microgranitoid enclave swarms in granitic plutons central sierra nevada california abstract microgranitoid enclaves are common in granitic plutons worldwide occurring individually and in homogeneous or heterogeneous swarms three plutons in the central sierra nevada batholith contain swarms with mostly heterogeneous suites of enclaves in the intermediate composition range and occur in a number of two dimensional shapes specifically as dikes small rafts lenses pipe vortices and large massive shapes swarms are characterized by various features including the nature of their boundary with the host their planar or non planar character internal geometry density of enclave packing presence or absence of schlieren and crystal aggregates and axial ratios and degree of preferred alignment of enclaves we propose that heterogeneous enclave swarms form by one or some combination of the following mechanisms 1 velocity gradient sorting parallel or normal to the flow 2 gravitational sorting or 3 break up of heterogeneous dikes common sites where enclave swarms form include pluton margins or internal viscosity walls within fractures and near the pluton roof

planform dynamics of the lower mississippi river this paper presents an analysis of the planform behaviour of the lower mississippi river lmr using a series of maps and hydrographic surveys covering the period 1765 1975 data allow analysis at various time and space scales using fixed and statistically defined reaches both before and after extensive channel modification previous research has interpreted planform change in relation to geomorphological or engineering regime type analyses of channel length and width for the lmr as a single system the analysis here is broadly consistent with these approaches but highlights the importance of meander geometry in the form of the radius of curvature width ratio this neglected factor helps resolve paradoxes relating to observed changes in sediment transport and channel stability when viewed over smaller time and space scales analysis of dynamics using fixed reach boundaries reveals a downstream trend in the pattern of planform behaviour which is closely related to the distribution of valley floor deposits and which also reflects neotectonic influences analysis of changes using statistically determined reach boundaries shows that over shorter time scales meander trains are continually formed and modified over a period of approximately 120 years zones of more or less dynamic behaviour thus move through the lmr the research also provides a context for 20th century engineering interventions to the river these have constrained the magnitude of planform adjustment but also altered the kind of response that is now possible in relation to changes in discharge and sediment load and as a consequence of internal feedbacks within the lmr system copyright 2006 john wiley sons ltd

discriminating stacked distributary channel from palaeovalley fill sand bodies in foreland basin settings abstract stacked fluvial distributary channel deposits and palaeovalley fills can form major multi storey sand bodies with similar thicknesses and with lateral extents often greater than a single exposure consequently they can be difficult to tell apart from one another using outcrop data this study addresses this problem by quantitatively analysing the architecture of five stacked fluvial distributary channel deposits and two palaeovalley fills from the pennsylvanian pikeville and hyden formations of the central appalachian basin usa the a priori interpretation of the sand bodies as stacked distributary channels and palaeovalley fills is possible because a robust in place coal seam correlation framework allows for the recognition of different basin scale architectures for each type aspect ratios 1000 and a regional basinward facies shift at the bases of palaeovalley fills sand body thickness storey thickness position and length of storey contacts within the sand body are similar in both types however they can be distinguished by different up system to down system changes in their respective architectures stacked distributary channel sand bodies thin down system display a decrease in storey thickness an increase in the mean position of storey heights in the sand body and a decrease in the length of storey contacts these trends are the result of down system decrease in channel size and confinement associated with radially distributive fluvial systems palaeovalley fill sand bodies thicken down system display an increase in storey thickness a decrease in the mean position of storey heights and a decrease in the length of storey contacts the increase in sand body and storey thickness are the result of down system increases in original channel size consistent with trunk axial fluvial systems fed by tributaries that predominate during valley formation the down system increase in amalgamation reflects a down system decrease in accommodation from the higher subsidence rate active margin of the basin and is therefore not necessarily characteristic of palaeovalley fill architectures in all basin settings this study emphasises the requirement for detailed correlation work and quantitative analysis of external and internal architectures before the interpretation of sand bodies as stacked distributary channels or palaeovalley fills

modeling singular mineralization processes due to fluid pressure fluctuations abstract mineralization in the earth s crust can be regarded as a singular process resulting in large amounts of mass accumulation and element enrichment over short time or space scales the elemental concentrations modeled by fractals and multifractals show self similarity and scale invariant properties we take the view that fluid pressure variations in response to earthquakes or fault rupture are primarily responsible for changes in solubility and trigger transient physical and chemical variations in ore forming fluids that enhance the mineralization process based on this general concept we investigated mineral precipitation processes driven by rapid fluid pressure reductions by coupling mineralization to a cellular automaton model to reveal the nonlinear mechanism of the orogenic gold mineralization process using simulation in the model fluid pressure can increase to the rock failure condition which was set as lithostatic pressure at a depth of 10 km 270 mpa due to either porosity reduction or dehydration reactions rapid drops in pressure resulting from fault rupture or local hydrofracture may induce repeated gold precipitation the geochemical patterns generated by the model evolve from depletion to enrichment patterns and from spatially random to spatially clustered structures quantified by multifractal models and geostatistics results show how metal elements self organize to form high metal concentration patterns displaying self similarity and scale invariance these transitions are attributed to the growth and coalescence of sub networks with different fluid pressures up to the percolation threshold resulting in a wide range of fluid pressure reductions and gold precipitation in the form of clusters the results suggest that cyclic evolution of fluid pressure and its effects on gold precipitation systems can effectively mimic the repeated mineralization superposition process and generate complex geochemical patterns characterized by a multifractal model the nonlinear behavior exhibits scale invariance and self organized critical threshold where mineral phase separations result from fluid pressure reductions associated with fault failure

decadal scale riverbed deformation and sand budget of the last 500 km of the mississippi river insights into natural and river engineering effects on a large alluvial river

