comment on the paper by a concha r oyarzun r lunar j sierra m doblas and j lillo the hiendelaencina epithermal silver base metal district central spain tectonic and mineralizing processes

numerical model of flow in ice covered channel a two dimensional numerical model for a dune bed channel is extended to describe the flow structure in a channel with a bed of prescribed geometry and roughness and a free floating ice cover of known roughness the model involves solution of the reynolds averaged navier stokes equations with the k turbulence model which accounts for wall roughness it is validated against recent experiments in channels with simulated ice covers of varying roughness and is applied to estimate the effect of an ice cover on the flow in a dune bed channel

a newly dated cretaceous hydrothermal event in the iberian ranges eastern spain and its significance within the mesozoic thermal history in the iberian peninsula abstract the iberian peninsula hosts the world class hg mining district of almaden besides pre hercynian ore bodies alpine cycle hg bearing veins are also present in the eastern iberian ranges espadan deposits we present both the first absolute ages 84 4 and 85 3 ma for a post hercynian hg deposit in spain obtained from primary muscovites and a complete compilation of published mesozoic radiometric absolute ages of the iberian peninsula we deduce that there are three main thermal episodes that affected the iberian peninsula which have been revealed after the comparison among the magmatic metamorphic and hydrothermal ages moreover the espadan hydrothermal system was active when both the cretaceous alkalic magmatism took place in southern portugal and in the pyrenees and during the opening of the bay of biscay

formation of ripples in erodible channels formation of ripples and dunes in erodible channels is analyzed by using the hydrodynamic model developed by kobayashi and madsen this issue applying the continuity equation of sediment the propagation velocity of the wavy bed is expressed in terms of the net fluxes of bed load along the wavy bed and suspended sediment out of the bed load transport layer the spatial variation of the bed load transport rate is derived by analyzing the balance of forces acting on a representative bed load particle on a sloping bed the net flux of the suspended sediment out of the bed load transport layer is obtained by solving the diffusion equation for the suspended sediment near the bed the stability analysis predicts that a perturbation that is either fairly short or long relative to the depth of flow will initially grow depending on whether the flow is hydraulically smooth or fully rough thus the model explains why ripples are not observed in experiments involving fairly coarse sediments since in these cases the flow is rough turbulent

ore lead and sulphur isotope pattern from the low temperature veins of the catalonian coastal ranges ne spain the lead isotopic composition of galenas from low temperature veins of the catalonian coastal ranges ne spain displays a small but distinct range of values 18 318 206pb 204pb 18 678 15 678 207pb 204pb 15 767 and 38 534 208pb 204pb 39 189 the data define a linear trend in the 208pb 204pb versus 206pb 204pb diagram that can be interpreted in terms of mixing of lead from different reservoirs the lead appears to be derived from a solution that preferentially leached granites of late hercynian age sulphur isotopic compositions of the galenas range from 8 5 to 7 3 but variations in a single deposit are small 1 2 pointing to different sources of sulphur in a 34s versus 206pb 204pb plot no clear correlation trends appear lead isotope data from deposits of similar characteristics situated within the hercynian orogenic belt as the linares la carolina district s spain and the inglesiente sulcis area sardinia show slight differences indicating a source area of similar lead isotopic composition in the ccr and linares la carolina districts the main source of lead is related to the hercynian granites of each area although small contributions from metasediments cannot be ruled out the contribution of lead from metasedimentary rocks is particularly seen in the sardinian hercynian vein type ores

numerical computation of sand dune migration with free surface flow 1 this paper presents a morphodynamic model for free surface flows over bed forms the model reproduces bed form evolution and migration in a physically based manner the flow model component of the coupled morphodynamic model which is two dimensional in the streamwise and vertical directions explicitly treats unsteadiness and nonhydrostatic effects comparison with measurements shows that the flow model accurately simulates both mean flow and turbulence structure induced by bed forms under free surface flow the flow model performance is enhanced by the use of a high order godunov scheme known as the cubic interpolated pseudoparticle cip technique to compute the advection phase of the navier stokes equation in addition an enhanced k turbulence closure with nonlinear terms is incorporated in the present model in order to allow better predictions of reynolds stress anisotropy in regions with flow separation performance of the nonlinear k model is compared with standard k closure in the context of the flow as well as morphodynamic simulation nonequilibrium bed load sediment transport is treated using a eulerian stochastic formulation of the sediment exchange process in terms of pickup and deposition functions the proposed approach for sediment transport explicitly considers the local flow variability during morphodynamic computation model results show that the vertical grid distribution pattern affects the simulation result particularly for bed form morphodymics the model successfully simulates some important physical features of bed form evolution such as amalgamation and asymmetric geometry the simulation results are in agreement with laboratory experiments as well as some commonly used prediction methods for geometric characteristics of bed forms

