the geochemical fingerprints of different tectonomagmatic environments using hygromagmatophile element abundances of tholeiitic basalts and basaltic andesites abstract using hygromagmatophile element abundances normalized to primordial mantle composition it is possible to discriminate between the tectonic settings of tholeiitic basalts and basaltic andesites 47 0 53 5 sio2 based on field and chemical evidence data from provinces or grouped localities have been compiled in order to establish chemical reference data sets for ocean island continental ocean ridge and floor subduction zone and back arc environments the disturbing effects of crustal contamination and hydrothermal alteration on the hygromagmatophile h element patterns are of minor significance in the recognition of plate tectonic settings on the basis of the data sets magmas from a number of ambiguous tectonic settings have been recognized using their h element patterns attention is directed to problems concerning rifting and drifting related basalts in an apparent continental setting and to the origin of ophiolite complexes using available data the pillow lavas of the troodos ophiolite complex cyprus are recognized as basalts erupted in a subduction zone environment

seismic images of the grenville orogen in ontario in 1990 lithoprobe acquired 240 km of seismic reflection data across parts of the central gneiss belt cgb and the central metasedimentary belt cmb within the western grenville province of southern ontario interpretation of these data in conjunction with geological constraints provided by bedrock mapping supports a model of northwest directed thrusting and crustal shortening for the grenville orogen within the cgb the parry sound shear zone is imaged as a 3 km wide zone of reflections dipping southeastward at 20 25 and soling at depths 7 km in the north and 3 km in the south beneath parry sound domain parry sound domain and the immediately adjacent domains are underlain by a gently southeast dipping reflective zone at 4 5 12 0 km depth interpreted as a detachment surface likely associated with the central britt shear zone this zone may have accommodated northwesterly transport of parry sound southern britt and northwestern rosseau domains over britt domain during grenvillian thrusting wit

migration of fluid phases and genesis of basalt magmas in subduction zones dehydration and hydration reactions in both the downgoing lithosphere and the overlying mantle wedge have been examined in order to understand the role of h2o in the production of magmas at convergent plate boundaries the subduction of oceanic lithosphere occurring with increasing pressures and rising temperatures causes liberation of h2o from the slab amphibole which can be stable to the highest pt conditions among hydrous phases in the slab decomposes at around 90 km depth it follows that the subducted lithosphere is essentially anhydrous beneath volcanic arcs lying more than 110 km above the slab and that the supply of slab derived h2o is not a direct trigger for the production of arc magmas instead the h2o released from downgoing lithosphere reacts with the forearc mantle wedge to crystallize hydrous minerals serpentine talc amphibole chlorite and phlogopite this hydrated peridotite is dragged downward on the slab toward higher pt regions and releases h2o to shallower potential magma source regions in the mantle wedge combining experimental data on the stability of serpentine and talc with the thermal structure in the mantle wedge it is concluded that those minerals decompose beneath the forearc region on the other hand high pt experimental and thermodynamic data suggest that dehydration of amphibole and chlorite in the downdragged hydrated peridotite can take place just beneath a volcanic front phlogopite in the peridotite decomposes to release h2o at a deeper level about 200 km h2o liberated from the hydrated peridotite causes partial melting of overlying mantle wedge peridotites along with the migration of h2o through the above processes subduction components especially large ion lithophile elements can be overprinted on the magma source region which governs the geochemical characteristics of arc magmas

bed load grain velocities and sediment transport rates theoretical consideration of the dynamics of bed load sediment transport leads to expressions for bed grain velocity and sediment transport rate as respectively ub a u u c and ib a tan u u c 0 c agreeing in form with many previous analyses the grain velocity equation agrees well with all experimentally determined velocities of single grains moving over fixed rough beds if a is allowed to vary with bed roughness and saltation height values of u c for such overriding grains are substantially less than normally accepted values the sediment transport rate equation predicts plane bed experimental data well over five orders of magnitude of ib values of a tan increase significantly from lower to upper stage plane beds due to an increase in a with suspended sediment concentration but also due to a decrease in tan with increasing transport stage and grain size as predicted by bagnold

