environmental isotopes meet 3d geological modelling conceptualising recharge and structurally controlled aquifer connectivity in the basalt plains of south western victoria australia summary to develop a conceptual model of recharge and inter aquifer connectivity for a complex aquifer system in southwestern victoria australia a three dimensional 3d geological model was constructed and used to examine the influence of the regional geology on groundwater composition and age as well as recharge mechanisms the major aquifers are three basalts differentiated on age and geomorphological features and an underlying palaeovalley deep lead system the upper fine grained sediments of the deep lead form an aquitard that separates the basalt from the permeable sands and gravels beneath recharge calculations chloride mass balance and water table fluctuation methods salinity stable isotope tritium and radiocarbon data show that volcanoes and the youngest basalts although volumetrically minor form preferential recharge areas for all the basalts up to 30 mm year and also recharge the deep lead sediments through volcanic necks that penetrate the aquitard infiltration through the thick clay rich soils on the older basalts is small typically 1 2 mm year and saline resulting in a progressive increase of groundwater salinity along the flow path in these basalts the comparison of fault location with groundwater age in the deep lead aquifer suggests that in some areas faults exert significant structural control on groundwater flow this study demonstrates the value of integrating geological hydrogeological and hydrochemical data to identify preferential recharge areas inter aquifer connectivity and the influence of faults on groundwater flow in a complex aquifer system

the 3d numerical modeling of subduction dynamics plate stagnation and segmentation and crustal advection in the wet mantle transition zone 1 water content in the mantle transition zone mtz has been broadly debated in the earth science community as a key issue for plate dynamics in this study a systematic series of three dimensional 3d numerical simulation are performed in an attempt to verify a hypothesis regarding the behavior of subducted oceanic plate and the role of crust in the mtz under wet conditions this hypothesis is based on the seismic observations of structural variations associated with large scale flattened high velocity anomalies i e stagnant slabs in the mtz in our model weak low viscosity fault zones wfzs which presumably correspond to the fault boundaries of large subduction earthquakes are imposed on the top part of subducting plates the phase transitions of olivine to wadsleyite and ringwoodite to perovskite magnesiowustite under both dry and wet conditions are considered based on recent high pressure experiments the effect of viscosity reduction of wet garnet is also considered for oceanic crust in the mtz results show that there is a substantial difference in the behaviors of subducting plate and the trace of crustal materials between the models under dry and wet conditions under wet conditions the subducting plate tends to stagnate with a maximum lateral extent of over 1000 km the weaker and denser crustal material garnet rich is fed into the wfzs and is advected faster than the plate main body of peridotite olivine rich thus the viscosity and density contrast between the crustal materials and the peridotite permits the plate segmentation under a wet mtz condition

using environmental isotopes and dissolved methane concentrations to constrain hydrochemical processes and inter aquifer mixing in the galilee and eromanga basins great artesian basin australia summary groundwater recharge processes water rock interaction and the hydraulic connectivity between aquifers of the galilee and eromanga basins in central queensland australia were investigated using stable 2 h 18 o 13 c and 87 sr 86 sr and radiogenic 36 cl isotopes and dissolved methane concentrations complemented by major ion chemistry the central eromanga and the upper sequence of the galilee basins are both sub basins of the great artesian basin gab and the coal seams of the galilee basin are currently explored for their potential as commercial coal seam gas deposits in order to understand the potential influence of depressurisation of coal seams required to release the gas on adjacent aquifers a detailed understanding of recharge processes and groundwater hydraulics of these basins prior to any development is required each of the different isotope systems were used in this study to provide different information on specific processes for example the assessment of 13 c and 87 sr 86 sr ratios suggested that carbonate dissolution is one of the major processes controlling the water chemistry within some aquifers in addition the combined assessment of 2 h 18 o and major ion chemistry indicates that transpiration is the primary process controlling the solute concentration in the gab recharge area whereas evaporation appears to be less significant groundwaters in the galilee basin recharge area outside the limits of the gab are different to any groundwater within the gab units this difference is attributed to the dissolution of potassium bearing micas which are absent in the gab groundwater age estimates based on 36 cl cl ratios suggest that there is a steady increase along the flow paths and this lack of anomalous age estimates from the recharge areas to the deeper parts of the basin indicates that there is no evidence for regional inter aquifer mixing based in isotopes only however dissolved methane concentrations and groundwater chemistry near faults indicates the potential mix of gas and or water from the coal seams into the gab groundwaters suggesting that there may be local influence of faults as gas water conduits

strontium isotopes as tracers to delineate aquifer interactions and the influence of rainfall in the basalt plains of southeastern australia summary to better understand the spatial distribution of groundwater salinisation in western victoria southeast australia the interactions between a surficial basalt aquifer and an underlying extensive palaeodrainage deep lead system were studied using a multi disciplinary approach combining strontium isotope analyses with major ion chemistry and the interpretation of geological and hydrogeological data the strontium isotopes proved particularly useful in delineating flow paths and hydraulic connections between the two aquifers which have contrasting 87sr 86sr ratios the freshest basalt groundwaters lie beneath volcanoes and have 87sr 86sr signatures close to the whole rock strontium isotope ratios of the basalts 0 7045 indicating the strong influence of basalt weathering with increasing distance from the eruption points basalt groundwaters become progressively more saline and the strontium isotope ratios evolve towards the more radiogenic signatures of local rainfall 0 710 0 711 due to the slow addition of infiltration concentrated by evapotranspiration during its passage through the thick clay rich soils developed on the basalt lavas overall the influence of rainwater on the strontium isotope signatures of the basalt groundwater is much greater than that of basaltic weathering indicating that rainwater can play a greater role in determining groundwater strontium composition than is often realised most parts of the palaeodrainage system beneath the basalt are preferentially recharged through the volcanoes as shown by strong downwards hydraulic gradients and groundwater 87sr 86sr ratios similar to the least radiogenic basalt groundwaters however in the northwestern part groundwater 87sr 86sr ratios are closer to those of the source material of the sediments palaeozoic bedrock indicating that here recharge occurs predominantly in the headwaters where the basalts are absent in the southern and western sections of the palaeodrainage system there is an upward flux into the overlying basalts as shown by strong upward hydraulic gradients and elevated strontium isotope signatures in basalt groundwaters this occurs because lateral groundwater flow in the palaeodrainage system is restricted by shallow subsurface basement ridges and ultimately discharges to the surface as salt lakes

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

on the separation of crustal component from subducted oceanic lithosphere near the 660 km discontinuity the recent mineral physics observations suggest that the crustal and mantle components of subducted oceanic lithosphere have distinct densities and viscosities the deformation of such chemically stratified oceanic lithosphere as it collides with the 660 km discontinuity is examined using a simple analytical model it is shown that the separation of the crustal component can occur through a small scale folding 10 20 km if the viscosity of the crustal garnetite layer is significantly higher than the surrounding mantle 1021 pa s but is less than 1023 pa s leading to a garnet enriched transition zone behind subduction zones

seismic evidence for a chemical heterogeneity in the midmantle a strong and slightly dipping seismic reflector beneath the mariana subduction zone 1 a clear later phase 80 s after the direct p wave is observed in most of individual seismograms recorded by a short period seismometer network in japan j array from a cluster of deep earthquakes that occurred at the northern mariana subduction zone this phase 1 shows a p wave particle motion 2 arrives later from earthquakes with shallower focal depths 3 has a steeper incident angle than that of p wave and 4 shows a deviation of a few degrees in the arrival azimuth from that of p wave we interpret it as an s to p converted wave which takes off downward from the source and is reflected at a velocity discontinuity reflector below the earthquakes travel time inversion shows that the seismic reflector dips southwest by 20 at 24 25 n 144 75 e and at a depth of 1115 km with a lateral extension at least 100 100 km the location corresponds to the lower edge of a high velocity anomaly in global tomographic models amplitude and waveform analyses suggest a decrease of s wave velocity by 2 6 and an increase of density by 2 9 within the reflector there is almost no difference in p wave velocity 1 between the reflector and the surrounding mantle the estimated thickness of the reflector is 12 km these observations indicate that the observed seismic structure is more likely to be a chemical reservoir rather than a purely thermal anomaly the seismic reflector might be a piece of subducted oceanic crust as suggested by a previous study it also could be related to the break down of the d phase of dense hydrous magnesium silicates at midmantle pressure condition reported by recent mineral physics studies both scenarios imply that mechanical chemical segregation might occur within the subducted slab at midmantle condition

