groundwater contamination from an inactive uranium mill tailings pile 2 application of a dynamic mixing model at riverton wyoming low ph process waters from an abandoned uranium mill tailings pile have been infiltrating into and contaminating the shallow water table aquifer the contamination process has been governed by transient infiltration rates saturated unsaturated flow as well as transient chemical reactions between the many chemical species present in the mixing waters and the sediments in the first part of this two part series white et al 1984 we presented field data as well as an interpretation based on a static mixing model as an upper bound we estimated that 1 7 of the tailings water had mixed with the native groundwater in the present work we present the results of numerical investigation of the dynamic mixing process the model dynamix dynamic mixing couples a chemical speciation algorithm phreeqe with a modified form of the transport algorithm trump specifically designed to handle the simultaneous migration of several chemical constituents the overall problem of simulating the evolution and migration of the contaminant plume was divided into three sub problems that were solved in sequential stages these were the infiltration problem the reactive mixing problem and the plume migration problem the results of the application agree reasonably with the detailed field data the methodology developed in the present study demonstrates the feasibility of analyzing the evolution of natural hydrogeochemical systems through a coupled analysis of transient fluid flow as well as chemical reactions it seems worthwhile to devote further effort toward improving the physicochemical capabilities of the model as well as to enhance its computational efficiency

the krasnouralsky profile in the middle urals russia a tomographic approach to vintage dss data abstract the middle urals region has been widely studied with geophysical methods over the past decades an integrated program is in progress to summarize this knowledge including modern reprocessing of controlled source seismic data this work is devoted to the krasnouralsky dss profile we applied modern tomography inversion algorithms in 2d and 2 5d on first break traveltime picks from an archive catalogue a number of initial models and various smoothing constraints were used to investigate the influence of starting models on the final model robustness and uncertainty of the recovered models were estimated with hypothesis testing and checkerboard tests the recovered velocity structure shows a thicker crust below the contact of the west uralian zone and the central uralian zone and below the tagil magnitogorsk zone deep high velocity anomalies on both sides of this zone are interpreted as crustal thinning or alteration of the crust by intrusions of mantle material our results suggest that it is worthwhile reinterpreting dss traveltime data with modern inversion techniques

modeling complex nonlinear geological processes abstract we review selected geological processes to which numerical modeling has been applied with the aim of describing some of the general approaches and applications of the modeling all of these examples involve multiphase fluid flow in some cases coupled with heat transport and phase changes first we describe modeling approaches to a human made geological system a potential underground radioactive waste repository next we describe recent advances in modeling two phase flow through random heterogeneous porous media we review recent modeling studies of fluid processes in magmatic systems especially focusing on melting and crystallization induced by magma chambers finally several research directions are suggested including improving our understanding of the linkage between small scale and field scale processes coupling across regimes e g surface water and ground water and further developments in the modeling of stochastic geological processes

preliminary results from a geophysical study across a modern continent continent collisional plate boundary the southern alps new zealand abstract the southern alps of south island new zealand is a young transpressive continental orogen exhibiting high uplift rates and rapid transcurrent movement a joint us nz geophysical study of this orogen was carried out in late 1995 and early 1996 to derive a three dimensional model of the deformation the measurements undertaken include active source and passive seismology magnetotelluric and electrical studies and petrophysics preliminary models for the active source seismic measurements across south island confirm in general terms a thickened crust under the southern alps a high velocity lower crustal layer and a major crustal discontinuity associated with the alpine fault the anisotropy in physical properties of the rocks of the plate boundary zone is clearly demonstrated in the preliminary results of laboratory seismic velocity measurements shear wave splitting and resistivity the mid crust under the southern alps coincides with a major electrical conductivity high which possibly corresponds to fluid in the crust the top lies at about 15 km close to the base of shallow seismicity east of the alpine fault offshore the marine reflection data have consistently imaged a reflective lower crust adjacent to south island these data are showing complex structure particularly off western and southeastern south island the complexity in structure high quality data and consistency in results from several techniques indicates that the south island experiment will contribute significantly to our knowledge of transpressive plate boundaries in particular and the continental lithosphere in general

a geochemical transport model for redox controlled movement of mineral fronts in groundwater flow systems a case of nitrate removal by oxidation of pyrite a one dimensional prototype geochemical transport model was developed in order to handle simultaneous precipitation dissolution and oxidation reduction reactions governed by chemical equilibria total aqueous component concentrations are the primary dependent variables and a sequential iterative approach is used for the calculation the model was verified by analytical and numerical comparisons and is able to simulate sharp mineral fronts at a site in denmark denitrification has been observed by oxidation of pyrite simulation of nitrate movement at this site showed a redox front movement rate of 0 58 m yr 1 which agreed with calculations of others it appears that the sequential iterative approach is the most practical for extension to multidimensional simulation and for handling large numbers of components and reactions however slow convergence may limit the size of redox systems that can be handled

