hydrothermal alteration and fluid chemistry of the endako porphyry molybdenum deposit british columbia hydrothermal alteration and fluid chemistry data of the early cretaceous endako porphyry molybdenum deposit british columbia provide new information on the hydrothermal fluids associated with low fluorine molybdenite mineralization molybdenite mineralization and hydrothermal alteration occur as early quartz molydenite stockwork veins with k feldspar bearing selvages and paragenetically later quartz molybdenite ribbon veins with sericite bearing selvages late hydrothermal alteration is associated with the development of kaolinite and postore tertiary age calcite veins fluid inclusions in early formed quartz molybdenite stockwork veins with k feldspar bearing alteration assemblages are dominated by moderate salinity 5 to 15 wt nacl equiv liquid rich type 1 and rare high salinity 30 to 45 wt nacl equiv halite bearing type 3 fluid inclusions type 1 and type 3 fluid inclusions in early veins homogenize between 390 and 430 c and 375 and 420 c respectively secondary fluid inclusions type 2 of low salinity 1 to 5 wt nacl equiv in these early veins are minor and homogenize between 130 and 285 c fluid inclusions in quartz molybdenite ribbon veins with sericite bearing alteration assemblages are dominated by moderate salinity liquid rich type 1 inclusions with minor type 2 fluid inclusions type 1 fluid inclusions of ribbon veins homogenize between 360 and 400 c fluid inclusions in postore calcite veins are of only type 2 fluid inclusions which homogenize at 209 c hydrothermal fluids recorded by type 1 and type 3 fluid inclusions in early veins were trapped under lithostatic to hydrostatic conditions between 0 3 and less than or equal to 2 0 kbar and 360 and 560 c postore fluids recorded by type 2 fluid inclusions were trapped under conditions less than or equal to 0 5 kbar and between 190 and 300 c quartz stockwork and ribbon veins possess 18o values of 8 4 0 2 n 9 and 8 4 0 6 n 13 respectively hydrothermal k feldspar and biotite from k feldspar alteration assemblages possess 18o values of 6 8 0 4 n 7 and 3 5 0 8 n 8 respectively oxygen isotope geothermometry of quartz biotite and quartz k feldspar pairs from k feldspar alteration assemblages yield temperatures between 200 and 490 c which is similar to the trapping temperatures of hydrothermal fluids determined from fluid inclusion studies associated with molybdenite mineralization the development of kaolinite and calcite veins the oxygen isotope temperatures of the quartz biotite and quartz k feldspar pairs suggest that k feldspar and biotite either record the approximate 18o composition of hydrothermal fluids associated with k feldspar alteration or have undergone 18o exchange with late stage hydrothermal fluids hydrogen isotope composition of quartz stockwork and ribbon veins fluid inclusion waters range between 105 and 173 per mil solute chemistry studies of fluid inclusion waters indicate that ore forming fluids from endako have low br cl and br na ratios and high i cl and i br ratios in comparison to porgera epithermal babine lake porphyry cu and st austell capitan pluton vein deposits associated with magmatic processes na k ratios of fluid inclusion waters yield temperatures 308 to 429 c similar to those determined from type 1 and type 3 fluid inclusions and stable isotope thermometry results from fluid inclusion and solute chemistry studies indicate the involvement of hydrothermal fluids exsolved from a crystallizing melt in the formation of the endako molybdenum deposit however oxygen and hydrogen isotope values deviate from the generally accepted magmatic compositions which suggests the early involvement of meteoric water in the ore forming fluids and ore genesis

three dimensional deformation measured in an alaskan glacier measurements of movement along 28 boreholes reveal the three dimensional flow field in a 6 million cubic meter reach of worthington glacier a temperate valley glacier located in alaska sliding at the bed accounted for 60 to 70 percent of the glacier s surface motion strain rates in the ice were low from the surface to a depth of about 120 meters but then increased rapidly toward the bed ice deformation was not affected by temporal changes in the sliding rate the three dimensional pattern of motion indicates that plane strain which is often assumed by models is a poor approximation of this viscous flow

carbon isotope systematics of archean au ag vein deposits in the superior province abundant carbonate is a characteristic feature of most archean mesothermal au ag vein deposits but the source of the c is controversial for superior province deposits collectively the maximum variation of average 13c values is from 9 0 0 7 1 n 19 darius to 0 6 1 6 1 n 7 cochenour willians and limiting 13c values are 13 6 and 1 3 at the deposit scale fe dolomites in nongraphitic lithologies are for the most part isotopically uniform where 13c 3 4 0 4 1 hollinger 3 2 0 3 mcintyre 4 7 1 7 dome 2 8 0 6 buffalo ankerite 3 6 0 5 macassa 3 2 0 3 bousquet 5 4 0 9 lamaque and 5 3 0 5 hasaga the restricted individual ranges of 13c values imply a corresponding uniformity to the ambient temperature and 13c c of the ore forming fluids within individual deposits small systematic variations of 13c carbonate arise from i interaction of hydrothermal fluids with carbonaceous rocks ii immiscible separation of co2 ch4 or iii

theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products publisher elsevier articletitle theoretical contemporary observational and palaeo perspectives on ice sheet hydrology processes and products journaltitle earth science reviews articlelink http dx doi org 10 1016 j earscirev 2016 01 010 content type article copyright copyright 2016 elsevier b v all rights reserved

long term changes of chemical weathering products in rivers heavily impacted from acid mine drainage insights on the impact of coal mining on regional and global carbon and sulfur budgets abstract the long term impacts of acid mine drainage amd on stream chemistry and regional carbon and sulfur budgets were explored using watersheds of pennsylvania underlain by extensive coal deposits areas of these watersheds have been mined for 200 yr yet mining activity decreased to 2 watersheds witnessed dramatic changes in ph alkalinity calcium magnesium and sulfate sulfate fluxes from these watersheds for instance were 4 12 times higher in the 1940s than they are currently fluxes of sulfate and magnesium from the susquehanna river at danville the major tributary to the chesapeake bay are currently 32 and 70 of what they were in the 1940s while alkalinity fluxes have doubled and ph has recovered 0 8 ph units the direct impact on regional carbon budgets through the degassing of co 2 from carbonates was intense during the height of amd but the long term regional impact is modest resulting in the loss of 3 1 tg of carbon to the atmosphere over the last century during the 1940s the export of amd derived sulfate to the 29 000 km 2 portion of the susquehanna river studied here was twice as large as the current input from so x deposition to the entire 71 000 km 2 susquehanna watershed this is surprising comparing the small spatial footprint of amd to the large footprint of the entire susquehanna watershed normalizing these export rates to coal production data we estimate that global sulfur releases from amd could account for 28 40 of riverine sulfate derived from pyrite oxidation and be equal to 20 of anthropogenic s from atmospheric deposition this study emphasizes the potential importance of amd to global s budgets particularly since coal mining is predicted to increase by 50 in the coming century

the effect of the subglacial water pressure on the sliding velocity of a glacier in an idealized numerical model in order to interpret observed short term variations of the sliding velocity of a glacier the effect of a variable subglacial water pressure on the sliding velocity has been studied using an idealized numerical model in particular the transient stages of growing or shrinking water filled cavities at the ice bedrock interface were analysed it was found that the sliding velocity was larger when cavities were growing than when they had reached the steady state size for a given water pressure the smallest sliding velocities occurred while cavities were shrinking when cavitation is substantial a small drop of water pressure below the steady state value e g by 0 5 bar can temporarily cause backward sliding a limiting water pressure at which sliding becomes unstable is derived the consequences of more realistic assumptions than those of the model are discussed

spatial variability in the flow of a valley glacier deformation of a large array of boreholes measurements of the deformation of a dense array of boreholes in worthington glacier alaska show that the glacier moves with generally bed parallel motion strain in the 200 m deep valley glacier is constant near the surface but follows a nonlinear vertical profile below a depth of about 120 m by a depth of 180 m the octahedral strain rate reaches 0 35 yr 1 the three dimensional velocity field shows spatial complexity with significant deviations from plane strain despite relatively simple valley geometry in the vicinity of the 6 10 6 m 3 study volume no evidence was found for time varying deformation or movement along localized shear planes observations were made by repeatedly measuring the long axis geometry of 31 closely spaced boreholes over a 70 day period and three additional holes after 1 full year of deformation the holes were spaced 15 to 30 m apart installation and measurement of such a large number of boreholes required the development of a semiautomated hot water drilling system that creates straight and vertical boreholes with uniform walls the equipment and procedures enables borehole profiles to be measured without the use of hole casing inclinometry measurements collected in the holes were processed analyzed for error and visualized as a fully three dimensional data set the new methods offer unique insight into small scale spatial and temporal variations in the pattern of flow in a valley glacier

evolution of subglacial water pressure along a glacier s length observations from along the length of bench glacier alaska usa show that the subglacial water pressure field undergoes a multiphase transition from a winter mode to a summer mode data were collected at the glacier surface the outlet stream and in a network of 47 boreholes spanning the length of the 7 km long glacier the winter pressure field was near overburden with low magnitude centimeter to meter scale and long period days to weeks variations during a spring speed up event boreholes showed synchronous variations and a slight pressure drop from prior winter values diurnal pressure variations followed the speed up with their onset associated with a glacier wide pressure drop and flood at the terminus stream diurnal variations with swings of up to 80 of overburden pressure were typical of mid summer several characteristics of our observations contradict common conceptions about the seasonal development of the subglacial drainage system and the linkages between subglacial hydrology and basal sliding 1 increased water pressure did not accompany high sliding rates 2 the drainage system showed activity characteristic of the spring season long before abundant water was available on the glacier surface 3 the onset of both spring activity and diurnal variations of the drainage system did not show a spatial progression along the length of the glacier

