the atmospheric transport of iodine 129 from fukushima to british columbia canada and its deposition and transport into groundwater the fukushima daiichi nuclear accident fdna released iodine 129 15 7 million year half life and other fission product radionuclides into the environment in the spring and summer of 2011 129i is recognized as a useful tracer for the short lived radiohazard 131i which has a mobile geochemical behavior with potential to contaminate water resources to trace 129i released by the fdna reaching canada pre accident and post accident rain samples collected in vancouver on saturna island and from the national atmospheric deposition program in washington state were measured groundwater from the abbotsford sumas aquifer was sampled to determine the fate of 129i that infiltrates below the root zone modeling of vadose zone transport was performed to constrain the travel time and retardation of 129i the mean pre accident 129i concentration in rain was 31 106 atoms l n 4 immediately following the fdna 129i values increased to 211 106 atoms l and quickly returned to near background levels however pulses of elevated 129i continued for several months the increases in 129i concentrations from both vancouver and saturna island were synchronized and occurred directly after the initial release from the fdna the 129i in shallow 3h 3he age 1 4 years wassenaar et al 2006 groundwater showed measurable variability through march 2013 with an average of 3 2 106 atoms l n 32 that was coincident with modeled travel times for fukushima 129i the groundwater response and the modeling results suggest that 129i was partially attenuated in soil which is consistent with its geochemical behavior however we conclude that the measured variability may be due to fukushima 129i entering groundwater

gravitational and tectonic forces controlling postcollisional deformation and the present day stress field of the alps constraints from numerical modeling 1 we perform numerical modeling to investigate the mechanisms leading to the postcollisional tectonic evolution of the alps we model the lithospheric deformation as a viscous thin sheet with vertically averaged rheology and coupled with surface mass transport the applied kinematic boundary conditions simulate the convergence between the adria indenter and the european foreland during the last 35 myr model predictions of elevation lithospheric structure erosion sedimentation pattern and vertical axis rotation are compared with observations of the planform shape of the chain topography crustal thickness distribution of rock exhumation and sediment thickness and paleomagnetic rotations thickening of the lithosphere in the alpine region is shown to be highly sensitive to the assumed viscosity law to the strength contrasts between the different regions and to the surface mass transport modeling results indicate that the large scale deformation of the alps during the postcollisional phase is mainly controlled by accommodation of convergence in a weak orogenic zone caught between a nearly rigid adria plate and a strong european foreland modeling of the present day stress field shows that 1 the present rotation of adria is responsible for the change of extension direction from strike perpendicular in the western alps to strike parallel in the east and 2 the strike perpendicular extension observed in the western alps is likely due to lateral variations of gravitational potential energy the results suggest a nne shift of about 700 km of the euler pole of adria relative to europe from its mean position during postcollisional deformation to the present day

surface kinematics in the alpine carpathian dinaric and balkan region inferred from a new multi network gps combination solution abstract the understanding of the intraplate tectonics of central europe requires a detailed picture of how stress is transferred from the interaction of the eurasian nubian and anatolian plates to the alpine carpathian pannonian and dinaric regions recent strain distribution is controlled by the adria horizontal push by the vrancea vertical slab pull and associated horizontal displacements and by the aegean anatolia extension and slab roll back we present a horizontal velocity field for the alpine carpathian pannonic dinaric and balkan regions resulting from a new combination of seven different gps networks formed from permanent and campaign stations dedicated velocity profiles in two specific regions are studied in detail one is the alpine pannonian region with a detailed picture of the ns indentation of the adria microplate into the southern alps in ne italy the deformation in the tauern window and the eastwards kinematics of a pannonian plate fragment the second study region includes transylvania the southern carpathians up to the aegean sea and albania where a major right lateral shear deformation exists as a consequence of the ne convergence of the apulia platform towards the dinarids and the ssw motion of macedonia western bulgaria and rumania related to the hellenic arc dynamics in the eastern mediterranean the profiles in the alpine pannonian area indicate that a velocity drop of 2 5 0 4 mm yr associated with the adria indentation concentrates on a segment of some 50 km south of the periadriatic fault the deformation becomes extensional by a similar amount just north of the periadriatic fault in the tauern window where the updoming of the tauern window implies vertical motion which could well be associated with surface extension in the ew profile we observe a sudden velocity change of 1 5 0 2 mm yr in 20 km corresponding to the right lateral lavant fault which seems to mark the border between dominant indentation kinematics to the west and dominant extrusion kinematics to the east three profiles are considered in southern and eastern europe one across the lower adriatic sea from apulia in italy to the southern dinarides which enables it to constrain the velocity drop associated with the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated with right lateral shear faults in albania the third profile crosses the transylvania region with a shortening of 2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc strain rate maps are presented in this regional scale showing the excellent agreement between fault plane solutions of crustal earthquakes and the eigenvectors of the gps derived two dimensional strain rate tensor three profiles are considered in the balkan and se carpathians one across the lower adriatic sea from apulia in italy to the southern dinarides which enables to constrain the velocity drop associated to the subduction of the adria microplate into the dinarides to 3 2 0 5 mm yr in 140 km the second profile is longitudinal and constrains the velocity inversion of 7 4 1 0 mm yr in 350 km associated to right lateral shear faults in macedonia a highly seismic region the third profile crosses the transylvania with a shortening2 3 1 0 mm yr in 220 km and the wallachian moesian region up to the chalcidic peninsula in n greece this lower part of the profile implies an extensional stretch of the upper crust of 3 2 0 9 mm yr in 440 km culminating in the hellenic arc

geochemistry of halogens in the milk river aquifer alberta canada abstract analytical data are presented for cl br and i on a regional scale for the milk river aquifer the three halides show strikingly similar spatial distributions and are highly correlated concentrations are low in the freshwater portions of the aquifer but increase by as much as two orders of magnitude along the margins however halide ratios reach nearly constant values moving down gradient suggesting the dominance of a common subsurface source for these ions ratios of cl i and cl br are less than those of seawater and fit an origin derived from the diagenesis of organic matter in the sediments halide ratios rule out leakage and or diffusion from the underlying colorado group as a major influence on the chemistry the favored hypothesis is altered connate seawater diffusing from low permeability units within the milk river formation as the primary source of salts this hypothesis of an internal source has important implications for solute sources in other aquifers affected by saline waters because it does not require the importation of a distant fluid the129i i ratio has a meteoric value in groundwater collected near the recharge area but ratios for downflow waters are only 8 70 of this value due to the 16 ma half life of129i these data indicate that most of the increase in dissolved i cannot derive from concentration of a meteoric source by ion filtration but must have a subsurface origin concentrations of129i producedin situ by spontaneous fission of238u attain measurable levels only in the oldest waters sampled ages 105a in which it may account for nearly 90 of the total dissolved129i concentration water ages based upon36cl cl data range up to 2 ma if uncorrected for any dilution by subsurface sources of dead cl if one assumes that the subsurface contributions of cl contribute at least 90 of total cl in the distal portion then the36cl based ages are reduced to 1ma somewhat greater than those estimated by hydrodynamic modeling

chlorine stable isotope studies of old groundwater southwestern great artesian basin australia abstract stable cl isotope ratios 37 cl 35 cl were measured in groundwater samples from the southwestern flow system of the great artesian basin australia to gain a better understanding of the cl sources and transport mechanisms 37 cl values range from 0 to 2 5 smoc and are inversely correlated with cl concentration along the inferred flow direction the cl isotopic compositions in conjunction with other geochemical parameters suggest that cl in groundwaters is not derived from salt dissolution mixing of the recharge water with saline groundwater cannot explain the relationship between 37 cl and cl concentration measured marine aerosols deposited via rainfall and subsequent evapotranspiration appear to be responsible for the cl concentrations observed in wells that are close to the recharge area and in groundwaters sampled along the southern transect 37 cl values measured in the leachate of the bulldog shale suggest that the aquitard is the subsurface source of cl for the majority of groundwater samples studied diffusion is likely the mechanism through which cl is transported from the pore water of the bulldog shale to the aquifer however a more detailed study of the aquitard rocks is required to verify this hypothesis

chlorine 36 dating of very old groundwater 1 the great artesian basin australia chlorine 36 has many advantages as a dating tool for very old groundwater these advantages include a suitable half life 3 01 x 10 sup 5 years simple geochemistry conservative behavior in groundwater and a general absence of subsurface sources at levels comparable to the atmospheric input recent advances in tandem accelerator mass spectrometry have permitted the analysis of sup 36 cl at low abundance expected following residence in the subsurface for 10 sup 6 years or more in order to test the suitability of sup 36 cl for dating very old groundwater the sup 36 cl cl ratios of 26 groundwater samples from the great artesian basin of australia have been measured groundwater ages calculated from the sup 36 cl data compare favorably with ages computed independently from hydrodynamic simulations

origin of iodine in the anadarko basin oklahoma an 129i study iodine comes almost exclusively from organic matter in sedimentary basins and therefore can be used as a source indicator for hydrocarbons the long lived half life 15 7 m y cosmogenic and fissiogenic isotope 129i has been applied to tracing brine migration in the anadarko basin oklahoma because all of the likely source formations for i are paleozoic the cosmogenic 129i component has decayed to undetectable levels and all of the measured 129i is of fissiogenic origin comparison of 129i 127i ratios measured in 12 brines from the platform area of the anadarko basin with ratios determined for potential source rocks reveals that the woodford shale is the probable source formation for the extremely high i concentr tions observed in these brines if the woodford shale is the exclusive source for i the time of expulsion can be constrained to between 2 and 90 ma although this date is much later than most estimates of expulsion time derived from conventional methods a case is presented for more recent expulsion in the northern part of the basin which was the sample area

regional scale tectonic evolution and the seismic velocity structure of the lithosphere and upper mantle the mediterranean region we present a numerical modeling approach designed for the verification of tectonic reconstructions and for a quantitative analysis of the seismic velocity structure of the lower lithosphere and upper mantle in this forward modeling procedure we use published reconstructions of the tectonic evolution of a region to predict the thermal structure from which we calculate physical quantities like p wave velocity basin subsidence and basement heat flow we show an application of this approach to two reconstructions of the late mesozoic and cenozoic evolution of the mediterranean region the resulting synthetic velocity models are tested against seismological models of the mantle structure obtained independently by delay time tomography subsidence and heat flow predictions are compared with actual observations to further constrain the geological assumptions underlying the forward models the mantle models predicted from reconstructions of the evolution of the mediterranean region correlate with major features in the tomographic images from our model results we conclude that the present distribution of seismic velocities in the mediterranean region is largely determined by the tectonic evolution during at least the last 40 m y this means we can verify processes represented in different tectonic scenarios with the seismologically determined velocity structure seen from a different perspective the model results contribute to understanding the causes of the velocity structure imaged by delay time tomography by showing how the tectonic evolution results in this structure

iodine budget in surface waters from atacama natural and anthropogenic iodine sources revealed by halogen geochemistry and iodine 129 isotopes abstract iodine enrichment in the atacama desert of northern chile is widespread and varies significantly between reservoirs including nitrate rich caliche soils supergene cu deposits and marine sedimentary rocks recent studies have suggested that groundwater has played a key role in the remobilization transport and deposition of iodine in atacama over scales of millions of years however and considering that natural waters are also anomalously enriched in iodine in the region the relative source contributions of iodine in the waters and its extent of mixing remain unconstrained in this study we provide new halogen data and isotopic ratios of iodine 129 i i in shallow seawater rivers salt lakes cold and thermal spring water rainwater and groundwater that help to constrain the relative influence of meteoric marine and crustal sources in the atacama waters iodine concentrations in surface and ground waters range between 0 35 m and 26 m in the tarapaca region and between 0 25 m and 48 m in the antofagasta region and show strong enrichment when compared with seawater concentrations i 0 4 m in contrast no bromine enrichment is detected 1 3 45 7 m for tarapaca and 1 7 87 4 m for antofagasta relative to seawater br 600 m these data coupled to the high i cl and low br cl ratios are indicative of an organic rich sedimentary source related with an initial fluid that interacted with meteoric water to produce a mixed fluid and preclude an exclusively seawater origin for iodine in atacama natural waters iodine isotopic ratios 129 i i are consistent with halogen chemistry and confirm that most of the iodine present in natural waters derives from a deep initial fluid source i e groundwater which has interacted with jurassic marine basement with variable influence of at least one atmospheric or meteoric source samples with the lowest isotopic ratios 129 i i from 215 to 1000 10 15 strongly suggest mixing between the groundwater and iodine storage in organic rich rocks with variable influence of volcanic fluids and pre anthropogenic meteoric water while samples with higher values 2000 93 700 10 15 indicate the input of anthropogenic meteoric fluid taking into account the geological hydrologic and climatic features of the atacama region we propose that the mean contribution of anthropogenic 129 i is associated with 129 i releases during nuclear weapon tests carried out in the central pacific ocean until the mid 1990 s 129 i i 12 000 10 15 this source reflects rapid redistribution of this radioisotope on a global scale our results support the notion of a long lived continental iodine cycle in the hyperarid margin of western south america which is driven by local hydrological and climate conditions and confirm that groundwater was a key agent for iodine remobilization and formation of the extensive iodine rich soils of atacama