geologic and geophysical investigation of two fine grained granites sierra nevada batholith california evidence for structural controls on emplacement and volcanism the johnson granite porphyry and the silver pass porphyry are two late stage porphyritic intrusions in the cretaceous sierra nevada batholith california both intrusions are characterized by fine grained textures miarolitic cavities pegmatite veins and abundant xenoliths microstructures in the johnson granite porphyry record magmatic flow magnetic fabrics in the johnson granite porphyry determined by anisotropy of magnetic susceptibility show that the poles to magnetic foliations define a nne ssw girdle and magnetic lineations plunge shallowly to moderately to the wnw and ese a gravity survey and three dimensional inversion indicate that the johnson granite porphyry is shallow and tabular extending to 1 5 km depth beneath the southwestern margin a second gravity anomaly was delineated southeast of the johnson granite porphyry suggesting the intrusion continues to depth the silver pass porphyry is deformed by the dextral rosy finch shear zone and records a gradient of high to low temperature solid state fabrics field and magnetic foliations in the silver pass porphyry are subvertical and lineations are shallowly plunging we propose that regional shear zones controlled the emplacement of these intrusions the johnson granite porphyry was emplaced in a three dimensional tension gash associated with the termination of the bench canyon shear zone the rosy finch shear zone facilitated the emplacement of the silver pass porphyry probably as a tension fracture associated with the shear zone the field observations and magnetic fabrics suggest that the johnson granite porphyry may record an extrusive event suggesting that volcanism may be related to deformation along active shear zones

connecting the backwater hydraulics of coastal rivers to fluvio deltaic sedimentology and stratigraphy fluvial channels encounter a backwater reach when they approach a standing body of water and recent studies have shown that the transition from normal flow to backwater influenced flow is associated with sediment mass extraction through deposition here we test the hypothesis that systematic changes in the geometry of channel belt deposits and sedimentary architecture occur across this transition using data from the late holocene mississippi southern usa and rhine the netherlands fluvio deltaic systems we use the estimated backwater length and average channel width as characteristic length scales to non dimensionalize the downstream trends in channel belt width for these systems the collapsed data follow similar trends suggesting that the observed variations in channel belt geometry and fluvio deltaic stratigraphy are tied to the location of the backwater transition zone these findings suggest a unifying hydraulic control on fluvio deltaic channel belts and provide a new framework for predicting and understanding the properties of ancient rivers in the coastal zone

a fractal relationship between vein thickness and gold grade in drill core from la codosera spain analysis of quartz vein thicknesses and gold grades in drill core from western spain indicates that both approximate a power law distribution suggesting an underlying fractal relationship log log plots of cumulative frequency n against vein thickness t show systematic changes in relation to gold grade the exponent d in a power law of the form n c t super d is lower for higher gold grades indicating that a greater proportion of the dilation is taking place on the thicker veins which are interpreted as providing interconnected conduits for gold bearing fluids thus monitoring the vein thickness distribution may provide a means of discriminating mineralized and barren structures in vein hosted mineral deposits

magmatic structures in the tuolumne intrusive suite california a new model for the formation and deformation of ladder dikes understanding the growth and differentiation of silicic magma chambers is a central issue in volcanology we use field observations of meter scale ladder dikes from the tuolumne intrusive suite tis california usa together with analogue experiments and scaling theory to demonstrate that prior to solidification these features are deformed and broken by shearing motions in the magma chamber from field observations the majority of the ladder dikes are 1 exposed perpendicular to gravity in a nearly horizontal slice through a solidified magma chamber 2 located near a contact specifically where they occur in large clusters with either host rock or another intrusive unit in the tis and 3 oriented roughly perpendicular to that contact the ladder dikes show evidence of breakup at the meter scale as well as at the centimeter scale mafic felsic banding we hypothesize that the ladder dikes are buoyant plumes in a stirred magma chamber in particular their orientation and deformation are related to their rise or descent velocity the stirring velocity within the chamber and the rheological contrast between the plume and ambient material the comparison between field data and laboratory experiments suggests that most of the ladder dikes deformed in a regime dominated by breakup from yielding under tension

depositional settings and history of the lower miocene fleming group refugio county texas as defined using seismic geomorphology abstract a study of the lower miocene fleming group in refugio county texas from 3 d seismic and wireline log data documents continuous strandplain and associated lower coastal plain fluvial systems along a wave dominated shoreline this study delineates and characterizes through the interpretation of seismic attributes and seismic geomorphology maps from 15 horizons three principal styles of stratal patterns 1 parallel and subparallel strike continuous sets of beach ridge and swale deposits within a strandplain system that prograded at least 12 km 2 sinuous channel belts in a coeval mixed load meanderbelt system and 3 acoustically dim nearly featureless seismic attribute patterns that record homogenous and topographically subdued shallow marine mudstones associated with transgressive marine deposits and flooding surfaces holocene depositional analogs for these lower miocene sandy strandplain deposits include the nayarit coastline in mexico whereas the lower coastal plain between galveston and corpus christi texas serves as an appropriate analog for mixed load meanderbelt systems the lower miocene coastline in refugio county consists of a regressive phase that was punctuated by two transgressive phases these episodes of marine transgression correspond to the anahuac formation and the marginulina a shale respectively succeeding events record complex amalgamated beach ridge deposits and coeval fluvial channel systems that exhibit patterns of channel migration erosion incision and downdip fusion of channel belts this study concludes that potential reservoir geometries and architectures in the lower miocene succession are much more complex than previously inferred the result of rapidly fluctuating and evolving strike fed shoreline systems and contemporaneous fluvial dip dispersal systems some manifested by shore parallel trends confined in swales improved reservoir development strategies in this prolific hydrocarbon bearing play should be guided by distribution of sandy depositional elements and the paleogeographic setting

