis of 40ar 39ar cooling ages and provenance data from synorogenic sediments emplacement of the dadeldhura thrust sheet took place in early miocene time the ramgarh thrust sheet was emplaced between 15 and 10 ma the lesser himalayan duplex began to grow by 10 ma simultaneously folding the north limb of the dadeldhura synform the main boundary thrust became active in latest miocene pliocene time transport of its hanging wall rocks over an 8 km high footwall ramp folded the south limb of the dadeldhura synform thrusts in the subhimalayan zone became active in pliocene time the minimum total shortening in this portion of the himalayan fold thrust belt since early miocene time excluding the tibetan zone is 418 493 km the variation depending on the actual amounts of shortening accommodated by the main central and dadeldhura thrusts the rate of shortening ranges between 19 and 22 mm yr for this period of time when previous estimates of shortening in the tibetan himalaya are included the minimum total amount of shortening in the foldthrust belt amounts to 628 667 km this estimate neglects shortening accommodated by small scale structures and internal strain and is therefore likely to fall significantly below the actual amount of total shortening

upper crustal shortening and forward modeling of the himalayan thrust belt along the budhi gandaki river central nepal a balanced cross section along the budhi gandaki river in central nepal between the main central thrust including displacement on that fault and the main frontal thrust reveals a minimum total shortening of 400 km minimum displacement on major orogen scale structures include 116 km on the main central thrust 110 km on the ramgarh thrust 95 km on the trishuli thrust and 56 km in the lesser himalayan duplex the balanced cross section was also incrementally forward modeled assuming a generally forward breaking sequence of thrusting where early faults and hanging wall structures are passively carried from the hinterland toward the foreland the approximate correspondence of the forward modeled result to observe present day geometries suggest that the section interpretation is viable and admissible in the balanced cross section the trishuli thrust is the roof thrust for the lesser himalayan duplex the forward model and reconstruction emphasize that the lesser himalayan duplex grew by incorporating rock from the footwall and transferring it to the hanging wall along the main himalayan thrust as the duplex developed the lesser himalayan ramp migrated southward the movement of lesser himalayan thrust sheets over the ramp pushed the lesser himalayan rock and the overburdens of the greater and tibetan himalayan rock toward the erosional surface this vertical structural movement caused by footwall collapse and duplexing in combination with erosion exhumed the lesser himalaya

carbonate hosted siliceous crust type mineralization of carnic alps italy austria abstract a carbonate hosted stratabound siliceous crust type sct mineralization base metal sulphides barite fluorite occurs over large areas of carnic alps and karawanken in the eastern alps it concerns a pervasively silicified lithological unit up to some tens of metres thick which caps the unconformity landscapes developed on epicontinental devonian dinantian carbonates the sct mineralization is directly overlaid by different transgressive siliciclastic sediments which range from lower carboniferous to lower permian the presence of fragments of the sct mineralization in the transgressive siliciclastic sediment bounds its whole lithological evolution within a short stratigraphic interval of lower carboniferous age selected features of the regional and lithostratigraphic setting are discussed the chemical characterisation is based on the statistical evaluation of compositional data of 581 selected samples three significant groups of elements have been distinguished 1 the hydrological and metasomatically active elements si ba f which show a strong negative correlation amongst themselves and characterise the silica saturated aqueous solutions 2 the terrigenous elements al 2 o 3 k 2 o fe tot tio 2 b be ce la nb v y zr which suggest a continental margin environment for silica deposition 3 the sulphide metals cu pb zn ni sb as hg cd which define the metalliferous signature of the sct mineralization some consistent but still debatable genetic aspects of the sct mineralization are as follow 1 silica may be supplied by illitization of clay rich basinal sediments during their diagenesis 18 o of microcrystalline quartz ranges from 18 5 and 24 6 and is very similar to 18 o of authigenic quartz deriving from diagenetic processes of illitization of clay rich basinal sequences 2 the diagenetic evolution of these sediments may trigger off the movement of silica rich marine pore waters 34 s of barite ranges from 15 5 to 19 3 with an average of 17 7 and are in good agreement with 34 s of sulphate in ocean waters of upper devonian lower carboniferous age 3 a convective hydrological system connected with sinsedimentary transtensive tectonics active in the carnic alps since the frasnian may be the transport mechanism of aqueous solutions 4 a weak drop in ph in the dominant carbonate environment represents the conditions for silica precipitation sct mineralization showing persistent independent and distinct characters occurs over large areas also in other sites of the alpine belt and outside italy and austria therefore it points to important markers for some sedimentary sequences as well as to a worldwide significant cyclic metallogenic event it represents a new ore deposit type within the carbonate hosted mineralization

stable isotope composition of f pb zn mineralization in the valle de tena spanish central pyrenees this study dealing with the stable isotope c o and s geochemistry of f pb zn deposits is part of an integrated metallogenetic study of the valle de tena central pyrenees the objective of this work is to place constraints on the origin of the mineralizing solutions and sources of sulphur and metals two types of mineralization have been identified 1 stratabound ores linked to an emersion episode that occurred during the namurian to westfalian transition portalet mines and 2 low temperature hydrothermal veins related to post hercynian extensional tectonics yenefrito and lanuza mines and tebarray occurrences stable isotopic study indicates that the source of mineralizing components was the local upper palaeozoic country rocks in the case of the stratabound portalet deposit biogenic sulphides and connate waters modified by some meteoric input through a karst surface in the case of vein deposits stable isotopes point toward either modified connate water or marine water as the mineralizing fluid with sulphur and metals derived from a mixture in different proportions of regional igneous and meta sedimentary country rocks