the mohorovicic discontinuity beneath the continental crust an overview of seismic constraints abstract the seismic signature of the moho from which geologic and tectonic evolution hypotheses are derived is to a large degree a result of the seismic methodology which has been used to obtain the image seismic data of different types passive source earthquake broad band recordings and controlled source seismic refraction densely recorded wide angle deep seismic reflection and normal incidence reflection using vibroseistm explosives or airguns have contributed to the description of the moho as a relatively complex transition zone of critical importance for the quality and resolution of the seismic image are the acquisition parameters used in the imaging experiments a variety of signatures have been obtained for the moho at different scales generally dependent upon bandwidth of the seismic source this variety prevents the development of a single universally applicable interpretation in this way source frequency content and source and sensor spacing determine the vertical and lateral resolution of the images respectively in most cases the different seismic probes provide complementary data that gives a fuller picture of the physical structure of the moho and its relationship to a petrologic crust mantle transition in regional seismic studies carried out using passive source recordings the moho is a relatively well defined structure with marked lateral continuity the characteristics of this boundary change depending on the geology and tectonic evolution of the targeted area refraction and wide angle studies suggest the moho to be often a relatively sharp velocity contrast whereas the moho in coincident high quality seismic reflection images is often seen as the abrupt downward decrease in seismic reflectivity the origin of the moho and its relation to the crust mantle boundary is probably better constrained by careful analysis of its internal details which can be complex and geographically varied unlike the oceanic moho which is formed in a relatively simple well understood process the continental moho can be subject to an extensive variety of tectonic processes making overarching conclusions about the continental moho difficult speaking very broadly 1 in orogenic belts still undergoing compression and active continental volcanic arcs the moho evolves with the mountain belt 2 in collapsed phanerozoic orogenic belts the moho under the collapse structure was formed during the collapse often by a combination of processes 3 in regions having experienced widespread basaltic volcanism the moho can result from underplated basalt and basaltic residuum in precambrian terranes the moho may be as ancient as the formation of the crust in others precambrian tectonic and magmatic processes have reset it we note that seismic reflection data in phanerosoic orogens as well as from precambrian cratonic terranes often show thrust type structures extending as deep as the moho and suggest that even where crust and mantle xenoliths provide similar age of formation dates the crust may be semi allochothonous

recharge in karst and dune elements of a semi arid landscape as indicated by natural isotopes and chloride abstract the rates and mechanisms of local recharge in a semi arid environment have been investigated beneath two major landscape settings in the murray basin in south australia these were calcrete flats with sinkholes and sand dunes in adjacent landscape settings five minor settings were investigated and identified as undisturbed calcrete primary older sinkholes secondary younger sinkholes sand dunes with native vegetation and sand dunes with introduced pasture data from a limited series of boreholes were interpreted to suggest that recharge varied from in excess of 100 mm yr 1 for secondary sinkholes to less than 0 1 mm yr 1 beneath sand dunes with native vegetation the data suggest that recharge under sand dunes has increased by more than two orders of magnitude following clearing of the native vegetation 50 yr ago as 90 of an area of 10 000 km2 has been cleared this clearing has ensured that inflow of saline groundwater to the adjacent river murray will increase and in view of the amount of salt stored in both the unsaturated and saturated zones will continue for a very long time at sites where the inferred recharge is lowest profiles of the chloride concentration of soil water are consistent with the hypothesis that there is in excess of 50 000 yr recharge stored in the thick unsaturated zone some evidence for changes in recharge rate over this time scale is seen

crustal structure of the siberian craton and the west siberian basin an appraisal of existing seismic data abstract we present a digital model sibcrust of the crustal structure of the siberian craton sc and the west siberian basin wsb based on all seismic profiles published since 1960 and sampled with a nominal interval of 50 km data quality is assessed and quantitatively assigned to each profile based on acquisition and interpretation method and completeness of crustal model the database represents major improvement in coverage and resolution and includes depth to moho thickness and average p wave velocity of five crustal layers sediments and upper middle lower and lowermost crust and pn velocity maps and cross sections demonstrate strong crustal heterogeneity which correlates weakly with tectono thermal age and strongly with tectonic setting sedimentary thickness varies from 0 3 km in stable craton to 10 20 km in extended regions typical moho depths are 44 48 km in archean crust and up to 54 km around the anabar shield 40 42 km in proterozoic orogens 35 38 km in extended cratonic crust and 38 42 km in the west siberian basin average crustal vp velocity is similar for the sc and the wsb and shows a bimodal distribution with peaks at ca 5 4 km s in deep sedimentary basins and 6 2 6 6 km s in parts of the wsb and sc exceptionally high basement vp velocities 6 8 7 0 km s at the northern border between the sc and the wsb indicate the presence of magmatic intrusions and are proposed to mark the source zone of the siberian lip the cratonic crust generally consists of three layers and high velocity lowermost crust vp 7 4 km s is observed only locally pn velocities are generally 8 2 km s in the sc and wsb and abnormally high 8 6 8 9 km s around kimberlite fields we discuss the origin of crustal heterogeneity and link it to regional crustal evolution

the root of the urals evidence from wide angle reflection seismics abstract the existence of a crustal root beneath the urals which would deflect the position of the moho by some 20 km is still largely controversial a french russian project carried out a wide angle reflection seismic experiment across the middle urals to image the moho topography along a 175 km profile running approximately east west north of ekaterinburg new data show a 6 km moho deflection beneath the central part of the orogen the moho reflectivity is variable along the section with very sharp reflections beneath the russian platform 45 km depth and fainter attenuated signals in the root zone 51 km depth even if this crustal root is not as thick as indicated by some previous speculations it makes the urals the only palaeozoic orogen in the world to show such a peculiarity a major ultramafic overload in the upper crust would partly balance the crustal root in accordance with isostatic equilibrium we finally postulate that sharp wide angle reflections from the moho can be considered indicative of a layered lower crust this would apply to the russian platform which maybe gained this structuring during the ordovician extensional regime