new insights into the origin of ladder dikes implications for punctuated growth and crystal accumulation in the cathedral peak granodiorite abstract ladder dikes are steep tabular bodies typically a meter or less thick composed of moderately dipping concave upward alternating dark i e schlieren and light bands oriented roughly perpendicular to the ladder dike margins these structures occur widely but sparsely in granitic rocks and are found prominently in the cathedral peak granodiorite cpg of the tuolumne intrusive suite previous studies have interpreted that ladder dikes form as a result of processes including the downward flow of crystal mush in cracks within strong crystal mush or by upward flow in steep tubes that migrate within a strong crystal mush our new observations indicate that ladder dikes formed by downward flow of crystal mush in troughs or valleys in a manner potentially comparable to trough bands in mafic layered intrusions extensions of the schlieren outward and upward away from the ladder dike margins into the host granite demonstrate that the host granite was deposited as mounds on both sides at the same time as the ladder dikes ladder dikes therefore record lateral flows of crystal mush on a magma chamber floor vertical exposures suggest these flows are on the order of ten meters thick some steep exposures on granite domes indicate multiple ladder dikes and flows over a stratigraphic height of 80 100 m later stratigraphically higher flows commonly deform and erode the top of an earlier flow and granitic material rich in k feldspar megacrysts has locally engulfed large blocks of ladder dikes demonstrating that the megacrysts were also transported in flows flows in the cpg are directed away from the center of the pluton toward the western and eastern margins and apparently spread along a strong crystal mush floor and into a rheologically complex cpg magma whereas established dynamical models for spreading single phase gravity currents with simple and complex rheologies explain the elongate geometry spacing and orientation of the tabular bodies the origin and character of the downward flows required to explain the trough band schlieren structures is challenging however an intermittent and progressive deposition of trough bands consistent with field observations is potentially explained if the two phase crystals and melt dynamics governing the response of the cpg magma to a new injection are considered

fluid rock interaction is decisive for the formation of tungsten deposits tungsten mineralization is typically associated with reduced granitic magmas of crustal origin while this type of magmatism is widespread economic tungsten deposits are highly localized with 90 produced from only three countries worldwide therefore the occurrence of reduced magmatism while necessary for tungsten enrichment seems to be insufficient to form such rare deposits here we explore the mechanisms that lead to wolframite precipitation and evaluate whether they may exert a decisive control on tungsten global distribution tungsten differs from other rare metals enriched in magmatic hydrothermal ore deposits because it is transported as an anionic species precipitation of the main tungstate minerals scheelite cawo 4 and wolframite fe mn wo 4 thus depends on the availability of calcium iron or manganese we demonstrate quantitatively that magmatic fluids at panasqueira portugal provide tungsten in solution whereas the host rock contributes the iron required to precipitate wolframite the combination of special source conditions with specific reactive host rocks explains why major wolframite deposits are rare and confined to a few ore provinces globally

zircon growth and recycling during the assembly of large composite arc plutons abstract concordant u pb zircon dates have been interpreted traditionally to date the crystallization ages of plutons because until recently analytical uncertainties have generally been large enough to encompass the anticipated duration of pluton growth advances in zircon tims analysis and geochronological studies by sims on zircon from young volcanic rocks along with evolving views of the evolution of magmatic systems makes it necessary to revaluate this interpretation assignment of unique pluton crystallization ages based on zircon dating is complicated by the propensity of zircon to survive multiple intrusive events that culminate in a large pluton distinctions must be made between true inherited zircon xenocrystic zircon derived from host rocks during magma ascent and or emplacement and multi stage growth of zircon during waxing and waning of magma reservoirs that solidify to form large plutons these complications are exemplified by recent high precision u pb zircon age dating from the cretaceous tuolumne and mt stuart batholiths which clearly show that the timeframe of pluton assembly was long 5 ma for mt stuart and 8 ma for tuolumne zircon crystals from samples from both batholiths exhibit appreciable concordant age dispersion for zircon several 10 5 yr up to 2 10 6 yr and assignment of statistically valid rock solidification ages is not possible from these data low zr in the rocks of each batholith indicates that magmas were initially strongly undersaturated in zircon when emplaced and inherited zircon is rare or absent recycling of zircon antecrysts during successive magmatic injections is the primary cause of the modest age dispersion of concordant zircon ages and is compatible with progressive growth of a large long lived crystal mush body because eruption of magma requires low to moderate crystal fraction and high temperatures relative to stored crystal mushes zircon crystals are more likely to be eradicated during thermal rejuvenation preceding major eruptions

predictable patterns in stacking and distribution of channelized fluvial sand bodies linked to channel mobility and avulsion processes despite the importance of channel avulsion in constructing fluvial stratigraphy it is unclear how contrasting avulsion processes are reflected in stratigraphic stacking patterns of channelized fluvial sand bodies as a proxy for how river depocenters shifted in time and space using an integrated geospatially referenced three dimensional data set that includes outcrop core and lidar data we identify for the first time in an outcrop study a predictive relationship between channelized sand body architecture paleochannel mobility and stratigraphic stacking pattern single story sand bodies tend to occur in vertically stacked clusters that are capped by a multilateral sand body indicating an upward change from a fixed channel system to a mobile channel system in each cluster vertical sand body stacking in the clusters implies reoccupation of abandoned channels after local avulsion reoccupational avulsion may reflect channel confinement location downstream of a nodal avulsion point that maintained its position during development of the sand body cluster and or aggradation and progradation of a backwater mediated channel downstream of a nodal avulsion point sand body clusters and additional multilateral sand bodies are laterally offset or isolated from each other implying compensational stacking due to regional switching of a nodal avulsion point to a new topographically lower site on the floodplain the predictive links between avulsion mechanisms channel mobility and resultant sand body distributions and stacking patterns shown in our findings have important implications for exploring and interpreting spatiotemporal patterns of stratigraphic organization in alluvial basins

a fractal measure of mass transfer in fluid rock interaction abstract exploring the mechanism of mass transfer is critical for characterizing geochemical behaviour of elements in fluid rock interaction and is useful for understanding the sequence of hydrothermal alteration the focus of this study is on identifying the spatial relationship between the concentration variation of elements and the distance of samples to the source of the hydrothermal fluid a mobility index mi was applied to represent the mass changes a value of mi 1 indicates gain of elements x from alteration to the source of hydrothermal fluids is observed for the enriched and depleted elements the relation can be expressed as mi cx d and mi cx d respectively where c is a constant and d is the fractal dimension such relations indicate a power law decrease increase of mi with the decreasing degree of alteration the fractal dimension provides an objective measure of the mass gain or loss the larger the fractal dimension the larger the mass change the fractal dimension sequence quantitatively reveals the activity of ore forming elements and the degree of mass changes in the process of hydrothermal fluid rock interaction which can provide critical information on hydrothermal alteration