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

thermal and kinematic modeling of bedrock and detrital cooling ages in the central himalaya 1 we introduce a new method that convolves detrital mineral cooling ages with digital elevation models to test numerical models of erosion in collisional orogens along a trans himalayan transect in central nepal we develop a kinematic and thermal model to predict variations in bedrock cooling ages in modern himalayan topography the model assumes a thermal steady state and utilizes a simple ramp and flat style decollement representing the main himalayan thrust the model also assumes a topographic steady state such that overthrusting is balanced by erosion to maintain a constant topographic profile erosion rates display strong spatial variations as a function of the angle between the slope of the topographic surface and the trajectories of rock particles approaching the surface to predict the detrital cooling age signal we combine the distribution of bedrock cooling ages within a catchment with the rate of erosion and distribution of muscovite predicted cooling age distributions are compared with detrital 40ar 39ar muscovite data to assess varying tectonic and erosion scenarios such cooling age distributions are very sensitive to how much of the total plate convergence is expressed as erosion of the overthrusting plate the best fit model assigns 4 6 km myr 1 of overthrusting equivalent to as much as 1 5 2 km myr 1 of vertical erosion to the asian plate although a trade off exists between ramp geometry along the decollement and the best fit rate only a narrow range of ramp dips decollement depths and erosionally compensated overthrusting rates are compatible with the observed detrital ages

deep seismic reflection evidence for continental underthrusting beneath southern tibet the himalaya and adjacent tibetan plateau constituting earth s largest region of elevated topography and anomalously thick crust formed as a consequence of cenozoic collision between india and asia itself considered the archetypal continent continent collision1 3 here we report the first results from an attempt to image the structure of the crust beneath this region using deep seismic reflection profiling our 100 km long profile acquired in the tethyan himalaya shows a mid crustal reflection that prob ably marks the active thrust fault along which the indian plate is underthrusting southern tibet upper crustal reflections with geo metries suggestive of large scale structural imbrication of the upper crust and moho reflections from the base of the double normal thickness crust underlying the region these results lend substantial support to the view that crustal thickening beneath southernmost tibet was accomplished by wholesale underthrusting of indian continental crust beneath the structurally imbricated upper crust comprising the tethyan himalaya

seismotectonics of the himalayan collision zone geometry of the underthrusting indian plate beneath the himalaya fault plane solutions and well determined focal depths of medium sized earthquakes topography and landsat imagery in conjunction with seismicity maps cross sections and available geological information are used to investigate the present tectonics of the himalayan continental collision zone most of the accurately located epicenters of events along the himalayan arc 78 e 95 e that occurred between 1961 and 1981 are concentrated in a narrow zone about 50 km wide lying between the northerly dipping main boundary mbt and main central mct thrusts most of these events are located just south of the mct though the epicenters of the events are in general well located their depths as determined by teleseismic travel time data are very unreliable events with accurately determined depths obtained from identification of surface reflected phases define a simple planar zone from about 10 km and 20 km depth with an apparent dip of about 15 this result is all the more remarkable considering that the events used were located along about an 1800 km length of the himalyan arc except for one all available focal mechanisms of events within this zone indicate shallow 30 north dipping thrusts this shallow north dipping zone apparently defines a part of the detachment that separates the underthrusting indian plate from the lesser himalayan crustal block the spatial extent and the geometry of this interplate thrust zone strongly indicate that the mbt and nearby subsidiary surface and blind thrusts rather than the mct are currently the most active structures of the himalayan arc we suggest that the great himalayan earthquakes m 8 occur along the same detachment surface as defined by the thrust type medium sized events events located to the south of the mbt and beneath the ganges foredeep show normal faulting with t axes perpendicular to the himalayan trend the above results suggest that the indian continental plate is underthrusting the himalayan crustal blocks in a relatively coherent and simple geometry and that this geometry is not much different from that observed along oceanic subduction zones the november 19 1980 earthquake that occurred near the mct near 88 5 e shows a predominantly strike slip focal mechanism one of the nodal planes of this mechanism is transverse to the himalayan structural grain and moreover this plane has a trend similar to that of the recently mapped yadong gulu rift in the tethyan himalaya and in southern tibet just northeast of the earthquake we interpret this predominantly left lateral strike slip mechanism to indicate a possible genetic relationship between transverse structural features in the underthrusting indian plate the kishangang basement fault and the upper himalayan blocks and tibet

source modeling of the 2015 mw 7 8 nepal gorkha earthquake sequence implications for geodynamics and earthquake hazards abstract the gorkha earthquake on april 25th 2015 was a long anticipated low angle thrust faulting event on the shallow decollement between the india and eurasia plates we present a detailed multiple event hypocenter relocation analysis of the mw 7 8 gorkha nepal earthquake sequence constrained by local seismic stations and a geodetic rupture model based on insar and gps data we integrate these observations to place the gorkha earthquake sequence into a seismotectonic context and evaluate potential earthquake hazard major results from this study include 1 a comprehensive catalog of calibrated hypocenters for the gorkha earthquake sequence 2 the gorkha earthquake ruptured a 150 60 km patch of the main himalayan thrust mht the decollement defining the plate boundary at depth over an area surrounding but predominantly north of the capital city of kathmandu 3 the distribution of aftershock seismicity surrounds the mainshock maximum slip patch 4 aftershocks occur at or below the mainshock rupture plane with depths generally increasing to the north beneath the higher himalaya possibly outlining a 10 15 km thick subduction channel between the overriding eurasian and subducting indian plates 5 the largest mw 7 3 aftershock and the highest concentration of aftershocks occurred to the southeast the mainshock rupture on a segment of the mht decollement that was positively stressed towards failure 6 the near surface portion of the mht south of kathmandu shows no aftershocks or slip during the mainshock results from this study characterize the details of the gorkha earthquake sequence and provide constraints on where earthquake hazard remains high and thus where future damaging earthquakes may occur in this densely populated region up dip segments of the mht should be considered to be high hazard for future damaging earthquakes