the holocene labrador current changing linkages to atmospheric and oceanographic forcing factors the role of labrador current lc in providing freshwater to the north atlantic and hence modulating the atlantic meridional overturning circulation amoc has been debated with very few data this study provides the first data on the relative speed of the lc for the past 9 2 ka using mean size of the sortable silt of sediments as a proxy from a mid shelf basin in the western labrador sea lc speed progressively intensified from 9 2 5 ka during which two meltwater events had minor influence the lc was fastest between 5 ka and 3 1 ka and gradually weakened after 3 1 ka the mean size of the sortable silt data shows overall co variations with similar existing data from deep water areas of the greater north atlantic suggesting an overarching link that modulates changes in both the near surface and deep north atlantic a dynamical link between the lc and amoc vigor is hypothesized in which high meltwater discharge in the labrador sea oriented the subpolar gyre spg more north south meridional weakening the spg and thus decelerating the upper limb of the amoc conversely reduction in lc transport during the late holocene due to the greater export of sea ice oriented the spg more east west

quantification of unsaturated zone alteration and cation exchange in zeolitized tuffs at yucca mountain nevada usa abstract zeolitized horizons in the unsaturated zone uz at yucca mountain nevada usa are an important component in concepts for a high level nuclear waste repository at this site the use of combined quantitative x ray diffraction and geochemical analysis allows measurement of the chemical changes that accompanied open system zeolitization at yucca mountain this approach also provides measures of the extent of chemical migration that has occurred in these horizons as a result of subsequent cation exchange mass balance analysis of zeolitized horizons with extensive cation exchange drill hole uz 16 and with only minimal cation exchange drill hole sd 9 shows that al is essentially immobile although zeolitization occurred in an open system the mass transfer of constituents other than water is relatively small in initial zeolitization in contrast to the larger scales of cation exchange that can occur after zeolites have formed cation exchange in the clinoptilolite mordenite zeolitized horizons is seen in downward diminishing concentration gradients of ca mg and sr exchanged for na and to lesser extent k comparison with data from drill hole sd 7 which has multiple zeolitized horizons above the water table shows that the upper horizons accumulate ca mg and sr to such an extent that transport of these elements to the deepest uz zeolitized horizon can be blocked quantitative analysis of zeolite formation yields insight into processes that are implied from laboratory studies and modeling efforts but are otherwise unverified at the site such analysis also yields information not provided by or contradicted by some models of flow and transport the results include the following 1 evidence of effective downward flow through zeolitic horizons despite the low permeability of these horizons 2 evidence that alkaline earth elements accumulated by zeolites are mostly derived from eolian materials in surface soils 3 validation of the very effective operation of unsaturated zeolitic horizons as cation exchange barriers 4 independent support of models that indicate average water infiltration rates of 5 mm yr over the past 10 ma and 5 evidence that the presence or absence of cation exchange profiles can be used to identify those portions of the site where transport through the uz is concentrated this last point is relevant to repository design because a knowledge of where transport takes place can be used to advantage in defining the boundaries of a repository such that high flux portions of the site can be avoided

isostatic compensation for a portion of the southern appalachians evidence from a reconnaissance study using wide angle three component seismic soundings wide angle reflections generated by five controlled blasts and over 110 timed quarry blasts in the southern appalachians were used to test models for isostatic compensation of topography the profiles cross the appalachian gravity gradient and gravity low and sample the highest elevations within the orogen migration of p sv and sh reflections suggests that crustal thickness varies from 35 to 39 km within the coastal plain and 37 39 km within the carolina terrane it increases northwestward from 40 to 45 km across the inner piedmont and then thickens to 50 52 km along the southeastern flank of the blue ridge mountains crustal thickness within the blue ridge mountains ranges from 47 to 56 km receiver functions for broadband stations goga and mync show a similar pattern in crustal thickness assuming airy compensation the correlation between elevation and moho depth suggests a range of 50 150 kg m 3 for the density contrast between the crustal root and mantle the greatest moho depths are associated not with the tallest peaks but rather with the broadest portions of the mountain chain this observation is consistent with regional bending of the lithosphere however the planar basement surface suggests that the root either predates alleghanian thrusting and therefore is unrelated to the present topography or formed in response to some other mechanism bounds on curvature of the basement surface suggest a lower bound of 30 40 km for the effective elastic thickness of the lithosphere this is consistent with previous estimates for the southern appalachians based on analysis of gravity data

sedimentology and history of sediment sources to the nw labrador sea during the past glacial cycle abstract the paleoceanography and sediment dynamics of the northernmost labrador sea provides critical records of glacial history glacially dominated sedimentation and paleocirculation a reference core at 938 m on the se baffin slope was investigated with new oxygen isotope stratigraphy x ray fluorescence geochemistry and 18 14c ams dates and correlated to 14 regional deep water cores the reference core provides a paleoceanographic and sediment source record over the last 40 ka overlying a 3 m thick blocky mass transport deposit over mis 5 autochthonous sediment detrital carbonate rich sediment layers h0 h4 based on bulk geochemistry were derived principally from hudson strait shortly after h2 and h3 the shelf crossing cumberland sound ice stream supplied dark brown ice proximal stratified sediments minor supply of carbonate rich sediment from baffin bay allows chronologic integration of the baffin bay and labrador sea detrital carbonate records and implies an open seaway through davis strait the counterparts of h3 h4 and h5 events in the deep labrador basin are 4 10 m thick units of thin bedded carbonate rich mud turbidites from glacigenic debris flows on the hudson strait slope the behavior of the hudson strait ice stream changed through the last glacial cycle in h1 and h2 the ice stream retreated back across the shelf but did not deglaciate hudson bay in h3 h5 it remained at the shelf break long enough to supply thick turbidites and subsequent retreat after h4 and h5 deglaciated hudson bay the maximum extent of ice streams in hudson strait cumberland sound and lancaster sound was not synchronous