reshaping of the hyporheic zone beneath river restoration structures flume and hydrodynamic experiments 1 in channel stream restoration structures readjust surface water hydraulics streambed pressure and subsurface hyporheic exchange characteristics in this study we conducted flume experiments pool riffle amplitude of 0 03 m and wavelengths of 0 5 m and computational fluid dynamic cfd simulations to quantify how restoration structures impacted hyporheic penetration depth dp and hyporheic vertical discharge rate qv restoration structures were channel spanning vanes with subsurface footers placed in the gravel bed at each riffle hyporheic vertical discharge rate was estimated by analyzing solute concentration decay data and maximum hyporheic penetration depth was measured as the interface between hyporheic water and groundwater using dye tracing experiments the cfd was verified with literature based flume hydraulic data and with dp and qz observations and the cfd was then used to document how dp and qz varied with flume discharge q ranging from 1 to 15 l s 3e 03 re 5e 04 flume experiments and cfd simulations showed that restoration structures increased qz and decreased dp creating a shallower but higher flux hyporheic zone qz had a positive linear relationship with q while dp initially grew as q increased but then shrunk when a hydraulic jump with low streambed pressured formed downstream of the structure the restoration structures created counter acting forces of increased downwelling head due to backwater effects and increased upwelling due to low streambed pressure and standing waves downstream of the structure

comment on flow resistance and bed form geometry in a wide alluvial channel by shu qing yang soon keat tan and siow yong lim

cu mn and ag mineralization in the quebrada marquesa quadrangle chile the talcuna and arqueros districts the quebrada marquesa quadrangle in chile exhibits a series of mineralizations comprising manto type manganese and copper deposits of lower cretaceous age and copper and silver veins of tertiary age the deposits are hosted by volcanic and volcaniclastic units of the arqueros hauterivian barremian and quebrada marquesa barremian albian formations three episodes of manganese mineralization mn1 3 are recognized within the study area hydrothermal activity leading to episodes 1 and 3 was of minor importance while the second one mn2 gave rise to major manto type deposits of both manganese and copper in the talcuna mining district extensional faulting during tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments arqueros formation this episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the arqueros ag and talcuna cu districts the latter veins cross cut the previous manto type copper deposits ore mineralogy is similar in both styles of mineralization manto and vein type and consists mainly of chalcopyrite and bornite with variable amounts of galena tetrahedrite vein related chalcocite sphalerite pyrite hematite digenite and covellite alteration processes at talcuna can be divided into two categories those related to the lower cretaceous manto type episode lk alteration chlorite epidote calcite albite prehnite zeolite and those associated with the locally mineralized normal faults of tertiary age tt alteration chlorite calcite sericite the arqueros silver veins display an ore mineralogy consisting of arquerite argentite native silver polybasite cerargyrite and pyrargyrite proustite associated alteration includes strong chloritization of the country rock the manto type deposits formed from fluids of salinity between 11 and 19 wt nacl equivalent and temperatures between 120 and 205 c mineralizing fluids during the vein type stage circulated at lower temperatures between 70 and 170 c with salinity values in a wide range from 3 to 27 wt nacl equivalent this distribution of salinities is interpreted as the result of the complex interplay of two different processes boiling and fluid mixing the former is considered to control the major mineralogical textural and fluid inclusion features of the vein type deposits we suggest that the lower cretaceous mineralization manto type stage developed in response to widespread hydrothermal activity geothermal field type involving basinal brines

mineral chemistry and phase relations of co ni arsenides and sulfarsenides from the baycheh bagh deposit zanjan province iran abstract the polymetallic hydrothermal veins of baycheh bagh deposit in nw iran occur in quartz carbonate veins which are hosted by oligocene to miocene volcanic mainly andesite and volcaniclastic agglomerate tuff rocks unconformably overlying metamorphic basement rocks three transitional paragentic stages of hypogene mineralization have been identified stage 1 includes base metal cu zn pb sulfides and gold and is succeeded by co ni fe as minerals and bismuth stage 2 and cu bi sulfides sulfosalts stage 3 stage 2 ni co fe mineralization is complex and is subdivided into three substages starting with sulfarsenides arsenopyrite alloclasite i ii followed by native bismuth triarsenides skutterudite i ii iii and diarsenides rammelsbergite safflorite and terminated by sulfarsenides gersdorffite cobaltite solid solution alloclacite iii skutterudite and alloclasite are present in several generations and preserve delicate growth zoning reflecting a multi stage episodic growth the sulfarsenides and arsenides reveal significant substitution of ni co fe as well as as and s reflecting compositional changes of the ore forming fluid e g activities of metals as s as well as changes in ph and oxidation state the mineral assemblages and comparison with similar as dominated vein type ni co mineralization elsewhere collectively referred to as five element veins suggest that the complex arsenide sulfarsenide assemblages formed at temperatures below 300 c baycheh bagh can be regarded as a member of this heterogeneous group of bi co ni as deposits a peculiarity of hydrothermal vein type mineralization at baycheh bagh is that initial epithermal cu au zn pb mineralization evolved into bi co ni as mineralization with time

