contrasting arc and morb like assemblages in the paleoproterozoic flin flon belt manitoba and the role of intra arc extension in localizing volcanic hosted massive sulphide deposits the flin flon belt trans hudson orogen manitoba and saskatchewan is the largest paleoproterozoic volcanic hosted massive sulphide vms district in the world with 118 7 million tonnes mt of z

petrogenesis of intermediate volcanic assemblages from the shebandowan greenstone belt superior province evidence for subduction during the neoarchean abstract research on the petrogenesis of andesites and their implications for geodynamic setting are an important facet to understanding controversial tectonic processes during the archean the genesis of archean intermediate volcanic rocks and their relationship to mantle and crust derived melts can either support subduction dominated tectonic processes or plume crust interactions this study describes the lithogeochemistry and nd isotopic composition of intermediate volcanic assemblages in the shebandowan greenstone belt of the wawa abitibi terrane that were deposited prior to deformation and tectonic assembly of the superior province the intermediate rocks of the shebandowan greenstone belt are unique in that they are voluminous are relatively weakly deformed and are low metamorphic grade and contain significant amounts of magnesian andesites and adakites the major and trace element geochemistry of the intermediate assemblages share many of the geochemical characteristics of modern volcanic and continental arcs these features include enriched th nb and th la ratios steeply dipping rare earth patterns and pronounced negative ti and nb anomalies on primitive mantle normalized diagrams additionally these rocks also contain distinct positive pb and cs anomalies without evidence of major mobility of these elements during secondary processes neodymium isotopic analyses indicate the interaction with older crust and show good correlations with evolved nd isotopic values with other crustal contamination proxies such as th ce and ti sc ratios modeling mixing and assimilation fractional crystallization interactions between plume derived and crustal melts reveal that plume crust interactions cannot explain the compositional array obtained from the intermediate rocks in the shebandowan greenstone belt a compilation of u pb geochronology for the shebandowan greenstone belt reveals that tholeiitic komatiite dominated strata are slightly older than the intermediate dominated strata given that these domains are structurally separated it is very likely that the shebandowan greenstone belt was formed in two different geodynamic settings these different geodynamic settings have important implications for the metallogeny of the belt and explain the relative enrichment of au and ni cu mineralization in the shebandowan greenstone belt relative to other ca 2720 ma assemblages in the wawa abitibi terrane

a markov model for beach changes on the holderness coast of england markov models offer an objective and quantitative method of assessing beach changes for a stretch of the holderness coast a beach classification scheme was devised and a probabilistic first order matrix model based on surveyed profile data was produced this could describe and predict transitions between beach types and between different time periods different profile types dominated different coastal locations and seasonal variations were seen in order to improve the accuracy of prediction throughout the year a second winter model was added to the original summer one although the models had been prepared independently of wave conditions a comparison of the wave record and beach transitions revealed that waves under 0 3 0 5 m high produced fairly static beaches when waves were between 0 5 and 1 0 m the beach was more dynamic and variable while waves over 1 0 m led to the depletion of the upper beach this was broadly in accordance with published theory markov models have the advantage that they can be adjusted periodically if conditions change and are thus useful for prediction on coasts for which no wave records exist

regional sea level southern oscillation and beach change new south wales australia coastal erosion is a problem of increasing concern that affects 60 of the world s sandy coastline1 this erosion has been attributed to increased storminess tectonic subsidence eustatic sea level rise decreased shoreward sediment movement from the shelf permanent longshore leakage of sediment from beach compartments shifts in global pressure belts resulting in changes in the directional component of wave climates and human interference2 3 no one explanation has worldwide applicability because all factors vary in importance regionally evaluation of factors is complicated by a lack of accurate continuous long term erosional data historical map evidence spanning 100 1 000 yr has been used in a few isolated areas4 7 however temporal resolution has not been sufficient to evaluate the effect of climatic variables air photographic evidence8 is restricted to the past 40 yr and often suffers from insufficient ground control for accurate mapping over time ground surveying of beaches was rarely carried out before 1960 and is often discontinuous in time and space i have resolved the problems of temporal and spatial continuity by studying change for the whole of stanwell park beach new south wales australia for the period 1895 1980 fig 1 i report here that using the average high tide wave run up position measured accurate to 2 5 m from oblique and vertical photographs changes could be linked to regional sea level variation and a globally significant climatic variable the southern oscillation so

the role of granitic intrusions in the evolution of the abitibi belt canada abstract the abitibi greenstone belt canada constitutes a segment of a broad volcanic arc that experienced three distinct periods of volcanic activity peaking at 2730 2725 2718 2714 and 2705 2700 ma during all three volcanic episodes which were generated by subduction related processes mantle plume derived komatiitic volcanic rocks were also added to the composite abitibi arc plume activity resulted in local regional extension and restricted later volcanism within the belt north south shortening produced thrusts and folds followed by se trending dextral strike slip faults between 2700 and 2692 ma the principal belt wide deformation subsequent e w dextral strike slip faulting limited to the major faults continued to 2690 2680 ma destor porcupine fault and even to 2680 2670 ma cadillac larder fault extensional structures resulting from the thickened crust developed around 2660 ma granitic intrusions are associated with all the volcanic episodes and phases of deformation and have been used to constrain the age of many of these events their role in stabilizing and adding to the volcanic crust is perhaps less well appreciated large synvolcanic tonalite dominated intrusions of the tonalite trondhjemite granodiorite ttg suite are associated with the three major periods of volcanic activity of the abitibi greenstone belt and are genetically related to the volcanism these synvolcanic intrusions occur both as high level flat cauldron subsidence complexes and as batholithic masses at the base of the oceanic crust tonalite gneiss dated from 2714 to 2703 ma occurring in structural culminations is considered to be arc underplated material the gneiss crystallized at depth and in contrast to the other tonalites does not appear to have intruded volcanic rocks the gneisses also record the earliest compressional deformation numerous intrusions of island arc affinity both the ttg and monzodiorite mzd suites form stocks and small plutons emplaced during the late phases of major deformation these are more numerous than voluminous and most of the tonalite end members of the suites probably intruded deeper within the sequence retarded by the now thickened crust large tonalite intrusions dominate the uplifted deeper sections adjacent to the abitibi belt in the kapuskasing uplift and grenville parautochthon and presumably make up much of the deep crust of the abitibi belt imaged in lithoprobe seismic profiles small stocks and dyke complexes characterize the late localized strike slip deformational phase these intrusions are porphyritic syenites and related rocks including some alkaline compositions garnetiferous granites of crustal derivation were emplaced in the final period of extensional activity around 2660 ma thus plutonic rocks are a volumetrically major overall component of the abitibi belt and were implicated in every phase of its development from early volcanic arc magmatic activity through the various stages of deformation to final stabilization as continental crust

upper mantle processes beneath the 2 7 ga abitibi belt canada a trace element perspective abstract mantle processes associated with volcanism in the abitibi belt remain poorly understood despite numerous detailed studies of its volcano sedimentary successions this paper employs log plots of nb y and zr y to distinguish the sources of well defined abitibi volcanic suites and to clarify processes in the upper mantle during greenstone belt development mafic rocks of the southern volcanic zone in the abitibi belt define two main trends on log plots of nb y versus zr y trends for the kidd munro assemblage and malartic block correspond to mixtures of strongly deleted plume asthenosphere and adakitic melts the shared trace element systematics of these volcanic successions confirm they are parts of a single authochthonous supracrustal assemblage that extended across the southern abitibi belt the younger kamiskotia assemblage and blake river group correspond to crustal extension episodes within an abitibi island arc trace element plots establish that they were derived from mantle plume related asthenosphere and not the late archean morb source upper mantle associated with island arc assemblages elsewhere in the southern superior province the data suggests widespread lateral flow of mantle plume asthenosphere occurred in the vicinity of the abitibi arc mantle mixing with adakitic melts continued between 2716 and 2698 ma the data are not consistent with wet komatiite models that generate ultramafic volcanic rocks from typical upper mantle following hydration of a mantle wedge chemical mixing trends for mafic magma sources indicate melt hybridization of the abitibi mantle wedge the trends require a slab melt origin for adakitic magmas rather than internal differentiation of underplated mafic crust comparisons with other 2 7 ga greenstone belts suggest that mantle plume interaction with archean subduction zones as proposed for the abitibi belt can be distinguished in the nb zr y systematics of associated mafic volcanic rocks