chloride imbalance in a catchment undergoing hydrological change upper barwon river southeast australia documenting whether surface water catchments are in net chemical mass balance is important to understanding hydrological systems catchments that export significantly greater volumes of solutes than are delivered via rainfall are not in hydrologic equilibrium and indicate a changing hydrological system here an assessment is made of whether a saline catchment in southeast australia is in chemical mass balance based on cl the upper reaches of the barwon river southeast australia has total dissolved solids tds concentrations of up to 5860mg l and cl concentrations of up to 3370mg l the high river tds concentrations are due to the influxes of groundwater with tds concentrations of up to 68 000mg l between 1989 and 2011 the median annual cl flux from the upper barwon catchment was 17 8 106kg 140kg a ha this represents 340 2230 of the annual cl input by rainfall to the catchment major ion and stable isotope geochemistry indicate that the dominant source of solutes in the catchment is evapotranspiration of rainfall precluding mineral dissolution as a source of excess cl the upper barwon catchment is not in chemical mass balance and is a net exporter of solutes the chemical imbalance may reflect the transition within the last 100ka from an endorheic lake system where solutes were recycled producing shallow groundwater with high tds concentrations to a better drained catchment alternatively a rise in the regional water table following land clearing may have increased the input of groundwater with high tds concentrations to the river system

strontium and carbon isotope tracers and the origins of soil carbonate in south australia and victoria abstract calcium carbonate occurs in soils in association with a variety of rock types in coastal and inland south australia and victoria the 87 sr 86 sr ratios of the coastal soil carbonates fall between 0 7094 and 0 7098 showing that the ocean is the principal source of calcium to nearly all soils near the coast and that contributions from bedrock are generally small an exception is the soil formed on the young volcano at mt gambier in which the average ratio for carbonate is about 0 7070 compared to 0 7041 for the volcanic ash the basaltic ash of the volcano is readily weathered and rich in calcium roughly 40 of strontium and 10 to 20 of the calcium in the soil carbonate derives from the ash and the balance from marine sources the 87 sr 86 sr ratios from soil carbonate gradually increase inland reaching values of 0 7152 these higher ratios reflect at least in part the increasing 87 sr 86 sr ratio of inland dust in contrast the ocean does not contribute significantly to the carbon pool of the soils we studied the 13 c pdb values of soil carbonates on kangaroo island and the higher rainfall areas of eastern victoria fall between 11 0 and 8 7 indicating that the carbonate formed in equilibrium with the c3 dominated vegetation typical of the region in the warmer inland areas to the north such as the eyre peninsula the 13 c value of soil carbonate averages 5 3 reflecting the higher proportion of c4 plants in the local biomass mixing with marine sources of carbonate cannot account for the observed carbon isotopic patterns the flux of carbon into soils from the ocean therefore must be small compared to that derived from plant respiration and decay

seismic scatterers at the shallowest lower mantle beneath subducted slabs abstract data from a western united states short period seismic network are analyzed in order to investigate anomalous later phases within a time window from about 10 s to 120 s after direct p waves for deep and intermediate depth earthquakes in circum pacific subduction zones the anomalous phases are best interpreted as s to p scattered waves wavelengths of 10 km from heterogeneities in the shallow lower mantle depths 950 km several s to p scatterers where elastic properties of the rocks must substantially change within several kilometers are detected in the shallowest 300 km of the lower mantle beneath four circum pacific regions kuril bonin fiji and peru around most of the observed scatterers the seismic tomography models have delineated high seismic velocity anomalies which are associated with recently subducted pacific slab or nazca slab the most likely origin of the scatterers would be basalt which used to form the oceanic crust interestingly enough the majority of the scatterers are located near the bottom boundaries of the slabs given rather moderate degrees of folding and or buckling of the pacific and nazca slabs in the shallowest lower mantle at the study areas the existence of the oceanic crust associated with the most recent slab subduction at the scattering sites is unlikely alternative and more likely explanations include the presence of ancient basaltic rocks localized dehydration of hydrous minerals or a sharp boundary between different rock fabrics such as isotropic and anisotropic lower mantle rocks associated with mantle flow dragged by the slab subduction

physical conditions producing slab stagnation constraints of the clapeyron slope mantle viscosity trench retreat and dip angles abstract recent seismic tomography has revealed various morphologies in the subducted lithosphere in particular significant flattening and stagnation of slabs around the 660 km boundary are seen in some areas beneath the northwestern pacific subduction zones we examined the cause of slab stagnation in terms of the clapeyron slope of the phase transformation from ringwoodite to perovskite magnesiowustite trench retreat velocity dip angles and high viscosity of the lower mantle based on two dimensional 2 d numerical simulations of thermal convection in particular we examined the conditions necessary for slab stagnation assuming a very small absolute value of the clapeyron slope which were proposed based on recent high pressure high temperature high p t experiments our calculations show that slabs tend to stagnate above the 660 km boundary with an increasing absolute value of the clapeyron slope viscosity jump at the boundary and trench retreat velocity and a decreasing initial dip angle stagnant slabs could be obtained numerically for a realistic range of parameters obtained from high p t experiments and other geophysical observations combining buoyancy high lower mantle viscosity and trench retreat we found that a low dip angle of a descending slab at the bottom of the upper mantle plays an important role in slab stagnation two main regimes underlie slab stagnation buoyancy dominated and viscosity dominated regimes in the viscosity dominated regime it is possible for slabs to stagnate above the 660 km boundary even when the value of the clapeyron slope is 0 mpa k

3d geological modeling of the kasserine aquifer system central tunisia new insights into aquifer geometry and interconnections for a better assessment of groundwater resources summary the challenge of this study was to create a 3d geological and structural model of the kasserine aquifer system kas in central tunisia and its natural extension into north east algeria this was achieved using an implicit 3d method which honors prior geological data for both formation boundaries and faults a current model is presented which provides defendable predictions for the spatial distribution of geology and water resources in aquifers throughout the model domain this work has allowed validation of regional scale geology and fault networks in the kas and has facilitated the first ever estimations of groundwater resources in this region by a 3d method the model enables a preliminary assessment of the hydraulic significance of the major faults by evaluating their influence and role on groundwater flow within and between four compartments of the multi layered kas hydrogeological system thus a representative hydrogeological model of the study area is constructed the possible dual nature of faults in the kas is discussed in the context that some faults appear to be acting both as barriers to horizontal groundwater flow and simultaneously as conduits for vertical flow also discussed is the possibility that two flow directions occur within the kas at a small syncline area of near feriana in summary this work evaluates the influence of aquifer connectivity and the role of faults and geology in groundwater flow within the kas aquifer system the current kas geological model can now be used to guide groundwater managers on the best placement for drilling to test and further refine the understanding of the groundwater system including the faults connectivity as more geological data become available the current model can be easily edited and re computed to provide an updated model ready for the next stage of investigation by numerical flow modeling