crustal evolution of the middle urals based on seismic reflection and refraction data abstract integration of seismic refraction and deep reflection data from the middle urals of central russia provides important new constraints on the structure of the uralian crust re analysis of the granit refraction profile and comparison with coincident reflection data from the esru profile shows a high velocity 7 6 7 8 km s root zone from c 45 to 55 km with low reflectivity beneath the urals we interpret this interval as crustal material consistent with previous russian interpretations of this velocity anomaly above this crustal root one of the principle features imaged on the esru profile is a thick zone 3 4 s twt of relatively strong reflectivity which may characterize the lower crust of the east european platform but is considerably shallower to the east at 8 12 s twt 25 37 km than in the west at 10 14 s twt 31 43 km reprocessing of 20 s records from the r 17 profile in the west siberian basin 315 km northeast of the esru profile reveals a similar pronounced lower crustal reflectivity between 11 14 s twt 34 43 km in the hinterland of the middle urals this lower crustal reflection fabric may represent a feature developed during collisional orogenesis or a younger property imparted through post orogenic extension future deep reflection profiling will be critical to address the continuity and accordingly the tectonic significance of this lower crustal reflectivity in the urals

crustal structure of the middle urals based on reprocessing of russian seismic reflection data summary reprocessed russian seismic reflection data combined with existing russian geological maps and seismic interpretations provide the basis for a revised tectonic interpretation of the upper crust in the middle urals the main uralian fault muf the principal suture of the urals separating the east european craton to the west from accreted terranes to the east is found to penetrate to depths of at least 18 km and perhaps much deeper with a uniform eastward dip of 35 after migration as the muf appears to truncate reflections in both the foreland and hinterland of the urals it is arguably one of the youngest structural features of the orogen basement rocks of the east european platform underthrust the suture and comprise the deep crust a minimum of 30 km east of the surface expression of the muf the tagil volcanic arc complex greater than 1000 km in length along strike comprises at least the upper 10 km of the crust east of the muf this terrane shallows eastwards where it appears to be truncated by the west dipping serov mauk fault based on correlation with surface geology the hinterland of the urals east of the muf is characterized by a previously unrecognized zone of discontinuous mid crustal reflectivity at depths of 14 16 km that is discordant with upper crustal reflections this mid crustal zone of reflectivity is interpreted to represent either a major subhorizontal structural detachment or a zone of magmatic intrusion

deep seismic survey images crustal structure of tornquist zone beneath southern baltic sea the tornquist zone is europe s longest tectonic lineament and bisects the continent in a nw se direction from the north sea off nw denmark to the black sea new deep seismic reflection and coinci

a unified view of craton evolution motivated by recent deep seismic reflection and refraction results summary an attempt is made to integrate recent continental seismic reflection refraction and geologic observations into a unified scheme of craton evolution 1 nascent continental crust of basaltic bulk composition is produced in island arcs as with oceanic crust moho in this setting lies within the magmatic edifice and corresponds to a downward transition from dominantly mafic cumulate rocks above to dominantly ultramafic cumulates below the petrologic crust mantle boundary lying 25 per cent deeper in the lithosphere has no seismic expression and corresponds to a depositional magmatic contact between cumulate ultramafic rocks above and residual mantle ultramafic tectonite below both contacts are presumably extensively disrupted by magmatic injection 2 island arcs are amalgamated into continents at collision zones delamination of the lower mafic ultramafic portion of the crust along with the mantle lithosphere during hard collisions acts as a mechanical refining process that pushes the bulk crust toward intermediate composition 3 subsequent extensional collapse of the overthickened crust together with thermal re equilibration of the lithosphere results in youthful stable continental crust which is 30 km thick with its top surface awash at sea level and has the bulk composition of andesite this crust characteristically exhibits extensional features half grabens in the upper portion and is prominently laminated in the lower portion due to the injection of modest amounts of basaltic magma in the form of sills during delamination the moho and petrologic base of the crust coincide in this setting and can correspond to either a ductile high strain zone or intrusive contact separating mafic intermediate composition material above from fertile mantle lherzolite below 4 subsequent cratonization is the cumulative effect of episodic injection of the crust by mafic magma at intervals of hundreds of myr as manifest by the ubiquitous overlapping dike swarms of the precambrian shields this results in net long term thickening of the crust by underplating shifts the bulk crust back toward mafic composition periodically produces a new deeper moho and petrologic crust mantle boundary that do not coincide and through repeated dike injection disrupts pre existing laminated reflectors the first magmatic injection event sweats out the light melting fraction in the pre existing andesitic crust producing voluminous granitic magmatism typified by the great proterozoic anorogenic granite rhyolite provinces subsequent injection events into refractory crust produce uplift with attendant erosional denudation of supracrustal sequences the cumulative result is shield type crust in which intermediate crustal levels are exposed over wide areas crustal thickness commonly exceeds 40 km average crustal velocity is somewhat higher than in younger stable crust and the crust is commonly complexly reflective diffractive throughout