geochemistry of the dundonald komatiite basalt suite and genesis of dundeal ni deposit abitibi subprovince canada the genesis of konatiites basalts and associated ninineralization in the dundonald township area on tario is critical to understanding the metallogenic evolution of the kidd munro assemblage one of the most primitive volcanic assemblages in the world the 2 5 kin thick stratigraphic succession has a basal calc alkalic basalt dacite rhyolite sequence 2716 8 2 1 ma u pb zircon cut by the dundonald peridotite gabbro sill 27077 ma u pb zircon overlain by komatiitic and basaltic flows containing magmatic ni sulfide mineral ization which are in turn overlain by chemically distinctive low ti basalt flows the dundonald komatiites correlate with komatiites in the footwall of the giant kidd creek volcanic associated massive sulfide deposit 40 km to the west but are slightly older than the komatiites of munro township which are 40 km to the east the dundonald komatiites comprise a munro type al undepleted komatiite suite with liquid compositions having a120 ffio o 18 to 22 and mgo up to 30 3 vet percent anhydrous n 24 most samples in the ko matiite suite have slightly depleted light bee contents with lan smn 0 6 to 1 1 and lan ybn 0 4 to 0 9 n 21 and negligible ti ti and zr zr anomalies their major and trace element geochemistry is consistent with a derivation by sigfificant partial melting of a chemically primitive mantle with little or no influence of majoritc garnet flows that are host to the dundeal and alexo ni deposits have distinctively high thpm nbpm ratios 1 7 n 3 suggesting crustal contamination and peperite textures that are consistent with contami nation from nearby graphitic argillite the chemically distinctive lmv ti basalts have 49 to 53 percent sios 4 5 to 9 5 percent mgo 18 8 to 21 5 percent a1203 0 30 to 0 37 percent tios moderately depleted light ree con tents with lan smn 0 9 to 1 2 and la n ybn 0 4 to 0 6 high ni cr and ba contents 570 6 800 390 630 90 320 ppm respectively n 6 their high ai203 contents place them in the calc alkalic field on a jensen cation plot although their trace element ratios zr y la yb are more consistent with a tholeiitic affinity they are compositionally identical to and they correlate with low ti basalts in the kidd creek volcanic complex their geochemistry is consistent with a derivation by partial melting of a refractory harzburgitic mantle that has undergone a previous melt extraction possibly influenced by a large ion lithophile enriched hydrous phase the empire flow is the thickest and most primitive komatiite flow and is host to the dundeal ni deposit re source of 0 4 mt at 2 0 ni the empire flow contains an elongate dunite peridotite basal unit interpreted as the core of a flow that thermally eroded into footwall heterolithic breccias and pillowed andesites the main dundeal ni horizon overlies part of the basal dunite peridotite unit within the flow channel and extends over the cutbank wall the dundeal deposit and the nearby dundonald south ni deposit have lo v total sulfide con tents and high ni s ratios 0 9 and 1 0 respectively in comparison to most komatiite hosted magmatic sulfide deposits the high ni tenor in sulfide is believed to be due to assimilation of reducing carbonaceous sediment which causes greater ni partitioning into the magmatic sulfide phase

dunefoot dynamics along the dutch coast the dynamics of the dunefoot along a 160 km portion of the dutch coast has been investigated based on a data set of annual surveys dating back to as early as 1850 the linearly detrended or residual dunefoot positions comprise an alongshore uniform and an alongshore non uniform component the former is expressed as 10 to 15 m of landward retreat along extensive 10 km stretches of coast during years with severe storm surges and as up to 5 m of seaward advance during years without significant storm activity the latter alongshore non uniform component is organized in sandwave like patterns which may have a longevity of decades to up to the duration of the entire data set 150 years their wavelengths vary along the coast from 3 5 to 10 km migration rates are 0 200 m a 1 dunefoot sandwaves are shown to be the shoreward extensions of similar sandwave patterns in the beach position the non uniform dunefoot behaviour constitutes at least 80 per cent of the total residual dunefoot dynamics implying that along the dutch coast residual dunefoot variability is controlled by temporal and spatial variability in beach characteristics and not by storm induced uniform erosion various potential mechanisms causing beach sandwaves are discussed copyright 2002 john wiley sons ltd

evidence of tsunami sedimentation on the southeastern coast of australia in coastal regions the highest magnitude storms cannot always be invoked to account for large scale anomalous sediment features any coastline in the pacific ocean region can be affected by tsunamis including australia which historically lacks evidence of such events geologically tsunamis along the new south wales coast have deposited a suite of holocene features that consist of anomalous boulder masses either chaotically tossed onto rock platforms and backshores or jammed into crevices highly bimodal mixtures of sand and boulders and dump deposits consisting of well sorted coarse debris in addition many coastal aboriginal middens were distributed by such events within estuaries tsunamis have left a record of stranded run up ridges that have been interpreted mistakenly as cheniers dating of such deposits indicates that several events have affected this coastline since 3000 bp in contrast to storm waves tsunamis can leave a depositional imprint of their passage characterized by chaotic sort

storminess and high tide beach change stanwell park australia 1943 1978 abstract coastal storms have been considered significant agents in transporting sediment modifying morphology and causing recent beach erosion along the new south wales coast the concomitance of storms warmer sea surface temperatures and poleward movement of the hadley cell was linked to beach erosion on stanwell park beach between 1943 and 1978 this result was defined using an accurately constructed compilation of coastal storms and a precisely measured time series of high tide positions taken from 105 oblique photographs the two data sets are amongst the best of their kind in the world indices of storm magnitude representing cumulative significant wave height were constructed at quarterly intervals and for the year prior to each photograph the quarterly and cumulative storm indices explain 9 9 and 16 6 respectively of the high tide variance at stanwell park each unit increase in the latter index equivalent to an additional 1 m in storm wave height shifts the high tide position shoreward by 0 47 m this is equivalent to the effect produced by a 1 cm rise in sea level while storminess is a crucial variable controlling high tide position on this beach its role cannot be separated easily from that produced by rainfall sea levels sea surface temperatures and atmospheric circulation along the east australian coast and across the pacific ocean over 40 of the high tide data variance on stanwell park beach can be accounted for in decreasing order of importance by rainfall storminess tropical pacific ocean air circulation and sea level these results have implications for other beaches in that single factors such as increased storminess or rising sea levels may not necessarily be the best factors for explaining recent worldwide beach erosion

theoretical constraints and chronological evidence of holocene coastal development in central and southern new south wales australia abstract holocene coastal evolution in new south wales has been interpreted essentially as the unfolding of the impact of marine transgression sea level on this coast supposedly reached its present height at 6 6 5 ka and varied

plutonism in the southern abitibi subprovince a tectonic and petrogenetic framework studies of plutonic rocks in archean terranes such as the southern abitibi subprovince have been an important component in the development of an accretionary tectonic model for the superior province in the southern abitibi subprovince pretectonic approximately 2 75 2 70 ga low k tholeiitic calc alkaline dioritic to tonalitic plutons e g bourlamaque batholith flavrian pluton are associated with volcanism and are interpreted to be derived from both partial melting of hydrated mantle during oceanic arc formation and fractionation of tholeiitic to calc alkaline basalt andesite pretectonic synvolcanic tholeiitic intrusions e g dundonald sill kamiskotia gabbroic complex 2 72 2 70 ga show in situ fractionation trends and locally have mixed magma textures with contemporaneous calc alkaline granitoids they are believed to be derived from a midocean ridge basalt morb like depleted mantle with little evidence for contamination by an older crustal component pre to syntectonic approximately 2 72 2 69 ga porphyry and tonalite plutons e g timmins porphyries round lake batholith have geochemical characteristics typical of archean tonalite trondhjemite suites considered to be derived from melting of basaltic rocks at high metamorphic grades late to post tectonic 2 69 ga diorite monzonite and syenite plutons e g watabeag batholith lamaque stocks otto stock have large ion lithophile element enriched calc alkaline to sho shonitic compositions these intrusions and associated timiskaming type volcanic rocks are attributed to melting of large ion lithophile element enriched mantle in the late stages of subduction late to post tectonic biotite muscovite granite intrusions contain a significant contribution of evolved crust e g s type characteristics of the preissac lacorne batholith in the southern abitibi subprovince the tectonic setting of mantle and crust derived intrusions is broadly comparable to magmatic processes in phanerozoic arcs and accreted terranes the plutonic rocks record a transition from pre to synaccretionary subduction related plutonic suites to late to postaccretionary suites derived from enriched mantle and crustal sources this framework provides a basis for understanding mineral deposits associated with intrusive rocks of the southern abitibi subprovince which range from ni cu sulfides in layered synvolcanic tholeiitic intrusions e g kamiskotia gabbroic complex ontario to volcanogenic sulfides in early tholeiitic and calc alkaline sequences e g flavrian pluton noranda district quebec to the spatial association of gold with late large ion lithophile element enriched intrusions e g lamaque plugs val d or district quebec

u pb ages and tectonic significance of late archean alkalic magmatism and nonmarine sedimentation timiskaming group southern abitibi belt ontario the paper presents u pb ages for zircons of the calc alkalic to alkalic igneous suite and associated alluvial fluvial sedimentary rocks of the timiskaming group in the late archean abitibi greensto

archean volcanoes in southwestern abitibi belt ontario and quebec form composition and development southwestern abitibi volcanic belt is composed of numerous deformed volcanoes that were originally circular to subcircular in outline 100 200 km in diameter and 10 16 km in stratigraphic thicknes