stress gradient coupling in glacier flow i longitudinal averaging of the influence of ice thickness and surface slope for a glacier flowing over a bed of longitudinally varying slope the influence of longitudinal stress gradients on the flow is analyzed by means of a longitudinal flow coupling equation derived from the vertically cross sectionally integrated longitudinal stress equilibrium equation by an extension of an approach originally developed by budd 1968 linearization of the flow coupling equation by treating the flow velocity u vertically averaged ice thickness h and surface slope in terms of small deviations u h and a from overall average datum values u 0 h 0 and 0 results in a differential equation that can be solved by green s function methods giving u x as a function of h x and x x being the longitudinal coordinate the result has the form of a longitudinal averaging integral of the influence of local h x and x on the flow u x u x u0 2l l 0 ln n nh n l exp x x l dx where the integration is over the length l of the glacier the operator specified deviations from the datum state and the term on which it operates which is a function of the integration variable x represents the influence of local h x x and channel shape factor x at longitudinal coordinate x on the flow u at coordinate x the influence being weighted by the influence transfer function exp x x l in the integral the quantity l that appears as the scale length in the exponential weighting function is called the longitudinal coupling length it is determined by rheological parameters via the relationship l 2h n n 3n where n is the flowlaw exponent n the effective longitudinal viscosity and n the effective shear viscosity of the ice profile n is an average of the local effective viscosity n over the ice cross section and n 1 is an average of n 1 that gives strongly increased weight to values near the base theoretically the coupling length l is generally in the range one to three times the ice thickness for valley glaciers and four to ten times for ice sheets for a glacier in surge it is even longer l 12h it is distinctly longer for non linear n 3 than for linear rheology so that the flow coupling effects of longitudinal stress gradients are markedly greater for non linear flow the averaging integral indicates that the longitudinal variations in flow that occur under the influence of sinusoidal longitudinal variations in h or with wavelength are attenuated by the factor 1 1 2 l 2 relative to what they would be without longitudinal coupling the short intermediate and long scales of glacier motion raymond 1980 over which the longitudinal flow variations are strongly partially and little attenuated are for 2l 2l 20l and 20l for practical glacier flow calculations the exponential weighting function can be approximated by a symmetrical triangular averaging window of length 4l called the longitudinal averaging length the traditional rectangular window is a poor approximation because of the exponential weighting the local surface slope has an appreciable though muted effect on the local flow which is clearly seen in field examples contrary to what would result from a rectangular averaging window tested with field data for variegated glacier alaska and blue glacier washington the longitudinal averaging theory is able to account semi quantitatively for the observed longitudinal variations in flow of these glaciers and for the representation of flow in terms of effective surface slope values exceptions occur where the flow is augmented by large contributions from basal sliding in the ice fall and terminal zone of blue glacier and in the reach of surge initiation in variegated glacier the averaging length 4l that gives the best agreement between calculated and observed flow pattern is 2 5 km for variegated glacier and 1 8 km for blue glacier corresponding to l h 2 in both cases if l varies with x but not too rapidly the exponential weighting function remains a fairly good approximation to the exact green s function of the differential equation for longitudinal flow coupling in this approximation l in the averaging integral is l x but is not a function of x effects of longitudinal variation of l are probably important near the glacier terminus and head and near ice falls the longitudinal averaging formulation can also be used to express the local basal shear stress in terms of longitudinal variations in the local stope stress with the mediation of longitudinal stress gradients

the sulphur isotope and hydrochemical characteristics of skeiðararsandur iceland identification of solute sources and implications for weathering processes the hydrochemistry of sulphur in the active outwash plain of skeioararsandur se iceland shows considerable variety reflecting differences in sources and processes and is investigated in this article using 34 s values of dissolved sulphate and igneous sulphide minerals 18 o h2o and ionic concentrations in waters seawater derived sulphate is a notable component only in the lower sandur 34 s so4 6 8 vcdt 34 s so4 in the skeioara glacial melt river range from 3 4 to 8 8 34 s the higher values occur during a flood event and reflect geothermal sulphate contributions from the grimsvotn caldera kettle hole lakes formed since the november 1996 jokulhlaup form important ecological niches and show evidence of coupled sulphide oxidation and carbonate and possibly silicate dissolution and have the lowest 34 s so4 values average 0 8 attributed to higher proportions of sulphide oxidation derived so 4 2 and or bacterially mediated sulphide oxidation the hydrochemistry of eastern sandur groundwater is influenced by a hydrothermal source of reduced sulphur from the grimsvotn caldera or a localized area of geothermal springs and contrasts with the hydrochemistry of the majority of groundwaters and the sula and gigjukvisl rivers in western and central skeioararsandur these have lower ca 2 mg 2 na k and so 4 2 concentrations and 34 s values consistent with sulphate derived from the oxidation of igneous sulphides in comparison to catchments dominated by atmospherically transported sulphate catchments such as this where the sulphur system is dominated by internal sources rock derived and geothermal will not be sensitive to the temporal decreasing trends in contributions from long range airborne sulphate resulting from reductions of sulphur emissions in north america and europe

water pressure and basal sliding on storglaciaren northern sweden the subglacial hydrology of the ablation area of storglaciaren a small valley glacier in northern sweden is dramatically affected by a subglacial ridge or riegel water pressures above this riegel are relatively constant while down glacier from it they vary significantly the lower part of the glacier accelerates in response to peaks in basal water pressure the upper part may be weakly coupled to the lower part during these peaks a power law fit of observed basal water pressures and measured surface velocities yields where u s is the surface velocity and p e is the effective water pressure ice overburden pressure minus subglacial water pressure data from findelengletscher reported by iken and bindschadler 1986 yield an identical exponent and a coefficient one order of magnitude larger the similar exponent implies that the process producing the velocity variations on both glaciers is similar the variations in velocity are inferred to be due to hydraulic jacking on both glaciers

influence of subglacial drainage conditions on the velocity distribution within a glacier cross section substrate properties and hydrological conditions at the base of haut glacier d arolla switzerland are nonuniform the thickness and grain size of subglacial sediment vary on length scales less than one ice thickness whereas hydrological conditions vary seasonally and on length scales of about one ice thickness transverse to ice motion there is a close relationship between the annually averaged velocity field and this nonuniformity of bed conditions basal motion dominates in an area with large water level variations in boreholes whereas ice deformation contributes significantly to total movement elsewhere localized enhanced basal motion occurs primarily in summer especially during a july spring event but this motion is barely discernible in annually averaged surface velocity measurements because transverse coupling suppresses surface expression of the basal motion discontinuity these results highlight the need to include representations of bed nonuniformity in models of glacier flow and to consider ice deformation and basal motion as interdependent processes

hydrological controls on the sources of dissolved sulfate in the heihe river a large inland river in the arid northwestern china inferred from s and o isotopes abstract the heihe river is one of the largest and most intensely exploited inland rivers of arid northwestern china which is currently threatened by water shortage and ecological problems driven by climate change and human activity to constrain so 4 2 sources to the river and evaluate the influence of hydrological processes on so 4 2 sources and transport in the large river basin chemical and isotopic measurements of surface and groundwater samples were carried out in the heihe river basin the river water had so 4 2 concentrations in a range of 117 316 mg l with an average of 199 mg l characterized by 34sso4 values ranging from 2 5 to 5 4 and 18oso4 values ranging from 1 8 to 10 2 the shallow groundwater had so 4 2 concentrations in a range of 54 1222 mg l with an average of 383 mg l characterized by 34sso4 values ranging from 0 to 7 4 and 18oso4 values ranging from 2 6 to 10 9 a significant correlation was found between 34sso4 and 18oso4 values of the river water a gradual downstream shift from lower 34sso4 and 18oso4 values to higher 34sso4 and 18oso4 values was observed for both the riverine and groundwater so 4 2 which corresponds to a change in the so 4 2 sources governed by the geology from oxidation of sulfides in the upstream part to dissolution of evaporite and or soil sulfate in the downstream part of the heihe river basin sulfate input dominated by sulfide oxidation via mountain groundwater discharge at the yingluo valley is a major contributor to river so 4 2 in the upper reaches admixture of groundwater so 4 2 enhanced by intensive agricultural activities is responsible for increasing river so 4 2 concentration in the middle reaches evapotranspiration effects in the lower reaches result in indirect mixture of groundwater so 4 2 via dissolution of soil sulfate that has cycled through the soil organic matter pool this study implies that mixing of groundwater so 4 2 with surface water is the dominant process affecting so 4 2 sources and s cycling of the heihe river which is controlled by the regional hydrological processes affected by natural and anthropogenic factors