an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada the milk river artesian aquifer underlies 15 000 km2 of southern alberta canada it consists of thin 30 75 m thick sandstone and is confined above by the pakowki shale typically 120 m thick and below by the colorado shale the aquifer subcrops in southern alberta and northern montana groundwater movement is to the north west and east from the outcrop area dominant recharge area cl and i concentrations increase in the direction of flow from less than 0 05 and 0 001 mmol l respectively near the recharge area to more than 140 and 0 15 mmol l at the northern edge of the aquifer similarly waters become more enriched in oxygen 18 and deuterium from less than 21 0 and 167 near the recharge area to values approaching 8 0 and 70 0 in the north isotope values in the recharge area plot on the global meteoric water line and indicate that the recharge waters are isotopically unaltered meteoric waters downgradient from the recharge area the data deviate from the meteoric water line slope of 6 3 instead of 8 0 three mechanisms have been advanced to explain the origin of the chemical and isotopic patterns the introduction of connate formation water through the colorado shale and subsequent mixing with infiltrating meteoric water a finite source of meteoric recharge mixing with more saline water in the aquifer and chemical and isotopic enrichment due to ion filtration hydraulic conductivity and hydraulic head data cl concentrations of drill cuttings and isotopic values from groundwater from the colorado shale provide arguments for reevaluating these ideas an alternative mechanism based on diffusion between saline isotopically enriched water in the colorado shale and fresher isotopically depleted water in the aquifer is tested using an analytical mass transport model although uncertainty exists in the model parameters results showed that the patterns in cl i 18o and 2h in the aquifer can be explained by aquitard diffusion further aquitard diffusion must be considered when using chlorine 36 dating methods in aquifer aquitard systems such as the milk river aquifer

lithospheric thermal regimes in europe abstract the heat flow pattern of europe derived from more than 8000 observations is dominated by a general northeast to southwest increase in geothermal activity which is the consequence of the tectonic evolution of the whole continent this paper reviews the history of the geothermal mapping of europe and describes the recently compiled set of geothermal maps of europe surface heat flow is correlated with the age of the last tectonothermal event with the near surface heat production and with the crustal thickness deep temperature distributions within the crust lithosphere are calculated for 1 d 2 d and simple 3 d models characteristic temperature depth curves are given for some of the major tectonic provinces and the results of various techniques are compared the value of the crustal heat contribution is assessed and a regional moho heat flow pattern is proposed the mohorovicic discontinuity is clearly not an isothermal surface neither is the heat flow from below the crust constant

measurements and interpretations of36cl in groundwater milk river aquifer alberta canada abstract the 36 cl cl ratios of 12 groundwater samples from the milk river aquifer were determined by accelerator mass spectrometry using known cl concentrations 36 cl concentrations were deduced approximately linear relations were observed between the logarithm of the 36 cl concentration the cl concentration and the distance from the recharge area along two flow paths the results are discussed in two approaches 1 in an interpretation of the linear relation between logarithm of the 36 cl concentration and cl concentration excluding and including in situ production of 36 cl 2 in a diffusion model the increase of the cl concentration with the distance from the recharge area is considered to be due to diffusion of cl from the underlying confining colorado shale to the aquifer flow velocities ranging between 0 04 and 0 14 m a and ages of the groundwater between 0 6 and 2 ma are obtained at a distance of 80 km from the recharge area

variations in 129i 127i ratios in recent marine sediments evidence for a fossil organic component abstract the value of the pre bomb 129 i 127 i ratio in the hydrosphere is important for the use of this isotope system for dating and tracing purposes in order to determine this value and to examine spatial variability 129 i 127 i ratios were measured in 25 sediment samples from five cores taken at geographically distinct coastal areas the results indicate a pre anthropogenic 129 i 127 i ratio of 1500 10 15 in good agreement with values derived from previous sediment and groundwater studies results from shallow sediments show that the layer of bioturbation is dominated by the addition of anthropogenic 129 i the good agreement between results for this layer from different cores supports the understanding that marine iodine is isotopically homogeneous and associated with organic material which is actively remineralized at the sediment water interface lower ratios down to 354 10 15 corresponding to an age of 32 5 ma and larger variations than expected were found in sections of the cores below the layer of bioturbation these observations can be explained by the presence of refractory fossil organic material transported by rivers to the sediments from uplifted continental shales the results suggest that marine iodine is present in two forms a labile component which is isotopically homogeneous and a refractory component which is associated with kerogen or other fossil organic compounds whose 129 i 127 i ratio reflects the age of these compounds 129 i 127 i ratios can be used to identify and date fossil organic material in recent sediments the presence of which can alter the assumptions underlying models of the global carbon cycle

application of isotopic methods to dating of very old groundwaters milk river aquifer alberta canada the aim of this joint project was to evaluate the usefulness of available geochemical and isotope techniques for dating very old groundwater this paper represents a synthesis of an iaea sponsored study for which purpose the milk river aquifer groundwaters were sampled from 16 wells during 1985 and subsequent years for the following measurements 2h 3h 13c 18o 14c 39ar 81kr 85kr noble gases including222rn 36cl 129i and u isotopes the milk river aquifer was selected for this study because several preceding investigations had established that this groundwater system contains waters whose ages range from recent to 1ma the present study has established that the milk river aquifer system is very complex both in terms of groundwater origin and in terms of the evolution of its chemical and isotopic contents however this apparent complexity proved to be an interesting challenge with respect to the use of different and complementary approaches to interpretation of the geochemical and isotope data in terms of groundwater residence time thus the groundwater ages based on the hydrodynamic model should be considered as a lower limit of the average groundwater age in the milk river aquifer 0 25ma while those based on the36cl cl data uncorrected for any dilution by dead cl should be considered as an upper limit 2ma the milk river aquifer international project is an excellent illustration of the variety of insight and increased confidence possible in flow system analysis when multiple independent dating methods are combined with detailed hydrogeological studies the conclusion of the present study is that the potential for dating of very old groundwaters by a variety of isotope techniques is very high provided a combination of methods is applied never a simple method by itself

miocene to present major fault linkages through the adriatic indenter and the austroalpine penninic collisional wedge alps of ne italy

natural iodine 129 as an environmental tracer abstract iodine 129 t 1 2 16 my is a naturally occurring tracer which can be used to study hydrologic and geologic processes on time scales up to 100 my the pre bomb atmospheric ratio 129 i i should have been constant in time and space and is the starting value in ground water recharge subsequent ratio changes in ground water should be determined by isotope contributions from three sources recharge water iodine leached from the formation and in situ uranium fission the mathematical expression of these time dependent processes forms the basis for dating and tracing applications the expected behavior of natural 129i in ground water is compared to results from field studies ground water samples from the great artesian basin australia provide an estimate of the atmospheric equilibrium ratio 6 10 13 down gradient changes in water up to 1 my old suggest that subsurface production can be significant the usefulness of 129i as an indicator of brine source and age is verified in brines collected in and around louisiana salt domes the method leads to ages of 7 and 9 my for two brine pockets trapped within jurassic salt and 32 to 40 my for oil field brines in miocene sands adjacent to the domes the results demonstrate the capability of tandem accelerator mass spectrometry to measure as few as 107 atoms of 129i in 10 mg i with 10 precision although such atom sensitivity can be achieved otherwise the accelerator technique is necessary to measure naturally low pre 1945 cosmogenic isotope ratios

a unified description of localization for application to large scale tectonics 1 localized regions of deformation such as faults and shear zones are ubiquitous in the earth s lithosphere however we lack a simple unified framework of localization that is independent of the mechanism or scale of localization we address this issue by introducing the effective stress exponent ne a parameter that describes how a material responds to a local perturbation of an internal variable being tested for localization the value of ne is based on micromechanics a localizing regime has a negative ne indicating a weakening behavior and localization is stronger for more negative 1 ne we present expressions for the effective stress exponent associated with several mechanisms that trigger localization at large scale brittle failure with loss of cohesion elastoplasticity rate and state dependent friction shear heating and grain size feedback in ductile rocks in most cases localization does not arise solely from the relation between stress and deformation but instead requires a positive feedback between the rheology and internal variables brittle mechanisms failure and friction are generally described by ne of the order of 100 shear heating requires an already localized forcing which could be provided by a brittle fault at shallower levels of the lithosphere grain size reduction combined with a transition from dislocation to diffusion creep leads to localization only if the grain size departs significantly from its equilibrium value because either large scale flow moves rocks through different thermodynamic environments or new grains are nucleated when shear heating or grain size feedback produce localization 1 ne can be extremely negative and can control lithospheric scale localization

travel time tomography of the european mediterranean mantle down to 1400 km abstract the 3 d p wave velocity structure of the mantle below europe the mediterranean region and a part of asia minor is investigated this study is a considerable extension of an earlier tomographic experiment that was limited to imaging upper mantle structure only here the earth s volume under study encompasses the mantle to a depth of 1400 km and we increase the number of international seismological centre isc data for inversion by a factor of four by taking more years of observation and by including data from teleseismic events the most important departure from the earlier study is that we do not use the jeffreys bullen model as a reference model but an improved radially symmetric velocity model the pm2 model which is appropriate for the european mediterranean mantle our inversion procedure consists of two steps first the radial model pm2 is determined from the isc delay times by a nonlinear trial and error inversion of the data as opposed to the jeffreys bullen model the new reference model has a high velocity lithosphere a low velocity zone and seismic discontinuities at depths of 400 and 670 km next the isc data are corrected for effects related to the change in reference model and inverted for 3 d heterogeneity relative to the pm2 model we follow this two step approach to attain a better linearizable tomographic problem in which ray paths computed in the pm2 model provide a better approximation of the actual ray paths than those computed from the jeffreys bullen model hence the two step scheme leads to a more credible application of fermat s principle in linearizing the tomographic equations inversion results for the 3 d heterogeneity are computed for both the uncorrected isc data and for the pm2 data the data fit obtained in the two step approach is slightly better than in the inversion of isc data using the jeffreys bullen reference model a comparison of the tomographic results demonstrates that the pm2 data inversion is to be preferred to assess the spatial resolution an analysis is given of hit count patterns sampling of the mantle by ray paths and results of sensitivity tests with 3 d synthetic velocity models the spatial resolution obtained varies with position in the mantle and is studied both in map view and in cross section in the well sampled regions of the mantle the spatial resolution for larger scale structure can qualitatively be denoted as reasonable to good and at least sufficient to allow interpretation of larger scale anomalies a comparison is made of the results of this study with independent models of s velocity heterogeneity obtained in a number of investigations and with a prediction of the seismic velocity structure of the mantle computed from tectonic reconstructions of the mediterranean region in the context of this comparison interpretations of large scale positive anomalies found in the mediterranean upper mantle in terms of subducted lithosphere are given specifically addressed are subduction below southern spain below the western mediterranean and italy and below the aegean in the last region a slab anomaly is mapped down to depths of 800 km