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

stratigraphy and paleohydrology of delta channel deposits jezero crater mars abstract the jezero crater open basin lake contains two well exposed fluvial sedimentary deposits formed early in martian history here we examine the geometry and architecture of the jezero western delta fluvial stratigraphy using high resolution orbital images and digital elevation models dems the goal of this analysis is to reconstruct the evolution of the delta and associated shoreline position the delta outcrop contains three distinct classes of fluvial stratigraphy that we interpret from oldest to youngest as 1 point bar strata deposited by repeated flood events in meandering channels 2 inverted channel filling deposits formed by avulsive distributary channels and 3 a valley that incises the deposit we use dems to quantify the geometry of the channel deposits and estimate flow depths of 7 m for the meandering channels and 2 m for the avulsive distributary channels using these estimates we employ a novel approach for assessing paleohydrology of the formative channels in relative terms this analysis indicates that the shift from meandering to avulsive distributary channels was associated with an approximately four fold decrease in the water to sediment discharge ratio we use observations of the fluvial stratigraphy and channel paleohydrology to propose a model for the evolution of the jezero western delta the delta stratigraphy records lake level rise and shoreline transgression associated with approximately continuous filling of the basin followed by outlet breaching and eventual erosion of the delta our results imply a martian surface environment during the period of delta formation that supplied sufficient surface runoff to fill the jezero basin without major drops in lake level but also with discrete flooding events at non orbital e g annual to decadal timescales

fluvial and submarine morphodynamics of laminar and near laminar flows a synthesis the interaction of flow with an erodible bed in alluvial rivers and deep sea channels gives rise to a wide range of self formed morphologies including channels ripples dunes antidunes alternate bars multiple row bars meandering and braiding as the flow is invariably turbulent in field manifestations of these morphologies there has been a tendency to assume that turbulence is necessary for them to form while turbulence undoubtedly has an important influence when it is present it is not necessary for any of these features indeed all of these features can be formed by the morphodynamic interaction of purely laminar or nearly laminar flow with an erodible bed this paper provides a survey and synthesis of a wide range of laminar or near laminar flow analogues of morphologies observed in the field laminar flow analogues of turbulent flow morphologies cannot and should not be expected to satisfy dynamic similarity in terms of all relevant dimensionless parameters what is of more significance is the convergence of the underlying physics it is illustrated in this paper that many existing theoretical frameworks for the explanation of turbulent flow morphodynamics require only relatively minor modification in order to adapt them to laminar flows

evaluation of the uncertainty in estimation of metal resources of skarn tin in southern china abstract this study is concerned with the problem of how many undiscovered mineral deposits can be expected to occur in the vicinity of any known deposit especially if the deposit is nearly mined out skarn tin deposits in southern china were chosen to demonstrate that fractal modeling can be a useful tool to characterize the spatial temporal distribution of mineral deposits and to quantify their grades and tonnages the results show that the spatial temporal distribution of skarn tin deposits as well as their grades and tonnages satisfy fractal statistic and suggest that 14 skarn tin deposits could be found around a known skarn tin deposit within a radius of 80 km monte carlo simulation was used to combine the number of deposits and the frequency distributions of grade and tonnage and to capture the uncertainty in estimation of metal resources at the 90 50 and 10 confidence levels tin metal resources amount to 6 ton 200 ton and 1 0 10 4 ton around a known tin deposit within a radius of 80 respectively

experimental simulation of element mass transfer and primary halo zone on water rock interaction abstract primary halo zone is an important theory for prospecting the deep blind ore body and predicting resource potential the common description of primary halo zone of multiple elements is based on their behaviors during hydrothermal alteration or mineralization a geofluid with multiple elements which are bi cu pb zn cd ag and as bearing ni and mo is prepared to simulate the dispersive transfer of elements in a hydrothermal fluid granite reaction at 15 mpa 100 c using a new constructed core flow through pressure vessel reactor core granite samples with 5 cm long after water rock reaction are cut into ten sections to analyze their major oxides and trace elements according to experiment results and the method of immobile plateau we determine that al and ti are immobile elements during the water rock reaction and the hydrothermal alteration of granite is a mass gained process the mobility index mi of each of experimental elements is calculated based on the immobile component al 2 o 3 the sequence of experimental elements is from as to ag pb zn cu bi ni cd and mo which are sorted on their values of mi in these reacted granite cores from near to far end respecting to the reaction fluid this result is consistent with the empirical sequence of zonation of primary halo elements which is derived from the statistical results from 58 gold deposits in china the denudation coefficient of primary halo zone zf or zfe is proposed to assess the degree of approaching to ore body on these experiments which is the averaged mi ratio of front halo elements to ore body halo elements the denudation coefficient of primary halo zone is applied on the cross section of gold ore body hosted in the granite of the linglong gold deposit located in the jiaodong peninsula of eastern china the degree of approaching to the gold ore body is clearly illustrated by the denudation coefficient of primary halo zone