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

rapid glacier sliding reverse ice motion and subglacial water pressure during an autumn rainstorm measurements of basal water pressure from 15 boreholes located at both local tens of meters and regional kilometers length scales were used to elucidate the pressure sliding relationship during an autumn rapid motion event on bench glacier alaska usa the 8 day event had two distinct phases each with a ten fold speed up with respect to winter velocity the water pressure in all 15 boreholes varied synchronously during the speed up the first phase of rapid sliding began after a peak in basal water pressure and continued while the pressure was elevated and stable or decreasing the second phase of rapid sliding occurred when the basal water pressure was low but increasing and terminated before the pressure peaked pressure and velocity do not appear unrelated but the pressure sliding relationship was not consistently linked to increasing decreasing or a critical water pressure the pressure variations and sliding accelerations are a response to a warm rainstorm although equally large input events occurred in weeks prior with no apparent response drainage system evolution therefore appears to play a key role in both the acceleration and the pressure velocity relationship basal cavity dynamics are likely responsible for three episodes of reverse up valley motion observed after enhanced sliding

dynamic controls on glacier basal motion inferred from surface ice motion 1 current heuristic laws that relate the motion of glaciers due to sliding along the bed to the subglacial water pressure fail to reproduce variations in sliding speed on timescales of specific hydrologic events such as lake drainage rainfall or surging this may be due to the importance of subglacial cavity evolution and shifts in the glacier stress field both of which are not accounted for in typical sliding laws we use multiple time series of surface motion over a 66 day period at brei amerkurjokull iceland to infer changes in bed separation and longitudinal force budget we observe multiple distinct periods of increased surface motion and uplift corresponding to periods of rainfall and or increased temperatures we find consistent hysteresis and lags between motion and variations in both the bed separation and longitudinal stress gradient that we attribute to the redistribution of normal stresses at the bed during cavity growth increases in the longitudinal stress gradient suggest a downglacier stress transfer during increased basal motion that is consistent with increased drainage system efficiency toward the terminus our results suggest that the transient evolution of the subglacial drainage system and shifts in the glacier stress field are important controls on basal motion

strong feedbacks between hydrology and sliding of a small alpine glacier 1 we report the spatial and temporal pattern of sliding on the 7 km long bench glacier alaska using five continuously recording gps antennas following motion of the surface ice distributed at 1 km spacing along the glacier center line we documented surface ice motion over 50 days during summer 2002 surface speeds in two previous winters constrain the motion component associated with ice deformation allowing isolation of the sliding speed history we observed two speedup events bracketing 2 weeks of steady slow sliding the first event was not associated with a meteorological trigger was more subtle than the second and propagated up glacier at a rate of several hundred meters per day the second event coincided with a warm up valley wind which triggered considerable melt of the glacier surface sliding speeds in this event reached 0 3 m d 1 and began almost simultaneously at all sites in the ablation area both the horizontal and vertical displacement time series can be explained by growth and collapse of cavities in the lee of bumps in the bedrock bed cavities grow during rapid sliding and decay by viscous creep we posit that effective pressure averaged over some large area of the bed is inversely proportional to the sliding speed this effective pressure then controls the collapse rate of cavities whose dimensions are estimated from a plausible stepped bed geometry this model explains well the horizontal and vertical surface displacement history through the first event and beginning of the second event the vertical record demands a substantial and abrupt drop in water pressure that departs from the posited sliding effective pressure relationship we argue that this pressure drop reflects establishment of efficient subglacial drainage also manifested in a nearly simultaneous step increase in water discharge in the exit stream the establishment of an efficient conduit system terminates sliding its maintenance inhibits further sliding over the remainder of the summer

mapping subglacial surfaces of temperate valley glaciers by two pass migration of a radio echo sounding survey high resolution maps of the glacier bed are developed through a pseudo three dimensional migration of dense array of radio echo sounding profiles resolution of three dimensional maps of subglacial surfaces is determined by the radio echo sounding wavelength data spacing in the field and migration based on synthetic radio echo sounding profile experiments the maximum resolution of the final map cannot exceed one half wavelength a methodology of field and processing techniques is outlined to develop a maximum resolution map of the glacier bed the field and processing techniques are used to develop a map of the glacier bed below part of worthington glacier a temperate valley glacier in south central alaska the field techniques and the processing steps used on the glacier result in a map of 20 m 20 m resolution

sliding with cavity formation we present a model for the determination of a sliding law in the presence of sub glacial cavitation this law determines the basal stress at a clean ice bedrock interf ace in terms of the velocity and effective pressure the method is based on an exact solut ion of the nye kamb linearly viscous sliding problem with cavities and uses ideas of lliboutry 979 to construct via re norma lization methods an approximate law for gene ral bedrock form we show that for a bedrock whose spectrum has a power law behaviour one obtains a sliding law which gives the basal shear stress proportional to a power of the velocity and to a power of the effective pressure the effect of subgl acial cavitation on the drainage system is exam ined using recent ideas of kamb for sufficiently high velocities drainage through a r6thlisberger tunnel system is unstable and drai nage takes place through the linked system of cavities this leads to a reduction of the effective pressure and by taking account of this one can rewrite the sliding law in terms of st ress and velocity only this sliding law can be multi v alued and it is suggested that this unde rlies the dynamic phenomenon of surges

evolution of ore fluids in the donggou giant porphyry mo system east qinling china a new type of porphyry mo deposit evidence from fluid inclusion and h o isotope systematics abstract the donggou mo deposit in the eastern qinling area china is a giant porphyry system discovered based on a targeting concept by using the tectonic model for collisional orogeny metallogeny and fluid flow cmf model mo mineralization is associated with the donggou aluminous a type granite porphyry and was formed during the early cretaceous in a tectonic regime of continental extension the orebodies mainly occur as numerous veinlets in the host rocks hydrothermal ore forming processes include at least three stages characterized by veinlets of 1 quartz k feldspar minor molybdenite 2 quartz molybdenite beryl and 3 quartz carbonate fluorite three types of fluid inclusions fis are distinguished in quartz and beryl in stages 1 and 2 i e aqueous w type carbonic aqueous c type and solid bearing s type with only aqueous fis observed in stage 3 minerals s type fis contain variable daughter minerals including halite chalcopyrite calcite and an unidentified transparent crystal but only halite can dissolve during heating halite bearing s type fis are mainly homogenized by halite dissolution at 182 416 c corresponding to salinities of 30 9 49 2 wt nacl equiv minor halite bearing s type fis are homogenized to liquid at 190 360 c via vapor disappearance with salinities of 29 1 36 2 wt nacl equiv other fis in minerals of stages 1 2 and 3 are homogenized at temperatures of 341 550 c 220 440 c and 125 225 c with salinities of 8 0 18 3 5 3 16 8 and 0 5 7 3 wt nacl equiv respectively the estimated minimum trapping pressures are up to 141 mpa in stage 1 and up to 81 mpa in stage 2 respectively corresponding to an initial mineralization depth of no less than 5 km the quartz in veinlets yields 18 o values of 8 5 10 0 corresponding to 18 o h 2 o values of 2 9 to 5 9 while the d h 2 o values of fluid inclusions range from 59 to 82 these data suggest that the ore fluids forming the donggou deposit changed from high temperature high salinity co 2 rich magmatic to low temperature low salinity and co 2 poor meteoritic fluids via boiling and mixing resembling those of other magmatic hydrothermal systems in qinling orogen and dabie shan this supports the notion that the porphyry systems generated in a post collisional tectonic setting were initially co 2 rich as indicated by abundant c type and co 2 bearing s type fluid inclusions

emplacement of a silicic lava dome through a crater glacier mount st helens 2004 06 the process of lava dome emplacement through a glacier was observed for the first time after mount st helens reawakened in september 2004 the glacier that had grown in the crater since the cataclysmic 1980 eruption was split in two by the new lava dome the two parts of the glacier were successively squeezed against the crater wall photography photogrammetry and geodetic measurements document glacier deformation of an extreme variety with strain rates of extraordinary magnitude as compared to normal alpine glaciers unlike normal temperate glaciers the crater glacier shows no evidence of either speed up at the beginning of the ablation season or diurnal speed fluctuations during the ablation season thus there is evidently no slip of the glacier over its bed the most reasonable explanation for this anomaly is that meltwater penetrating the glacier is captured by a thick layer of coarse rubble at the bed and then enters the volcano s groundwater system rather than flowing through a drainage network along the bed

metallogeny during continental outgrowth in the columbia supercontinent isotopic characterization of the zhaiwa mo cu system in the north china craton abstract the eastern qinling molybdenum belt eqmb in central china represents the largest mo province in the world located at the southern margin of the north china craton this mo province is largely associated with mesozoic granitoids here we report re os isochron age of 1761 33 ma 2 mswd 2 9 from molybdenite in the recently discovered zhaiwa porphyry mo cu system within the eqmb this age coincides with the peak eruption period 1 78 1 75 ga of the xiong er group volcanic rocks which unconformably overlie the taihua supergroup and are interpreted to have developed on a continental arc the re concentrations 1 to 43 ppm of the zhaiwa molybdenites are similar to those of typical porphyry cu mo au systems developed on continental arcs the 34 s values of the zhaiwa ores 2 7 7 3 average 5 2 suggest that the sulfur was mainly sourced from a magmatic system the sulfides from the ores yield sr i average of 0 70533 similar to that of the xiong er group 0 70547 albeit higher than that of the kuanping group 0 70334 and lower than the taihua supergroup 0 70763 suggesting a mixed source the average e nd 1 76 ga of the sulfides from the ores 0 9 falls between the averages of the taihua supergroup ca 6 8 and the kuanping group ca 7 4 the pb isotope ratios of the ores are similar to but slightly higher than those of the taihua supergroup reflecting preferential leaching of radiogenic pb from the taihua supergroup by magmatic fluids integrated data and interpretations constrain the zhaiwa mo cu deposit to be a porphyry mineral system developed within a ca 1 76 ga continental arc related to oceanic plate subduction beneath the southern margin of the north china craton a correlation between tectonic settings and metallogenic types clearly indicate that the xiong er group was formed in a volcanic arc confirming paleo mesoproterozoic continental outgrowth along the margins of the columbia supercontinent the isotopic characterization of the zhaiwa deposit provides new insights into the enigma of the widespread distribution of large and super large mo deposits of eqmb along the southern margin of the north china craton