sources sinks and long term cycling of iodine in the hyperarid atacama continental margin abstract the atacama region in northern chile hosts the driest desert on earth and is the world s premier iodine production province the origin of iodine enrichment in atacama is controversial and fundamentally different processes have been invoked over the years that involve marine eolian and more recently deep sedimentary fluid and groundwater sources as a result of the very limited geochemical iodine data in atacama and the western south american margin the origin of iodine enrichment in this region still remains elusive in this study we present a comprehensive survey of iodine concentrations and isotopic ratios 129i i of different reservoirs in the atacama desert of northern chile including nitrate soils supergene copper deposits marine sedimentary rocks geothermal fluids groundwater and meteoric water nitrate soils along the eastern slope of the coastal cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of 0 12 ppm with a mean concentration of 700 ppm soils above giant copper deposits in the central depression are also highly enriched in iodine 100 s of ppm range and cu iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits further east in the precordillera jurassic sedimentary shales and limestones show above background iodine concentrations the latter averaging 50 ppm in the southern portion of the study area the highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the coastal range 3 5 10 ppm and in geothermal waters 1 3 ppm along the volcanic arc although highly variable the iodine isotopic ratios 129i i of jurassic marine sedimentary rocks 300 600 10 15 nitrate soils 150 1500 10 15 and waters 215 10 15 are consistently low

timing kinematics and cause of aegean extension a scenario based on a comparison with simple analogue experiments abstract since the early 1970s most geodynamic models proposed for the eastern mediterranean consider that the initiation of extension in the aegean during the late middle miocene or later was a direct consequence of the westward extrusion of anatolia away from the arabia eurasia collision front in the late 1990s a few models have taken into account the increasing evidence for an earlier initiation of aegean extension arising mostly from the analysis of deformation within the various alpine metamorphic complexes of the area based largely on our own investigations we first present a review of the data that reliably constrain the minimum age for the initiation of extension in these complexes it shows that regional scale extension with a pattern of stretching orientations similar to that of the pliocene pleistocene was already strongly active in the aegean before the onset of arabian indentation into eurasia lower miocene vs middle or upper miocene this implies that the initiation of aegean extension did not result from the lateral extrusion of anatolia instead extension may have started owing to a process of gravity spreading of the continental lithosphere that had previously been thickened during alpine collision the main arguments favouring this interpretation are presented and a preliminary scenario is proposed for the neogene evolution of the eastern mediterranean in which lateral extrusion of anatolia occurred lately during southward spreading of the aegean lithosphere in order to test this hypothesis further physical experiments simulating the horizontal spreading of a continental lithosphere toward a free boundary have been carried out the analysis of various elements of the deformation field displacements strain rotations fault pattern and kinematics both in the experiments and in the aegean domain reveals an excellent agreement between the two not only do early stages of aegean extension appear to fit the gravity spreading hypothesis but so does the recent to present internal deformation of the aegean transverse e w active shortening observed in the northern aegean is commonly taken as one of the most striking pieces of evidence that aegean extension results from the lateral extrusion of anatolia the experiments indicate that such transverse shortening may equally develop as a result of pure gravity spreading associated with a pattern of faults and rotations that compares well with that of the northern aegean pure dextral shearing along some strands of the north aegean trough fault system and the related development of an asymmetric pattern of faults in the northern aegean are eventually the only features that evidently arise from the extrusion of anatolia since less than 3 ma finally we argue that during the early stages of aegean extension since at least 21 ma and until ca 11 ma the distribution of extensional strain on a regional scale has been controlled by the distribution of earlier thickening post thickening thermal weakening through partial melting of deep levels of the crust probably accounts for the localization of extensional strain within the areas of thick crust restoring the aegean in its most likely configuration at the onset of bulk crustal extension suggests that 1 the extensional strain rate remained roughly constant or has eventually decreased since the onset of aegean extension and 2 the amounts of extension before and after 16 ma have been roughly equal

comment on reinterpretation of 36cl data physical processes hydraulic interconnections and age estimates in groundwater systems by e mazor abstract mazor 1992 has reinterpreted several previous 36 cl studies the studies he revised used extensive physical hydrogeological data to aid in interpretation of the 36 cl measurements major ion chemistry and other isotope tracers were considered in order to evaluate the groundwater geochemistry the studies then used simple geochemical models to account for cl behavior in the subsurface the result of these 36 cl dating studies was in reasonable agreement with both numerical models of the aquifer systems and with independent geochemical studies mazor 1992 has reinterpreted these studies based on the assumption that spatial variation in chemical and isotope data should be attributed to unspecified discontinuities in the flow regime the conceptual models of aquifer hydrodynamics resulting from this approach differ radically not only from the previous 36 cl interpretations but also from the findings of virtually all previous hydrogeological and geochemical investigations although mazor s reinterpretations are provocative he does not show how they explain the data of the numerous previous studies better than the conceptual models presented by the authors of those studies nor has he demonstrated that his new models are consistent with the fundamental physical laws governing groundwater flow until this is satisfactorily accomplished i will continue to prefer the original 36 cl interpretations

indentation of a continent with a built in thickness change experiment and nature orogens oblique to the direction of plate convergence are currently attributed to obliquity between the margins of one or both of the sutured continents to their direction convergence we use a single analogue experiment and natural examples to illustrate a potential additional factor variations in strength of the indented continent at a high angle to the convergence direction the wavelengths of structures in laterally shortened lithosphere depend on the strength of the most competent layers lateral variations in crustal thickness must therefore lead to structures oblique to any applied lateral compression an analogue experiment was performed to explore this phenomenon a two layer indented continent was modelled by a brittle upper crust of sand above a lower crust of high viscosity polymer floating on a single layer of low viscosity syrup representing the mantle the well known strike slip structures allowing lateral escape to distant weak boundaries were hindered by lateral boundaries in front of the indenter this allowed us to focus on the effects of a thickness change built into the indented continent along a zone parallel to the direction in which a vertical rigid wall advancing at a steady rate represented the indenter vertical escape led to an orogenic belt oblique to the advancing wall this obliquity influences subsequent lateral escape model scaling and interpretations are based on extended thin sheet approximation etsa and standard theories of faulting four sectors of the alpine himalayan orogen iran tunisia the eastern alps and the himalaya are oblique to the continental convergence direction and we point to thickness changes at high angles to the suture that may account for this geometry as crustal thicknesses north of oblique sectors of the himalayas are not yet known we speculate on them we infer from the main difference between our experiment and all our examples chosen from nature that vertical orogenic escape was oblique to our model suture but can be parallel to natural sutures

correlation between shear wave upper mantle structure and tectonic surface expressions application to central and southern germany we have inverted fundamental mode rayleigh waveforms in the frequency range from 20 to 100 s to obtain a three dimensional s velocity distribution beneath central and southern germany the data come from 27 teleseismic events recorded at 17 broadband stations in germany and adjacent areas this results in 56 paths between pairs of stations each pair lying on the same great circle with an epicenter the phase differences between the waveforms recorded at a pair of stations have been inverted directly for the path averaged s velocity perturbation between the two stations all path models were then combined into a single three dimensional model the most prominent features of the obtained model are 1 low velocities beneath the eger graben which are an expression of the deep reaching rift structure 2 high velocities between 40 and 120 km depth beneath northern bavaria caused by an apparent thickening of the lithosphere toward the south 3 high velocities in the uppermost mantle beneath the southern rhine graben area presently inactive with respect to rifting suggesting the absence of present upwelling hot mantle material and 4 low velocities beneath the presently experiencing rifting northern branch of the central european rift system including the northern part of the rhine graben and the rhenish massif west of the river rhine with the volcanic fields of the eifel these reduced velocities indicate a broad updoming of the lithosphere asthenosphere boundary our model suggests a strong correlation between upper mantle s wave structure at depths down to 200 km and tectonic surface expressions

prediction of faulting from the theories of elasticity and plasticity what are the limits elasticity rigid plasticity and elasto plasticity are the simplest constitutive models used to describe the initiation and evolution of faulting however in practice the limits of their application are not always clear in this paper we test the behaviour of these different models using as examples tectonic problems of indentation of a die compression with basal shear bending of a plate and normal faulting around a dike by comparing the results of these tests we formulate some guidelines that may be useful for the selection of an appropriate constitutive model of faulting the theory of elasticity reasonably predicts the initiation of the fault pattern but gives erroneous results for large strains the theory of rigid plasticity is more appropriate for large deformations where the geometry of faults can be found by the method of characteristics this method works well for zones of failure that are not severely constrained by elastic material outside e g when faults are connected to the free surface a viscous substratum or a zone of weakness non associated elasto plasticity is the most complete theory among those considered in this paper it describes the evolution of faults from the initiation of localized deformations to the formation of a complicated fault network

the thermal structure of the mediterranean upper mantle a forward modelling approach we develop and present an approach for gaining insight into the thermal structure of the upper mantle in a tectonically active region as a starting point for the analysis we use regional geological reconstructions based on data from surface geology shallow seismics and paleomagnetism for these reconstructions we determine the necessarily associated upper mantle processes such as subduction we then forwardly model the thermal structure of upper mantle corresponding with the geological reconstruction used in this way we obtain an estimate of a very important characteristic the temperature distribution of the upper mantle that is independent from those estimates from the usual deep seismic methods if sufficient detailed information on the seismological structure of the region is available a quantitative test of our modelling results is possible via the temperature dependence of seismic velocities we apply our approach to the mediterranean area for which we will test the reconstruction published by dercourt et al 1986

strontium isotopic evidence on the chemical evolution of pore waters in the milk river aquifer alberta canada abstract strontium isotope ratios were measured on 13 rock 18 leachate and 28 pore water samples from the milk river aquifer the confining argillaceous formations and the glacial till mantling the recharge area strontium isotope ratios 87sr 86sr of pore waters from the aquifer confining units and the glacial till ranged from 0 7069 to 0 7082 the 87sr 86sr ratios in aquifer pore waters decrease with increasing distance from the aquifer recharge area and this is interpreted to be the result of mixing and water rock interaction within the aquifer the solute composition of the recharging groundwater is modified by the local lithology causing distinct geochemical patterns along different flow paths within the aquifer whole rock 87sr 86sr ratios indicate that the shales and till are generally more radiogenic than the aquifer sandstone the authigenic carbonate cements and rock forming minerals comprising the major lithologic units had little apparent influence on the pore water sr chemistry carbonate cement leachates from the till and the aquifer sandstone are more radiogenic than those from the confining shale formations feldspar separates from the aquifer sandstone have relatively radiogenic sr isotope ratios whereas bentonites from the milk river and colorado shale formations have whole rock and leachate sr isotope ratios that are relatively unradiogenic ratios of most milk river aquifer pore waters are lower than those of any leachates or whole rocks analyzed except the bentonites the 87sr 86sr ratios of exchangeable sr in the bentonites are similar to ratios found in the more evolved pore waters simple rock water interaction models calculated for the whole rock leachate and exchangeable ion pore water pairs indicate that ion exchange with bentonite clays within the milk river and colorado shale formations appears to influence the isotopic evolution of the pore water sr in each of these units

controls on the distribution of major ions in pore waters of a thick surficial aquitard transport and geochemical processes controlling the chemical and isotopic composition of pore waters in the upper 45 m of a thick surficial clay rich till battleford formation were studied the upper 3 m of the till is oxidized and fractured the remaining 77 m of the till the aquitard is nonfractured and unoxidized concentrations of total dissolved solids so42 na mg2 and k decrease with depth through the unoxidized zone to a depth of about 15 m below ground below which the concentrations remain constant a similar trend was observed for alkalinity however the decrease in concentration occurs over 20 m in contrast to these ions ca2 concentrations increase with depth through the upper 20 m unoxidized zone below which the concentrations remain relatively constant the distribution of dissolved ions shows the presence of two end members elevated solute concentrations in the oxidized zone attributed to geochemical weathering that occurred since the start of the holocene and connate pleistocene age water at depths between 20 and 45 m abiotic and biotic geochemical reaction rates in the aquitard were shown to be extremely slow or not occurring

