one kilometre thick ultramylonite sierra de quilmes sierras pampeanas nw argentina abstract we describe a 1 km thick ultramylonite forming the high strain base of the 3 5 km thick el pichao shear zone in the sierra de quilmes this shear zone thrusted granulite facies migmatites onto amphibolite facies rocks during the 470 ma famatinian orogeny strain grades upwards from ultramylonites to weakly sheared migmatites across the 3 5 km zone and the mylonitic rocks define a geochemical field narrower than the protolith suggesting they underwent mixing and homogenization through shearing ultramylonites this thick are uncommon the width of a shear zone in the absence of significant compositional rheological contrasts controlling strain localization is controlled by the balance between shear heat generation and diffusion under typical crustal conditions a strain rate of 10 12 s 1 is required to form a 1 km thick ultramylonite and this is achieved when large movement velocities are imposed across the shear zone we postulate that the el pichao shear zone and its thick ultramylonite accommodated a significant fraction of convergence velocities driving the orogeny and that the wide mylonitic shear zones characteristic of the cambrian ordovician deformation of the sierras pampeanas result from the convergent movement being taken up by only a few active major shear zones

isotope data from ice station weddell implications for deep water formation in the weddell sea helium isotope data 3he 4he ratios and 4he concentrations and h218o h216o ratios obtained from stations occupied during the drift of ice station weddell february to june 1992 are used together with hydrographic data to study formation of deep and bottom water in the western weddell sea the data indicate deep and bottom water formation along the entire track of the ice station 71 4 to 65 8 s 53 w ice shelf water isw seems to contribute significantly to the formation of weddell sea deep water wsdw and weddell sea bottom water wsbw in the southern part of the drift track toward the north the fraction of isw contained in wsdw wsbw decreases this trend is overlaid by high isw fractions in the deep and bottom waters found in the vicinity of the larsen ice shelf the fraction of western shelf water wsw in wsbw shows the opposite trend increasing from south to north the combined fraction of isw and wsw in waters with potential temperatures below 0 c is about 20 corresponding to a roughly 200 m thick layer overall wsw seems to contribute approximately 2 to 3 times more water than isw to the water column below the 0 c isotherm using the estimated flow of isw over the sill north of the filchner depression of 1 sv foldvik et al 1985a together with the ratio of wsw plus winter water ww to isw we calculate a value of about 5 sv for the formation rate of wsbw with a potential temperature of 0 7 c about one third of this flux represents near surface waters wsw ww which have recently been equilibrated with the atmosphere whereas pure isw contributes about 10

comment one kilometre thick ultramylonite sierra de quilmes sierras pampeanas nw argentina by m a finch r f weinberg m g fuentes p haslova and r becchio journal of structural geology 72 2015 33 54

a dual porosity model for water level response to atmospheric loading in wells tapping fractured rock aquifers a fractured rock aquifer may be viewed as a permeable fracture network embedded within a less permeable porous matrix this permeability contrast gives rise to distinct pressure fields in the pore space and fractures and therefore to a response to atmospheric loading different from that of nonfractured porous media assuming that fracture sizes and orientations are uncorrelated and sufficiently random to ensure homogeneous and isotropic elastic behavior of the rock mass at the continuum scale an effective stress model proposed by tuncay and corapcioglu 1995 is used to develop a linear elastic stress strain relationship for dual porosity media elastic constants of the fractured rock mass required by the model are estimated using theoretical relations derived by budiansky and o connell 1976 the stress strain relationship and the coupled continuity equations for flow in deformable fractured media are combined to derive expressions for the undrained static confined barometric efficiency of a dual porosity medium two limiting cases are considered the initial instantaneous pressure response in the pore space and fractures due to a change of confining stress and the later stage of pressure equilibrium between the two phases the dual porosity response model developed here may be used to characterize hydraulic properties in fractured aquifers including low porosity and low permeability media the model is evaluated on water level hydrograph data from a borehole tapping fractured volcanic rocks water level and barometric data are supplemented by independent measurements of matrix porosities fracture spacing and rock elastic properties allowing an assessment of total porosity and specific storage at the site for the observed static confined barometric efficiency of 0 78 the instantaneous pressure response model yields plausible values for both parameters

tectono metamorphic evolution of a convergent back arc the famatinian orogen sierra de quilmes sierras pampeanas nw argentina

seepage into a mountain tunnel and rain infiltration abstract to clarify the processes governing recharge of rainwater into an unconfined aquifer in a mountain basin the seepage rate of water into a mountain tunnel was monitored continuously between may 1988 and december 1991 in yura wakayama western japan the electrical conductivity and ionic composition of the seepage water was also measured regularly from june 1989 the mountain is composed of fractured sedimentary rocks such as sandstones and cherts seepage appeared only at specific locations on the roof of the tunnel seepage was measured through overlying sandstones of 10 m depth and cherts of 5 m depth time variations in the discharge suggested that seepage is formed both by rapid flow and basic flow components which correspond to the so called fissure flow and matrix flow this was confirmed by analysis of time variations in the concentration of chemical species in the seepage water fissure flow contributes the initial increment of seepage discharge immediately after the occurrence of rainfall and its velocity for sandstone can be represented by a function only of water content n is constant and larger in winter than in summer but n remains constant at approximately two infiltration time in fissures through the base of the cherts is negligible compared with that through the overlying soil layer whereas matrix flow through sandstones persists through the year for cherts it disappears within a week after rainfall events and its decay is dependent on the seasonal magnitude of evapotranspiration the behavior of the matrix flow for sandstones can be analyzed through a kinematic wave model as can the fissure flow