diurnal fluctuations in borehole water levels configuration of the drainage system beneath bench glacier alaska usa water levels were measured in boreholes spaced along the entire length of bench glacier alaska usa for a period in excess of 2 years instrumented boreholes were arranged as nine pairs along the center line of the glacier and an orthogonal grid of 16 boreholes in a 3600 m 2 region at the center of the ablation area diurnal fluctuations of the water levels were found to be restricted to the late melt season pairs of boreholes spaced along the length of the ablation area often exhibited similar fluctuations and diurnal changes in water levels three distinct and independent types of diurnal fluctuations in water level were observed in clusters of boreholes within the grid of boreholes head gradients suggest water did not flow between clusters and a single tunnel connecting the boreholes could not explain the observed pattern of diurnal water level fluctuations inter borehole and borehole cluster connectivity suggests the cross glacier width of influence of a segment of the drainage system connected to a borehole was limited to tens of meters a drainage configuration whereby boreholes are connected to a somewhat distant tunnel by drainage pipes of differing lengths often hundreds of meters is shown with a numerical test to be a plausible explanation for the observed borehole behavior

timing of the yuchiling giant porphyry mo system and implications for ore genesis the yuchiling mo deposit is a recently discovered giant porphyry system in the east qinling mo belt china its apparent causative intrusion i e the yuchiling granite porphyry is the youngest intrusion phase 4 of the heyu multiphase granite batholith which was emplaced between 143 and 135 ma new robust constraints on the formation of the yuchiling porphyry mo system are provided by combined zircon u pb biotite 40ar 39ar and molybdenite re os dating zircon grains from the mo mineralized granite porphyry yield weighted 206pb 238u age of 134 0 1 4 ma n 19 2 error mswd 0 30 magmatic biotite from the same sample yield a 40ar 39ar plateau age of 135 1 1 4 ma 2 error and an inverse isochron age of 135 6 2 0 ma n 7 2 error mswd 10 8 which are effectively coincident with the zircon u pb age within analytical error three pulses of mineralization can be deduced from the molybdenite re os ages namely 141 137 and 134 ma which agree well with the zircon u pb ages of granitic phases 1 2 and the yuchiling porphyry phase 4 respectively these well constrained temporal correlations indicate that mo mineralization was caused by pulses of granitic magmatism and that the ore forming magmatic hydrothermal activity responsible for the yuchiling porphyry mo system lasted about 8 ma the yuchiling mo deposit represents a unique style of porphyry mo system formed in a post collision setting and associated with f rich high k calc alkaline intrusions which differ from convergent margin associated porphyry mo deposits

waves of accelerated motion in a glacier approaching surge the mini surges of variegated glacier alaska u s a periods of dramatically accelerated motion in which the flow velocity increases suddenly from about 55 cm d to a peak of 100 300 cm d and then decreases gradually over the course of a day occurred repeatedly during june and july 1978 81 in variegated glacier alaska a surging type glacier that surged in 1982 83 these mini surges appear to be related mechanistically to the main surge the flow velocity peak propagates down glacier as a wave at a speed of about 0 3 km h over a reach of about 6 km in length it is accompanied by a propagating pressure wave in the basal water system of the glacier in which after a preliminary drop the pressure rises rapidly to a level greater than the ice overburden pressure at the glacier bed and then drops gradually over a period of 1 2 d usually reaching a new low for the summer the peak velocity is accompanied by a peak of high seismic activity due to widespread fresh crevassing it is also accompanied by a rapid uplift of the glacier surface amounting to 6 11 cm which then relaxes over a period of 1 2 d maximum uplift rate coincides with the peak in flow velocity the peak in accumulated uplift lags behind the velocity peak by 2 h the uplift is mainly due to basal cavitation driven by the high basal water pressure although the strain wave associated with the mini surge motion can also contribute basal cavitation is probably responsible for the pulse of high turbidity that appears in the terminal outflow stream in association with each mini surge in the down glacier reach where the mini surge waves are attenuating the observed strain wave corresponds to what is expected for the propagating pulse in flow velocity but in the reach of maximum mini surge motion the strain wave has a form quite different possibly related to special features in the mini surge initiation process from that point up stream the flow acceleration in the mini surges is due to enhanced basal sliding caused by the high basal water pressure and the consequent reduction of bed friction a preliminary velocity increase shortly before the pressure wave arrives is caused by the forward shove that the main accelerated mass exerts on the ice ahead of it and the resulting preliminary basal cavitation causes the drop in water pressure shortly before the pressure wave arrives the mini surge wave propagation is controlled by the propagation of the water pressure wave in the basal water conduit system the propagation characteristics result from a longitudinal gradient up glacier increase in hydraulic conductivity of the basal water system in response to the up glacier increase of the basal water pressure in the mini surge wave the mini surge waves are initiated in a succession of areas situated generally progressively up glacier during the course of the summer season in these areas presumably melt water that has accumulated in subglacial reservoirs is released suddenly into the basal water system immediately below generating a pressure rise that propagates down stream from there relationships of the mini surges to the main surge are seen in the role of high basal water pressure in causing the rapid glacier motion in both phenomena in the pulse propagation features of both and in the high outflow turbidity associated with both the mini surges of variegated glacier have a strong resemblance to movement and uplift events observed in unteraargletscher and findelengletscher switzerland this bears on the question whether the mini surges are a particular characteristic of surge type glaciers prior to surge

borehole video analysis of a temperate glacier englacial and subglacial structure implications for glacier flow models video observations made in 16 boreholes drilled through a deforming valley glacier affirm that temperate glacier ice may be reasonably well represented as homogeneous in glacier flow models but raise warnings about the complexities of basal boundary conditions and glacier sliding discrete englacial structures including clear ice layers voids and water conduits compose a total of 3 of the ice mass planar features clear ice layers are oriented near vertical and are not aligned with the sense of shear strain meaning that the layers probably do not influence the homogeneity of the strain both direct observations of the ice and analysis of its light reflectance suggest an increase in crystal size and decrease in bubble content with depth however previous laboratory work indicates that such changes are unimportant in terms of the viscosity of the ice observations of the basal boundary or sliding surface indicate that there are areas of both hard bedrock and soft deformable till which should cause spacial and temporal gradients in sliding rate

hydrological discharges and motion of fels and black rapids glaciers alaska u s a implications for the structure of their drainage systems characteristics of the hydrology and motion of black rapids and fels glaciers alaska were observed from 1986 to 1989 hydrological measurements included stage electrical conductivity and suspended sediment concentration in the discharge stream of each glacier and were made at 0 5 1 h intervals continuously through most of the melt seasons variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time lapse photography 1 d time resolution strain meters 0 5 1 h resolution and seismometers set up to count acoustic emissions both glaciers show similar seasonal diurnal and short term event changes in hydrological discharges and ice speed the hydrological behavior is analyzed in terms of a fast sub system composed of surface streams moulins and large tunnels with discharge that responds rapidly and a slow sub system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day the timing and amplitude of water discharge in the diurnal cycle indicate that roughly 10 40 of the water is routed directly into the fast system the remaining 90 60 of the water enters the slow system dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related a small time lag from discharge maximum minimum to solute minimum maximum suggests that the fast system is confined to roughly the lowermost 30 40 of the full glacier length the residence time of water in the fast system is short compared to 1 d the slow system contains both short and long residence time passages characteristics of the diurnal cycles are somewhat variable through the melt season but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur which suggests parallel evolution of the variables that control the response of the fast system events were characterized by contemporaneous increases in suspended sediment concentration in the discharge water and distinct changes in straining on the glaciers events caused by increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water the correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products hydrological differences between black rapids and fels glaciers can be explained by differences in the size of the glaciers if there is a difference in bed structure that explains the difference in dynamics surge black rapids glacier versus non surge fels glacier it does not affect the hydrological parameters that were observed

re os and sr nd pb isotope constraints on source of fluids in the zhifang mo deposit qinling orogen china abstract the zhifang mo deposit is located in the northeastern qinling orogen along the southern margin of the north china craton the deposit represents a quartz vein system hosted in the mesoproterozoic xiong er group volcanic rocks we identify three hydrothermal stages early middle and late characterized by veinlets of quartz pyrite quartz molybdenite pyrite chalcopyrite galena sphalerite and quartz carbonate assemblages respectively five molybdenite samples from the zhifang deposit yield re os ages ranging from 241 2 1 6 ma to 247 4 2 5 ma with an isochron age of 246 0 5 2 ma 2 mswd 7 4 and a weighted mean age of 243 8 2 8 ma 2 mswd 5 5 the re os age shows that the mo mineralization occurred during the indosinian orogeny and suggests that the mineralization is unrelated to the yanshanian magmatism or the paleo mesoproterozoic volcanic hydrothermal event this study also reports a new sr nd pb isotope dataset from ore sulfides in an attempt to constrain the source of the ore forming fluids ten sulfide samples from middle stage of the zhifang mo deposit yield i sr t ratios of 0 710286 0 711943 with an average of 0 711004 e nd t values between 19 5 and 14 8 with an average of 16 7 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 126 17 535 15 374 15 466 and 37 485 37 848 with averages of 17 380 15 410 and 37 631 respectively one pyrite from the early stage yield i sr t of 0 722711 0 722855 with an average of 0 722783 which is higher than those of the middle stage sulfides and suggests equilibration with wallrocks the e nd t values are in the range of 17 3 to 16 6 with a mean at 17 0 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios are 17 386 15 405 and 37 622 respectively the ore sulfides show higher pb isotope ratios higher e nd t and lower i sr t values than the host rocks the results suggest that the ore forming fluids had lower i sr t and higher e nd t values than the ore sulfides and were possibly sourced from the dengfeng complex the southward subduction of the north china craton beneath the huaxiong block during the triassic was possibly responsible for the formation of the waifangshan orogenic mo system

