sea salt aerosol groundwater salinization in the litorale romano natural reserve rome central italy a yearly survey in a piezometric network was realized in the litorale romano natural reserve rome central italy collecting water table and chemo physical data monthly chemo physical surveys highlighted a groundwater salinization variability in a coastal unconfined aquifer the aquifer is mostly composed by aeolian sands of a still preserved dune ridge environment on which a pine forest develops the groundwater salinity variability resulted is connected to the wind pattern and rainfalls in fact wind speed higher than 4 m s is responsible for generating sea salt aerosols ssa from sea surface a statistical analysis was performed for wind with a speed higher than 4 m s to detect wind orientation the dry deposition of ssa on the tree foliage appeared correlated to the westerly winds blowing in the springtime when the rainy season occurs the ssa is washed out from the trees and it is directed to groundwater where an enhancement of the electrical conductivity ec values is noticed whenever rain events occur and winds are not westerly a dilution of groundwater salinity takes place and consequently a reduction of ec chemical analyzes were realized as well they confirmed that groundwater of piezometers located close to the coast line is enriched of ssa elements

geochemical and boron strontium and oxygen isotopic constraints on the origin of the salinity in groundwater from the mediterranean coast of israel in order to identify the origin of the salinity and formation of saline plumes in the central part of the mediterranean coastal aquifer of israel we determined the elemental and boron strontium and oxygen isotopic compositions of fresh and brackish groundwater cl up to 1500 mg l we distinguish between two key anthropogenic sources 1 sewage effluents used for irrigation with high na cl so4 cl and b c1 ratios and low br cl ratios relative to seawater ratios low 11b values 0 10 and high 18o values 4 and 2 imported water from the sea of galilee that is artificially recharged to the aquifer with high br cl 3 10 3 and 18o values 1 and a low 87sr 86sr ratio of 0 70753 the brackish groundwater from the saline plumes have relatively low na cl ratios 0 5 0 8 and high ca mg mg cl and ca so4 hco3 1 ratios relative to seawater ratios marine so4 cl and br cl ratios 11b values of 24 8 49 9 18o of 2 95 to 4 73 and 87sr 86sr ratios of 0 708275 0 708532 the composition of most of the investigated groundwater from the saline plumes differs from those of the anthropogenic sources imported water fresh uncontaminated groundwater 87sr 86sr of 0 70866 11b of 20 30 and saline water from the adjacent eocene aquitard only in areas of artificial recharge does local groundwater have high br cl and 18o values that are typical to the sea of galilee the linear relationships between chloride and most of the ions including b and sr the relatively high 11b 30 and low 18 o 4 values and the chemical signature of the saline plumes e g marine br cl and so4 cl ratios suggest that 1 mixing processes control the chemical composition of the brackish water within the aquifer and 2 the saline postulated end member has a chemical composition that resembles modified seawater with a marine and higher 11b values and a 87sr 86sr ratio of 0 7083 we propose that most of the salinization phenomena and the formation of saline plumes in the inner parts of the coastal aquifer are derived from upconing of underlying natural saline water bodies and enhanced by overexploitation and draw down of the overlying fresh groundwater

mantle kinematics driving collisional subduction insights from analogue modeling abstract since several decades the processes allowing for the subduction of the continental lithosphere less dense than the mantle in a collision context have been widely explored but models that are based upon the premise that slab pull is the prominent driver of plate tectonics fail the india asia collision where several episodes of continental subduction have been documented constitute a case study for alternative views one of these episodes occurred in the early collision time within the asian plate where continental lithosphere not attached to any oceanic lithosphere subducted southward in front of the indian lithosphere during its northward subduction that followed the oceanic subduction of the tethys ocean this process known as collisional subduction has a counter intuitive behavior since the subduction is not driven by slab pull it has been speculated that the mantle circulation can play an important role in triggering collisional subduction but a detailed qualitative analysis of it is not available yet in this work we explore the southward subduction dynamics of the asian lithosphere below tibet by means of analogue experiments with the aim to highlight how the mantle circulation induces or responds to collisional subduction we found that during the northward oceanic subduction analogue of tethys subduction attached to the indenter indian analogue the main component of slab motion is driven vertically by its negative buoyancy while the trench rolls back in the mantle the convective pattern consists in a pair of wide convective cells on both sides of the slab but when the indenter starts to bend and plunge in the mantle trench motion reverses its advance transmits the far field forces to two upper plates asian analogues the more viscous frontal plate thickens and the less viscous hinterland plate which is attached to the back wall of the box subducts during this transition a pair of sub lithospheric convective cells is observed on both sides of the asian analogue slab driven by the shortening of the frontal plate it favors the initiation of the backwall plate subduction such subduction is maintained during the entire collision by a wide cell with a mostly horizontal mantle flow below tibet passively advecting the asian analogue slab experimental results suggest that once the tectonic far field force related to the forward horizontal motion becomes dominant upon the buoyancy forces trench advancing and the transmission of the tectonic force to the upper and backwall plates are promoted this peculiar condition triggers the subduction of the backwall plate despite it is light and buoyant

delineation of lithosphere structure and characterization of the moho geometry under the himalaya karakoram tibet collision zone using surface wave tomography

multiple episodes of continental subduction during india asia convergence insight from seismic tomography and tectonic reconstruction abstract high wavespeed tomographic anomalies shallower than 1100 km beneath the india asia collision zone are interpreted as continental slabs subducted during collision combining anomaly positions with paleogeographic reconstructions of india we constrain the spatio temporal evolution of multiple episodes of continental subduction likely related to these anomalies this study highlights the different evolution at lithospheric scales of the western and eastern parts of the collision zone the evolution of the western part is characterized by two episodes of steep subduction of the northern margin of india the first episode involving an area with a lateral extent as large as 1500 km started at about 40 30 and ended by a slab break off process at 15 ma the second episode consists on subduction beneath the hindu kush mountains since 8 ma to the east of the collision zone no anomaly related to steep subduction along the northern edge of india is found we interpret two tomographic anomalies beneath the eastern border of the indian plate beneath burma and beneath the andaman sea as the result of two successive episodes of southeastward extrusion followed by subduction we suggest that both extruded portions were initially located along the northern margin of india and that they slid around the eastern syntaxis then southward along the eastern boundary of indian plate both portions subducted along the eastern border of india south of the eastern syntaxis we provide a rough estimate of the amount of indian lithosphere consumed during these subduction and extrusion episodes by comparing this amount with the total amount of indian lithosphere at the onset of collision we conclude that these processes accommodated most of the india asia convergence during collision

hydrochemical characteristics and groundwater quality assessment in bushehr province sw iran the chemical quality of groundwater of bushehr southwest of iran was assessed for its suitability for drinking purposes hydro geochemical studies were carried out in this area to identify the geochemical processes and their relation to groundwater quality a total of 19 water samples were collected from the aquifer the samples were then analyzed for different physicochemical properties such as ph total dissolved solids tds total hardness th calcium magnesium carbonate bicarbonate sulfate and chloride concentrations in this study the average tds content was in the range of 4419 10 066 mg l l and other important parameters of water such as th 1200 3500 mg l 1 and chloride 1046 3855 mg l 1 were also higher than the maximum permissible limits specified by who on the basis of concentrations of major elements studies of the study area showed that the total samples collected are unsuitable for drinking linear increase in sodium and chloride of the total dissolved ion indicated a dissolution of halite in the study area salinity of the aquifer is mainly a result of the dalaki river recharge dissolution of evaporated minerals intraformation and also agricultural returned water the dissolution of evaporite minerals such as halite and gypsum has increased the concentration of total dissolved solids and of sulfate in the shahpour river and also groundwater entering the study area has caused salinity in this river

deep burial of asian continental crust beneath the pamir imaged with local earthquake tomography an inclined zone of intermediate depth seismicity beneath the pamir orogen in central asia has been interpreted as southward subduction of a slab of asian lithosphere however it is not known whether asian lithosphere subducts intact or only partially we used arrival times of shallow and intermediate depth earthquakes recorded with a temporary 2008 2010 seismic network in this region to invert for 3d models of seismic velocities in an attempt to answer this question with local seismicity reaching depths of up to 240 km the deep structure of the pamir could be illuminated with high resolution the resulting velocity models show a north south contrast in crustal seismic velocities in the pamir with very low p velocities 5 7 5 9 km s at 15 30 km depth coupled with relatively low vp vsvp vs 1 70 at mid crustal levels in the southern part of the orogen at sub moho depths we image an arcuate high velocity 8 2 8 6 km s slab dipping south in the eastern pamir and east in the pamir s southwest underlying the intermediate depth earthquakes on top of the high velocity slab and just above the onset of deep seismicity between a depth of 60 to 100 km very low compressional wavespeeds around 7 1 km s and high vp vsvp vs ratios 1 80 attest to subducted crustal rocks additionally we carried out 2d numerical thermomechanical modeling of the continental collision in the pamir focusing on the fate of the crust and mantle lithosphere of the asian and indian plates seismic velocities were computed from the modeling results and the resulting images were compared with the velocity distributions obtained from seismic traveltimes combining tomography and modeling results we infer that a substantial amount of crustal material is pulled down beneath the pamir by cold mantle lithosphere to depths of at least 80 100 km from there on only lower crust and mantle lithosphere continue their subduction and earthquakes occur inside the lower crustal layer probably due to metamorphic reactions the buoyant asian upper and middle crust does not penetrate deeper into the mantle but pools at this depth level from where it might eventually exhume or relaminate