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

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

strong seismic coupling underneath garhwal kumaun region nw himalaya india abstract no great earthquake has occurred in the garhwal kumaun region of nw himalaya in the past 500 years or more we report results of continuous gps measurements from 28 sites from the region to suggest that the convergence rate in this part of the himalaya is about 18 mm yr which is leading to strain accumulation in the region the main himalayan thrust mht in the frontal part of the himalaya under the outer and southern lesser himalaya is strongly coupled for a width of about 85 km the midcrustal ramp where earthquakes of himalayan seismic belt occur exhibits low coupling strong coupling on the mht beneath the outer and lesser himalaya is homogeneous except in the very shallow updip part of the mht subduction of sediments of the indo gangetic plains or the delhi hardwar ridge does not seem to influence coupling a high rate of strain accumulation which has continued for more than 500 years on a strongly coupled mht makes this one of the most earthquake vulnerable segments of the himalayan arc

seismic tomography structure of the 1999 chamoli earthquake source area in the garhwal himalaya simultaneous inversion of about 5000 seismic phase data of 391 aftershocks of the 29 march 1999 chamoli earthquake m b 6 3 recorded by 28 closely spaced temporary and permanent seismic stations sheds new light on understanding the seismogenic structure of the source area the best located 160 aftershocks m d 2 0 4 0 with root mean square error less than 0 2 sec and epicentral and depth error less than 1 km are clustered at a depth range of 8 16 km above the plane of detachment the interface between the himalayan sedimentary wedge and the indian shield the mainshock nucleated by thrust faulting at the fault end where the alakananda fault meets the plane of detachment at a depth of 15 km and the aftershocks occurred by shear adjustment at the alakananda fault the 3d p and s wave velocity structures of the source area show an east west trending low velocity zone lvz the lvz is comparable with the north dipping or near vertical alakananda fault on the surface it extends from the surface down to 15 km depth it broadens in the north south direction at shallower 0 10 km depth and narrows at deeper depth 10 15 km the p wave tomography shows a high velocity zone hvz at the eastern margin of the lvz the mainshock and the aftershocks occurred at the contact of these two zones and within the hvz the s wave velocity structure resembles that of the p wave but it shows an lvz at the mainshock source area at a depth of 15 km where the higher p wave velocity structure hvz is observed the seismogenic source area is thus characterized by a higher v p v s or higher poisson s ratio at the fault end this anomaly may be due to fluid filled fractured rock matrix which might have contributed to the nucleation of the mainshock manuscript received 17 june 2002

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

aftershocks of the march 1999 chamoli earthquake and seismotectonic structure of the garhwal himalaya the aftershocks of the chamoli earthquake m b 6 3 of 28 march 1999 are analyzed to understand the seismotectonic structure of the garhwal himalaya the permanent as well as temporary microearthquake network data are used the mainshock occurred on the basement thrust by thrust faulting the aftershocks on the other hand are triggered at the seismogenic faults to the south of the main central thrust mct by thrust faulting as well as by strike slip faulting and all the events occurred above the plane of detachment basement thrust the mct is not the seismogenic fault

rupture of the indian slab in the 2011 mw 6 9 sikkim himalaya earthquake and its tectonic implications unlike the other himalayan plate boundary segments the eastern nepal to bhutan himalayan region is not known to have generated prominent shallow thrust faulting earthquakes typical of the ongoing convergence this region features strike slip earthquakes over the depth ranges of 40 120 km indicating intraslab deformation here we present for the first time a slip distribution model for the largest recorded intraslab strike slip earthquake in this region the mw 6 9 sikkim event that occurred on 18 september 2011 relying on kinematic source process modeling our results indicate a ne sw trending steeply dipping sinistral source zone within the underthrusting indian slab the rupture propagated radially with a low rupture velocity of 1 7 km s breaking a large asperity of 20 a 20 km 2 with a maximum slip of 1 6 m the rupture nucleated at a depth of 45 km and reached upper mantle depths the computed coseismic stress drop value is 13 6 mpa we suggest that most of the aftershocks occurred on the conjugate plane possibly due to stress triggering stress inversion of focal mechanisms indicates a transpressive stress regime throughout the crust and pure strike slip regime in the upper mantle we observed a unimodal distribution of earthquakes beneath the higher himalaya this indicates a strong brittle indian slab and unravels a scenario of an eventual breakup of the lithosphere the key trigger might be variation in the convergence rates along the himalayan arc 2019 american geophysical union all rights reserved

southward extrusion of tibetan crust and its effect on himalayan tectonics the tibetan plateau is a storehouse of excess gravitational potential energy accumulated through crustal thickening during india asia collision and the contrast in potential energy between the plateau and its surroundings strongly influences the modern tectonics of south asia the distribution of potential energy anomalies across the region derived from geopotential models indicates that the himalayan front is the optimal location for focused dissipation of excess energy stored in the plateau the modern pattern of deformation and erosion in the himalaya provides an efficient mechanism for such dissipation and a review of the neogene geological evolution of southern tibet and the himalaya shows that this mechanism has been operational for at least the past 20 million years this persistence of deformational and erosional style suggests to us that orogens like other complex systems can evolve toward steady state configurations maintained by the continuous flow of energy the capacity of erogenic systems to self organize into temporally persistent structural and erosional patterns suggests that the tectonic history of a mountain range may depend on local energetics as much as it does on far field plate interactions

geochemical patterns of a sheared fluorite vein parzan spanish central pyrenees the formation of parzan fluorite lead extension type vein spanish central pyrenees is related to the post hercynian hydrothermal activity widespread not only in the pyrenees but in western europe as well the lode was later strongly deformed during the alpine orogeny with textural modifications and destruction of primary fluid inclusions in order to determine if geochemical signatures of the vein were disturbed during alpine deformation post ore fluid inclusions and quartz oxygen isotopes have been addressed microthermometry and x ray microanalysis of frozen inclusions confirm the na ca cl character of post ore fluid circulations and indicate that they were originally derived from a single source triassic connate waters oxygen isotope data on quartz formed during deformation along with trace element geochemistry suggest that the geochemical signatures of the vein mainly ree and 87sr 86sr were apparently not reset during deformation the ree content of fluorites is very high up to 0 12 the chondrite normalized ree patterns display a continuous decrease from la to lu sulphur isotope data for the parzan vein is outside the typical deep seated range suggesting dominantly crustal sources of sulphur for sulphides while formation waters may be proposed for barite parzan fluorites have the most radiogenic sr values of all the investigated fluorite deposits in central pyrenees they scatter in the range of both the igneous rocks and the cambrian ordovician and triassic detrital sequences of the parzan area if ree contents and 87sr 86sr ratios reflect the primary stage of vein filling as suggested by the good correlation between both geochemical signatures the linear array between 87sr 86sr and 1 ree is suggestive of a mixing process the 34s 18o and 87sr 86sr parameters in barite which postdates the fluorite also provide strong evidence that barite deposition is a result of fluid mixing such an interpretation is in line with present day ideas for the genesis of many of the f ba pb zn vein deposits in the hercynian belt of iberia