activity diagrams for clinoptilolite susceptibility of this zeolite to further diagenetic reactions clinoptilolite is the predominant zeolite in diagenetically altered volcanic rocks at yucca mountain nevada having formed by posteruptive reactions of ground water with vitric tuffs in the pyroclastic deposits compositional variations of clinoptilolites in the fractured and zeolitized tuffs not presently in contact with ground water and the vulnerability of zeolites to burial diagenesis raise questions about the long term stability of clinoptilolite equilibrium activity diagrams were calculated for clinoptilolite solid solutions in the seven component system ca na k mg fe al si plus h sub 2 o employing available thermodynamic data for related minerals aqueous species and water stability fields are portrayed graphically assuming the presence of potassium feldspar saponite and hematite and using ranges of activities for sio sub 2 and al sup 3 defined by the saturation limits for several silica polymorphs gibbsite kaolinite and pyrophyllite the clinoptilolite stability field broadens with increasing atomic substitution of ca for na and k for ca reaches a maximum for intermediate activities of dissolved al and decreases with increasing temperature the thermodynamic calculations show that ground water of the sodium bicarbonate type is approximately in equilibrium at 25c with calcite and several zeolites including heulandite and calcic clinoptilolite mg rich clinoptilolites are stabilized in ground water depleted in ca sup 2 the activity diagramsmore indicate that prolonged diagenetic reactions with ground water depleted in al enriched in na or ca and heated by the thermal envelope surrounding buried nuclear waste may eliminate sorptive calcic clinoptilolites in fractured tuffs and underlying basal vitrophyre less

seasonal variability of the labrador current and shelf circulation off newfoundland 1 three dimensional finite element models were established for the newfoundland and labrador shelf to investigate climatological monthly mean wind and density driven circulation the model was forced using wind stresses from the national center for environmental prediction national center for atmospheric research reanalysis data prescribed at the sea surface large scale remote forcing determined from a north atlantic model monthly mean temperature and salinity climatology and m2 tide on the open boundary the model results were examined against various in situ observations moored current meter tide gauge and vessel mounted acoustic doppler current profiler data and satellite drift measurements and discussed together with literature information the seasonal mean circulation solutions were investigated in terms of relative importance of wind to density forcing for the labrador current the model results indicate significant seasonal and spatial variations consistent generally with previous study results and in approximate agreement with observations for the major currents the region is dominated by the equatorward flowing labrador current along the shelf edge and along the labrador and newfoundland coasts the labrador current is strong in the fall winter and weak in the spring summer the mean transport of the shelf edge labrador current is 7 5 sv at the seal island transect and 5 5 sv through the flemish pass the seasonal ranges are 4 5 and 5 2 sv at the two sections respectively density and wind driven components are both important in the inshore labrador current the density driven component dominates the mean component of the shelf edge labrador current while the large scale wind forcing contributes significantly to its seasonal variability

palaeozoic tectonic evolution of the middle urals in the light of the esru seismic experiments abstract a new compilation of deep seismic reflection data in combination with the results of recent geological and isotopic investigations provides the basis for significantly refined structural and evolutionary models of the middle urals many of the major structural boundaries observed at the surface e g main uralian thrust main uralian normal fault serov mauk fault prianitchnikova shear zone can be followed on the seismic reflection data to depths of 8 15 km only a few features can be traced through the horizontal to shallow dipping zones of middle crustal reflectivity that extend beneath much of the middle urals exceptions might be the deevo thrust and a newly discovered deep band of moderately dipping reflections beneath the west siberian basin that may represent the remnants of an ancient subduction zone the reflectivity of the lower crust and moho are similar beneath the hinterland of the urals and below the western part of the west siberian basin suggesting that in both places they have the same extensional origin accretion of various exotic terranes to the eastern margin of baltica during late palaeozoic time involved considerable shortening of the continental margin the accreted terranes e g tagil petrokamensk and alapaevsk arc complexes consist mostly of island arc material formed during mid and late palaeozoic time closely associated with the island arcs are several high grade metamorphic complexes e g salda and murzinka adui complexes that were exhumed during and after late palaeozoic convergence towards the end of the orogeny several north south trending strike slip faults e g sisert fault were active after the orogeny major periods of tectonism and magmatism in the middle urals resulted in the extrusion of the siberian trap basalts crustal stretching and or underplating and the formation of the west siberian basin the planet s largest intracontinental sedimentary basin finally a period of renewed thrust faulting often reactivating older faults led to the inversion of the mesozoic basins