hydrogeochemical characteristics of groundwater from the two main aquifers in the red river delta vietnam abstract in the red river delta situated in the northern part of vietnam nearly its entire population depends solely on groundwater for daily water consumptions for this reason groundwater quality assessments must be carefully carried out using hydrogeochemical properties to ensure effective groundwater resource planning for the delta s present and future groundwater use in this study the spatial and seasonal changes in the hydrogeochemical characteristics of groundwater in the two main aquifers of the rrd were investigated by analyzing the physicochemical data obtained in 2011 from 31 conjunctive wells in the delta s holocene unconfined aquifer hua and pleistocene confined aquifer pca using the piper diagram and the gibbs diagram results of the data analysis show that the groundwater in both aquifers in the upstream area of the delta is dominated by the ca 2 hco 3 water type while the na cl dominates along the middle stream and downstream areas seasonal changes in the hydrogeochemical facies in both aquifers comparing the results for the dry and the rainy seasons were detected in about one third of the sampling wells which were mainly located at the upstream portion of the delta the hydrogeochemical facies of hua were different from that of pca by about 45 of the sampling wells in both the dry and the rainy seasons which were found mostly in the upstream and middle stream areas

arcuate pamir in the paleogene insights from a review of stratigraphy and sedimentology of the basin fills in the foreland of ne chinese pamir western tarim basin abstract the tectonic evolution of the pamir bears essential information for understanding intracontinental tectonic processes within the context of india asia convergence however it is unclear whether the arcuate shape of the pamir is entirely the result of the india asia collision or may have been in part an inherited pre cenozoic feature in this study we address the evolution of the ne chinese pamir during the paleogene by reviewing the stratigraphy of twelve sections in the western tarim basin and the establishment of sedimentary facies the results indicate three episodes of deposition of alluvial coarse sediments in the foreland regions of ne chinese pamir during the 1 early paleocene 2 late paleocene to early eocene and 3 middle eocene to oligocene respectively these are correspondingly attributed to 1 retroarc deformation in an andean type margin of the southern asia during subduction of the neo tethys ocean 2 the immediate response in the pamir to the india asia collision and 3 continued india asia convergence the alluvial conglomerates with grain size up to 5 10 cm imply a transport distance

teleseismic tomography of the southern puna plateau in argentina and adjacent regions abstract we performed a teleseismic p wave tomography study using seismic events at both teleseismic and regional distances recorded by a temporary seismic array in the argentine puna plateau and adjacent regions the tomographic images show the presence of a number of positive and negative anomalies in a depth range of 20 300 km beneath the array the most prominent of these anomalies corresponds to a low velocity body located in the crust most clearly seen in the center of the array 27 s 67 w between the cerro peinado volcano the cerro blanco caldera and the farallon negro in the east this anomaly southern puna magmatic body extends from the northern most part of the array and follows the line with the highest density of stations towards the south where it becomes smaller it is flanked by high velocities on the west and the east respectively on the west the high velocities might be related to the subducted nazca plate on the northeast the high velocity block coincides with the position of the hombre muerto basin in the crust and could be indicating an area of lithospheric delamination where we detected a high velocity block at 100 km depth on the eastern border of the puna plateau north of galan this block might be related to a delamination event in an area with a thick crust of paleozoic metamorphic rocks at the border between puna and eastern cordillera in the center of the array the southern puna magmatic body is also flanked by high velocities but the most prominent region is located on the east and is interpreted as part of the sierras pampeanas lithosphere with high velocities the position of the sierras pampeanas geological province is key in this area as it appears to limit the extension of the plateau towards the south

geochemical processes and solute transport at the seawater freshwater interface of a sandy aquifer geochemical processes occurring at a seawater freshwater interface were studied in a shallow coastal siliclastic aquifer containing minor amounts of calcite data were collected from 106 piezometers in a 120 m transect from the coastline and landward in the first 40 m from the coastline a wedge of saltwater is intruding below the freshwater aquifer the aquifer is strongly reduced with mineralization of organic matter by methanogenesis in the freshwater aquifer and sulfate reduction dominating in the most seaward part of the saline aquifer the spatial separation of cations in the aquifer indicated a slow freshening process where ca2 from freshwater displaced the marine cations na and mg2 from the exchanger complex the resulting loss of ca2 from solution decreases the saturation state for calcite and possibly causes calcite dissolution a storm flooding event was recorded where pulses of dense seawater sank through the fresh aquifer as a result the terminal electron accepting process switched from methanogenesis to sulfate reduction the pulses of sinking seawater also triggered cation exchange reactions where ca2 was expelled from the exchanger by seawater na and mg2 the released ca2 is being flushed from the aquifer by groundwater flow and this export of ca2 will in the long term cause decalcification of the sediment the water composition in the aquifer is in a transient state as the result of various processes that operate on different timescales oxidation of organic matter occurs continuously but at a rate decreasing on a geological time scale the freshening of the aquifer operates on the timescale of a few years the episodic flooding and sinking of seawater through the aquifer proceeds in the course of days to weeks but occurs irregularly with years in between

hydrochemical characterization of drinking groundwater with special reference to fluoride in an arid area of china and the control of aquifer leakage on its concentrations the objective of the study is to determine the distribution and origin of fluoride in two confined aquifers within the depth of 80 240 m mid deep confined aquifers in shizuishan city an arid area in northwest china based on geological and hydrogeological conditions the distribution patterns of fluoride in the two confined aquifers were studied correlation analysis was used to reveal the mechanisms and reactions influencing the groundwater chemistry the control of aquifer leakage induced by intense groundwater abstraction on fluoride concentrations was also discussed the results show that the concentration of f in some locations of the study area is beyond the limit of the standards for drinking water quality of china correlation analysis shows that the major reactions occurring in the confined aquifers are dissolution of gypsum fluorite and halite and precipitation of calcite and dolomite groundwater leakage from shallow aquifers is also responsible for the elevation of fluoride in mid deep confined aquifers the research is a scientific basis for the rational development and utilization of groundwater in this area and it may be referenced by international scholars for similar research in other parts of the world

impact of the geomorphology and soil management on the development of waterlogging in closed drainage basins of egypt and saudi arabia this paper investigates the interplay of the catchment geomorphology hydrology and soil properties on the development of waterlogging and land degradation within different dry land catchments in egypt and saudi arabia multi temporal remote sensing data of the landsat thematic mapper and enhanced thematic mapper were collected and processed to detect the land cover changes and development of cultivations within the two areas the shuttle radar topography mission digital elevation model were hydrologically processed to delineate the catchment morphometrical parameters and to examine the spatial distribution of cultivated fields and their relation to the extracted drainage networks the fluvial channels of the farafra oasis have largely been obliterated by the prevailing aridity and often buried under aeolian deposits the soil of these areas are mainly lithic with a high calcium carbonate content thus limiting the downward percolation of excess irrigation water and therefore develop perched water table and seepage through the buried fluvial channels on the other hand the cultivations of tabuk catchment which has similar geomorphologic setting to the farafra oasis have shown no signs for waterlogging this situation is could be related to the different soil properties the spatial distribution of cultivated areas and the adopted irrigation methods via pivots the inactive alluvial channels landforms and irrigation methods have to be considered when planning for a new cultivation in dry land catchments to better control waterlogging hazard the dry drainage concept can be implemented as the drainage and seepage water which can be conveyed into certain abandoned playas for evaporation

modeling the evolution of continental subduction processes in the pamir hindu kush region several geological and geophysical studies suggest the presence of two converging subduction zones in the western syntaxis of the india eurasia collision zone with steep northward subduction of indian lithosphere beneath the hindu kush and southward subduction of asian lithosphere under the pamir we investigate the geometry and the timing of these subduction processes seismic tomography images are used to constrain the geometry of the two slabs under the pamir and the hindu kush by measuring the tomographically inferred length of the indian slab under the hindu kush region and by comparison with paleomagnetic reconstructions we estimate that the process of indian slab break off most likely occurred at the early stage of the collision at ca 44 48 ma we infer that after slab break off western india continued its northward motion until its northern boundary reached the present hindu kush region where it began to subduct we estimate an age for the initiation of subduction in this region of about 8 ma we apply 2d thermo kinematic and rheological numerical modeling to compute the temperature distribution and brittle field along two vertical sections across the hindu kush and pamir regions for the hindu kush we introduce parameters reproducing fast and near vertical subduction whereas in the pamir region we use the results from published studies to reproduce slower subduction modeling results indicate that faster subduction under the hindu kush results in a deeper brittle region which is consistent with observed deeper seismicity than in the pamir region