sand dunes in steady flow at low froude numbers dune height evolution and flow resistance the development of sand dunes in an erodible bed exposed to flowing water is considered using a numerical flow model the bed is initially given a small perturbation which is followed in the time domain examples are given where a sinusoidal perturbation reaches the fully developed steady equilibrium shape the flow modeling is based on a k turbulence closure the sediment transport is assumed to be bed load only with an avalanche like movement on the steep dune front the model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength is sufficiently short results of the dune development are presented for different initial wavelengths it is demonstrated that an equilibrium shape is developed for a range of wavelength depth ratios as long as this ratio is sufficiently small

a flume experiment on the development of subaqueous fine gravel dunes from a lower stage plane bed 1 determining the hydraulic conditions whereby gravel dunes first develop in subaqueous environments is fundamental as their presence may influence engineering solutions designed to maintain bed stability in addition estimates of the flow conditions associated with preserved gravel bed forms in sedimentary sequences are useful for reconstructing the depositional environments and geometries of for example oil and gas bearing geological strata consequently a series of experiments considered dune initiation in these experiments defects and latterly incipient dunes developed from lower stage plane gravel beds during near threshold conditions of motion crit 1 0 1 016 and long periods of marginal bed load transport rates the three dimensional defects were almost imperceptible positive ovoid features with heights of one or two grain diameters and lengths and spans of a few decimeters after 17 hours of flow incipient low amplitude simple two dimensional dunes developed from the defects with heights ranging between 0 029 and 0 055 m nonequilibrium wavelengths of 1 4 m and spans of 0 6 0 9 m continued development over several days with crit ratios of around 1 3 resulted in near equilibrium two dimensional dunes with wavelengths averaging 2 6 3 5 m and spans equal to the flume width 4 m the inception of incipient dunes could be predicted using bulk flow models however this approach was not suitable for the prediction of defect development near bed turbulence in the form of small scale sweep events of limited breadth controls the initiation of defects but larger scale coherent turbulent structures in the outer flow are related to dune development significantly both defects and incipient dunes can exist at the same time which indicates that the effects of sweeps on the bed morphology persist at the same time as larger scale turbulent structures are beginning to effect sediment transport

a model for flow over two dimensional bed forms when non cohesive sediment is set in motion by a unidirectional flow waves of sand often result moreover these waves typically are asymmetrical with steep lee faces that produce flow separation behind each wave a wake region forms which grows in height and decays in strength with distance downstream producing a near bottom acceleration the no slip condition at the bed however requires an internal boundary layer to form beneath the wake region which retards the flow there the interaction of these flow processes produces a local maximum in the boundary shear stress downstream of a bump even over an otherwise flat bed because the erosion rate is proportional to the stress divergence for bed load and weak suspended load transport erosion will occur upstream of this point and desposition will occur downstream of it thus influencing the bottom shape herein the equations of motion are solved for the accelerating internal boundary layer beneath a wake the resulting velocity and boundary shear str

mesozoic fluorite veins in ne spain record regional base metal rich brine circulation through basin and basement during extensional events abstract basinal brines are commonly involved in the formation of hydrothermal base metal ore deposits in sedimentary basins although in many instances the source of metals is often thought to be the underlying basement rocks the evidence of brine infiltration through the basement is sometimes directly found in vein systems in fracture zones crosscutting the basement that is the case of the fluorite barite base metal veins found throughout the hercynian basement of europe north africa and the appalachians a geochemical study of brines trapped in these veins can reveal their origin and evolution but also their mineralizing potential and coupled with the timing of fluid circulation can give clues to elucidate the role of these or similar brines in the genesis of base metal mineralizations together with their possible links to tectonic events the sm nd dating of fluorite samples from one of these veins in ne spain the rigros fluorite vein has yielded an age of 137 25 ma 2 mswd 0 40 the vein formation took place during the late jurassic early cretaceous rifting event in the western european basins which is related to the opening of the atlantic inclusion fluids in samples from rigros and another vein system from the same region the berta fluorite vein have been studied with microthermometry crush leach and la icp ms the brines trapped in the two studied vein systems are na ca cl k mg brines with homogenization temperatures 120 c and salinities up to 25 equiv mass nacl the source of this salinity is related to evaporated seawater at least in the halite precipitation field and to the leaching of mesozoic halite and gypsum sequences by seawater and or meteoric water the basinal brines later evolved through water rock interaction with the crystalline basement resulting in some sodium loss and potassium calcium strontium the latter inferred from isotope data and barium enrichment the analyzed brines have concentrations of zn between 3 and 790 ppm of pb between 3 and 995 ppm and of fe between 27 and 2639 ppm which are similar to those reported in comparable hydrothermal veins and mississippi valley type deposits but higher than in most present day sedimentary brines despite the fact they were able to transport large amounts of metals no significant precipitation of sulfides occurred in the veins and consequently the mineralizing potential of these brines was still preserved after fluorite vein formation