storm generated variations in nearshore beach topography abstract a series of nearshore beach profile measurements from the outer banks of north carolina spanning a four month period have been examined for temporal variations in nearshore topography principal component analysis of the profile data indicates that most of the variation in nearshore topography occurs in four principal modes two quasiseasonal and two subseasonal the first principal component or eigenvector corresponds to a bar berm function the second to a terrace function combined the first two vectors explain 76 3 of the total variance the third and fourth components representing subseasonal modes are a ridge and runnel and a storm bar function respectively both occur in direct response to storm wave activity although the bar berm and terrace modes of profile variation have been previously identified using principal component analysis techniques the subsequent modes have not the ridge and runnel function accounts for 10 6 of total profile variability and the storm bar function accounts for 5 0

archean neptunian fissures and early history of the destor porcupine fault zone timmins ontario canada neptunian dikes and fissures are intimately associated with a minor archean sedimentary basin near timmins ontario in the southwestern part of abitibi subprovince of the canadian shield these structures are associated with the late archean timiskaming unconformity and were formed by clastic sedimentation in fissures opened by the reactivation and dilation of basement faults along a major crustal shear a pull apart origin is indicated for the sedimentary basin by published township maps and the underground geology of the dome gold mine the neptunian dikes and fissures are discussed in relation to previous stratigraphic and tectonic interpretations of the timmins area

hydraulics of interrill overland flow on stone covered desert surfaces the hydraulics of interrill overland flow on stone covered desert surfaces depend on the resistance to flow which may be partitioned into grain resistance form resistance wave resistance and rain resistance efforts to model large scale roughness in open channels suggest that resistance to overland flow on such surfaces is a function of grain reynolds number froude number flow depth and the size shape spacing and pattern of the roughness elements the effect of flow depth on flow resistance f is often hidden in the flow reynolds number re in laboratory and field studies alike f re relations have been found to be convex upward and negatively sloping and these shapes have been explained in terms of the progressive inundation of the roughness elements where laboratory or field based models have been developed for predicting f they invariably contain percent stone cover the prominence of this variable reflects the strong influence of stone size and spacing on flow resistance a laboratory study shows that where the froude number f 0 50 wave resistance increases with stone cover and dominates resistance to flow on all surfaces with stone covers greater than 10 a field study indicates that where f 0 50 and wave resistance is inconsequential grain and form resistance typically account for about 5 and 95 of f respectively these findings have important implications for sediment transport modeling because percent grain resistance is equal to percent grain shear stress and it has recently been suggested that in overland flow as in river flow sediment transport capacity is determined by grain shear stress rather than total shear stress a laboratory study however demonstrates that this is not the case sediment transport capacity is in fact greater than predicted by grain shear stress because energy dissipated in the wakes of roughness elements in overland flow is transformed into turbulence sufficiently close to the bed to affect sediment transport

3d reconstruction of volcanic and ore forming environments of a giant vms system a case study from the kidd creek mine canada abstract the archean north rhyolite is a bimodal suite of rocks located directly northwest of but structurally separate from the kidd creek volcanogenic massive sulfide deposit which has produced 140 4 million tonnes of ore grading 2 29 wt cu 6 15 wt zn 0 22 pb and 86 2 g t ag the stratigraphy of the north rhyolite is identical to that of the kidd creek mine consisting from oldest to youngest of ultramafic flows aphyric rhyolite quartz porphyritic rhyolite and basalt flows divisible into a low tio2 basalt unit 1 55 wt with minor interflow graphitic argillites the north rhyolite is interpreted to be the folded continuation of the kidd creek mine stratigraphy similar alteration patterns in the north rhyolite and the kidd creek mine stratigraphy as well as significant copper and zinc values within the thickest portions of rhyolite domes and ridges of the north rhyolite suggests the potential for economically significant mineralization within the north rhyolite stratigraphy correlation between alteration mineralization and the rhyolite domes and ridges demonstrate the volcanic structures through which the rhyolite was extruded also acted as hydrothermal fluid pathways and were controlling structures in ore formation a 3d volcanic reconstruction showing the paleo seafloor at the time of ore formation illustrates that the rhyolite flows of the north rhyolite were emplaced into the same subsidence structure as the strata of the kidd creek mine area this 3d model generated by translating complex geological data acquired through core logging and underground mapping indicates the volcanic setting of and ore forming environment at kidd creek is much larger than previously thought and provides new spatial data that can be used in exploration targeting

structural history of the manitouwadge greenstone belt and its volcanogenic cu zn massive sulphide deposits wawa subprovince south central superior province structural analysis of the manitouwadge greenstone belt integrated with detailed mapping and geochronological and petrographic studies reveals a complex early deformation history that significant

subaqueous calderas in the archean abitibi greenstone belt an overview and new ideas abstract the 300 700 km abitibi greenstone belt in canada contains numerous world class archean volcanogenic massive sulfide vms deposits yet documentation of archean subaqueous calderas hosting such deposits is lacking the modern sunrise deposit in the myojin knoll caldera of the izu bonin arc shows that submarine calderas are first order sites for vms the hunter mine and normetal calderas as well as the blake river megacaldera complex are reviewed with respect to geometry regional geology physical volcanology dyke emplacement and hydrothermal carbonate alteration these subaqueous calderas are placed into the geodynamic context of the abitibi greenstone belt the abitibi belt displays a complex history of oceanic arc formation evolution collision and fragmentation with numerous types of volcanic edifices and sedimentary basins controlled by oblique subduction and mantle plumes analogue models yielding new insights into the sequence of caldera forming events and their synvolcanic fault patterns are applied to explain archean examples underpressure experiments develop a consistent sequence of fault patterns that compare favourably with natural caldera events during subsidence two sets of faults propagate from the magma chamber margin 1 early reverse outward dipping faults and 2 normal inward dipping faults the largest massive sulfide deposits form preferentially at the caldera margin based on experimental studies and detailed facies mapping the hunter mine caldera is of the segmented piecemeal variety and the normetal caldera is akin to a piston structure the blake river megacaldera contains 1 the e w trending misema 2 the nw trending new senator and 3 the ne trending noranda calderas with the latter two being nested graben type calderas consistent with oblique archean subduction the poorly documented hydrothermal carbonate alteration is discussed and a new exploration model for calderas is presented the alteration study was evaluated at three levels microprobe analysis geochemical staining of drill core and whole rock analyses there were two principal stages of alteration related to vms formation an early silicification phase developed either at depth and or at the seawater interface whereby silicification was bedding parallel in fine grained volcaniclastic deposits near the water surface a pervasive and extensive semi conformable carbonate alteration zone with a discordant focused root zone along faults evolved subsequently three distinct carbonate pairings were observed 1 proximal siderite sideroplesite fe ankerite next to the vms deposit 2 an intermediate ankerite fe dolomite zone and 3 a distal calcite dolomite zone the carbonate phase is associated with the mineralizing event transitions between carbonate species are subtle and changes are indicated by mineral assemblage overlap the silica carbonate hydrothermal alteration pattern is a replacement product and is far more widespread than has been documented this alteration can be easily confused with primary carbonates and chemical precipitation deposits e g banded iron formation if detailed volcano sedimentary facies mapping with alteration has not been conducted and if outcrop is insufficient

gold mineralization at the syenite hosted beattie gold deposit duparquet neoarchean abitibi belt canada le gisement de beattie est situe dans la ceinture de roches vertes de l abitibi a proximite de la faille porcupine destor et est associe a une syenite porphyrique les corps mineralises ont une ressource totale inferee de 2 77moz contenu dans 56 2mt de minerai a 1 53g t d or dans le gisement de beattie deux styles de mineralisation sont presents a controle lithologique et a controle structural la mineralisation a controle lithologique est limitee exclusivement a la syenite alteree en carbonates de fer cette mineralisation represente du minerai a basse teneur mais fort tonnage dans lequel l or est porte par la pyrite arsenifere et l arsenopyrite l or est invisible il se presente sous la forme de solution solide dans le c ur poreux et riche en arsenic des pyrites la mineralisation a controle structural est presente uniquement dans des zones de cisaillement adjacentes et incluses dans la syenite le minerai est a haute teneur dans des zones de breches silicifiees a caractere hydraulique et tectonique dans des veines de quartz cherteux dans des veines polymetalliques intensement silicifiees et dans des dykes de syenite trachytique tres alteree l or y est visible sous forme d electrum dans les microfractures des pyrites brechifiees les deux styles de mineralisation et les alterations font partie d une evolution paragenetique commune dans un environnement magmatique hydrothermal des phases initiales oxydantes ont evolue en conditions reduites a la faveur de fluides magmatiques et externes riches en co2 ce changement d etat d oxydation a entraine la precipitation des sulfures et la cristallisation de l or invisible dans la pyrite arsenifere et l arsenopyrite une phase d alteration ulterieure dominee par des fluides hydrothermaux riches en silice a pour resultat la brechification des sulfures et leur redistribution dans des corridors siliceux ainsi que la remobilisation de l or dans les microfractures des pyrites brechifiees les compositions calculees de 18o et d sur les veines de quartz associees a cet evenement tardif sont respectivement 7 67 o et 66 o indiquant une dominance des fluides magmatiques avec une probable composante metamorphique cet evenement syn metamorphique transition d2 d3 est associe a un fort enrichissement en hg te mo ag sb as et se le style de cristallisation de l or dans le gisement de beattie est une consequence de la dominance des regimes en systemes ouverts tant au niveau de l incorporation dans le magma de l arsenic qui controle la precipitation de l or invisible que de la circulation tardive de fluides hydrothermaux riches en silice qui sont a l origine de la remobilisation de l or le gisement de beattie partage des affinites avec des gisements associes aux intrusions intrusion related gold deposit des gisements epithermaux a tendance neutre a intermediaire et des gisements de type mesothermaux mots cles de l auteur gisement d or porphyre archeen or invisible remobilisation de l or