regional groundwater flow paths in trans pecos texas inferred from oxygen hydrogen and strontium isotopes summary stable isotopes radiogenic isotopes and major ion chemistry are used to constrain flow paths in a fracture controlled regional groundwater flow system in far west texas the flow system occurs in permian and cretaceous sedimentary rocks and cenozoic alluvial basin fill samples from springs and wells in the study area were analyzed for major ions and hydrogen oxygen and strontium isotopes d and 18o values fall close to the global meteoric water line indicating that these values have not been significantly affected by evaporation or mineral water reactions 18o values from samples along the regional flow path are lower by as much as 3 relative to local recharge values the distribution of stable isotope values throughout the study area suggests that lower 18o values represent recharge during cooler climatic conditions rather than latitude or altitude effects 87sr 86sr values for water samples from along the regional flow path range from 0 7093 to 0 7148 with the highest values at the upgradient end of the flow system these values are significantly higher than expected for groundwaters dominated by dissolution of permian and cretaceous marine carbonates and evaporites the high 87sr 86sr values reflect dissolution of minerals of precambrian and early paleozoic origin in the crystalline rocks of the carrizo and baylor mountains and alluvial basin fill at the upgradient end of the flow system contours of 87sr 86sr values indicate a zone of high 87sr 86sr water that corresponds to the regional groundwater flow paths mass balance mixing models and mineral reactions models indicate a three end member mixing system modified by dissolution of strontium bearing minerals in the alluvial fill at the upgradient end of the flow system

structural framework of the edwards aquifer recharge zone in south central texas the edwards aquifer the major source of water for many communities in central texas is threatened by population growth and development over its recharge zone the location of the recharge and confined zones and the flow paths of the aquifer are controlled by the structure of and deformation processes within the balcones fault system a major system of predominantly down to the southeast normal faults we investigate the geologic structure of the edwards aquifer to assess the large scale aquifer architecture analyze fault offset and stratigraphic juxtaposition relationships evaluate fault zone deformation and dissolution and fault system architecture and investigate fault block deformation and scaling of small scale intrablock normal faults characterization of fault displacement shows a pattern of aquifer thinning that is likely to influence fault block communication and flow paths flow path constriction may be exacerbated by increased fault segment connectivity associated with large fault displacements also increased fault zone deformation associated with larger displacement faults is likely to further influence hydrologic properties overall faulting is expected to produce strong permeability anisotropy such that maximum permeability is subhorizontal and parallel to fault bedding intersections at all scales aquifer permeability is either unchanged or enhanced parallel to faults and in many cases decreased perpendicular to faults

a new correction model for 14c ages in aquifers with complex geochemistry application to the neogene aquifer belgium abstract the objective of this paper is to build a general correction model that takes into account all the different radiocarbon dilution reactions and resolving the processes that are geochemically aging the groundwater in the neogene aquifer for this 13 c and radiocarbon in groundwater are investigated with their relationship to other chemical components in groundwater the 13 c values in the neogene aquifer are influenced by various geochemical reactions like calcite dissolution oxidation of organic matter and methanogenesis calcite dissolution and ch 4 production increase 13 c while the oxidation of organic matter decreases 13 c in the groundwater the reactions that modify 13 c also influence the 14 c activity due to the complex geochemical environment existing correction models are not applicable to this situation a correction model for initial 14 c activity is formulated in which the different c sources that influence 14 c activity are taken into account it is observed that recent dissolved organic matter plays an important role in redox reactions the corrected 14 c ages lie between 0 792 and 6 425 ka representing the maximum age if a part of the organic matter that oxidises is fossil the determined age will represent an overestimated age

geochemistry of ground waters from the great artesian basin australia herczeg a l torgersen t chivas a r and habermehl m a 1991 geochemistry of ground waters from the great artesian basin australia j hydrol 126 225 245 ground waters from the confined lower cretaceous jurassic aquifer of the great artesian basin australia gab are characterised by na hco 3 type waters throughout the eastern and central parts of the basin and na sq c1 type waters in the western part sodium and bicarbonate increase in concentration from the northeastern margins to the southwestern discharge areas along the regional groundwater flowlines a mass balance and equilibrium model for major dissolved species and stable carbon isotopes of dissolved inorganic carbon show that the chemical trends observed are caused by mass transfer reactions involving cation exchange of na for ca mg carbonate dissolution and reactions between na and kaolinite to form na smectite the stable carbon isotopic composition of dissolved inorganic carbon dic increases from values of about 15 o near the basin margins to 6 o in the interior of the basin an inverse relationship exists between 6 3c and dic indicating addition of enriched carbon as the ground waters move basinwards a t2c 3c mass balance indicates that the trend toward heavier 6 3c values in the interior of the basin results from bacterial reduction of carbon dioxide to produce methane rather than dissolution of and equilibration with carbonate minerals the gab aquifer system is apparently open to co which is the product of in situ anaerobic fermentation producing co 2 enriched in t3c the chemical evolution of the major dissolved species and carbon isotope distribution in the eastern and central parts of the gab can then be envisaged as an initial pco 2 up to several orders of magnitude above atmospheric level is acquired within the recharge area by plant respiration and oxidation of organic matter in the soil zone initially silicate and carbonate minerals may dissolve at least in some parts of the basin resulting in increased alkalinity higher ca and mg concentrations and a 6 3c concentration of the dic of around 12 0 processes such as cation exchange of na for ca and mg in addition to the removal of some na by reverse weathering which produces a na smectite dominate in the interior of the gab the chemistry of ground waters derived from the western recharge areas is controlled by evaporite dissolution as indicated by very high ci br ratios

understanding the salinisation process for groundwater in an area of south eastern australia using hydrochemical and isotopic evidence abstract increases in groundwater salinity down gradient are a common occurrence in catchments throughout australia exacerbating the effects of dryland salinisation in discharge areas groundwater hydrochemical and isotopic data from the willaura catchment in south eastern australia which is affected by both primary natural and secondary human induced salinity allowed the factors that cause the down gradient trend in salinisation within this catchment to be determined the overall salinity of the groundwater 0 8 70 ms cm is controlled by evapotranspiration which concentrates cyclic salts in the unsaturated zone greatly increasing the salinity of the soil water to 3700 6400 mg l cl the progressive addition of this saline soil water to fresher groundwaters recharged on the catchment margins causes a gradual increase in salinity down gradient the groundwater stable isotope compositions show that most recharge occurs in winter and spring groundwater salinities increase around the saline lakes of the discharge zone due to direct evaporation from shallow watertables and minor dissolution of halite as indicated by cl br ratios mineral water interactions within the aquifers cause a slight overall reduction in salinity conversion of kaolinite to smectite and illite and cation exchange of na for ca2 on smectites cause na cl mg2 cl k cl si cl and hco3 cl ratios to progressively decline and ph to gradually increase down gradient oxidation of organic matter causes a strong decrease in the redox potential of the groundwaters down gradient the groundwater ages increase from modern containing tritium on the catchment margins to 8000 years based on 14c dating at the end of the 25 km flow path the older groundwaters are isotopically heavier than the younger waters probably due to recharge during a wetter climate in the early holocene the groundwater ages show clearly that the progressive addition of saline soil water causing groundwaters to become more saline down gradient has occurred throughout the holocene and may explain the occurrence of primary salinisation within many australian catchments

using hydrogeochemistry to understand inter aquifer mixing in the on shore part of the gippsland basin southeast australia groundwater in the latrobe valley in the gippsland basin of southeast australia is important for domestic agricultural and industrial uses this sedimentary basin contains a number of aquifers that are used for water supply dewatered for open pit coal mining and which are potentially influenced by off shore oil and gas production major ion chemistry together with stable and sr isotope data imply that the main hydrogeochemical processes are evapotranspiration with minor silicate and carbonate weathering methanogenesis and so4 reduction in reduced groundwater associated with coal deposits have also occurred groundwater has estimated 14c ages of up to 36ka and is largely 3h free carbon 14 ages are irregularly distributed and poorly correlated with depth and distance from the basin margins the observations that the geochemistry of groundwater in aquifers with different mineralogies are similar and the distribution of 14c ages is irregular implies that the aquifers are hydraulically connected and horizontal as well as vertical inter aquifer mixing occurs the connection of shallow and deeper aquifers poses a risk for the groundwater resources in gippsland as contaminants can migrate across aquifers and dewatering of shallow units may impact deeper parts of the groundwater system