numerical model of turbulent flow over sand dune a two dimensional numerical model based on solution of the reynolds averaged navier stokes equations and the k turbulence model which takes into account sand grain roughness is developed to describe the flow in a fixed dune bed channel the model predicts the velocity and turbulence fields as well as the pressure and friction distributions along the dune the details of the flow in the separation eddy are calculated the model predictions are in general agreement with existing detailed experimental data in a rectangular channel with two dimensional dunes of typical but regular shape the calculated pressure and friction distributions enable determination of the resistance components of the channel without further empiricism however compared to a well known and representative semiempirical engineering formula for the prediction of resistance of natural dune bed channels the two dimensional numerical model predicts significantly different contributions of friction and pressure to the total resista

the evolution of the lorraine evaporite basin implications for the chemical and isotope composition of the triassic ocean abstract during the upper triassic times about 75 m of halite with minor anhydrite was deposited in the lorraine basin samples of halite and sulfates were systematically collected from a borehole intersecting the sequence the chemical evolution of the original brine was investigated by x ray microanalysis of primary inclusions trapped in halite the original brines were of the na mg k ca cl type being consistent with the mineral association of halite and minor anhydrite their solute content can be reproduced by evaporation of present day ocean composition in an open basin however some modifications are required the inflow of a small excess of cacl 2 into the basin 1 2 to 1 9 of the total recharge is required to explain the low so 4 values analyzed in fluid inclusions the same inflow helps to explain more satisfactorily the low na and high cl contents the back reaction of the brine with previous ca sulfate that forms polyhalite could explain the low and variable k values analyzed the excess of ca with respect to present day seawater and the formation of so 4 poor evaporite sequences is the rule rather than the exception in the geological record we have not been able to assess the ultimate origin of the ca excess in the basin nevertheless the great variation of the so 4 content within short vertical distances centimeter scale suggests that these variations are due to processes taking place within the evaporite basin rather than to changes in the composition of the ocean at a global scale the isotopic composition of sulfur and oxygen was determined using samples of sulfates from the same borehole the 34 s values of 21 samples analyzed show a narrow variation 34 s 15 5 0 4 the 18 o values of eight samples analyzed show a wider range of variation 18 o 13 0 1 1 none of the processes which modify the values such as sulfate reduction or additional sulfate sources continental recycling of sulfates from the margins were clearly identified the values of 34 s sw 15 7 to 14 5 and 18 o sw 13 7 to 12 2 for the sulfate dissolved in the triassic ocean explain the values of the sulfates interbedded in the halite of the lorraine basin and most analyses reported in the literature

mechanics of flow over ripples and dunes a simple predictive model for velocity and boundary shear stress fields over two dimensional bedforms of finite amplitude is presented herein and the results of that model are compared with flume data the production of a wake due to separation of the flow near the bedform crest and the subsequent interaction of this wake region with a developing nonuniform boundary layer downstream of the flow reattachment point are treated using the method of mclean and smith 1986 their model is modified in order to take account of the flow response to short wavelength obstructions more accurately and to include the effects of wakes from upstream bedforms as these wakes coalesce in the interior the theory is also extended to include the region between the bedform crest and the reattachment point thereby providing a spatially complete field of velocity and shear stress results of the calculations are found to be in good agreement with laboratory measurements taken over immobile bedforms using a laser doppler velocimeter our finite amplitude flow model is shown to yield accurate predictions of the fluid dynamical effects ultimately responsible for the morphology of well developed natural bedforms

geochemical patterns of a sheared fluorite vein parzan spanish central pyrenees the formation of parzan fluorite lead extension type vein spanish central pyrenees is related to the post hercynian hydrothermal activity widespread not only in the pyrenees but in western europe as well the lode was later strongly deformed during the alpine orogeny with textural modifications and destruction of primary fluid inclusions in order to determine if geochemical signatures of the vein were disturbed during alpine deformation post ore fluid inclusions and quartz oxygen isotopes have been addressed microthermometry and x ray microanalysis of frozen inclusions confirm the na ca cl character of post ore fluid circulations and indicate that they were originally derived from a single source triassic connate waters oxygen isotope data on quartz formed during deformation along with trace element geochemistry suggest that the geochemical signatures of the vein mainly ree and 87sr 86sr were apparently not reset during deformation the ree content of fluorites is very high up to 0 12 the chondrite normalized ree patterns display a continuous decrease from la to lu sulphur isotope data for the parzan vein is outside the typical deep seated range suggesting dominantly crustal sources of sulphur for sulphides while formation waters may be proposed for barite parzan fluorites have the most radiogenic sr values of all the investigated fluorite deposits in central pyrenees they scatter in the range of both the igneous rocks and the cambrian ordovician and triassic detrital sequences of the parzan area if ree contents and 87sr 86sr ratios reflect the primary stage of vein filling as suggested by the good correlation between both geochemical signatures the linear array between 87sr 86sr and 1 ree is suggestive of a mixing process the 34s 18o and 87sr 86sr parameters in barite which postdates the fluorite also provide strong evidence that barite deposition is a result of fluid mixing such an interpretation is in line with present day ideas for the genesis of many of the f ba pb zn vein deposits in the hercynian belt of iberia

