prediction of alluvial channel pattern of perennial rivers abstract purely braided meandering and straight channels can be considered as end members of a continuum of alluvial channel patterns several researchers have succeeded in separating channel patterns in fields defined by flow related parameters however the discriminators of the principal channel patterns derived from these diagrams all require some a priori knowledge of the channel geometry in this paper a method is presented which enables prediction of the equilibrium conditions for the occurrence of braided and high sinuosity meandering rivers in unconfined alluvial floodplains the method is based on two almost channel pattern independent boundary conditions median grain size of the river bed material and a potential specific stream power parameter related to bankfull discharge or mean annual flood and valley gradient this can be regarded as a potential maximum of the available flow energy corresponding to the minimum sinuosity condition p 1 based on an analysis of 228 datasets of measurement sites along rivers from many parts of the world an independent discriminating function was found that separates the occurrence of braided rivers and meandering rivers with p 1 5 the function applies to equilibrium conditions of rivers that neither incise nor show rapid aggradation with a bankfull or mean annual flood discharge above 10 m3 s and a median bed material grain size between 0 1 and 100 mm

combined gas and ion chromatographic analysis of fluid inclusions applications to archean granite pegmatite and gold quartz vein fluids the first stage in the interpretation of bulk fluid inclusion analytical data involves consideration of the relative amounts and types of fluid inclusions in a sample in order to determine which inclusion type dominates the volatile and or ion bulk analytical data this then permits discussion of processes affecting fluid chemistry such as fluid mineral equilibria metasomatism and phase separation and leads to constraints on primary source region fluid composition this interpretive procedure has been applied to data obtained by combined gas and ion chromatographic analysis of well characterized samples from the archean tanco granitic pegmatite southeastern manitoba and the hollinger mcintyre and kerr addison archean au quartz vein systems northern ontario the bulk composition of an homogeneous late stage magmatic fluid in lower intermediate zone vug quartz from the tanco pegmatite is 90 6 mol h2o 3 35 mol co2 2 45 mol li 2 40 mol cl 1 01 mol na and other trace species 1 mol the li li na ratio of 0 69 0 008 for this fluid is greater than a published experimental determination of 0 45 0 02 for a comparable system probably owing to the co2 rich nature of the vug quartz fluids the halogen cl br i and alkali metal enriched nature of this fluid is consistent with the advanced degree of igneous fractionation of the pegmatite compared to estimated bulk earth values the br cl ratio of 12 9 10 3 molar is high and may be the result of igneous fractionation while the i cl ratio 140 10 6molar is low suggesting that another process governs i behaviour tanco quartz zone samples show trace gas depletion trends comparable to those obtained from samples trapping phase separated fluids in low pressure geothermal systems trends in the tanco cation anion data reflect both fluid mineral equilibria and phase separation effects li and cl show a closely correlated decrease with increasing co2ch4 ratio while na shows no change consistent with partitioning of li and cl in favour of the co2 rich phase which could have contributed to the calcite and holmquistite bearing propylitic alteration zone around the pegmatite average bulk compositions for hollinger mcintyre and kerr addison fluids are similar and consist of 80 90 mol h2 2 15 mol co2 1 3 mol cl 2 4 mol na and trace species 1 mol hollinger mcintyre volatiles show clear wall rock reaction effects while kerr addison fluids show strong phase separation trends br cl ratios of 5 5 to 10 10 3 for hollinger mcintyre and kerr addison fluids are greater than bulk earth while i cl 106 ratios are low with a range from 20 105 hollinger mcintyre and tanco samples dominated by secondary brine inclusions have br cl 103 ratios of 13 and 15 respectively showing that these secondary fluids are distinct from shield brines br cl 3 to 5 5 10 3 both of these samples have distinctive trace hydrocarbon signatures

spatial and temporal patterns in channel change on the snake river downstream from jackson lake dam wyoming abstract operations of jackson lake dam jld have altered the hydrology and sediment transport capacity of the snake river in grand teton national park prior research has provided conflicting assessments of whether the downstream river was perturbed into sediment surplus or sediment deficit in this paper we present the results of an aerial photo analysis designed to evaluate whether the history of channel change indicates either significant deficit or surplus of sediment that could be expressed as narrowing or expansion of the channel over time we analyze changes in braid index channel width channel activity and net channel change of the snake river based on four series of aerial photographs between 1945 and 1969 a period of relatively small main stem floods widespread deposition and up to 31 reduction in channel width occurred throughout the snake river between 1969 and 2002 a period of large main stem floods the style of channel change reversed with a decrease in braid index and an increase in channel width of up to 31 these substantial changes in the channel downstream from the dam primarily occurred in multithread reaches regardless of proximity to tributaries and no temporal progression of channel narrowing or widening was observed we demonstrate that channel change downstream from jld is more temporally and longitudinally complex than previously described

geomorphic and vegetation changes in a meandering dryland river regulated by a large dam sauce grande river argentina abstract this paper investigates post dam geomorphic and vegetation changes in the sauce grande river a meandering dryland river impounded by a large water conservation dam as the dam impounds a river section with scarce influence of tributaries sources for fresh water and sediment downstream are limited changes were inspected based on i analysis of historical photographs imagery spanning pre 1961 and post dam 1981 2004 channel conditions for two river segments located above and below the dam and ii field survey of present channel conditions for a set of eight reference reaches along the river segments whilst the unregulated river exhibited active lateral migration with consequent adjustments of the channel shape and size the river section below the dam was characterized by i marked planform stability 93 to 97 and by ii vegetation encroachment leading to alternating yet localized contraction of the channel width up to 30 the present river displays a moribund stable channel where i redistribution of sediment along the river course no longer occurs and ii channel forms constitute a remnant of a fluvial environment created before closing the dam under conditions of higher energy in addition to providing new information on the complex geomorphic response of dryland rivers to impoundment this paper represents the very first geomorphic assessment of the regulated sauce grande and therefore provides an important platform to underpin further research assessing the geomorphic state of this highly regulated dryland river

the volatile geochemistry of magmatic h2o co2 fluid inclusions from the tanco zoned granitic pegmatite southeastern manitoba canada abstract gas chromatographic analyses using 105 c heated on line crushing as the release system and photoionization pid and micro thermal conductivity tcd detectors of 17 samples 2 g in duplicate from three zones of the tanco granitic pegmatite se manitoba indicate that h2o and co2 generally account for 99 mol of the volatiles detected from fluid inclusions in bulk the balance of the volatiles comprises trace amounts of n2 ar co ch4 c2h4 c2h6 c2h2 cos c3h6 c3h8 c4h8 isobutylene and n c4h10 in order of retention time samples of vug quartz beryl fringe and some samples from the quartz zone show little variation in co2 ch4 ratio from crush to crush suggesting that the same fluids are released by both crushes in general the analyses of sample and duplicate are consistent the volatile chemistries of all the samples are consistent with the results of fluid inclusion microthermometric and petrographic observations e g higher ch4 in beryl fringe samples with lower co2 melting points of 57 3 1 0 c n 61 the fluid trapped by the inclusions in a sample of lower intermediate zone liz vug quartz pv 18 6 core shows no petrographic or microthermometric evidence for h2o co2 phase separation and represents an internal probably magmatically derived fluid the volatile composition of this fluid is 95 6 mol h2o 4 3 mol co2 436 ppm ch4 277 ppm n2 19 ppm ar 3 ppm c2h6 1 ppm cos 1 ppm c3h8 0 3 ppm c2h4 98 ppb c2h2 plus so2 and trace c3h6 this composition i e h2o co2 ch4 n2 s species not included is comparable to those of high temperature 400 c volcanic gases e g white island new zealand mt st helens usa and is therefore compatible with a magmatic origin the salinity of this fluid ranges from 0 31 to 1 96 mcl 1 x 6 6 1 3 1 eq wt nacl which is higher than that predicted by the partition experiments of webster and holloway 1988 suggesting that the cl solubility limit of the late stage tanco melt may have been reached h2o co2 phase separation has influenced the bulk chemistry of the volatiles released from the fluid inclusions in the vug quartz beryl fringe and quartz zone preferential trapping is indicated in the latter two cases by the presence of higher amounts of co2 than are present in the fluid prior to phase separation liz vug quartz clear trends in the ratios of co2 trace gases indicate that the trace volatiles partitioned during phase separation resulting in n2 ch4 and the c2 hydrocarbons being preferentially incorporated into the co2 rich phase the occurrence of such depletion trends implies that the pegmatite was partially open to co2 loss the gases partition into the co2 rich phase in the following order n2 co 2 ch 4 slopes vary from as little as 0 7 co 2 n 2 to as much as 105 co 2 c 3 h 6 however the behavior of the individual hydrocarbons is complex reflecting the opposing or additive effects of cooling and phase separation

theoretical regime equations for mobile gravel bed rivers with stable banks a system of rational regime equations is developed for gravel bed rivers with stable banks using the optimality theory ot the optimality theory is based on the premise that equilibrium river geometry is characterised by an optimum configuration defined here as maximum sediment transport efficiency theoretical dimensionless equations are derived for width depth slope width depth ratio and meandering braiding transition independent dimensionless variables comprise discharge sediment concentration and relative bank strength which is defined as the ratio of the critical shear stresses for the bank and bed sediments discharge exponents and general form of the equations agree well with previously developed empirical relations relative bank strength is used to parameterise the influence of riparian vegetation on bank strength and is evaluated by calibrating against observed width depth ratio once calibrated the hydraulic geometry of natural gravel rivers is well described by the theoretical equations including discrimination between meandering and braiding channels the results provide strong support for the assumption that equilibrium or regime river behavior is equivalent to an optimal state and underline the importance of bank strength and sediment load as controls on hydraulic geometry

analysis of fluid inclusions in seafloor hydrothermal precipitates testing and application of an integrated gc ic technique the principal research objective was to test an integrated gas gc and ion chromatographic ic technique for analysis of trapped fluids in seafloor hydrothermal precipitates and to compare the results with independently analyzed vent fluids twenty three samples of chalcopyrite pyrite sphalerite barite and anhydrite from hydrothermal chimneys from four seafloor sites axial seamount juan de fuca ridge the vai lili vent field lau basin the tag hydrothermal field mid atlantic ridge and the 21 n vent field east pacific rise as well as of pyrite marcasite and quartz from the tag mound were analyzed a new type of blank for sulphides and sulphates was also developed water contents obtained by gc analysis are in agreement with known compositions of seafloor hydrothermal solutions also the volatiles occur in the same order of abundance as in vent fluids co2 n2 co ar o2 ch4 cos c2 c3 hydrocarbons for all analyzed hydrothermal fluids the mean cl concentrations are similar to those for the respective measured vent fluid compositions furthermore the gc ic results are directly comparable to salinity data determined by microthermometric methods nh4 can be enriched and is most probably formed by decomposition of organic matter volatile concentrations in fluid inclusions and data from vent fluids differ significantly for some of the investigated sites furthermore the gc data indicate systematic variations regarding the volatile contents of trapped fluids from different active seafloor hydrothermal systems fluid inclusion volatile data of samples from the ashes vent field at axial seamount define an inclined array consistent with phase separation

anabranching rivers their cause character and classification anabranching rivers consist of multiple channels separated by vegetated semi permanent alluvial islands excised from existing floodplain or formed by within channel or deltaic accretion these rivers occupy a wide range of environments from low to high energy however their existence has never been adequately explained they occur concurrently with other types of channel pattern although specific requirements include a flood dominated flow regime and banks that are resistant to erosion with some systems characterized by mechanisms to block or constrict channels thereby triggering avulsion the fundamental advantage of an anabranching river is that by constructing a semi permanent system of multiple channels it can concentrate stream flow and maximize bed sediment transport work per unit area of the bed under conditions where there is little or no opportunity to increase gradient on the basis of stream energy sediment size and morphological characteristics six types of anabranching river are recognized types 1 3 are lower energy and types 4 6 are higher energy systems type 1 are cohesive sediment rivers commonly termed anastomosing with low w d ratio channels that exhibit little or no lateral migration they are divisible into three subtypes based on vegetative and sedimentary environment type 2 are sand dominated island forming rivers and type 3 are mixed load laterally active meandering rivers type 4 are sand dominated ridge forming rivers characterized by long parallel channel dividing ridges type 5 are gravel dominated laterally active systems that interface between meandering and braiding in mountainous regions type 6 are gravel dominated stable systems that occur as non migrating channels in small relatively steep basins anabranching rivers represent a relatively uncommon but widespread and distinctive group that because of particular sedimentary energy gradient and other hydraulic conditions operate most effectively as a system of multiple channels separated by vegetated floodplain islands or alluvial ridges