soil erodibility and processes of water erosion on hillslope abstract the importance of the inherent resistance of soil to erosional processes or soil erodibility is generally recognized in hillslope and fluvial geomorphology but the full implications of the dynamic soil properties that affect erodibility are seldom considered in canada a wide spectrum of soils and erosional processes has stimulated much research related to soil erodibility this paper aims to place this work in an international framework of research on water erosion processes and to identify critical emerging research questions it focuses particularly on experimental research on rill and interrill erosion using simulated rainfall and recently developed techniques that provide data at appropriate temporal and spatial scales essential for event based soil erosion prediction results show that many components of erosional response such as partitioning between rill and interrill or surface and subsurface processes threshold hydraulic conditions for rill incision rill network configuration and hillslope sediment delivery are strongly affected by spatially variable and temporally dynamic soil properties this agrees with other recent studies but contrasts markedly with long held concepts of soil credibility as an essentially constant property for any soil type properties that determine erodibility such as soil aggregation and shear strength are strongly affected by climatic factors such as rainfall distribution and frost action and show systematic seasonal variation they can also change significantly over much shorter time scales with subtle variations in soil water conditions organic composition microbiological activity age hardening and the structural effect of applied stresses property changes between and during rainstorms can dramatically affect the incidence and intensity of rill and interrill erosion and therefore both short and long term hillslope erosional response similar property changes linked to climatic conditions may also significantly influence the stability and resilience of plant species and vegetation systems full understanding of such changes is essential if current event based soil erosion models such as wepp and eurosem are to attain their full potential predictive precision the complexity of the interacting processes involved may however ultimately make stochastic modelling more effective than physically based modelling in predicting hillslope response to erodibility dynamics

short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model a time series of 6 5 years of daily observations of beach states and wave characteristics from southeastern australia was analyzed with the aim of determining the degree to which time varying beach state can be explained and predicted the six commonly occurring beach states dissipative longshore bar trough rhythmic bar and beach transverse bar and rip low tide terrace and reflective discussed earlier were related by means of discrete discriminant analyses to the parameter hb wst where hb is breaker height ws is the fall velocity of the beach sand and t is peak breaker period using a total of 1545 cases two values were used in the analyses the immediate value occurring on the day the particular state was observed and a weighted mean value expressing recently antecedent conditions the immediate value made a negligible contribution to explaining day to day beach state observations however the antecedent conditions showed a strong relationship and provide a successful means of prediction by examining cases where the time derivatives of both state and were near zero it was possible to define the equilibrium conditions associated with each state directions of change erosional or accretionary are predicted in terms of departures of from the equilibrium value appropriate to the beach state prevailing at the time change begins

experimental studies of collapse calderas we present experiments to investigate the formation of calderas using inflatable balloons in a medium of fused alumina powder this system provides a model of a magma chamber in an homogeneous elastic media which scales to volcanic systems in terms of geometry and strength of the media three kinds of experiment were performed i the balloon was inflated and then deflated simulating pre emption tumescence and caldera collapse ii the balloon was deflated without prior inflation simulating caldera formation without pre eruption tumescence iii three balloons were inflated and deflated in a line simulating multiple magma chambers the influence of magma chamber shape was investigated using different shaped balloons balloon inflation formed a dome with a surface pattern of shallow polygonal fractures centrally and radial fractures peripherally uplift occurs along deep inward dipping concentric reverse faults deflation generated depressions with an outer set of concentric ring fractures surrounding a central funnel formed by sagging along numerous minor faults some of which formed during doming during collapse the concentric reverse faults were converted to normal faults and the radial normally faulted fractures were converted to reverse faults without prior tumescence an outer set of near vertical ring faults surround a flat central depression due to collapse of a coherent block an inner set of outward dipping reverse ring faults also develop the experimental caldera area increased with balloon size and increased as the balloon depth decreased for a given balloon volume and depth collapse area is significantly smaller if doming had occurred prior to collapse arcuate fractures can provide the pathways for magma ascent during pre emption tumescence smith bailey 1968 but the shallow radial and polygonal fracture systems may also influence vent location changes in fault geometry and sense of movement extension to compression and vice versa occur when subsidence initiates and can account for changes in vent location that occur in many eruptions multiple overlapping collapse calderas are associated with magma chamber migration whereas nested calderas can result from the activity of a single magma chamber

experiments on cauldron formation a polygonal cauldron and ring fractures abstract the sequence of formation of the motojuku type cauldron fujita et al 1970 is summarized as follows 1 doming due to ascent of a magma body 2 development of normal faults which produce a polygonal cauldron and 3 eruption of acidic to intermediate pyroclastic material model experiments on a scale of 1 200 000 reveal that ascent of the magma body which was imitated by a ball of hardened putty produced a polygonal cauldron composed of radial and concentrically arranged short fractures on the roof of a dome no ring fractures were formed this type of cauldron develops near the surface on the other hand emission of magma which was imitated by evaporation of a ball of dry ice in brittle powdered material caused ring faults dipping outward and a circular cauldron without up or downwarping this type of cauldron develops upward from the magma body the former model is equated to the motojuku type cauldron and the latter model to the other types of cauldrons with ring fractures

the duparquet formation sedimentation in a late archean successor basin abitibi greenstone belt quebec canada in the south central part of the abitibi greenstone belt a succession of archean epiclastic sediments at least 2 km thick was deposited in the duparquet basin the destor porcupine fault and a secondary fault that splays off the major fault define the margins of this basin which is at least 15 km long and up to 2 5 km wide sedimentary evidence of tectonic influence includes i rapid vertical and lateral facies changes over tens of metres ii cyclic repetition of facies associations iii mixed fining upward coarsening upward fining upward sequences in conglomerate units iv local derivation of most clasts and v asymmetric distribution of fan deltas and braid deltas along the strike of the fault bounded basin three basic facies associations are recognized i conglomerate sandstone facies association csfa ii sandstone argillite facies association safa and iii argillite sandstone facies association asfa the csfa which predominates at the faulted basin margins constitutes 60

numerical and experimental models on the formation mechanism of collapse basins during the green tuff orogenesis of japan the geological model about volcanism of the green tuff geosyncline deduced from the field observations consists of the following processes 1 dome shaped uplift with a mean diameter of 30 km 2 collapse of the central part of the domes forming basins with a mean diameter of 10 km 3 volcanic activity inside the collapse basins it is considered that these consecutive processes resulted from the magmatic uplift from a deep part of the crust

archean wrench fault tectonics and structural evolution of the blake river group abitibi belt quebec structural analysis of the blake river group volcanic rocks in the rouyn noranda region shows the formations to be distributed largely in z shapes resulting from the interference of two early fold systems oriented west northwest east southeast and east west respectively the first of these two fold systems is probably related to the shortening associated with left lateral movement along the two major fractures in the region namely the porcupine destor and larder lake cadillac faults the second system appears to be the result of north south compression perpendicular to the two major fractures the two major faults the first system of early folding the normal and reverse faults and the minor dextral and sinistral strike slip faults that have been observed in the blake river group rocks can all be integrated into one tectonic system that of wrench fault tectonics the orientations of the principal structures recognized in the abitibi belt major shear zones folding and faulting suggest that the d