repeated cfc sections at the greenwich meridian in the weddell sea 1 repeated observations of the tracer chlorofluorocarbon 11 cfc 11 for a section along the greenwich meridian from antarctica 70 s to about 50 s are presented for the period 1984 1998 the cfc sections display a highly persistent pattern a middepth cfc minimum in the central weddell sea is bounded laterally by elevated levels of dissolved cfcs at the southern margin of the weddell basin and by a column of elevated cfc concentrations around 55 s near to the northern margin part of the latter column covers waters of the antarctic circumpolar current which indicates that a moderate portion of these waters was ventilated in the weddell sea deep cfc maxima adjoining the southern and northern margins of the weddell basin indicate advective cores of recently ventilated waters the southern core supports previous notions of deep water import into the weddell sea from the east for all deep and bottom waters the portions ventilated on the cfc timescale 50 years are small effective initial cfc saturations for these portions are estimated to be between 60 and 70 using in part new data from off the filchner ronne ice shelf for various cfc features along the section mostly advective cores ventilated fractions and mean ages of these fractions were obtained with error limits the procedure was to fit an age distribution of a prescribed form to cfc 11 time series for these features constructed from the various realizations of the cfc section the ages are between 3 and 19 years and the ventilated fractions range between 6 and 23 indicating a rather limited ventilation of the interior weddell sea subsurface layer waters on the cfc timescale it is shown that the concurrent cfc 12 data provide little additional information the work demonstrates a high information content of repeated tracer observations and encourages similar approaches also in other ocean regions

a lumped parameter model of groundwater influx to a mine adit in mountainous terrain 1 acidic and metal laden drainage from the portals of abandoned mines is a serious environmental problem in wet mountainous regions where steep hydraulic gradients ensure that fresh recharge waters are continuously flushed through the workings hydrogeological characterization of these sites is hampered by their geological complexity and their frequent inaccessibility this paper presents a material balance model for the groundwater capture zone associated with influx to a mountainside adit the model can be used to estimate bulk hydraulic properties of the rock surrounding an adit from hydrograph data commonly recorded at its portal this application is illustrated using data from the myra falls mining camp vancouver island british columbia by simultaneously fitting base flow recession slopes for hydrographs of discharge water table elevation and head in an underground borehole the model yields plausible and well constrained estimates of hydraulic conductivity porosity skin factor and hydraulic gradient

ordovician back arc foreland and ocloyic thrust belt development on the western gondwana margin as a response to precordillera terrane accretion 1 the famatina belt southern central andes records a circa 470 m y shortening episode ocloyic orogeny affecting the peri gondwanan back arc basin in response to the accretion of the precordillera terrane collision created distinct features across and along the margin some of which persisted into the present andean structure from east to west the ocloyic deformation is recorded across the telescoped region of famatina represented by 1 an east vergent fold thrust belt evftb involving a major angular unconformity between early and middle ordovician rocks 2 a highly deformed volcano sedimentary belt and 3 an east vergent ductile shear zone affecting famatinian granites axis attitudes of ordovician refolded anticlines in the evftb show west east tectonic transport in agreement with kinematics of ocloyic high strain belts indicating shortening orthogonal to the present pacific margin eastward displacement of the ordovician volcanic arc at 27 s latitude together with a documented sinistral slip zone across the proto andean margin suggests tectonic indentation

physical and geochemical properties across the atlantic pacific water mass front in the southern canadian basin temperature salinity nutrients oxygen and halocarbon data collected in the arctic ocean reveal a frontal structure previously unrecognized in the hydrography of the canadian basin samples were collected on a 1300 km section extending from the beaufort sea in the canada basin to the east siberian sea in the makarov basin these data collected in 1993 aboard the ccgs henry larsen reveal a lateral boundary between water masses of atlantic and pacific origin the term water mass assembly is introduced to describe the basic arrangement or vertical stacking of water masses found in the arctic ocean recognizing that water mass components within each assembly may differ from basin to basin using historical data two primary water mass assemblies are defined each consisting of three layers an upper layer an atlantic layer and a deep layer these two assemblies are marked by important differences one assembly here defined as the western arctic wa assembly is characterized by an upper layer of relatively fresh high nutrient water of pacific origin below this by an atlantic layer with a core temperature generally below 0 5 c and finally by a deep layer of higher salinities and colder temperatures about 0 5 c than found in the overlying atlantic layer the second assembly here defined as eastern arctic ea assembly is characterized by the absence of pacific water in the upper layer below this by an atlantic layer core as warm as 2 to 3 c and by a colder about 0 9 c deep layer because the presence or absence of pacific origin water is a key characteristic distinguishing the two assemblies we will refer to the water mass boundary between the two assemblies as the atlantic pacific front earlier research indicated that water masses in the arctic ocean were separated by a front above the lomonosov ridge into the canadian and eurasian basins although all larsen 93 stations from the canada basin a1 d1 display classic wa assembly characteristics the makarov basin station e1 shows ea assembly characteristics in the upper and atlantic layers and a wa assembly deep layer this suggests a relocation in the position of the atlantic pacific boundary away from the lomonosov ridge further larsen 93 data show the transition region between the atlantic and deep layers is fresher in the makarov basin than corresponding water in either the canada or eurasian basins implying a source of cold low salinity water perhaps from the laptev and east siberian shelves the front separating these two assemblies lies above the mendeleyev ridge and is marked by large lateral gradients in all measured properties in particular the penetration of anthropogenic halocarbons is 2 to 3 times deeper in the makarov basin than in the canada basin implying enhanced rates of ventilation this suggests that direct exchange between the canadian and eurasian basins has occurred recently near the perimeter and that physical and chemical properties including contaminants may have been transported by boundary currents more quickly from one basin to the other