river channel change during the last 50 years in the middle yangtze river the jianli reach intensive anthropogenic disturbances have affected the channel of the middle yangtze river since the 1950s this paper selects the jianli reach as an example to examine human impact on channel change in the middle yangtze river 1 100 000 channel distribution maps from 1951 1961 and 1975 and 1 25 000 navigation charts from 1981 and 1997 were employed to reconstruct channel change in the study reach the result indicates that the channel under the constraint of levees along the riverbanks underwent a minor widening but frequent bank failure due to susceptible bank structure and increase in water discharge the bank failure promoted bar growth in the channel cross section changes and quantitative calculations of erosion and deposition based on the dem derived from navigation charts present a pattern of over bank sedimentation and riverbed incision the stage and duration of floods have increased following levee construction and bank revetment

the role of vegetation in the formation of anabranching channels in an ephemeral river northern plains arid central australia as the distribution and abundance of vegetation in drylands is often controlled by the greater availability of water along river channels riparian vegetation has the potential to influence significantly dryland river form process and behaviour this paper demonstrates how a small indigenous shrub the inland teatree melaleuca glomerata influences the formation and maintenance of anabranching channels in a reach of the ephemeral marshall river northern plains arid central australia here the marshall is characterized by ridge form anabranching where water and sediment are routed through subparallel multiple channels of variable size which occur within a typically straight channel train channels are separated by channel train ridges narrow flow aligned vegetated features or by wider islands by providing a substantial element of boundary roughness dense stands of teatrees growing on channel beds or atop the ridges and islands influence flow velocities flow depths and sediment transport resulting in flow diversion bank and floodplain erosion and especially sediment deposition ridges and islands represent a continuum of forms and their formation and development can be divided into a three stage sequence involving teatree growth and alluvial sedimentation 1 teatrees colonize a flat sandy channel bed initiating the formation of ridges by lee side accretion individual ridges grow laterally vertically and longitudinally and maintain a geometrically similar streamlined lemniscate form that presents minimum drag 2 individual ridges grow in size and interact with neighbouring ridges causing the lemniscate forms to become distorted ridges in the lee of other ridges tend to be protected from the erosive effects of floods and survive whereas individual teatrees or small ridges exposed to flow concentrated between larger ridges tend to be removed 3 ridges lengthen and coalesce with downstream ridges eventually subdividing the channel train into well defined anabranches this sequence turns a channel initially obstructed with dense and chaotic stands of teatrees into a well organized system of ridge form anabranches in the moderate to low gradient marshall river which is colonized by an abundance of within channel vegetation and subject to declining downstream discharges this helps to minimize flow resistance thereby maintaining an efficient water and sediment flux copyright 2000 john wiley sons ltd

microthermometric laser raman spectroscopic and volatile ion chromatographic analysis of hydrothermal fluids in the paleozoic muruntau au bearing quartz vein ore field uzbekistan fluid inclusions in quartz and scheelite from flat steeply dipping central and stockwork type quartz veins within the muruntau au bearing quartz vein ore field have been investigated in a reconnaissance study using fluid inclusion mapping microthermometry laser raman spectroscopy and integrated gas and ion chromatography for bulk volatile and cation anion analysis muruntau central veins are dominated by inferred early co2 bearing fluid inclusions in contrast flat quartz veins contain considerable numbers of low density pure aqueous inclusions on deformation and recrystallization related microstructures fluid phase separation is indicated for samples from the muruntau central ore veins by fluid inclusion observational work as well as by microthermometry and bulk fluid geochemistry co2 ch4 co2 n2 and co2 c2 and c3 hydrocarbon ratios salinity data however in flat veins and all samples from the myutenbai deposit no evidence for fluid immiscibility could be found quartz microstructural results and fluid inclusion data suggest formation of the low grade mineralized flat veins before the main stage of hydrothermal activity and considerable variation in the geochemical conditions during fluid evolution in the muruntau and myutenbai deposits mixing of fluids from different sources in variable proportions may be inferred from halide geochemistry furthermore fluid inclusion br cl ratios differ significantly for samples from different vein types fluid phase separation is suggested as a mechanism for the precipitation of au from the hydrothermal fluid in the muruntau high grade au mineralized central veins

synthetic fluid inclusions viii vapor saturated halite solubility in part of the system nacl cacl2 h2o with application to fluid inclusions from oceanic hydrothermal systems abstract halite solubility along part of the vapor saturated liquidus in the system nacl cacl 2 h 2 o has been determined using the synthetic fluid inclusion technique data allow the construction of liquidus isotherms for temperatures up to 500 c and bulk compositions containing 60 wt total salt and as much as 25 wt cacl 2 combined with previous data for the binary system nacl h 2 o and for the ternary system nacl cacl 2 h 2 o in the low salinity low temperature region a preliminary ternary phase diagram can be constructed that remains incomplete only in the cacl 2 rich region results are applied to the interpretation of saline fluid inclusions from quartz veins in oceanic metagabbros and can be applied to many other natural inclusions containing aqueous solutions with nacl and cacl 2 the dominant solutes microthermometric measurements at equilibrium of the melting temperature of ice tm ice and of the dissolution temperature of halite tm halite are sufficient to determine the bulk composition of the nacl cacl 2 h 2 o fluid

preliminary evaluation of trace hydrocarbon speciation and abundance as an exploration tool for footwall style sulfide ores associated with the sudbury igneous complex ontario canada deposits of cu ni platinum group elements pge rich sulfides occur along the north range footwall of the sudbury igneous complex ontario canada the deposits have been modified chemically mineralogically and texturally by multiple syn to postmagmatic hydrothermal events and are hosted mainly within sudbury breccia a contact metamorphosed and hydrothermally altered impact breccia the composition of c1 to c6 unsaturated and saturated hydrocarbons in bulk fluid inclusion volatiles in the matrix of the sudbury breccia was investigated using in line rock crushing gas chromatography gc in order to compare the hydrocarbon composition of this rock type in breccia zones containing economic footwall sulfide deposits at the morrison deposit levack mine north range sudbury ontario with barren breccia zones trace hydrocarbons possibly abiogenic in origin occur throughout the sudbury igneous complex footwall and country rocks investigated however there are differences in the composition and abundance of bulk hydrocarbons released from mineralized and barren sudbury breccia when fluid inclusions are opened volatiles released from samples of sudbury breccia from sulfide mineralized and sulfide barren environments showed the following 1 higher average abundances of light saturated hydrocarbons c1 c4 and an approximately 2 higher total abundance of hydrocarbons mol g of rock basis associated with samples from the mineralized study area and 2 comparable average unsaturated hydrocarbon abundances in both settings but a larger range in unsaturated hydrocarbon abundances in the mineralized study area differences in bulk hydrocarbon abundance and composition reflect differences in the abundance and hydrocarbon content of fluid inclusions trapped in the barren and mineralized sudbury breccia zones in addition the compositional modification of circulating fluids by processes and conditions unique to the mineralized sudbury breccia environment may have occurred prior to inclusion entrapment e g modification by mineral catalysts differences in temperature and oxygen fugacity preliminary spatial analysis of the hydrocarbon distribution within and surrounding the morrison deposit shows that the total hydrocarbon abundance in the sudbury breccia does not change with orebody proximity within a single host breccia zone however volatiles trapped in the sudbury breccia matrix near the top of the footwall deposit where it is physically connected to contact style ni cu pge ores have elevated unsaturated hydrocarbon abundances e g propene compared to other parts of the same breccia zone distal to this zone of physical connection samples of the pge enriched sudbury breccia and mineralized veins containing alteration assemblages characteristic of the footwall ore styles have higher unsaturated hydrocarbon abundances and unsaturated saturated ratios compared to sudbury breccia and vein samples that are pge poor localized enrichments in unsaturated hydrocarbons in sudbury breccia zones may be the result of specific ore minerals and metal complexes involving the pge and group viii metals that acted as catalytic agents modifying the composition of initially light saturated hydrocarbon species prior to entrapment in fluid inclusions to apply the analysis of hydrocarbon compositions in trapped fluid inclusions to discriminating mineralized from barren zones of sudbury breccia samples from targeted areas were compared to samples of barren sudbury breccia background although a large data set is presented here to establish these compositional fields analysis of smaller sample subsets from each environment yields a statistically significant separation between the two environments total hydrocarbon abundance c3 c1 ratios and unsaturated saturated hydrocarbon ratios are useful indicators of sulfide ore proximity and may help delineate regions enriched in pge

morphology hydrology and evolution of the anastomosing ovens and king rivers victoria australia anastomosing channels form the characteristic stream pattern of the riverine plain of southeastern australia investigations of the ovens and king rivers in northeastern victoria show that the individual channels and reaches of channels vary markedly in channel morphology and age young channels have large bankfull flows low sinuosity large meander wavelength steep gradients and are unstable they are incised channels that are rapidly eroding their bed and banks old channels however have small bankfull flows high sinuosity small meander wavelength gentler gradients and are relatively stable the multiple channels develop by avulsion as individual channels become older and more sinuous they also become more hydraulically inefficient thus increasing proportions of flood discharge are displaced overbank this overbank flow concentrates in relatively straight flood plain depressions and it erodes a new channel which develops by both up and down valley incision down valley incision is initiated at outflow points and up valley incision is initiated where the overbank flow rejoins the main channel with time both channel segments join to form a new anabranch of the anastomosing channel system large anastomosing channel networks have been identified in ancient rocks by stratigraphers and sedimentologists on the basis of studies of the anastomosing ovens and king rivers it is very likely that these channel networks are composed of channels of different ages hence even at one stratigraphic level not all of the anabranches functioned simultaneously nevertheless as a result of anabranch incision which intersects older channels at depth a three dimensional network of paleochannels can form that permits fluid flow throughout the network

the impact of the three gorges dam on the downstream distribution and texture of sediments along the middle and lower yangtze river changjiang and its estuary and subsequent sediment dispersal in the east china sea abstract the grain size of river sediments changes systematically downstream from source to sink and is influenced by catchment lithology geomorphology hydrology oceanography and in modern settings anthropogenic impacts compared with small gravel bedded river systems less is known about large sandy bed rivers particularly from the river source to marine sink in the present study we examine longitudinal changes in sediment grain size along the middle and lower yangtze river downstream of the three gorges dam tgd and along the major sediment dispersal pathway into the east china sea over a total length of 2100 km we also examine the spatial patterns of seabed sediment grain size in the east china sea adjacent to the yangtze estuary 70 000 km 2 in area in particular we consider the impact of the tgd on the grain size of the riverbed and seabed sediments before the construction of the tgd the relationship between median grain size and distance along the sandy bed of the middle and lower yangtze showed a downstream fining trend that was exponential in form after the tgd was built erosion caused an abrupt gravel sand transition to develop in the section immediately downstream of the tgd in the yangtze estuary flocculation and subsequent deposition of suspended riverine mud during the slack water period between flood and ebb tides led to the formation of an abrupt sand mud transition muddy deposits along the major longshore sediment dispersal route also show an exponential fining trend however towards the open east china sea the modern riverine muds are replaced seawards by older sands the mud margin there was found to have retreated landward significantly over the post tgd period due to erosion driven by the significant decrease in sediment supply from the yangtze river we expect that the impact of the tgd on the grain size of bed sediments in the yangtze river and the east china sea will continue for some time and the change in the grain size of bed sediments there will become more pronounced