fluid inclusions in pre ore minerals from the carbonate hosted mercury deposits in the espadan ranges eastern spain abstract the fluids associated with pre ore minerals in the carbonate hosted mercury veins from the espadan ranges eastern spain have been studied using microthermometry cryo sem eds raman spectroscopy and crush leach analyses in order to determine their origin and the processes responsible for mineralization three primary fluid inclusion types have been found in quartz and dolomite 1 type s composed of liquid vapour mainly co 2 halite 2 type s v composed of liquid high density co 2 double bubble halite and 3 type v composed of high density co 2 n 2 mixtures type s fluid inclusions are preferentially trapped in betxi type veins characterized by the presence of hydrothermal dolomite whereas type v fluid inclusions are trapped almost exclusively in eslida type veins which were without dolomite from these data two different fluids can be inferred to occur during the period of formation of the veins 1 a complex polysaline brine of nacl kcl cacl 2 mgcl 2 so 4 2 h 2 o composition with a salinity of up to 33 eq wt nacl and a 2 co 2 n 2 rich fluid the brine halogen composition points to its secondary origin caused by the dissolution of underlying marine evaporites it is thought that these deposits were formed during jurassic or cretaceous rifting periods as a consequence of fluid mixing between a high salinity secondary brine and connate waters the generation of a co 2 n 2 rich phase caused the pressure increase of the fluids that favoured the hydraulic fracturing of the enclosing rock dolostone the origin of this volatile rich phase probably occurred due to the oxidation and thermochemical breakdown of the organic matter contained in the host rock this event is recorded by the coetaneous trapping of both aqueous and carbonic fluids in quartz crystals the formation conditions for the hypogene sulphide paragenesis are obscure but the coincidence between the preferential trapping of type v fluid inclusions the absence of hydrothermal dolomite and the major abundance of mercury in eslida type veins is thought to be linked to a mercury fractionation event to the vapour phase during the release of the volatiles

shape and dimensions of stationary dunes in rivers the shape and dimensions length height of sand dunes in rivers are calculated by use of the measured bed shear stress distribution downstream a rearward facing step the transport of sediment is split up into bed load and suspended load which makes it possible to explain the transition to plane bed the model can predict flow resistance curves in alluvial streams

origin of the atrevida vein catalonian coastal ranges spain mineralogic fluid inclusion and stable isotope study atrevida is a ba f base metal vein located in the catalonian coastal ranges of spain about 100 km southwest of barcelona the vein cuts paleozoic metasediments and granites of the hercynian basement and triassic red beds at the base of an overlying transgressive sequence the atrevida vein can be divided into three parts on the basis of mineralogy the lower level contains sugarlike quartz fluorite minor barite the middle level contains a breccia of banded barite basement rocks cemented by a complex sulfide arsenide assemblage with galena ni sulfide ag sulfosalt and native silver veinlets the upper level contains symmetrical bands of white barite late calcite and marcasite are found in geodes the only alteration observed is quartz sericite chlorite after k feldspar and biotite where the vein cuts granite host rocks fluid inclusions in fluorite homogenize at 110 degrees c and have salinities of 21 wt percent nacl equiv inclusions in sphalerite homogenize at 90 degrees c and have salinities of 22 wt percent nacl equiv eutectic results in both minerals are as low as 59 degrees c indicating that the trapped fluids are complex cacl 2 bearing polysaline brines fluid inclusions in late calcite homogenize at 0 3 degrees c indicating that low salinity waters invaded the vein system during calcite deposition sulfur and oxygen isotope analyses reveal that vein barites have delta 34 s values of 14 to 17 9 per mil cdt and delta 18 o values of 9 5 to 12 2 per mil smow barite also occurs as cement in the triassic red beds with delta 34 s 15 3 per mil and delta 18 o 10 6 per mil both the sulfur and the oxygen isotope compositions are within the ranges reported for lower triassic to lower jurassic age evaporites banded galena from the middle level of the vein has delta 34 s values between 6 3 and 8 9 per mil and rimming anglesite has delta 34 s values of 21 to 30 9 per mil galena from the central breccia has delta 34 s values of 14 9 to 16 1 per mil and coexisting sphalerite is about 10 per mil quartz in the lower level of the vein has delta 18 o in the range 20 7 to 22 7 per mil we infer that sulfate in the vein was derived directly from seawater or from a solution which dissolved evaporites as it descended through the triassic section along the fault zone barite and sulfides were precipitated where the sulfate bearing solution mixed with an ascending ba rich brine the reduced sulfur found in the vein may have been carried by the ascending brine banded galena and may also have been produced by bacterial reduction of sulfate from a surficial source galena in breccia oxidizing nonmarine waters were introduced into the hydrothermal system giving rise to anglesite rims on galena mineralization took place in the late triassic during an extensional tectonic regime characterized by a high geothermal gradient atrevida and similar barite veins found throughout the catalonian coastal ranges formed along basin margin faults near a paleosurface formed on hercynian basement on a broader scale low temperature veins are known to occur throughout western europe and northern africa if atrevida is representative of the group then the formation of these veins may be linked to mesozoic extensional tectonics