the status of central seismic gap a perspective based on the spatial and temporal aspects of the large himalayan earthquakes abstract the central himalaya considered as a prominent seismic gap is generally believed to be the most vulnerable segment due for a great plate boundary earthquake m 8 two significant historical earthquakes are known to have occurred in this region in ad 1505 and 1803 interpreted by some workers as great earthquakes occurrences of these events question the validity of central himalaya being a seismic gap here we analyze the macroseismal data from the central himalaya and the gangetic plains and suggest that neither of these earthquakes can be qualified as a plate boundary type event and the size of at least the 1803 does not exceed mw 7 7 our studies further indicate that the central himalayan frontal thrusts may be undergoing a quiescence of 1000 years in terms of generation of great earthquakes assuming a steady elastic strain accumulation due to plate convergence and its simple translation as periodic great earthquakes such long quiescence may appear intriguing we suggest that the long term quiescence and the spatial and temporal clustering that characterize the distribution of large earthquakes in the himalaya is a manifestation of the tectonic deformation associated with a highly evolved fold and thrust belt our analyses also indicate that the large moderate earthquakes are mostly concentrated on higher level thrusts these structures probably accommodate most of the seismogenic slip in the himalaya and the rest of the strain could possibly be expended on passive folding consequently great earthquakes m 8 are relatively infrequent as in the case of central himalaya apparently leading to long periods of quiescence

paleoseismological evidence of surface faulting along the northeastern himalayan front india timing size and spatial extent of great earthquakes the similar to 2500 km long himalayan arc has experienced three large to great earthquakes of m w 7 8 to 8 4 during the past century but none produced surface rupture paleoseismic studies have been conducted during the last decade to begin understanding the timing size rupture extent return period and mechanics of the faulting associated with the occurrence of large surface rupturing earthquakes along the similar to 2500 km long himalayan frontal thrust hft system of india and nepal the previous studies have been limited to about nine sites along the western two thirds of the hft extending through northwest india and along the southern border of nepal we present here the results of paleoseismic investigations at three additional sites further to the northeast along the hft within the indian states of west bengal and assam the three sites reside between the meizoseismal areas of the 1934 bihar nepal and 1950 assam earthquakes the two westernmost of the sites near the village of chalsa and near the nameri tiger preserve show that offsets during the last surface rupture event were at minimum of about 14 m and 12 m respectively limits on the ages of surface rupture at chalsa site a and nameri site b though broad allow the possibility that the two sites record the same great historical rupture reported in nepal around a d 1100 the correlation between the two sites is supported by the observation that the large displacements as recorded at chalsa and nameri would most likely be associated with rupture lengths of hundreds of kilometers or more and are on the same order as reported for a surface rupture earthquake reported in nepal around a d 1100 assuming the offsets observed at chalsa and nameri occurred synchronously with reported offsets in nepal the rupture length of the event would approach 700 to 800 km the easternmost site is located within harmutty tea estate site c at the edges of the 1950 assam earthquake meizoseismal area here the most recent event offset is relatively much smaller 2 5 m and radiocarbon dating shows it to have occurred after a d 1100 after about a d 1270 the location of the site near the edge of the meizoseismal region of the 1950 assam earthquake and the relatively lesser offset allows speculation that the displacement records the 1950 m w 8 4 assam earthquake scatter in radiocarbon ages on detrital charcoal has not resulted in a firm bracket on the timing of events observed in the trenches nonetheless the observations collected here when taken together suggest that the largest of thrust earthquakes along the himalayan arc have rupture lengths and displacements of similar scale to the largest that have occurred historically along the world s subduction zones

isotopic composition of strontium in the valle de tena spanish central pyrenees fluorite deposits relevance for the source of elements and genetic significance the fluorite deposits of the valle de tena central pyrenees include stratabound portalet and vein lanuza and tebarray deposits the formation of which are linked to a namurian westfalian emersion episode and to post hercynian hydrothermal systems similar to those occurring elsewhere in hercynian europe in this study strontium isotopes were used to determine the source s of strontium and by inference calcium of the fluorite mineralizations as well as the nature of the ore forming fluids fluorite and calcite from each deposit have similar 87sr 86sr ratios portalet 0 7085 0 7108 lanuza 0 7086 0 7104 and tebarray 0 7086 0 7101 in all deposits the sr isotope composition of most of the ca minerals is more radiogenic than that of the host limestones this indicates that the ca minerals contain a mixture of sr derived locally from the host limestones and 87 sr enriched sr leached from silicate minerals in the siliciclastic portion of the basement sequence and in granites from the study area volcanic rocks are ruled out as a significant sr source for the fluorite deposits the observed trend in 87sr 86sr versus 1 sr support a fluid rock interaction model which satisfactorily reproduces the marked 87sr enrichment in the fluorites and calcites from the deposits