significant decadal channel change 58 67 years post dam accounting for uncertainty in topographic change detection between contour maps and point cloud models abstract construction of digital elevation models dems and the subtraction of dems between different points in time as a method to determine temporal patterns of scour and fill is a highly valuable procedure emerging in geomorphology these dems of differences dods must be assessed for error in order to distinguish actual topographic change from uncertainty and surface error current methods include 1 uniformly excluding all values that fall below a minimum threshold 2 using a spatially variable approach such as the construction of minimum level of detection lod grids or 3 the creation of a fuzzy inference system although spatially variable methods for determining error have been more accurate in excluding noise without discarding large amounts of meaningful data a challenge remains in performing dods against preexisting contour based maps for which no original point data are available the goals of this study were to 1 develop a method that overcomes the unknown point density of contour and other historical data sets and allows for some assessment of dod uncertainty on the basis of information on topographic variability 2 perform comprehensive uncertainty analysis testing to understand the opportunities and constraints associated with this new method and 3 report and interpret the overall pattern and volume of decadal topographic change for a regulated river 67 years post dam in light of alternate conjectured mechanisms of post dam longitudinal profile adjustment the key feature of the new approach is the introduction of a high density artificial point grid that samples the topographic variability evident in the available historical data set the testbed used to develop and assess this new dod method was the 37 5 km lower yuba river california historical data consisted of 0 6 m contours from a 1999 survey while a more detailed point cloud was available for the most recent survey in 2006 2008 to evaluate uncertainty in the method this study applied seven different uncertainty metrics of varying strictness t 1 t 1 96 uniform 0 3 m exclusion t 1 plus uniform 0 3 m exclusion t 1 with lod minimum at 0 3 t 1 96 plus uniform 0 3 m exclusion and t 1 96 with lod minimum at 0 3 and two different dod adjustment methods exclusion and subtraction a stringent approach involving joint use of the contour half interval and the spatially distributed lod grid at a 95 confidence limit excluded 44 3 of the study area from spatial assessment of channel change and volumetric change computation this preferred approach yielded an estimated 2 518 million m 3 of total scour and 2 455 million m 3 of total fill in 7 9 years after considering different mapping epochs the net annual average export was 17 000 m 3 32 500 tons to the feather river and a river valley sediment yield of 2205 tons km 2 year this amount is 36 of the post dam annual yield of gravel and cobble to the upstream reservoir that blocks sediment conveyance into the study domain suggesting that the lowland system is still highly dynamic 67 years after the dam was built the scientific significance of this is that the response of rivers to dams can be far more long lasting and complex depending on the suite of cumulative societal impacts to rivers the ability to account for spatially explicit dod uncertainty i e data retention when uncertainty is low and data removal when uncertainty is high when comparing historic contour based and modern point cloud based dems will allow for more detailed and reliable dods and sediment budgets in these cases

bifurcation dynamics and avulsion duration in meandering rivers by one dimensional and three dimensional models at river bifurcations water and sediment are divided over two branches the dynamics of the bifurcation determine the long term evolution centuries of the downstream branches potentially leading to avulsion but the dynamics are poorly understood the long term evolution can only be studied by one dimensional models because of computational costs for such models a relation describing the sediment division is necessary but only few relations are available and these remain poorly tested so far we study the division of sediment and the morphodynamics on a timescale of decades to centuries by idealized three dimensional modeling of bifurcations with upstream meanders and dominantly bed load transport an upstream meander favors one bifurcate with more sediment and the other with more water leading to destabilization the bifurcations commonly attain a highly asymmetrical division of discharge and sediment after a few decades to a few centuries depending on combinations of the relevant parameters although past work on avulsions focused on slope advantage we found that bifurcations can be quasibalanced by opposing factors such as a bifurcate connected to the inner bend with a downstream slope advantage nearly balanced bifurcations develop much slower than unbalanced bifurcations which explains the observed variation in avulsion duration in natural systems which branch becomes dominant and the timescale to attain model equilibrium are determined by the length of the downstream bifurcates the radius of the upstream bend a possible gradient advantage for one bifurcate and notably the width depth ratio the latter determines the character of the bars which may result in overdeepening and unstable bars the distance between the beginning of the upstream bend and the bifurcation determines the location of such bars and pools which may switch the dominant bifurcate in fact when the bifurcation is quasibalanced by opposing factors any minor disturbance or a different choice of roughness or sediment transport predictor may switch the dominant bifurcate the division of sediment is nearly the same as the division of flow discharge in most runs until the discharge division becomes very asymmetrical so that a bifurcate does not close off entirely this partly explains the sustained existence of residual channels and existence of anastomosing rivers and the potential for reoccupation of old channel courses we develop a new relation for sediment division at bifurcations in one dimensional models incorporating the effect of meandering the flow and sediment divisions predicted by two existing relations and the new relation for one dimensional models are in qualitative agreement with the three dimensional model these one dimensional relations are however of limited value for wider rivers because they lack the highly three dimensional bar dynamics that may switch the direction of bifurcation evolution the potential effects of bed sediment sorting bank erosion and levee formation on bifurcation stability and avulsion duration are discussed

mass spectrometric identification of boric acid in fluid inclusions in pegmatite minerals direct on line mass spectrometric analyses were performed on volatiles released from micro scopic fluid inclusions in quartz feldspar and tourmaline from the miarolitic belo horizonte 1 pegmatite in the san jacinto district and himalaya pegmatite dike system in the mesa grande district of southern california these analyses are the first inclusion volatile studies to indicate the presence of significant and variable concentrations of b compounds in pegmatite formation fluids boron appears as boric acid b oh 7 which is found at levels ranging from less than detection limit 10 mole fraction to as high as 10m4 mole fraction high b concentrations are seen in inclusion fluids from miarolite filling quartz cleavelandite variety albite feldspar and schorl tourmaline from the belo horizonte l while negligible amounts appear in late stage green pink zoned gem elbaite tourmalines from that mine fluid inclusions in quartz as well as grey and pink tourmaline from the miarolites in the himalaya mine have undetectable levels of b compounds in addition to confirming the presence of very high boric acid concentrations in some pegmatite forming solutions observations of large variations in abundance may urovide new constraints on fluid chemical evolution trends during the genesis of these regionally and baragenetically complex gem deposits

channel patterns braided anabranching and single thread a new channel pattern classification is presented based on theoretically derived channel pattern discriminant functions the thresholds are formulated as power laws that relate the critical slope associated with a change in channel pattern to dimensionless discharge and relative bank strength one threshold demarcates the boundary between stable single thread channels both straight and meandering and stable multiple thread channels anabranching another threshold separates anabranching from braided channels where braided channels are considered to be fundamentally unstable the exponents of the thresholds are nearly identical to that in the threshold equation originally proposed by leopold and wolman 1957 and the coefficients are quite similar as well an analysis of their data set using our dimensionless approach reveals that no fundamental difference exists between meandering and straight patterns and thus data from both types are grouped together under the more general heading of single thread channels furthermore we demonstrate that over a limited range of conditions an unstable single thread channel can form stable multiple threads but that for systems far from the threshold bounding the single thread channels the number of divisions required to produce stable anabranches grows geometrically this motivates a separation of multiple thread channels into anabranching and braided types our theoretical thresholds are then compared against several large data sets of field data and the results broadly confirm our proposed thresholds

why some alluvial rivers develop an anabranching pattern anabranching rivers have been identified globally but a widely accepted and convincing theoretical explanation for their occurrence has remained elusive using basic flow and sediment transport relations this study analyzes the mechanisms whereby self adjusting alluvial channels can anabranch to alter their flow efficiency sediment transport capacity per unit of stream power it shows that without adjusting channel slope an increase in the number of channels can produce a proportional decrease in flow efficiency a finding particularly relevant to understanding energy consumption in some braided rivers however anabranching efficiency can be significantly increased by a reduction in channel width as occurs when vegetated alluvial islands or between channel ridges form the counteracting effects of width reduction and an increasing number of channels can cause with no adjustment to slope an otherwise unstable system underloaded or overloaded to achieve stability as with other river patterns anabranching can be characterized by stable equilibrium or accreting disequilibrium examples copyright 2007 by the american geophysical union

fluid characteristics of vein and altered wall rock in archean mesothermal gold deposits certain trends in alteration are commonly observed near archean mesothermal gold deposits this study was designed to monitor the changes in composition of fluid inclusions using solid probe mass spectrometry by 1 establishing and verifying systematic changes in the composition of the fluid during fluid rock interaction 2 characterizing the composition and behavior of fluids in the vein and the wall rock in order to establish a link between them 3 elucidating new insights on the role of fluid immiscibility in gold deposition and 4 scrutinizing the results for potential use in exploration three representative sites of gold mineralization were chosen a large deposit with appreciable amounts of free gold sigma mine in val d9or a second deposit with a smaller amount of free gold norbeau mine in chibougamau and a third area of gold mineralization with altered wall rock and little veining tadd prospect in chibougamau fluid inclusions were carefully selected to sample different alteration zones and the gold mineralization at each site in most of the cases varying degrees of unmixing of co 2 h 2 o were noted mass spectra results show that during alteration all generations of inclusions at all sites contained co 2 and h 2 o for the alteration hosted deposit a decrease in x sub co 2 could be mapped outward from the mineralized zone the most striking result was that fluid inclusions associated with the main mineralizing episode at sigma showed a nearly complete segregation into co 2 and h 2 o end members this can be interpreted as the result of extreme fluid pressure fluctuations this characteristic was absent from the norbeau veins where free gold exists in very limited amounts a test on a high grade ore shoot from the doyon mine resulted in a pattern similar to sigma we suggest extreme pressure fluctuations were limited in vein hosted deposits like norbeau and gold was precipitated essentially from fluid rock mineral interaction unmixing was the most likely cause of free gold deposition mineralizing systems may have undergone major fracturing events at time of free gold deposition this study suggests high co 2 h 2 o ratios are related to gold mineralization in altered rock hosted deposits but that the ratio may be an unreliable guide in vein hosted deposits because of the variable unmixing pattern of co 2 h 2 o fluids decrepitometry may prove a useful and rapid method for identifying co 2 h 2 o unmixing and bonanza gold potential

assessment of gas hydrate and free gas distribution on the south shetland margin antarctica based on multichannel seismic reflection data summary processing and interpretation of a grid of intermediate resolution multichannel seismic reflection profiles collected on the ne sector of the south shetland continental margin allowed us to map the lateral extent of a bottom simulating reflector bsr the margin an accretionary wedge located off the northern tip of the antarctic peninsula consists of two distinct and superimposed tectonic regimes an older regime is related to mesozoic middle cenozoic subduction related tectonism a younger one is associated with a mainly extensional tectonic phase and related to the oligocene development of the western scotia sea the occurrence of the bsr appears to be controlled by the geological structure of the margin the bsr lacks continuity near basement structures main geological discontinuities and faults on the other hand the amplitude and continuity of the bsr are not affected by the presence of folded structures and undeformed sedimentary layering we found that the bsr is mostly confined to the ne sector of the south shetland margin where propagation of faulting associated with the shackleton fracture zone may have driven migration of natural gas towards the surface and created the conditions for a bsr to appear the application of reflection tomography techniques allowed us to reconstruct the averaged seismic velocity field between the seafloor and bsr in order to map the depth of bsr by averaging the observed velocity structure above and below the bsr and applying a theoretical model of elastic wave propagation in porous media we attempted as rigorous a quantitative assessment as possible of the natural gas present as gas hydrate above the bsr and as free gas between the bsr and the base of gas reflector bgr

predicting channel patterns brewer paul lewin j 2001 predicting channel patterns geomorphology 40 pp 329 339 rae2008