consonorm_lg new normative minerals and alteration indexes for low grade metamorphic rocks the consonorm lg method provides a standardized solution for approximating metamorphic parageneses as well as indexes for estimating chemical and mineralogical changes caused by hydrothermal alteration consonorm lg is designed for rocks dominated by silicates fe ti oxides and or carbonates and it approximates the main parageneses of greenschist and lower amphibolite grade metamorphic rocks for three sets of temperature and pressure conditions 350 c and 2 5 kbars 450 c and 2 5 kbars 575 c and 2 kbars for each model the norm calculates the main paragenesis using an acfmnk tetrahedron a convenient way of representing a large number of silicate assemblages in addition to silicate minerals consonorm lg calculates fe ti oxides and other accessory minerals from minor elements as well as sulfides from analyzed s or from analyzed metals and carbonates from analyzed co2 or from normative co2 estimated from loss on ignition loi consonorm lg also calculates several alteration indexes to estimate fe mg e g chloritization ca e g propylitic alteration na and k acid alterations e g sericitization phyllic alterations and al gain e g argillization carbonatation indexes are also calculated using the amount of normative minerals formed by this type of alteration i e carbonates chlorite and muscovite the normative calculation is validated using published whole rock analyses and petrographic descriptions alteration indexes are validated using several natural samples of alteration halos around base metal and gold deposits

punctuated sand transport in the lowermost mississippi river 1 measurements of sand flux and water flow in the mississippi river are presented for a portion of the system 35 50 km upstream from the head of its subaerial delta these data are used to provide insight into how nonuniform flow conditions present in the lower reaches of large alluvial rivers affect the timing and magnitude of sand transport near the river outlet field surveys during both low and high water discharge include 1 sequential digital bathymetric maps defining mobile river bottom topography which were used to estimate bed material flux 2 multiple water velocity profiles and 3 multiple suspended sediment profiles collected using a point integrated sampler these data show that total sand transport increases by two orders of magnitude over the measured range in water discharge 11 300 to 38 400 m3 s 1 during low water discharge no sand is measured in suspension and sand discharge via bed form migration is minimal during high water discharge 54 of the sand discharge is measured in suspension while 46 of the sand discharge is part of bed form migration the component of boundary shear stress associated with moving this sediment is estimated using a set of established sediment transport algorithms and values for the total boundary shear stress are predicted by fitting logarithmic velocity functions to the measured profiles the estimates of boundary shear stress using measurements of suspended sand transport bed form transport and downstream oriented velocity profiles are internally consistent moreover the analyses show that boundary shear stress increases by nearly 10 fold over the measured water discharge range we show how this increase in shear stress is consistent with backwater flow arising where the river approaches its outlet the hydrodynamic properties of backwater flow affect the timing and magnitude of sand flux and produce punctuated sand transport through the lowermost mississippi river our field data are used to evaluate the influence of this sand transport style on development of the mixed bedrock alluvial channel for the lowermost mississippi river

mapping singularities with stream sediment geochemical data for prediction of undiscovered mineral deposits in gejiu yunnan province china abstract this paper proposes the concept of singularity for characterizing hydrothermal mineralization processes a singular physical process may result in anomalous amounts of energy release or material accumulation within a narrow spatial temporal interval mineralization can be considered as a type of singular process due to large amounts of material accumulation and element enrichment a spatial singularity mapping technique is developed based on the local singularity involved in the context of multifractal theory it assembles geochemical map at different scales and calculates an index indicating the scaling characteristics of enrichment and depletion of geochemical concentration at multiple scales this index was used for quantifying spatial singularity of mineralization associated geochemical anomalies a case study for the gejiu tin polymetallic mineral district yunnan province china demonstrates that the concepts of singularity and the singularity mapping technique are applicable and useful for delineating anomalies caused by mineralization and for predicting the locations of undiscovered mineral deposits

spatial distribution of ore deposits conventional spatial distributions such as the negative binomial and neyman scott have been proposed as models for the clustered distribution of ore deposits b b mandelbrot has proposed that ore deposits are clustered at many different scales and that fractal distributions are appropriate the apparent fractal characteristics of geologic controls on the locations of hydrothermal deposits self similar systems of fractures circulation cells and magmatic intrusions support his proposal examination of the spatial distribution of 4775 hydrothermal precious metal deposits in the basin and range western united states reveals fractal distributions acting within two scale ranges together covering the entire range from 1 to 1000 km this result gives additional credibility to concepts of regional controls on mineralization such as metallogenic provinces and tectonostratigraphic terranes the distribution of these ore deposits about a known occurrence follows a regular radial density law within a range of radii r of 1 to 15 km the probability density function of these deposits is given by d 0 46 r 1 17 and within a range of radii of 15 to 1000 km by d 0 08 r 0 83 where d is deposits per square kilometre

construction solidification and internal differentiation of a large felsic arc pluton cathedral peak granodiorite sierra nevada batholith the tuolumne batholith tb sierra nevada batholith usa is an archetypal large zoned arc intrusion c 1200 km 2 previous work proposed that compositional zonation observed in the tb was produced in situ by inward differentiation of a large magma chamber and or large scale intrachamber magma mixing recent geochronology shows that the tb was intruded over 8 9 ma making single pulse fractionation or mixing in a magma chamber of tb dimensions unlikely we examine processes responsible for compositional variation in the cathedral peak granodiorite which is the largest mapped unit of the tb new field geochemical and geochronological work along a roughly contact perpendicular 5 km transect indicates 1 magmatic foliation is steeply dipping 60 2 field evidence for repeated separation of crystals from melt and local magma mixing is observed 3 u pb zircon ages at opposing ends of the transect are indistinguishable within error c 87 5 ma 4 bulk composition varies only modestly but trace elements show variable degrees of scatter 5 end t and 87 sr 86 sr i have small variation compared with that in the whole tb geochemical and isotopic data are compatible with fractionation of major silicates and accessory minerals however the geochemical spatial variation minor isotopic variation and field evidence suggest that fractionation was highly disorganized and also involved mixing with new input magma and remobilization of crystal mush as the pluton solidified our observations are consistent with the construction of a large and dynamic magma system within the last c 1 ma of tb growth