mapping of the 410 and 660 km discontinuities beneath the japanese islands 1 a family of core reflected shear waves generated by the 28 june 2002 vladivostok deep earthquake including near vertical reflections from the 410 and 660 km discontinuities were recorded by 500 tiltmeters of the hi net and 60 broadband seismometers of the f net in japan the observed upper mantle reflections were cross correlated with synthetics calculated on the basis of the spectral element method for a fully three dimensional earth model using the earth simulator supercomputer to accurately determine the depths of the reflection points the mapped upper mantle discontinuities were compared with a high resolution p wave tomographic image the 660 km discontinuity is depressed at a constant level of 15 km along the bottom of the horizontally extending aseismic slab under southwestern japan the transition from the normal to the depressed level occurs within a lateral distance of less than 200 km observations suggest that the reflections from the 410 km discontinuity interfere with those from slab related structures on top of this discontinuity leading to a spuriously large elevation of the 410 km discontinuity in and near the subducted slab records at stations relatively free from such interference effects however still imply elevation of this discontinuity within the slab

stable isotope geochemistry of cold co2 bearing mineral spring waters daylesford victoria australia sources of gas and water and links with waning volcanism abstract mineral springs in the victorian central highlands australia have high co 2 contents and naturally effervesce 13 c values of co 2 gas and dissolved inorganic carbon are 10 6 to 7 0 and 5 9 to 0 1 respectively with a net 13 c of 8 to 3 the carbon in these waters was derived from a mantle source associated with local pliocene to recent basaltic newer volcanic province rocks previously reported 3 he 4 he 1 2 3 1 relative to air and high he ne ratios are also consistent with the presence of magmatic volatiles silica contents imply that the waters were never heated above 130 c and that the system is not hydrothermal the occurrence of carbonated mineral springs in a relatively small region of the newer volcanics province where volcanic activity ceased several thousands of years ago may be due to the presence of late intrusions combined with deep circulation of water through deeply weathered and fractured ordovician basement a region of low seismic velocity under the daylesford area potentially images those intrusions most spring waters have 18 o and 2 h values of 8 to 6 and 45 to 35 respectively and lie to the left of the local and global meteoric water lines the anomalously low 18 o values results from co 2 exsolution at low temperatures which strongly partitions 18 o into the gas the lack of waters lying to the right of the local meteoric water line also implies that water rock interaction at elevated temperatures did not occur the 2 h values are lower than contemporary meteoric water suggesting that the waters may have recharged under colder climate conditions several thousand years ago the local ordovician rocks are gold bearing the present spring system is cold and would not efficiently transport au however volcanic is waning and the spring systems at the time of volcanism may have been hotter and able to redistribute au

mantle provinces under north america from multifrequency p wave tomography this is a survey of mantle provinces large scale seismic anomalies under north america from the surface down to 1500 1800 km depth the underlying p velocity model was obtained by multifrequency tomography a waveform based method that systematically measures and models the frequency dependence of teleseismic body waves a novel kind of three dimensional rendering technique is used to make the considerable structural complexities under north america accessible in the transition zone and below the north american mantle is dominated by seismically fast provinces which represent distinct subduction episodes of the farallon plate i attempt to date and interpret the various slab fragments by reconciling their present positions with paleotrench locations from plate tectonic reconstructions and with major geologic surface episodes differences in vertical sinking velocity have led to large vertical offsets across adjacent coeval slabs some of the mantle provinces have not been discussed much previously including 1 a seismically slow blanket overlying the oldest farallon subduction along the eastern continental margin 2 a transition zone slab coeval with the laramide orogeny ca 80 60 myr which i discuss in analogy to the stagnant slab subduction style commonly found in the western pacific today 3 the lower mantle root of present day cascadia subduction which may have started out as intraoceanic subduction 4 a lower mantle slab under arizona and new mexico the last material to subduct before strike slip motion developed along the san andreas boundary and 5 two narrow plate tears thousands of kilometers long one of which is the subducted conjugate of the mendocino fracture zone

a graphical method to evaluate predominant geochemical processes occurring in groundwater systems for radiocarbon dating a graphical method is described for identifying geochemical reactions needed in the interpretation of radiocarbon age in groundwater systems graphs are constructed by plotting the measured 14c 13c and concentration of dissolved inorganic carbon and are interpreted according to specific criteria to recognize water samples that are consistent with a wide range of processes including geochemical reactions carbon isotopic exchange 14c decay and mixing of waters the graphs are used to provide a qualitative estimate of radiocarbon age to deduce the hydrochemical complexity of a groundwater system and to compare samples from different groundwater systems graphs of chemical and isotopic data from a series of previously published groundwater studies are used to demonstrate the utility of the approach ultimately the information derived from the graphs is used to improve geochemical models for adjustment of radiocarbon ages in groundwater systems

differences in groundwater and chloride residence times in saline groundwater the barwon river catchment of southeast australia abstract the residence times of groundwater and chloride and the processes contributing to the development of saline total dissolved solids tds up to 45 379 mg l groundwater within the barwon river catchment of southeast australia were investigated using major ion stable isotope 18 o 2 h and 13 c and radioactive isotope 3 h 14 c 36 cl geochemistry the elevated groundwater salinity in the region is primarily due to evapotranspiration and recycling of solutes in saline lakes with minor contributions from weathering of halite silicate and calcite minerals groundwater residence times estimated from 14 c vary from modern to 20 ka for groundwater with lower 14 c activities the estimated residence times vary significantly depending on the assumed flow model and the 14 c activity of recharge chloride residence times downgradient of lake murdeduke a saline through flow lake in the centre of the catchment are greater than the corresponding groundwater residence times due to the recycling of cl within the lake precise estimates of chloride residence time could not be determined using 36 cl due to r 36 cl in precipitation being lower than that of groundwater this is most likely due to r 36 cl values in rainfall having been higher in the past than they are at present due to climate variability 18 o 2 h and 13 c values also suggest that the region has experienced increasingly more evaporative conditions with time the results of this study demonstrate that while cl is a useful tracer of hydrological processes it must be applied carefully in arid and semi arid regions of the world in particular recharge rates calculated using chloride mass balance may be underestimated where recycling of cl has occurred

microbial origin of australian coalbed methane bituminous coal seam gases from the permian sydney and bowen basins australia are characterized by 1 methane ethane ratios greater than or equal to 1000 2 dgr13c and dgrd values for methane of 60 10 pmil pdb and 217 17 pmil smow respectively 3 carbon dioxide contents of less than 5 and 4 dgr13c co 2 ch4 values of 55 10 pmil pdb these data suggest that microbial reduction of co2 rather than traditional thermogenic reactions is mainly responsible for gas composition invasions by co2 of deep seated external origins are readily recognized by their isotopic compositions 7 2 pmil pdb

a new precipitation weighted method for determining the meteoric water line for hydrological applications demonstrated using australian and global gnip data summary the relationship between 2h and 18o in precipitation at a site known as the local meteoric water line lmwl is normally defined using an ordinary least squares regression olsr which gives equal weighting to all data points regardless of the precipitation amount they represent however smaller precipitation amounts are more likely to have a lower d excess due to re evaporation of raindrops below the cloud base or biases in the sampling method in this paper we present an equation for a precipitation amount weighted least squares regression pwlsr that will correct these biases for use in groundwater and surface hydrology applications new lmwl equations are presented for australian sites in the global network of isotopes in precipitation gnip where the pwlsr consistently produces a lmwl with a larger gradient than the olsr perth and alice springs exhibit the largest change in slope this is consistent with the higher frequency of small monthly precipitation amounts with low d excess values occurring at these sites in summer for perth and throughout the year for alice springs the pwlsr method was also applied to 288 stations in the gnip data base n 36 and the difference between the slopes of the lmwls a slopepwlsr slopeolsr calculated for these stations the mean change in slope a was 0 12 with 56 of sites showing an increase in slope or positive a value and 44 having a decrease in slope or negative a sites with mediterranean climates showed the greatest increase in slope the magnitude of the change in slope followed some general trends showing a positive correlation with average 2h and 18o composition and rainfall variability and negative correlation with period of record n