evolution of a bifurcation in a meandering river with adjustable channel widths rhine delta apex the netherlands rivers may dramatically change course on a fluvial plain such an avulsion temporarily leads to two active channels connected at a bifurcation here we study the effect of dynamic meandering at the bifurcation and the effect of channel width adjustment to changing discharge in both downstream branches on the evolution of a bifurcation and coexisting channels as an example we reconstructed the last major avulsion at the rhine delta apex we combined historical and geological data to reconstruct a slowly developing avulsion process spanning 2000 years and involving channel width adjustment and meandering at the bifurcation based on earlier idealised models we developed a one dimensional model for long term morphodynamic prediction of upstream channel and bifurcates connected at the bifurcation node the model predicts flow and sediment partitioning at the node including the effect of migrating meanders at the bifurcation and channel width adjustment bifurcate channel width adaptation to changing discharge partitioning dramatically slows the pacing of bifurcation evolution because the sediment balance for width adjustment and bed evolution are coupled the model further shows that meandering at the bifurcation modulates channel abandonment or enlargement periodically this explains hitherto unrecognised reactivation signals in the sedimentary record of the studied bifurcation meander belts newly identified in our geological reconstruction historical maps show that bifurcation migration due to meander bend dynamics increases the bifurcation angle which increases the rate of closure of one bifurcate the combination of model and reconstruction identifies the relevant timescales for bifurcation evolution and avulsion duration these are the time required to fill one downstream channel over one backwater length the time to translate one meander wavelength downstream and for strong river banks the adaptation timescale to adjust channel width the findings have relevance for all avulsions where channel width can adjust to changing discharge and where meandering occurs copyright 2011 john wiley sons ltd

anabranching and maximum flow efficiency in magela creek northern australia 1 anabranching is the prevailing river pattern found along alluvial tracts of the world s largest rivers hydraulic geometry and bed material discharge are compared between single channel and anabranching reaches up to 4 times bank full discharge in magela creek northern australia the anabranching channels exhibit greater sediment transporting capacity per unit available stream power i e maximum flow efficiency mfe simple flume experiments corroborate our field results showing the flow efficiency gains associated with anabranching and highlight the prospect of a dominant anabranch which is found in many anabranching rivers these results demonstrate that anabranching can constitute a stable river pattern in dynamic equilibrium under circumstances in which a continuous single channel would be unable to maintain sediment conveyance we propose the existence of a flow efficiency continuum that embraces dynamic equilibrium and disequilibrium vertically accreting anabranching rivers

formation of tonalite in island arcs by seawater induced anatexis of mafic rocks evidence from the lyngen magmatic complex north norwegian caledonides abstract the lyngen magmatic complex lmc of north norway consists of a western suite of layered gabbros of normal mid oceanic ridge basalt n morb affinity and an eastern suite of layered gabbronorites quartz bearing gabbros and diorites quartz diorites of iat island arc tholeiitte to boninitic affinity the boundary between the suites is defined by a large scale ductile shear zone the rypdalen shear zone rsz in this shear zone anatectic tonalites were generated by partial melting of the gabbro in the presence of an h 2 o bearing fluid phase quartz from the tonalites contains early secondary and secondary liquid dominated inclusions 88 99 wt h 2 o with an average salinity of 18 wt calculated as nacl eq combined gas and ion chromatography shows that the major ions in the fluid are cl ca 2 na with smaller amounts of k mg 2 sr 2 br and no 3 the dominant non h 2 o volatile species is n 2 0 5 10 and small amounts of co 2 ch 4 and other hydrocarbons are also present the cation concentrations in the fluid are variable due to element exchange during interaction of the fluids with the tonalites amphibolites and metagabbros of the rsz the fluid contributed na and k to the melt and gained ca 2 in exchange explaining the variable na ca 2 ratio of the fluid the br and cl contents of the fluid inclusions plot on the same line as evaporating sea water which strongly suggests a seawater origin for the fluid phase and a seawater source fits well with other geochemical signatures and the tectonic setting of the lmc it is suggested that seawater escaped from a subducting slab and was channelled along the rypdalen shear zone this caused anatexis of the gabbro generating tonalitic melts at 0 5 0 9 gpa and 680 800 c

the geomorphologic response of a large pristine alluvial river to tremendous deforestation in the south american tropics the case of the araguaia river article i nfo article history accepted 11 december 2008 available online xxxx the geomorphic response of the araguaia river to catastrophic deforestation of the cerrado since 1970s is discussed with a mean annual discharge of 6500 m 3 s and a drainage area of 380 000 km 2 the araguaia river is the main system draining the savannas of central brazil here we demonstrate that the river is undergoing a substantive increase in bed load transport and changes in its geomorphology a multi approach methodology was used and involved detailed geomorphologic mapping for three decades 60 70 and 90 a budget of erosional and deposition areas using gis volumetric calculations and estimations of bed load transport our results show that the alluvial plain is undergoing active sedimentation and 233 mt of sediments were stored by channel activity in a reach 570 km long of the middle araguaia the bed load transport has increased 31 from 6 6 mt in the sixties to 8 8 mt in the 1990s and the channel pattern has been metamorphosed to some extent this is an outstanding current example of short term geomorphic response to deforestation in a large pristine tropical fluvial system without direct human interventions in the channel

geomorphic response of the jingjiang reach to the three gorges project operation upstream damming often causes significant downstream geomorphic adjustments remarkable channel changes have occurred in the jingjiang reach of the middle yangtze river since the onset of the three gorges project tgp therefore it is important to investigate the variations in different fluvial variables for better understanding of the channel evolution characteristics as an example of the jingjiang reach recent geomorphic adjustments in the study reach have been investigated quantitatively including variations in sediment rating curve fluvial erosion intensity channel deformation volume and bankfull channel geometry these fluvial variables adjusted in varying degrees in response to the altered flow and sediment regime caused by the tgp operation a focus of this study has been especially paid on the variation in the bankfull channel geometry calculated bankfull dimensions at section and reach scale indicate that i there were significant bank erosion processes in local regions without bank protection engineering with empirical relations being developed to reproduce the variation in bankfull widths at four typical sections ii the variation in the reach scale channel geometry occurred mainly in the component of bankfull depth owing to the construction of large scale bank revetment works with the depth increasing from 13 7 m in 2002 to 15 0 m in 2014 and with an increase in the corresponding bankfull area of about 11 and iii the reach scale bankfull channel dimensions responded to the previous five year average fluvial erosion intensity during flood seasons at zhicheng with higher correlations for the depth and area being obtained when calibrated by the measurements in 2002 2012 furthermore these developed relations for the section and reach scale bankfull channel geometry were also verified by the observed data in 2013 2014 with encouraging results being obtained this article is protected by copyright all rights reserved

geochemical investigations to explain iodine overabundances in antarctic meteorites abstract iodine bromine and chlorine concentrations were determined in different antarctic meteorite specimens eucrites high iron and low iron chondrites with isotope dilution mass spectrometry in all antarctic meteorites i overabundances have been analysed compared with the concentrations for non antarctic meteorites of the same class half of the antarctic specimens show especially high concentrations of more than 1 g a similarly high enrichment effect in antarctic meteorites was not found for br and cl but smaller cl excesses could be observed in some eucrites and high iron chondrites by analysing different types of antarctic rocks a significant decrease of the i concentration but not of the br and cl concentration was determined from the surfaces to the centers of the rocks this shows that atmospheric i compounds interact with the surfaces of antarctic rocks and therefore with those of antarctic meteorites as well analyses of atmospheric halogens show that the gaseous compound ch 3 i is probably responsible for the i overabundance in antarctic meteorites and rocks chloride and bromide are found in particles derived from sea spray in antarctic aerosols deposition of halogens in antarctic snow near the coast shows i cl ratios 10 190 higher than the average value for seawater the corresponding br cl ratios are in the same range as seawater on the basis of our results and of other reported data we construct a preliminary hypothesis for a geochemical i cycle in antarctica taking into consideration long distance and short distance transportation of different i compounds from the coast to inland antarctica

the waihi epithermal gold silver base metal sulfide quartz vein system new zealand temperature and salinity controls on electrum and sulfide deposition the large andesite hosted quartz vein system at waihi contains a major epithermal au ag deposit total production of 6 4 moz au and 39 9 moz ag ag au 6 2 it is notable for a large vertical extent up to 575 m of economic au ag ore a pervasive adularia quartz illite chlorite pyrite alteration zone bounds the larger quartz veins and is associated with veinlets of quartz calcite pyrite adularia illite this zone is enveloped by an illite quartz adularia chlorite calcite pyrite alteration zone which grades out through a transition zone characterized by interlayered illite smectite into a smectite chlorite calcite alteration zone in the least altered andesites the formation of the adularia quartz chlorite calcite pyrite and some illite in these alteration assemblages was associated with an initial stage of vein filling by platy calcite and quartz this was followed by a main stage of quartz and sulfide vein filling with crustiform quartz at deeper levels and colloform quartz plus minor adularia at shallow levels deposition of main stage quartz and sulfides was accompanied by illite overprinting adularia in the wall rock and filling fractures in the quartz calcite pyrite adularia veinlets sulfide bearing bands associated with the main stage quartz show a zonation with decreasing depth from a coarse grained sphalerite galena pyrite chlorite assemblage at deep levels to a finer grained sphalerite galena pyrite chalcopyrite acanthite electrum assemblage at medium to shallow levels fluid inclusion studies indicate that the main stage quartz was deposited from fluids which ranged in temperature and composition from up to 295 c and 1 7 wt percent nacl equiv at depth to 190 c and 0 2 wt percent nacl equiv at shallow levels these are true salinities because the fluids extracted from the fluid inclusions have low co 2 contents 0 05 0 24 wt quartz within electrum poor zn pb fe sulfide bands was deposited at higher temperatures 295 242 c and salinities than quartz in electrum bearing zn pb fe cu ag sulfide bands 260 190 c temperature versus depth profiles for fluid inclusions with evidence of boiling indicate that the paleowater table was located about 160 m above the present erosion level during deposition of the main stage quartz minor amethyst as the final stage of vein filling was locally preceded by inesite and was not associated with sulfides and electrum amethyst was deposited at 253 to 170 c from fluids containing up to 4 5 wt percent nacl equiv these higher salinities are attributed to concentration of salts in the residual liquid by localized open system boiling chloride depth chloride enthalpy and 18 o water enthalpy plots indicate mixing of deep fluids up to 1 7 wt nacl for the main stage quartz with very low salinity steam heated ground water oxygen isotope 18 o values for vein quartz and amethyst range from 6 1 to 11 6 per mil and for vein calcite from 2 29 to 9 4 per mil calculated 18 o water values define a trend from 2 9 per mil at shallow levels to 0 6 per mil at depth extrapolation of the dilution trend on a 18 o water enthalpy plot indicates that the deep fluid 18 o water 0 6 was mixed with heated 160 180 c ground water of local meteoric water composition 5 5 dilution of a deep chloride fluid 1 2 wt nacl equiv carrying zinc and lead as chloride complexes with steam heated ground water is inferred to have been responsible for deposition of the electrum poor zn pb fe sulfide assemblage from 300 to 240 c at a paleodepth below about 500 m deposition of this assemblage may also have been promoted by decrease of sulfur in solution through loss of h 2 s gas by boiling during episodic fracturing the decrease in salinity following dilution favored the transport of gold silver and copper as hydrosulfide complexes and led to the deposition of the electrum bearing zn pb fe cu ag sulfide assemblage over a temperature range of 260 to less than 190 c at paleodepths of 500 to less than 250 m in this assemblage the decrease of sulfur in solution as a result of deposition of the associated chalcopyrite pyrite and galena is a likely mechanism for electrum deposition