coastal storm characterization and morphological impacts on sandy coasts the present work deals with storm classification using the storm power index and beach morphological response to storm events in the gulf of cadiz sw spain over the 1958 2001 period 377 events divided into five classes ranging from weak to extreme were characterized classes i weak and ii moderate accounted for 60 and 23 of events respectively class iii significant were 9 of the recorded events and classes iv severe and v extreme accounted for 5 and 2 respectively the probability of storm occurrence per year ranged from 93 for class i to 15 for class v in order to characterize beach response to storm events 214 beach profiles carried out with a monthly periodicity over the 1996 1998 period along the chipiona rota littoral were analysed as well as published data different beach types were observed i intermediate beaches underwent important vertical relief changes ranging from 0 3 m to 1 33 m associated with average slope changes from tan 0 06 to tan 0 03 ii the dissipative beaches were characterized by smaller and homogeneous foreshore vertical changes from c 0 36 m to 0 65 m according to the parallel retreat mechanism characterized by small slope variations from tan 0 025 to tan 0 035 and iii intermediate with rock shore platform experienced small morphological and foreshore slope variations related to both beach pivoting and parallel retreat mechanisms the most important morphological changes were due to the impact of usually weak and moderate events during october and november that produced berm erosion and upper foreshore lowering and the impact of severe significant and extreme events in december and january which produced dune escarpment overwash and or damage to coastal structures copyright 2011 john wiley sons ltd

gold bearing fault zones related to late archean orogenic folding of upper and middle crust in the abitibi granite greenstone belt ontario abstract this work investigates the structures of the abitibi granite greenstone belt ontario with a focus on regional scale folds and on regional scale auriferous fault zones the folds and the fault zones resulted from late archean orogenesis the analysis is based on studies of surface geology and on modelling of the gravity field amphibolite grade orthogneiss was involved in the regional folding that also deformed the overlying greenstones folding resulted in uplift of the orthogneiss that preserves the metamorphic mineral assemblage ferropargasite garnet biotite andesine quartz geothermobarometric calculations indicate recrystallization of a metatonalite sample under peak paleopressures of 7 0 1 2 to 7 9 1 1 kb providing evidence that folding involved crust to depths of at least 18 25 km the regional bouger anomaly map reveals previously unrecognized first order folds interpretation of the bouger anomaly map also confirms that granitic batholiths are hosted by anticlines a wavelet based inversion method was used to determine the locations orientations and continuations at depth of the maxima of density contrasts the maximum density contrasts correspond to steeply dipping geological contacts on the limbs of the open to tight regional scale folds regional scale fault zones only have prominent gravity signatures where they correspond to sheared rocks on the limbs of folds modelled gravity profiles were used to produce profiles that visualize the shapes of batholiths and greenstone bodies within the present day upper crust the granitic batholiths have tabular shapes which are locally folded with preserved main body thicknesses of 1 3 km the greenstones form keels corresponding to synclines some of which reach 5 6 km depth the results of this study confirm that the principal deformational response of the abitibi granite greenstone belt to late archean collisional tectonics was large half wavelength 10 40 km folding of the upper and middle crust our results and interpretations also strongly suggest the regional scale fault zones which are loci for orogenic gold deposits are fold related structures they represent quasi continuous lineaments of shearing and faulting on the limbs of regional folds and locally in the cores of detachment anticlines as shown in a previous paper

stratigraphic setting and timing of the montagne d or deposit a unique rhyacian au rich vms deposit of the guiana shield french guiana abstract in french guiana the montagne d or gold deposit 5 moz at 1 5 g t au is located in the northern branch of the rhyacian paramaca greenstone belt the sulphide deposit is hosted by a south facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative e w striking and steeply south dipping foliation the volcanic sequence is composed of three members 1 the lower unit in the stratigraphic footwall 2 a bimodal mafic felsic formation hosting the orebody and 3 the upper sedimentary and volcanic rocks unit in the stratigraphic hanging wall the bimodal formation is dominated by calc alkaline felsic volcanic rocks in the west interbedded interdigitated with tholeiitic mafic rocks in the east pillowed mafic flows and graded bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment the mineralization consists of thick and laterally extensive sulphide zones forming 1 stratiform sulphide disseminations 2 structurally transposed stringer stockworks and 3 thin layers of deformed semi massive sulphides the gold rich sulphide mineralization consists mainly of pyrite pyrrhotite and chalcopyrite with minor sphalerite magnetite galena and arsenopyrite hosted by chlorite sericite rich alteration zones mainly developed in the felsic tuff facies u pb zircon geochronology shows that most of the montagne d or volcanic and intrusive sequence has crystallized during a multi cycle magmatic event from ca 2152 ma to ca 2130 ma a porphyry intrusion crosscutting the ore yields a u pb zircon age of 2117 6 5 1 ma hence constraining a minimum age for the auriferous sulphide mineralization this also indicates that the sulphide mineralization was coeval with arc magmatism demonstrating the volcanogenic nature of the montagne d or gold deposit

storm graded layers on inner continental shelves examples from southern brazil and the atlantic coast of the central united states abstract size graded layers have been reported from the united states and brazilian atlantic continental shelves amid a bedform association that includes ripples megaripples sand waves and sand ridges graded layers are most apparent in the lag gravels and shell hashes that overlie an older substrate in the troughs between sand ridges but also occur as thinner isolated beds within the sand ridges at least four different models seem to be applicable to graded bed formation the stratigraphic graded model grading occurs within and immediately above the basal lag gravel of the holocene transgressive sand sheet it is a consequence of the generation of the sand sheet by erosional shoreface retreat such graded sequences are formed by landward facies displacement over thousands of years but the process is storm mediated and sequences may contain thinner storm graded layers the storm graded model calls for entrainment of sediment by storm flow and subsequent graded deposition under waning energy in the bedform migration model the migration of megaripples and sand waves may produce thin graded beds at any level within the holocene sand sheet and sand ridge migration can cause graded sequences in the basal part of the holocene sand sheet the bottom liquefaction model relies on storm wave pumping of the seafloor sands with their resultant liquefaction and settling of coarser clasts beds in which sorting is confined to coarse shell material may be of this origin these models are believed to be complementary rather than mutually exclusive

shoreline evolution of the holland coast on a decadal scale the decadal evolution of the dunefoot position along 120 km of the holland coast is analysed firstly a new definition of dunefoot is introduced based on hydrodynamic and morphologic considerations which is not affected by local and instantaneous processes occurring immediately before the bathymetric survey the dunefoot evolution over decadal scales indicates the existence of spatial and temporal oscillations in the shoreline position with magnitudes of 2 3 km length and a periodicity of 4 15 years two main controlling factors of this behaviour are identified 1 influence of sub aqueous bar systems and 2 changes in the storm wave conditions reaching the coast although the precise controlling processes of the relation between the dunefoot and the subaqueous profile still remain unclarified we introduce the concept that the development of a morphological bar cycle requires a fixed amount of time integrated forcing that is proportional to the cumulative effect of storm waves beach mobility along the holland coast on decadal scales 10 20 m is similar or lower than mobility introduced by storms or by seasonal cycles however it is important to consider these changes for the possible implications on the local vulnerability of the coast to extreme events copyright 1999 john wiley sons ltd

4d history of the nimbus vhms ore deposit in the yilgarn craton western australia abstract due to its unique mineralogy in the archaean yilgarn craton the origin of the high grade nimbus ag zn au deposit has been contentious for a number of years recent interpretations of the deposit as a shallow water and low temperature volcanic hosted massive sulphide vhms deposit with epithermal characteristics i e a hybrid bimodal felsic deposit were based on detailed studies of its volcanology mineralogy hydrothermal alteration assemblages geochemistry multiple s isotopes and trace element content of sulphide however this model has been questioned in favour of a late epithermal fault hosted system effective greenfields exploration for similar deposits elsewhere requires a robust deposit model and well understood timing of ore formation we present a comprehensive multi disciplinary study to further constrain the processes involved in the evolution of nimbus and generate a 4d evolutionary model of the system host rock dacite formation is well constrained by shrimp u pb zircon geochronology to c 2703 ma re os ages for the first sulphide phase gives an imprecise maximum age to the ore formation of 2682 110 ma high precision pb isotope variations in ore stage and late galenas track changes in the sulphides over time complemented by new geochronology the pb isotope data indicates that the polymetallic ore precipitation happened at the same time as the volcanism with the second generation indicating minor local remobilisation of pb in late quartz carbonate veins at c 2630 ma 40ar 39ar dating of sericite altered plagioclase from foliated dacite and u pb shrimp dating of syn to post deformation monazites have yielded ages of 2630 ma the late event at c 2630 ma is most likely related to widespread late low ca granite emplacement across the eastern goldfields this study provides arguments that suggest that nimbus is a syn volcanic deposit the ore timing is consistent with the model of replacement type vhms deposit with the age of the main mineralisation similar to the age of the dacitic host rocks at 2703 ma the late event modifies the pre existing ore and overprints the previous ore related alteration ages from the altered plagioclase high precision double spiked pb isotope constraints from late quartz carbonate veins provides an opportunity to vector to hidden deposits