compensation of paleozoic orogens a comparison of the urals to the appalachians abstract the urals and appalachians are two paleozoic mountain belts with similar geologic and morphologic features we combine geophysical bouguer gravity and deep seismic sounding and geological observations from the ural mountains to test whether the surficial similarities of these paleozoic orogens extend to include deep lithospheric structure and compensation mechanism we find the combined data suggest support of the mountains by a stiff continental slab which is depressed by an effective subcrustal load in addition to the topography as has been recently proposed for the appalachians our preferred model which fits the geophysical data and predicts the presence and shape of the ural foredeep to the west of the mountains requires eastward directed underthrusting of the russian platform behaving as an elastic plate more than 50 km thick it is unlikely that an elastic plate this stiff could have resulted from conductive cooling of a thermal plate only 125 km thick the weight of the existing mountains on such an elastic plate is insufficient to produce the deflection of the moho inferred from seismic and gravity data an additional load on the elastic plate may be provided by a buried mass of similar origin to surface outcrops of dense mafic and ultramafic rocks in the eastern urals alternatively the load may represent the effect of a shallowing of the moho east of the mountains which is a remnant of a buried passive continental margin seismic data and bouguer gravity anomalies suggest that the effect of the subsurface mass anomaly is at least as great as the present day topography and that the russian plate flexurally underthrusts the urals for more than 100 km we speculate that similar effective subsurface loads may exist at younger continental orogens but are obscured by the topographic load in less eroded mountain belts

a reactive transport model of neptunium migration from the potential repository at yucca mountain abstract characterization and performance assessment studies for the potential high level nuclear waste repository at yucca mountain have identified 2 3 7 np as a radionuclide of concern for the proposed repository to predict the migration of neptunium after a repository breach an understanding of the relevant hydrologic and geochemical processes is required the hydrologic flow in the unsaturated zone at yucca mountain is dependent on the infiltration rate the stratigraphy of the vadose zone and the heat generated by the decaying radioactive waste the geochemical processes that strongly affect 2 3 7 np migration include solubility limited release of 2 3 7 np from the near field environment aqueous speciation of neptunium into non sorbing carbonate hydroxy complexes and the sorbing npo 2 cation sorption of neptunium onto the zeolitic tuffs via an ion exchange mechanism and radioactive decay the finite element heat and mass transfer fehm code was used to investigate the coupled effects of chemical interactions and heat on neptunium transport from the potential repository to the water table the selective coupling method is introduced to solve these reactive transport problems the simulations indicate that in the absence of irreversible changes in the hydrologic and transport properties the heat pulse does not significantly affect the migration of neptunium as the time scale of heat pulse propagation is shorter than the time scales associated with neptunium release and migration water chemistry particularly ph calcium and sodium concentration significantly affect the retardation of neptunium by the zeolitic rocks between the repository and the water table

the moho depth map of the european plate summary the european plate has a 4 5 gy long and complex tectonic history this is reflected in the present day large scale crustal structures a new digital moho depth map is compiled from more than 250 data sets of individual seismic profiles 3 d models obtained by body and surface waves receiver function results and maps of seismic and or gravity data compilations we have compiled the first digital high resolution map of the moho depth for the whole european plate extending from the mid atlantic ridge in the west to the ural mountains in the east and from the mediterranean sea in the south to the barents sea and spitsbergen in the arctic in the north in general three large domains within the european plate crust are visible the oldest archean and proterozoic crust has a thickness of 40 60 km the continental variscan and alpine crust has a thickness of 20 40 km and the youngest oceanic atlantic crust has a thickness of 10 20 km

structural regularities in the lithosphere of continents and plate tectonics abstract two fundamental but competing earth science concepts have been under discussion in russia the first one that of endogenous regimes is based on the assumption that permanent vertical relationships or long term interactions between the crust and upper mantle control crustal evolution significant horizontal movements of the lithosphere as required by the second concept that of global plate tectonics would destroy these crust mantle interactions certain regular features of the crust and upper mantle support the endogenous regime concept and are difficult to explain in terms of conventional plate tectonics in particular the close correlation between near surface features and deep 400 km mantle inhomogeneities suggests that many geological structures are deeply rooted in the mantle moreover geophysical studies have failed to reveal a well defined and continuous asthenosphere at relatively shallow depths 100 km that would allow lithospheric plates to be transported over large distances and the rheology of the lithosphere itself is found to be sufficiently inhomogeneous as to cast doubt on the principle of thin rigid plates in contrast palaeomagnetic and other data require that horizontal movements of many near surface geological structures must have taken place to explain this apparent contradiction it is suggested here that the crust and its connected deep root are capable of gliding along one of the deep mantle phase transition zones with respect to the inner earth

microparticle concentration variations linked with climatic change evidence from polar ice cores the microparticle concentrations in three deep ice cores reveal a substantial increase in the concentration of insoluble particles in the global atmosphere during the latter part of the last major glaciation the ratio of the average particle concentration in the late glacial strata to that in the holocene strata is 6 1 for the core from dome c antarctica 3 1 for the core from byrd station antarctica and 12 1 for the core from camp century greenland whether this temporal correlation between increased atmospheric particle load and the lower surface temperatures is directly causal is unknown however the variations in these two parameters must be satisfactorily resolved in any successful hypothesis that addresses the causes of climatic change

deep structure of the urals region and its seismicity abstract this article deals with the problem of the seismicity of the urals region taking into account peculiarities of the deep structure ascertained by deep seismic investigations along profiles with a general extent of about 10 000 km the scheme of seismotectonic zoning of the urals and the adjacent territories was compiled on the basis of data generalization on the seismicity and some determined regularities of the earthquake epicentres distribution and peculiarities of the earth s crustal structure the extent of the middle urals region with abnormal seismicity was determined three regions of abnormal seismicity were determined additionally the polar urals the prevolga the tyumen ishym regions within these regions the seismogenic zones were marked