functional relationships between vegetation channel morphology and flow efficiency in an alluvial anabranching river 1 water and sediment flux interactions are examined in magela creek an alluvial anabranching sand bed river in the northern australian tropics dense riparian vegetation stabilizes the channels and floodplains thereby preventing erosional instability at flow depths up to 6 2 times bankfull and discharges up to 15 times bankfull narrow anabranching channels characterize 92 of the alluvial reach and transport bed load more efficiently than short reaches of wide single channels yet overall 29 12 of the bed load is sequestered and the average vertical accretion rate is 0 41 0 17 mm yr 1 along the 12 km study reach the most effective discharge for transporting sediment 40 45 m3 s 1 is consistent at all 5 stations 10 channels examined and is equivalent to the channel forming discharge it has an average recurrence interval of 1 01 years occurs for an exceptionally long portion 13 15 of the annual flow duration and averages a remarkable 2 1 times bankfull the high flow efficiency i e bed load transport rate to stream power ratio of the anabranches is facilitated by low width depth channels with banks reinforced by vegetation colonnades of bank top trees confine high velocity flows overbed i e over the channel bed at stages well above bankfull at even larger overbank flows momentum exchange between the channels and forested floodplains restrains overbed velocities in some cases causing them to decline thereby limiting erosion magela creek exhibits a complicated set of planform cross sectional and vegetative adjustments that boost overbed velocities and enhance bed load yield in multiple channels while restraining velocities and erosion at the largest discharges

splitting rivers at their seams bifurcations and avulsion river bifurcations are critical but poorly understood elements of many geomorphological systems they are integralelements of alluvial fans braided rivers fluvial lowland plains and deltas and control the partitioning of water and sediment throughthese systems bifurcations are commonly unstable but their lifespan varies greatly in braided rivers bars and channels migrate splitand merge at annual or shorter timescales thereby creating and abandoning bifurcations this behaviour has been studied mainly bygeomorphologists and fluid dynamicists bifurcations also exist during avulsion the process of a river changing course on afloodplain or in a delta which may take 102 103years and has been studied mainly by sedimentologists this review synthesizesour current understanding of bifurcations and brings together insights from different research communities and different environmen tal settings we consider the causes and initiation of bifurcations and avulsion the physical mechanisms controlling bifurcation andavulsion evolution mathematical and numerical modelling of these processes and the possibility of stable bifurcations we end thereview with some open questions copyright 2012 john wiley sons ltd

structural controls on formation of the hollinger mcintyre au quartz vein system in the hollinger shear zone timmins southern abitibi greenstone belt ontario the hollinger meintyre au quartz carbonate pyrite vein system the largest known in the superior province approximately 995 t au is localized within a 450 to 600 m wide northeast southwest trending ductile brittle shear zone the hollinger shear zone this shear zone is characterized by a strong east northeast striking foliation that dips 80 degrees s and a prominent elongation stretching lineation plunging 60 degrees to the east kinematic and strain indicators such as folded veins and fractures asymmetrical strain shadows lineations and asymmetries of foliation trajectories indicate complex movement however a reverse oblique dextral component of displacement appears to have been dominant during and after the main period of au quartz vein mineralization successive stages of vein formation were largely synchronous with shear zone development since dilation occurred in secondary shear fractures that broadly reflect the shear zone stress system at the scale of a stope or individual vein structure vein morphologies commonly reflect local development of arrays of tension gash veins followed by vein formation by hydraulic fracturing along reidel r shear fractures and then principal displacement fractures d this process resulted in the characteristic combination of irregular quartz veins with superimposed banks of parallel veins and stringers slightly oblique to foliation veins parallel to foliation are thought to have resulted from a combination of reorientation of early veins and hydraulic fracturing along shear zone foliation planes on a broader scale the position and plunge of the most productive central ore zone is controlled by the occurrence of favorable lithologic units e g permeable central subgroup breccias favorable stratigraphic contacts interflow horizons and competency contrasts combined with large scale anisotropies in this case the position and attitude of the quartz feldspar porphyry intrusions within the shear zone particularly the pearl lake porphyry the hollinger mcintyre vein system is best interpreted as having developed under lithostatic pressure fluid migration was localized within a more extensive shear zone by the presence of earlier felsic intrusions and permeable lithologies vein orientations and morphologies were then controlled by dilation of a variety of secondary shear and tension fractures which formed in response to late reverse dextral movement the hollinger shear zone is superimposed on an earlier fabric which also affects timiskaming sediments mineralization is thus post timiskaming in age and similar in relative timing and controls to other examples of au quartz vein mineralization in the southern abitibi greenstone belt such as the kirkland lake larder lake and val d or camps the 2673 super 6 sub 2 ma age for an albitite dike which immediately predates au quartz vein mineralization in the mcintyre mine corresponds to the late timiskaming phase the hollinger shear zone is one of three alignments two of which are known to be ductile brittle shear zones which relate most of the major known au quartz vein systems in the timmins area e g dome mine

cl br and i analyses of metamorphic and sedimentary rocks by isotope dilution mass spectrometry isotope dilution mass spectrometry with negative thermal ions was applied to determine cl br and i in rocks which in part contained less than 100 ppb of br and i two sets of samples have been investigated a a series of al rich metapelites of increasing metamorphic grade from the damara orogen namibia and b fresh and hydrothermally altered greywackes from the pb zn deposit bad grund in germany it was found that regional metamorphism of al rich metapelites causes no strong fractionation of the halides the br cl ratios in the metapelites are similar to those of sea water the i cl and i br ratios however are 500 times higher the i depleted in the ocean most probably is associated with organic matter stored in sediments the unaltered greywackes from near the pb zn vein have about the same concentrations of halides as the metamorphic al rich pelites by contrast the hydrothemally altered greywackes contain about twice as much cl and i and about 2 5 times as much br as the unaltered samples the element ratios however are similar for all three categories of rocks thereby indicating that sea water played no role in the hydrothermal system

applications of tomography to borehole and reflection seismology about ten years ago a selected group of amoco research geophysicists was asked to participate in a study to predict the important geophysical problems of the next decade sven treitel the patriarch of amoco geophysical research went to the blackboard and wrote v x z as a followup to this ken kelly the leader of amoco s inversion group wrote v x y z the two geophysicists essentially placed velocity estimation in two and three dimensions as the leading problems in exploration geophysics

fluid chemistry of archean seafloor hydrothermal vents implications for the composition of circa 3 2 ga seawater seafloor hydrothermal vents of mid archean age ca 3230 ma have been identified and mapped in the barberton greenstone belt south africa and are known as the ironstone pods fluid inclusion homogenization temperature data when combined with gas chromatographic data provide a minimum calculated water depth for the pods of 982 m ironstone pod hydrothermal fluid endmember concentrations mg 0 of various dissolved components derived from bulk fluid inclusion crush leach experiments include cl 730 mmol l br 2 59 i 0 058 na 822 nh4 11 4 k 21 5 ca 42 6 and sr 0 15 this hydrothermal fluid also contains up to 1 07 mol co2 0 03 mol n2 0 02 mol ch4 262 ppm cos and minor amounts of c2 c4 hydrocarbons hydrothermal endmember ca sr and nh4 in particular and to a lesser degree k i and co2 commonly plot on or very close to modern vent fluid trends by contrast endmember na and br concentrations are distinct higher from modern vent fluids high i and nh4 concentrations are consistent with contributions from sediments and or organic matter calculated 18oh2o values for the pod hydrothermal endmember fluid define a narrow range from 0 9 to 1 6 very similar to that of modern vent fluid values 0 4 2 1 a best estimate for the ironstone pod seawater endmember composition is cl 920 mmol l br 2 25 so4 2 3 i 0 037 na 789 nh4 5 1 k 18 9 mg 50 9 ca 232 and sr 4 52 barberton seawater components are commonly within an order of magnitude of modern seawater values with the exception of significantly higher 1 nh4 ca and sr in the inclusions sulfate concentrations are minimum estimates for barberton seawater fluid inclusion samples containing the greatest amount of seawater component have higher n2 up to 0 1 mol and low co2 when compared to samples dominated by the hydrothermal endmember fluid barberton ambient seawater is considered to have been an evaporative brine of nacl cacl2 composition during the time of pod deposition ironstone pod fluid inclusion seawater endmember br cl and i cl values of 2 45 10 3 and 40 2 10 6 respectively are within error of bulk earth 2 38 10 3 and 190 10 6 and are consistent with the chemistry of 3 23 ga barberton seawater being buffered by the mantle

round hill shear zone hosted gold deposit macraes flat otago new zealand evidence of a magmatic ore fluid the 0 8 moz round hill shear zone hosted gold deposit is one of several located on or near the hyde macraes shear zone macraes flat new zealand field relationships show stockwork veins are the oldest part of the hydrothermal system followed by flat and ramp veins hanging wall shear veins formed early but have been modified by late deformation fluid inclusion microthermometric results for dominant type i inclusions show that flat and ramp veins have the same average wt percent nacl equiv values 2 2 0 6 and were precipitated from the same fluid salinity data for these veins overlap with those from hanging wall veins average 1 3 0 3 and stockwork veins 1 6 0 6 for vein margins 0 9 0 3 for vein centers although both of the latter trend toward lower overall wt percent nacl equiv values suggesting mixing between relatively dilute and more saline end members all of the above veins have similar temperatures of homogenization t h ranging between 110 and 188 c fluid inclusion trapping temperatures are considered to be 300 c equating to a 10 km depth of formation carbon dioxide dissolved in the hydrothermal fluid is responsible for up to one third of fluid inclusion apparent salinities stockwork and hanging wall veins thus have true salinities of 1 wt percent nacl equiv 0 17 molal and flat and ramp veins have true salinities of fluid inclusion volatiles from round hill and other macraes deposits are dominated by h 2 o 99 02 99 69 mol with lesser co 2 0 14 0 76 mol n 2 0 03 0 32 mol and ch 4 0 06 0 17 mol noticeable concentrations of hydrocarbons occur in many of the samples fluid inclusion cation and anion data show few components of relatively low concentration are dissolved in the hydrothermal fluid consistent with co 2 corrected microthermometric measurements a range in fluid inclusion d h 2 o values obtained for the round hill deposit is coincident with the different vein types and also indicates mixing between two fluids one fluid is considered to be o isotope shifted meteoric water as trapped by the early stockwork veins and has the lowest d h 2 o values of 80 per mil the other fluid is represented by flat and or ramp and hanging wall veins that have d h 2 o values up to 40 per mil the macraes d h 2 o data show a trend toward the magmatic water end member for geothermal systems associated with convergent plate boundaries and are consistent with a 25 to 50 percent magmatic component in the macraes hydrothermal system

bankfull hydraulic geometry the role of in channel vegetation and downstream declining discharges in the anabranching and distributary channels of the gwydir distributive fluvial system southeastern australia abstract australian rivers frequently exhibit long periods of low or no flow trees and shrubs that grow on the channel bed and discharges that decline downstream four channels of the gwydir distributive fluvial system gwydir and mehi rivers carole and moomin creeks greatly contrast the hydraulic geometry of most other rivers particularly in the way they respond to changes in discharge downstream data describing 167 cross sections across all four streams are assembled into standard exponential bivariate hydraulic geometry plots with the relationships shown to exist outside the range of previously investigated downstream changes i e in contrast to the commonly obtained exponents for width b depth f and velocity m of 0 5 0 4 and 0 1 respectively comparatively low exponents for width b 0 0 4 and high values for velocity m 0 26 0 42 reflect the importance of slope in accommodating changes in discharge in sharp contrast with nearly all previous hydraulic geometry investigations where discharge increases downstream and slope decreases in the gwydir system slope declines in sympathy with discharge resulting in a marked downstream decline in stream power the presence of in channel vegetation is also argued to be a highly significant influence on the downstream hydraulic geometry of these streams because these streams are frequently dry trees grow in abundance on the bed appearing to displace the flow laterally and causing the channels to widen and shallow downstream an adjustment that contrasts the high mud content of the boundary the result is a very different hydraulic geometry in this anabranching distributary system to that commonly described for other types of river