the setting style and role of magmatism in the formation of volcanogenic massive sulfide deposits throughout earth s history all volcanogenic massive sulfide vms hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry petrochemical assemblages indicative of formation at anomalously high temperatures within extensional geodynamic environments in mafic dominated juvenile ophiolitic vms environments there is a preferential association with mafic rocks with boninite and low ti tholeiite mid ocean ridge basalt morb and or back arc basin basalt affinities representing forearc rifting or back arc initiation mid ocean ridges or back arc basin spreading or back arc basins respectively felsic rocks in juvenile oceanic arc environments in archean terrains are high field strength element hfse and rare earth element ree enriched in post archean juvenile oceanic arc terrains felsic rocks are commonly hfse and ree depleted and have boninite like to tholeiitic signatures in vms environments that are associated with continental crust i e continental arc and back arc and dominated by felsic volcanic and or sedimentary rocks evolved environments felsic rocks are the dominant hosts to mineralization and are generally hfse and ree enriched with calc alkalic a type and or peralkalic affinities representing continental arc rifts continental back arcs and continental back arcs to continental rifts respectively coeval mafic rocks in evolved environments have alkalic within plate ocean island basalt like and morb signatures that represent arc to back arc rift versus back arc spreading respectively the high temperature magmatic activity in vms environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments e g mid ocean ridges back arc basins and intra arc rifts underplated basaltic magma provides the heat required to drive hydrothermal circulation extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting the latter leading to the formation of vms associated rhyolites in felsic dominated and bimodal vms environments rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of vms related hydrothermal fluids rifts are also critical in creating environments conducive to preservation of vms mineralization either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement style mineralization in sedimented rifts subvolcanic intrusions are also products of the elevated heat flow regime common to vms forming environments shallow level intrusive complexes i e within 1 3 km of the seafloor may not be the main drivers of vms related hydrothermal circulation but are likely the manifestation of deeper seated mantle derived heat i e 3 10 km depth that drives hydrothermal circulation these shallower intrusive complexes are commonly long lived i e millions of years and reflect a sustained thermally anomalous geodynamic environment such a thermally anomalous environment has the potential to drive significant hydrothermal circulation and therefore multi phase long lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile vms environment the absence of intrusive complexes however does not indicate an area of low potential as they may have been moved or removed due to post vms tectonic activity in some cases shallow level intrusive systems contribute metals to the vms hydrothermal system

u pb geochronology of archean metasedimentary rocks in the pontiac and abitibi subprovinces quebec constraints on timing provenance and regional tectonics abstract u pb isotopic ages of single detrital zircons have been obtained from metasandstones in the northern part of the pontiac subprovince and from the cadillac kewagama and lac caste groups within the southern abitibi subprovince youngest detrital zircon ages from these sequences are 2685 2686 2687 and 2693 ma respectively the lac fourniere pluton which intrudes pontiac group metasedimentary rocks is dated at 2682 1 ma a similar age was previously measured from a pluton that cuts the kewagama group these data bracket deposition of greywacke in the pontiac and abitibi subprovinces to 2685 3 ma in contrast the youngest zircon found in a volcaniclastic unit interbedded with timiskaming group metawacke is 2673 2 ma while the age of a pluton that intrudes the timiskaming is 2672 1 ma thus the timiskaming group is distinctly younger than the other metasedimentary rocks the normalized probability distributions of detrital zircon ages from the pontiac and the abitibi metasedimentary rocks as well as of dated igneous rocks from the southern abitibi subprovince all show that their major zircon populations formed in the age range 2685 2710 ma the distributions for the abitibi metaturbidites and dated igneous rocks are very similar suggesting that metasedimentary rocks in the abitibi belt were mostly derived from the surrounding granite greenstone terrain the largest peak of the pontiac distribution is a few million years younger than that from the abitibi metasedimentary rocks but there is a correlation between major peaks and both groups show similar age ranges for older pre abitibi components 2750 2850 and 3020 3030 ma deposition of the ca 2685 ma sediments was virtually syn deformational based on previous field geochemical and isotopic studies as well as the detrital zircon age data the pontiac group may represent a foreland basin that may have developed from an accretionary prism the source of much of the sediment may have been an uplifted extinct continental arc to the north the arc was mostly eroded into the sediment basin and perhaps tectonically overridden by a southward advancing nappe complex comprised of its back arc basin now partly preserved in the southern volcanic zone of the abitibi subprovince metaturbidites exposed between metavolcanic assemblages within the greenstone belt may represent overturned unconformities at the structural base of the greenstones these were brought up by high angle faults which also localized deposition of non marine timiskaming type sediments it is tentatively suggested that pontiac type metasedimentary rocks extend most of the way beneath the abitibi subprovince the oldest part of the basin emerging as the quetico group in the western superior province

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

mean sea level and beach width variation at scarborough western australia abstract a sixteen year record of beach width change at six profile stations on scarborough beach in the perth metropolitan area of western australia was analysed by eliot and colleagues their results described long term beach progradation measured over the sixteen years and identified cyclic beach changes with periods of 0 5 1 0 3 5 and 7 0 yrs and a long term secular progradational trend in this paper the beach width measurements from scarborough are compared with twelve years of mean sea level record from fremantle western australia approximately 18 km south of scarborough beach the annual cycles of each respond in an inverse manner such that a 1 cm rise in mean sea level corresponds with a 1 m decrease in the beach width the sea level rise leads the beach width retreat by approximately one fifth of a cycle a long period oscillation of 3 5 yrs in the mean sea level shows a similar 100 1 ratio for beach gradation with a lead of approximately one tenth of a cycle however the secular trend in beach width change was not evident in the mean sea level record indicating that the progradation is tied to other processes such as a northerly sediment drift related to prevailing sw swell and associated current activity

storm generated sedimentary structures in subtidal marine facies with examples from the middle and upper ordovician of southwestern virginia abstract the role of storms is of major importance in forming stratification in open shelf facies though storm processes on modern shelves are not fully understood enough is known to see how sediments are influenced storms transport sand away from coastal areas and suspend and transport sand and mud on the open shelf when wave base is lowered storms generate winnowed lag deposits of shells or gravel but coarser sediment and shells of megafauna are little transported except in very near shore environments the martinsburg formation middle and upper ordovician of southwestern virginia was deposited on a storm influenced open marine platform in contrast to the classic turbidite flysch basin of the martinsburg in the great valley of virginia to the northeast deposition of most martinsburg sediments was due to storms sediments deposited during single storm events occur in characteristic fining upward sequences 1 to 80 cm thick in both carbonate and terrigenous clastic dominated areas of the platform individual storm deposits consist of a sharp erosional base overlain by a couplet of whole fossil packstone and laminated calcarenite siltite or quartzose siltstone to very fine sandstone which is gradational to shale packstones are typically intraclastic have shells aligned parallel o bedding and convex up often with adhering or contained mud and have abundant infiltration textures such as cement filled shelter voids packstones grade abruptly to a laminated bed with horizontal plane lamination large and small scale in phase undulatory lamination and wave ripple cross lamination commonly occurring in ordered vertical sequences laminated beds contain escape burrows are weekly graded and have irregularly mounded upper bed surfaces laminated beds grade upward to shale containing horizontal branching burrows and marine fossils the faunal content of the fining upward sequences matches that of the interbedded shale storm generated beds vary greatly in thickness laterally and frequently pinch out completely fining upward sequences formed by scouring winnowing and suspension of the sand and mud during the height of the storm to form the erosional base and autochthonous lag of whole fossils storms preferentially preserve whole fossils rather than fragmenting them infiltration of finer sediment into the lag deposit and deposition of the laminated bed occurred as the storm waned laminated beds are molded into a distinctive suite of sedimentary structures by wave generated currents the shale represents deposition of finest storm suspended material and continued hemipelagic sedimentation similar sequences are widely distributed in the geologic record variability of storm generated sequences can be related to changing water depth thus storm deposits may be useful in basin analysis to estimate relative water depths and trace transgressive and regressive events

petrogenetic and geodynamic origin of the neoarchean dore lake complex abitibi subprovince superior province canada the neoarchean ca 2728 ma anorthosite bearing dore lake complex in the northeastern abitibi subprovince quebec was emplaced into an association of intra oceanic tholeiitic basalts and gabbros known as the obatogamau formation the obatogamau formation constitutes the lower part of the roy group which is composed of two cycles of tholeiitic to calc alkaline volcanic and volcaniclastic rocks siliciclastic and chemical sedimentary rocks and layered mafic to ultramafic sills in this study we report major and trace element results and nd sr pb and o isotope data for anorthosites leucogabbros gabbros and mafic dykes from the dore lake complex and spatially associated basalts and gabbros of the obatogamau formation to assess their petrogenetic origin and geodynamic setting field and petrographic observations indicate that the dore lake complex and associated volcanic rocks underwent extensive metamorphic alteration under greenschist facies conditions resulting in widespread epidotization 20 40 and chloritization 10 40 of many rock types plagioclase recrystallized mainly to anorthite and albite endmembers erasing intermediate compositions metamorphic alteration also led to the mobilization of many elements e g lile and transition metals and to significant disturbance of the rb sr and u pb isotope systems resulting in 1935 150 and 3326 270 ma errorchron ages respectively the sm nd isotope system was less disturbed yielding an errorchron age of 2624 160 ma on many binary major and trace element diagrams the least altered anorthosites and leucogabbros and the gabbros and mafic dykes of the dore lake complex plot in separate fields signifying the presence of two distinct magma types in the complex the gabbros and mafic dykes in the dore lake complex share the geochemical characteristics of tholeiitic basalts and gabbros in the obatogamau formation suggesting a possible genetic link between the two rock associations initial end 2 6 to 5 0 and 18o 6 1 to 7 9 values for the dore lake complex and gabbros of the obatogamau formation end 2 8 to 4 0 18o 7 3 to 8 0 are consistent with depleted mantle sources all rock types in the dore lake complex and the roy group share the trace element characteristics of modern arc magmas suggesting a suprasubduction zone setting for these two lithological associations on the basis of regional geology and geochemical data we suggest that the dore lake complex and the obatogamau formation represent a dismembered fragment of a suture zone like many phanerozoic ophiolites resulting from closure of a back arc basin between 2703 and 2690 ma