scaling relationships and evolution of distributary networks on wave influenced deltas 1 no genetic model can explain the variability in distributary network pattern on modern deltas here we derive scaling relationships for two processes known to create distributary channels and with these laws construct a simple model for distributary network evolution the first process is mouth bar deposition at the shoreline and subsequent channel bifurcation the second is avulsion the wholesale abandonment of a channel in favor of a new path the former creates relatively small networks with power law distributions of channel length the latter generates relatively few backwater scale distributaries frequency magnitude plots of channel length on natural deltas agree with theoretical predictions and show a clear separation in scale that reflects these processes mouth bar distributary lengths scale with the width of the parent channel and avulsive distributary lengths scale with the backwater length intermediate channel lengths are relatively rare wave energy controls network topology by suppressing mouth bar development thereby preferentially eliminating smaller scale distributaries

hydrothermal alteration zoning and gold concentration at the kerr addison archean lode gold deposit kirkland lake ontario kerr addison a major archcan lode gold deposit of the abitibi belt with a production of approximately 10 x 10 6 oz au approximately 320 metric tons up to 1983 is localized in a zone of talc carbonate and chlorite carbonate rocks immediately south of a regional structural break the kirkland lake larder lake fault zone relict volcanic textures taken in conjunction with the ratios of diag nostic relatively less mobile elements collectively indicate that most of the wall rocks of the mine were originally mafic and ultramafic rocks along with their clastic derivatives regional greenschist facies metamorphism is locally superposed by a distinct zonation of gold associated hydrothermal alteration characterized by massive introduction of co 2 coupled with variable enrichments of alkali metals and calcium which produced systematic trends of alteration mineral assemblages alteration types of the initial stage contain chlorite which is replaced by muscovite or albite in the advanced stage of alteration with a concomitant increase in the proportion of carbonate minerals numerous generations of crosscutting veins are enveloped by alteration borders in which the sequence of the al bearing minerals namely albite mus covite and chlorite develop from the vein to the wall rocks always in a systematic sequence the same sequence is observed at a larger scale from the ore zone to the periphery of the mine area the intensity of alteration can be monitored by saturation indices co 2 ca fe mg for carbonates and 3k na al 3k al and na al for muscovite albite muscovite and albite respectively molar ratios plots of the moving averages of these indices across the 3 850 ft level of the mine reveal a remarkable correspondence to variations of gold abundance suggesting a genetic relationship of gold enrichment to hydrothermal alteration on a broad scale gold is concentrated to the south of the kirkland lake larder lake fault zone and at a more detailed scale in the transition zone between carbonate muscovite and carbonate albite alteration types during advanced alteration fluid x sub co 2 was approximately 0 1 and na k asymp 10 volcanics of the kinojevis and larder lake groups are 18 o enriched relative to pristine tholeiites and possess distinct mineral delta 18 o values probably due to different conditions of marine water alteration during or shortly after extrusion in domains of advanced alteration these are all shifted down to a common narrow bracket here 18 o 16 o and d h data indicate fairly constant temperatures 270 degrees 300 degrees c and a common isotopic composition of hydro thermal fluids delta 18 o 5ppm delta d 30 to 50ppm across the alteration zoning these results are in common with many other archcan lode gold deposits fe dolomite has a uniform delta 13 c value of 2 8 or 0 42 per mil 1sigma throughout the footwall and ore zones but it is enriched by approximately 1 per mil in the graphite free hanging wall rocks fluid delta 13 c value was 4 or 1 per mil reflecting either a magmatic carbon reservoir or mixtures of marine carbonate carbonaceous and magmatic sources the enrichment of gold at one side of the kirkland lake fault zone is interpreted to be the result of development of a metasomatic zoning induced by gradients in oxidation state the precious metal being concentrated in the reducing side zonation of alteration types south of the kirkland lake larder lake fault zone represents various steps of a continuous process of incremental changes of the rocks to adapt to the composition of an externally generated fluid successive generations of fracture arrays and veins have the same alteration patterns and thus the composition of the incoming hydrothermal fluid seems to have remained essentially unchanged through time gold mineralization at the kerr addison mine and its contiguous alteration halo are interpreted to be the result of repeated cycles of hydraulic fracturing fluid penetration and local reaction with rocks fluid rock interaction produced lateral variations of fluid composition which led to gold concentration probably due to gradients in ph preferentially at the interface between the carbonate muscovite and carbonate albite alteration types which is also the site of pyrite concentration the alteration assemblages and specific site of gold pyrite concentration at kerr addison are common to several other described archcan lode gold deposits

a three dimensional numerical model of sediment transport erosion and deposition within a network of channel belts floodplain and hill slope extrinsic and intrinsic controls on floodplain dynamics and alluvial architecture a three dimensional numerical model of sediment transport erosion and deposition within a network of channel belts and associated floodplain is described sediment and water supply are defined at the upstream entry point and base level is defined at the downstream edge of the model sediment and water are transported through a network of channels according to the diffusion equation and each channel has a channel belt with a width that increases in time the network of channels evolves as a result of channel bifurcation and abandonment avulsion the timing and location of channel bifurcation is controlled stochastically as a function of the cross valley slope of the floodplain adjacent to the channel belt relative to the down valley slope and of annual flood discharge a bifurcation develops into an avulsion when the discharge of one of the distributaries falls below a threshold value the floodplain aggradation rate decreases with distance from the nearest active channel belt channel belt degradation results in floodplain incision extrinsic extrabasinal allogenic and intrinsic intrabasinal autogenic controls on floodplain dynamics and alluvial architecture were modelled and sequence stratigraphy models were assessed input parameters were chosen based on data from the rhine meuse delta to examine how the model responds to extrinsic controls the model was run under conditions of changing base level and increasing sediment supply rises and falls in base level and increases in sediment supply occurred over 10 000 years rising base level caused a wave of aggradation to move up valley until aggradation occurred over the entire valley frequency of bifurcations and avulsions increased with rate of base level rise and aggradation rate channel belt width varied with water discharge and the lifespan of the channel belt wide connected channel belts and high channel deposit proportion occurred around the upstream inflow point because of their high discharge and longevity less connected smaller channel belts occurred further down valley such alluvial behaviour and architecture is also found in the rhine meuse delta during base level fall valley erosion occurred and the incised valley contained a single wide channel belt during subsequent base level rise a wave of aggradation moved up valley filling the incised valley bifurcation and avulsion sites progressively moved upstream relatively thin narrow channel belts bordered and cut into the valley fill these results differ substantially from existing sequence stratigraphy models the increase in sediment supply from upstream resulted in an alluvial fan most bifurcations and avulsions occurred at the fan apex nodal avulsion and channel belts were the widest and the thickest here giving high channel deposit proportion due to their high discharge and longevity the width and thickness of channel belts decreased down valley due to decreased discharge longevity and aggradation rate this behaviour occurs in modern alluvial fans intrinsic controls also affect floodplain dynamics and alluvial architecture variation of aggradation rate bifurcation frequency and number of coexisting channel belts occurred over periods of 500 to 2000 years compared with 10 000 years for extrinsic controls this variation is partly related to local aggradation and degradation of channel belts around bifurcation points channel belts were preferentially clustered near floodplain margins because of low floodplain aggradation rate and topography there