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

transition from oblique subduction to collision in the northern luzon arc taiwan region constraints from bathymetry and seismic observations we systematically study the detailed bathymetry seismicity and source parameters of large and moderate sized earthquakes that occurred in the northern luzon arc taiwan region between 1964 and 1996 the purpose is to characterize the transition from oblique subduction to regional collision in terms of the distribution of morphological features the characteristics of seismogenic structures and the corresponding state of strain to the south of 21 5 n the existence of a subduction zone is clearly shown by both bathymetry and seismicity the subducted eurasia slab reaches a maximum depth of 200 km and the depth decreases sharply as it approaches taiwan focal mechanisms indicate that the subducted slab is in downdip extension for depths 150 km but switches to downdip compression at greater depths to the north of 23 n collision is clearly the predominant process with broad deformation on both sides of the suture in between the transition is accommodated by a distributed thrust deformation zone in the frontal portion of the accretionary prism closure of the forearc basin and the right lateral ne sw striking taitung canyon fault zone tcfz these structures resolve the differential movements between the subduction and collision zones and will repeatedly change their positions as the collision propagates southwestward the present day plate boundary follows the axis of the manila trench in the south broadens significantly in the zone of transition and finally becomes a zone of several tens of kilometers in width across eastern taiwan the deformation front on the other hand is located between the western foothills and coastal plain in taiwan then connects to the manila trench to the south seismic strain tensors indicate that the region to the north of tcfz has a compression rate 15 times larger than that to the south the northern luzon arc shows characteristics of oblique subduction but the effects of collision are not as significant within the subducted eurasian lithosphere as comparing to the subducted philippine sea plate beneath the southernmost ryukyu arc

radioisotope dynamics the origin and fate of nuclides in groundwater the use of radionuclides as clocks for groundwater dating and as probes to investigate the geometry and spatial extent of the contact area between rocks and water is reviewed subsurface production rates for 222 rn 37 ar 55 kr 39 ar 36 cl 3 he 4 he and 40 ar in various rock types are listed measured rn fluxes from the surface of sandstone grains and from pieces of granite point to scale dependent diffusion coefficients the temporal evolution of subsurface produced 222 rn 37 ar 85 kr and 39 ar activities in groundwaters yields radionuclide escape factors between 0 1 and 9 for the stripa granite sweden and between 1 and 4 for the milk river sandstone canada the combination of 3 h 85 kr 39 ar 14 c 36 cl 4 he in the uk triassic sandstone aquifer allows groundwater dating up to 40 000 a very old groundwaters can be studied using cl 36 cl and 4 he evolution as demonstrated in the milk river aquifer in canada

integrated hydrogeochemical isotopic and geomorphological depiction of the groundwater salinization in the aquifer system of delhi india abstract the problem of salinization in the delhi aquifer that currently exhibits rapid landuse change is conspicuous and severe salinization may be caused either by a single process or a combination of different processes including anthropogenic related activities water logging and evaporative concentration of salts influx of natural saline water upconing of brines from the deeper parts of the aquifer and airborne salts depositions however there is a lack of well proven theory that can explain the salinity of the order of 5000 s cm in the deeper aquifers of delhi this work identifies inconclusiveness in the previous theories of marine ingression evaporation enrichment and subsequent leaching of salt further the study depicts a conceptual understanding of the origin of salinity in groundwater based on the integrated investigations of groundwater quality age and stable isotopic fingerprinting as well as gis based mapping of geomorphic features in order to explain the salinity observed in groundwater of nct delhi a phenomenological scenario is illustrated and supported by additional evidences the highest average ec value was for the shallow aquifer and is strongly symptomatic of anthropogenic influences on groundwater chemistry piper diagram showed heterogeneous water type and sufficient recharge mixing of the groundwater from different aquifers the relationship between cl br ratios vs cl indicated dissolution of salt deposits containing evaporative fraction present in the unsaturated zones or in the sediments of deeper aquifers and leaching of evaporative minerals from dunes of the adjacent thar desert cl so 4 2 ratio suggested the presence of connate seawater halite dissolution and concentration of dissolved salts by evapo transpiration of river water diverted for irrigation the results show that the closed inland marine conditions developed and buried with the active sedimentation in the geological past in this region and further intensive exploitation of groundwater and enhanced evaporation have together resulted in saline playa condition in some part of the region the scenario was further verified by matching the required condition for the formation of salt pan or playa with the existing geo morphological conditions of the area isotopic results indicate that salinity flushing is possible and proceeds in the areas of freshwater recharge

fast mechanisms for the formation of new plate boundaries abstract we demonstrate the important role played by non linear feedback in promoting the fast breakup of the continental lithosphere and the formation of new plate boundaries we compare the difference in fluid dynamic and elasto visco plastic approaches and emphasize the advection of stresses in finite element models with large strain lagrangian formulation two types of instabilities were found at multiple time length scales ranging from 100 years and km scale to 0 1 myr and 100 km scale one mechanism relies on the thermo mechanical elasto plastic energy conversion and the other stems from the void volatile interaction elasticity takes on a guiding role in the propagation of shear zones closely followed by a thermal wave which is again followed by a wave of volatiles this last mechanism consolidates the fault zones and establishes the plate boundary for a geological time scale using a fully coupled thermal mechanical approach we obtain for the first time a two dimensional solution which shows that the constant velocity boundary conditions can lead to episodic avalanche type tectonic phases within

helium and argon isotopes in rocks minerals and related ground waters a case study in northern switzerland abstract to address the problems related to the transfer of helium and argon isotopes from rocks into related aquifers the concentrations of u th li and k and helium and argon isotopes were measured in a sedimentary sequence from tertiary to permo carboniferous and in crystalline rocks in northern switzerland in addition to whole rock samples mineral separates have also been investigated the observed concentrations of 3 he 4 he and 40 ar in rocks minerals and groundwaters are compared to calculated values which would result from in situ radiogenic production in a closed system this comparison shows that the rocks and minerals have almost completely lost radiogenic in situ produced helium loss of 3 he and 4 he has been controlled by different retention capacities of the rock forming and accessory minerals and fillings therefore measured 3 he 4 he ratios in these rocks can differ from the calculated production ratios the deviation is generally less than a factor of 3 however in certain chemical sediments e g anhydrites elevated ratios of 3 he 4 he up to 15 10 8 which is 20 times the production ratio were observed it is postulated that 3 h the precursor of 3 he might be chemically bound in such sediments during the 12 3 years half life of 3 h and that the beta decay energy of 3 h is too small to liberate 3 he the calculated closed system concentrations of helium in groundwater exceed the measured ones by up to three orders of magnitude implying that the water rock system has not been a closed system since the time of sedimentation and that movable waters have removed helium to a discharge area and to the atmosphere stagnant old waters however could contain high concentrations of helium and supply it to younger movable waters aquitards with low permeability permian shales appear to be a more important source of helium isotopes than water bearing rocks permian sandstones high abundances of all parent elements in the shales almost complete loss of radiogenic helium and the enhanced production ratio of 3 he 4 he 7 2 10 8 in these rocks similar to the ratio observed in the neighbour permian aquifer 9 4 10 8 suggest the shale as a major source of helium isotopes for this aquifer and diffusion as a principal process for helium transfer from the stagnant porewaters in shales into the movable waters in sandstones some sedimentary rocks e g permian sandstones and shales contain more helium than could have been produced since the time of sedimentation while permian sandstones mainly have retained this excess rare gas component they have released radiogenic helium the difference in the retention of these two components most probably demonstrates that migration of radiogenic helium from damage tracks along crystal imperfections to grain boundaries is an important process controlling its loss the abundances of excess 3 he and 4 he in rocks cannot be predicted by in situ production calculations studies of rocks and minerals are required the average ratio of 40 ar 36 ar 385 in groundwaters collected from permian sediments from the weiach borehole is much higher than that in the aquifers from the crystalline basement below the sediments radiogenic 40 ar in permian sediments is mainly liberated by diagenetic water rock interactions the low contribution of radiogenic 40 ar in deep aquifers of the crystalline basement and the fact that chlorine concentrations in groundwaters from the basement are also much lower than in the overlaying permian aquifer eliminates a hypothetical upwards fluid flux from this study we envisage intrabasin sources for helium and argon isotopes in groundwaters with mainly lateral migration of waters through sedimentary layers at different rates and diffusion of helium from slower velocity older waters in more stagnant zones shales into flow passes with highervelocity younger waters in sections with higher permeability sandstones an external source for noble gases is not required in such a model

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

comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz the milk river aquifer in southern alberta combines apparently simple classical confined aquifer hydrodynamics with somewhat enigmatic groundwater geochemistry of conservative solutes over the past 10 years five major papers have focused on the geochemistry of milk river aquifer groundwater most recently hendry and schwartz 1988 have proposed a different mechanism aquitard diffusion to explain the milk river geochemistry they described and evaluated previously proposed geochemical processes especially ion filtration hendry and schwartz 1988 concluded that ion filtration and the other proposed mechanisms were not supported by the data they then described the aquitard diffusion mechanism and used a simple analytical model to simulate observed aquifer trends in cl sup minus and sup 18 o from the results of this exercise they concluded that diffusion from the aquitards was controlling the solute distributions in the aquifer finally they interpreted previously published sup 36 cl data and new profiles of cl sup minus in the aquitards in terms of the diffusion model upon review the authors do not find the arguments against ion filtration to be as damaging as hendry and schwartz indicate nor do they find the evidence for aquitard diffusion to be as persuasive in this study they will first evaluate hendry andmore schwartz s arguments against ion filtration then they will review the arguments in favor of aquitard diffusion and finally the authors will address the implications for the interpretation of the vertical cl sup minus profiles and the sup 36 cl data less

subcrustal earthquakes in the northern apennines italy evidence for a still active subduction previously unreported subcrustal earthquakes have been located up to 90 km depth beneath the northern apennines italy these earthquakes occur beneath a zone of abundant upper crustal seismicity mostly confined to the upper 20 km of the crust although there are relatively few well located subcrustal earthquakes there appears to be a general southwestward deepening of the hypocenters from the adriatic to the tyrrhenian sea consistent with other geophysical data which suggest that the adriatic lithosphere is presently subducting beneath the northern apennines

initiation and propagation of shear zones in a heterogeneous continental lithosphere continental plates represent rheologically heterogeneous media in which complex finite strain fields may develop due to interaction of plate tectonic processes with intraplate heterogeneities such a deformation pattern is displayed by the borborema shear zone system in northeastern brazil it involves continental scale curvilinear e w trending right lateral transcurrent shear zones that branch off from a major ne trending right lateral strike slip deformation zone formed at the northern termination of the sao francisco craton and that finally terminate in transpressive metasedimentary belts we suggest that this strain field results from the compressional deformation of a highly heterogeneous continental lithosphere composed of a stiff domain craton and rheologically weaker domains basins the effect of a low viscosity domain on the deformation of a continental plate and in particular the perturbation induced by this domain on the development of a shear zone formed at the termination of a stiff block were investigated using numerical modeling the low strength domain induces an enhanced strain localization and the geometry of the shear zone is significantly modified it is either split forming a branched shear zone system in which one branch maintains its original orientation while the other rotates toward the low viscosity domain or completely rotated toward the weak block the perturbation of the finite strain field depends on the ability of the weak domain to accommodate deformation which is controlled by its initial viscosity contrast relative to the surrounding lithosphere its orientation relative to the convergence direction and its distance from the shear zone initiated at the termination of the stiff block the interaction between imposed boundary conditions tectonic forces and plate geometry and the internal structure of the plate may give rise to highly heterogeneous strain fields as exhibited by the borborema shear zone system in which intraplate rheological heterogeneities induce the development of branched or sinuous shear zones a heterogeneous continental plate subjected to a normal convergence may therefore display significant lateral variations in strain intensity with shear zones bordering nearly undeformed blocks and in deformation regimes and vertical strains that would result in contrasting metamorphic and uplift histories

cutting of the european continental lithosphere plasticity theory applied to the present alpine collision presently active european alpine collision has a history of more than 100 myr convergence we investigate the collisional contact problem of an apparently rigid african promontory currently the italy adria block iab steadily penetrating at 1 cm yr over at least the past 45 myr into the deformable european plate we assume that neither continental subduction nor delamination occurs presently in the 300 km wide contact zone enabling use of the indenter indentee approach a key parameter is the aspect ratio h a defined by the width of the deformable foreland over the width of the indenter itself this parameter controls the activation of two fundamentally different modes of deformation 1 classical indentation mode for h a 4 4 described by previous authors and having effect only in a portion of the deformable plate in the vicinity of the indenter and 2 cutting mode for h a 4 4 giving plane strain longitudinal splitting of the entire deformable plate and plastic separation of the two halves we use a matrix operator method to solve for slip lines in the mixed boundary value problem obliquity velocity friction stress of the european alpine case implications are as follows 1 plane stress vertical lithospheric thickening is the first indentation mode of continental collision and 2 for the present ratio of h a 3 deformation is in the cutting mode and slow plane strain intraplate extension rifting is predicted this mode explains the intraplate stress field obtained from borehole and earthquake data considering that the paleoindenter probably has been larger than the iab it is inferred that h a has been below 4 4 since at least the end of the eocene and that consequently the intraplate graben system lower rhine rhine bresse limagne is due to the cutting of the european plate by alpine collision