constraints on the geodynamic evolution of the southern superior province u pb la icp ms analysis of detrital zircon in successor basins of the archean abitibi and pontiac subprovinces of ontario and quebec canada abstract to investigate the tectonic development of the southern superior province new u pb laser ablation inductively coupled mass spectrometry analysis of detrital zircon was conducted on graywacke samples from successor basins of the abitibi and pontiac subprovinces the three successor basin successions investigated are the 2690 2685 ma porcupine assemblage and the 2679 2669 ma timiskaming assemblage of the abitibi subprovince and the 2682 ma sedimentary rocks of the pontiac subprovince predominately neoarchean zircon grains 80 95 of the total zircon population reflect local sources in the abitibi and pontiac subprovinces the successor basins were deposited within 100 ma of the majority of the detrital zircon grains primary crystallization ages which is consistent with patterns observed at modern convergent margin settings porcupine assemblage samples contain 5 mesoarchean zircon while pontiac subprovince and timiskaming assemblage samples contain 18 and 13 respectively no local mesoarchean sources exist in the abitibi or pontiac subprovinces suggesting input from an adjacent hinterland the higher proportion of mesoarchean zircon in the timiskaming assemblage relative to the porcupine assemblage suggests that detritus from the hinterland was more prevalent during the later stages of collision probably as a result of progressive uplift and denudation of the hinterland the high proportion of mesoarchean zircon in the pontiac subprovince sedimentary rocks may reflect an additional mesoarchean source comparison to previously published geochronology data for the superior province indicates that the hinterland was to the northwest and is in part composed of the winnipeg river marmion and opatica subprovinces patterns of contractional deformation successor basin formation and felsic plutonism progressively young to the south in the southern superior province and are interpreted in terms of accretionary processes detrital transport across subprovince or terrane boundaries progressive hinterland emergence and foreland directed propagation of the deformational front recorded by successor basins is similar to that observed in modern style collisional or accretionary orogens

geological evolution of the manitouwadge greenstone belt and wawa quetico subprovince boundary superior province ontario constrained by u pb zircon dates of supracrustal and plutonic rocks fifty million years of archean evolution is recorded in the manitouwadge greenstone belt and the wawa quetico boundary region from ca 2720 ma volcanism and subvolcanic plutonism associated with m

the evolution of the southern abitibi greenstone belt in light of precise u pb geochronology this paper summarizes u pb zircon ages for the archean southern abitibi greenstone belt and integrates them together with zircon and baddeleyite data for three new samples into a general framework for the evolution of the region new ages are reported for the ghost range gabbroic complex 2713 super 7 sub 5 ma and for a pyroclastic volcanic rock of the gauthier group 2700 or 3 ma a previously determined age of 2701 super 3 sub 2 ma for the felsic volcanic skead group is confirmed by magmatic zircons from a second sample that also contains a xenocrystic component or 2720 ma indicating that the skead volcano was built on top of an older volcanic sequence the compiled ages show that the southern abitibi greenstone belt developed between 2750 and 2670 ma the earliest ages date remnants of volcanic complexes that occur at the periphery of the belt major preorogenic magmatism was confined mainly to the period 2720 to 2700 ma in general each episode was characterized by the essentially coeval formation of komatiitic tholeiitic and calc alkalic igneous rocks taking into consideration the known geologic geochemical and isotopic data this association is consistent with evolution in paired active are and back are systems older crust was absent from the region but it may have interacted with these arcs and rift systems farther to the west the extensional regime was followed by a period of compression that caused folding and thrusting emplacement of calc alkalic plutons and deposition of turbidites between 2700 and 2688 ma the magmatism became predominantly alkalic during the main timiskaming period between 2681 and 2676 ma this event was accompanied by the deposition of alluvial fluvial sequences and was followed by renewed compression that caused polyphase folding and thrusting probably between approximately 2676 and 2670 ma lamprophyre dikes were associated with these final stages of deformation postorogenic activity includes faulting and episodes of hydrothermal activity locally associated with gold mineralization ages in the range 2630 to 2580 ma for hydrothermal minerals e g titanite and rutile camflo suggest a correlation of these events with lower crustal magmatism and metamorphism as recorded for example in the adjacent kapuskasing zone

structural evolution of a gold bearing transtensional zone within the archean porcupine destor deformation zone southern abitibi greenstone belt eastern ontario canada abstract the garrison camp comprises four structurally distinct orogenic gold deposits that formed in different host lithologies during progressive deformation detailed field mapping drill core logging and geochronological constraints suggest that the 2678 2 ma garrison granitic stock played a fundamental rheological role in the location of the four deposits initial local shear movement occurred along the southwestern margin of the stock leading to the development of the nw trending sinistral ne side up buffonta shear zone which hosts the buffonta deposit subsequently a transtensional zone formed between the ne trending sinistral porcupine destor and munro deformation zones which host the 903 and jonpol deposits respectively finally a local change in shortening orientation from ne to nnw caused westerly directed extension resulting in the formation of the younger gold bearing veins composing the garrcon deposit in situ u pb laser ablation inductively coupled plasma mass spectrometry performed on monazite grains formed within the shear fabric of the munro deformation zone indicates that transtension occurred at 2657 15 ma therefore at least three of the four deposits formed subsequent to crystallization of the garrison granitic stock the reported u pb dates represent the first direct age constraints on the movement along a gold bearing deformation zone in the southern abitibi greenstone belt

hillslope runoff and erosion as affected by rolled erosion control systems a field study a replicated field study using rainfall simulation and overland flow application was conducted in central oahu hawaii on a clay dominated oxisol with a 9 slope three main treatment groups were examined a bare treatment a group of four rolled erosion control systems recss with open weave designs and a group of five randomly oriented fibre recss a total of 1122 measurements of runoff and erosion were made to examine treatment differences and to explore temporal patterns in runoff and sediment flux all erosion control systems significantly delayed the time required to generate plot runoff under both simulated rainfall 35 mm h 1 and the more intense trickle flow application 114 mm h 1 once runoff was generated during the rainfall application phase the bare treatment runoff coefficients were significantly lower than those from the two groups of recss as surface seal disruption by rilling is inferred to have enhanced infiltration in the bare treatments during the more intense phase of overland flow application the reverse pattern was observed interrill contributing area roughness was reduced on the bare treatment facilitating increased runoff to well developed rill networks meanwhile the form roughness associated with the recss delayed interrill flow to the poorly organized rills that formed under some of the recss regardless of runoff variations between treatments sediment output was significantly lower from all surfaces covered by recss the median cumulative sediment output from the bare surfaces was 6 9 kg compared with 1 2 kg from the open weave recss and 0 2 kg from the random fibre recss the random fibre systems were particularly effective under the more stressful overland flow application phase with 63 times less sediment eroded than the bare treatments and 12 times less than that from the open weave systems architectural design differences between the two groups of recss are discussed in light of their relation to erosion process dynamics and shear stress partitioning copyright 2006 john wiley sons ltd

host rock and structural controls on the nature and timing of gold mineralization at the holloway mine abitibi subprovince ontario the holloway mine a mesothermal gold deposit is located within the western abitibi subprovince ontario mineralized zones that contain microscopic gold within pyrite are hosted by a sequence of metakomatiites mafic to felsic metavolcanic and metasedimentary rocks there were two mineralization events however the early one was the main event in terms of the amount of gold mineralization this event was associated with albitization silicification chloritization and sericitization in addition to pyritization the later mineralization is associated with sericitization and pyritization carbonate and sericite alterations are associated with both mineralizing events results of u pb zircon age dating of rocks within the sequence constrains the main mineralization event to 2672 ma ore lenses of the holloway deposit are enveloped by 080 striking steeply south dipping zones of intense deformation and fabric development within the porcupine destor deformation zone the shear zones are characterized by a strong foliation and locally an associated extension lineation the ore lenses are interpreted to represent lithons that were formed by boudinage of the more competent mineralized zones which are pervasively albitized analysis of geochemical data demonstrates that the ree th nb hf ti fe and al were largely immobile with respect to the albite quartz chlorite sericite and hematite alterations locally preserved textures such as abundant varioles and spherulites indicate that the host metavolcanics were relatively evolved rocks geochemical data show they have an iron enrichment trend typical of tholeiitic mafic to felsic suites and that they were derived through fractional crystallization of parent basalt because of their high fe mg ratios the rocks reacted with hydrothermal solutions carrying gold presumably as thio complexes to form pyrite which scavenged the gold