volatile control of contrasting trace element distributions in peralkaline granitic and volcanic rocks anomalous enrichments of zr 500 ppm zn 100 ppm nb 25 ppm y 60 ppm th 20 pm u 5 ppm lree 230 ppm and hree 35ppm and high rb sr 5 characterize peralkaline granites in contrast to their peraluminous and calc alkaline equivalents within the peralkaline suite comenditic and pantelleritic volcanics exhibit two to five fold increases in the concentrations of these trace elements over comagmatic granites these cannot be explained by crystal liquid fractionation processes and require the evolution of a sodium enriched fluid corresponding trace element increases in the granites in areas of alkali metasomatism support this argument and reflect the partial confinement of this volatile phase within the high level magma chambers ree studies in particular might eventually allow an evaluation of the role of cl versus f and co3 complexing in the evolution of the volatile fluid

metabasalts axial hot springs and the structure of hydrothermal systems at mid ocean ridges knowledge of the chemical transfer and mineralogical transformations that occur when sea water reacts with basalt at elevated temperatures and pressures can be used along with geological and geophysical data to deduce the typical structure and evolutionary sequence for hydrothermal systems within the oceanic crust along the axis of a mid ocean ridge studies of metabasalt and metadiabase dredged from fault scarps along the axial valley of the mid atlantic ridge reveal consistent relationships among the bulk chemistry of the altered rocks and their secondary mineralogy mineral abundances and mineral compositions especially for chlorite these relationships can be interpreted in terms of the distribution of alteration with respect to time temperature and water rock ratio in young crust assemblages of chl ab ep act chl ab ep act qtz chl ab qtz and chl qtz are produced at successively higher effective sea water to rock ratios within the temperature range of the greenschist facies 250 to 450 c toward higher ratios chlorites tend to become more mg rich pillow basalts of layer 2 are commonly altered under these conditions by sea water on the descending rather than the ascending limb of a convection system this type of alteration which reflects moderately high water rock ratios may characteristically occur above a still partially molten magma chamber as the magma chamber solidifies and is then penetrated more pervasive alteration of the deeper part of layer 2 and of layer 3 occurs at lower water rock ratios producing solutions such as those recovered from springs on the galapagos rift and the east pacific rise at 21 n localized upwelling limbs of the convection system can produce veins filled with quartz sulfides and fe rich chlorite

test of a method to calculate near bank velocity and boundary shear stress detailed knowledge of the flow and boundary shear stress fields near the banks of natural channels is essential for making accurate calculations of rates of near bank sediment transport and geomorphic adjustment this paper presents a high resolution laboratory data set of velocity and boundary shear stress measurements and uses it to test a relatively simple fully predictive numerical method for determining these distributions across the cross section of a straight channel the measurements are made in a flume with a fairly complex cross section that includes a simulated cobble roughened floodplain the method tested is that reported by kean and smith in riparian vegetation and fluvial geomorphology in 2004 which is modified here to include the effects of drag on clasts located in the channel the calculated patterns of velocity and boundary shear stress are shown to be in reasonable agreement with the measurements the principal differences between the measured and calculated fields are the result of secondary circulations which are not included in the calculation better agreement with the structure of the measured streamwise velocity field is obtained by distorting the calculated flow field with the measured secondary flow calculations for a variety of narrower and wider configurations of the original flume geometry are used to show how the width to depth ratio affects the distribution of velocity and boundary shear stress across the channel

precise zircon geochronology in the adirondack lowlands and implications for revising plate tectonic models of the central metasedimentary belt and adirondack mountains grenville province ontario and new york new high precision single grain dating of leucogranites from the adirondack lowlands dated previously by multigrain zircon methods at ca 1416 ma wellesley island and ca 1285 1230 ma hyde sch