u pb zircon ages constrain the architecture of the ultrahigh pressure qinling dabie orogen china new shrimp and tims zircon ages 40ar 39ar ages and eclogite locations contribute significantly to our understanding of the ultrahigh pressure dabie shan 1 the geographic extent of the yangtze craton that was subducted to ultrahigh pressure extends to the northern edge of the dabie shan 2 the northern half of the dabie shan is a magmatic complex intruded over a 10 myr interval between 137 and 126 ma that accommodated 100 n s stretching of the pre existing collisional architecture 3 granitic orthogneisses and enclosing ultrahigh pressure paragneisses have indistinguishable zircon populations the population of triassic zircon ages ranges from 219 to 245 ma leading us to question the prevailing assumption that 219 ma zircons formed at ultrahigh pressure and to propose instead that they reflect late retrogression at crustal pressures following the bulk of exhumation

reply to the comment by f tornos et al we welcome the discussion of our paper by tornos et al the epithermal character of the hiendelaencina veins might have been an assumption in the early to mid 1980s however this early idea has been reaffirmed after many years of research involving fieldwork and mineralogical sulphur isotopes and fluid inclusions studies the same applies to the alleged extensional frame a tectonic episode now well documented not only in central spain spanish central system doblas 1987 doblas et al 1988 doblas 1991 but in france french central massif menard and molnar 1988 malavieille et al 1990 munoz et al 1992 the deposits are hosted by metamorphic rocks and the nearest volcanic outcrops to hiendelaencina are those of atienza andesites some 12 km northward this is the reason why the relationships between the atienza volcanics and the hiendelaencina veins were initially regarded as obscure these stephanian permian volcanic outcrops are only local evidence of the late variscan magmatism which in the case of hiendelaencina remained concealed it is evident that the geologic environments of hiendelaencina and atienza are very different see discussion p 88 of the paper as a direct consequence of this the local structural conditions led to contrasted expressions of the late variscan magmatism i e subaereal at atienza and hypabyssal at hiendelaencina

strontium and sulphur isotope geochemistry of low temperature barite fluorite veins of the catalonian coastal ranges ne spain a fluid mixing model and age constraints sulphur and strontium isotope analyses from the low temperature barite fluorite veins of the catalonian coastal ranges ne spain reveal the nature and source of the ore forming fluids and constrain the ages of the mineralizations sulphur isotope values in the barite 34s 15 to 20 are similar to those of sulphates in nearly triassic jurassic evaporites 34s 11 to 19 87sr86sr isotopic composition ratios of barites and fluorites are 0 7094 0 7167 the variation of 87sr86sr within individual veins suggests that the sr had two different sources granites rocks in the hercynian basement and seawater or evaporites of triassic early jurassic age vein formation is modelled as a two component mixing process in which the s and sr isotopic composition of the end members change with time the observed difference in mean s and sr isotopic compositions among the veins is interpreted to reflect differences in mineralization age ore deposition occurred between 225 and 195 ma triassic to early jurassic in all cases except the berta mine which may be as young as miocene

calculation of dune morphology 1 the shape and dimensions of dunes formed in an erodible bed and exposed to flowing water are investigated by using a numerical model the flow is calculated using a curvilinear flow model where we combine a k turbulence closure scheme with a sediment transport description and the equation of continuity for the sand bed the complete flow description allows for a discussion about what determines the length of dunes from the equation of continuity for sediment it turns out that the sediment transport over dunes is proportional to the local height of the dune this means that the maximum height of the sand wave occurs at the location of maximum sediment transport we relate the dune length to the location of maximum sediment transport it is demonstrated that the effect of streamline curvature is essential for determining the location of maximum sediment transport at low bed shear stresses due to an overshoot in bed shear stress for large dimensionless bed shear stresses the downstream decay of turbulence from the former dune is demonstrated to play a major role

the age and origin of the barite fluorite pbzn veins of the sierra del guadarrama spanish central system spain a radiogenic nd sr and stable isotope study fluorite and barite rich veins sulphides of the sierra del guadarrama spanish central system are usually hosted by hercynian granitoids zoned fluorites from one of these veins have a sm nd age of 145 18 ma this age is similar to the k ar ages obtained in other hydrothermal rocks of the spanish central system 156 152 ma and confirms the existence of an important hydrothermal event during the late jurassic probably related to extensional fracturing accompanying the opening of the north atlantic ocean the 87sr 86sr ratio found in fluorite and barite 0 7154 0 7207 is in most cases lower than that found in the host granitoids 0 7194 and 0 7209 suggesting more than one source of strontium this in turn supports previous models that involve mixing of two fluids during mineralization an ascending hot 300 c and low salinity fluid and a shallow cooler 100 c and more saline brine the ascending fluid probably reacted to a variable extent with the host granitoids and the most likely source for the shallow fluid derived from a marine evaporitic environment with a low 87sr 86sr ratio 0 7069 in the late jurassic the calculated end composition of the fluorites 8 8 to 7 6 as well as the 147sm 144nd variation found in this mineral 0 153 0 405 do not conflict with the mixing model although they can be largely explained by interaction of the ascending fluid with the host granitoids sulphur isotopic compositions of sulphides range between 3 4 and 0 8 and those of barites from 15 5 to 15 8 the near 34s value of the sulphides suggests that their sulphur was derived from the hydrothermal leaching of the granitoids by the ascending fluid the 34s value of barite is consistent with upper jurassic marine sulphate as the source of sulphate in the shallow fluid the absence of equilibrium between reduced and oxidized sulphur species can be easily interpreted as a consequence of the short residence time of the mixed fluid in the open fractures at temperatures between 250 and loo c although no pre cretaceous sediments are found on this part of the iberian hercynian basement the data presented here support the existence of a shallow platform joining central spain with the iberian or the subbetic realm in late jurassic times