tracer dating and ocean ventilation the interpretation of transient tracer observations depends on difcult to obtain information on the evolution in time of the tracer boundary conditions and interior distributions recent studies have attempted to circumvent this problem by making use of a derived quantity age based on the simultaneous distribution of two complementary tracers such as tritium and its daughter helium 3 the age is defined with reference to the surface such that the boundary condition takes on a constant value of zero we use a two dimensional model to explore the circumstances under which such a combination of conservation equations for two complementary tracers can lead to a cancellation of the time derivative terms an interesting aspect of this approach is that mixing can serve as a source or sink of tracer based age we define an idealized ventilation age tracer that is conservative with respect to mixing and we explore how its behavior compares with that of the tracer based ages over a range of advective and diffusive parameters transient tracers such as tritium and tritiugenic helium 3 chlorofiuorocarbons especially cfc 11 and cfc 12 and radiocarbon produced by nuclear bomb tests have entered the oceans primarily during the past 30 years the inherent time scale of these tracers matches very well typical time scales for thermocline ventilation as well as other important oceanic processes such as deep water formation they have been used with some success to study the time scales of thermocline ventilation e g sarrniento 1983 jenkins 1987 and oxygen utilization rates our e g jenkins 1977 1980 1982 1987 as well as other processes such as equatorial upwelling rates broecker et al 1978 quay et al 1983 wunsch 1984 and transport of upper north atlantic deep water weiss et al 1985 the problem of coping with the nonsteady state aspect of these tracers has been dealt with in many ways few of them truly satisfactory for example rooth and ostlund 1972 chose to estimate the diapycnic diffusivity in a region where there was some evidence that the tracer distributions were approximately in steady state at the time of their measurements wunsch 1984 used a similar steady state assumption in his study of equatorial upwelling using bomb radiocarbon such an argu ment cannot be applied in most regions of the ocean however indeed one can question whether it applies even in the above situations therefore one generally would expect that it would be necessary to know something about the evolution of the tracer concentration in time as well as the time history of the boundary conditions for that tracer over the same span of time for example sarrniento s 1983 tritium box model of the thermocline solved the conserva tion equation for the period of time between 1952 before nuclear bomb tests had injected a significant amount of tritium into the oceans and 1972 when a single realization of the tracer field was obtained by a series of field studies the surface concentration time history of dreisigacker and roether 1978 was used as a boundary condition such an l now at deutsche forschungs und versuchasanstalt ftir luft

unconfined groundwater flow calculation into a tunnel abstract unconfined flow of groundwater into a tunnel is analyzed by a numerical model the model is based on the finite element method for the solution of nonsteady groundwater flow with a free surface the numerical results are compared with those obtained from analytical approximations to be in the same order of magnitude these results are used to estimate the rate of water inflows during tunnel construction

the interpretation of pump test data from a disused underground mine abstract a pump test was carried out in a disused underground mine water was extracted from surrounding aquifers through the network of old workings comprising the mine because of the intricacy of these workings the unknown amount of water storage associated with them the heterogeneous nature of the aquifer with which they are connected and the dependence of pump rate on water level the use of conventional methods of pump test interpretation was inappropriate hence a mathematical model incorporating linear flow sink storage and a connection to the regional groundwater regime is postulated the equation for water movement within this model is solved in the laplace transform domain and a fast efficient method of numerical inverse laplace transformation is presented model parameters are then estimated by least squares inversion and these estimates are used to make predictions of long term inflow to the mine

renewal and circulation of intermediate waters in the canadian basin observed on the scicex 96 cruise during the summer of 1996 the nuclear submarine uss pogy occupied a line of stations extending through the middle of the canadian basin between about 88 n 44 w lomonosov ridge and about 78 n 144 w center of the canada basin ctd niskin bottle casts extending to 1600 m were carried out at eight stations providing the first high quality temperature salinity cfc tritium and 3he data obtained from this region although xctd data had previously been collected in this region these data along with data from stations at the basin boundary to the south and west reveal the presence of well ventilated intermediate water beneath the halocline in the center of the canada basin indicating renewal times of the order of 1 2 decades the least ventilated intermediate water was observed at the northern end of the canada basin along the southern flank of the alpha ridge intermediate water is derived from the atlantic ocean and enters the arctic ocean through fram strait and the barents sea it flows around the arctic basins in boundary currents and splits in the eastern amundsen basin with one branch crossing the lomonosov ridge and flowing along the east siberian continental slope and the other flowing along the eurasian flank of the lomonosov ridge from the 1996 scientific ice expedition scicex 96 observations we conclude that the branch that flows along the east siberian continental slope transports this water to the chukchi rise where it apparently enters the central canada basin with some flow continuing along the boundary to the southern canada basin the fram strait branch water mixes extensively with waters from the canadian basin during its transit along the east siberian continental slope being diluted by a factor of about 5 by the time it reaches the central canada basin the barents sea branch water does not undergo such extensive mixing and is diluted by a factor of only about 2 when it reaches the central canada basin

on the use of carbon tetrachloride as a transient tracer of weddell sea deep and bottom waters antarctic bottom waters have long been known to be a mixture of circumpolar deep water and shelf water recent observations show that in the antarctic bottom waters of the scotia sea and northern weddell sea the ratios of carbon tetrachloride ccl4 to chlorofluorocarbons cfc 11 12 are inconsistent with the ratios observed in the surface layer of the weddell sea this is the result of a deficit of ccl4 in the bottom waters and renders the compound unsuitable for use as a transient tracer from which apparent ages can be derived directly the summer near surface temperature minimum of antarctic surface water exhibits a similar inconsistency demonstrating that ccl4 can be removed from cold waters with high oxygen levels probably through a biological process it is inferred that shelf water features a similar ccl4 deficit which is transferred to the new antarctic bottom waters upon formation accounting for the observed deep ccl4 deficit