triassic mineralization with cretaceous overprint in the dahu au mo deposit xiaoqinling gold province constraints from shrimp monazite u th pb geochronology abstract the xiaoqinling terrane in central china is the second largest gold producing area in china previous application of age constraints has yielded ages for the gold mineralization ranging from paleoproterozoic through triassic indosinian to jurassic and cretaceous yanshanian shrimp u th pb dating of hydrothermal monazite in a mo mineralized quartz vein from the dahu au mo deposit in the northern xiaoqinling terrane identifies two mineralization episodes hydrothermal monazite intergrown with molybdenite yields an initial precipitation age of 216 5 ma which is identical to but more precise than the molybdenite re os isochron age of 218 41 ma a younger generation of monazite is distinguished by data falling on a mixing array it is inferred that the younger monazite was formed at the expense of the older ones during the yanshanian probably during a single event that occurred at 125 ma combining these results with available geochronological data and geological evidence we conclude that molybdenum mineralization accompanied by monazite deposition took place in the indosinian followed by a yanshanian tectono hydrothermal event that resulted in large scale gold mineralization in the xiaoqinling terrane our observation demonstrates that monazite is sensitive to hydrothermal overprint and thus is useful for dating fluid infiltration event

pb sr nd isotope constraints on the fluid source of the dahu au mo deposit in qinling orogen central china and implication for triassic tectonic setting abstract the dahu au mo deposit is a structure controlled lode system occurring in the northern xiaoqinling terrane huaxiong block qinling orogen this paper reports a new sr nd pb isotope dataset obtained for ore sulfides and the hostrocks within the taihua supergroup in an attempt to constrain the source of the ore forming fluids from a new dimension 16 sulfide samples yield i sr ratios of 0 70470 0 71312 with an average of 0 70854 e nd t values between 13 5 and 18 1 with average of 15 1 and 206 pb 204 pb i 207 pb 204 pb i and 208 pb 204 pb i ratios of 17 033 17 285 15 358 15 438 and 37 307 37 582 with averages of 17 162 15 405 and 37 440 respectively 5 gneiss samples from the taihua supergroup yield i sr ratios of 0 70947 0 73201 averaging 0 72294 e nd t values of 20 0 to 31 1 averaging 25 1 and 206 pb 204 pb i 207 pb 204 pb i 208 pb 204 pb i ratios of 17 127 18 392 15 416 15 604 and 37 498 37 814 with averages of 17 547 15 470 and 37 616 respectively these data show that the ore sulfides have less radiogenic sr nd pb isotope systematics than the hostrocks and suggest that the ore forming fluids which interacted with the wallrocks to form ores must be sourced from a depleted mantle or a depleted subducted oceanic slab in combination with the spatial scenario and geochemical signatures of the triassic magmatites and mineral systems we argue that in the triassic the mianlue ocean was not completely closed and that the northward oceanic plate subduction still survived along the mian lue suture which caused the late triassic magmatism and associated mineralization in qinling orogen including the au mo dahu deposit

instruments and methods direct measurement of sliding at the glacier bed sliding at the base of trapridge glacier yukon territory canada was measured using a drag spool we describe this simple and inexpensive instrument as well as its installation and operation from 1990 to 1992 seven sites were instrumented with drag spools at six of the sites basal sliding during the period of observation accounted for 50 70 of the total flow observed at the glacier surface the contribution from ice creep is known to be small so most of the remaining surface motion must be attributed to subglacial sediment deformation for the seventh site the observed sliding rate was 90 of the total flow an indication that the sliding contribution varies spatially across the bed diurnal variations in the response of one of our instruments appear to be correlated to subglacial water pressure fluctuations and are interpreted in terms of changes in sliding velocity rather than the opening and closing of basal cavities

paleoproterozoic positive δ13ccarb excursion in the northeastern sino korean craton evidence of the lomagundi event abstract the 2 33 2 06 ga positive 13 c carb excursion associated with environmental change and the breakup of the kenorland or superia supercontinent is called the lomagundi or jatulian event or great oxidation event and has been reported in many early precambrian cratons but not yet in the sino korean craton the guanmenshan formation of the liaohe group occurs in the northeastern part of the sino korean craton 13 c carb and 18 o values in 42 samples from this formation range from 3 5 5 9 v pdb and 15 4 24 8 v smow respectively showing a clear positive 13 c carb excursion that characterizes the lomagundi event thirty five of the 42 samples with less hydrothermal alteration have higher 13 c carb and 18 o carb values than the other 7 samples obviously affected by fluid flow confirming that it was fluid flow that reduced the 13 c carb and 18 o carb values this positive 13 c carb excursion places deposition of the guanmenshan formation within the age range of 2 33 2 06 ga

tectonic implications from re os dating of mesozoic molybdenum deposits in the east qinling dabie orogenic belt abstract the east qinling dabie molybdenum belt is part of a larger east west trending metallogenic belt in eastern china most of the molybdenum deposits occur as porphyry or porphyry skarn type but there are also some vein type deposits following systematic re os dating of molybdenite from 13 deposits and comparisons with two previously dated deposits we have recognized that the molybdenum mineralization in the east qinling dabie belt was developed during hydrothermal activity linked to magmatism and the emplacement of granitoid stocks three pulses of granitoid magmatism and mo mineralization are recognized corresponding to significant tectonic events in the east qinling dabie belt vein type deposits dated at 233 221 ma were formed in detachment fractures indicating localized extension within the collisional setting of the north china and yangtze cratons i type and transitional i and s type granites and related mineralization dated at 148 138 ma may have formed part of a continental magmatic arc with widespread magmatism and back arc extension caused by subduction of the izanagi or paleopacific plate beneath the eurasian continent in a wnw ese direction in the late jurassic early cretaceous both s type and transitional s and i type granite associated porphyry molybdenum deposits dated at 131 112 ma are part of an extensive mineralization event throughout east china that can be ascribed to regional large scale lithospheric thinning delamination and thermal erosion

how do glaciers surge a review the quasi periodic oscillations between normal and fast motion exhibited by surge type glaciers provide the best observational opportunity to determine limiting conditions that allow fast motion the measurements from variegated glacier prove that its surge motion is caused by rapid sliding induced by high water pressure this arises from a major restructuring of the basal hydraulic system which impedes water discharge prior to and during surge although the evolving glacier geometry and stress distribution play a principal enabling role the seasonal timing of two distinct surge pulses each initiated in winter and terminated in summer indicates a major influence from variable external water inputs this influence is not considered in existing surge models and should promote caution in the use of data from temperate and subpolar surge type glaciers to deduce surge potential in polar ice masses the spatial spreading of surge motion from a zone of local initiation occurs by stress redistribution which may spread the surging zone rapidly upglacier or downglacier inside a region of active ice and by mass redistribution with compressional thickening at the surge front which enables down glacier propagation into less active ice the data from other surge type glaciers including the extensive data from medvezhiy glacier are not inconsistent with the above processes but are inadequate to establish whether completely different mechanisms operate in some surges the way by which water accumulates and produces fast sliding is not established in detail for any surge type glacier and may be different on different glaciers depending for example on the presence or absence of unconsolidated debris between the ice and rock

diurnal water pressure fluctuations timing and pattern of termination below bench glacier alaska usa observations from basal water pressure sensors along the length of bench glacier alaska usa show that diurnal fluctuations of water pressure are seasonal and restricted to summer most notable about these fluctuations is their disappearance in the late summer and early autumn long before the seasonal end of diurnal meltwater input here we present data documenting the end of diurnal water pressure fluctuations during the 2002 and 2003 melt seasons the end of diurnal fluctuations occurred abruptly in multiple boreholes spaced meters to kilometers apart there was no obvious spatial progression of termination events and a clear correlation with meteorological forcing or discharge in the outlet stream was not apparent after diurnal pressure fluctuations ended basal water pressure returned to a high generally steady value either in an irregular pattern or by a distinct increase this high water pressure was interrupted by episodic acyclic events throughout the autumn before becoming stable and high in winter

glacier slip and seismicity induced by surface melt many of the key processes governing fast glacier flow involve interaction between a glacier and its basal hydrological system which is hidden from direct observation passive seismic monitoring has shown promise as a tool for remotely monitoring basal processes but lack of glacier bed access prevents clear understanding of the relationships between subglacial processes and corresponding seismic emissions here we describe direct measurements of basal hydrology sliding and broadband seismicity made in a unique subglacial facility in norway during the onset of two summer melt seasons in the most pronounced of these episodes rapid delivery of surface meltwater to the bed briefly enhanced basal slip following a period of elevated high frequency seismic activity related to surface crevassing subsequent ground tilt derived from ultralong period seismic signals was associated with subglacial bedrock deformation during transient pressurization of the basal hydraulic system these signals are interpreted to represent hydraulic jacking as the supply of water to the bed exceeded the capacity of the hydraulic system enhanced slip terminated 2 5 h after it started when ice bed decoupling or increased connectivity in the basal cavity network relieved cavity overpressure the results support theoretical models for hydraulic jacking and illustrate how melt induced increases in speed can be short lived if cavity growth or ice bed decoupling allows basal water more efficient drainage

combined measurements of subglacial water pressure and surface velocity of findelengletscher switzerland conclusions about drainage system and sliding mechanism interpretation des mesures de pression dans les forages et des vitesses superficielles la comparaison avec les modeles suggere que l on a neglige le frottement du aux debris dans les modeles et qu il n existe jamais de chenaux cylindriques rectilignes