numerical simulations of mantle flow around slab edges abstract a simple kinematic dynamic model of mantle flow around the slab edge is constructed in order to understand the flow complexity there the flow velocity on the top and the small boundary region around the shallow plate boundary is kinematically imposed in order to achieve a subduction like feature and the flow in other part is dynamically calculated the geometry of the plate mimics the region around the junction of aleutian islands and kamchatka that are examples of the convergent transform fault plate boundaries in a simple model in which the overlying plate is almost stationary the lateral flow from the mantle under the subducting slab to the mantle under the neighboring plate is of minor importance once the slab penetrates into the high viscosity layer where the downward flow encounters the resistance similar situation was found when the trench is advancing that is the trench moves toward the overlying plate for the case with retreating trench that is the trench moves toward the subducting plate a lateral flow exists even after the slab penetrates into the high viscosity layer although its magnitude is significantly smaller than that of the plate velocity the presence of a low viscosity layer just beneath the subducting plate may promote the emergence of lateral flow a significant lateral flow is observed when the high temperature anomaly that is buoyant and low viscosity block carried by the movement of subducting plate approaches the slab these results may have important implications for the possible existence of trench parallel flow in the sub slab mantle

wet subduction versus cold subduction 1 in situ x ray diffraction study of post spinel transformation in hydrous peridotite 2 wt h2o indicates that the phase boundary is shifted to higher pressures by 0 6 gpa relative to anhydrous peridotite at 1473 k whereas it shows no obvious shift at high temperature around 1873 k a linear equation for the boundary is p gpa 0 002 t k 26 3 which is applicable for temperatures below 1800 k the present data shows that a significant part of the depressions seen in the 660 km seismic discontinuity may be affected by existence of water it is also well resolved that the olivine wadsleyite phase transformation corresponding to the 410 km seismic discontinuity is shifted to lower pressures by 1 2 gpa by the addition of water thus the topography of seismic discontinuities in the transition zone associated with slabs can be attributed not only to cold subduction but also wet subduction

plastic deformation of garnets systematics and implications for the rheology of the mantle transition zone abstract plastic properties of materials with garnet structure have been studied under wide temperature conditions ranging from room temperature to 95 of the melting temperatures using uniaxial compression and hot microhardness tests garnets studied include single crystals of oxide garnets y 3 al 5 o 12 gd 3 ga 5 o 12 and y 3 fe 5 o 12 and silicate garnets various solid solutions including grossular almandine andradite pyrope spessartine and uvarovite both uniaxial compression and hot hardness tests indicate that there is a general trend in the plasticity of garnets when the data are compared at normalized conditions t t m and and that the resistance to plastic deformation in garnets is significantly higher than most of the other minerals in the earth s mantle based on both stress dip tests and microstructural observations it is proposed that the creep strength of garnet is largely controlled by the resistance to dislocation glide rather than by recovery processes this conclusion is consistent with the high peierls stress inferred from the hot hardness tests the high peierls stress in garnets is presumably due to the large unit cell i e long burgers vectors and or the bcc packing which are common to all garnets we postulate therefore that the present results can be applied to the strength of high pressure garnet majorite and suggest that garnet rich layers in the earth such as subducted oceanic crust in the transition zone or a possibly garnet rich bottom part of the transition zone will be considerably stronger than surrounding regions

significance of the connection between bedrock alluvium and streams a spatial and temporal hydrogeological and hydrogeochemical assessment from queensland australia abstract catchment scale hydrological and hydrogeological investigations commonly conclude by finding that particular stream reaches are either gaining or losing they also often assume that the influence of bedrock aquifers on catchment water balances and water quality is insignificant however in many cases such broad findings are likely to oversimplify the spatial and temporal complexity of the connections between the different hydrological system components particularly in regions dominated by cycles of droughts and flooding from a modelling perspective such oversimplifications can have serious implications on the process of identifying the magnitude and direction of the exchange fluxes between the surface and groundwater systems in this study we use 3d geological modelling and historic water chemistry and hydraulic records to identify the origins of groundwater at different locations in the alluvium and along the course of streams in the lockyer valley queensland australia a catchment impacted by a severe drought millennium drought from 1998 to 2009 followed by extensive flooding in 2011 we also demonstrate how discharge from the sub alluvial regional scale volcanic and sedimentary bedrock influences the water balance and water quality of the alluvium and streams the investigation of aquifer geometry via development of a three dimensional geological model combined with an assessment of hydraulic data provided important insights on groundwater flow paths and helped to identify areas where bedrock aquifers interact with shallow alluvial aquifers and streams multivariate statistical techniques were then applied as an additional line of evidence to groundwater and surface water hydrochemical data from large historical datasets this confirmed that most sub catchments within the lockyer valley have distinct water chemistry patterns which result from mixing of different water sources including discharge from the sub alluvial bedrock importantly in addition to the observed spatial variability time series hydrochemical groundwater and surface water data further demonstrated that the hydraulic connection between alluvial aquifers streams and sub alluvial bedrock aquifers is temporally dynamic with very significant changes occurring at the transition from normal to drought conditions and following flooding affecting both catchment water quality and water balances

future supercontinent assembled in the northern hemisphere terra nova 23 333 338 2011 abstract continental masses were amalgamated broken apart and reassembled within supercontinents during different times in earth history here we attempt to predict the configuration of a potential future supercontinent based on a numerical simulation model of mantle convection the mantle convection in our model is driven by a density anomaly compiled from a global seismic tomography model the temporal evolution of a highly viscous continent with an initial present day configuration is simulated for over 250 ma the result reveals that australia eurasia north america and africa would gather in the northern hemisphere to form the future supercontinent on the other hand antarctica and south america remain in the present day position even after 250 ma from present and do not join the future supercontinent amalgam the configuration of the future supercontinent numerically simulated herein is broadly consistent with the hypothetical model of the future supercontinent amasia speculated from geological correlations

water transport into the deep mantle and formation of a hydrous transition zone abstract the phase relations in the peridotite water system to the top of the lower mantle reveal that a certain amount of water can be transported and stored in the transition zone by various hydrous minerals resulting in formation of a hydrous transition zone results of preliminary experiments to clarify the effect of water on kinetics of the olivine wadsleyite transformation are given and show that water enhances the transformation kinetics significantly there are potential dehydration sites in the deep mantle four sites along the descending slabs depending on their temperature profiles i e the mantle wedge of the subduction zone mantle transition zone top of the lower mantle where hydrous ringwoodite and superhydrous phase b decompose and deep in the lower mantle around 1200 1500 km depth where decomposition of phase d g occurs we also expect one site of dehydration melting at the base of the upper mantle where the hot mantle plume hydrated in the transition zone can be dehydrated the transition zone can serve as a water absorber for the mantle scale water circulation system some of the recent seismic works including the p wave tomography images reveal the existence of low velocity anomalies in the transition zone suggesting possibly a wet transition zone elevation of the 410 km discontinuity and lack of clear evidence for a metastable olivine wedge in cold slabs may be consistent with the equilibrium phase transformation from olivine to wadsleyite in cold and wet slabs on the basis of our kinetic study of the transformation under wet conditions

in situ x ray diffraction study of the effect of water on the garnet perovskite transformation in morb and implications for the penetration of oceanic crust into the lower mantle abstract the phase boundary of the transformation of garnet to perovskite in hydrous mid ocean ridge basalt morb was determined by in situ high pressure and high temperature x ray diffraction xrd experiments the garnet bearing assemblage was formed in experiments at pressures below 21 gpa in contrast an assemblage of mg perovskite ca perovskite stishovite cf phase and or nal phase is stable at pressures above 21 gpa garnet and perovskite bearing assemblages were synthesized at a pressure range of 20 25 gpa and a temperature range of 1000 1600 c on the basis of our results we have located the garnet perovskite phase boundary and find that it can be described by the following equation p gpa 0 004t c 17 5 which positions it 2 gpa lower under dry conditions if the top 7 km of the slab is colder than 1200 c in the transition zone perovskite will appear at a depth shallower than that where ringwoodite decomposes this result indicates that the morb layer becomes denser than the peridotite portion of the slab throughout the transition zone and the lower mantle and thus no density crossover would exist between basalt and underlying peridotite along the cold subducting slab geotherm