freshwater sources to the coastal ocean off northeastern north america evidence from h2 18o h2 16o oxygen isotope h218o h216o salinity data identify freshwater sources along the northeastern north american continental margin the oxygen isotope 18o salinity s properties of various water types are distinguished sea ice formation on the labrador shelf is shown to influence 18o s values it is estimated that 2 3 m of freshwater is extracted from the water column to form sea ice it is hypothesized that waters on the scotian shelf gulf of maine and the middle atlantic bight are composed of slope water diluted by an upstream low salinity source this upstream source is a mixture of brine enriched labrador shelf water and st lawrence river water the 18o value of the apparent freshwater component 18os 0 of waters on the scotian shelf and farther south is 20 which has been used to suggest a sole high latitude freshwater source we show instead that the st lawrence river contributes 35 of the freshwater on the scotian shelf in agreement with the physical oceanographic evidence the remaining freshwater is supplied by high latitude rivers dominated by arctic runoff finally the isotope evidence identifies baffin bay as an important pathway by which freshwater from the arctic ocean can reach the labrador sea

the crustal structure of central east greenland ii from the precambrian shield to the recent mid oceanic ridges we present a 3 d crustal model of the east greenland fjord region between 69 n and 74 n the model covers the precambrian shield and the caledonian orogenic belt the adjoining devonian and mesozoic basins the continent ocean transition and the cenozoic oceanic areas as far as the kolbeinsey and the mohns mid oceanic ridges existing seismic models of the crustal structure are extrapolated into adjacent areas using 3 d gravity modelling for this purpose we compile a new regional scale bouguer anomaly map the precambrian shield west of the caledonian orogen approximately west of 32 w shows a mean thickness of 35 km with only small scale undulations this thickness is at the lower limit of the global range in shield thickness the caledonian orogen exhibits a pronounced mountain root with overall crustal thicknesses up to 51 km beside the urals the east greenland caledonides are one of the two palaeozoic mountain belts where a crustal root has preserved to the present day continuation of the crustal model to the east beyond the continent ocean transition yielded thicknesses of the crystalline oceanic crust from 9 km near the kolbeinsey ridge to 3 km west of the mohns ridge differences in the thermal structures of the old continental and the young oceanic lithosphere are responsible for the low density mantle beneath the oceanic crust which is also demonstrated by 3 d gravity modelling

structure of the lithosphere below the southern margin of the east european craton ukraine and russia from gravity and seismic data abstract the present study was undertaken with the objective of deriving constraints from available geological and geophysical data for understanding the tectonic setting and processes controlling the evolution of the southern margin of the east european craton eec the study area includes the inverted southernmost part of the intracratonic dnieper donets basin ddb donbas foldbelt df its southeastern prolongation along the margin of the eec the sedimentary succession of the karpinsky swell ks the southwestern part of the peri caspian basin pcb and the scythian plate sp these structures are adjacent to a zone along which the crust was reworked and or accreted to the eec since the late palaeozoic in the bouguer gravity field the southern margin of the eec is marked by an arc of gravity highs correlating with uplifted palaeozoic rocks covered by thin mesozoic and younger sediments a three dimensional 3d gravity analysis has been carried out to investigate further the crustal structure of this area the sedimentary succession has been modelled as two heterogeneous layers mesozoic cenozoic and palaeozoic in the analysis the base of the sedimentary succession top of the crystalline precambrian basement lies at a depth up to 22 km in the pcb and df ks areas the residual gravity field obtained by subtracting the gravitational effect of the sedimentary succession from the observed gravity field reveals a distinct elongate zone of positive anomalies along the axis of the df ks with amplitudes of 100 140 mgal and an anomaly of 180 mgal in the pcb these anomalies are interpreted to reflect a heterogeneous lithosphere structure below the supracrustal sedimentary layers i e moho topography and or the existence of high density material in the crystalline crust and uppermost mantle previously published data support the existence of a high density body in the crystalline crust along the ddb axis including the df caused by an intrusion of mafic and ultramafic rocks during late palaeozoic rifting a reinterpretation of existing deep seismic sounding dss data on a profile crossing the central ks suggests that the nature of a high velocity density layer in the lower crust crust mantle transition zone is not the same as that of below the df rather than being a prolongation of the ddb df intracratonic rift zone the present analysis suggests that the ks comprises at least in part an accretionary zone between the eec and the sp formed after the palaeozoic

a temporal stable isotopic δ18 o δd d excess comparison in glacier meltwater streams taylor valley antarctica in this paper we describe the importance of hyporheic dynamics within andersen creek and von guerard stream taylor valley antarctica from the 2010 11 melt season using natural tracers water collection started at flow onset and continued with weekly hyporheic zone sampling the water 18o and d values were isotopically lighter in the beginning and heavier later in the season d excess measurements were used as an indicator of mixing because an evaporative signature was evident and distinguishable between two primary end members glacier meltwater and hyporheic zone hyporheic zone influence on the channel water was variable with a strong control on streamwater chemistry except at highest discharges this work supports previous research indicating that von guerard stream has a large widespread hyporheic zone that varies in size with time and discharge andersen creek with a smaller hyporheic zone displayed hyporheic zone solute interaction through the influence from subsurface hypersaline flow overall the evolution of taylor valley hyporheic zone hydrology is described seasonally in mid december the hyporheic zone is a dynamic system exchanging with the glacier meltwater in the channel and with diminishing flow in january the hyporheic zone drains back into the channel flow also impacting stream chemistry this work adds new information on the role of hyporheic zone stream interaction in these glacier meltwater streams