fluid evolution of the yuchiling porphyry mo deposit east qinling china the yuchiling mo deposit east qinling china belongs to a typical porphyry mo system associated with high k calc alkaline intrusions the pure co2 pc co2 bearing c aqueous h2o naci w and

feedbacks between coupled subglacial hydrology and glacier dynamics on most glaciers and ice sheet outlets the majority of motion is due to basal slip a combination of basal sliding and bed deformation the importance of basal water in controlling sliding is well established with increased sliding generally related to high basal water pressure but the details of the interactions between the ice and water systems has not received much study when there is coupling between the systems here we use coupled subglacial hydrology and ice dynamics models within the community ice sheet model to investigate feedbacks between the ice and water systems the dominant feedback we find is negative sliding over bedrock bumps opens additional cavity space which lowers water pressure and in turn sliding we also find two small positive feedbacks basal melt increases through frictional heat during sliding which raises water pressure and strain softening of basal ice during localized speedup causes cavities to close more quickly and maintain higher water pressures our coupled modeling demonstrates that a sustained input of surface water to a distributed drainage system can lead to a speedup event that decays even in the absence of channelization due to increased capacity of the system through opening of cavities which is enhanced through the sliding opening feedback we find that the negative feedback resulting from sliding opening is robust across a wide range of parameter values however our modeling also argues that subglacial channelization is required to terminate speedup events over timescales that are commensurate with observations of late summer slowdown on mountain glaciers

spatial and temporal evolution of rapid basal sliding on bench glacier alaska usa we measured the surface velocity field during the summers of 1999 and 2000 on the 7 km long 185 m thick bench glacier alaska usa in the spring of both years a short lived pulse of surface velocity 2 4 times the annual mean velocity propagated up glacier from the terminus at a rate of 200 250md 1 displacement attributable to rapid sliding is 5 10 of the annual surface motion while the high velocity event comprised 60 95 of annual basal motion sliding during the propagating speed up event peaked at 6 14 cm d 1 with the highest rates in mid glacier continuous horizontal and vertical gps measurements at one stake showed divergence and then convergence of the ice surface with the bed as the velocity wave passed with maximum surface uplift of 8 16 cm high divergence rates coincided with high horizontal velocities suggesting rapid sliding on the up glacier side of bedrock steps initiation of the annual speed up event occurred during the peak in englacial water storage while the glacier was entirely snow covered basal motion during the propagating speed up event enlarges cavities and connections among them driving a transition from a poorly connected hydrologic system to a well connected linked cavity system sliding is probably halted by the development of a cnduit system

basal sliding of ice stream b west antarctica a tethered stake apparatus is used to measure basal sliding in a borehole on ice stream b west antarctica about 300 km upstream east from its grounding line near the head of the ross ice shelf a metal stake emplaced at the top of a layer of unfrozen till underlying the ice is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding the measured sliding motion includes any actual slip across the ice till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface this 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment based on features of the record of apparent sliding alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm in any case it is small compared to the seismically inferred till thickness of 9 m measured apparent sliding averages 69 of the total motion of 1 2 m d 1 over 26 days of observation if a 3 5 day period of slow apparent sliding 8 of the total motion is included in the average the occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c 80 and c 8 of the total motion on a time scale of a few days however it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole if the slow period is therefore omitted the indicated average basal sliding rate is 83 of the total motion in either case basal sliding predominates as the cause of the rapid ice stream motion in the last 2 days of observation the average apparent sliding rate reached 1 17 m d 1 essentially 100 of the motion of the ice stream if till deformation contributes significantly to the ice stream motion the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer these observations if applicable to the west antarctic ice sheet in general pose complications in modeling the rapid ice streaming motion

mechanical and hydrologic basis for the rapid motion of a large tidewater glacier 1 observations the data presented in part 1 of this paper meier et al this issue are here used to assess the role of water input output water storage and basal water pressure in the rapid movement of columbia glacier alaska consistently high basal water pressures mostly in the range from 300 kpa below to 100 kpa above the ice overburden pressure are responsible in an overall way for the high glacier flow velocities 3 5 9 m d 1 which are due mainly to rapid basal sliding caused by the high water pressure diurnal fluctuation in basal water pressure is accompanied by fluctuation in sliding velocity in what appears to be a direct causal relation at the upglacier observation site the water pressure fluctuation tracks the time integrated water input less a steady withdrawal as expected for the diurnally fluctuating storage of water in the glacier far from the terminus at the downglacier site the situation is more complex diurnal peaks in water level which are directly related to intraglacial water storage as well as to basal water pressure are shifted forward in time by 4 hours probably as a result of the effect of diurnal fluctuation in water output from the glacier which affects the local water storage fluctuations near the terminus because of the forward shift in the basal water pressure peaks which at the downglacier site lead the velocity peaks by 6 hours a mechanical connection between water pressure and sliding there would have to involve a 6 hour quarter period delay however the nearly identical nature of the diurnal fluctuations in velocity at the two sites argues for a single consistent control mechanism at both sites the velocity variations in nondiurnal speed up events caused by extra input of water on the longer timescale of several days are only obscurely if at all correlated with variations in basal water pressure but correlate well with water storage in the glacier it appears that small variations in water pressure 100 kpa sufficient to produce the observed velocity variations 15 30 are mostly masked by pressure fluctuations caused by spontaneous local reorganizations of the basal water conduit system on a spatial scale much smaller than the longitudinal coupling length over which basal water pressure is effectively averaged in determining the sliding velocity at the achieved level of observation the clearest though not complication free control variable for the sliding velocity variations is basal water storage by cavitation at the glacier bed

basal conditions and glacier motion during the winter spring transition worthington glacier alaska u s a observations of the motion and basal conditions of worthington glacier alaska u s a during late winter and spring melt seasons revealed no evidence of relationship between water pressure and sliding velocity measurements included borehole water levels used as a proxy for basal water pressure surface velocity englacial deformation sliding velocity and time lapse videography of subglacial water flow and bed characteristics the boreholes were spaced 10 15 m apart six were instrumented in 1997 and five in 1998 in late winter the water pressure field showed spatially synchronous fluctuations with a diurnal cycle the glacier s motion was relatively slow and non cyclic in spring the motion was characterized by rapid diurnally varying sliding the basal water pressure displayed no diurnal signal but showed high magnitude fluctuations and often strong gradients between holes this transition in character of the basal water pressure field may represent a seasonal evolution of the drainage system from linked cavities to a network of isolated patches and conduits these changes occurred as the glacier was undergoing a seasonal velocity peak the apparent lack of correlation between sliding velocity and water pressure suggests that local scale water pressure does not directly control sliding during late winter or early in the melt season

sources of stream sulphate in headwater catchments in otter creek wilderness west virginia usa upland forested catchments in the appalachian plateau region receive among the greatest rates of atmospheric sulphur s deposition in the eastern usa although coal mines and s bearing minerals in bedrock may also contribute to stream acidity in this region watershed mass balance and stable s isotopic values 34s of sulphate so42 were used to assess the contributions to stream so42 from atmospheric and lithogenic sources at yellow creek yc a headwater catchment on the appalachian plateau in west virginia oxygen isotopic values 18o of water were used to study catchment hydrology stream output of so42 was c 60 of atmospheric s deposition during a relatively dry year whereas atmospheric s input was nearly balanced by stream output during a year with above normal amounts of precipitation the temporal patterns and values of 34s were similar between bulk precipitation and stream water at two upper elevation sites at the lowest elevation site stream 34s values were similar to bulk precipitation values during the dormant season but were slightly lower than precipitation during the low flow summer probably as the result of a greater proportion of stream water being derived from deep hydrological flowpaths that have contacted s bearing minerals with low 34s values in coal seams stream 34s values at yc were significantly higher than at coal run a catchment containing abandoned coal prospects and having a greater amount of s bearing minerals than yc results suggested that lithogenic s is a relatively minor source and that atmospheric deposition is the principal source of stream so42 and thus stream acidity at yc copyright 2001 john wiley sons ltd

the relationship between subglacial water pressure and velocity of findelengletscher switzerland during its advance and retreat findelengletscher switzerland advanced about 250 m between 1979 and 1985 and retreated thereafter subglacial water pressure surface velocity and surface strain rate were determined at several sites the measurements were made early in the melt seasons of 1980 1982 1985 and 1994 and in the autumn of 1983 and the winter of 1984 changes of surface geometry were assessed from aerial photographs the estimated basal shear stress changed little between 1982 and 1994 nevertheless large changes in the relationship of subglacial water pressure and surface velocity were observed which cannot be reconciled with the most commonly used sliding law unless it is modified substantially consideration of possible reasons indicales that a change in the subglacial drainage system occurred probably involving a change in the degree of cavity interconnection isolated cavities damp the variations in sliding velocity that normally result from changes in water pressure because the pressure in isolated cavities decreases as the sliding speed increases in contrast by transmitting water pressure fluctuations to a larger area of the bed interconnected cavities amplify the effect of water pressure fluctuations on sliding speed thus we suggest that an observed decrease in velocity for a given water pressure between 1982 and 1994 was a consequence of a decrease in the interconnectedness of the subglacial cavity system