a special issue devoted to abitibi ore deposits in a modern context preface the abitibi greenstone belt which is part of the larger abitibi subprovince in the superior province of the canadian shield e g card and ciesielski 1986 is the largest known archcan greenstonegranite terrane 300 km n s x 400 450 km mineral production and reserves are significant particularly in relation to volcanogenic massive sulfide deposits and structurally controlled archcan goldbearing quartz vein systems the term au quartz vein being used in the sense of lindgren 1933 e g the gold quartz veins of ontario p 662669 volcanogenie massive sulfide production and reserves to 1989 1990 total 424 million metric tons

channel evolution on the dammed elwha river washington usa abstract like many rivers in the western u s the elwha river washington has changed substantially over the past century in response to natural and human forcing the lower river is affected by two upstream dams that are slated for removal as part of a major river restoration effort in preparation for studying the effects of dam removal we present a comprehensive field and aerial photographic analysis of dam influence on an anabranching gravel bed river over the past century with the dams in place loss of the upstream sediment supply has caused spatial variations in the sedimentary and geomorphic character of the lower elwha river channel bed sediment is armored and better sorted than on the naturally evolving bed upstream of the dams on time scales of flood seasons the channel immediately below the lower dam is fairly stable but progresses toward greater mobility downstream such that the lowermost portion of the river responded to a recent 40 year flood with bank erosion and bed elevation changes on a scale approaching that of the natural channel above the dams in general channel mobility in the lowest 4 km of the elwha river has not decreased substantially with time enough fine sediment remains in the floodplain that given sufficient flood forcing the channel position sinuosity and braiding index change substantially the processes by which this river accesses new fine sediment below the dams rapid migration into noncohesive banks and avulsion of new channels allow it to compensate for loss of upstream sediment supply more readily than would a dammed river with cohesive banks or a more limited supply of alluvium the planned dam removal will provide a valuable opportunity to evaluate channel response to the future restoration of natural upstream sediment supply

h2och4naclco2 inclusions from the footwall contact of the tanco granitic pegmatite estimates of internal pressure and composition from microthermometry laser raman spectroscopy and gas chromatography abstract fluid inclusions in tourmaline and quartz from the footwall contact of the tanco granitic pegmatite s e manitoba were studied using microthermometry mt laser raman spectroscopy lrs and gas chromatography gc ch 4 bearing aqueous inclusions occur in metasomatic tourmaline of the footwall amphibolite contact the internal pressures estimated from mt are lower than those obtained from lrs mean difference 54 19 bars the difference is probably due to errors in the measurement of th ch 4 v and to the presence of clathrate at th ch 4 v into which co 2 had been preferentially partitioned lrs estimates of pressure 125 184 bars are believed to be more accurate aqueous phase salinities based on lrs estimates of pressure are higher than those derived using the data from mt 10 20 eq wt nacl the composition of the inclusions determined by gc bulk analysis is 97 3 mol h 2 o 2 2 mol ch 4 0 4 mol co 2 250 ppm c 2 h 6 130 ppm n 2 33 ppm c 3 h 8 11 ppm c 2 h 4 and 3 ppm c 3 h 6 plus trace amounts of c 4 hydrocarbons the composition is broadly similar to that calculated from mt 92 h 2 o and 8 ch 4 with 7 eq wt nacl dissolved in the aqueous phase and 2 mol co 2 dissolved in the ch 4 phase as expected due to the dominance of a single generation of inclusions in the tourmaline however two important differences in composition are 1 i the ch 4 to co 2 ratio of this fluid determined by gc is 5 33 which is significantly lower than that indicated by mt 49 0 and 2 ii the h 2 o content estimated from mt is 92 mol compared to 98 mol from gc gc analyses may have been contaminated by the presence of secondary inclusions in the tourmaline however the rarity of the latter suggests that they cannot be completely responsible for the discrepancy the differences may be accounted for by the presence of clathrate during measurement of th ch 4 critical which would reduce co 2 relative to ch 4 in the residual fluid and by errors in visually estimating vol h 2 o the compositions of the primary inclusions in tourmaline are unlike any of those found within the pegmatite and indicate that the fluid was externally derived probably of metamorphic origin inclusions in quartz of the border unit of the pegmatite are secondary and are either aqueous 18 to 30 eq wt cacl 2 th total 184 14 c or carbonic tm co 2 for the carbonic inclusions ranges from 57 5 to 65 4 c and is positively correlated with th co 2 analyses of x ch 4 based on lrs agree within 5 mol of those derived from mt and together indicate a range of compositions from 5 to 50 mol ch 4 in the co 2 phase bulk analysis by gc gives 99 0 mol h 2 o 0 6 mol co 2 0 4 mol ch 4 160 ppm n 2 7 ppm c 2 h 6 4 ppm c 3 h 8 and 2 ppm c 2 h 4 with trace amounts of cos carbonyl sulphide and c 3 h 6 the level of h 2 o in the analysis is consistent with the dominance of the aqueous inclusions in these samples and the ch 4 co 2 ratios are consistent with estimates from mt and lrs the preservation of variable ratios of ch 4 co 2 in inclusions 2 diffusion out of the inclusions nor reduction of fluids leaving the pegmatite were responsible for the more oxidized chemistries of the border unit inclusions relative to those in the tourmaline of the metasomatised amphibolite the compositions of the inclusions in the quartz lie between those of the fluid trapped by the tourmaline externally derived and the measured composition of a co 2 bearing pegmatitic fluid which indicates that the secondary fluids trapped in the border unit quartz were produced by late mixing

channel adjustments in response to the operation of large dams the upper reach of the lower yellow river the yellow river in china carries an extremely large sediment load river channel form and lateral shifting in a dynamic partly meandering and partly braided reach of the lower yellow river have been significantly influenced by construction of sanmenxia dam in 1960 liujiaxia dam in 1968 longyangxia dam in 1985 and xiaolangdi dam in 1997 using observations from huayuankou station 128 km downstream of xiaolangdi dam this study examines changes in the river before and after construction of the dams the temporal changes in the mean annual flow discharge and mean annual suspended sediment concentration have been strongly influenced by operation of theses dams observations of sediment transport coefficient ratio of sediment concentration to flow discharge at a station hydraulic geometry and bankfull channel form observed from 1951 to 2006 have shown that although variations in flow and sediment load correspond to different periods of dam operation changes in channel form are not entirely synchronous with these the channel has been subject to substantial deposition due to the flushing of sediment from sanmenxia dam resulting in a marked reduction in bankfull cross sectional area flows below bankfull had a greater impact on channel form than higher flows because of very high sediment load at a station hydraulic geometry shows that the variation of channel cross sectional area below bankfull in this wide and relatively shallow system largely depends on changes in width such at a station changes are significantly influenced by 1 events below bankfull and 2 overbank floods bankfull depth is the main component of channel adjustment in that depth adjusts synchronously with channel area the channel adjusts its size by relatively uniform changes in depth and width since 1981 channel morphology is not the product of single channel forming flow frequency it is determined by the combination of relatively low flows that play an important role in fine sediment transport and bed configuration as with relatively high flows that are effective at modifying the channel s morphology the sediment transport coefficient is a useful index for efficiently guiding the operation of the dams in a way that would minimize channel changes downstream sedimentation over the nearly 60 years of study period caused the lower yellow river to aggrade progressively the only significant exception being the two years following completion of sanmenxia dam

fluid regime and ore formation in the tungsten yttrium deposits of kyzyltau mongolian altai evidence for fluid variability in tungsten tin ore systems abstract the kyzyltau ore field is located in the northern part of the mongolian altai mountains w y be mo mineralization occurs in veins and stockworks in granites felsic volcanics basaltic flows and conglomerates the main ore minerals in the veins are wolframite fluorite beryl and minor molybdenite inclusions in hydrothermal quartz fluorite and beryl from veins as well as in magmatic quartz in vein hosting granites of the ulaan uul buraat uul and tsunkheg deposits were investigated using microthermometry and laser raman spectroscopy pseudosecondary primary inclusions in the kyzyltau ore veins are predominantly liquid rich aqueous inclusions containing variable amounts of co 2 as the main gas component and showing n 2 ch 4 ratios 1 secondary inclusions contain no or only trace concentrations of gases as indicated by clathrate melting the t h values of pseudosecondary primary inclusions in veins are between 180 and 433 c fluid inclusion data indicate that phase separation processes leading to fluid immiscibility occurred in vuggy quartz ii and green fluorite ii in the ulaan uul and buraat uul ore veins phase separation pressures of 100 350 bars were estimated fluorite i from the kyzyltau ore field shows a strong enrichment of hree and a strong negative eu anomaly common for rare metal bearing ore systems fluorite ii from buraat uul and tsunkheg is characterized by a change in the incorporation of rare earth elements ree with decreasing hree contents and a decreasing eu anomaly the ree distribution patterns in fluorite ii from ulaan uul remained unchanged compared with fluorite i despite a strong increase in the total ree content a review of the literature shows that from high temperature fe rich k dominated brines cassiterite ores can precipitate in quartz veins together with fe chlorite and fe tourmaline bolivian type if phase separation of a gas rich low salinity and fe rich fluid occurs cassiterite wolframite ores may be deposited cornwall devon type the deposits of kyzyltau are characterized by low fe alteration assemblages a predominance of sodium over potassium high contents of ree and y and a lack of extended tin mineralization despite the tin potential of the ore systems fluid inclusion data as well as geochemical and geological indications suggest formation of the tungsten deposits near the tops of li f rich sub volcanic intrusions we interpret the ph of the mineralizing fluid to be the main factor controlling wolframite precipitation in the kyzyltau ore field fluid wall rock interactions a lowering of the temperature and unmixing processes in the ore fluid generated contributions to neutralization and buffering of the acid co 2 bearing fluid into a ph range where tungstates were precipitated it can be inferred that formation of tungsten ores without precipitation of extended tin mineralization is possible in deposits characterized by high potential tin and tungsten according to this inference tin mineralization may be found in a more favourable setting in the vicinity of the kyzyltau deposits

patterns of alluvial rivers the pattern planform of a river can be considered at vastly different scales depending upon both the size of the river and the part of the fluvial system that is under consideration figure 1 for example in the broadest sense river patterns comprise a drainage network dendritic parallel trellis etc figure la the type of pattern is of interest to geomorphologists and geologists who interpret geologic conditions from aerial photographs at another scale a river reach which in figure lb is meandering is of interest to the geomorphologist who is interested in what that pattern reveals about river history and behavior and to the engineer who is charged with maintaining navigation and preventing major instability when a single meander is examined figure 1 c the hydraulics offtow the sediment transport and the potential for bank erosion are of concern in addition the sedimentologist is interested in the distribution of sediment within the bend bed forms within the channel figure ld and sedimentary structures figure ie which also establish a component of roughness for the hydraulic engineer finally the individual grains figure if provide geologic information on the sediment sources the nature of sediment loads and the feasibility of dredging for gravel there is an interaction of hydrology hydraulics geology and geomorphology at all scales which emphasizes the point that the fluvial system as a whole cannot be ignored even though only a component of the system is to be studied in this review only the patterns or planforms of alluvial rivers are discussed although it is apparent that the hydrologic and sediment yield characteristics of the drainage basin figure la as well as its geologic history cannot be ignored in the explanation of the pattern of any river