an enhanced image of the pamir hindu kush seismic zone from relocated earthquake hypocentres summary we determine the shape of the seismic zone in the pamir hindu kush region de ned by 30 42 0 n 68 78 0 e by obtaining improved hypocentral locations with 90 per cent con dence limits of less than 30 km the depth error bar for most of the earthquakes of about 6000 shallow and intermediate depth earthquakes available s and depth phase arrival times are also used together with the p wave arrival times in the joint hypocentre determination technique to obtain the best possible hypocentral locations the study region is divided into three depth ranges 0 60 60 160 and 160 km the 0 60 km depth zone is then subdivided laterally into 19 blocks with the deeper regions divided into two blocks each the improved delineation of the seismic zone obtained by using the relocated hypocentres implies that the intermediate depth seismicity in the pamir hindu kush region is most simply explained by a single s shaped seismic zone 700 km long and no more than 30 km wide and with most activity concentrated at 100 300 km depth the main features observed are 1 the eastward steepening of the north dipping hindu kush seismic zone through to its overturning at its eastern end beneath the pamirs where it dips to the southeast 2 the curvature and forking of the subducting slab at depths greater than 200 km within the eastern part of the hindu kush seismic zone 3 the very abrupt cut oi in intermediate depth seismicity at 90 110 km depth with no extension to shallower depths under the pamirs and with a persistent gap between the intermediate and shallow seismicity in the northern pamirs and 4 the unusual horizontal t axes for intermediate depth earthquakes of the pamir seismic zone which align with its curvature this study shows that the seismic zone under the hindu kush has stress axes which follow the classical pattern for subducting slabs controlled by gravity whereas the pamir region has horizontal t axes that follow the trend of the contorted seismic zone this suggests that the pamir seismic zone is a slab deformed due to ow in the upper mantle

cenozoic intracontinental deformation and exhumation at the northwestern tip of the india asia collision southwestern tian shan tajikistan and kyrgyzstan along the ghissar alai range of the southwestern tian shan southwestern kyrgyzstan northern tajikistan the deformation front of the india asia collision the pamir tibet orogen is interacting with the intra continental tian shan orogen without the intervening tarim craton apatite fission track n 33 3 3 145 6 ma 27 10 ma and u th he n 32 1 9 26 1 ma 56 10 ma thermochronologic ages suggest approximate isothermal holding very slow cooling to weak reheating during relative tectonic quiescence between 150 15 ma accelerated exhumation 0 2 1 0 km myr median 0 5 km myr and cooling 11 16 c myr occurred over the last 10 myr geomorphologic parameters incision and river steepness and concavity confirm the youth of the southwestern tian shan s mountain building high exhumation cooling rates correlated with pronounced local relief produced by cenozoic faults reactivating inherited late paleozoic structures regions with similarly young exhumation are centered along rims of rigid crustal blocks in the central and eastern tian shan structurally the ghissar alai range is a broad east trending zone of dextral transpression that includes the northern tajik basin illiak fault zone and the pamir thrust system of the frontal northern pamir it is the particular deformation field at the northwestern tip of the india asia collision the interaction of the westward gravitational collapse of the pamir plateau into the tajik basin with the bulk northward motion of the pamir that transformed the southwestern tian shan into a dextral transpression belt the dextral transpression in the southwestern tian shan contrasts with sinistral strike slip shear localized along inherited fault zones accommodating dominant north south shortening in the central and eastern tian shan the deformation field influenced by the pamir and the associated young exhumation make the ghissar alai range a unique feature in the tian shan orogen

using hydrochemical and isotopic data to determine sources of recharge and groundwater evolution in an arid region a case study in the upper middle reaches of the shule river basin northwestern china understanding sources of recharge and mechanisms for hydrogeochemical evolution of groundwater in the shule river basin an arid inland river basin in northwestern china is essential for successful water resource management sources of water and associated groundwater recharge processes were investigated using hydrogeological hydrogeochemical and isotopic methods the study area was divided into three parts changma the shule valley and the beishan area the hydrogeochemical and isotopic analysis results show that groundwater in changma mainly originated from precipitation in the qilian mountains lateral flow from changma is the primary recharge mechanism while direct recharge by infiltration of precipitation can be neglected in the shule valley minerals within the aquifer material e g halite calcite dolomite and gypsum dissolve into water that recharges the groundwater system therefore strong linear relationships were found between na and cl and between ca2 mg2 and so42 hco3 with stoichiometry ratios of approximately 1 1 in both cases groundwater quality in the region is generally good with low salinity and hardness local precipitation is the only source of recharge for groundwater in the beishan area low groundwater velocity and dry climatic conditions suggest that dissolution of minerals from the aquifer material controls hydrogeochemical evolution water rarely travels from the beishan area to the shule valley therefore almost all the groundwater in the shule valley originates from changma global climate change and loss of glaciers in the qilian mountains may lead to a reduction of recharge therefore the groundwater resources of the shule valley must be managed to sustain water supply

elucidating the sources and mechanisms of groundwater salinization in the ziz basin of southeastern morocco in the ziz basin located in arid area in southeastern morocco surface waters are scarce and local populations are entirely dependent on groundwater resources for drinking and irrigation in order to evaluate the main factors controlling the origin and salinization of groundwater resources we have investigated the chemical and stable isotope compositions of groundwater and surface water in different areas in the ziz basin upstream and downstream from the hassan addakhil dam which is the major man made reservoir in the basin a large variation in water quality was observed specifically an increase in salinity from north upstream to the reservoir with tds 460 mg l to south downstream tds 16 000 mg l in the northern portion of the basin the low saline groundwater is composed primarily of ca2 and mg2 due to dissolution of carbonate formations in the high atlas mountains in contrast the major dissolved consequents of saline waters are cl so4 2 and na apparently due to dissolution of evaporite minerals gypsum and halite in some areas elevated nitrate contents imply anthropogenic contamination derived from local agriculture the stable isotopes data 18o 8 6 to 8 3 and 2h 55 7 to 53 8 indicate that the high atlas mountains upstream of the reservoir constitute the major source of water to the ziz basin given that this arid basin is entirely dependent on groundwater resources long term salinization of groundwater in the ziz basin could lead to negative effects and reduction of the local agricultural productivity in addition to the degradation of drinking water quality in this region

interaction of the indian and asian plates under the pamir and hindu kush regions insights from 3 d shear wave velocity and anisotropic structures

vegetation and climate changes during the late pliocene and early pleistocene in sw turkey comment to the published paper by jimenez moreno et al quaternary research 84 2015 448 456

crustal structure of the indian shield new constraints from teleseismic receiver functions teleseismic earthquake waveform data from 10 broadband stations spread over the indian shield and in operation since 1997 were analyzed to infer the crustal structure using the receiver function technique the south indian shield is characterized by a 33 39 km thick and remarkably simple crust with an average poisson s ratio close to 0 25 the archaean crust is devoid of any prominent intra crustal discontinuities the velocity contrast at the well developed moho is large resulting in very clear p to s conversions as well as first order multiples in contrast the predominantly proterozoic crust in the northern part of the shield exhibits a complex character due to the presence of additional seismic discontinuities moho conversions which are considerably weaker compared to the archaean terrains indicate crustal thicknesses of more than 40 km

handbook of environmental isotope geochemistry vol 1 the terrestrial environment a p fritz and j ch fontes editors elsevier amsterdam 1980 xii 532 pp u s 90 25 dfl 185 00

saltwater intrusion and nitrate pollution in the coastal aquifer of dar es salaam tanzania dar es salaam quaternary coastal aquifer is a major source of water supply in dar es salaam city used for domestic agricultural and industrial uses however groundwater overdraft and contamination are the major problems affecting the aquifer system this study aims to define the principal hydrogeochemical processes controlling groundwater quality in the coastal strip of dar es salaam and to investigate whether the threats of seawater intrusion and pollution are influencing groundwater quality major cations and anions analysed in 134 groundwater samples reveal that groundwater is mainly affected by four factors dissolution of calcite and dolomite weathering of silicate minerals seawater intrusion due to aquifer overexploitation and nitrate pollution mainly caused by the use of pit latrines and septic tanks high enrichment of na and cl near the coast gives an indication of seawater intrusion into the aquifer as also supported from the na cl signature on the piper diagram the boreholes close to the coast have much higher na cl molar ratios than the boreholes located further inland the dissolution of calcite and dolomite in recharge areas results in ca hco3 and ca mg hco3 groundwater types further along flow paths ca2 and na ion exchange causes groundwater evolution to na hco3 type from the phreeqc simulation model it appears that groundwater is undersaturated to slightly oversaturated with respect to the calcite and dolomite minerals the results of this study provide important information required for the protection of the aquifer system

wind induced salt wedge intrusion in the tiber river mouth rome central italy the wind effect on river water quality was illustrated by means of thermohaline measurements carried out in the tiber river in may 2012 the survey was carried out using a boat in stations located in the two tiber branches fiumara grande and traiano canal thermohaline variables salinity and temperature were used to describe the water type patterns and to define the salt wedge position although the river flow rate was rather high saltwater intrusion happened wind data suggested that the more probable cause of salt wedge intrusion was the wind action especially wind speeds higher than 4 m s are able to dominate the sea current at surface layers determining an increase in the sea level therefore westerly winds determined a seawater inflow in the river mouths

abundant aftershock sequence of the 2015 mw7 5 hindu kush intermediate depth earthquake the 2015 m w7 5 hindu kush earthquake occurred at a depth of 213 km beneath the hindu kush region of afghanistan while many early aftershocks were missing from the global earthquake catalogues this sequence was recorded continuously by eight broad band stations within 500 km here we use a waveform matching technique to systematically detect earthquakes around the main shock more than 3000 events are detected within 35 d after the main shock as compared with 42 listed in the advanced national seismic system catalogue or 196 in the international seismological centre catalogue the aftershock sequence generally follows the omori s law with a decay constant p 0 92 we also apply the recently developed double pair double difference technique to relocate all detected aftershocks most of them are located to the west of the hypocentre of the main shock consistent with the westward propagation of the main shock rupture the aftershocks outline a nearly vertical southward dipping plane which matches well with one of the nodal planes of the main shock we conclude that the aftershock sequence of this intermediate depth earthquake shares many similarities with those for shallow earthquakes and infer that there are some common mechanisms responsible for shallow and intermediate depth earthquakes