listric normal faulting during postorogenic extension revealed by 40ar 39ar thermochronology near the robertson lake shear zone grenville orogen canada the robertson lake shear zone is a major plastic to brittle extensional shear zone in the grenville orogen that bounds the mazinaw and sharbot lake domains and provides information on the style of late extension and the unroofing history of the orogen argon isotope data were collected from hornblende and micas to determine 40ar 39ar ages constrain the temperature time histories of these two domains and infer the unroofing history of the region hornblende cooling ages across the mazinaw domain footwall show little variation indicating uniform unroofing of the footwall since 950 ma phlogopite muscovite and biotite cooling ages of the footwall are 924 to 890 ma the cooling history of the mazinaw domain is characterized by slow cooling after peak metamorphism circa 1000 ma accelerated cooling 4 5 c m y from 950 ma to 890 ma and an average cooling rate of 1 c m y to circa 590 ma when these rocks were at or near the surface the cooling history of sharbot lake hanging wall domain is drastically different than that of the mazinaw domain hornblende and biotite cooling ages in the central portion of the domain are 1009 and 969 ma respectively indicating a cooling rate of 5 c m y after slow cooling from metamorphic temperatures biotite and phlogopite cooling ages determined from samples located at different distances from the shear zone do not lie along the same cooling curve indicating that the cooling history varied across the domain cooling rates in the hanging wall adjacent to the shear zone are low 2 c m y a biotite cooling age 1029 ma and preservation of an amphibole growth age 1205 ma in the hanging wall adjacent to the shear zone reflect shallow crustal levels for this sample since 1205 ma these data indicate that the hanging wall away from the shear zone was unroofed from deeper crustal levels faster and much later than the hanging wall adjacent to the shear zone the varied cooling histories across the region are resolved by listric normal faulting that lead to uniform unroofing of the footwall and differential unroofing across the hanging wall due to rotation during fault displacement

mantle and slab contributions in arc magmas destructive plate margins are major sites of terrestrial magmatism that have long had a key role in models for the generation of continental crust and the development of chemical heterogeneities in the upper mantle in these models it is important to evaluate the nature and size of contributions from preexisting crust in the generation of magmas above subduction zones and to constrain the size of the fluxes of different elements from the subducted crust and the overlying mantle wedge in arc magmas kay 1 980 hawkesworth ellam 1 989 hawkesworth et al 1 99 1 a mcculloch gamble 1 99 1 the more mobile components of the subducted oceanic crust are the products of element fractionation processes in the upper continental crust the ocean basins and hydrothermal systems on the ocean floor they therefore have distinctive isotope and even trace element ratios that in principle should be readily distinguished from those in peridotite in the mantle wedge prior to subduction in practice however element ratios are almost certainly fractionated during shallow level dehydration of sub ducted material and at greater depths where material from the slab appears to contribute in the generation of arc magmas moreover the isotope signal of slab derived material may be heavily diluted by exchange with

the aqueous geochemistry of the rare earth elements and yttrium 4 monazite solubility and ree mobility in exhalative massive sulfide depositing environments abstract although there is considerable evidence that rare earth elements ree and particularly the light ree lree have been mobile in the alteration zones below many massive sulfide deposits there is some disagreement over the cause of this mobility most researchers have argued or implied that the ree were mobilized by analogues of modern seafloor hydrothermal vent fluids however the few measurements that have been made of the ree concentrations of these modern fluids suggest that their ability to mobilize ree is negligible in order to shed further light on this problem we have carried out calculations of monazite solubility monazite is thought to be the principal host for the lree in a model vent fluid at temperatures from 200 to 300 c these calculations show that at 300 c the model fluid will contain 0 08 ppb ce 0 07 ppb la and 0 03 ppb nd at 200 c the concentrations increase to 0 54 ppb 0 37 ppb and 0 15 ppb respectively a decrease in ph of one unit at 300 c also increases ree solubility significantly 7 4 ppb ce 5 7 ppb la and 1 1 ppb nd these solubilities are similar to the concentrations of ree measured in seafloor hydrothermal vent fluids however they are considerably lower than required to account for the scale of ree mobility in alteration zones associated with massive sulfide deposits if the mass ratio of typical hydrothermal vent fluid to rock reached 1000 concentrations of ree in the altered rock the predicted to be in the range