landscape disequilibrium on 1000 10 000 year scales marsyandi river nepal central himalaya in an actively deforming orogen maintenance of a topographic steady state requires that hillslope erosion river incision and rock uplift rates are balanced over timescales of 10 5 10 7 years over shorter times 10 5 years hillslope erosion and bedrock river incision rates fluctuate with changes in climate on 10 4 year timescales the marsyandi river in the central nepal himalaya has oscillated between bedrock incision and valley alluviation in response to changes in monsoon intensity and sediment flux stratigraphy and 14 c ages of fill terrace deposits reveal a major alluviation coincident with a monsoonal maximum ca 50 35 ky bp cosmogenic 10 be and 26 al exposure ages define an alluviation and reincision event ca 9 6 ky bp also at a time of strong south asian monsoons the terrace deposits that line the lesser himalayan channel are largely composed of debris flows which originate in the greater himalayan rocks up to 40 km away the terrace sequences contain many cubic kilometers of sediment but probably represent only 2 8 of the sediments which flushed through the marsyandi during the accumulation period at f10 4 year timescales maximum bedrock incision rates are f7 mm year in the greater himalaya and f1 5 mm year in the lesser himalayan mahabarat range we propose a model in which river channel erosion is temporally out of phase with hillslope erosion increased monsoonal precipitation causes an increase in hillslope derived sediment that overwhelms the transport capacity of the river the resulting aggradation protects the bedrock channel from erosion allowing the river gradient to steepen as rock uplift continues when the alluvium is later removed and the bedrock channel re exposed bedrock incision rates probably accelerate beyond the long term mean as the river gradient adjusts downward toward a more equilibrium profile efforts to document dynamic equilibrium in active orogens require quantification of rates over time intervals significantly exceeding the scale of these millennial fluctuations in rate d 2003 elsevier b v all rights reserved

decoupling of erosion and precipitation in the himalayas the hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks1 2 3 most such models invoke a stream power rule in which either increased discharge or steeper channel slopes cause higher erosion rates spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain here we combine observations from a meteorological network across the greater himalaya nepal along with estimates of erosion rates at geologic timescales greater than 100 000 yr from low temperature thermochronometry across a zone of about 20 km length spanning the himalayan crest and encompassing a more than fivefold difference in monsoon precipitation significant spatial variations in geologic erosion rates are not detectable decreased rainfall is not balanced by steeper channels instead additional factors that influence river incision rates such as channel width and sediment concentrations must compensate for decreasing precipitation overall spatially constant erosion is a response to uniform upward tectonic transport of greater himalayan rock above a crustal ramp

gravity anomalies flexure of the indian plate and the structure support and evolution of the himalaya and ganga basin bouguer gravity anomalies along four profiles across the western himalaya and ganga basin show large deviations from local isostatic equilibrium a deficit of mass characterizes the ganga basin and an excess underlies the lesser himalaya both can be understood if the indian plate is flexed down by the distributed load of part of the mountains the cross sectional shape of the ganga basin seems to be controlled by the deflection of the indian plate which we compute assuming the indian plate to overlie an inviscid fluid from the shapes of both bouguer anomaly profiles and the basement topography we place bounds on the flexural rigidity of such a plate if the ganga basin is a steady state feature then the age of the basal sediments in a given locality should be proportional to the distance of that locality from the southern edge of the basin if the rate of convergence of india and the himalaya were constant that rate should equal the distance divided by the corresponding age we find a rate of 10 to 15 mm a for the last 15 to 20 ma which is consistent with a large part of the 50 mm a rate of convergence between india and eurasia being absorbed by the eastward extrusion of parts of tibet profiles of bouguer gravity anomalies show only a small peak or plateau over the southern edge of the lesser himalaya implying that the boundary between the light sediments of the ganga basin and the heavier crustal rocks of the lesser himalaya is not sharp and that there exists some light material beneath the range we infer that some sediment deposited in the ganga basin has been underthrust beneath the lesser himalaya but the quantity is small most of this sediment probably is scraped off the indian plate to make the foothills of the range we find that the load of the high himalaya is too large to be supported solely by elastic stress in the indian plate if the flexural rigidity of the plate is constant and if no other external forces act on the plate the observed gradient in bouguer gravity anomalies increases from an average of about 1 mgal km over the ganga basin and lesser himalaya to about 2 mgal km over the high himalaya this increase in the gravity gradient implies that the moho dips more steeply 10 15 beneath the high himalaya than beneath the lesser himalaya 2 3 we interpret this steepening of the moho to be due to a weakening of the plate which allows it to bend more sharply beneath the high himalaya than farther south with the inclusion of a weak segment of indian plate beneath the high himalaya calculated anomalies show a somewhat increased gradient beneath the high himalaya but when the weight of the entire himalaya is used as a load on the plate calculated anomalies are more negative than observed therefore an external force system is needed to support much of the weight of the high himalaya as well as to bend the plate sufficiently beneath the high himalaya the magnitudes of the bending moment and the force per unit length that must be applied to the end of the plate are compatible with their sources being gravity acting on a part of india s mantle lithosphere stripped of its crust and underthrust beneath southern tibet

electrical resistivity cross section across the garhwal himalaya proxy to fluid seismicity linkage abstract magnetotelluric mt measurements along a profile cutting across the garhwal himalaya of india are inverted to obtain 2 d electrical resistivity structures of the himalayan wedge and of the underthrusting indian plate the imaged resistivity cross section is dominated by a low angle north east dipping intra crustal high conducting layer ic hcl with an average thickness of 5 km at transition from the lesser himalaya to the higher himalaya the ic hcl is marked by a ramp structure across which its top jumps from a depth of 8 km to 13 km high conductivity of the layer is caused by pounding of upward propagating metamorphic fluids trapped by tectonically induced neutral buoyancy in compression regime of the himalaya the mechanical weakening effects of the fluids counteract the fault normal stresses thereby facilitating thrust type earthquakes on a plane imaged as the top of the ic hcl it is suggested that in the himalaya collision belt like the active subduction zone the active seismic plane forming seat of large and great earthquakes is located a few kilometers above the top of the down going plate in this tectonic setting the high conductance ramp symbolizes a block of low shear strength and high strain which under the deviatoric stresses release accentuated stresses into the brittle crust thereby generating small but more frequent earthquakes in the narrow himalayan seismic belt in response to either the co seismic pumping or the stress transfer during inter seismic period the upward infiltration of fluid fluxes into the over pressurized zones sufficiently reduces the shear strength of local thrusts and shear zones turning these into locales of concentrated seismicity