deep structure of the alps what do we really know abstract in the last five decades the deep structure of the alps has been probed by every geophysical method applicable and the resulting amount of data is unmatched for any other orogen in this study an attempt is made to review the data and the proposed structural models with the aim of separating the certain from the probable and from the speculative information this can be achieved by first reviewing the theoretical resolving power and ambiguity of the applied interpretation methods and then analysing the proposed models the methods reviewed are inversion of surface wave data teleseismic and local earthquake seismic tomography near vertical reflection seismology wide angle reflection and refraction seismology and gravity modelling all information about the moho rated as certain is combined to give a moho map of the alpine area the information rated as certain and probable and additional qualitative arguments are used to discuss a crustal model of the western and central alps represented by two cross sections major structural elements in this crustal model are a thick overthrust penninic nappe system wedging at mid to lower crustal levels a discontinuous moho and strong variations along the strike of the orogen whereas the structures of the european upper crust and of the penninic nappe system are well constrained only few and isolated lower crustal structural elements are rated as certain finally the shape of the lower lithosphere in the alps is discussed by review and comparison of the results from surface wave teleseismic travel time residual and tomographic studies qualitative arguments suggest the existence of a lithospheric root or slab beneath the alps probable tomographic information suggests a south vergent european lithospheric slab beneath the southern alps and the po plain despite the considerable number of studies aimed at resolving the deepest part of alpine orogeny the available quantitative information on the sub moho structure cannot be rated as certain

in situ production of 36cl in uranium ore a hydrogeological assessment tool in situ neutron activation of 35cl within the rock and groundwater of geologic deposits that have elevated concentrations of uranium provides a hydrogeological tracer we determine the production rate and mobility of 36cl in the 1 3 billion year old cigar lake uranium ore deposit accelerator mass spectrometry was used to map the concentrations of 36cl in the ore and in the groundwater that were up to 100 times greater than those encountered in unmineralized portions of the host sandstone aquifer the residence time of this mobile anion in groundwater within the mineralized zone ranged from 14 to 280 kyr these residence times are consistent with the hydraulic and geochemical data suggesting significant control of cl and groundwater movement by the clay rich matrix of the mineralized zone

strain localisation and weakening of the lithosphere during extension we explore the sensitivity of extensional systems to the thermal structure of the lithosphere using numerical simulations that fully couple the energy momentum and continuity equations the rheology of the lithosphere is controlled by weakening processes such as shear heating that localises strain into shear zones and faults numerical models show that during extension of an initially unpatterned lithosphere structures develop spontaneously out of basic thermodynamic energy fluxes and without the imposition of ad hoc rules on strain localisation this contrasts with the classical mohr coulomb theory for brittle localisation which prescribes the angles of faults by a mathematical rule our results show that the mode of extension is sensitive to subtle changes in rheology heat flux and geometry of the system this sensitivity lies at the core of the variety and complexity observed in extensional systems localisation processes make the lithosphere weaker than previously estimated from the brace goetze quasi static approach consequently typical estimates for plate tectonic forces are capable of splitting the lithosphere under extension even without the role of active magmatism

hydrogeology and hydrochemistry of the milk river aquifer system alberta canada a review abstract the milk river aquifer system consists of 30 60 m of cretaceous sandstone located within the milk river formation southern alberta canada the milk river formation is confined below by 500m of shale of the colorado group and above by up to 120 m of shale the pakowki formation the dominant recharge area for the aquifer is the sweetgrass hills montana where the aquifer crops out from the recharge area the groundwater flows to the north east and west calculated groundwater residence times at the north end of the aquifer about 100 km north of the recharge area range from 250 to 510 ka limited hydrological data from the confining shales suggest that cross formational flow does not occur systematic patterns are observed in major ions na cl hco 3 co 3 and so 4 stable isotopes 18 o and deuterium and field ph on a regional scale several mechanisms have been proposed to explain the geochemical evolution of the groundwaters

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

neogene patterns of relative plate motion for africa europe some implications for recent central mediterranean tectonics a detailed relative motion picture for the neogene africa europe plate kinematics is presented the kinematic reconstruction was carried out using the finite difference solution between the rotation parameters determined for anomalies 7 to 2 in the africa north america europe plate motion circuit the analysis shows a motion of africa with respect to europe which is nne directed during late oligocene to burdigalian times becoming nnw trending from the langhian to the early tortonian from upper tortonian times onward the motion changes to a clear north west directed convergence major late neogene tectonic features of the central mediterranean region can to a large extent be explained within the context of the reconstructed major plate motions late tortonian to recent africa europe slip vectors are compatible with a variety of geological phenomenoa such as north west directed subduction beneath calabria south east translation of calabria and extension in the tyrrhenian sea north west trending slip vectors from thrust earthquakes between gibraltar and sicily and dextral strike slip across the north african margin

reply to comment on an alternative view on the origin of chemical and isotopic patterns in groundwater from the milk river aquifer canada by m j hendry and f w schwartz

the displacement of connate water from aquifers a mathematical model is developed for the mixing of meteoric and original formation waters in homogeneous aquifers the theoretical analysis indicates that geologic formations that have had a few to a few tens of pore volumes of meteoric water pass through them may be at steady state with respect to further displacement of their contained fluids depending on constraints in the recharge area the steady state may vary from near meteoric water throughout the whole formation to a spatial variation in concentration ranging from meteoric water in the recharge areas to highly concentrated water at the discharge ends of the system the former condition is attained when the recharge area incorporates the total depth and breadth of the formation where this condition is not satisfied the concentrations that evolve are controlled by the original concentration of the formation water the composition of recharging meteoric water the dispersion parameters and the size of the recharge area in comparison to the total breadth of the formation as measured along its strike for heterogeneous formations the concentration patterns that evolve seem to depend further on contrasts in hydraulic conductivity this is demonstrated in the milk river sandstone which is characterized by several extensive zones of dilute water within narrow high conductivity pathways and marked increases in concentration in adjacent lower permeability rock in parts of the aquifer where higher permeability pathways appear to be absent the isochlores form a broad linear band with a marked increase in concentration in the flow direction

a dynamical model for generating eurasian lithospheric stress and strain rate fields effect of rheology and cratons for most continents stress models driven by plate boundary forces have successfully reproduced the main characteristics of the stress field however eurasia has remained a challenge due to its large areas of intraplate deformation we present a set of three dimensional models of the upper mantle lithosphere system for a simplified geometry of the eurasian plate where we try to match the first order characteristics of the stress and strain rate fields simultaneously for typical elastic viscous or plastic rheologies high stress levels are required in order to produce realistic convergence rates between india and asia our models show robustly that such stresses are transmitted throughout most of the plate dominating locally generated stresses even in distal regions such as europe in a manner that is not compatible with observations cratons with roots that extend deep into the mantle are unable to provide a significant stress shielding effect unless the viscosity contrast between the asthenosphere and the underlying mantle is around 100 or greater a damage rheology for the lithosphere with history dependent behavior and material softening by a viscosity reduction of several orders of magnitude is shown to eliminate this conundrum continental convergence at high velocity but low stress is facilitated by the formation of long lived shear zones similar to those observed north of the himalayas the low stress associated with the collision together with the decoupling effect of the shear zones causes the distal stress field in europe to be controlled by the effects of the neighboring boundaries in agreement with observations

on elevated fluoride and boron concentrations in groundwaters associated with the lake saint martin impact structure manitoba abstract hydrogeological investigations conducted by the geological survey of canada in the lake saint martin region of manitoba have confirmed earlier reports of naturally elevated f and b concentrations in local groundwaters fluoride and b concentrations are highly correlated r 2 0 905 and reach 15 1 mg l and 8 5 mg l respectively virtually all groundwaters with f concentrations greater than the drinking water limit of 1 5 mg l are from wells within the lake saint martin impact structure a 208 ma complex crater 23 km in diameter underlying a large part of the study area the high f groundwaters can be classified into two groups according to their anionic and isotopic compositions group i samples consist of na mixed anion groundwaters with cl greater than 100 mg l and highly depleted 18 o compositions indicative of recharge under much cooler climatic conditions than at present samples belonging to this group exhibit a striking relationship to crater morphology and are found in an arcuate belt within the southern rim of the impact structure group ii high f samples consist of na hco 3 so 4 groundwaters with little cl and less depleted 18 o compositions samples belonging to this group are associated with groundwaters recharged locally on a low ridge within the impact structure this paper traces the probable source of high f groundwaters to phosphatic pellets in shales of the winnipeg formation a regional basal clastic unit which sub crops at shallow depth beneath the crater rim as a result of more than 200 m of structural uplift associated with the impact event this extensive aquifer is known elsewhere in southern manitoba for its naturally softened groundwaters and locally elevated f concentrations group i groundwaters are interpreted as discharge from the winnipeg formation where it abuts against crater fill deposits group ii high f groundwaters are interpreted as modern recharge from within the impact structure displacing group i groundwaters thus elevated f and b concentrations observed in groundwaters of the lake saint martin area represent the geochemical signature of upwelling from a deep regional aquifer the previously unsuspected discharge zone occurs within an isolated sub crop of the aquifer formed as a result of structural uplift caused by the impact event

halogen geochemistry of the mcmurdo dry valleys lakes antarctica clues to the origin of solutes and lake evolution abstract we have determined the halogen and boron concentrations in the ice covered lakes of taylor valley antarctica to better establish the sources of salts and evolutionary histories of these unusual water bodies in addition we report on a series of 129 i measurements that were compared with previous 36 cl data that also help constrain the source of solutes and histories of the lakes the new data when put into context of previous work on these systems over the past forty years allow us to make the following conclusions the primary source of solutes to lake hoare the youngest of the lakes is the dissolution of marine aerosols and aeolian salts and the chemical weathering of dust on the glaciers the geochemistry of lake fryxell the brackish water lake is primarily dominated by the diffusion from a halite saturated brine at the sediment water interface and the recent infilling of the lake by glacier meltwater these waters have chemical weathering and marine aerosols components lake bonney has two distinct lobes whose hypersaline hypolimnia have different chemistries both of the lobes are remnants of ancient marine waters that have been modified by the input of weathering products this lake has also been modified by periods of cryogenic concentration when solutes have been lost via mineral precipitation thus the geochemistry of lake bonney owes its unusual geochemistry in part to variations in the climate in the taylor valley over at least the past 300kyr the 129 i data from the taylor valley are similar to those from fracture fluids in crystalline rocks from the northern hemisphere

lithospheric scale structures from the perspective of analogue continental collision abstract analogue models were employed to investigate continental collision addressing the roles of 1 a suture zone separating different crustal blocks 2 mid crustal weak layers and 3 mantle strengths these models confirmed that low amplitude lithospheric and crustal buckling is the primary response to shortening with a wavelength mainly controlled by the strong upper crust and or lithospheric mantle with increasing shortening bivergent thrusts formed across the brittle layers equivalent to upper crust at inflection points of the buckles while ductile layers lower crust and mantle continued being folded the resulting geometries displayed pop ups and pop downs above the boundaries sutures between blocks further shortening led to wider thrust bounded deformation zones belts in front of the stronger blocks identified as effective indenters during shortening upward extrusion into belts allowed exhumation of deep material weak layers enhanced strain localisation these modelling results have similarity in large scale structures of modern orogens and are relevant to the understanding of natural collisional processes

decoupling of solutes and water in regional groundwater systems the murray basin australia documenting the origins residence times and movement of groundwater and the solutes that it contains is critical to understanding hydrogeological systems this study uses cl mass balance to determine the cl accession time i e the time required for cl to accumulate and cl to estimate the residence times of cl in the victorian portion of the murray basin southeast australia much of the murray basin contains saline groundwater with total dissolved solids tds concentrations commonly 14 000 mg l and locally up to 300 000 mg l the total mass of cl stored in the victorian portion of the basin is estimated as between 12 400 and 47 100 mt using present day rainfall totals and cl concentrations in rainfall the cl accession time is 170 to 650 ka aquifer thicknesses and groundwater salinity both increase westwards in this part of the murray basin consequently the cl accession times increase westward from 0 1 0 6 ka to 286 1080 ka by contrast c activities of the majority of the groundwater are 2 pmc and commonly much higher notwithstanding the difficulty in correcting c residence times the widespread occurrence of groundwater with above background c activities implies that groundwater residence times are generally 30 ka which is substantially shorter than the cl accession times rcl the ratio of cl to total cl 10 values of the groundwater are between 20 and 230 and are uncorrelated with cl concentrations while it is difficult to determine precise cl residence times the observation that the rcl values are significantly higher than those that represent secular equilibrium with the aquifer matrix rcl of 5 to 10 indicates that they are up to a few hundred thousand years and similar to the cl accession times the rcl values together with the geology of the aquifers stable isotope ratios and major ion geochemistry precludes halite dissolution incorporation of connate water or the long term diffusion of cl from clays as mechanisms of producing the elevated cl concentrations rather it is most likely that the high cl concentrations result from recycling of solutes in saline lakes and playas or repeated cycles of evapotranspiration in the unsaturated zone