a first study of sf6 as a transient tracer in the southern ocean abstract halogenated transient tracers such as the chlorofluorocarbons cfc 11 cfc 12 and cfc 113 are commonly used in oceanographic studies these compounds enter the ocean via the atmosphere and their transient atmospheric concentrations make them valuable as oceanic tracers the trends of rapidly rising atmospheric concentrations of these tracers are however broken and the oceanic signal becomes increasingly more difficult to decipher there is a need for a new transient tracer to complement the existing suit of tracers especially for recently ventilated water masses one compound that looks promising in this respect is sulphur hexafluoride sf 6 an inert gas whose atmospheric concentration is rising rapidly in this paper the use of sf 6 as a transient tracer in recently ventilated waters is discussed and the method for determination of sf 6 in seawater is described tracer data from a section in the atlantic sector of the southern ocean along 6 e from 60 s to 40 s occupied during january 1998 are presented the antarctic polar front found close to 50 s was studied with a densely sampled section down to 400 m depth and sf 6 cfc 12 ratios are used to deduce ventilation ages and dilution factors a comparison of apparent ages derived from a variety of tracers is presented together with the uncertainties in these estimates this work demonstrates that sf 6 is a useful and valuable transient tracer for waters ventilated during the last 20 years

anthropogenic chlorofluoromethanes in the greenland and norwegian seas the concentrations of two industrially produced chlorofluoromethanes ccl3f f 11 and ccl2f2 f 12 have been measured in the water column and in the marine atmosphere of the greenland and norwegian seas measurable concentrations of these two chlorofluoromethanes have penetrated to the deep basins of both of these regions and the general characteristics of their vertical distributions are similar to those of the bomb produced radioisotopes injected into the atmosphere on a similar time scale the data have been fitted to a time dependent box model based on deep convective mixing in the greenland sea and lateral exchange between the deep basins the model calculations for the two chlorofluoromethanes in the greenland sea give similar results with a time scale for deep convection of about 40 years the time scale for lateral mixing between the deep greenland sea and the deep norwegian sea is estimated to be 20 to 30 years although the agreement between the calculations for the two chlorofluoromethanes is limited by analytical uncertainties at the low concentrations found in the deep norwegian sea and by uncertainties in the model assumptions

flow toward storage tunnels beneath a water table 1 two dimensional flow a system of parallel tunnels is excavated in saturated rock of low permeability for storing oil or lpg in order to contain the product permanent water inflow has to be maintained in absence of recharge this flow causes a continuous drop of the water table a numerical scheme based on the boundary integral elements method is used in order to determine the water table motion the inflow to galleries and the velocity on the perimeter both oil filled and empty galleries are considered the shape of the galleries is maintained fixed while the spacing and the distance to an impervious bottom is varied an analytical approximate solution valid for sufficiently high water table above the galleries top is also derived this solution is extended to the cases of vertical recharge above the free surface and lpg filled galleries the solution of the two dimensional flow problem can be used in order to determine 1 the time required for the water table to drop from its initial position to the gallery top or to the product level in absence of recharge 2 the water velocity on the gallery perimenter and 3 the total inflow to the gallery

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

geodynamic evolution and tectonostratigraphic terranes of northwestern argentina and northern chile in ordovician time gondwana in the area of northwestern argentina and northern chile had a west facing active margin the evolution of this margin culminated in the ocloyic orogeny at the end of ordovician time this orogeny was caused by the collision of the allochthonous arequipa antofalla terrane with this margin the early paleozoic evolution of northwestern argentina and northern chile contrasts markedly with the accretionary history of central argentina and central chile where the precordillera and chilenia terranes docked in the late ordovician and late devonian periods respectively an inspection of the available stratigraphic and geochronological data on sedimentary volcanic and plutonic units of the southern central andes of northern chile and northwestern argentina reveals a lull in magmatic and metamorphic activity lasting for 100 m y from early silurian to early late carboniferous time this is interpreted as corresponding to a tectonic scenario in which the present andean margin was a passive margin of gondwana this passive margin developed in response to the rifting off of a part of the arequipa antofalla terrane the present location of this block is unknown late carboniferous time marks the renewed onset of subduction initiating the andean plate tectonic setting still prevalent today recently proposed models explain the late ordovician orogeny by the collision of laurentia with western south america during laurentia s clockwise motion around south america and away from its position in the neoproterozoic supercontinent in its present form this hypothesis is difficult to reconcile with the paleozoic tectonostratigraphic evolution of the southern central andean region

the distribution of 14c and 39ar in the weddell sea carbon 14 and 39ar data from the weddell sea are presented and discussed values of 14c and 39ar are low in the winter mixed layer 14c 90 to 125 39ar 85 modern these low values are consistent with the surface layer dynamics which is dominated by entrainment of relatively old water of circumpolar origin and reduced gas exchange during sea ice cover the 14c and 39ar values of the deep and bottom waters range from 160 to 150 and 38 to 57 modern respectively the 14c values of weddell sea bottom water wsbw found in the central weddell sea along a 0 longitude section are only slightly higher than those of the overlying weddell sea deep water wsdw showing that the influence of bomb 14c on these waters is small part of the wsbw with higher 14c values observed in the northwestern weddell sea seems to escape through the south sandwich trench and part seems to mix from a boundary current into the central weddell sea the observed 14c distribution is consistent with the hypothesis that ice shelf water isw is a source of wsbw a simple conceptual model of the surface layer dynamics is used to estimate the prebomb 14c values of surface water and winter water to be about 140 and 130 respectively using mixing ratios between wsdw and shelf water derived from temperature salinity and 3he data the prebomb 14c values of wsbw are estimated to be 157 potential temperature of wsbw 0 7 c the 39ar concentration of wsbw with a potential temperature of 0 7 c is determined to be 57 modern bomb radiocarbon water column inventories are estimated and discussed