subduction of the indian lithosphere beneath the tibetan plateau and burma abstract subduction of the indian lithosphere under eurasia plays an important role in the tectonic evolution of the tibetan plateau and surrounding regions to improve our knowledge of pertinent mantle structures through tomographic imaging we combine p wave arrival time data from temporary arrays in tibet and stations of the chinese seismograph network with reprocessed data from the international seismological centre the new images reveal considerable spatial variations in mantle structure along the collision zone and the horizontal distance over which presumed continental indian lithosphere slides northward beneath the plateau decreases from west where it underlies the himalayas and the entire plateau to east where no indication is found for present day underthrusting beyond the himalayan block and indus tsangpo suture p wavespeed appears low in the shallow mantle beneath much of central and eastern tibet these observations suggest that indian lithosphere underlies only the southwestern part of the plateau and that the central and northeastern part is underlain by lithosphere of asian origin the continental parts of the indian plate that currently underthrust or subduct below the plateau appear generally detached from the oceanic slab fragments that subducted longer ago and that have been detected deeper in the mantle except perhaps in the central part of the collision zone 80 90 e this suggests that ongoing india eurasia collision must increasingly be driven by other forces such as subduction of the indian plate further west and east e g beneath indochina our images reveal structures associated with eastward subduction along the burmese arc southeast of the eastern himalayan syntaxis the tengchong volcanic complex in southwest china is marked by slow wave propagation to 150 km depth suggesting a causal link to subduction along the burmese arc the low velocities beneath the red river fault region extend to greater depth and may be related to upper mantle processes further southeast

variation of rayleigh wave group velocity dispersion and seismic heterogeneity of the indian crust and uppermost mantle we present group velocity dispersion results from a study of regional fundamental mode rayleigh waves propagating across the indian region 1 d path averaged dispersion measurements have been made for 1001 source receiver paths and these combined to produce tomographic images between 15 and 45 s period because of the dense station coverage in peninsular india these images have substantially higher lateral resolution for this region than is currently available from global and regional group velocity studies testing of the group velocity model shows that the average resolution across the region is about 7 5 for the periods used in this study the tomographic maps demonstrate that while the indian shield is characterized by high crustal and uppermost mantle group velocities comparatively lower velocities exist beneath the himalaya due to the thickened crust and beneath the gangetic plains caused by the mollasse sediments and recent alluvium cover in the himalayan foredeep northeastern india north of the shillong plateau also displays higher velocities similar to the south indian shield indicative of colder crust beneath the region the northern bay of bengal shows extremely low velocities due to the thick sediment blanket of the bengal fan likewise the katawaz basin in southern pakistan shows lower velocities that resemble those seen in the bay of bengal the geometry of the velocity contours south of the katawaz basin closely matches the prograding indus fan in the arabian sea finally the tibetan plateau has lower group velocities compared to the indian shield at all periods as a result of the thick crust beneath southern tibet

a view into crustal evolution at mantle depths abstract crustal foundering is an important mechanism in the differentiation and recycling of continental crust nevertheless little is known about the dynamics of the lower crust the temporal scale of foundering and its role in the dynamics of active margins and orogens this particularly applies to active settings where the lower crust is typically still buried and direct access is not possible crustal xenoliths derived from mantle depth in the pamir provide a unique exception to this the rocks are well preserved and comprise a diverse set of lithologies many of which re equilibrated at high pressure conditions before being erupted in their ultrapotassic host lavas in this study we explore the petrological and chronological record of eclogite and felsic granulite xenoliths we utilized accessory minerals zircon monazite and rutile for coupled in situ trace element analysis and u th pb chronology by laser ablation split stream inductively coupled plasma mass spectrometry each integrated analysis was done on single mineral zones and was performed in situ in thin section to maintain textural context and the ability to interpret the data in this framework rutile thermo chronology exclusively reflects eruption 11 17 0 06 ma which demonstrates the reliability of the u pb rutile thermo chronometer and its ability to date magmatic processes conversely zircon and monazite reveal a series of discrete age clusters between 55 11 ma with the youngest being identical to the age of eruption matching age populations between samples despite a lack of overlapping ages for different chronometers within samples exhibit the effectiveness of our multi mineral approach the ree systematics and age data for zircon and monazite and ti in zircon data together track the history of the rocks at a million year resolution the data reveal that the rocks resided at 30 40 km depth along a stable continental geotherm at 720 750 c until 24 20 ma and were subsequently melted densified and buried to 80 90 km depth 20 km deeper than the present day moho at 930 35 c the material descended rapidly accelerating from 0 9 1 7 mm yr 1 to 4 7 5 8 mm yr 1 within 10 12 myr and continued descending after reaching mantle depth at 14 13 ma the data reflect the foundering of differentiated deep crustal fragments 2 9 3 5 g cm 3 into a metasomatized and less dense mantle wedge through our new approach in constraining the burial history of rocks we provided the first time resolved record of this crustal recycling process foundering introduced vestiges of old evolved crust into the mantle wedge over a relatively short period c 10 myr the recycling process could explain the variability in the degree of crustal contamination of mantle derived magmatic rocks in the pamir and neighboring tibet during the cenozoic without requiring a change in plate dynamics or source region

early evolution of the pamir deep crust from lu hf and u pb geochronology and garnet thermometry determining early orogenic processes within the pamir tibet orogen represents a critical step toward constructing a comprehensive model on the tectonic evolution of the region here we investigate the timing and cause of prograde metamorphism of cenozoic metamorphic rocks from the pamir plateau through lu hf geochronology u pb rutile thermochronology and garnet thermometry regional prograde metamorphism and heating to 750 830 c as constrained by thermometry occurred between 37 and 27 ma prograde growth of garnet first occurred in the south pamir and spread to the central pamir during the following 10 m y the early metamorphism is attributed to high mantle heat flow following the ca 45 ma break off of the indian slab south of the pamir our investigation confirms a long lived thermal history of the pamir deep crust before the miocene and provides a causal link between break off enhanced mantle heat flow and prograde heating of the subduction hanging wall

dense gnss profiles across the northwestern tip of the india asia collision zone triggered slip and westward flow of the peter the first range pamir into the tajik depression

seismic images of the biggest crash on earth in plate tectonics the upper layer of earth the lithosphere consists of rigid plates that shift over geological time scales data from global positioning surveys have estimated that the entire indian subcontinent has moved over the past 50 years about 2 m to the north diving slowly underneath tibet this giant collision has been ongoing for 50 million years and has thrown up the highest mountains as well as the largest and highest plateau on earth not only is the world climate strongly influenced by this massive plateau average elevation of 5000 m but the collision also causes catastrophic earthquakes in southern central and eastern asia

cumulative and coseismic during the 2016 m w 6 6 aketao earthquake deformation of the dextral slip muji fault northeastern pamir orogen

geochemical evolution and timescale of seawater intrusion into the coastal aquifer of israel this study is an attempt to quantify the geochemical processes and the timescale of seawater intrusion into a coastal aquifer from changes in the major ionic composition of the water and the natural distribution of the cosmogenic isotopes 14c and 3h for that purpose we sampled saline and brackish groundwaters from the israeli coastal aquifer a multilayer sampler mls was used to obtain very high resolution 10 cm profiles across the fresh saline water interface fsi the chemical and stable isotope data revealed three distinct water types end members that are located in different zones on the route to the coastal aquifer 1 slightly modified mediterranean seawater sws 2 slightly diluted with up to 20 fresh groundwater saline groundwater sds and 3 fresh groundwater fgw the sws samples generally show an excess of total alkalinity and total dissolved inorganic carbon dic and a depletion of 13cdic and 14cdic with respect to normal seawater indicating that anaerobic oxidation of organic matter is the first diagenetic reaction that affects seawater during its penetration into the bottom sediments sds waters appear when sws is slightly diluted gain ca2 and sr2 and is depleted in k suggesting that the main processes that transform sws into sds are slight dilution with fresh groundwater and cation exchange at the fresh saline water interface sds generally shows conservative mixing with fgw inspection of chemical data from coastal aquifers around the world indicates that intensive ion exchange in slightly diluted saline groundwater is a globally important phenomenon of seawater intrusion most of our saline groundwater samples contain substantial amounts of 3h suggesting that penetration of mediterranean seawater and its inland travel to a distance of 50 100 m onshore occurred 15 30 yr ago this is supported by the 14cdic mass balance that explains the relatively low 14cdic activities in the sds as influenced by diagenesis and not by simple radioactive decay