carbon isotope characterization of powder river basin coal bed waters key to minimizing unnecessary water production and implications for exploration and production of biogenic gas abstract compared to other natural waters water associated with biogenic natural gas is enriched in 13 carbon shallow coal seams regularly contain abundant resources of biogenic gas as such water associated with biogenic gas in these coal beds is isotopically distinct from other waters the production of gas from coal beds requires the removal of large volumes of produced water thus a method of discerning coalbed reservoir water from other natural waters surface and groundwater is important to both the coalbed natural gas cbng industry and associated environmental and regulatory agencies although isotopic tracers have been employed to identify coalbed natural gas produced waters the isotopic variability within the reservoir has not been documented and explained in this study we present the isotopic compositions of dissolved inorganic carbon oxygen and hydrogen for water produced from 197 cbng wells in the powder river basin of wyoming and montana this extensive database allows us to distinguish variations in isotopic compositions that may occur by multiple processes these include variations that identify efficient dewatering of coal beds variations characterizing incomplete hydraulic isolation of coal beds from adjacent strata and the subsequent mixing of groundwaters variations related to well completion design and variations associated with geochemical and biogenic processes that occur along groundwater flow paths these data suggest that little change in 13 c dic occurs within the reservoir as a result of water and gas production thus the carbon isotopic composition informs other processes within the reservoir unrelated to coalbed natural gas recovery the 13 c dic and d of groundwater vary along flow path across the basin reflecting different methanogenic pathways that are associated with different isotopic fractionations and the pathways that dominate in different areas within the basin in areas where several producing coal seams are present the 13 c dic and d of produced waters from each seam are distinct therefore on a local scale the isotopic composition of produced water can identify the particular coal seam from which water and gas are withdrawn the methods and results presented in this case study provide examples that illustrate how water quality and isotopic data can be used to determine the hydraulic connectivity between coal and non coal strata identify and quantify water from individual coal horizons as well as predict and understand the isotopic variability of the reservoir

hydrogen diffusivity in wadsleyite and water distribution in the mantle transition zone abstract the kinetics of the hydrogen diffusivity in synthesized polycrystalline wadsleyite was measured by ir spectroscopy in order to determine the diffusion coefficient of hydrogen in wadsleyite the major constituent mineral in the mantle transition zone with the composition of mg0 89fe0 11 2sio4 the hydration experiments were conducted at 15 16 gpa and temperature range from 900 to 1200 c with mg oh 2 as the water source by kawai type multi anvil apparatus the diffusion rate obtained here is considered to be an effective diffusion coefficient with the grain size of 9 m involving contributions both from the lattice diffusion and the grain boundary diffusion the temperature dependence of diffusion of hydrogen in polycrystalline wadsleyite was determined to be dh 9 6 10 6 exp 123 32 kj mol 1 rt at 15 gpa hydrogen diffusion rate in wadsleyite is roughly consistent with the average diffusivity of hydrogen in olivine in recent years several authors have suggested a possibility of the hydrous transition zone and the distribution and transport properties of water are still debated on the basis of water dependence of the electrical conductivity the water content in the mantle transition zone was estimated from the observed conductivity by using the nernst einstein relation the results obtained here show that the distribution of water should be quite heterogeneous throughout the mantle transition zone

spatial estimation of debris flows triggering rainfall and its dependence on rainfall return period abstract forecasting the occurrence of debris flows is fundamental for issuing hazard warnings and often focuses on rainfall as a triggering agent and on the use of empirical rainfall thresholds based on rain gauge observations a recognized component of the uncertainty associated with the use of rainfall thresholds is related to the sampling of strongly varying rainfall variability with sparse rain gauge networks in this work we examine the spatial distribution of rainfall depth in areas up to 10 km from the debris flow initiation points as a function of return period and we exploit this information to analyze the errors expected in the estimation of debris flow triggering rainfall when rain gauge data are used in particular we investigate the impact of rain gauge density and of the use of different interpolation methods high resolution adjusted radar rainfall estimates representing the best available spatially distributed rainfall estimates at the debris flows initiation point and in the surrounding area are sampled by stochastically generated rain gauge networks characterized by varying densities debris flow triggering rainfall is estimated by means of three rainfall interpolation methods nearest neighbor inverse distance weighting and ordinary kriging on average triggering rainfall shows a local peak corresponding to the debris flow initiation point with a decay of rainfall with distance which increases with the return period of the triggering rainfall interpolation of the stochastically generated rain gauge measurements leads to an underestimation of the triggering rainfall that irrespective of the interpolation methods increases with the return period and decreases with the rain gauge density for small return period events and high rain gauge density the differences among the methods are minor with increasing the return period and decreasing the rain gauge density the nearest neighbor method is less biased because it makes use only of the closest rain gauge to the debris flow initiation point on the contrary inverse distance weighting and ordinary kriging which are using rain gauges located farther from the debris flows in addition to the closest one exhibit negative biases that increase with return period the standard deviation of the interpolated values is larger when the nearest neighbor is used with respect to inverse distance weighting and ordinary kriging for large return period and low rain gauge density the differences among the methods are minor

groundwater visualisation system gvs a software framework for integrated display and interrogation of conceptual hydrogeological models data and time series animation summary management of groundwater systems requires realistic conceptual hydrogeological models as a framework for numerical simulation modelling but also for system understanding and communicating this to stakeholders and the broader community to help overcome these challenges we developed gvs groundwater visualisation system a stand alone desktop software package that uses interactive 3d visualisation and animation techniques the goal was a user friendly groundwater management tool that could support a range of existing real world and pre processed data both surface and subsurface including geology and various types of temporal hydrological information gvs allows these data to be integrated into a single conceptual hydrogeological model in addition 3d geological models produced externally using other software packages can readily be imported into gvs models as can outputs of simulations e g piezometric surfaces produced by software such as modflow or feflow boreholes can be integrated showing any down hole data and properties including screen information intersected geology water level data and water chemistry animation is used to display spatial and temporal changes with time series data such as rainfall standing water levels and electrical conductivity displaying dynamic processes time and space variations can be presented using a range of contouring and colour mapping techniques in addition to interactive plots of time series parameters other types of data for example demographics and cultural information can also be readily incorporated the gvs software can execute on a standard windows or linux based pc with a minimum of 2 gb ram and the model output is easy and inexpensive to distribute by download or via usb dvd cd example models are described here for three groundwater systems in queensland northeastern australia two unconfined alluvial groundwater systems with intensive irrigation the lockyer valley and the upper condamine valley and the surat basin a large sedimentary basin of confined artesian aquifers this latter example required more detail in the hydrostratigraphy correlation of formations with drillholes and visualisation of simulation piezometric surfaces both alluvial system gvs models were developed during drought conditions to support government strategies to implement groundwater management the surat basin model was industry sponsored research for coal seam gas groundwater management and community information and consultation the virtual groundwater systems in these 3d gvs models can be interactively interrogated by standard functions plus production of 2d cross sections data selection from the 3d scene rear end database and plot displays a unique feature is that gvs allows investigation of time series data across different display modes both 2d and 3d gvs has been used successfully as a tool to enhance community stakeholder understanding and knowledge of groundwater systems and is of value for training and educational purposes projects completed confirm that gvs provides a powerful support to management and decision making and as a tool for interpretation of groundwater system hydrological processes a highly effective visualisation output is the production of short videos e g 2 5 min based on sequences of camera fly throughs and screen images further work involves developing support for multi screen displays and touch screen technologies distributed rendering gestural interaction systems to highlight the visualisation and animation capability of the gvs software links to related multimedia hosted online sites are included in the references