chlorine 36 in groundwater as a palaeoclimatic indicator the east midlands triassic sandstone aquifer uk the36cl contents of groundwaters from the east midlands triassic sandstone have been used to deduce rainfall its chloride content and evapotranspiration during the late pleistocene at this time the regional precipitation and evapotranspiration would have been reduced relative to the modern and holocene climate it is estimated that the infiltration was reduced by about 40 mm a 1 the method for evaluation of these palaeoclimatic parameters is dependent upon the major cl source being a marine aerosol fall out this is the general case but groundwater east of the exploited zone of the aquifer contains chloride which is derived from saline formation water with a marinecl br ratio and in equilibrium with the in situ neutron flux the fall out of cosmogenic36cl at the geomagnetic latitude 56 2 n is evaluated as 30 6 atoms m 2s 1 and is significantly greater than that estimated from the theoretical fall out curve of bentley et al 1 the bomb peak of36cl remains entirely within the unconfined zone of the aquifer the assessment of groundwater residence time from the36cl chronometer is shown to be impossible for this aquifer

the relationship between he and cl as a criterion for the formation of groundwater composition abstract the analysis of the relationship between 1611 parallel determinations of helium and chloride concentrations in the groundwater of crystalline shields and sedimentary basins was performed the comparison showed that groundwaters have helium and chlorides concentrations in the range of 1 8 10 8 to 6 8 mol m3 and of 5 6 10 3 to 6488 mol m3 respectively and relatively stable he rcl ratios equal to 5 5 10 5 in sedimentary basins and 7 5 10 4 in crystalline shields such behavior of helium and chlorides shows that the formation of the groundwater composition is determined primarily by the processes of mixing fresh meteoric and saline sea waters with ancient brines from great depths during sedimentation sea water penetrates the subsurface and mixes with ancient brines on land fresh meteoric waters dilute the mixtures of seawater and ancient brines most of the radiogenic 4he and chlorides comes from the subsurface ancient brine the radiogenic 4he in the host rocks plays a secondary role therefore the concentration of 4he in saline groundwater reflects the size of the impurities of the ancient brine with a very high content of 4he rather than the residence time within the subsurface

using iodine isotopes to constrain supergene fluid sources in arid regions insights from the chuquicamata oxide blanket although iodine is rare in crustal settings previous studies have documented its occurrence in the supergene zones of base and precious metal ore deposits in arid environments in this report we present a novel application of the iodine 129 129i isotope tracer to iodine rich samples from the world s largest supergene cu profile at the chuquicamata deposit in northern chile where anomalous concentrations of this element have been reported all supergene marshite cui samples from chuquicamata and iodine rich soil above the mansa mina deposit have 129i i isotope ratios 190 560 10 15 that are significantly lower than those of surface waters i e 1 500 10 15 indicating that iodine was most likely derived from a reservoir of marine origin rather than a meteoric and or atmospheric source geochemical modeling shows that the long term dilution of iodinerich deep formation waters by meteoric water during the main stage of supergene alteration 40 10 ma resulted in fluid 129i i ratios that are within the range of mineral soil 129i i ratios observed at chuquicamata strongly suggesting that iodine was remobilized from the lower jurassic to mid cretaceous marine basement results from this study show that iodine isotopes can be successfully applied to trace the origin and nature of supergene fluids in iodine rich oxide blankets leach caps and soils above buried cu deposits and also to constrain the timescales of fluid circulation during supergene enrichment

stress field variations in the swiss alps and the northern alpine foreland derived from inversion of fault plane solutions 1 this study is devoted to a systematic analysis of the state of stress of the central european alps and northern alpine foreland in switzerland based on focal mechanisms of 138 earthquakes with magnitudes between 1 and 5 the most robust feature of the results is that the azimuth of the minimum compressive stress s3 is generally well constrained for all data subsets and always lies in the ne quadrant however within this quadrant the orientation of s3 changes systematically both along the structural strike of the alpine chain and across it the variation in stress along the mountain belt from ne to sw involves a progressive counterclockwise rotation of s3 and is most clear in the foreland where it amounts to 45 50 this pattern of rotation is compatible with the disturbance to the stress field expected from the indentation of the adriatic block into the central european plate possibly together with buoyancy forces arising from the strongly arcuate structure of the moho to the immediate west of our study area across the alps the variation in azimuth of s3 is defined by a progressive counterclockwise rotation of about 45 from the foreland in the north across the helvetic domain to the penninic nappes in the south and is accompanied by a change from a slight predominance of strike slip mechanisms in the foreland to a strong predominance of normal faulting in the high parts of the alps the observed rotation can be explained by the perturbation of the large scale regional stress by a local uniaxial deviatoric tension with a magnitude similar to that of the regional differential stress and with an orientation perpendicular to the strike of the alpine belt the tensile nature and orientation of this stress is consistent with the spreading stress expected from lateral density changes due to a crustal root beneath the alps

constraints on extension of continental lithosphere the extension of the continental lithosphere is considered in terms of the deformation of a thin viscous sheet with a temperature dependent rheology which is governed primarily by the strength of the upper mantle the lithosphere is subjected either to a constant strain rate or to a strain rate decreasing with time corresponding to the stretching of a region of fixed volume with a constant velocity boundary condition the progress of the extension is influenced by the decrease in strength of the lithosphere owing to its attenuation and by an increase in strength resulting from cooling the relative importance of these two effects depends on two parameters a dimensionless strain rate and the total strain for a given strain rate the extending lithosphere goes through two phases as the strain increases in the first the effect of thinning the lithosphere is predominant and the average strength of the lithosphere remains close to and perhaps slightly below its original strength in the second the effect of cooling of the lithosphere leads to very rapid increase in strength as a function of strain resulting presumably in an effective limit on the degree of stretching that the lithosphere experiences for the case of strain rate decreasing with time when the initial strain rates are of order 10 15s 1 this maximum extension is between 100 and 150 for a strain rate of 10 l4 s 1 the maximum lies around 400 to 500 at higher strain rates than this very large extension may occur before cooling significantly affects the strength of the lithosphere this model accords well with the constraints available from the continental margins of the north atlantic

a hydrogeochemical approach to evaluate the occurrence and source of salinization in the shallow aquifers of the southeastern imphal valley in the indo myanmar range of northeast india the imphal valley is an intramontane basin confined within an anticlinorium of several anticlines and synclines in the disang group of rocks of tertiary age this valley of more than 2 million people is occupied by fluvio lacustrine deposits of quaternary age and is located in the central part of the indo myanmar range of northeast india the hydrogeochemical parameters of temperature ph orp tds na cl br ba b sr li 18o hco3 k mg ca no3 po4 so4 in 173 samples using ion chromatograph icp aes icp oes icp ms and 37 dugwells were studied to understand the occurrence and origin of salinization process for the first time the order of abundance of ions is identified as hco3 na cl ca mg k no3 po4 sr br b ba li so4 five hydrochemical facies na cl ca mg hco3 na hco3 ca mg hco3 cl and ca mg cl represent the types of waters the saline dominated water types na cl and na hco3 represent piedmont and the rest of the facies represent alluvial plain and flood plain groundwaters durov s diagram reveales initial and intermediate stages of groundwater evolution isotope 18o gibbs diagram and ions scatter plots suggest evaporation and crystallization processes leading to halite encrustation in the disang shales negative eh low no3 and the absence of so4 indicates reduced condition coupled with rich dissolve organic matters leading to elevation of salts in soils around piedmont where the rock type is exclusively of the disang shales trilinear plot correlation matrix and water table flow analysis suggest salinization of groundwater originates in piedmont groundwater and disseminates towards alluvial plain and flood plain along the flow path

is the adriatic an african promontory seismicity patterns and fault plane solutions for the largest recent earthquakes in the adriatic region are used to test the hypothesis that the adriatic is a promontory of the african continental mass the horizontal projections of the slip vectors for the 24 best constrained focal mechanisms trend at a high angle to those predicted for the africa eurasia collision and so the adriatic cannot be thought of as a promontory of africa the slip vectors define an instantaneous pole of rotation that describes anticlockwise rotation of the adriatic relative to eurasia the adriatic is a stable continental block moving within the broad zone of deformation between africa and eurasia

extension during continental convergence with application to the tibetan plateau the tibetan plateau is the product of crustal thickening caused by the collision between india and asia and is the largest active example of extensional tectonics in a zone of continental collision throughout most of the tertiary the tectonics of the plateau were dominated by north south shortening a significant proportion of which took place on east west striking thrust faults for the last 5 m y or so the plateau has been thinning by the mechanism of extension on north south trending normal faults previous investigations of the collision have been able to account for the large scale features of the tertiary deformation but have failed to explain the transition in the late tertiary to quaternary strain rate field of the plateau from north south compression to east west extension the transition could in principle be effected by a reduction in the rate of convergence between india and asia or by a uniform reduction in strength of the whole continental lithosphere of asia it could not however be effected by a reduction in strength of the elevated region alone this produces increased compressional strain rates in the weakened zone an alternative explanation for the transition to extension comes from considering the thermal evolution of thickened continental lithosphere the lower part of the lithosphere consists of a thermal boundary layer which when thickened by horizontal shortening is colder and denser than its surroundings convective instability of the thickened thermal boundary layer and its replacement by hot asthenosphere would rapidly raise the surface elevation and gravitational potential energy of the overlying part of the lithosphere the convective instability would happen in a time brief compared with the collision time scale 50 m y in the case of india and asia but would only occur after there had already been substantial thickening of the lithosphere numerical experiments show that for a range of lithospheric parameters the increase in surface height as much as 2 km and of potential energy 5 to 10 1012 n m 1 resulting from convective instability of the lower lithosphere are sufficient for east west extension to replace north south compression as the dominant feature of the stress field of the tibetan plateau

the recent crustal stress field in central europe trajectories and finite element modeling the recent crustal stress field of central europe and especially of the adjoining areas to the east is presented in terms of the directions of maximum horizontal stress shmax the analysis is based on fault plane solutions in situ stress measurements geologic fault slip determinations and repeated precise geodetic triangulations a bending of the direction of shmax from the well known nw se direction in the western part of the study area to directions of ne sw to e w in the eastern part is shown first results on the recent crustal stress field of the study area were presented by grunthal and stromeyer 1986 who substantiated this tendency of bending in the central and eastern parts of the study area by few observations only therefore one aim of this paper was to compile observations on the areas with few data points generally these additional data confirm the previously established pattern in some areas especially in the pannonian basin the stress features became more complicated compared with those solely based on a few data points the second part of the paper presents steady state elastic finite element model calculations to provide some possible explanations of the observed stress orientations as a result of plate driving forces simulation of the north atlantic seafloor spreading and the northward directed motion of the african plate by appropriate boundary loads produces a pattern of shmax directions for the western part of the eurasian plate which is compatible with the broad scale observed stress directions subregional anomalies such as the fanlike stress pattern perpendicular to the arc of the western alps or the radial directions around the pannonian basin can be explained only when additional stress producing features are introduced overmodulating the regional field rigorous introduction of physically constrained model parameters for all these features was not feasible to date therefore the preliminary empirical model calculations presented in this paper are attempts to discuss which features have the most influence on the stress field they are in a regional scale the north atlantic seafloor spreading the northward motion of the african and the arabian plate and obviously subregionally increased stiffness of the apulian promontary as well as of the bohemian massif