fluid inclusion and s c o pb isotope study of pb zn cu ag hydrothermal veins from central and northern portugal metallogenic implications abstract the pb zn cu ag hydrothermal veins from central and northern portugal occur in two distinct districts aveiro moinho da pena carvalhal palhal and telhadela and braganca ferronho vale da madre estevais and olgas the ore veins are composed by sulfides galena sphalerite chalcopyrite pyrite several quartz generations in both districts and dolomite as a gangue mineral in the aveiro district palhal and telhadela a mineralogical fluid inclusion and s c o pb isotopic study was carried out on ore mineralization with the aim to explain its genesis and metallogenic evolution aqueous fluids of h2o cacl2 or h2o nacl cacl2 in composition were identified in both districts the th tmi evolution starts with fluids of medium temperature 250 oc and low to moderate salinity 1 eq wt nacl in the aveiro district and 0 5 eq wt in the braganca district evolving to lower temperatures 250 to 100 oc and higher salinity for the aveiro district 20 eq wt nacl and lower salinity 4 eq wt nacl for the braganca district fluids of high salinity 20 eq wt nacl were trapped during the final stage at temperatures below to 100 c a mixing magmatic and meteoric fluid explained the wide negative values range of 34s measured for the samples from the aveiro district high positive 34s values measured on samples collected from the braganca district confirm a seawater source the c and o stable isotope measured on dolomite and calcite show a 13c depleted source for both carbonates pointing to a carbon source s related to the organic matter oxidation the pb isotope data confirm an uranogenic and a thoriogenic source the pb zn ore deposits from the aveiro and braganca districts are related to episodes of fluid circulation in the upper crust during late to post variscan period the lack of spatial and temporal relationship with magmatic episodes and the presence of basinal and superficial origin fluids support this idea

tail structure and bed friction velocity distribution of gravity currents propagating over an array of obstacles the bed friction velocity distribution and sediment entrainment potential of boussinesq compositional gravity currents propagating over a series of obstacles and over a smooth surface respectively are analysed based on high resolution three dimensional large eddy simulations the investigation focuses on the parameter regime for which currents with a high volume of release go through an extended slumping phase with approximately constant front velocity tokyay constantinescu meiburg j fluid mech vol 672 2011 570 605 under these conditions a quasi steady regime is reached between consecutive obstacles that is similar to the steady regime observed for constant density channel flows over bottom obstacles at a given location this quasi steady regime is reached in the tail of the current after the passage of the front and the associated hydraulic jumps reflected from the first few downstream obstacles a double averaging procedure is employed to characterize the global changes in the structure of the tail region between currents with a high volume of release propagating over smooth surfaces and over obstacles reynolds number induced scale effects on the flow and turbulence structure within the tail region are discussed in some detail the presence of this quasi steady regime is significant since the simulations with obstacles show that most of the sediment is entrained by the tail of the current rather than by its front a detailed analysis of the effects of the obstacle shape on the quasi steady mean flow and turbulence structure is presented which provides insight into why gravity currents over dunes can entrain more sediment than gravity currents over ribs of comparable size finally the bed friction velocity distributions and the potential to entrain sediment are compared for a compositional current with a high volume of release during the slumping phase and a current with a low volume of release for which transition to the buoyancy inertia phase occurs a short time after the release of the lock gate

comparison of hyporheic exchange under covered and uncovered channels based on linked surface and groundwater flow simulations 1 hyporheic exchange is an important process upon which stream biogeochemical cycling is dependent the potential for hyporheic exchange in covered channels i e ice covered channels karst conduits fractures with permeable sediments has not yet been assessed we characterize the potential for hyporheic exchange in covered channels using linked turbulent channel flow groundwater flow simulations simulations show that hyporheic exchange occurs in covered channels which have shallower hyporheic zones and larger hyporheic fluxes than equivalent depth equivalent discharge uncovered channels we also analyzed hyporheic exchange for the case of freely floating covers with rough undersides and found that hyporheic exchange decreases with increasing cover roughness which in turn is driven by subdued bed topography a response to additional resistance due to covers the results suggest that hyporheic exchange occurs in covered channels and may be just as or perhaps more important to the ecology and biogeochemistry of these channels than to open channel streams