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

revisiting the 1991 uttarkashi and the 1999 chamoli india earthquakes implications of rupture mechanisms in the central himalaya abstract the central himalaya has attracted much attention due to its potential to host a great earthquake an inference based on the history of earthquakes and the geodetic slip estimates the largest and earliest historically documented earthquake in the central himalaya occurred in 1803 m 7 7 near uttarkashi on its western part much before the great event of 1934 mw 8 2 located farther to the east both of which were felt severely in the gangetic plain south of the mountain front the seismotectonic model by seeber and armbruster 1981 predicts that large great earthquakes originate on the main himalayan thrust mht and their ruptures propagate southward to the main frontal thrust mft the rupture of the april 25 2015 mw 7 8 gorkha nepal earthquake however was southeast directed with a southwest directed slip and its mw 7 3 aftershock on may 12 also showed a similar slip direction post 2015 we revisited the 1991 uttarkashi mw 6 7 and the 1999 chamoli mw 6 5 earthquakes in india both of which had originated on the mht flat but show ssw directed slips as reported in this study ruptures of both these earthquakes fell short of reaching the mft just as the historically documented 1803 earthquake but their shaking effects were felt in the southern plains these observations compel us to conclude that the varying rupture modes exhibited by the himalayan earthquakes are controlled primarily by the geometry of the flat ramp flat system

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

hydrothermal events in the valle de tena spanish western pyrenees as evidenced by fluid inclusions and trace element distribution from fluorite deposits abstract this paper provides further evidences from fluorite and calcite geochemistry and from fluid inclusion studies for the origin of the valle de tena fluorite deposits the valle de tena spanish western pyrenees contains two kinds of fluorite mineralizations 1 vein type deposits located in the vicinity of the panticosa granite and enclosed by devonian carbonate facies and 2 carbonate hosted mineralizations on highly silicified lower carboniferous limestones based on geological evidences the latter deposits can be referred to as permo triassic microthermometrical measurements on two phase water rich inclusions with high liquid to vapor ratios yield homogenization temperatures ranging from 100 to 200 c for the two deposit types salinities range from 4 0 to 11 6 eq wt nacl for carbonate hosted deposits and from 12 5 to 21 3 eq wt nacl for vein mineralizations ree contents are variable and highest abundances are found in the fluorite from lanuza and tebarray green flurite these later fluorite mineralizations have primary ree patterns with positive eu anomalies which possibly reflect the alteration of feldspar the ree distribution patterns of fluorites and calcites from the carbonate hosted mineralizations are different from those occurring as veins the decrease of lree in the former resulted in roof shaped ree patterns the negative eu anomalies as well as the trace element distribution allow us to deduce that the fluid from which these later ca minerals were formed was probably equilibrated with the sedimentary country rocks the fluid inclusion geochemical geologic and preliminary stable isotope data support two temporally distinct hydrothermal systems accounting for the fluorite formation and suggest a sedimentary basin source for the ore fluids high salinity fluids basement brines are involved in the formation of the vein type deposits whereas the subsequent carbonate hosted mineralizations were formed by mobilization of the fluorite veins by formation waters the most likely fluorite deposition mechanism is cooling with minor contribution of fluid rock interaction in such context magmatic activity is considered as heat source the above mineralization events possibly span a time from permian to triassic which is in close agreement with the timing of hydrothermal processes documented throughout the hercynian europe

structural evolution of orogenic wedges interplay between erosion and weak decollements orogenic wedges commonly display an inner wedge where crystalline units have been exhumed and an outer wedge formed by imbricated sedimentary units detached from the basement analog experiments have shown that similar structures can emerge naturally in the presence of weak decollements due to the interplay between erosion and deformation in this study we further investigate this hypothesis using two dimensional visco elasto plastic numerical models our experiments assume a basal and an intermediate decollement within the wedge experiments with a frictional strength of the basal decollement lower or equal to that of the intermediate decollement show a structural evolution of fold and thrust belts dominated by out of sequence thrusting conversely when the intermediate decollement is weaker than the basal decollement distinct outer and inner wedges are formed this process leads to episodic migration of midcrustal ramps tectonic underplating and antiformal stacking facilitated by erosion comparison between our models and the himalayan wedge suggests a low effective friction 0 10 which is probably due to dynamic weakening during large m8 himalayan earthquakes the deeper decollement along which the lower plate thrusts beneath the high himalaya must be a thermally activated ductile shear zone with an apparent friction of 0 18 fold and thrust belts worldwide exhibit various architectures in which different decollement levels might be activated thus our study provides a framework to help assess under which conditions a variety of structures observed in orogenic systems can arise

the grid work texture of authigenic microcrystalline quartz in siliceous crust type sct mineralized horizons siliceous crust type sct formations are pervasive silicified horizons associated with fluoritebarite polymetallic sulfide mineralization in carbonate rocks they almost invariably show a peculiar grid work texture formed by microcrystalline quartz the mineralogical and textural features of several sct samples from italy spain france china and brazil were investigated by optical and electron microscopy and x ray and neutron powder diffraction the resulting 001 pole figures exhibit two main components of orientation of the crystallographic c axis with respect to the normal to the sample surface one located at about 35 and the other in the range 60 85 the observed textural features are seen in all samples and they appear to be independent of the age and geographical location of the sct formation the observed grid work texture is tentatively interpreted as forming by nucleation of quartz seeds on specific faces of surrounding crystals the observed morphology and the regularly oriented populations of crystals are consistent with simultaneous growth of quartz crystals having well defined reciprocal orientations the grid work texture of quartz in sct horizons is similar to the type reported for magadi type cherts which are commonly interpreted as formed by magadiite mediated silica precipitation processes since the genesis of sct deposits is totally unrelated to alkaline lake genetic processes it is concluded that cherts showing strongly textured patterns of microcrystalline quartz may have a different origin than magadi type deposits