extension in the central metasedimentary belt of the ontario grenville timing and tectonic significance a laterally extensive zone of southeast dipping marble mylonites in the central metasedimentary belt cmb of the southern ontario grenville the bancroft shear zone records southeast directed extension and a displacement of about 10 12 km calcite graphite carbon isotope thermometry indicates that the maximum temperature at which shearing occurred was ca 450 c in contrast carbon isotope fractionations 13 c cc gr within the marble protolith consistently give temperatures of 650 700 c the bancroft shear zone postdates 1060 ma and older high grade shear zones in the central gneiss belt and the cmb that are associated with northwest directed thrusting comparison of the temperature data from the retrograde marble mylonites with cooling curves for the cmb gives a late grenvillian age range of 935 1010 ma for the extensional event the geometric relation between thrusting and normal faulting in the cmb is comparable to that in parts of the himalayas and southern tibet and similarly we interpret late normal faulting in the cmb to be a result of gravitational collapse of a thrust thickened crust in contrast to the himalaya tibet region however accretion in the grenville becomes older in the direction of regional thrusting

geochemical and temporal evolution of cenozoic magmatism in western turkey mantle response to collision slab break off and lithospheric tearing in an orogenic belt post collisional magmatism in western anatolia began in the eocene and has occurred in discrete pulses throughout the cenozoic as it propagated from north to south producing volcano plutonic associations with varying chemical compositions this apparent sw migration of magma tism and accompanying extension through time was a result of the thermally induced collapse of the western anatolian orogenic belt which formed during the collision of the sakarya and tauride anatolide continental blocks in the late paleocene the thermal input and melt sources for this prolonged magmatism were provided first by slab break off generated aesthenospheric flow then by lithospheric delamination related aesthenospheric flow followed by tectonic extension driven upward aesthenospheric flow the first magmatic episode is represented by eocene granitoid plutons and their extrusive carapace that are linearly distributed along the izmir ankara suture zone south of the marmara sea these suites show moderately evolved com positions enriched in incompatible elements similar to subduction zone influenced subalkaline magmas widespread oligo miocene volcanic and plutonic rocks with medium to high k calc alkaline compositions represent the next magmatic episode partial melting and assimilation fractional crystallization of enriched subcontinental lithospheric mantle derived magmas were important processes in the genesis and evolution of the parental magmas which experienced decreasing subduction influence and increasing crustal contamination during the evolution of the eocene and oligo miocene volcano plutonic rocks collision induced lithospheric slab break off provided an influx of aesthenospheric heat and melts that resulted in partial melting of the previously subduction metasomatized mantle lithosphere beneath the suture zone producing the eocene and oligo miocene igneous suites the following magmatic phase during the middle miocene 16 14 ma developed mildly alkaline bimodal volcanic rocks that show a decreasing amount of crustal contamination and subduction influence in time both melting of a subduc tion modified lithospheric mantle and aesthenospheric mantle derived melt contribution played a significant role in the generation of the magmas of these rocks this magmatic episode was attended by region wide extension that led to the formation of metamorphic core complexes and graben systems aesthenospheric upwelling caused by partial delamination of the lithospheric root beneath the western anatolian orogenic belt was likely responsible for the melt evolution of these mildly alkaline volcanics lithospheric delamination may have been caused by peeling off during slab rollback the last major phase of magmatism in the region starting c 12 ma is represented by late miocene to quaternary alkaline to super alkaline volcanic rocks that show oib like geochemical features with progressively more potassic compositions increasing toward south in time these rocks are spatially associated with major extensional fault systems that acted as natural conduits for the transport of uncontaminated alkaline magmas to the surface the melt source for this magmatic phase carried little or no subduction component and was pro duced by the decompressional melting of aesthenospheric mantle which flowed in beneath the atte nuated continental lithosphere in the aegean extensional province this time progressive evolution of cenozoic magmatism and extension in western anatolia has been strongly controlled by the interplay between regional plate tectonic events and the mantle dynamics and provides a realistic template for post collisional magmatism and crustal extension in many orogenic belts