quantitative field constraints on the dynamics of silicic magma chamber rejuvenation and overturn the catastrophic eruption of large volume crystal rich silicic magmas is often proposed to be a consequence of reheating melting and overturn of partially molten buoyant silicic material following repeated injection of dense hot mafic magma to test this rejuvenation hypothesis we analyze at high spatial resolution 33 examples of deformed interfaces between intrusive mafic and silicic layers in two plutons of the coastal maine magmatic province usa these deformed interfaces are thought to record the buoyant overturn of silicic crystal mush layers apparently in response to the injection and cooling of hot dense mafic magmas we use spectral analysis and scaling theory along with petrologic and textural data to identify characterize and understand periodic deformations from the scale of individual crystals 1 cm to the thicknesses of mafic and silicic layers deformations at the largest scale lengths 100 m are at wavelengths comparable to or greater than silicic layer thicknesses and support a conjecture that mafic recharge can cause large scale rayleigh taylor type overturning of silicic mushy layers by contrast the smallest scales of individual crystals probably record effects related to production and buoyancy driven rise of melt from the tops of silicic mushes in contact with overlying hot basalt whereas intermediate scales are explained by compaction our results constrain the evolution of a thermal rejuvenation event and potentially identify a condition for a large scale overturn of the magma chamber that may lead to eruption this work provides the first quantitative field based constraints on some of the key physical processes inherent to the rejuvenation hypothesis

backwater controls of avulsion location on deltas river delta complexes are built in part through repeated river channel avulsions which often occur about a persistent spatial node creating delta lobes that form a fan like morphology predicting the location of avulsions is poorly understood but it is essential for wetland restoration hazard mitigation reservoir characterization and delta morphodynamics following previous work we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length i e the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin to explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges results show that avulsion is less likely in the downstream portion of the backwater zone because during high flow events the water surface is drawn down near the river mouth to match that of the offshore plume resulting in river bed scour and a reduced likelihood of overbank flow furthermore during low discharge events flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel fill timescale there both mechanisms favor preferential avulsion in the upstream part of the backwater zone these dynamics are fundamentally due to variable river discharges and a coupled offshore river plume with implications for predicting delta response to climate and sea level change and fluvio deltaic stratigraphy

magmatic erosion of the solidification front during reintrusion the eastern margin of the tuolumne batholith sierra nevada california the tuolumne batholith sierra nevada california consists of several nested granitoid units and is an example of upper crustal normally zoned intrusions the two outermost units of the batholith are separated by a wide gradational contact in what is interpreted to represent a large magma chamber in the potter point area near the eastern margin of the batholith the gradational contact is cross cut by a network of interconnected mafic felsic sheets which grade into zones of magmatic erosion by stoping where the host granodiorite between the sheets was entirely removed and replaced by younger enclave rich quartz diorite we interpret these features to record disruption of a steep solidification front which migrated inwards from the eastern batholith margin and separated the mushy to solidified margin from the remaining active magma chamber when intersecting the gradational contact the solidification front started to break up via a network of tectonically driven fractures accompanied by simultaneous injection of localized magma pulses the solidification front break up is interpreted here as an initial stage of a recycling process whereby older magma mush is disrupted and incorporated into younger magma batches a process we propose to have been widespread along internal contacts in the tuolumne magma chamber

backwater and river plume controls on scour upstream of river mouths implications for fluvio deltaic morphodynamics sediment flux from rivers to oceans is the fundamental driver of fluvio deltaic morphodynamics and continental margin sedimentation yet sediment transport across the river to marine boundary is poorly understood coastal rivers typically are affected by backwater a zone of spatially decelerating flow that is transitional between normal flow upstream and the offshore river plume flow deceleration in the backwater zone as well as spreading of the offshore plume should render rivers highly depositional near their mouths leading to sedimentation and eventual elimination of the backwater zone at steady state this reasoning is counter to observations of riverbed scour erosional bed forms and long lived backwater zones near the mouths of some coastal rivers e g mississippi river united states to explain these observations we present a quasi 2 d model of a coupled fluvial backwater and offshore river plume system and apply it to the mississippi river results show that during high discharge events the normal flow depth can become larger than the water depth at the river mouth resulting in drawdown of the water surface spatial acceleration of flow and erosion of the riverbed as proposed by lane 1957 the transition to drawdown and erosion is ultimately forced by spreading of the offshore river plume this points to the need to model coupled river and river plume systems with a dynamic backwater zone under a suite of discharges to accurately capture fluvio deltaic morphodynamics and connectivity between fluvial sediment sources and marine depositional sinks