thrust tectonics crustal shortening and the structure of the far eastern nepal himalaya balanced and restored structural sections across the far eastern nepal himalaya have been constructed in order to determine the structure and evolution of the himalayan orogenic wedge and the amount of tectonic shortening the region has undergone since the initiation of thrusting along the main central thrust mct the far eastern nepal himalaya is comprised of three distinct thrust bound tectonic packages the higher himalayan crystalline thrust sheet the lesser himalayan metasediment thrust package and the sub himalayan imbricate fan the higher himalayan crystallines consisting of kyanite and sillimanite bearing gneisses intruded by the miocene jannu leucogranites have been thrust over the lesser himalayan metasediments along the mct for a distance of 140 km to 175 km the lesser himalayan metasediments are a 12 km thick unit consisting primarily of phyllites metaquartzites and mylonitic augen gneisses in which garnet biotite and chlorite metamorphic zones are exposed in progressively deeper structural levels the lesser himalayan metasediment thrust package is underlain by a decollement the main detachment fault mdf which lies at a calculated depth of between 6 and 10 km underneath the mahabharat lekh and at a calculated depth of 20 to 25 km north of the tamar khola dome the tamar khola dome overlies a footwall ramp along the mdf where the mdf cuts upsection through the lesser himalayan metasediments the lesser himalayan thrust package probably has an internal structure aproximating a hinterland dipping duplex with the mct and the mdf corresponding to the roof and floor thrusts respectively both the tamar khola thrust an out of sequence breach thrust and the main boundary thrust mbt are splay thrusts off of the mdf the sub himalaya consisting of nonmetamorphosed sedimentary rocks displays an emergent imbricate fan geometry and is underlain by the southern continuation of the mdf which lies at a depth of 5 5 km to 6 km beneath the siwalik hills folding and thrusting within the lesser himalayan thrust package and the sub himalayan imbricate fan have accomodated 45 to 70 km of tectonic shortening total north south shortening across the higher lesser and sub himalaya of far eastern nepal south of the tibetan plateau has been of the order of 185 km to 245 km and has occurred at an average rate of 7 4 mm to 15 3 mm per year since the initiation of the mct between 16 and 25 ma

global positioning system measurements of indian plate motion and convergence across the lesser himalaya we use global positioning system gps measurements acquired from 1991 to 1995 to constrain the motion of sites in bangalore in southern india and kathmandu nepal relative to a global gps network these measurements permit estimates of the northward motion of the indian plate and convergence between the southern himalaya and the indian subcontinent the velocities of bangalore and kathmandu in the itrf92 reference frame agrees with that predicted by the nnr nuvel1a plate motion model for indian plate motion and differ from that predicted for the australian plate confirming the independent motion of the indian and australian plate fragments no significant motion was detected between bangalore and kathmandu during the three years from 1991 1994 even though kathmandu is located in the hanging wall of the active himalayan thrust system the himalayan thrust system is thought to accommodate 18 7 mm yr of convergence and has been the source of several historic m 8 earthquakes the absence of motion of kathmandu relative to the indian plate can be explained if the thrust system is presently locked south of the greater himalaya our preferred model has no steady slip on the detachment south of the greater himalaya and steady slip at a rate greater than 6 mm yr 1 3 of the long term convergence rate can be ruled out at 95 confidence level

separation and recovery of various sulphur species in sedimentary rocks for stable sulphur isotopic determination abstract existing methods to extract particular forms of sulphur in rocks and sediments are reviewed and evaluated for application in a chemical scheme to recover sulphur as either ag2s or baso4 precipitates for isotopic analysis the s species distinguished include acid soluble sulphides and sulphates elemental s pyrite barite and various categories of organically bound s there is no evidence of cross contamination or isotopic fractionation during the separation as applied to mixtures synthesized from internal control samples the precision obtained on repetitive extractions is equivalent to that of the measurement technique itself typically 0 2 in the 34s value the chemical separation scheme is demonstrated by application to sections of peat collected from the howards pass xy deposit in the yukon territory canada

characterization of geological boundaries using 1 d wavelet transform on gravity data theory and application to the himalayas we investigate the use of the continuous wavelet transform for gravity inversion the wavelet transform operator has recently been introduced in the domain of potential fields both as a filtering and a source analysis tool here we develop an inverse scheme in the wavelet domain designed to recover the geometric characteristics of density heterogeneities described by simple shaped sources the 1 d analyzing wavelet we use associates the upward continuation operator and linear combinations of derivatives of any order in the gravity case we first demonstrate how to localize causative sources using simple geometric constructions both the upper part of the source and the whole source can be studied when considering low or high altitudes respectively the homogeneity degree of the source is deduced without prior information and allows us to infer its shape introducing complex wavelets we derive analytically the scaling behavior of the wavelet coefficients for the dyke and the step sources the modulus term is used in an inversion procedure to recover the thickness of the source the phase term provides its dip this analysis is performed on gravity data we measured along a profile across the himalayas in nepal good agreement of our results with well documented thrusting structures demonstrates the applicability of the method to real data also deeper less constrained structures are characterized

plio plistocene in sequence thrust propagation along the main central thrust zone kumaon garhwal himalaya india new thermochronological data abstract the kumaon and garhwal himalayas nw india have similar geologic tectonic topographic and precipitation pattern however low temperature thermochronological age pattern varies significantly along the strike as well as across the strike of major faults here we interpret the new set of thermochronological age data across the strike of major faults namely vaikrita thrust vt munsiari thrust mt berinag thrust bt and the baijnath nappe along pindari valley in the kumaon garhwal himalaya in the present work 18 new apatite fission track aft ages of samples collected along a north south transect have been reported ages in the hanging wall of vt which range from 2 1 0 2 to 4 2 0 7 ma have been found to be becoming younger linearly with distance from north to the vt this trend crosses the vt with significant jump in ages in the south of the vt ages are lying between 0 3 0 1 and 3 9 0 8 ma and show linear variation with distance from the vt to bt no significant jump in ages across the mt is observed and the linear trend of younging southward is continuing till the bt the break and displacement in age pattern with youngest ages close to thrusts possibly indicate progressive late thrust movement it reflects sequential uplift and cooling towards the south from the vt to bt which is consistent with an in sequence style of thrust propagation we compare our new data to the published thermochronological data from its adjacent traverses along the goriganga and dhauliganga valleys 25 km away from the present traverse towards east and west respectively in the kumaon garhwal himalaya in order to understand potential along strike variations in the kinematics our observations indicate a dynamic coupling between tectonic and surface processes in the garhwal kumaon himalaya and support that the geometry of crustal scale faults and their associated kinematics control exhumation pathways of rocks