meandering anabranching river channel change in response to flow sediment regulation data analysis and model validation abstract anabranching river has been recognized as an independent river pattern a variety of investigations have attempted to disclose the formation of anabranching rivers however most previous studies mainly focused on the controls of anabranching channels formation the mechanism of transition among sub channels with varying flow sediment regime in anabranching rivers has been poorly understood in this study we used multi source data sets to investigate the changes in river channels and island wugui island about 7 km2 along the 27 km long jianli reach tashiyi tianziyihao in the middle yangtze river nine landsat images 1987 1990 1994 1996 2000 2003 2006 2010 and 2014 with 30 m spatial resolution were used to map the channel planform dynamics obvious changes in channel width and morphology of the island were observed during 1987 2014 the width of the left branch had reduced from 1041 m to 340 m while the width of the right branch had increased from 632 m to 1531 m during 1994 1996 the main river channel shifted from the left branch to the right during the period of 1987 2014 the total width of the compound cross section increased and the mean length width ratio of the island increased from 3 59 to 4 32 the mean annual flow discharge increased about 9 and mean annual suspended sediment concentration and sediment transport coefficient the ratio of mean annual suspended sediment concentration to mean annul flow discharge decreased about 75 and 76 respectively from 1951 to 2009 in response to the operation of gezhouba dam and three gorges dam the meandering anabranching channel planform adjusted by narrowing the island width and enlarging compound cross section in response to upstream water sediment regime the shift of the main river channel from left branch to the right may resulted from the increase in flow discharge and decrease in sediment transport coefficient since 1980s the adjustment has been intensified by the changes in the sediment transport rate after 1995 after the main channel was switched from left branch to right branch the flow sediment diversion capacity was kept stable with a diversion percentage of 90 in right branch due to the persistent influence of the three gorges dam the right branch will function as the main channel for a long time before the meandering anabranching system achieves equilibrium the shift and stability of main channel was closely related with the relative magnitude of flow sediment partition in each branch the significance of this study is that we successfully manifested the main channel shift process of anabranching river with the support of direct hydromorphological observation and theoretical verification

geochemistry of fluid inclusions from the mcintyre hollinger gold deposit timmins ontario canada type 1 h 2 o co 2 type 2 h 2 o co 2 type 3 ch 4 co 2 h 2 o and type 4 ch 4 fluid inclusions type 1 type 3 and some type 2 inclusions are primary or pseudosecondary in origin whereas type 4 and most type 2 inclusions are secondary the primary or pseudosecondary type 1 and 2 inclusions homogenized at temperatures of 220 degrees to 385 degrees c secondary type 2 inclusions homogenized at 160 degrees to 215 degrees c crushing tests confirm the presence of co 2 in samples with type 1 and 2 inclusions visually estimated x co2 values in type 1 inclusions range from 3 to 24 mole percent with bulk molar volumes of 19 to 28 cm 3 mole mineralizing fluids were at equilibrium with graphite at temperatures of 380 degrees to 480 degrees c and pressures of 1 to 3 kb calculated oxygen fugacities lie near the quartz fayalite magnetite buffer the mineralizing fluids differ compositionally from fluids in other types of ore deposits but resemble fluids derived from metamorphic rocks and deep level felsic intrusions modified journal abstract

ore forming fluids in archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec canada archean gold bearing quartz veins at the sigma mine occur in deformed metavolcanics intruded by two generations of preore porphyries the veins were emplaced during a late compressional tectonic event and they consist primarily of quartz tourmaline carbonates pyrite and scheelite vein minerals have been deformed and are also cut by abundant healed fractures outlined by fluid inclusions in the veins gold typically occurs in late fractures and in recrystallized quartz microthermometric sem eda leachate analysis and gas chromatographic techniques were used to study fluid inclusions in quartz most fluid inclusions at sigma occur in late fractures and are secondary the fluid inclusions are commonly found in fractures parallel to or less commonly within gold bearing fractures and are genetically related to the gold three types of fluid inclusions are identified 1 high salinity na ca cl aqueous inclusions 25 34 wt salt with small amounts of co 2 some containing halite calcite and nahcolite as daughter minerals 2 co 2 rich inclusions containing small amounts of h 2 o and ch 4 and 3 low salinity h 2 o co 2 inclusions 10 equiv wt nacl with co 2 contents which are variable but commonly in the range of 15 to 30 mole percent co 2 leachate analyses show that in addition to na and ca the aqueous fluids contain minor amounts of k fe mg and li homogenization temperatures of h 2 o co 2 inclusions with constant phase ratios range from 285 degrees to 395 degrees c those of aqueous inclusions range from 60 degrees to 295 degrees c the aqueous and co 2 rich inclusions are interpreted to have trapped two coexisting fluids resulting from the unmixing of a homogeneous h 2 o co 2 parent fluid itself occasionally trapped in late fractures the ore bearing fluid is interpreted to be a low salinity 10 equiv wt nacl fluid containing 15 to 30 mole percent co 2 at minimum temperatures in the range of 285 degrees to 395 degrees c the relatively low homogenization temperatures of aqueous inclusions are interpreted to be the result of co 2 effervescence from a co 2 saturated aqueous fluid due to pressure fluctuations at the time of entrapment it is also proposed that the onset of gold deposition is related to the onset of fluid unmixing

aperture compensation tomography1 conventional velocity analysis can handle a horizontally stratified medium well there is no indication though that it will be as successful when applied to a more complicated geological structure in fact a small angle of incidence may transform to a wide angle reflection event for a dipping interface in this case conventional velocity analysis may lead to large errors and thus cannot be applied seismic tomography is attractive as it is virtually free from any restrictions imposed on the velocity distribution in the model space or on the setup of a seismic experiment it is important however to recall that seismic tomography yields results of inferior quality compared to medical tomography this paper investigates the reason for this and how to suppress a significant blurring of seismic tomograms unlike medical tomography one cannot provide full angular coverage of the model space in a typical seismic experiment the sources and the receivers cannot surround an unknown object inside the earth to provide a complete spectrum of view angles incomplete angular coverage may lead to the occurrence of large inaccuracies in the computed tomograms especially when the initial model is poorly chosen we demonstrate a method of suppressing the adverse effects related to an incomplete angular recording this is compensation tomography which can be used efficiently in the case of a limited angular aperture numerical experiments illustrate the theory

patterns of anabranching channels the ultimate end member adjustment of mega rivers abstract large fluvial systems adjust to a combination of controls to form distinctive channels which represent a dominant factor in the evolution of floodplain geomorphology and sedimentology fluvial geomorphology has commonly classified river channels into meandering straight and braiding patterns which are seen to represent a continuum of channel geometry anabranching patterns rivers with multiple channels however are characteristic of many rivers the identification of a combination of variables that discriminates specific channel patterns has been a significant focus of research in fluvial geomorphology the development of this body of knowledge however has been established from medium and small rivers and laboratory flume studies very few of these research ideas developed from analysis of large fluvial systems this paper assesses the pattern of channel adjustment of large fluvial systems by employing hydraulic geometry discharge w d slope grain size stream power specific stream power and froude number q mean 1000 m 3 s the study demonstrates that methods currently used to discriminate channel patterns are not useful when applied to very large rivers further with the exception of the lower mississippi alluvial rivers with mean annual discharges greater than 17 000 m 3 s here classified as mega rivers do not generate single thread meandering or typical braided patterns these mega rivers develop anabranching patterns

numerical simulation of bar and island morphodynamics in anabranching megarivers 1 bar and island morphodynamics in the world s largest anabranching rivers are investigated using a new numerical model of hydrodynamics sediment transport bank erosion and floodplain development operating over periods of several hundred years simulated channel morphology is compared to that of natural rivers and shown to be realistic both in terms of the statistical characteristics of channel width depth and bar shape distributions and mechanisms of unit bar compound bar and island evolution results demonstrate that bar and island stability may be sensitive to hydrologic regime because greater variability in flood magnitude encourages the formation of emergent bars that can be stabilized by vegetation colonization simulations illustrate a range of mechanisms of unit bar generation that are linked to local bed or bank instabilities this link may explain the reduced frequency of unit bars observed in some large anabranching rivers that are characterized by stable vegetated islands and slow rates of channel change model results suggest that the degree to which sand sized bed material is carried in suspension likely represents an important control on bar morphodynamics and channel network evolution because of its influence on sand transport direction consequently differences in the partitioning of the total sand load between bed load and suspension may provide a partial explanation for contrasting styles of anabranching in the world s largest sand bed rivers these results highlight a need for spatially distributed flow and sediment transport data sets from large rivers in order to support improved parameterizations of sand transport mechanics in morphodynamic models

co2 rich gases from lakes nyos and monoun cameroon laacher see germany dieng indonesia and mt gambier australia variations on a common theme abstract helium r a 3 0 to 5 6 and carbon 13 c from 7 2 to 3 4 isotopic compositions and relative co 2 ch 4 n 2 he and ar contents of co 2 rich gases from lakes nyos and monoun cameroon laacher see germany dieng volcanic plateau indonesia and a well at mt gambier australia point to a common essentially magmatic origin absorption of the original magmatic gases into deeply circulating groundwater and equilibration of the resulting solutions with crustal rock at temperatures of about 300 c fix co 2 and ch 4 contents on further rise the solutions start to boil separating gas rich vapors which on encountering an impermeable barrier may accumulate to form gas pockets with steadily increasing pressures in the case of sufficiently high gas contents the pressures may exceed lithostatic pressures leading to a blow out or a pneumatic eruption dieng otherwise gas may accumulate to form a stable pocket mt gambier minor leakage from such pockets may lead to surface discharges of co 2 rich gases as at laacher see re absorption into shallow groundwater to the formation of the low salinity co 2 charged waters encountered at lakes nyos and monoun the occurrence of these high co 2 low temperature systems is likely to be favored in tectonically active regions allowing deep possibly mantle gases to rise but with sufficiently low regional heat flows to prevent the establishment of large scale geothermal activity

fluid inclusion geochemistry of high grade vein hosted gold ore at the pamour mine porcupine camp ontario this study was undertaken to characterize fluid inclusions associated with high grade vein hosted gold at the pamour mine in the porcupine camp of ontario and to compare them with fluid inclusions in quartz veins associated with wall rock hosted gold which is much more common the pamour mine contains two principal types of orebodies metasediment hosted fracture zones and larger metavolcanic or metasediment hosted quartz carbonate veins gold in the veins is distributed erratically attains very high grades locally and increases in grade at higher levels zoned alteration around the veins is dominated by addition of k 2 o co 2 as s and cao and depletion of na 2 o k 2 o co 2 and s are concentrated in the hanging wall and the intensity of co 2 and h super metasomatism increases upward in the mine roughly parallel to the trend seen in gold values gold was introduced along with sphalerite galena calcite chlorite and chalcopyrite late in the paragenetic history after brittle deformation of earlier vein hosted quartz tourmaline feldspar and pyrite sphalerite that is directly associated with high grade gold contains two types of primary inclusions a co 2 ch 4 fluid 20 45 mole ch 4 and an h 2 o rich liquid with a carbonaceous phase co 2 ch 4 as well as muscovite and graphite daughter minerals aqueous phase salinity estimates range from 2 to 9 equiv wt percent nacl and sem analyses of evaporitic residues of thermally decrepitated inclusions contain nacl and cacl 2 with lesser amounts of kcl mgcl 2 s zn and fe these two inclusion types appear to represent immiscible fluids trapped along the solvus in the h 2 o co 2 ch 4 salt system at temperatures of 325 degrees or 25 degrees c and pressures of 1 to 2 kbars these fluids are similar to those observed in vein quartz at the mcintyre and hollinger deposits where most gold is hosted by wall rocks except that co 2 immiscibility appears to have been more widespread at pamour the separation of immiscible fluids of the type identified in this study would increase the f sub o 2 and ph of the residual fluid owing to the partitioning of h 2 s ch 4 and co 2 into the carbonaceous phase the net effect of these changes would be to decrease the solubility of bisulfide complexed gold suggesting that co 2 immiscibility is an important contributor to gold deposition within veins where wall rock interaction is limited it is not clear whether all vein hosted gold formed from such unmixing or only the higher grade ore shoots