on the occurrence and wider implications of anomalously low δd fluids in quartz veins south cornwall england a chemical and hydrogen isotopic study has been carried out on quartz hosted fluid inclusions from three different quartz carbonate sulphide sulphate veins from southwest england two fluid types have been identified in these veins by fluid inclusion microthermometry 1 a low temperature 80 150 c saline 20 27 wt nacl cacl2 equiv nacl cacl2 brine and 2 a moderate temperature 200 c low salinity 0 5 wt nacl equiv fluid d values for the brines range from 39 to 103 and values for the dilute fluids are in the range 46 to 79 both fluid types have at least some values of d which are defined as anomalous i e cannot be directly related to either a low d source fluid or to modification of a source fluid by common physicochemical processes such as evaporation or boiling examination of these data in the given geological context suggest the anomalously low values are unlikely to be attributable to analytical artifacts or post entrapment changes of the fluid inclusions similarly fluid interaction with a suitable mineral or organic phase cannot adequately explain the data we conclude that an as yet unidentified process is responsible for producing low d fluids in southwest england and that this may be a common phenomenon in low temperature basinal environments

mineralization mechanisms in the shangfanggou giant porphyry skarn mo fe deposit of the east qinling china constraints from h o c s pb isotopes abstract the giant shangfanggou skarn porphyry mo fe deposit one of the largest mo deposits in the east qinling orogen is hosted by the neoproterozoic luanchuan group on the southern margin of the north china craton the mineralization occurs mainly as veinlets and in veinlet disseminated form within altered schists skarns hornfelses and or marbles the hydrothermal alteration and mineralization at shangfanggou took place over four stages stage 1 involved potassic alteration and silicification in the porphyry skarnization and magnetization in carbonate strata and hornfelsization in schists quartz molybdenite veins associated with phyllic alteration were produced in the porphyry during stage 2 along with sericitization chloritization serpentinization and silicification in the skarns hornfelses and or marbles quartz polymetallic sulfide veins related to phyllic alteration were produced during stage 3 and ore barren quartz calcite pyrite veins associated with weak carbonatation were produced during stage 4 c o and d isotope compositions of hydrothermal calcite dolomite magnetite phlogopite and quartz from different stages of mineralization during the formation of the shangfanggou deposit range from 12 9 to 8 8 3 2 to 22 7 and 100 to 80 respectively sulfur isotope compositions of sulfides from the ores of the shanfanggou deposit range from 3 6 to 4 4 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 17 648 to 18 742 apart from one magnetite with a value of 20 78 15 526 to 15 690 and 38 197 to 39 823 in the shanfanggou deposit the evolution of the ore forming fluids in the shangfanggou deposit as revealed by 18 o d and 13 c isotope studies was one of progressive modification of the magmatic fluids through fluid wall rock interactions along conduits during fluid ascent and this signifies the involvement of formation strata water during the earlier stages of mineralization and the predominance of meteoric waters over magmatic fluids in the later stages the carbon sulfur and lead isotope compositions suggest mixing took place between the magmas and the host rocks within the region integrating the data obtained from studies of the regional geology ore geology fluid inclusions and c h o s pb isotope geochemistry we conclude that the shangfanggou mo fe deposit is a porphyry skarn type system that formed during a transition from compressional to extensional tectonics during the jurassic early cretaceous continental collision between the north china craton and yangtze craton the ore materials were sourced from magmatic ore forming fluids that mixed with components derived from carbonaceous wall rocks during their ascent and which were gradually mixed with meteoric waters especially in the later stages

ore geology fluid inclusions and four stage hydrothermal mineralization of the shangfanggou giant mo fe deposit in eastern qinling central china article i nfo the eastern qinling central china containing more than 20 mesozoic porphyry skarn systems is the most important mo province in the world the shangfanggou giant mo deposit luanchuan county henan province is a porphyry skarn system hosted in a lithologic association comprising carbonaceous sandstone shale carbon ate and chert within the neoproterozoic luanchuan group mo ores are mainly altered porphyry skarn and hornfels with minor altered gabbro the mineralization process includes four stages potassic alteration of the porphyry and skarnization of dolomite marble in stage 1 stockworks of quartz molybdenite sulfide stage 2 pyrite quartz sulfides stage 3 and carbonate quartz fluorite stage 4 respectively mo mineralization was generally associated with strong silicification and or phyllic alteration the fluid inclusions in minerals include three compositional types i e co2 bearing c type aqueous w type and daughter mineral bearing s type minerals formed in stages 1 to 3 contain all the three types of fis but the stage 4 minerals only contain the w type fis oxides and cu phosphate are recognized as daughter minerals in s type inclusions in minerals of stage 1 whereas the daughter sulfide and reducing gases such as co ch4 h 2 sa nd c2h6 can be observed in quartz of stages 2 and 3 suggesting that the ore forming fluids were initially oxidizing and then evolved to reducing boiling fluid inclusion assemblages can be observed in minerals formed in stage 2 or earlier but not in stage 3 or later fluid boiling caused co2 escape oxygen fugacity decrease and rapid precip itation of ore minerals and was a key factor causing mo mineralization at shangfanggou data and interpreta tions presented in this contribution show that the fluids forming the shangfanggou mo deposit evolved from co2 rich high salinity hypothermal to co2 poor low salinity epithermal low t the mo mineralization at theshangfanggoudepositmainlyoccurredatdepthof6 6 7 0 km deeperthanthemajorityofporphyrysystems in volcanic arcs which resulted from a co2 rich magma fluid system originating from partial melting of thick ened lower crust the shangfanggou mineral system developed during 158 134 ma when the yangtze north china continental collision began to evolve from compression to extension magmatic hydrothermal deposits developed in a continental collision regime are generally formed by co2 rich high salinity fluids

evolution and paragenetic context of low δd hydrothermal fluids from the panasqueira w sn deposit portugal new evidence from microthermometric stable isotope noble gas and halogen analyses of primary fluid inclusions abstract the evolution paragenetic context and origin of remarkably low d hydrothermal fluids from the hercynian panasqueira w sn cu ag deposit have been investigated through a combined microthermometric stable isotope halogen and noble gas fluid inclusion study large variations in d between 60 and 134 have been observed in primary fluid inclusions from growth zones in a quartz crystal pa66 paragenetically constrained to the main sulfide stage mss of ore formation the same fluids exhibited relatively constant fluid inclusion homogenisation temperatures 254 to 260 c salinities 7 4 to 8 7 wt nacl equivalent and calculated fluid 18o 3 8 to 4 4 all the fluids exhibited 40ar excesses mean molar br cl and i cl ratios varied from 2 3 10 3 4 2 10 3 and 8 10 4 10 10 4 respectively with the more br rich fluids being associated with the more deuterium depleted fluids the low palaeolatitude of panasqueira throughout the main stages of ore formation and the overwhelming predominance of meteoric fluids in the main late and post ore mineralising fluids with d of 40 to 65 lends little support for any models involving low d palaeometeoric water the limited range of 40ar cl ratios 1 1 10 5 1 6 10 5 also precludes boiling during the mss or mixing of meteoric water with highly fractionated deuterium depleted magmatic waters as viable mechanisms for producing the low d fluids the high br cl and i cl of the mss fluids indicate significant fluid interactions with organic rich sediments or metasediments in particular regionally abundant carboniferous coals or coaly sediments that are inferred to be depleted in deuterium by around 85 compared to palaeometeoric water the large range of d observed in the mss fluids may be explained by isotopic exchange of palaeometeoric water with these coals at varying water rock wt wt ratios between 0 02 and 0 002 with fluid oxygen isotopic compositions controlled by exchange with the beira schists such a model is consistent with the requirements that any satisfactory model must take into account viz i the relative constancy of temperature salinity 40ar and fluid 18o during excursions to low d ii the high i cl and br cl ratios observed and iii the coincidence of these low d fluids with the onset of precipitation of polymetallic sulfides and phosphates under reducing conditions the model indicates that meta sedimentary sources of ore forming components became increasingly important during the evolution of the panasqueira sn w deposit and accounts in part for the observed progression from oxide dominated to base metal sulfide dominated parageneses

oxygen isotopes in glacier river water austre okstindbreen okstindan norway there is no discernible river discharge from austre okstindbreen norway in winter any water formed by basal melting is likely to be stored in isolated cavities or sediments at the bed in summer a baseflow component of discharge relatively depleted of 18 o is diluted by water more enriched in 18 o glacier ice meltwater with a high 18 o value passes rapidly through channelized systems and emerges in the glacier river within a few hours headward extension of the systems in late summer may tap water stored within the glacier since the previous summer s close down stored water also is released during early melt season events when the low capacity drainage systems cannot accommodate inputs the high 18 o value indicates that the probable source of the released water is glacier ice or low altitude snowfall stratigraphic variations of 18 o values resulting from changing weather conditions characterize the accumulating winter snowpack during the melt season the mean 18 o value of the residual pack rises the water leaving it depleted of 18 o passes slowly through the glacier smoothing out variations of supply 18 o values of rain vary between and within events and their effect on glacier river 18 o values is unpredictable

short term velocity and water pressure variations down glacier from a riegel storglaciaren sweden during the 1991 94 summer field seasons time correlated measurements of water pressure and surface speed were made over and down glacier from a major riegel on storglaciaren sweden measurements were made at sub hourly time scales in order to discern details in the diurnal cycle large water input events typically associated with rain storms produced coherent lagged surface velocity responses that could be understood in terms of till deformation or decoupling and these have been discussed elsewhere the consequences of smaller diurnal water pressure events were more enigmatic in that acceleration of ice flow generally preceded the onset of the local water pressure rise from consideration of these data and other work done on the hydrology of storglaciaren we infer that the ice in this area is generally pushed from behind via a relaxation in extensional strain across the riegel hence accelerations occur in response to increases in water pressure that occur up glacier and that precede local water pressure rises in addition following a period of large storm events surface speeds became more spatially coherent and were in phase with the diurnal ater pressure cycle this suggests that the large water pressure events lead to a spatially more homogeneous subglacial drainage system sliding laws need to take into accoun such temporal changes in spatial coherence of the subglacial drainage system