suturing and extensional reactivation in the grenville orogen canada sutures are zones of weakness within orogenic belts that have the potential to become reactivated during orogenic evolution the robertson lake shear zone marks a major tectonic boundary in the southeastern grenville orogen of canada that has been intermittently active for at least 130 m y the shear zone played a major role in the compressional stage of the orogenic cycle as well as during postorogenic collapse the zone separates the elzevir terrane to the west and the frontenac terrane to the east sphene ages u pb indicate that these two terranes have distinct tectonothermal histories and that the shear zone represents a cryptic suture in its current state the shear zone is a low angle 30 ese dip plastic to brittle extensional shear zone that separates the mazinaw footwall and sharbot lake hanging wall domains integration of structural metamorphic and chronologic data leads to a model that describes the complete evolution of this fundamental tectonic boundary that evolved from an early compressional zone ca 1030 ma to a late extensional zone until at least 900 ma

the geon 14 arc related mafic rocks from the central grenville province the late paleoproterozoic to mesoproterozoic ca 1 7 1 2 ga evolution of the active southeastern margin of laurentia terminated with the grenvillian continental collision and the development of a large hot long duration orogen at ca 1 09 0 98 ga as a result much of the hinterland of the grenville province consists of paleoproterozoic and mesoproterozoic rocks mostly preserved as an imbricate stack of high grade gneisses that represent a potential repository of active margin processes this study presents geochronologic geochemical and isotopic analyses of two granulite facies suites of ca 1 45 1 40 ga mafic tholeiites from the canyon domain manicouagan area central grenville province one suite consists of 1439 76 68 ma high feti mafic sills with end values of 0 4 tdm 2 57 2 72 ga indicate derivation from variably depleted to enriched morb type mantle sources probably in an extensional back arc setting before intrusion in a ca 1 5 ga supracrustal metasedimentary sequence the other

mobile bed friction at high shear stress analysis demonstrates and experiments confirm that the frictional behavior of mobile beds at high shear stress is inherently different from either of the two classical cases smooth wall and rough wall for those two cases the characteristic lengths for friction are based on viscosity and grain size respectively for the new mobile bed friction relation this length varies with the thickness of the shear layer occupied by the moving bed load particles this thickness is itself directly related to shear stress giving rise to the prediction that at high shear stress shields ordinate greater than unity the effective roughness ratio effective roughness particle diameter should be approximately five times the shields ordinate the high shear stress experimental results show a variation in accord with the prediction

an 1161 ma suture in the frontenac terrane ontario segment of the grenville orogen in the central metasedimentary belt of the grenville orogen we recognize two contrasting packages of rocks within what traditionally has been interpreted as a continuous intact stratigraphic sequence metamorphosed under upper amphibolite facies to granulite facies conditions the two packages are separated by a thrust fault the hanging wall of which was transported northwestward relative to rocks of the footwall upper greenschist to lower amphibolite grade marbles make up the footwall whereas the allochthon contains granulites metamorphosed prior to deposition of an unconformably overlying quartzite and intrusion of a compositionally diverse suite of 1179 1162 ma plutons emplacement of the pluton saturated allochthon occurred at 1161 ma and metamorphosed platformal carbonates into the marbles of the footwall we interpret this thrust as part of a fundamental suture within the grenville orogen