tethyan subducted slabs under india abstract tomographic imaging of the mantle under tibet india and the adjacent indian ocean reveals several zones of relatively high p wave velocities at various depths under the hindu kush region in northeastern afghanistan and southern tajikistan a regional northward dipping slab is seen in the entire upper 600 km of the mantle and is apparently still attached to the lithosphere of the indian plate under northern pakistan this same slab shows a roll over structure with the deeper portion overturned and dipping southward as can also be seen in the distribution of earthquake hypocenters farther east southeast e g in the vicinity of nepal a well resolved anomaly below 450 km depth is connected to the slab under the hindu kush but seems to be separated from the lithosphere above 350 km these upper mantle anomalies are interpreted as the remnants of delaminated sub continental lithosphere that went down when greater india continued to converge northward with asia after 45 ma the deeper high velocity anomalies under the indian sub continent appear clearly separated from the shallower ones as well as from each other and are inferred to represent remnants of oceanic lithospheric slabs that have sunk into the lower mantle and were subsequently overridden by the indian plate they occur at depths between 1000 and 2300 km and occasionally descend down to the core mantle boundary the anomalies form three parallel wnw ese striking zones we interpret the two southern zones as remnants of oceanic lithosphere that was subducted when the neo tethys ocean closed between india and tibet in the cretaceous and earliest tertiary the northern deep mantle zone under northern afghanistan the himalayas and the lhasa block in southern tibet may represent the last subducted remnant of the paleo tethys ocean which is thought to have closed before the hauterivian stage of the early cretaceous the middle zone continues southeastward as a rather straight high velocity zone towards sumatra where it becomes convex southward and parallel to the subduction zone under the sunda arc comparison of this straight middle zone near india with the shallower upper 600 1000 km northern zone which displays a cusp like shape near the yunnan sw china syntaxis of the eastern himalayas supports the notion that the shallow northern zone represents later subduction than the deeper middle zone the suggestion of a counterclockwise rotation 20 of the indian plate during tertiary indentation of asia is supported by these features the present day latitudes of 5 35 n of the deep slabs under india and adjacent areas correspond to the approximate paleolatitudes of the cretaceous subduction zones the slab remnants in the middle mantle occur therefore near the ancient locations where they started their downward journey which implies that lateral movements in the deeper mantle were not large

crustal and uppermost mantle velocity structure along a profile across the pamir and southern tien shan as derived from project tipage wide angle seismic data summary utilizing seismic refraction wide angle reflection data from 11 approximately in line earthquakes 2 d p and s velocity models and a poisson s ratio model of the crust and uppermost mantle beneath the southern tien shan and the pamir have been derived along the 400 km long main profile of the tipage tien shan pamir geodynamic program project these models show that the crustal thickness varies from about 65 5 km close to the southern end of the profile beneath the south pamir through about 73 6 km under lake karakul in the north pamir to about 57 7 km 50 km south of the northern end of the profile in the southern tien shan average crustal p velocities are low with respect to the global average varying from 6 26 to 6 30 km s 1 the average crustal s velocity varies from 3 54 to 3 70 km s 1 along the profile and thus average crustal poisson s ratio varies from 0 23 beneath the central pamir in the south central part of the profile to 0 265 towards the northern end of the profile beneath the southern tien shan the main layer of the upper crust extending from about 2 km below the earth s surface to 27 km depth below sea level b s l has average p velocities of about 6 05 6 1 km s 1 except beneath the south central part of the profile where they decrease to around 5 95 km s 1 this is in contrast to the s velocities which range from 3 4 to 3 6 km s 1 and exhibit the highest values of 3 55 3 6 km s 1 where the p velocity is lowest thus for the main layer of the upper crust is 0 26 beneath the profile except beneath the south central part of the profile where it decreases to 0 22 the low value of 0 22 for under the central pamir the along strike equivalent of the qiangtang terrane in tibet is similar to that within the corresponding layer beneath the northern lhasa and southern qiangtang terranes in central tibet and is indicative of felsic rocks rich in quartz in the state the lower crust below 27 km b s l has p velocities ranging from 6 1 km s 1 at the top to 7 1 km s 1 at the base further for this layer is 0 27 0 28 towards the northern end of the profile but is low at about 0 24 beneath the central and southern parts of the profile which is similar to the situation found in the northeast tibetan plateau the low values can be explained by felsic schists and gneisses in the upper part of the lower crust transitioning to granulite facies and possibly also eclogite facies metapelites in the lower part within the uppermost mantle the average p velocity is about 8 10 8 15 km s 1 and is about 0 26 assuming an isotropic situation then a relatively cool 700 800 c uppermost mantle beneath the profile is indicated this would in turn indicate an intact mantle lid beneath the profile an upper mantle reflector dipping from 104 km b s l 120 km from the southern end of the profile to 86 km b s l 155 km from the northern end of the profile has also been identified the preferred model presented here for the crustal and lithospheric mantle structure beneath the pamir calls for nearly horizontal underthrusting of relatively cool indian mantle lithosphere the leading edge of which is outlined by the pamir seismic zone this cool indian mantle lithosphere is overlain by significantly shortening warm asian crust the moho trough that is a feature seen beneath some other orogenic belts for example the alps and the urals beneath the northern pamir may mark the southern tip of the actively underthrusting tien shan crust along the main pamir thrust

mesozoic ophiolites sutures and arge scale tectonic movements in afghanistan abstract the tectonic history of afghanistan appears to be the result of successive accretion of fragments of gondwana to the active margin of laurasia since the end of the paleozoic the margin in afghanistan lies along the present herat and panjshir faults south of hindu kush swings around the central pamirs and can presumably be traced along the present western altyn tagh and kunlun faults in tibet north of this boundary paleozoic rocks have been deformed in the upper paleozoic whereas south of it there is no trace of the hercynian orogeny the first collision of gondwanian fragments with laurasia probably occurred in the early mesozoic along the hindu kush and kunlun to the south ophiolites along the panjao and pangong nu chiang sutures respectively in central afghanistan and central tibet testify for another suturing event in the upper jurassic or lower cretaceous the indus tsangpo suture between india and tibet corresponds in eastern afghanistan to two ophiolite subbelts near kabul and khost both ophiolite complexes have been emplaced between maestrichtian and lower eocene by choking of two northward dipping subduction zones after complete contact between the indian and asian continents was achieved presumably in the end of eocene the penetration of india into asia caused large scale intra continental shortening a large part of the shortening was accommodated by strike slip faulting along mesozoic and more ancient sutures central afghanistan in particular was extruded to the west along the herat suture by the protrusion of the pamir wedge it subsequently collided with the lut block

geochemical modeling of the madison aquifer in parts of montana wyoming and south dakota stable isotope data for dissolved carbonate sulfate and sulfide are combined with water compo sition data to construct geochemical reaction models along eight flow paths in the madison aquifer in parts of wyoming montana and south dakota the sulfur isotope data are treated as an isotope dilution problem whereas the carbon isotope data are treated as rayleigh distillations all reaction models reproduce the observed chemical and carbon and sulfur isotopic composition of the final waters and are partially validated by predicting the observed carbon and sulfur isotopic compositions of dolomite and anhydrite from the madison limestone the geochemical reaction models indicate that the dominant groundwater reaction in the madison aquifer is dedolomitization calcite precipita tion and dolomite dissolution driven by anhydrite dissolution sulfate reduction ca mg2 ina cation exchange and halite dissolution are locally important particularly in central montana the groundwater system is treated as closed to c02 gas from external sources such as the soil zone or cross formational leakage but open to c02 from oxidation of organic matter coupled with sulfate reduction and other redox processes occurring within the aquifer the computed mineral mass transfers and modeled sulfur isotopic composition of madison anhydrites are mapped throughout the study area carbon 14 groundwater ages adjusted for the modeled carbon mass transfer range from modem to about 23 000 years b p and indicate flow velocities of 7 7 ftlyr 2 1 26 5 rnlyr most horizontal hydraulic conductivities calculated from darcy s law using the average 14 c flow velocities are within a factor of 5 of those based on digital simulation the calculated mineral mass transfer and adjusted 14 c groundwater ages permit determination of apparent rates of reaction in the aquifer the apparent rate of organic matter oxidation is typically 0 12 jlidol uyr sulfate and to a lesser extent ferric iron are the predominant electron acceptors the kinetic biochemical fractionation of 34 s between sulfate and hydrogen sulfide is approximately 44 o at 25 c with a temperature variation of

the giant shakhdara migmatitic gneiss dome pamir india asia collision zone 1 geometry and kinematics 1 cenozoic gneiss domes comprise one third of the surface exposure of the pamir and provide a window into the deep crustal processes of the india asia collision the largest of these are the doubly vergent composite shakhdara alichur domes of the southwestern pamir tajikistan and afghanistan they are separated by a low strain horst top to sse noncoaxial pervasive flow over the up to 4 km thick south pamir shear zone exhumed crust from 30 40 km depth in the 250 80 km shakhdara dome the top to nne alichur shear zone exposed upper crustal rocks in the 125 25 km alichur dome the gunt shear zone bounds the shakhdara dome in the north and records alternations of normal shear and dextral transpression it contributed little to bulk exhumation footwall exhumation along two low angle normal sense detachments resulted in up to 90 km syn orogenic n s extension extension in the southwestern pamir opposes shortening in a fold thrust belt north of the domes and in particular in the tajik depression where an evaporitic decollement facilitated upper crustal shortening gravitational collapse of the pamir plateau margin drove core complex formation in the southwestern pamir and shortening of the weak foreland adjacent to the plateau overall this geometry defines a vertical extrusion scenario comprising frontal and basal underthrusting and thickening and hanging gravitationally driven normal shear in contrast to the himalayan vertical extrusion scenario erosion in the pamir was minor preserving most of the extruded deep crust including the top of the south pamir shear zone at peak elevations throughout the dome