sources of sulfur in the nandong underground river system southwest china a chemical and isotopic reconnaissance abstract sulfur isotopic compositions 34s and major ions were measured in groundwater and surface waters in order to elucidate the source s of elevated so 4 2 content in some of these waters in the nandong underground river system nurs located in an agricultural and urbanization dominated area in sw china the major chemical composition of analyzed groundwater and surface water from nurs was characterized by ca hco3 or ca mg hco3 type in forested and grass land areas and ca cl no3 so4 or ca mg cl no3 so4 type in urban and agricultural areas respectively the anomalously high so 4 2 concentrations in waters collected from urban and agricultural areas indicated a likely anthropogenic origin for so 4 2 the groundwater collected from forested and grass land areas was characterized by relatively low 34 s so 4 2 from 1 7 to 4 3 and low so 4 2 concentrations of less than 10 mg l 1 consistent with an origin for so 4 2 in these waters from a mixture of rainfall derived so 4 2 and so 4 2 from oxidation of bedrock sulfide high so 4 2 groundwater and surface water 20 mg l 1 collected from urban areas was characterized by elevated 34 s so 4 2 from 8 3 to 12 1 compared to lower 34 s so 4 2 in samples from cultivated land areas 3 7 to 6 4 indicating that the so 4 2 in these two groups of waters resulted from different anthropogenic sources the s isotopic composition of so 4 2 in urban areas is consistent with addition of so 4 2 from detergent sewage whilst in cultivated land areas isotope composition indicates that additional so 4 2 could be derived from fertilizers and or increased oxidation of sulfide

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

glacier surge mechanism 1982 1983 surge of variegated glacier alaska the hundredfold speedup in glacier motion in a surge of the kind the kind that took place in variegated glacier in 1982 1983 is caused by the buildup of high water pressure in the basal passageway system which is made possible by a fundamental and pervasive change in the geometry and water transport characteristics of this system the behavior of the glacier in surge has many remarkable features which can provide clues to a detailed theory of the surging process the surge mechanism is akin to a proposed mechanism of overthrust faulting

water flow through temperate glaciers understanding water movement through a glacier is fundamental to several critical issues in glaci ology including glacier dynamics glacier induced floods and the prediction of runoff from glacierized drainage basins to this end we have synthesized a conceptual model of water movement through a temper ate glacier from the surface to the outlet stream pro cesses that regulate the rate and distribution of water input at the glacier surface and that regulate water movement from the surface to the bed play important but commonly neglected roles in glacier hydrology where a glacier is covered by a layer of porous perme able firn the accumulation zone the flux of water to the glacier interior varies slowly because the firn tempo rarily stores water and thereby smooths out variations in the supply rate in the firn free ablation zone in con trast the flux of water into the glacier depends directly on the rate of surface melt or rainfall and therefore varies greatly in time water moves from the surface to the bed through an upward branching arborescent net work consisting of both steeply inclined conduits formed by the enlargement of intergranular veins and gently inclined conduits spawned by water flow along the bottoms of near surface fractures crevasses engla cial drainage conduits deliver water to the glacier bed at a limited number of points probably a long distance downglacier of where water enters the glacier englacial conduits supplied from the accumulation zone are quasi steady state features that convey the slowly varying water flux delivered via the firn their size adjusts so that they are usually full of water and flow is pressurized in contrast water flow in englacial conduits supplied from the ablation area is pressurized only near times of peak daily flow or during rainstorms flow is otherwise in an open channel configuration the subglacial drainage system typically consists of several elements that are distinct both morphologically and hydrologically an up glacier branching arborescent network of channels in cised into the basal ice conveys water rapidly much of the water flux to the bed probably enters directly into the arborescent channel network which covers only a small fraction of the glacier bed more extensive spatially is a nonarborescent network which commonly includes cav ities gaps between the glacier sole and bed channels incised into the bed and a layer of permeable sediment the nonarborescent network conveys water slowly and is usually poorly connected to the arborescent system the arborescent channel network largely collapses during winter but reforms in the spring as the first flush of meltwater to the bed destabilizes the cavities within the nonarborescent network the volume of water stored by a glacier varies diurnally and seasonally small temper ate alpine glaciers seem to attain a maximum seasonal water storage of 200 mm of water averaged over the area of the glacier bed with daily fluctuations of as much as 20 30 mm the likely storage capacity of subglacial cavities is insufficient to account for estimated stored water volumes so most water storage may actually occur englacially stored water may also be released abruptly and catastrophically in the form of outburst floods

subglacial modulation of the hydrograph from glacierized basins the extent of basin glacierization has important implications for the hydrograph in part because snow firn and ice impart different delays in water transport through the system here the significance of subglacial drainage morphology in modulating the hydrograph is examined with a one dimensional physically based model the conceptual model of subglacial drainage comprises both fast and slow elements respectively associated with summer and winter drainage regimes the additional possibility of a permeable glacier substrate is taken into account by allowing water transport in a subglacial aquifer forced by prescribed rates of melt water delivery to the glacier bed the model predicts glacier discharge by drainage system provenance the effects of 1 hard versus soft glacier beds 2 subsurface permeability and groundwater flow and 3 glacier geometry are then investigated hydrograph character in the form of peak timing and amplitude symmetry with respect to the forcing and the amplitude of diurnal fluctuations is affected by the partitioning of water through the various flow elements hard beds and impermeable substrates maximize the discharge routed through the fast drainage system in the simulations generally resulting in higher seasonal discharge maxima and stronger diurnal variations in discharge high hydraulic transmissivities either at the glacier bed or in underlying strata hinder the development of the fast drainage system in the simulations producing hydrographs of lower amplitude glacier geometry has a modest effect with adverse bed slopes very thick or very thin ice and short glacier lengths favouring prolonged drainage through the slow system these results suggest that the morphology and evolution of the subglacial drainage system may play a significant role in determining the character of the hydrograph from glacierized basins

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

variations in the surface velocity of an alpine cirque glacier following pioneering work in norway cirque glaciers have widely been viewed as rigidly rotating bodies this model is incorrect for basin filling cirque glaciers as we have demonstrated at west washmawapta glacier a small glacier in the canadian rocky mountains here we report observations at the same glacier that assess whether complex temporal variations of flow also occur for parts of three summers we measured daily displacements of the glacier surface in one year four short duration speed up events were recorded three of the events occurred during the intervals of warmest weather when melt was most rapid the fourth event occurred immediately following heavy rain we interpret the speed up events as manifestations of enhanced water inputs to the glacier bed and associated slip lubrication by increased water volumes and pressures no further speed ups occurred in the final month of the melt season despite warm temperatures and several rainstorms the dominant subglacial water system likely transformed from one of poorly connected cavities to one with an efficient channel network the seasonal evolution of hydrology and flow resembles behaviors documented at other larger temperate glaciers and indicates that analyses of cirque erosion cannot rely on simple assumptions about ice dynamics

identifying the influence of geology land use and anthropogenic activities on riverine sulfate on a watershed scale by combining hydrometric chemical and isotopic approaches abstract throughout the last few decades sulfate concentrations in streamwater have received considerable attention due to their dominant role in anthropogenic acidification of surface waters the objectives of this study conducted in the oldman river basin in alberta canada were to determine the influence of geology land use and anthropogenic activities on sources concentrations and fluxes of riverine sulfate on a watershed scale this was achieved by combining hydrological chemical and isotopic techniques surface water samples were collected from the main stem and tributaries of the oldman river on a monthly basis between december 2000 and march 2003 and analyzed for chemical and isotopic compositions at a given sampling site sulfate sources were primarily dependent on geology and did not vary with time or flow condition with increasing flow distance a gradual shift from 34 s values 10 and 18 o values 0 of riverine sulfate indicating evaporite dissolution and soil derived sulfate in the predominantly forested headwaters to negative 34 s and 18 o values suggested that sulfide oxidation was the predominant sulfate source in the agriculturally used downstream part of the watershed significant increases in sulfate concentrations and fluxes with downstream distance were observed and were attributed to anthropogenically enhanced sulfide oxidation due to the presence of an extensive irrigation drainage network with seasonally varying water levels sulfate s exports in an artificially drained subbasin 64 kg s ha yr were found to exceed those in a naturally drained subbasin 4 kg s ha yr by an order of magnitude our dataset suggests that the naturally occurring process of sulfide oxidation has been enhanced in the oldman river basin by the presence of an extensive network of drainage and irrigation canals

the dynamic response of kennicott glacier alaska usa to the hidden creek lake outburst flood glacier sliding is commonly linked with elevated water pressure at the glacier bed ice surface motion during a 3week period encompassing an outburst of ice dammed hidden creek lake hcl at kennicott glacier alaska usa showed enhanced sliding during the flood two stakes 1 2 km from hcl revealed increased speed in two episodes both associated with uplift of the ice surface relative to the trajectory of bed parallel motion uplift of the surface began 12 days before the flood initially stabilizing at a value of 0 25m two days after lake drainage began further uplift reaching 0 4m occurred while surface speed peaked at 1 2md maximum surface uplift coincided with peak discharge from hcl high water level in a down glacier ice marginal basin and low solute concentrations in the kennicott river each of these records is consistent with high subglacial water pressure we interpret the ice surface motion as arising from sliding up backs of bumps on the bed which enlarges cavities and produces bed separation the outburst increased water pressure over a broad region promoting sliding inhibiting cavity closure and blocking drainage of solute rich water from the distributed system pressure drop upon termination of the outburst drained water from and depressurized the distributed system reducing sliding speeds expanded cavities then collapsed with a 1 day time scale set by the local ice thickness