a new transient tracer measured vertical distribution of ccl2fcclf2 f 113 in the north pacific subarctic gyre the first quantitative marine measurements of trichlorotrifluoroethane f 113 were made in the north pacific subarctic gyre in july of 1986 using a modification of the analytical procedure developed for the transient tracers f 11 and f 12 gammon et al 1982 wisegarver and cline 1985 the measured mixed layer concentration was 0 29 0 02 pm l the corresponding atmospheric mixing ratio was 35 1 pptv rasmussen scale below a subsurface maximum both f 11 and f 113 were found to fall off exponentially with increasing depth f 113 reaching effective blank levels first the significance of adding f 113 to the existing suite of measurable oceanic transient tracers rests in the possibility of age dating water masses by their f 113 f 11 ratio with near annual resolution for the period since 1977

the distribution of tritium and cfcs in the weddell sea during the mid 1980s abstract transient tracer data tritium cfc11 and cfc12 from the southern central and northwestern weddell sea collected during polarstern cruises ant iii 3 ant v 2 3 4 and during andenes cruise nare 85 are presented and discussed in the context of hydrographic observations a kinematic time dependent multi box model is used to estimate mean residence times and formation rates of several water masses observed in the weddell sea ice shelf water is marked by higher tritium and lower cfc concentrations compared to surface waters the tracer signature of ice shelf water can only be explained by assuming that its source water mass western shelf water has characteristics different from those of surface waters using the transient nature of tritium and the cfcs the mean residence time of western shelf water on the shelf is estimated to be approximately 5 years ice shelf water is renewed on a time scale of about 14 years from western shelf water by interaction of this water mass with glacial ice underneath the filchner ronne ice shelf the ice shelf water signature can be traced across the sill of the filchner depression and down the continental slope of the southern weddell sea on the continental slope new weddell sea bottom water is formed by entrainment of weddell deep water and weddell sea deep water into the ice shelf water plume in the northwestern weddell sea new weddell sea bottom water is observed in two narrow deep boundary currents flowing along the base of the continental slope classically defined weddell sea bottom water 0 7 c and weddell sea deep water 0 7 c 0 c are ventilated from the deeper of these boundary currents by lateral spreading and mixing model based estimates yield a total formation rate of 3 5sv for new weddell sea bottom water 1 0 c and a formation rate of at least 11sv for antarctic bottom water 0 5 c

early evolution of the proto andean margin of south america from a detailed study of a 500 km transect in the sierras pampeanas central west argentina two pre silurian tectono magmatic episodes are recognized and defined each culminating in micro continental collisions against the proto andean margin of gondwana the pampean orogeny started in early cambrian time with short lived subduction indicated by ca 535 ma calc alkaline granitoids following pampean terrane collision burial to granulite facies conditions ca 9 kbar generated widespread migmatites and ca 520 ma highly peraluminous granites in the eastern sierras pampeanas after brief quiescence a second major episode the famatinian orogeny started with subduction ca 490 ma forming a wide continental arc and ensialic backarc basin this heralded the approach of laurentia to gondwana during which the precordillera terrane separated from the southern appalachian region finally colliding with gondwana in silurian devonian time

tectono metamorphic evolution of a high to medium grade ductile deformed metagabbro metadiorite from the arenosa creek shear zone western sierras pampeanas argentina abstract textural and compositional changes affecting a quartzose metagabbro metadiorite in a ductile shear zone which is part of the early palaeozoic famatinian orogenic belt of the western sierras pampeanas argentina allow reconstruction of its tectono metamorphic evolution as well as the metamorphic conditions achieved on the basis of paragenetic associations and microfabrics three overprinted deformation events are differentiated a a relict ductile event developed within the granulite facies at temperatures exceeding 800 c and pressures 5 5 5 kbar b a two stage mylonitic deformation event under high to medium grade metamorphic conditions at temperatures 500 700 c and pressures between 6 and 7 kbar and c a brittle deformation event developed at low greenschist facies below 400 c evidence of the first event is preserved in the protolith although the subsequent deformation obliterated it partially slight modal and chemical changes were detected between the protolith and its mylonitic products deformation ages of the mylonites that vary from 441 9 1 9 ma to 438 7 1 9 ma are internally consistent and compatible with existing geological and geochronological data for the region suggesting that during the famatinian orogeny the western margin of gondwana was characterized by several episodes of ductile deformation that varied in time and space

chlorofluoromethanes in the northeast pacific ocean measured vertical distributions and application as transient tracers of upper ocean mixing the vertical distributions of the man made chlorofluoromethanes ccl3f f 11 and ccl2f2 f 12 have been measured at two locations in the eastern north pacific ocean to depths greater than 500 m at both sites 46 n 125 w off the washington oregon coast and 50 n 140 w in the gulf of alaska the halomethane concentrations were found to fall off exponentially with increasing depth below the mixed layer for f 11 at 50 n the surface concentration 3 2 10 12 mol l was found to be in saturation equilibrium with the measured atmospheric concentration 190 pptv the measured chlorofluoromethane profiles have been interpreted in terms of a one dimensional model for the vertical diffusion advection of an exponentially driven conservative tracer into a bottomless ocean in the appropriate limit of transient steady state the projected profiles are simple exponentials described by an advective diffusive scale depth h which is a function of the vertical eddy diffusivity kz the upwelling velocity w and the characteristic time for the exponential growth of the tracer concentration at the boundary at the two ocean locations studied the freon thermocline depth scales were in the range h 120 140 m with f 12 generally 10 20 deeper than f 11 at 50 n the f 11 and f 12 vertical profiles gave consistent values of vertical diffusivity kz 1 2 1 3 cm2 s 1 and upwelling velocity w 12 14 m yr 1 the model also allows a simple scaling from one exponentially driven transient tracer freon to another fossil fuel co2 leading to a predicted mean depth of penetration of fossil fuel co2 of approximately 300 m in the eastern north pacific