subduction and slab breakoff controls on asian indentation tectonics and himalayan western syntaxis formation 1 we test the link between large scale asian continent deformations and indian slab subduction and breakoff during convergence by means of three dimensional numerical models of the subducting upper plates system we find that the subduction of the buoyant continent results in the reduction of convergence velocity comparable to that observed in the indian motions yet the upper plate deformation remains accommodated in a narrow belt along a straight margin comparable rates are measured when the subducting slab breakoff is modeled although the convergent margin deforms and curves markedly with large underplating contiguous to ongoing subduction similar to what observed along the himalayan range the models support the interpretation of the himalayan western syntaxis evolution the progressive curvature of the indian margin and the underthrusting as a consequence of the indian slab breakoff the modeled slab detachment is followed by short lived large stresses in the upper plate interiors propagating at large distance from the margin with a trend similar to several major asian lithospheric faults such localized stress has likely provided the conditions for the formation of the central asian intracontinental faulting the bangong red river and the altyn tagh faults that followed successive indian slab breakoff episodes continent subduction and breakoff during india asia convergence offer an explanation for the different deformation mechanisms as the long lived understhrusting and the episodic lithospheric faulting in the asian continent and their link to deep processes

hydrogeochemical assessment of groundwater quality during dry and rainy seasons for the two main aquifers in hanoi vietnam groundwater from the holocene unconfined aquifer hua and pleistocene confined aquifer pca is the major source of drinking and domestic water in hanoi vietnam a clear understanding of the groundwater hydrogeochemical properties particularly their changes during the dry and rainy seasons is invaluable for the management and protection of this important water resource in this study the changes in the hydrogeochemical properties of groundwater during the dry and rainy seasons were investigated by analyzing the major ions ca2 mg2 na k hco3 so4 2 cl that were recently obtained in 2011 from 13 conjunctive sampling wells for hua and pca in hanoi the hydrogeochemical assessment was carried out using the piper and gibbs diagrams based on the results at least 30 of the sampling wells in both aquifers exhibited changes in the hydrogeochemical facies during the dry and rainy seasons most of the changes occurred for the cation type facies while the anion type remained unchanged moreover the hydrogeochemical facies of hua was found to be different from that of pca by approximately 50 of the sampling wells for both the dry and rainy seasons in addition the gibbs diagram showed apparent differences in the weight ratios cl cl hco3 between pca and hua the results revealed that rock weathering is the main process involved in the evolution of chemical composition of groundwater but agricultural activities and salty paleowater are the other important factors that affect the groundwater chemistry in some parts of the study area

factors controlling mechanisms of groundwater salinization and hydrogeochemical processes in the quaternary aquifer of the eastern nile delta egypt in this study combining interpretations of conservative dissolved ions and environmental isotopes in water were used to investigate the main factors and mechanisms controlling groundwater salinization and hydrogeochemical processes in the eastern nile delta egypt hydrogeochemical and isotopic study has been carried out for 61 water samples from the study area total dissolved solid tds contents of groundwater are highly variable rising along flowpath from the south 410 mg l to the north 14 784 mg l implying significant deterioration and salinization of groundwater based on tds and ionic ratios groundwater samples were classified into three groups in low saline groups water chemistry is greatly influenced by cation exchange mineral dissolution precipitation anthropogenic pollutants and mixing with surface water whilst in high saline groups water chemistry is affected by salt water intrusion reverse cation exchange and evaporation the chemical constituents originating from saline water sources reverse ion exchange and mineral dissolution are successfully differentiated using ionic delta and saturation index approaches the 18o 2h relationship plots on a typical evaporation line suggesting potential evaporation of the recharging water prior to infiltration isotope evidence concludes that the groundwater have been considerably formed by mixing between depleted meteoric water recharged under different climatic conditions and recently infiltrating enriched surface water and excess of irrigation water the 18o data in conjunction with chloride concentrations provide firm evidence for impact of dissolution of marine origin evaporite deposits during past geologic periods on groundwater salinity in the northern region moreover the relation between 14c activities and cl concentration confirms this hypothesis

implications of shortening in the himalayan fold thrust belt for uplift of the tibetan plateau 1 recent research in the himalayan fold thrust belt provides two new sets of observations that are crucial to understanding the evolution of the himalayan tibetan orogenic system first u pb zircon ages and sm nd isotopic studies demonstrate that 1 greater himalayan medium to high grade metasedimentary rocks are much younger than true indian cratonic basement and 2 these rocks were tectonically mobilized and consolidated with the northern margin of gondwana during early paleozoic orogenic activity these observations require that greater himalayan rocks be treated as supracrustal material in restorations of the himalayan fold thrust belt rather than as indian cratonic basement in turn this implies the existence of greater himalayan lower crust that is not exposed anywhere in the fold thrust belt second a regional compilation of shortening estimates along the himalayan arc from pakistan to sikkim reveals that 1 total minimum shortening in the fold thrust belt is up to 670 km 2 total shortening is greatest in western nepal and northern india near the apex of the himalayan salient and 3 the amount of himalayan shortening is equal to the present width of the tibetan plateau measured in an arc normal direction north of the indus yalu suture zone this information suggests that a slab of greater indian lower crust composed of both indian cratonic lower crust and greater himalayan lower crust with a north south length of 700 km may have been inserted beneath the tibetan crust during the cenozoic orogeny we present a modified version of the crustal underthrusting model for himalayan tibetan orogenesis that integrates surface geological data recent results of mantle tomographic studies and broadband seismic studies of the crust and upper mantle beneath the tibetan plateau previous studies have shown that incremental mesozoic and early cenozoic shortening had probably thickened tibetan crust to 45 55 km before the onset of the main cenozoic orogenic event thus the insertion of a slab of greater indian lower crust with maximum thickness of 20 km tapering northward could explain the cenozoic uplift of the tibetan plateau the need for tibetan crust to stretch laterally as the greater indian lower crust was inserted may explain the widespread east west extension in the southern half of the plateau our reconstruction of the himalayan fold thrust belt suggests that indian cratonic lower crust of presumed mafic composition and high strength should extend approximately halfway across the tibetan plateau to the banggong suture from there northward we predict that the tibetan plateau is underlain by more felsic and therefore weaker lower crust of greater himalayan affinity two slab break off events are predicted by the model the first involved neotethyan oceanic lithosphere that foundered 45 35 ma and the second consisted of greater indian lithosphere most likely composed of greater himalayan material that delaminated and foundered 20 10 ma asthenospheric upwelling associated with the break off events may explain patterns of cenozoic volcanism on the tibetan plateau although the model predicts a northward migrating topographic front due solely to insertion of greater indian lower crust the actual uplift history of the plateau was complicated by early middle tertiary shortening of tibetan crust

restoration of cenozoic deformation in asia and the size of greater india a long standing problem in the geological evolution of the india asia collision zone is how and where convergence between india and asia was accommodated since collision proposed collision ages vary from 65 to 35 ma although most data sets are consistent with collision being underway by 50 ma plate reconstructions show that since 50 ma 2400 3200 km west to east of india asia convergence occurred much more than the 450 900 km of documented himalayan shortening current models therefore suggest that most post 50 ma convergence was accommodated north of the indus yarlung suture zone we review kinematic data and construct an updated restoration of cenozoic asian deformation to test this assumption we show that geologic studies have documented 600 750 km of n s cenozoic shortening across and north of the tibetan plateau the pamir hindu kush region accommodated 1050 km of n s convergence geological evidence from tibet is inconsistent with models that propose 750 1250 km of eastward extrusion of indochina approximately 250 km of indochinese extrusion from 30 to 20 ma of indochina suggested by se asia reconstructions can be reconciled by dextral transpression in eastern tibet we use our reconstruction to calculate the required size of greater india as a function of collision age even with a 35 ma collision age the size of greater india is 2 3 times larger than himalayan shortening for a 50 ma collision the size of greater india from west to east is 1350 2600 km consistent with robust paleomagnetic data from upper cretaceous paleocene tethyan himalayan strata these estimates for the size of greater india far exceed documented shortening in the himalaya we conclude that most of greater india was consumed by subduction or underthrusting without leaving a geological record that has been recognized at the surface