dynamical mechanisms controlling formation and avalanche of a stagnant slab abstract we performed a numerical study to understand the dynamical mechanism controlling the formation and avalanche of a stagnant slab using two dimensional dynamical models of the integrated plate mantle system with freely movable subducting and overriding plates we examined slab rheology as a mechanism for producing various styles of stagnating or penetrating slabs that interact with the 410 km and 660 km phase transitions the simulated results with the systematically changed rheological parameters are interpreted using a simple stability analysis that includes the forces acting on the stagnant slab slab plasticity that memorizes the shape produced by past deformation generates slab stagnation at various depths around the 660 km phase transition the slab stagnates even beneath the 660 km phase boundary with a gentle clapeyron slope feedbacks between trench backward migration and slab deformation promote each other during the slab stagnation stage slab viscosity also determines the final state of the subducted slab that is it continues stagnation or initiates penetration a low viscosity slab can finally penetrate into the lower mantle because the growth time of the rayleigh taylor instability is shorter after the avalanche the direction of the trench migration changes depending on the lower mantle slab viscosity

plate tectonics on the early earth limitations imposed by strength and buoyancy of subducted lithosphere the tectonic style and viability of modern plate tectonics in the early earth is still debated field observations and theoretical arguments both in favor and against the uniformitarian view of plate tectonics back until the archean continue to accumulate here we present the first numerical modeling results that address for a hotter earth the viability of subduction one of the main requirements for plate tectonics a hotter mantle has mainly two effects 1 viscosity is lower and 2 more melt is produced which in a plate tectonic setting will lead to a thicker oceanic crust and harzburgite layer although compositional buoyancy resulting from these thick crust and harzburgite might be a serious limitation for subduction initiation our modeling results show that eclogitization significantly relaxes this limitation for a developed ongoing subduction process furthermore the lower viscosity leads to more frequent slab breakoff and sometimes to crustal separation from the mantle lithosphere unlike earlier propositions not compositional buoyancy considerations but this lithospheric weakness could be the principle limitation to the viability of plate tectonics in a hotter earth these results suggest a new explanation for the absence of ultrahigh pressure metamorphism uhpm and blueschists in most of the precambrian early slabs were not too buoyant but too weak to provide a mechanism for uhpm and exhumation

environmental isotopes as indicators of inter aquifer mixing wimmera region murray basin southeast australia abstract complex groundwater flow systems in confined aquifers that result from geological structures stratigraphic changes or the absence of efficient aquitards are difficult to constrain using physical parameters alone despite a relatively simple aquifer configuration the distribution of groundwater total dissolved solids tds concentrations 13c values 87sr 86sr ratios and 14c activities a14c in groundwater in the wimmera region of the southern murray basin implies that considerable inter aquifer flow has occurred given the presence of both silicate and carbonate aquifers 13c values and 87sr 86sr ratios are the key parameters that demonstrate inter aquifer flow locally between 40 and 95 of water from one aquifer has infiltrated the underlying aquifer homogenising many aspects of the groundwater geochemistry groundwater residence times estimated from a14c range from modern to 30 ka and the distribution of 14c residence times confirm that inter aquifer flow is regional scale and long term recharge of the deepest aquifers occurs across a broad region and not solely at the basin margins vertical leakage rates are 6 10 10 3 m year and long term recharge rates 0 1 0 2 mm year

grain growth kinetics of ringwoodite and its implication for rheology of the subducting slab abstract grain growth rates of mg2sio4 and mg0 9fe0 1 2sio4 ringwoodites have been studied under the conditions of the mantle transition zone at a pressure of 21 gpa and temperatures ranging from 1473 to 2023 k using a kawai type high pressure apparatus the grain growth rates were expressed by gn g0n k0texp h rt where g m is grain size at time t s and g0 is the initial grain size at t 0 with n 4 5 0 8 and h 414 kj mol and log k0 20 4 1 6 m4 5 s for mg0 9fe0 1 2sio4 ringwoodite and h 456 kj mol and logk0 20 2 1 4 m4 5 s for mg2sio4 ringwoodite using these kinetic parameters for grain growth we estimated the grain size of ringwoodite in the cold subducting slabs to be less than 100 m this suggests that the dominant deformation mechanism in the subducting slab is diffusion creep it is also likely that some cold slabs are softer than the warmer surrounding mantle

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

core mantle boundary topography estimated from numerical simulations of instantaneous mantle flow core mantle boundary cmb topography is estimated from numerical simulations of instantaneous mantle flow in a three dimensional spherical shell geometry density anomaly models of the earth s mantle are derived from geodynamic models constrained principally by seismic tomography results to account for the small 1 5 km cmb topographic relief inferred from recent seismological results lateral viscosity variations in the mantle compositionally dense piles in the deep mantle and a low viscosity d layer are all required for the numerical models low viscosity subducting slabs in the lower mantle serve to reduce the topographic amplitude below high velocity regions i e the circum pacific belt the existence of dense piles may cause the local topographic depressions even below low velocity regions i e the south pacific and atlantic africa regions

the influence of trench migration on slab penetration into the lower mantle abstract a two dimensional numerical convection model in cartesian geometry is used to study the influence of trench migration on the ability of subducted slabs to penetrate an endothermic phase boundary at 660 km depth the transient subduction history of an oceanic plate is modelled by imposing plate and trench motion at the surface the viscosity depends on temperature and depth a variety of styles of slab behaviour is found depending predominantly on the trench velocity when trench retreat is faster than 2 4 cm a the descending slab flattens above the phase boundary at slower rates it penetrates straight into the lower mantle although flattening in the transition zone may occur later leading to a complex slab morphology the slab can buckle independent of whether it penetrates or not especially when there is a localised increase in viscosity at the phase boundary flattened slabs are only temporarily arrested in the transition zone and sink ultimately into the lower mantle the results offer a framework for understanding the variety in slab geometry revealed by seismic tomography

three dimensional geological modelling and multivariate statistical analysis of water chemistry data to analyse and visualise aquifer structure and groundwater composition in the wairau plain marlborough district new zealand summary concerns regarding groundwater contamination with nitrate and the long term sustainability of groundwater resources have prompted the development of a multi layered three dimensional 3d geological model to characterise the aquifer geometry of the wairau plain marlborough district new zealand the 3d geological model which consists of eight litho stratigraphic units has been subsequently used to synthesise hydrogeological and hydrogeochemical data for different aquifers in an approach that aims to demonstrate how integration of water chemistry data within the physical framework of a 3d geological model can help to better understand and conceptualise groundwater systems in complex geological settings multivariate statistical techniques e g principal component analysis and hierarchical cluster analysis were applied to groundwater chemistry data to identify hydrochemical facies which are characteristic of distinct evolutionary pathways and a common hydrologic history of groundwaters principal component analysis on hydrochemical data demonstrated that natural water rock interactions redox potential and human agricultural impact are the key controls of groundwater quality in the wairau plain hierarchical cluster analysis revealed distinct hydrochemical water quality groups in the wairau plain groundwater system visualisation of the results of the multivariate statistical analyses and distribution of groundwater nitrate concentrations in the context of aquifer lithology highlighted the link between groundwater chemistry and the lithology of host aquifers the methodology followed in this study can be applied in a variety of hydrogeological settings to synthesise geological hydrogeological and hydrochemical data and present them in a format readily understood by a wide range of stakeholders this enables a more efficient communication of the results of scientific studies to the wider community