origin and ages of mode waters in the brazil malvinas confluence region during austral winter 1994 the ventilation of the main thermocline associated with the formation of subtropical mode water stmw and subantarctic mode water samw within the brazil malvinas confluence region is investigated using satellite data hydrographic data and dissolved cfcs as transient tracers during the winter of 1994 two types of stmw were observed both types 26 24 and 26 46 were formed within the warm pool of the south atlantic central water sacw the samw is found on the 27 10 density surface this surface lies in the minimum salinity layer of the antarctic intermediate water aaiw the mode waters are dated using cfc ratios to our knowledge this is the first estimate of the age of the mode waters in the region using the cfc 113 cfc 11 ratio method the lighter stmw was being formed during the cruise the heavier stmw was found to be 6 3 years old and is thought to have circulated in the subtropical gyre without losing its primary properties the samw or the lightest aaiw has an age of 3 2 years this water is very young compared with the oldest 10 5 years and heaviest component of the aaiw which circulates within the subtropical gyre the formation of the stmw in the confluence region is dependent on the southward extension of the brazil current

the ordovician sierras pampeanas puna basin connection basement thinning and basin formation in the proto andean back arc article i nfo the ordovician sierras pampeanas located in a continental back arc position at the proto andean margin of southwest gondwana experienced substantial mantle heat transfer during the ordovician famatina orogeny converting neoproterozoic and early cambrian metasediments to migmatites and granites the high grade metamorphic basement underwent intense extensional shearing during the early and middle ordovician contemporaneously up to 7000 m marine sediments were deposited in extensional back arc basins covering the pre ordovician basement extensional ordovician tectonics were more effective in mid and lower crustal migmatites than in higher levels of the crust at a depth of about 13 km the separating boundary between low strain solid upper and high strain lower migmatitic crust evolved to an intra crustal detachment the detachment zone varies in thickness but does not exceed about 500 m the formation of anatectic melt at the metamorphic peak and the resulting drop in shear strength initiated extensional tectonics which continued along localized ductile shear zones until the migmatitic crust cooled to amphibolite facies p t conditions p t d t data in combination with field evidence suggest significant ca 52 crustal thinning below the detachment corresponding to a thinning factor of 2 1 ductile thinning of the upper crust is estimated to be less than that of the lower crust and might range between 25 and 44 constituting total crustal thinning factors of 1 7 2 0 while the migmatites experienced retrograde decompression during the ordovician rocks along and above the detachment show isobaric cooling this suggests that the magnitude of upper crustal extension controls the amount of space created for sediments deposited at the surface upper crustal extension and thinning is compensated by newly deposited sediments maintaining constant pressure at detachment level thinning of the migmatitic lower crust is compensated by elevation of the crust mantle boundary the degree of mechanical coupling between migmatitic lower and solid upper crust across the detachment zone is the main factor controlling upper crustal extension basin formation and sediment thickness in the back arc basin the initiation of crustal extension in the back arc however crucially depends on the presence of anatectic melt in the middle and lower crust consumption of melt and cooling of the lower crust correlate with decreasing deposition rates in the sedimentary basins and decreasing rates of crustal extension

deep water renewal in lake issyk kul 1 the deep water renewal rates of lake issyk kul are studied using the time dependent anthropogenically produced tracers sulfur hexafluoride sf 6 chlorofluorocarbons cfcs and tritium helium 3 sf 6 and the cfcs are used to calibrate a mixing model from which the vertical age distribution is calculated and found to be comparable to the sf 6 apparent ages based on this model the mean age of the water below 100 m depth is 6 1 yrs the mean oxygen consumption rate for the same depth range is 6 4 mol kg 1 yr 1 and the mean remineralization rates for nitrate phosphate and silicate are 0 53 0 003 and 0 67 mol kg 1 yr 1 respectively

basin wide circulation and ventilation study in the east sea sea of japan using chlorofluorocarbon tracers abstract near synoptic basin wide distributions of the chlorofluorocarbon cfc tracers were observed during the summer of 1999 in the east sea sea of japan to study its circulation and ventilation the cfcs penetrate throughout the water column and the bottom water bw cfc concentrations have increased over measurements made in 1995 and 1996 indicating a continuous weak renewal of deep waters in the east sea during this recent period the cfc 11 water column inventory estimated in 1999 2000 5500 nmol m 2 is substantially higher than that of the adjacent north pacific ocean a striking anticorrelation between the bw dissolved oxygen and cfc concentrations in the japan basin is attributed to more active vertical mixing along the basin boundary a dynamically isolated deep eastern japan basin and recent changes in deep water ventilation the bw of the eastern japan basin with the lowest cfc content is the oldest water parcel in the east sea although it is colder and contains higher oxygen concentration than the surrounding bw active entrainment of overlying deep water is inferred from the unexpectedly higher bw cfc concentrations in the yamato basin this may explain why the yamato basin bw is warmer and less oxygenated than the other basins in the east sea although it is believed to be a terminus of the ventilated dws mesoscale anticyclonic eddies which have been fused with other deeply convected waters in the northwestern east sea seem to play an important role in transferring surface water properties to depths greater than 2500 m the subsurface cfc maximum centered within the typical east sea intermediate water esiw layer is more widely distributed south of the subpolar front than previously reported the esiw consists primarily of the colder and fresher winter surface water in the northern region that has subducted below the subpolar front

a generalized transport theory water mass composition and age abstract a general theory to describe and understand advective and diffusive ocean transport is reported it allows any passive tracer field with an atmospheric source to be constructed by superposing sea surface contributions with a generalized green s function called the boundary propagator of the passive tracer equation the boundary propagator has the interpretation of the joint water mass and transit time distribution from the sea surface the theory thus includes the classical oceanographic idea of water mass analysis and extends it to allow for a distribution of transit times from the sea surface the joint water mass and transit time distribution contains complete information about the transport processes in the flow it captures this information in a more accessible way than using velocity and diffusivity fields however at least for the case of sequestration and transport of dissolved material by the ocean circulation the boundary propagator is thus the natural quantity to consider when discus