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

seismic imaging of subducting continental lower crust beneath the pamir abstract exhumation of ultra high pressure metamorphic rocks testifies that the continental crust can subduct to significant depth into the mantle despite its buoyancy however direct observation of ongoing subduction of continental crust is rare the pamir is regarded as a possible place of active continental subduction because of the intermediate depth seismicity crustal xenoliths and estimates of crustal shortening versus convergence rates here we present for the first time receiver function images from a passive source seismic array traversing the tien shan and the pamir plateau showing southward subduction of eurasian continental crust in the eastern pamir we observe a southerly dipping 10 15 km thick low velocity zone lvz that extends from 50 km depth near the base of the crust to more than 150 km depth with a dip angle increasing to subvertical while the upper and mid crustal material seems to be shortened and incorporated into the pamir the lower eurasian crust detaches and subducts in its deeper part 80 km the lvz envelopes the intermediate depth earthquakes our observations imply that the complete arcuate intermediate depth seismic zone beneath the pamir traces a slab of subducting eurasian continental lower crust

groundwater resource degradation in coastal plains the example of the cecina area tuscany central italy abstract the paper describes the degradation of the groundwater resources in the cecina area where seawater intrusion b contamination and no 3 pollution are all affecting the heavily exploited pleistocene aquifer over pumping has brought water levels to about 0 m a s l as far as about 7 km from the shore line thereby promoting the seawater intrusion the intrusion which is characterized by cation exchange phenomena and ca cl type waters enters the plain mostly through the shallower horizons the saline front which advanced from 0 5 to 1 km in 4 a has by now reached the foot of the hills to the east of the town where it is also affecting wells of the local aqueduct boron contamination linked to past discharge of industrial waste transported downstream by the river reached concentrations as high as 3 5 mg l in the mid 1980s although a decreasing trend is now under way b content is still close to 1 mg l the presence of high no 3 which together with the seawater intrusion represents a major issue for groundwater management in the area is linked to the widespread utilization of fertilizers nitrate concentration which reaches a maximum of about 300 mg l in the shallow aquifer horizons and then decreases rather regularly with depth is strongly influenced by precipitation however irrigation also contributes significantly to transporting the no 3 contamination to depth as clearly shown by 18 o data the severe decline in the quality of the groundwater resource in the cecina area is further compounded by an overall decrease in water availability in the region of tuscany as evidenced by long term monitoring of precipitation and fluvial discharge

a tomographic image of indian lithosphere break off beneath the pamir hindukush region summary the p and s seismic anomalies in the upper mantle beneath the pamir hindukush collision zone and surrounding areas are investigated using more than 4 10 5 traveltimes from 5775 events located in the study region recorded by the stations of the worldwide seismic network and reported in the isc catalogue all available epicentral distance ranges of seismic rays are considered all sources are relocated using an algorithm which includes the double difference method in addition source parameters are corrected in the main inversion step simultaneously with the velocity models the high reliability of the resulting p velocity images is confirmed by various tests the s model provides much smoother patterns which are however generally consistent with p anomalies our model shows a complex image of lithospheric plate under the study region under sw hindukush the northwards subducting indian plate is imaged throughout the upper mantle and transition zone further to the ne within a 300 km wide zone the upper part of the plate overturns and then the slab breaks off after it narrows at 250 km depth the tomographic model also provides evidence for the southward subduction of the lithosphere beneath the southern tien shan down to at least 250 km depth to the north of tarim we observe a northward dipping of the tarim plate down to 500 km depth at the crustal depth our model shows alternating belts of high and low velocities parallel to the main thrusting faults which indicate complex crustal structure in this region

cl br ratios and environmental isotopes as indicators of recharge variability and groundwater flow an example from the southeast murray basin australia abstract systematic variations in cl br ratios together with r 36 cl values 14 c activities and 18 o values reflect differences in groundwater recharge and define groundwater flow paths in the riverine province of the southeast murray basin in groundwater from the shallowest shepparton formation homogenisation of cl br and 18 o values and a decline in 14 c activities with depth imply that vertical flow dominates the 14 c activities define variations in pre land clearing recharge in the palaeovalleys of present day rivers deep leads which contain sandier sediments higher recharge 0 5 to 1 4 mm year produced relatively fresh groundwater tds 36 cl values in groundwater from the goulburn subcatchment zones of groundwater with variable cl br ratios in the deeper calivil renmark aquifer also allow the detection of rapid leakage from the surface that has the potential to compromise groundwater resources

dynamics of slab detachment 1 we investigate the dynamics of slab detachment around the detachment zone and evaluate the amount of time necessary for slabs to detach the study combines results of two dimensional 2d state of the art thermomechanical numerical simulations and a 1d analytical solution for viscous necking under gravity we show that the dominant deformation mechanism during slab detachment is viscous necking independent of the depth of slab detachment when the slab dip is moderate 35 70 slab detachment is partly affected by localized simple shearing in the colder parts of the slab brittle fracturing breaking plays a minor role during slab detachment our 2d thermomechanical models indicate that the duration of slab detachment quantified from the onset of slab thinning until the actual detachment i e vanishing of slab pull force is relatively short 250 km can occur within a short time interval 1 ma which has implications for geodynamic interpretations using slab detachment as explanation for processes such as melting exhumation or surface uplift the thinning of the slab during detachment observed in 2d simulations agrees well with predictions from a 1d analytical solution indicating that the 1d solution captures the first order features of the detachment process we also evaluate the impact of shear heating on the duration of slab detachment the predictions of a simple semi analytical solution based on dimensionless parameters agree well with our and previously published results

cretaceous evolution of the central asian proto paratethys sea tectonic eustatic and climatic controls the timing and mechanisms of the cretaceous sea incursions into central asia are still poorly constrained we provide a new chronostratigraphic framework based on biostratigraphy and magnetostratigraphy together with detailed paleoenvironmental analyses of cretaceous records of the proto paratethys sea fluctuations in the tajik and tarim basins the early cretaceous marine incursion in the western tajik basin was followed by major marine incursions during the cenomanian ca 100 ma and santonian ca 86 ma that reached far into the eastern tajik and tarim basins these marine incursions were separated by a turonian coniacian ca 92 86 ma regression basin wide tectonic subsidence analyses imply that the early cretaceous sea incursion into the tajik basin was related to increased pamir tectonism we find that thrusting along the northern edge of the pamir at ca 130 90 ma resulted in increased subsidence in a retro arc basin setting this tectonic event and coeval eustatic highstand resulted in the maximum observed geographic extent of the sea during the cenomanian ca 100 ma the following turonian coniacian ca 92 86 ma major regression driven by eustasy coincides with a sharp slowdown in tectonic subsidence during the late orogenic unloading period with limited thrusting the santonian ca 86 ma major sea incursion was likely controlled by eustasy as evidenced by the coeval fluctuations in the west siberian basin an early maastrichtian cooling ca 71 70 ma potentially connected to global late cretaceous trends is inferred from the replacement of mollusk rich limestones by bryozoan and echinoderm rich limestones

hydrochemistry of the saline groundwaters of the lower mersey basin permo triassic sandstone aquifer uk saline groundwater occurs at depth in the triassic sandstones of the northern end of the cheshire basin in northwest england major and minor ion data suggest that the origin of the salinity is dissolution of evaporite deposits the salinity probably developed in an interval following the tertiary inversion of the basin which would have allowed faulted contact between the sandstones and the overlying evaporite sequence of the mercia mudstone group isotope evidence suggests the saline waters to have been considerably diluted by presumably dispersive mixing with a meteoric water recharged under cool and therefore quaternary climatic conditions comparison with other uk permo triassic basin brines suggests the merseyside waters are not unusual except in terms of the importance of exchange reactions and dilution by quaternary recharge waters these factors are due to the shallow maximum burial depth of the aquifer and the preservation of smectites and also to the geometry of the aquifer and its low permeability faults in the light of the water chemistry data it is suggested in a slight modification of the proposal of naylor et al q geol soc lond 146 685 699 1988 that the cheshire basin mineralization resulted from mixing of the relatively oxidized so4 rich evaporite brines with the reduced so4 poor metal rich barich coal measures brines which were expelled through faults from the coal measures during basin inversion some degree of oxyhydroxide stripping of the sandstones by the coal measures brines would have enhanced metal concentrations the water resulting from the mixing of brines would have been far from equilibrium and the barite and sulphide precipitation followed along the faults

ionic and isotopic ratios for identification of salinity sources and missing data in the gaza aquifer abstract groundwater is the only source of fresh water in the gaza strip however it is severely polluted and requires immediate effort to improve its quality and increase its usable quantity intensive exploitation of groundwater in the gaza strip over the past 40 years has disturbed the natural equilibrium between fresh and saline water and has resulted in increased salinity in most areas salinization in the coastal aquifer may be caused by a single process or a combination of different processes including seawater intrusion upconing of brines from the deeper parts of the aquifer flow of saline water from the adjacent eocene aquifer return flow from irrigation water and leakage of wastewater each of these sources is characterized by a distinguishable chemistry and well known isotopic ratios in this paper na cl so4 cl br cl ca hco3 so4 and mg ca ionic ratios were used to distinguish different salinization sources 11b and 87sr 86sr isotopic composition were also included in the model to study their importance in this monitoring task the task of monitoring and the associated decision making process are characterized by a high degree of uncertainty with respect to input data and accuracy of models for this reason probabilistic expert systems and more specifically bayesian belief networks bbns are used to identify salinization origins the bbn model incorporates the theoretical background of salinity sources area specific monitoring data that are characteristically incomplete in their coverage expert judgment and common sense reasoning to produce a geographic distribution for the most probable sources of salinization the model is also designed to show areas where additional data on chemical and isotopic parameters are needed

groundwater salinization in shallow aquifers adjacent to a low altitude inland salt lake a case study at yuncheng basin northern china measurements of chemical composition and environmental isotopes were conducted to investigate the main geochemical processes controlling the salinization of shallow groundwater adjacent to an inland salt lake in the yuncheng basin hydrogeochemical and isotopic studies were carried out by collecting thirty shallow groundwater two rainfalls and one salt lake water samples from the study area about 80 of the shallow groundwater samples had total dissolved solids more than 500 mg l implying significant water quality deterioration in the study area shallow groundwater showed a clear increased salinity along regional flow paths toward the center of the basin where a salt lake is located results of environmental isotopes ionic ratio and saturation indices calculation indicated that the major geochemical processes responsible for groundwater salinization included dissolution of evaporites halite gypsum and mirabilite cation exchange and evapotranspiration groundwater salinization as a result of salt lake intrusion from the salt lake was limited to the northern shore of the lake