numerical models of ductile rebound of crustal roots beneath mountain belts crustal roots formed beneath mountain belts are gravitationally unstable structures which rebound when the lateral forces that created them cease or decrease significantly relative to gravity crustal roots do not rebound as a rigid body but undergo intensive internal deformation during their rebound and cause intensive deformation within the ductile lower crust 2 d numerical models are used to investigate the style and intensity of this deformation and the role that the viscosities of the upper crust and mantle lithosphere play in the process of root rebound numerical models of root rebound show three main features which may be of general application first with a low viscosity lower crust the rheology of the mantle lithosphere governs the rate of root rebound second the amount of dynamic uplift caused by root rebound depends strongly on the rheologies of both the upper crust and mantle lithosphere and third redistribution of the rebounding root mass causes pure and simple shear within the lower crust and produces subhorizontal planar fabrics which may give the lower crust its reflective character on many seismic images

the southern urals decoupled evolution of the thrust belt and its foreland a consequence of metamorphism and lithospheric weakening an analysis is presented of the mechanisms of tectonic evolution of the southern part of the urals between 48n and 60n in the carboniferous triassic a low tectonic activity was typical of the area in the early carboniferous after closure of the uralian ocean in the late devonian a nappe 10 15 km thick overrode a shallow water shelf on the margin of the east european platform in the early late carboniferous it is commonly supposed that strong shortening and thickening of continental crust result in mountain building however no high mountains were formed and the nappe surface reached the altitude of only 0 5 km no high topography was formed after another collisional events at the end of the late carboniferous in the second half of the early permian and at the start of the middle triassic a low magnitude of the crustal uplift in the regions of collision indicates a synchronous density increase from rapid metamorphism in mafic rocks in the lower crust this required infiltration of volatiles from the asthenosphere as a catalyst a layer of dense mafic rocks 20 km thick still exists at the base of the uralian crust it maintains the crust up to 60 km thick at a mean altitude 0 5 km the mountains 1 5 km high were formed in the late permian and early triassic when there was no collision their moderate height precluded asthenospheric upwelling to the base of the crust which at that time was 65 70 km thick the mountains could be formed due to delamination of the lower part of mantle root with blocks of dense eclogite and or retrogression in a presence of fluids of eclogites in the lower crust into less dense facies the formation of foreland basins is commonly attributed to deflection of the elastic lithosphere under surface and subsurface loads in thrust belts most of tectonic subsidence on the uralian foreland occurred in a form of short impulses a few million years long each they took place at the beginning and at the end of the late carboniferous and in the late permian rapid crustal subsidence occurred when there was no collision in the urals furthermore the basin deepened away from thrust belt these features preclude deflection of the elastic lithosphere as a subsidence mechanism to ensure the subsidence a rapid density increase was necessary it took place due to metamorphism in the lower crust under infiltration of volatiles the absence of flexural reaction on the uralian foreland on collision in thrust belt together with narrow wavelength basement deformations under the nappe indicate a high degree of weakening of the lithosphere such deformations took also place on the uralian foreland at the epochs of rapid subsidences when there was no collision in thrust belt

the main features of the interface between the crust and the upper mantle in the middle urals in the vicinity of the deep drillhole sg 4 abstract analysis of both p and s wave seismic data from the middle urals supports the existence of a multi layered crust mantle transition zone and a deep crustal root along the central axis of the urals data from deep seismic sounding dss nuclear explosions rubin i and quartz quarry blasts from industrial sources and wide angle experiments krasnouralsky and uwars are integrated to form the basis for this study the crust mantle transitional complex begins in the eastern part of the pre uralian foredeep where it consists of relatively thin layers thickness 3 5 km with alternating high and low velocity layers toward the axis of the urals the transition zone thickens to 10 15 km beneath the tagil arc before thinning toward the east uralian zone the average interval p wave velocity for the transition zone varies from 7 3 7 8 km s the thickness of the crust is found to reach a maximum of 55 60 km in the vicinity of the super deep borehole sg4 in the area of sg 4 the moho shallows from the tagil zone west to the central urals uplift and western urals fold zone the upper mantle is characterized by a nearly uniform velocity of 8 5 km s

on thermohydrologic conditions near high level nuclear wastes emplaced in partially saturated fractured tuff 2 effective continuum approximation this paper presents an effective continuum approximation for modeling of fluid and heat flow in fractured porous media the approximation is based on the thermohydrologic behavior observed in detailed simulations with explicit consideration of fracture effects see the companion paper part 1 the crucial concept in the development of an effective continuum approximation is the notion of local thermodynamic equilibrium between rock matrix and fractures where applicable it provides a substantial simplification of the description of fluid and heat flow in fractured porous media we derive formulas for effective continuum characteristic curves relative permeabilities and capillary pressures in terms of the properties of fracture and matrix continua respectively numerical simulations demonstrate that under favorable conditions the effective continuum approximation closely matches predictions obtained from an explicit modeling of fracture effects it is also demonstrated that the approximation breaks down under unfavorable conditions very tight rock matrix a simple criterion for the applicability of an effective continuum approximation is derived from consideration of diffusive processes a quantitative evaluation shows the criterion to be consistent with results of our numerical simulations