slab breakoff a model for syncollisional magmatism and tectonics in the alps slab breakoff is the buoyancy driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision in a recent paper davies and von blanckenburg 1994 have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts breakoff will lead to heating of the overriding lithospheric mantle by upwelling asthenosphere melting of its enriched layers and thus to bimodal magmatism breakoff will also lead to thermal weakening of the subducted crustal lithosphere thereby allowing buoyant rise of released crustal slices from mantle depths in this paper we present a test of this model in the tertiary evolution of the european alps in the alps both basaltic and granitoid magmatism occur between 42 and 25 ma following the closure of oceanic basins by subduction and continental collision the granitoids are now well established to result from mixing of basalt with assimilated continental crust to identify the tectonically crucial origin of the partial mantle melts we have compiled all published geochemical and isotopic data of numerous mafic dykes occurring throughout the whole alpine arc their trace element and isotopic composition suggests that they have been formed by low degree melting of the mechanically stable lithospheric mantle we see no evidence for melting of asthenospheric mantle it was thus not decompressed to depths shallower than 50 km once initiated rapid lateral migration of slab breakoff will result in a linear trace of magmatism in locally thermal weakened crust this explains why all alpine magmatic rocks intruded almost synchronously along a strike slip fault the periadriatic lineament a compilation of ages from penninic high pressure rocks subducted to depths of up to 100 km shows that subduction took place at circa 55 40 ma followed by uplift at 40 35 ma from the short time interval between their uplift and the onset of magmatism we infer that both processes have been induced by the breakoff the slab breakoff model fulfills its predictions in the case of the alps and therefore supports the assumptions made in the theoretical model on a geological basis we believe that the characteristic association of magmatic activity with the return of high pressure rocks to the surface allows the identification of this process in the earth s mountain belts

physical modeling of slow seafloor spreading a properly scaled thermo mechanical experimental model of slow seafloor spreading is developed to investigate the mechanism of lithosphere accretion the melt of a specially fabricated hydrocarbon compositional system is cooled from above in a tank the crystallizing upper layer the lithosphere possesses semiplastic semibrittle properties horizontal tension of the layer is produced by a paddle drawn at a constant rate spreading in the model is very unstable asymmetric and involves regular jumps of the spreading center scaling up the experimental results to match seafloor spreading gives the length of the jumps of the order of 10 km and the period of the order of 105 106 years the jumps normally occur in the wall of a rift valley resulting in quasiplastic stretching of the lithosphere at this place and then in the formation of two intersecting major normal fault zones crossing the plate from some shallow depth to the base the wedge separated by these zones rises up symmetrically prior to the cessation of movement along one zone with motion only continuing along the other from this moment the deformation becomes asymmetrical the material crystallized at the base of the lithosphere is dragged along the active zone to the upper horizons of the plate and to the surface this process leads to both the nonisostatic uplifting of the central part of the pulled block and subsidence near the inlet on the surface of the fault detachment zone which forms the center of this asymmetric lithospheric accretion at a specific stage under the action of both horizontal tension and vertical nonisostatic forces the strength of the pulling block is exceeded within the rift valley the result is the next jump of the spreading center to the point of breakage and a repetition of the whole cycle the jump can also occur at other places weakened during previous cycles normally the asymmetry of the spreading alternates at a new center the dimensions of the valley as well as the overall seafloor relief are strongly dependent on the spreading rate v the lower the v value the rougher the relief the jumps of the spreading centers are not synchronous along the plate boundary moreover they can be of different types with varying distances and in opposite directions on adjacent segments of the spreading axis leading to the occurrence of transfer or accommodation zones

shear wave velocity variations in the upper mantle beneath central europe summary a new model eur s91 of shear wave velocity variations in the upper mantle beneath central europe and surrounding regions down to a depth of 670km is presented the model is derived from the inversion of the waveforms of 217 seismograms using the partitioned waveform inversion method for the seismogram in the time window from the s wave arrival to the fundamental mode of the rayleigh wave the seismograms were mostly assembled from digitally recording long period and broad band stations in europe the resulting 3 d model accurately predicts most of the observed waveforms in a wide band of frequencies body waves were fit for frequencies up to 60mhz the fundamental rayleigh mode which at high frequencies is more prone to scattering and multipathing was generally low passed at 25 mhz the resolving power of the data set depends strongly on the density of available wave paths and varies as a function of geographical position small scale heterogeneities like the subducted lithosphere in the hellenic collision zone were imaged in the region with the highest density of wave paths which indicates an optimum resolution of better than 200 km the main new results of this study pertain to the transition between east and central europe we present new information about the structure below the tornquist teisseyre zone ttz the ttz is generally regarded as the boundary between the precambrian crust of the baltic shield russian platform and the younger crust of central europe our 3 d s velocity model reveals that below this line a sharp lateral boundary extends down to at least 140 km depth with high velocities beneath the baltic shield and russian platform contrasting to the low velocities beneath the younger regions of europe the observed velocity contrast across the ttz is largest between the pannonian basin and the russian platform where it is equal to 12 per cent at 80 km depth at depths of 300 400 km the ttz is underlain by a zone of low s velocity which indicates a local thinning of the deeply rooted high velocity structure or tectosphere that underlies most of eastern europe in addition to these new results on the transition region between east and central europe a number of features that are present in other tomographic results have been confirmed the precambrian provinces of europe are characterized by high s velocities low velocities are found beneath the pannonian basin the western mediterranean northern aegean sea turkey and a small region south west of the massif central the lithosphere beneath the paris basin has a positive s velocity anomaly the resolution of all these anomalies has been established with sensitivity tests

origin of halogens and their use as environmental tracers in aquifers of thriassion plain attica greece the processes that control halide concentrations in coastal aquifers of the thriassion plain in greece include both natural and anthropogenic factors as follows evapotranspiration dissolution of evaporites domestic sewage as well as dissolution of minerals containing fluoride groundwater monitoring data indicate that the cl br mass ratio ranges between 43 and 1510 ratios ranging round the value 292 are attributed to sea intrusion 300 600 to domestic sewage and 900 1510 to dissolution of evaporites the evaporation of irrigated water plays an important role as well fluoride concentrations ranging from 0 1 up to 9 94 mg l possibly originate from holocene as well as plio pleistocene sediments which contain organic material it is also likely that fluoride originates from fluorite dissolution or comes from palaeozoic middle triassic volcano sedimentary rocks which occur around the wider area and constitute the basement of the study area in those rocks the alteration of biotite to chlorite takes place under the influence of hydrothermal fluids as the thriassion plain is close to south aegean volcanic arc where volcanic activity exists

129i and 36cl in dilute hydrocarbon waters marine cosmogenic in situ and anthropogenic sources abstract the long lived halogen radioisotopes 129 i and 36 cl provide valuable information regarding the source of fluids in hydrocarbon systems and in localized areas where infiltration of younger meteoric water has occurred despite the utility of these two isotopes in providing time signatures for fluid end members considerable uncertainty remains regarding the interpretation of intermediate age waters in hydrologic systems these waters are likely the result of the combination of two or more halogen sources at some time in the past each with its own characteristic concentration and isotopic composition in order to unravel the evolution of these intermediate age waters the effect that infiltration of meteoric water has on the isotopic composition of older formation waters is modeled also evaluated is the effect that the timing of dilution has on 129 i and 36 cl signatures observed in the present specifically the hypothesis that halogen isotopic signatures imparted by the mixing of brine and meteoric waters early in the development of a sedimentary basin are quantitatively different from those imparted by the mixing of old brines with recent meteoric waters the modeled results are compared to previously published isotopic data from production wells in the fruitland formation coalbed methane system portions of the basin preserve enough of the original brine source to retain 129 i i ratios roughly recording the age of deposition of organic matter 73 76 ma even where some degree of dilution by meteoric water has occurred however the 129 i signatures of waters that presently contain less than 10 of the original formation water component indicate that mixing has occurred within the past 10 ma consistent with recently published 4 he data both 36 cl concentrations and 36 cl cl ratios show that waters containing more than 10 formation water are all in secular equilibrium with the host formation coals in contrast waters with less than 1 of the original formation water s cl content all have 36 cl cl ratios which are greater than secular equilibrium values indicating the migration of meteoric water into the coal formation more recently than 2 ma although 36 cl signatures in the fruitland formation are not significantly affected by anthropogenic input 129 i i ratios in a subset of samples that retain less than 1 of the initial formation water component suggest input of anthropogenic 129 i during the past 50 a

stable isotope geochemistry of dissolved chloride in relation to hydrogeology of the strongly exploited quaternary aquifers north china plain deep quaternary groundwater is the main source for industrial domestic and agricultural water supply in the north china plain ncp there is currently a regional decline of groundwater levels deterioration of water quality and environmental geological problems induced by increasing exploitation of the ncp quaternary aquifer system to trace sources and transport processes of dissolved cl in a regional aquifer system and to reveal hydrogeological characteristics of quaternary complexes 37cl 18o and d and chemical compositions including f cl br of the deep groundwater sampled from the northern flow system of the ncp were measured along the west east groundwater flow paths the measured 37cl values decreased from 0 39 to 2 22 smoc along the groundwater flow direction with increasing cl concentrations marine aerosol input via rainfall is the main source of cl in the deep groundwater near the recharge areas and subsequent evaporation evapotranspiration appears to be responsible for cl accumulation mixing of recharge water with water of high cl and low 37cl accounts for the pattern of 37cl and cl concentration observed in aquifer 3 along the west east transect the water with high cl and low 37cl is likely from pore water released from compacted clays induced by over exploitation of deep groundwater suggesting that clay is a dominant subsurface source of cl for groundwater where a regional depression cone is present in the quaternary aquifers the groundwater of aquifer 4 in the huang hua depression is potentially mixed with an upward flux of cl from the neogene aquifer through subvertical faults diffusion and ion filtration are two mechanisms invoked to explain the highly negative 37cl data for groundwater of aquifer 4 in the yanshan haixing areas which provides new insight into solute migration and the hydraulic relationship in the strongly exploited groundwater system this study using the conservative solute cl provides additional important information for further investigations of the geochemistry of a wide range of reactive solutes in the quaternary aquifer system so guiding water resource management

heat generation associated with collision of two plates the himalayan geothermal belt abstract an analysis of heat discharged by thermal fluids along the c 3000 km long himalayan geothermal belt hgb shows that heat transfer is concentrated along 30 to 50 km wide heat bands which are associated with at least 600 geothermal systems the bands have been interpreted as segments of major concentric slip lines caused by plastic deformation of the ductile crust within the asian plate resulting from plate collision assuming that this crust behaves like an ideal plastic medium the heat transfer within and along a slip line can be estimated it amounts to c 55 mw m2 for a 40 km wide band estimates of present day heat discharges point to 20 35 mw m2 for convective and 10 30 mw m2 for anomalous conductive losses less well constrained for a heated crustal strip in the greater lhasa area computed geotherms indicate that partial melting can develop at c 30 to 50 km depth within heat bands the spatial asymmetry of heat discharged in the hgb heat bands in the eastern himalaya transfer about 2 3 times more heat than does the entire western himalaya can be explained by a counterclockwise rotational penetration of the indian into the asian plate

underground production of radionuclides in the milk river aquifer alberta canada abstract most cosmogenic radionuclides that may be used to estimate groundwater ages in excess of 100 ka are also produced underground by in situ nuclear reactions radioactive equilibrium between in situ production and decay would be approached within such long residence times radionuclide production by in situ nuclear reactions within the groundwater and within its host rock has been calculated theoretically and compared with some measured radionuclide contents of the groundwater the fractional transfer of in situ produced 37 ar 39 ar and 222 rn from rock to groundwater necessary to account for the total measured groundwater contents were found to be similar although site specific the implications for radionuclide release mechanisms and for groundwater dating by the use of cosmogenic radionuclides including those which are applicable for very old groundwaters 36 cl 81 kr 129 i are discussed

chlorine 36 dating of very old groundwater 2 milk river aquifer alberta canada the milk river aquifer in southern alberta canada consists of sandstone interbedded between thick shale units the groundwater is confined and discharges by both upward and downward leakage through the shales the concentration of cl increases by about 2 orders of magnitude downgradient through the aquifer this cl increase complicates 36cl dating of the system climatic changes flushing of connate water introduction of cl from older water below the aquifer and ion filtration have been proposed as possible explanations for the increase the 36cl data show a consistent decrease of the 36cl cl ratio downgradient but an increase in the 36cl concentration downgradient in certain parts of the aquifer dates calculated from the 36cl cl ratio show a reasonable distribution in light of the hydraulic controls on the system whereas dates calculated from the 36cl concentration give negative ages this suggests that ion filtration is responsible for the cl increase and that the 36cl cl dates are to be preferred we estimate water ages to be more than 2 m y near the distal end of the aquifer