are equilibrium multichannel networks predictable the case of the regulated indus river pakistan arguably the current planform behaviour of the indus river is broadly predictable between chashma and taunsa pakistan the indus is a 264 km long multiple channel reach remote sensing imagery encompassing major floods in 2007 and 2010 shows that the indus has a minimum of two and a maximum of nine channels with on average four active channels during the dry season and five during the annual monsoon thus the network structure if not detailed planform remains stable even for the record 2010 flood 27 100 m3 s 1 recurrence interval 100 years bankline recession is negligible for discharges less than a peak annual discharge of 6000 m3 s 1 80 of mean annual flood the maximum flow efficiency mfe principle demonstrates that the channel network is insensitive to the monsoon floods which typically peak at 13 200 m3 s 1 rather the network is in near equilibrium with the mean annual flood 7530 m3 s 1 the mfe principle indicates that stable networks have three to four channels thus the observed stability in the number of active channels accords with the presence of a near equilibrium reach scale channel network insensitivity to the annual hydrological cycle demonstrates that the timescale for network adjustment is much longer than the timescale of the monsoon hydrograph with the annual excess water being stored on floodplains rather than being conveyed in an enlarged channel network the analysis explains the lack of significant channel adjustment following the largest flood in 40 years and the extensive indus flooding experienced on an annual basis with its substantial impacts on the populace and agricultural production

anastomosis and the continuum of channel pattern anastomosing rivers are characterized by multiple channels separated by islands excised from the floodplain their status relative to the continuum concept of channel pattern is assessed with channel pattern defined in terms of three variables flow strength bank erodibility and relative sediment supply using an ordinal scaling l ow m oderate h igh the traditional forms of straight meandering and braided have respective representations of l l l m l m l m and h h m h in terms of those variables the anastomosing pattern is on average represented by l l m h but not so definitively as other forms specification of the third element sediment supply is particularly hampered by the paucity of data but aggradation a characteristic of many anastomosing rivers can be thought of as symptomatic of a moderately high rate of supply relative to the ability for onward transport a sufficiently high rate of supply to a channel with low flow strength and resistant banks would induce shoaling and or lateral constriction that locally forces flow out of the main channel and ultimately leads to the cutting of anabranches a flow regime characterized by concentrated floods of relatively large magnitude is also regarded as highly conducive to the formation of new channels where low bank erodibility constrains channel capacity anastomosis may in certain cases represent a transitional form of channel pattern but there is no denying the longevity of some anastomosing systems

riparian vegetation and the late holocene development of an anabranching river magela creek northern australia many anabranching rivers are characterized by dynamic interactions between fluvial processes and riparian vegetation but uncertainties surround the processes and time scales of anabranch development we use geomorphological investigations and optically stimulated luminescence osl dating to determine spatial and temporal trends in the development of anabranching along a 6 5 km long reach of magela creek in the seasonal tropics of northern australia many trees and shrubs that survive the wet season floods establish on the sandy beds and lower banks such that anabranches divide and rejoin around numerous ridges and islands that are formed mainly by accretion in the lee of in channel vegetation and less commonly by excision from formerly continuous island or flood plain surfaces once ridges and islands form colonizing vegetation maintains their stability by increasing sediment cohesion and decreasing flow erosivity over the holocene magela creek has vertically aggraded and extended in length by delta progradation into madjinbardi billabong resulting in a time sequence of anabranches and associated ridges and islands from older upstream to younger downstream osl ages for islands in the upstream and middle reaches are ca 1 6 ka and older and the narrow deep anabranches width depth w d typically 10 30 have few in channel obstructions farther downstream island osl ages are ca 0 7 ka and younger anabranches tend to be wider and shallower w d 30 with more obstructions and splays and locally scoured island and floodplain surfaces are more common based on these findings previous flow and sediment transport measurements and theoretical analyses we posit that there is a decline in anabranch efficiency from an upstream equilibrium system in mass flux balance to a downstream disequilibrium system characterized by bed aggradation and localized island and floodplain erosion in the downstream reaches inefficient high w d and obstructed anabranches do not persist because they either aggrade and are abandoned or they are subdivided into more efficient lower w d and less obstructed anabranches as a result of the interactions between in channel vegetation growth and ridge and island accretion or local excision consequently a more efficient anabranching system gradually develops with characteristics similar to those in the upstream reaches this enhances downstream sediment transfer which enables ongoing delta progradation and provides fresh sediment surfaces for vegetation to colonize and initiate new anabranches the osl ages from magela creek demonstrate that a recognizable but relatively inefficient anabranching system can develop within a few centuries while adjustment to a more efficient system occurs over a few millennia

fluid chemistry of veining associated with an ancient microearthquake swarm benmore dam new zealand steeply dipping strata in the vicinity of benmore dam otago new zealand are complexly deformed metasedimentary rocks of the torlesse supergroup middle triassic age over an exposed area 100 m wide 25 m high these strata are disrupted by a fault fracture mesh comprising conjugate coulomb shears interlinked by extensional and extensional shear fractures all formed in a common stress field and hosting quartz prehnite epidote calcite veining the combined effect of these structures is shortening perpendicular to beddings and subvertical extension so that in their present attitude they correspond to a set of conjugate thrust faults with associated extension fractures on the evidence of incremental vein textures the development of this distributed fault fracture mesh is interpreted as resulting from a fluid driven microearthquake swarm which postdated regional low grade metamorphism mechanical considerations suggest that the migrating hydrothermal fluids were significantly overpressured possibly to approximately lithostatic values if the mesh structure developed in its present attitude fluid inclusion microthermometric studies show that benmore vein quartz contains two phase aqueous inclusions with salinities between 1 4 and 2 9 wt nacl equivalent and homogenization temperatures t h between 189 and 217 c the assemblage quartz prehnite epidote suggests trapping temperatures t t of 280 c requiring the addition of an 70 c correction to t h values late calcite contains inclusions with noticeably lower salinity 0 0 0 9 wt nacl and t h values 129 175 c studies on quartz pumpellyite calcite veins from nearby lake aviemore show similar fluid inclusion salinity and t h values fluid inclusion gas analyses show all the vein samples to be dominated by h 2 o 99 3 99 9 mol with few other gases apparent including ch 4 0 5 n 2 0 1 co 2 0 1 and c 2 c 4 hydrocarbons cation and anion analyses when combined with the gas data show that nacl dominates the fluid inclusion salinities oxygen isotope results when combined with calculated t t values indicate that the water responsible for the deposition of benmore and aviemore quartz had 18 o compositions of 9 4 and 4 8 respectively calcite 13 c values between 25 3 and 38 0 are indicative of oxidation of ch 4 to co 2 as a result of hydrothermal fluids interacting with organic rich sediments fluid inclusion delta d h 2 o values for benmore range between 73 and 89 compared to 109 for the one aviemore sample this research has demonstrated that 1 water of meteoric origin probably from subantarctic latitudes penetrated to 6 km depth and underwent an oxygen isotope shift before depositing the benmore aviemore veins 2 the migrating hydrothermal fluids were likely overpressured well above hydrostatic to near lithostatic values if the mesh structure was active in its present orientation and 3 fluid migration was coupled to distributed brittle failure in the prevailing stress field self generating a permeable fault fracture mesh

the morphometric variation of islands in the middle and lower yangtze river a variational analytical explanation abstract anabranching rivers are formed of islands of various shapes and this study applies a variational analytical approach to explain the morphology of islands of a particular basic shape a theoretically modeled anabranching river is developed based on observations from the middle and lower yangtze river which alternates between a single channel and a two channel anabranching reach with islands approximately triangular in planform such that one anabranch is longer than the other the equilibrium condition of the model river is derived from a variational investigation of basic relationships of flow continuity channel boundary resistance bedload transport and energy conservation in the anabranching river we demonstrate that when such a system reaches stationary equilibrium the triangular planform of the island is determined by the proportions of water and sediment passing through the two channels we also show that the shorter straight channel takes a larger proportion of sediment relative to its proportion of water for the island to take a streamlined morphology the difference between the proportions of water and sediment discharge entering each channel needs to be as small as possible when the paired proportions of water and sediment discharge take different values the streamlined morphologies of the island vary in a wide range in comparison with the measured morphologies of the five islands located in the middle lower yangtze river the theoretically determined lengths of the islands are remarkably consistent varying from the corresponding field measurements by a range of

fluid inclusions in the system h2o ch4 nacl co2 from metasomatic tourmaline within the border unit of the tanco zoned granitic pegmatite s e manitoba abstract fluid inclusions from the tourmaline phase of alteration of the footwall amphibolite from the tanco zoned granitic pegmatite lie in the system h2o ch4 nacl co2 these inclusions contain a liquid and vapour phase at room temperature and develop a second liquid phase on cooling in the range 77 to 95 c the second liquid and the vapour are methane isochores for inclusions showing vapour phase ch4 homogenisation were constructed from the equations of jacobs and kerrick 1981 the intersections of these isochores with the univariant melting curves for methane clathrate hydrates give estimates of salinity for the inclusions of between 7 and 10 equivalent wt nacl which are lower than those derived from measurement of the depression of the melting point of ice a result consistent with salt exclusion by clathrate the bulk composition of the fluid is estimated to be 91 mol h2o 6 mol ch4 2 equiv mol nacl and calculation of fo2 from the bulk inclusion composition gives values near wi at these conditions which is unreasonably low for fluids derived from the pegmatite which were probably between qfm and hm the metasomatic fluids may have resulted from fluid mixing in the wall rock immediately adjacent to the pegmatite the fluid derived from the pegmatite a h2o co2 fluid introduced the b necessary to form tourmaline in the amphibolite on the other hand it is suggested that ch4 h2o may have been derived from a metamorphic fluid which formed in equilibrium with graphite at lower oxygen fugacities at 400 600 c and which was present in the wall rock at the time of pegmatite emplacement supporting evidence is provided by pegmatite wall zone fluids with higher ch4 5 equiv mol in co2 than the bulk of the pegmatite h2o co2 fluids 0 8 mol in co2 suggesting marginal fluid contamination

defining large river channel patterns alluvial exchange and plurality abstract large rivers have anabranching channels with components that may be defined as braided meandering or straight this paper shows that application of such holistic terminologies is complicated by recognition of within type and transitional type variety a confusingly varied use of terms and a coverage of pattern characteristics that for many large rivers is incomplete in natural states big rivers can be plural systems in which main accessory tributary and floodplain channels and lakes differ functionally and vary in terms of morphological dynamics a distinction is drawn between the hydrological and geomorphological connectivity of components in big river plural systems at any one time even at flood stage only some channels are geomorphologically active six types of geomorphological connectivity are described that range from coupled through to partially coupled and decoupled the interplay between geomorphological and hydrological connectivity in large rivers is shown to determine habitat status and therefore ecological diversity for improved understanding of the dynamics as well as the forms of these large composite systems it is helpful to 1 adopt element level specification not only for sediment bodies but also for functioning channels 2 track the sediment transfer processes and exchanges that produce channel forms over the highly varied timescales operating within large rivers and 3 recognise the ways in which partially coupled and connected geomorphological systems produce naturally a composite set of forms at different rates such augmenting information will provide an improved platform for both river management and ecological understanding

avulsion regimes in southeast texas rivers avulsions relatively sudden changes in course or establishment of new anabranches are an important process in alluvial rivers their key role in floodplain construction and alluvial architecture and the general conditions favouring avulsions are well known however avulsion processes and evolution and the factors controlling avulsion regimes are poorly understood in the southeast texas coastal plain where avulsions are common features of the river valleys avulsions were studied on the lower brazos navasota trinity neches and sabine rivers using a combination of aerial imagery digital elevation models and field surveys avulsions have important influences on the surface morphology and contemporary processes in all five rivers features associated with avulsions are active and distinct throughout the study area and all the rivers have experienced geologically if not historically recent avulsions however no two of the study rivers have the same contemporary avulsion regime first order differences in avulsion style are controlled by the stage of valley filling and within the three rivers characterized by an unfilled incised valley antecedent morphology associated with late quaternary and holocene coastal and fluvial deltaic processes accounts for the major differences in the navasota 27 avulsions in 185 km and neches 21 in 340 km rivers subchannels associated with avulsions exist in all stages of development from active to infilled and some have occurred in recent decades the other rivers have fewer avulsions but both the sabine and trinity have experienced historic channel shifts only the brazos river has experienced no avulsions within the past c 300 years results show that even within a region of similar environmental controls and geological history local variations in inherited morphology can result in different avulsion regimes copyright 2008 john wiley sons ltd