basin structure and tertiary magmatism on skye nw scotland the emplacement of igneous material into upper crustal rocks of sedimentary basins is likely to be strongly controlled by the geometry of the pre existing basin structures these controls are investigated using examples from the tertiary igneous complexes of skye part of the sea of hebrides basin of nw scotland the basin consists of an array of half graben related to se dipping normal faults these pre volcanic mesozoic structures are traced near the igneous complexes using geological relationships preserved unconformably beneath the widespread basaltic lava fields the unconformity represents a period of cretaceous uplift and denudation of the basin and its flanks entirely pre dating the tertiary volcanism of nw scotland this unconformity seals stratigraphically the major basin faults preserving field relationships that permit the tracing of these faults in the country rocks to the tertiary intrusions the major camasunary fault is separated from the raasay fault via a series of minor graben linked by a series of steep nw se trending faults that transfered mesozoic displacements between the principal fault strands a broad range of igneous material of various compositions was intruded into part of the mesozoic sea of hebrides basins and their flanks during palaeocene times different emplacement styles and different structural controls are found the major gabbroic centres do not appear to be controlled by upper crustal structures having been emplaced into the footwalls of major faults however minor synmagmatic displacements on the basin faults may have been sufficient to generate dilatational sites in these footwall positions thereby facilitating emplacement in contrast the granitic melts have been emplaced as sheets and domed into the sediments and overlying lava pile reactivating segments of the basin fault network doming occurred from an array of sills the stratigraphic levels of which can be reconstructed using structural relationships preserved in the roofs and walls of the intrusions the sill levels and their transgressive forms are strongly related to inferred mesozoic basin structures the major fold structures of tertiary age in southern skye are interpreted as accommodating granitic emplacement rather than crustal shortening the nw se mesozoic transfer fault trend appears to have strongly influenced the segmentation of the granite domes these interpretations are illustrated using field relationships mapped in the vicinity of the coire uaigneich granophyre it is concluded that although the higher parts of the basin faults were reactivated to facilitate the doming of granitic intrusions the deeper levels of the mesozoic faults show no evidence of substantial reactivation

the role of gravity and magma in the structural evolution of a deformed archean volcanic centre timmins ontario canada a deformed bimodal subaqueous volcanic centre in the western archean abitibi subprovince of the canadian shield contains structures comparable with those of relatively undisturbed igneous complexes similarities include an annular fold pattern initiated by structural doming and downsagging of basaltic flows prior to the terminal felsic volcanism during this cycle an ancestral dome was ruptured by a northeasterly regional graben defined by fossil fault scarps preserved beneath the terminal volcanic deposits fissure vents developed along the northwest boundary of the graben gradually drained the underlying magma chamber and transformed the crest of the dome into a central collapse basin surrounded by an annular anticlinal uplift marking the inner periphery of the former dome basalts on the basinward side of the fissure vents became detached along interflow argillites and glided into the central collapse forming secondary gravity folds within the uppermost basalts subaqueous deposition of felsic debris occurred in the graben and subsiding collapse basin succeeded by postvolcanic turbidites the annular folds were modified by two phases of regional deformation separated by an episode of archean molasse sedimentation along the reactivated south boundary of the paleograben

minor storm impact on the beachface of a sheltered sandy beach abstract during a squall at sorrento western australia winds exceeded 50 km h 1 for 6 5 h and gusted up to 80 km h 1 at the storm peak profiles of adjacent cusp horn and cusp embayment locations were surveyed half hourly for over 40 h spanning onset and passage of the storm in conjunction with measurement of water table fluctuation and swash ranging the sequence of beach changes followed the storm structure although with lag effects related to tide groundwater and swash interaction with the local morphology four phases of beachface adjustment were apparent these were 1 a period of adjustment to rising tide and energy conditions during which the cusp horn was eroded and sediment was deposited in the embayment 2 beachface erosion as storm tide and watertable approached their peak 3 a period of adjustment to declining energy conditions falling tide and watertable levels that began immediately after the storm peak on the cusp horn and at mid ebb tide in the embayment and 4 steady beachface accretion through mid to low tide conditions in the latter part of storm passage beach responses on the cusp horn and embayment hence were dissimilar with net erosion resulting on one and net deposition on the other

time transgressive archean unconformities underlying molasse basin fill successions of dissected oceanic arcs superior province canada abstract late archean diachronous unconformities underlying tectonically controlled coarse clastic successions are located throughout the superior province of canada examples studied in detail include hiatuses at the base of the timmins and kirkland basins in the abitibi greenstone belt and the crowduck and stormy basins in the wabigoon subprovince the timmins molasse basin fill succession overlies a high angle subaerial unconformity separating deepwater turbiditic deposits from fluvial conglomerates a subaerial erosional unconformity defines the contact between mafic flows and overlying felsic volcaniclastic deposits and fluvial conglomerates of the kirkland basin the crowduck and stormy successions are characterized by shallow water and subaerial unconformities between quartz feldspar porphyry stocks and clastic deposits the pronounced characteristics of the molasse basins which include 1 basal unconformities with older sedimentary volcanic or plutonic rocks 2 bounding fault systems 3 ba

stratigraphy and u pb zircon geochronology of kidd creek implications for the formation of giant volcanogenic massive sulphide deposits and the tectonic history of the abitibi greenstone belt within the context of a structural stratigraphic analysis of the giant kidd creek cu zn ag deposit precise u pb zircon ages have been obtained for five critical rock units associated with the deposit massive flow banded footwall rhyolite is dated at 2714 3 1 2 ma slightly younger than a previously published age of 2717 2 ma on nearby rhyolite breccia extrusive rhyolite in the immediate hanging wall to the main ore lenses is dated at 2711 5 1 2 ma leaving an interval of one to several million years for the formation of the deposit we consider the demonstrated longevity of the kidd creek hydrothermal system as a major control on its giant size age constraints together with the size of the deposit suggest a time averaged rate of base metal sulphide deposition of about 10 100 t year peak rates were likely one to possibly two orders of magnitude above time averaged rates hence 100 1000 t year or higher detrital zircon ages on greywackes in the structural footwall to the deposit support structu

u pb zircon geochronology in the southwestern abitibi greenstone belt superior province the abitibi belt is the largest continuous greenstone belt in the superior province of the canadian shield it comprises several composite komatiitic tholeiitic calc alkalic and sedimentary sequences that are folded transected by major faults and intruded by various generations of plutonic rocks precise u pb geochronology has been carried out in the belt for the past decade to solve chronostratigraphic and metallogenetic problems this paper presents new zircon ages and reassesses previously published ones now refined by the addition of abraded and concordant zircon analyses volcanic and subvolcanic units of the timmins area yield the following ages 2727 1 5 ma for a tuff of the upper deloro formation 2703 1 5 ma for a tuff of the upper tisdale formation and 2698 4 ma for the krist fragmental assigned to the top of the tisdale formation the age of a dunite intrusive into the upper deloro formation is revised at 2707 3 ma whereas the aquarius diorite east of timmins yields a poorly define

evolution of 3 1 and 3 0 ga volcanic belts and a new thermotectonic model for the hopedale block north atlantic craton canada a new model for evolution of the archean hopedale block based on mapping and supporting u pb geochronological and geochemical studies is highlighted by i ca 3 25 ga emplacement of igneous precursors of maggo gneiss ii g iii emplacement of the hopedale mafic dykes iv 3 1 ga deposition of hunt river volcanic rocks v ca 3 0 ga deposition of florence lake volcanic rocks vi 2 88 2 96 ga greenschist to amphibolite facies fiordian metamorphism and formation of penetrative northeast striking fiordian structures and vii emplacement of a suite of 2 89 2 83 ga tonalite to granite intrusions which partially overlap and locally postdate fiordian metamorphism and deformation the hunt river and florence lake volcanic sequences are different in age but similar in most other respects the former consists mainly of amphibolite facies mafic metavolcanic rocks and lesser amounts of komatiite flows and metasedimentary and 3105

behaviour of beach profiles during accretion and erosion dominated periods beach profiles have been surveyed at monthly intervals between 1972 and 1988 at moruya on the south coast of new south wales australia four profile sites have been used as a data set to provide an understanding of changes to beach volume width and shape moruya beach represents a moderately high energy microtidal environment which responds in a dramatic way to major storm events such as those experienced in the mid 1970s this study distinguishes between profile characteristics associated with such a period erosion dominated or edp compared with periods when accretion dominated adp accompanied by foredune expansion in both height and width