estimation of depth to fresh salt water interface and its implications for sustainable groundwater resource management a case study of the coastal strip of dar es salaam tanzania dar es salaam city is highly depending on groundwater resources since 1997 the resulting overexploitation is entailing the risk of seawater intrusion this problem has been systematically investigated for the first time and appears to be wide spread determining the depth of the fresh salt water interface was deemed crucial in the view of sustainable exploitation of the dar es salaam quaternary coastal aquifer system vertical electrical soundings ves and horizontal resistivity profiles have shown a decrease of resistivity with depth and toward the coastline cross sections have shown the presence of salt water in the aquifer near the coastline and the boundary between fresh and saline waters is mapped the surface prospection resistivity data showed comparable results as reflected in hydrochemical lithological cross sections and resistivity well logs salt water was found mostly in the area within 2 km of the coastline and the depth to the interface in this zone is ranging from 1 3 to 20 m away from the coastline the interface if present is at greater depth ves executed at kurasini 4 km from the sea showed the fresh salt water interface at a greater depth 43 m

velocity structure of the pamir hindu kush region possible evidence of subducted crust the arrival times of compressional p and shear s waves from approximately 580 microearthquakes recorded by a temporary array in the pamir hindu kush region in central asia are used to deduce one and three dimensional velocity structures of this region the results for one dimensional structures imply that the moho is at 70 5 depth also there is a velocity reversal near 160 km depth which is inferred to be the beginning of the low velocity zone this reversal continues to depths of approximately 230 km below 230 km velocities are somewhat higher than those of normal mantle at similar depths 9 3 km s versus 8 4 km s for p waves the outstanding feature of the results for three dimensional velocity structures is a broad 40 km centrally located region with 8 to 10 lower velocities than those in the surrounding regions this low velocity region envelopes the seismic zone at depths between 70 and 150 km the region may actually extend beyond these depths but the results for shallower and deeper structure lack sufficient resolution to decide several tests using both hypothetical and real data were performed to estimate the reliability of the three dimensional solutions the results of these tests suggest that the inferred velocities are reasonably accurate representations of the average velocities in the blocks although one must be cautious of the effects of averaging in interpreting the solution the low velocity region is inferred to be a manifestation of substantial quantities of subducted continental crust therefore while subduction has occurred in the pamir hindu kush the results of the three dimensional inversions suggest that continental rather than only oceanic lithosphere has been subducted to depths of at least 150 km appendices are available with the entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j81 013 1 00 payment must accompany order

geometry of the pamir hindu kush intermediate depth earthquake zone from local seismic data 1 we present new seismicity images based on a two year seismic deployment in the pamir and sw tien shan a total of 9532 earthquakes were detected located and rigorously assessed in a multistage automatic procedure utilizing state of the art picking algorithms waveform cross correlation and multi event relocation the obtained catalog provides new information on crustal seismicity and reveals the geometry and internal structure of the pamir hindu kush intermediate depth seismic zone with improved detail and resolution the relocated seismicity clearly defines at least two distinct planes one beneath the pamir and the other beneath the hindu kush separated by a gap across which strike and dip directions change abruptly the pamir seismic zone forms a thin approximately 10 km width curviplanar arc that strikes east west and dips south at its eastern end and then progressively turns by 90 to reach a north south strike and a due eastward dip at its southwestern termination pamir deep seismicity outlines several streaks at depths between 70 and 240 km with the deepest events occurring at its southwestern end intermediate depth earthquakes are clearly separated from shallow crustal seismicity which is confined to the uppermost 20 25 km the hindu kush seismic zone extends from 40 to 250 km depth and generally strikes east west yet bends northeast toward the pamir at its eastern end it may be divided vertically into upper and lower parts separated by a gap at approximately 150 km depth in the upper part events form a plane that is 15 25 km thick in cross section and dips sub vertically north to northwest seismic activity is more virile in the lower part where several distinct clusters form a complex pattern of sub parallel planes the observed geometry could be reconciled either with a model of two sided subduction of eurasian and previously underthrusted indian continental lithosphere or by a purely eurasian origin of both pamir and hindu kush seismic zones which necessitates a contortion and oversteepening of the latter

assembly of the pamirs age and origin of magmatic belts from the southern tien shan to the southern pamirs and their relation to tibet 1 magmatic rocks and depositional setting of associated volcaniclastic strata along a north south traverse spanning the southern tien shan and eastern pamirs of kyrgyzstan and tajikistan constrain the tectonics of the pamirs and tibet the northern pamirs and northwestern tibet contain the north facing kunlun suture the south facing jinsha suture and the intervening carboniferous to triassic karakul mazar subduction accretion system the latter is correlated with the songpan garze hoh xi system of tibet the kunlun arc is a composite early paleozoic to late paleozoic triassic arc arc formation in the pamirs is characterized by 370 320 ma volcanism that probably continued until the triassic the cryptic tanymas suture of the southern northern pamirs is part of the jinsha suture a massive 227 ma batholith stitches the karakul mazar complex in the pamirs there are striking similarities between the qiangtang block in the pamirs and tibet like tibet the regional structure of the pamirs is an anticlinorium that includes the muskol and sares domes like tibet the metamorphic rocks in these domes are equivalents to the karakul mazar songpan garze system granitoids intruding the qiangtang block yield 200 230 ma ages in the pamirs and in central tibet the stratigraphy of the eastern pshart area in the pamirs is similar to the bangong nujiang suture zone in the amdo region of eastern central tibet but a triassic ocean basin sequence is preserved in the pamirs arc type granitoids that intruded into the eastern pshart oceanic basin arc sequence 190 160 ma and granitoids that cut the southern qiangtang block 170 160 ma constitute the rushan pshart arc cretaceous plutons that intruded the central and southern pamirs record a long lasting magmatic history their zircons and those from late miocene xenoliths show that the most distinct magmatic events were cambro ordovician 410 575 ma triassic 210 250 ma likely due to subduction along the jinsha suture middle jurassic 147 195 ma subduction along rushan pshart suture and mainly cretaceous middle and late cretaceous magmatism may reflect arc activity in asia prior to the accretion of the karakoram block and flat slab subduction along the shyok suture north of the kohistan ladakh arc respectively before india and asia collided the pamir region from the indus yarlung to the jinsha suture was an andean style plate margin our analysis suggests a relatively simple crustal structure for the pamirs and tibet from the kunlun arc in the north to the southern qiangtang block in the south the pamirs and tibet likely have a dominantly sedimentary crust characterized by karakul mazar songpan garze accretionary wedge rocks the crust south of the southern qiangtang block is likely of granodioritic composition reflecting long lived subduction arc formation and cretaceous cenozoic underthrusting

deep india meets deep asia lithospheric indentation delamination and break off under pamir and hindu kush central asia abstract subduction of buoyant continental lithosphere is one of the least understood plate tectonic processes yet under the pamir hindu kush at the northwestern margin of the india asia collision zone unusual deep earthquakes and seismic velocity anomalies suggest subduction of asian and indian lithosphere here we report new precise earthquake hypocenters detailed tomographic images and earthquake source mechanisms which allow distinguishing a narrow sliver of indian lithosphere beneath the deepest hindu kush earthquakes and a broad arcuate slab of asian lithosphere beneath the pamir we suggest that this double subduction zone arises by contrasting modes of convergence under the pamir and hindu kush imposed by the different mechanical properties of the three types of lithosphere involved while the buoyant northwestern salient of cratonic india bulldozes into cratonic asia forcing delamination and rollback of its lithosphere india s thinned western continental margin separates from cratonic india and subducts beneath asia this torn off narrow plate sliver forms a prominent high velocity anomaly down to the mantle transition zone our images show that its uppermost section is thinned or already severed and that intermediate depth earthquakes cluster at the neck connecting it to the deeper slab providing a rare glimpse at the ephemeral process of slab break off

synchronous oligocene miocene metamorphism of the pamir and the north himalaya driven by plate scale dynamics gneiss domes in the pamir central asia and the himalaya provide key data on mid to deep crustal processes operating during the india asia collision laser ablation split stream inductively coupled plasma mass spectrometry lass icp ms data from monazite in these domes yield a time record from u th pb dates and a petrologic record from rare earth element ree abundances seven samples from the pamir and six samples from the north himalayan gneiss domes yield almost identical monazite dates of ca 28 15 ma most monazite has invariant heavy ree hree abundances two samples however have older monazite that records progressive hree depletion and two samples have younger monazite that records progressive hree enrichment these variations in hree are compatible with increasing garnet abundance prograde metamorphism until ca 20 ma and decreasing garnet abundance thereafter the change from hree depletion to enrichment may record a transition from crustal thickening and heating to dome exhumation and cooling this documentation of synchronous barrovian metamorphism within domes of indian crust along the margin of the orogen himalaya and within domes of asian crust within the core of the orogen pamir is best explained by a plate scale driving force rather than by local events we propose that widespread synchronous thickening was initiated by the resumption of indian subduction following slab breakoff and then terminated by a second slab tearing event both plate scale events inferred from tomography