modeling the drift of ridged sea ice a view from below 1 the influence of long parallel pressure ridge keels on the ice water drag and the fluid velocity under ice in a rotating non stratified ocean is studied using a numerical model turbulence in the water is modeled by a two equation eddy viscosity model designed for adverse pressure gradient flow along both smooth and rough ice without assuming the logarithmic law of the wall to be valid the simulations show the violation of this law in flow beneath the ice keels the numerical results demonstrate that the orientation of the ice keels relative to the ice drift direction and the ice keel depth have a significant influence on the ice water drag coefficient the drag turning angle the near ice velocity and the turbulence fields application to free drifting wind driven sea ice yields changes in the deflection angle between the wind stress and ice drift directions of about 40 depending on the pressure ridge orientation relative to the drift direction in addition the results define a region where the ice drift direction is sensitive to changes in the wind stress direction

introduction to special section on marine sand wave and river dune dynamics marine sand waves and river dunes are rhythmic patterns formed at the interface between a sandy bed and turbulent flows driven by tidal and river currents their origin development and dynamics are far from being fully understood to enhance the discussion on this topic we organized the international conference marine sand wave and river dune dynamics marid in april 2004 in enschede netherlands scientific papers that originated from the marid conference are presented in this special section this introduction places these papers in the context of recent progress

recurrent hydrothermal activity induced by successive extensional episodes the case of the berta f pb zn vein system ne spain abstract a mineralogical and geochemical fluid inclusion stable and radiogenic isotopes study of the berta f pb zn vein system has identified the source and temperature of the fluid reservoirs involved and proved the existence of two separate hydrothermal events at the mine scale which reflect distinct periods of regional fluid circulation main stage minerals fluorite i sulphides calcite i and barite i precipitated by mixing between a polysaline h 2 s bearing 34 s 11 brine up to 23 nacl eq salinity and a more dilute fluid 18 o from 3 2 to 0 at temperatures between 80 and 150 c the progressive increase in 87 sr 86 sr ratio from the early precipitated minerals 0 71242 in calcite i to the late ones 0 71894 in fluorite ii is mainly but not exclusively due to a difference in age separating the two hydrothermal events the assumed genetic model for the main stage fluorite i is based on a convective circulation of surficial waters leaching the crystalline basement rocks acquiring a high salinity high 87 sr 86 sr ratios and a high temperature these fluids then mixed with low salinity low temperature waters having a low 87 sr 86 sr ratio an at least jurassic age is suggested for the main period of vein filling contemporaneous with the extensional regime during the mesozoic when fluid circulation was probably enhanced by crustal thinning during the early burdigalian lower miocene a new period of important extension in this area took place hydrothermal activity related to this new and younger extensional regime is geochemically different and produced a distinctive mineralogical record developing a set of veinlets filled with green octahedral fluorite fluorite ii calcite ii and barite ii the sr isotope compositions of these late stage vein minerals are compatible with leaching the granodiorite host rocks during recent times the existence of successive hydrothermal events in the same area is not surprising as geothermal systems like la garriga samalus are still active and currently precipitating fluorite

long term fluid circulation in extensional faults in the central catalan coastal ranges p t constraints from neoformed chlorite and k white mica the neoformation of chlorite and k white mica in fault rocks from two main faults of the central catalan coastal ranges the valles and the hospital faults has allowed us to constrain the p t conditions during fault evolution using thermodynamic modeling crystallization of m1 and m2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton 290 c t 370 c in the permian after that three tectonic events have been distinguished the first tectonic event attributed to the mesozoic rifting is characterized by precipitation of m3 and m4 phengite together with chlorite and calcite c1 at temperatures between 190 and 310 c the second tectonic event attributed to the paleogene compression has only been identified in the hospital fault with precipitation of low temperature calcite c2 the shortcut produced during inversion of the valles fault was probably the responsible for the lack of neoformed minerals within this fault finally the third tectonic event which is related to the neogene extension is characterized in the valles fault by a new generation of chlorite associated with calcite c4 and laumontite formed at temperatures between 125 and 190 c in the absence of k white mica differently the hospital fault is characterized by the precipitation of calcite c3 during the syn rift stage at temperatures around 150 c and by low temperature fluids precipitating calcites c5 c6 and pc1 during the post rift stage during the two extensional events mesozoic and neogene faults acted as conduits for hot fluids producing anomalous high geothermal gradients 50 c km minimum

higher order moments of velocity fluctuations in an open channel flow with large bottom roughness the present study was undertaken to examine the effect of surface roughness on the higher order velocity moments in a turbulent open channel flow the wall roughness is large and the ratio of the roughness size to the depth of flow ranges from 0 1 to 0 15 flow over two types of roughness conditions ribs and dunes are examined and compared with that over a smooth open channel in the case of the rib roughness three different spacings are used p k 4 5 9 and 18 here p distance between the leading edges of two consecutive ribs and k height of a rib with square cross section the shape of the smooth wall dunes was geometrically similar to that commonly used in previous studies in an effort to understand the influence of local wall roughness rough wall dunes are also used in the present study the variables of interest include higher order moments conditional statistics based on a quadrant analysis relationship of higher order moments to the reynolds stress and energy production although there