origin of a preferential avulsion node on lowland river deltas river deltas are built by cycles of lobe growth and abrupt channel shifts or avulsions that occur within the backwater zone of coastal rivers previous numerical models differ on the origin of backwater scaled avulsion nodes and their consistency with experimental data to unify previous work we developed a numerical model of delta growth that includes backwater hydrodynamics river mouth progradation relative sea level rise variable flow regimes and cycles of lobe growth abandonment and reoccupation for parameter space applicable to lowland deltas we found that flow variability is the primary mechanism to cause persistent avulsion nodes by focusing aggradation within the backwater zone backwater scaled avulsion nodes also occur under less likely scenarios of initially uniform bed slopes or during rapid relative sea level rise and marine transgression our findings suggest that flow variability is a fundamental control on long term delta morphodynamics

paleocene wilcox cross shelf channel belt history and shelf margin growth key to gulf of mexico sediment delivery abstract shelf margins prograde and aggrade by the incremental addition of deltaic sediments supplied from river channel belts and by stored shoreline sediment this paper documents the shelf edge trajectory and coeval channel belts for a segment of paleocene lower wilcox group in the northern gulf of mexico based on 400 wireline logs and 300 m of whole cores by quantitatively analyzing these data and comparing them with global databases we demonstrate how varying sediment supply impacted the wilcox shelf margin growth and deep water sediment dispersal under greenhouse eustatic conditions the coastal plain to marine topset and uppermost continental slope succession of the lower wilcox shelf margin sediment prism is divided into eighteen high frequency 300 ky duration stratigraphic sequences and further grouped into 5 sequence sets labeled as a e from bottom to top sequence set a is dominantly muddy slope deposits the shelf edge of sequence sets b and c prograded rapidly 10 km ma and aggraded modestly 80 m ma characterizes sequence sets d and e which is associated with smaller 9 10 m thick on average and isolated channel belts this stratigraphic trend is likely due to an upward decreasing sediment supply indicated by the shelf edge progradation rate and channel size as well as an upward increasing shelf accommodation indicated by the shelf edge aggradation rate the rapid shelf edge progradation and large rivers in sequence sets b and c confirm earlier suggestions that it was the early phase of lower wilcox dispersal that brought the largest deep water sediment volumes into the gulf of mexico key factors in this lower wilcox stratigraphic trend are likely to have been a very high initial sediment flux to the gulf because of the high initial release of sediment from laramide catchments to the north and northwest possibly aided by modest eustatic sea level fall on the texas shelf which is suggested by the early flat shelf edge trajectory high amalgamation of channel belts and the low overall aggradation rate of the sequence sets b and c

river morphodynamic evolution under dam induced backwater an example from the po river italy abstract river systems evolve in response to the construction of dams and artificial reservoirs offering the possibility to investigate the short term effects of base level oscillations on fluvial architecture a major effort has been dedicated to the understanding of river response downstream of large dams where deep channel incisions occur in response to the removal of sediment that is sequestered in the upstream reservoir integrating field observations and numerical modeling results this work quantifies the sedimentary and morphological changes of the po river italy upstream of the isola serafini dam to investigate the impact of dam induced backwater on river morphodynamics the construction of a reservoir generates a new base level that forces an upstream shift of alluvial lithofacies and a change in the planform geometry of the river the lateral migration rate of the channel is up to 45 m yr upstream of the influence of backwater flow and ca 10 m yr at the transition from normal to backwater flow conditions 30 km from the dam within this reach a reduction of the bed shear stress promotes deposition of coarse grained sediment and the emergence of the gravel sand transition of the river the lateral migration of the channel continuously decreases over time and rates 5 m yr can be observed in the reservoir backwater zone this trend is accompanied by the drowning of channel bars the reduction of river competence and an increase in bedform spacing oscillatory backwater and drawdown surface water profiles can be observed closer to the dam which are associated with varying low discharge and high discharge events respectively while low flow conditions persisting for much of the year allow the deposition of fine grained sediment high discharge events promote not only the resuspension and transport of fine material but also the progressive erosion of channel bars and the overall deepening of the thalweg this study provides a clear picture of the river evolution in response to the construction of a hydropower dam that may be of help in predicting how other fluvial systems will respond to future human interventions moreover the result of how changes in base level and oscillations in water surface profile backwater and drawdown control river hydro morphodynamics and sediment transport may provide new insights when reconstructing ancient fluvial and deltaic sequences

variability of channel belt dimensions and the consequences for alluvial architecture observations from the holocene rhine meuse delta the netherlands and lower mississippi valley u s a abstract over the past decades many studies have focused on the dimensions of channel belt sand bodies referred to as channel belts in fluvial deposits because of their relevance for hydrocarbon exploration and production some field studies have revealed a significant downstream decrease of channel belt width and width thickness ratio along the length of the channel belt to verify whether this is a common feature in fluviodeltaic settings eight holocene channel belts in the rhine meuse delta the netherlands were selected and one in the lower mississippi valley u s a we determined channel belt geometry width or width thickness ratio using geological geomorphological maps and detailed cross sections based on borings it was found that the width of channel belts encased in cohesive deposits decreases by a factor of 4 to 6 5 in a downstream direction along the length of the channel belts the width thickness ratio decreases by a factor of 2 5 to 5 on the other hand the width of a channel belt incised in a noncohesive substrate remains constant along its entire course these observations are related to longitudinal changes in bank erodibility and stream power it is suggested that bank erodibility is the dominating factor determining the geometric properties of channel belts and the variability therein at least in the rhine meuse delta the currently available alluvial architecture models most likely overestimate sand quantities and connectedness in alluvial successions because channel belt dimensions are held constant in all models we therefore propose that the factors bank erodibility and stream power which influence width and width thickness ratio of channel belts should be incorporated in future alluvial architecture models in order to make more realistic estimates of sand quantities in river deltas