apparent loss of cfc 113 in the upper ocean we report and evaluate data of the chlorofluorocarbon cfc 113 in comparison with concurrent data for cfc 12 from cruises into the temperate north atlantic the tropical western pacific the eastern mediterranean and the weddell sea we consistently find cfc 113 deficiencies in the warmer upper waters which we interpret as cfc 113 depletion at rates of the order of 3 per year with possibly accelerated rates in the mixed layer or near the surface these results severely limit a tracer utility of cfc 113 in the warm upper waters of the ocean tracer applications in the deep waters of the ocean should be much less affected since cfc 113 loss in such waters appears to be far slower this also holds for the eastern mediterranean despite its rather warm deep waters for the weddell sea the data indicate a cfc 113 deficiency 20 in the shelf waters which converts into a similar deficiency in newly formed deep and bottom water such cfc 113 deficiency has to be accounted for in southern ocean tracer work future work is proposed to study cfc 113 loss in the ocean in additional detail and to elucidate the loss mechanism s on which our data give little clue

vertical profiles of ccl3f f 11 and ccl2f2 f 12 in the central arctic ocean basin the anthropogenic chlorofluoro methanes ccl3f f 11 and ccl2f2 f 12 have been measured to depths of 1800 m in the canada basin of the arctic ocean approximate position 85 50 n 108 50 w the measurements were made as part of the canadian expedition to study the alpha ridge cesar during april 1983 surface layer concentrations beneath the ice were 4 79 10 12 mol kg f 11 and 2 11 10 12 mol kg f 12 both profiles exhibit a rapid concentration decrease with depth through the halocline and very low but detectable concentrations at depths of 350 900 m in the atlantic layer in the arctic ocean deep water 900 1800 m concentrations are at or below our practical detection limit of 0 01 10 12 mol kg the profiles have been interpreted using two extreme case lateral ventilation models in order to place bounds on the water column ventilation rates the ventilation age of the upper portion of the halocline 60 150 m increases with depth from 4 to 14 years the core of the atlantic layer at this location appears to have been isolated from the surface for at least 30 years

hot orogens tectonic switching and creation of continental crust many granulite terrains were too hot to have formed during continental collision rather along with many high grade metamorphic terrains that typify continental crust most formed in accretionary orogens during tectonic switching when prolonged lithospheric extension was interrupted by intermittent transient contraction based on modern and ancient examples tectonic switching occurs when slab retreat induces upper plate extension causing arc splitting formation of microcontinent slivers and backarc basins then intermittent arrival of buoyant oceanic plateaus induces transient flat subduction or slab flip and crustal thickening during slab retreat basaltic magmas produced from decompressed asthenosphere advect into the extending orogen causing granulite facies metamorphism and granite generation but subsequent thickening during flat subduction cools the region thickening is focused in the thermally softened backarc region and if sediment filled a hot short lived 10 m y narrow 50 100 km orogenic belt forms such thickening is often misleadingly ascribed to arc or microcontinent collision once slab retreat mode is reestablished lithospheric extension recommences and a new arc backarc system forms generally outboard arrival of another plateau will reverse the procedure and another short lived hot orogen will form within the orogenic system cycles of tectonic switching efficiently produce continental crust

ordovician metamorphism and plutonism in the sierra de quilmes metamorphic complex implications for the tectonic setting of the northern sierras pampeanas nw argentina towards unravelling the geodynamic setting of the northern sierras pampeanas nw argentina we describe the tectono metamorphic and geochronologic evolution of sub greenschist to granulite facies metamorphic sediments granitoid plutons and pegmatites in the ordovician sierra de quilmes metamorphic complex the protoliths of the metasediments are represented by a sequence of turbidites and minor calcsilicate rocks of the neoproterozoic to cambrian puncoviscana formation the metamorphic complex consists of four zones including the 1 chlorite 2 biotite muscovite 3 garnet cordierite sillimanite and 4 orthopyroxene zones zones 3 and 4 show an increasing degree of anatexis reaching large scale diatexis in the orthopyroxene zone at p t conditions exceeding 800 c and 600 mpa at or shortly after the metamorphic peak the granitic to tonalitic cafayate pluton intruded approximately along the boundary between anatectic and non anatectic rocks retrograde near isobaric cooling of the middle crust was accompanied by non penetrative ductile shearing at granulite to amphibolite facies p t conditions evidence for significant prograde deformation is absent in the sierra de quilmes metamorphic complex monazite and titanite u pb isotopic data constrain the metamorphic peak in migmatites and calcsilicate rocks to be at or slightly prior to 470 ma retrograde amphibolite facies mineral reactions led to continuous formation of monazite and titanite during slow cooling between 470 ma and 455 ma u pb data the composite cafayate pluton intruded over a time interval of several million years between 477 ma sm nd isochron and 460 ma monazite and titanite u pb isochron followed by pegmatites a younger group of pegmatites was emplaced in the country rocks at the end of the ordovician 440 ma rb sr mineral isochrons postdating most of the retrograde shear zones resetting of the muscovite k ar and 40ar 39ar system in weakly deformed pegmatites and crystallisation of new muscovite in low grade metamorphic sediments at 400 416 ma is attributed to minor late greenschist and sub greenschist facies metamorphism and deformation the massive early ordovician heat transfer the absence of major prograde deformation and subsequent prolonged phases of non penetrative deformation in the high grade metamorphic zones during slow near isobaric cooling contradict crustal thickening and continent collision models as have been proposed for the southern sierras pampeanas we suggest continuous or stepwise extensional tectonics in a back arc or a mobile belt tectonic environment for the ordovician sierra de quilmes and the northern sierras pampeanas in general an extensional setting of the northern sierras pampeanas in the ordovician is in agreement with the coeval formation of marine extensional sediment basins in vicinity of the sierras pampeanas in northwestern argentina and southern bolivia