in situ x ray diffraction study of post spinel transformation in a peridotite mantle implication for the 660 km discontinuity abstract we present the phase relations in anhydrous cao mgo feo al2o3 sio2 pyrolite to examine the influence of compositional difference between pyrolite and mg2sio4 on the post spinel phase transformation it is shown that in the pyrolite system the transformation occurs at about 0 5 gpa lower pressure relative to mg2sio4 we have carried out several in situ x ray diffraction experiments on ringwoodite to mg perovskite ferropericlase and backward transformations and found that post spinel transformation boundary can be expressed as p gpa 0 0005 t k 23 54 using the gold equation of state by tsuchiya t tsuchiya first principles prediction of the p v t equation of state of gold and the 660 km discontinuity in earth s mantle j geophys res 108 2003 doi 10 1029 2003jb002446 the interval for coexisting ringwoodite and mg perovskite was found to be 0 1 0 5 gpa the discrepancy between our data and the depth of the seismic discontinuity global average 654 km is about 20 km at 1850 k based on the results of in situ measurements we confirmed that the difference in chemical composition between pyrolite and mg2sio4 cannot modify the clapeyron slope of the post spinel transformation using experimental data and assuming the average mantle temperature 1850 k at 660 km we can account for only a half of variations in the depth of the 660 km discontinuity in subduction zones and at hot spots an additional explanation for the observed seismological variations at the 660 km discontinuity is required and may reflect influence of other minor components or volatiles

revision of fontes garnier s model for the initial 14c content of dissolved inorganic carbon used in groundwater dating abstract the widely applied model for groundwater dating using 14c proposed by fontes and garnier fg or 2 using different fractionation factors if the exchange process is dominated by soil co2 gas as opposed to solid carbonate mineral typically calcite an analysis of the fg however 14c0 will be slightly underestimated finally in carbonate systems undergoing complex geochemical reactions such as oxidation of organic carbon radiocarbon ages are best estimated by inverse geochemical modeling techniques

late quaternary environmental change and human impact around lake bolac western victoria australia the late quaternary history of the lake bolac region is reconstructed from sedimentary and pollen analysis of lake and swamp sequences and is supported by archaeological remains from lunette sediments freshwater deposits recovered from lake turangmoroke appear to date from the last glacial period when the vegetation was composed of herbfield and grassland subsequent dry conditions at the end of the pleistocene caused the deflation of some accumulated sediments on refilling the lake had become saline as moisture availability increased casuarina woodland dominated by allocasuarina verticillata became the regional vegetation cover domination by casuarina ended ca 8000 7000 yr bp probably as a result of rising saline ground water tables casuarinas were replaced to some degree by eucalypts augmented by the development of a riverine eucalyptus camaldulensis woodland swamp deposition commenced in the channel of neighbouring fiery creek at ca 4000 yr bp most likely as the result of a reduction in stream flow with decreased precipitation despite suggestions of significant impact on the vegetation by aboriginal people from other sites in southeastern australia there is no evidence of any alteration here from periods of occupation dated to around 13 000 yr bp and after 3500 yr bp the period of european occupation though is marked by significant changes in fire patterns reduced tree cover loss of floristic diversity increased erosion rates and salinity levels and decreased water levels journal ot quaternary science

microbial generation of economic accumulations of methane within a shallow organic rich shale although methane of bacterial origin is ubiquitous in marine and freshwater sediments economic accumulations of bacterial gases occur mainly at depths of several kilometres in tertiary basins that had high sedimentation rates1 2 here we present an integration of geochemical and isotopic data from gas and water extracted from the upper devonian antrim shale along the northern margin of the michigan basin which demonstrates that significant volumes of bacterial gas have been generated in organic rich shales at depths of less than 600 metres the antrim shale is mainly a self sourced reservoir in contrast to conventional gas deposits that have migrated from a source to a reservoir and has become one of the most actively exploited gas reservoirs3 in the united states the gas forming processes operating at shallow depths in the antrim shale are not unique4 and an understanding of these processes should lead to the identification and development of other economic non conventional gas deposits around the world

estimating 14c groundwater ages in a methanogenic aquifer this paper addresses the problem of 14c age dating of groundwaters in a confined regional aquifer affected by methanogenesis increasing ch4 concentrations along the groundwater flow system and 13c and 14c isotopic data for dissolved inorganic carbon dissolved organic carbon and ch4 clearly show the effect of methanogenesis on groundwater chemistry inverse reaction path modeling using netpath indicates the predominant geochemical reactions controlling the chemical evolution of groundwater in the aquifer are incongruent dissolution of dolomite ion exchange methanogenesis and oxidation of sedimentary organic matter modeling of groundwater 14c ages using netpath indicates that a significant part of groundwater in the alliston aquifer is less than 13 000 years old however older groundwater in the range of 15 000 23 000 years is also present in the aquifer this paper demonstrates that 14c ages calculated using netpath incorporating the effects of methanogenesis on the carbon pools provide reasonable groundwater ages that were not possible by other isotopic methods

lower mantle scattering profiles and fabric below pacific subduction zones abstract the earth s mantle is compositionally evolving principally through the process of mid ocean ridge basalt production 95 by lithospheric area but also by way of arc magmatism 5 and continental growth reymer a schubert g 1984 phanerozoic addition rate to the continental crust and crustal growth tectonics 3 63 77 rowley d b 2002 rate of plate creation and destruction 180 ma to present geol soc am bull 114 927 933 convection eventually must mix these products back into the mantle but the details of the mixing process are unknown we report here new observational data documenting the location of differentiated material in the present day lower mantle and scattering power profiles with depth small scale 10 km objects which efficiently scatter short period s waves are present in the mantle lying below the pacific ocean rim at depths between 1100 and 1800 km we also observe a reduction in scattering power with depth indicating that the objects represent bodies richer in differentiated basalt than the surrounding mantle the scattering objects appear to be deformed to various degrees and usually form clusters separated from each other by a distance of 100 to 200 km the clusters probably represent folds of the order of 100 km probably corresponding to early stage of mixing process because the scattering power does not increase with depth neither does a permanent barrier to flow exist in the mid mantle nor does the intrinsic density of basalt prevent re entrainment into mantle flow from the bottom of the mantle

south pacific hotspot swells dynamically supported by mantle flows the dynamics of mantle plumes and the origin of their associated swells remain some of the most controversial topics in geodynamics here we construct a numerical model of the mantle flow beneath the french polynesia region our study is based on a new regional seismic tomography model which high resolution allows obtaining information at the scale of plumes we find excellent correlations between the observed and the modeled dynamic swells between the modeled flow pattern and the active volcanism and between the buoyancy fluxes obtained from our numerical model and the ones deduced from the swells morphology these outstanding fits reveal for the first time that a direct link exists between the surface observations and mantle flows

origin of methane in the elk valley coalfield southeastern british columbia canada coalbead methane is part of the non conventional gas reservoirs and makes a significant contribution to gas production in some parts of the world initially it was assumed that coalbed methane was of thermogenic origin but most recent studies based on isotope and chemical data and taking into account the hydrogeology of the basin have demonstrated that secondary biogenic gases are formed in many coal bearing basins this study using a similar approach evaluated the origin of the gas in the elk valley coalfield located in british columbia canada isotope data in methane samples collected from testhole wells and piezometers show a range that varies from 51 8 to 65 4 and 303 to 415 for 13c and 2h respectively the 2h data which are among the most depleted data reported for coalbed methane have to be related to the very depleted 2h values of the groundwater 148 to 163 isotope and chemical data collected from dic show a trend of increasing 13c values 11 9 to 34 9 associated with an increase in dic concentration 216 to 1650 mg l the most 13c depleted dic and low dic waters are found in the shallow groundwater flow system representing conditions close to recharge areas while the most 13c enriched dic and high concentration dic waters are found in the discharge areas associated with a deep groundwater flow system the dic pattern which is typical for methanogenic aquifers and the isotope data obtained in methane samples clearly indicate that the gas found in the elk valley coalfield is mainly biogenic in origin this study reaffirms that an approach that combines an evaluation of the groundwater flow system the isotopic characterization and concentration pattern of the main carbon pools ch4 and dic and the isotopic characterization of the groundwater is needed to fully evaluate the origin of gases in coal basins