average strain rate in the italian crust inferred from a permanent gps network ii strain rate versus seismicity and structural geology summary high quality weekly solutions for the coordinates of 45 permanent gps stations spanning 1 6 years and covering the alpine mediterranean area are used to estimate a horizontal velocity field aligned with the itrf2000 velocity datum after subtracting model velocities for the eurasian plate we show that the residual velocity field north of the apennines in the adriatic dinaric region describes a nne trending tectonic flow with a negative velocity gradient from 6 mm yr 1 ne of the apennines to virtually zero ne of the dinarids in the calabria region we observe a divergent pattern with nnw orientation which turns to west as one moves north towards tuscany very small residual velocities are observed for stations in the sardinia corsica block spain southern france and north of the alps this regional pattern of velocities defines areas of intraplate strain on the basis of good station coverage and of a strain rate value above a threshold we define five provinces calabria central apennines both in the extensional regime and north adriatic eastern alps and south adriatic under compression we show that the orientations of the principal strain rate axes agree with the stress pattern that is inferred from local seismicity a comparison of the geodetically determined strain rate with the strain rate associated with the seismic moment of earthquakes in the past 30 yr shows that each province may differ considerably from the others in the amount of seismic moment that is accommodated by surface strain for example the umbria seismic sequence of 1997 seems to have released a seismic moment that was not exceptionally large but concentrated over a short time interval so that the equivalent coseismic strain rate was larger than the value observed geodetically on average depending on the assumptions on the seismogenic volume and time span 70 100 per cent of the surface strain seems to be accommodated by the release of seismic moment in the upper italian crust

using halogens cl br i to understand the hydrogeochemical evolution of drought derived saline porewater beneath a prairie wetland abstract numerous closed basin prairie wetlands throughout the prairie pothole region ppr of north america maintain moderate surface pond salinities total dissolved solids tds from 1 to 10 g l 1 under semiarid climate by accumulation of gypsum and saline lenses of sulfate rich porewater tds 10 g l 1 in wetland sediments during droughts in order to understand the hydrogeochemical origin and composition of these saline porewaters we made a detailed geochemical survey of cl so42 br and i in the porewater pondwater and upland groundwater of a typical closed basin prairie wetland p1 in the cottonwood lake study area north dakota concentrations of cl ranged up to 5 9 mm in the saline porewaters and was strongly correlated with so42 and br pearson s r 0 7 p

modeling shear zones in geological and planetary sciences solid and fluid thermal mechanical approaches abstract shear zones are the most ubiquitous features observed in planetary surfaces they appear as a jagged network of faults at the observable brittle surface of planets and in geological exposures of deeper rocks they turn into smoothly braided networks of localized shear displacement leaving centimeter wide bands of mylonitized reduced grain sizes behind the overall size of the entire shear network rarely exceeds kilometer scale at depth although mylonitic shear zones are only visible to the observer when uplifted and exposed at the surface they govern the mechanical behavior of the strongest part of the lithosphere below 10 15 km depth mylonitic shear zones dissect plates thus allowing plate tectonics to develop on the earth we review the basic multiscale physics underlying mylonitic ductile shear zone nucleation growth and longevity and show that grain size reduction is a symptomatic cause but not necessarily the main reason for localization we also discuss a framework for analytic and numerical modeling including the effects of thermal mechanical couplings thermal elasticity the influence of water and void volatile feedback the physics of ductile shear zones relies on feedback processes that turn a macroscopically homogenously deforming body into a heterogeneously slipping solid medium positive feedback can amplify strength heterogeneities by cascading through different scales we define basic intrinsic length scales of strength heterogeneity such as those associated with plasticity grain size fluid inclusion and thermal diffusion length scale for an understanding ductile shear zones we need to consider the energetics of deformation shear heating introduces a jerky flow phenomenon potentially accompanied by ductile earthquakes additional focusing due to grain size reduction only operates for a narrow parameter range of cooling rates for the long time scale deformational energy stored inside the shear zone through plastic dilation or crystallographic and shape preferred orientation consumes only a maximum of 10 of energy dissipated in the shear zones but creates structural anisotropy shear zones become long living features with a long term memory a special role is attributed to the presence of water in nominally anhydrous minerals we show that water directly affects the mechanical equation of state and has the potential to synchronize viscous and plastic flow processes at geological time scale we have shown that fully coupled finite element calculations using mechanical data from the laboratory can reproduce the basic mode of deformation of an entire mylonitic shear zone the next step of modeling lies in benchmarking basic feedback mechanism in field studies and zooming into the braided network of shear zone structure without losing the large scale constraint numerical methods capable of fulfilling the goal are emerging these are adaptive wavelet techniques and hybrid particle finite element codes which can be run over a computational grid across the net

melt instabilities in an intraplate lithosphere and implications for volcanism in the harrat ash shaam volcanic field nw arabia we investigate melt generation in a slowly extending lithosphere with the aim of understanding the spatial and temporal relationships between magmatism and preexisting rift systems we present numerical models that consider feedback between melt generation and lithospheric deformation and we incorporate three different damage mechanisms brittle damage creep damage and melt damage melt conditions are calculated with a helmholtz free energy minimization method and the energy equation is solved self consistently for latent heat and shear heating effects using a case of a slowly extending 1 1 5mm yr continental lithosphere with a relatively low surface heat flow similar to 50mw m 2 we show that melt rich shear bands are nucleated at the bottom of the lithosphere as a result of shear heating and damage mechanisms upon further deformation melt zones intersect creep damage zones thus forming channels that may be used for the melt to migrate upward if a preexisting structure resides only in the brittle crust it does not control the path of melt migration to the surface and melt filled channels propagate from the bottom upwards independently of upper crustal structures in contrast a preexisting weak structure that reaches a critical depth of 20km allows fast similar to 2ma propagation of melt filled channels that link melt damage from the bottom of the lithosphere to near surface structures our model results may explain the short time scale volume and magma extraction from the asthenosphere through a low surface heat flow lithosphere such as observed for example in the harrat ash shaam volcanic field northwestern arabia which developed in the arabian plate and is spatially linked to the azraq sirhan graben

dissolved gases in the milk river aquifer alberta canada abstract geochemical relations between the noble gases 40 ar 36 ar ratio n 2 and ch 4 contents of groundwaters from the milk river aquifer albert canada have been investigated the ch 4 contents for many of the groundwaters are several times their n 2 contents and cause degassing to occur as the hydrostatic pressure decreases during their ascent in the wells recharge temperatures derived for those groundwaters that were not degassed indicate that the youngest groundwaters were recharged under cooler climatic conditions than prevailed during earlier recharge this conclusion is supported by the stable isotope compositions of the groundwater the 4 he concentration in the groundwater varies with depth according to the theoretical concentration depth profile for accumulated radiogenic 4 he in the aquifer and its adjacent shales the corresponding flux of 4 he to the atmosphere is 4 he production rate excess radiogenic 40 ar is associated with ch 4 and both gases originated within the adjacent shales the ch 4 is biogenic and was produced in an aqueous environment which ranged from marine to freshwater as the connate fluids in these marine shales were replaced the degassing process has been modelled to explain the residual dissolved gas contents of the groundwater and to show that the ch 4 n 2 ratio in situ was 12

an integrated approach for identification of potential aquifer zones in structurally controlled terrain wadi qena basin egypt abstract wadi qena basin represents one of the most promising regions for future development in egypt fresh water supplies are crucial for such plans we provide an integrated remote sensing landsat aster dem geoeye 1 geophysical aeromagnetic isotopic 18 o 2 h field stratigraphic and structural interpretation and geochemical major dissolved ions approach to delineate zones of potential groundwater resources in wadi qena basin four water bearing horizons were sampled fractured crystalline aquifer nubian aquifer system nas post nubian aquifer system pnas and the quaternary aquifer findings include 1 spatial analysis of remote sensing data in a gis environment indicates extensive structural deformation by dextral faults trending ne sw i e qena safaga shear zone qs and sinistral faults trending nw se i e najd shear zone and sufficient surface water supply from the east through wadi fattera sub basin 2 analysis of geophysical data indicates that these faults control the water bearing horizons in the subsurface 3 isotopic analysis reveals four isotopic groups including two end members one mixed group and one mixed and evaporated group group i highly depleted fossil nubian waters range 18 o from 6 39 to 6 74 and 2 h from 48 21 to 52 46 group ii modern waters in fractured basement range 18 o from 1 41 to 1 51 and 2 h from 5 46 to 6 04 group iii a mixed cluster between nas and modern waters range 18 o from 4 82 to 5 05 and 2 h from 33 28 to 38 54 and group iv samples which have both mixing between the nubian and meteoric waters and also have a considerable deviation from the global meteoric water line gmwl range 18 o from 0 58 to 4 69 and 2 h from 19 59 to 38 68 4 samples with a mixed isotopic signature in group iii which tap the nas and are located along the main channel of wadi fattera area 3600 km 2 provide evidence for modern recharge along surface exposures of the nas and enhanced infiltration along deep seated faults 5 samples with a mixed isotopic signature in group iv which tap the quaternary and pnas aquifers and are located along deep seated faults provide evidence of artesian upward leakage from the deep nas into the shallower quaternary and pnas aquifers the present study improves our understanding of the role of structural control and modern recharge in exploration for aquifer potential in arid environments

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

modeling surface gps velocities in the southern and eastern alps by finite dislocations at crustal depths abstract the indentation of the adria plate into the southern and eastern alps is an ongoing collisional process accompanied by seismicity surface and rock uplift and lateral escape we present a 3d quantitative description of the process by combining gps and structural data with an elastic dislocation model horizontal velocities of 70 austrian and italian permanent gps stations in the eastern and southern alps serve as boundary condition on the free surface of an elastic half space containing six rectangular faults each with a uniform slip rate the geometry of the rectangular faults and the slip rate vector are constrained by least squares taking into account the structural setting of the area and the geographic distribution of the velocity data we find that the surface velocities of the order of some mm yr require reverse north side of the tauern window transpressional giudicarie north alpine wrench corridor pustertal dinarides and normal brenner fault slips ranging from 10 to 30 mm yr at crustal depths the regional stress pattern computed from fault plane solutions agrees with the principal directions of our rectangular fault planes the model although constrained by horizontal velocities only predicts a pattern of vertical motion which qualitatively agrees with known phenomena such as the surface uplift in the tauern window area of the order of up to few mm yr if the heat on the shearing fault planes is removed mostly by upwards diffusion the absence of large heat anomalies on the earth s surface suggests for nominal geotherms shear stresses and concentration of subcrustal radiogenic elements that the time of initiation of the slip dates to pliocene hence more recent than late oligocene miocene time of collision of the adria indenter

using the cl br ratio as a tracer to identify the origin of salinity in aquifers in spain and portugal summary a study on the applicability of the cl br molar ratio for identifying the origin of groundwater salinity is presented according to the experience gained in spain and portugal cl br ratios in atmospheric bulk deposition have helped to distinguish groundwater in which cl derives only from atmospheric sources from groundwater in which cl is contributed by endogenous lithological or anthropogenic sources considering the seawater cl br ratio of 655 4 cl br ratios may be increased up to 1500 in groundwater by the addition of wastewater loaded with nacl or leaching of solid waste and decreased to 300 by the use of br based pesticides or leaching farm animal or septic waste leaching and dissolution of natural and industrial nacl and of gypsum rich formations containing some nacl may yield cl br ratios between one thousand and several thousand although leaching of potassium halides near salt mines produces cl br ratios below the seawater ratio when cl content in groundwater is not affected by extreme evaporation up to halite saturation at 6 2 mol l 1 of nacl and if there are no other cl sources recharge by rainfall can be estimated by relating cl in atmospheric bulk deposition to derived groundwater the cl br ratio appears to be a good tracer for discriminating non atmospheric cl contributions to groundwater provided chemical analyses are accurate since its variability is not wide data have been collected from different areas of spain and portugal and are explained and illustrated by two cases described in detail the donana aquifer in southwest spain and the canary islands both showing the mixing paths