flow near submarine canyons driven by constant winds circulation over coastal submarine canyons driven by constant upwelling or downwelling wind stress is simulated and analyzed with a primitive equation ocean model astoria canyon on the west coast of north america is the focus of this study and model results are consistent with most major features of mean canyon circulation observed in astoria canyon near surface flow crosses over the canyon while a closed cyclone occurs within the canyon upwelling prevails within the canyon and is larger than wind driven upwelling along the adjacent shelf break water rises from depths reaching 300 m to the canyon rim and subsequently onto the adjacent shelf onshore flow within the canyon is driven by the onshore pressure gradient force due to the free surface slope created by the upwelling wind and is enhanced by the limitation to alongshore flow by the canyon topography density gradients largely compensate the surface slope with realistic stratification but continual upwelling persists near the edges of the canyon within the upper canyon 50 150 m below the canyon rim a cyclone is created by flow turning into the canyon mouth separating from the upstream edge and advecting toward the downstream rim below this layer the cyclone is created by vortex stretching due to the upwelling downwelling winds create nearly the opposite flow in which compression and momentum advection create a strong anticyclone within the canyon momentum advection is found to be important both in creating strong circulation within the canyon and in allowing the surface flow to cross the canyon undisturbed model results indicate that astoria like submarine canyons produce across shore transport of sufficient volume to flush a continental shelf in a few 2 5 years

geochemistry of mine waters draining a low sulfide gold quartz vein deposit bralorne british columbia abstract the bralorne and pioneer mines now inactive produced over 4 million ounces of au from an orogenic lode au deposit located on the eastern edge of the coastal mountains of sw british columbia between 2007 and 2009 drainage from a recently developed exploration adit was investigated in order to better understand and anticipate potential environmental management issues associated with the development of this type of deposit in the future portal discharge rate and specific conductance were monitored continuously over a 14 month period during which 36 water samples were collected additional samples were collected from flooded workings within the adit concentrations of as and sb at the portal range as high as 1738 and 316 g l respectively while those in the mine pool reach 3304 and 349 g l respectively effluent chemistry is mildly alkaline ph 8 7 and is dominated by na ca mg hco3 and so4 geochemical inverse modeling of effluent composition indicates weathering of albite 2515 kg a ferroan dolomite 718 kg a pyrite 456 kg a arsenopyrite 23 kg a and stibnite 2 kg a modeled sulfide reaction coefficients normalized by their corresponding host rock concentrations suggest that oxidation of arsenopyrite is 25 times slower than that of pyrite whereas oxidation of stibnite is 1 5 times faster oxidative dissolution of arsenopyrite and stibnite releases 10 6 kg a of as and 1 1 kg a of sb of which 57 and 46 respectively are sorbed to ferrihydrite and gibbsite on the bed of the shallow channel through which the mine pool drains to the portal although mass balance calculations predict the formation of sufficient ferrihydrite to sorb 100 of the as dissolved in the mine pool this attenuation process was ineffective possibly because the precipitated sorbents settled to the bottom of the water column or because of competition for sorption sites from ca and hco3 the dissolved sb as molar ratio in portal effluent 0 082 is much greater than the sb as ratio of the mineralization 0 002 because of slower arsenopyrite oxidation and somewhat lesser sorption of sb

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

oxygen 18 and helium as tracers of ice shelf water and water ice interaction in the weddell sea oxygen 18 and helium isotope data from stations located in the filchner depression on the continental slope of the southern weddell sea and in the central weddell sea are presented and discussed the 18o and 4he signals imprinted on the water circulating under the filchner ronne ice shelf ice shelf water or isw due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the filchner depression from the weddell sea low 18o values are correlated with high 4he concentrations in the isw found in the filchner depression minimum 18o values 0 8 maximum 4he concentrations about 4 7 10 8 cm3 stp g 1 the fraction of glacial meltwater contained in the isw found in the filchner depression is estimated to about 6 to 7 the 18o and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that isw contributes significantly to the weddell sea bottom water wsbw on the basis of a inultiparameter water mass analysis it is discussed which fraction of the wsbw originates from isw and which other shelf waters potentially could contribute to wsbw

an analytical solution for the capture zone of two arbitrarily located wells abstract a capture zone of pumping well s in an aquifer with regional groundwater flow has been widely used to help design a pump and treat system for groundwater containment and remediation based on the theorem of potential and the principle of superposition an analytical solution is derived in this study to calculate the capture zone for two arbitrarily located wells that pump water from a confined aquifer at an equal flow rate the general two well capture zone is composed of two sub capture zones one for each well the shapes of the two sub capture zones and their relative locations change with variations of the orientation and the separation of the two wells the solution can be useful in verifying available numerical codes as well as in solving practical field problems

fluid flow patterns around a well bore or an underground drift with complex skin effects a semianalytic solution is given for steady state flow around a well bore or a drift with a complex skin the hydraulic conductivity of the skin may vary continuously as a function of the radial distance from the well or drift and may also be radially anisotropic such configurations can be found around damaged or acidized well bores or around a drift near which the stress redistribution induces changes in hydraulic conductivity purely radial flow regional flow around an open or cemented hole without pumping or injection and combined regional and radial flow are considered variations of hydraulic potential and darcy velocity in various radial directions are studied for several cases and are found to be strongly affected by a complex skin it is shown that the convergence of the streamlines toward the borehole which is used in applications involving the point dilution method of measuring regional flow velocity is significantly enhanced by a complex negative skin negative skin values may also reduce the size of the capture zone of a withdrawal well head distribution and tracer transport in combined radial and regional flow around a drift have also been modeled it is demonstrated that tracer breakthrough curves from an experiment of tracer transport from an injection zone in the rock to the drift can be significantly affected by the fluid flow pattern around the drift so the commonly used radial pattern may lead to erroneous results for tracer dispersivity