numerical modeling of mountain building interplay between erosion law and crustal rheology 1 coupling between erosion and tectonics is thought to play a determinant role in orogenic evolution here we investigate the interplay in this coupling between the assumed erosion law and the crustal rheology at the margin of a collisional plateau like the himalaya of central nepal lithospheric deformation is calculated over a time scale of 100 kyr by a 2d finite element model that incorporates the rheological layering of the crust and the main features of the convergence across the range for the upper boundary condition two surface processes were tested a linear diffusion model and a 1d1 2 integrative model including fluvial incision along the fluvial network and hillslope erosion by landsliding model results and their sensitivity to the chosen combinations of erosion law and crustal properties are discussed in light of the constraining geologic and geomorphologic observations in contrast with the conclusions of cattin and avouac 2000 where a compliant quartz rich crustal rheology and diffusion law were required we combine a composite quartz diabase rheology for the crust with fluvial incision erosion law to account for erosion and elevation profiles across the himalaya of central nepal more generally it is proposed that because of the interplay between the dominant denudation conditions and the rheology of the crust both well documented erosion rates and processes can provide significant constraints on crustal properties within an active orogen

constraints on himalayan deformation inferred from vertical velocity fields in nepal and tibet spirit leveling data from the nepal himalaya between 1977 and 1990 indicate localized uplift at 2 3 mm yr in the lesser himalaya with spatial wavelengths of 25 35 km and at 4 6 mm yr in the greater himalaya with a wavelength of 40 km leveling data with significantly sparser spatial sampling in southern tibet between 1959 and 1981 suggest that the himalayan divide may be rising at a rate of 7 5 5 6 mm yr relative to central tibet we use two dimensional dislocation modeling methods to examine a number of structural models that yield vertical velocity fields similar to those observed although these models are structurally nonunique dislocation models that satisfy the data require aseismic slip rates of 2 7 mm yr on shallow dipping faults beneath the lesser himalaya and rates of 9 18 mm yr on deep thrust faults dipping at 25 n near the greater himalaya unfortunately the leveling data cannot constrain long wavelength uplift 100 km across the himalaya and unequivocal estimates of aseismic slip in central nepal are therefore not possible in turn the poor spatial density of leveling data in southern tibet may inadequately sample the processes responsible for the uplift of the greater himalaya despite these shortcomings in the leveling data the pattern of uplift is consistent with a crustal scale ramp near the greater himalaya linking shallow northward dipping thrust planes 3 6 beneath the lesser himalaya and southern tibet aseismic slip on the potential rupture surface of future great earthquakes beneath the nepal himalaya south of this ramp appears not to exceed 30 of the total convergence rate between india and southern tibet resulting in an accumulating slip deficit of 13 8 mm yr

metallogenesis at the terramonte pb zn ag quartz vein portugal geological mineralogical and geochemical evidences abstract the pb zn ag quartz vein from terramonte cuts the neoproterozoic cambrian schist greywacke complex this orebody was partially exploited the paragenetic sequence consists of four stages containing quartz accompanied mainly by arsenopyrite and pyrite in the first stage sphalerite in the second stage galena showing many inclusions of several sulphosalts in the third stage and carbonates in the fourth remobilization stage several sulphide and sulphosalt grains are oscillatory zoned the chemical distinction between lighter and darker zones in backscattered images of arsenopyrite pyrite sphalerite and freibergite is due to substitutions in the mineral lattices but the distinction between these zones in semseyite is due to a higher pb content and a lower sb content in the lighter zone than in the darker zone and the metal and metalloid are the main constituents in the solid solution but are not correlated the sb ag and bi substitute for pb in galena but did not cause any zoning ore deposition was possible due to mixing of a hypersaline fluid with up to 26 wt nacl equivalent and occasionally with cacl2 up to 17 wt which carried the metallic content of the fluid with an extremely low salinity fluid of presumed meteoric origin that percolated down into the basement the metals could have been leached from a mixture of mainly metasediments and also previous sb au deposits by fluids that acquire high salinity in one of two probable ways leaching of salt beds or following seawater evaporation the entire mineralizing event probably occurred at a relatively low temperature possibly between 120 and 230 c remobilization of pb zn ag as sb and cu will be due to the tectonic evolution of the opening of the atlantic ocean this vein is probably of alpine age

the siwaliks of western nepal ii mechanics of the thrust wedge abstract comparison between numerical models and structural data is used for a better understanding of the evolution of the siwalik thrust belt of western nepal the numerical model involves discontinuities within a critical wedge model a kinematic forward model of serial cross sections and a linear diffusion algorithm to simulate erosion and sedimentation in western nepal large piggy back basins duns are located above thick thrust sheets that involve more than 5500 m of the neogene siwalik group whereas piggy back basin sedimentation is less developed above thinner thrust sheets 4300 m thick numerical model results suggest that thrust sheet thickness and extension of wedge top basins are both related to an increase of the basal decollement dip beneath the duns the west dang transfer zone wdtz is a n ne trending tectonic lineament that limits the westward extent of the large piggy back basins of mid western nepal and is linked to a thickening of the himalayan wedge eastward the wdtz also affects the seismotectonics pattern the geometry of the thrust front the lateral extent of lesser himalayan thrust sheets and the subsidence of the foreland basin during middle siwalik sedimentation numerical models suggest that the individualisation of the piggy back basins at the transition between the middle siwalik and upper siwaliks followed the deposition of the middle siwaliks that induced a geometry of the foreland basin close to the critical taper as wdtz induces an e w thickning of the himalayan wedge it could also induce a northward shift of the leading edge of the ductile deformation above the basal detachment in greater himalayas of far western nepal field data locally suggest episodic out off sequence thrusting in the frontal thrust belt of western nepal whereas numerical results suggests that episodic out off sequence reactivation could be a general characteristic of the himalayan wedge evolution often hidden by erosion