crustal assimilation in the burnt lake metavolcanics grenville province southeastern ontario and its tectonic significance three intimately interbedded suites of volcanic rocks are identified geochemically in the burnt lake area of the belmont domain in the central metasedimentary belt and their petrogenesis is evaluated the burnt lake back arc tholeiitic suite comprises basalts similar in trace element signature to tholeiitic basalts emplaced in back arc basins formed in continental crust the burnt lake continental tholeiitic suite comprises basalts and andesites similar in trace element composition to continental tholeiitic sequences the burnt lake felsic pyroclastic suite comprises rhyolitic pyroclastics having major and trace element compositions that suggest that they were derived from crustal melts rare earth element models suggest that the burnt lake back arc tholeiitic rocks were formed by fractional crystallization of mafic magmas derived by approximately 5 partial melting of an amphibole bearing depleted mantle enriched in light rare earth elements by a subduction component the modelling also suggests that t

chapter 10 mid miocene volcanic and plutonic rocks in the lake mead area of nevada and arizona production of intermediate igneous rocks in an extensional environment

the petrogenesis of mafic minor intrusions and volcanics of the central metasedimentary belt grenville province canada morb and oib sources abstract numerous separate suites containing mafic igneous rocks each characterized by its own trace element signature have been identified and described in the western part of the elzevir terrane of the central metasedimentary belt of the grenville province in canada the average compositions of the mafic rocks from the tudor and turriff volcanics and the low zirconium lzs intermediate zirconium izs high zirconium hzs calc alkaline cas highly fractionated tholeiite hft and ultra potassic uks suites of minor intrusions all show negative nb and ti anomalies on chondrite normalized multi element plots this series of rock suites with their characteristic anomalies have been interpreted as being emplaced in a marginal basin formed on attenuated continental crust similarities in multi element plots and the results of petrogenetic calculations suggest that the turriff lavas lzs izs and tudor lavas and hzs suites were all formed from melts derived from the same spinel lherzolite source the composition of this source is considered to be similar to that from which mid ocean ridge basalts are derived modified by crustal contamination the hft cas and uks rocks were formed from melts derived from various garnet lherzolite sources these sources may be modelled as having a trace element composition similar to that from which ocean island basalts are derived modified to different extents by subduction derived components

neural network prediction of alluvial stream bedforms abstractsubstantial laboratory field and theoretical studies have been carried out by many to understand alluvial stream bedform origin their shapes equilibrium with the flow and their deposit

the queensborough mafic ultramafic complex a fragment of a meso proterozoic ophiolite grenville province canada abstract the queensborough mafic ultramafic complex occurs as a fault bounded block up to 10 km wide and having an area 220 km2 it lies in the grimsthorpe domain of the bancroft elzevir mazinaw sharbot lake terrane in the central metasedimentary belt of the grenville province it has been suggested without adequate supporting data that the complex may represent oceanic crust a fragment of an ophiolite or even a metavolcanic sequence made up of basaltic and komatiitic flows the geological and tectonic significance of the complex is assessed using field relationships petrography and geochemistry structurally the lowest part of the complex comprises a series of ultramafic rocks characterized by metre scale compositional layering represented by several different metamorphic assemblages of talc chlorite carbonate anthophyllite and actinolite tremolite these assemblages indicate that the original rocks were cumulate peridotites and pyroxenites the ultramafic rocks are overlain structurally by a series of mafic rocks predominantly massive to highly sheared gabbros the gabbros are penetrated by a series of mafic dykes and include a few small enclaves of pillowed mafic volcanics major and trace element chemistry shows that the mafic rocks represent a fractionally crystallized sequence of tholeiitic gabbros lavas and mafic dykes and that the ultramafic cumulates are co genetic the regional geological setting and the trace element signatures of the mafic rocks suggest that they were formed in a back arc basin comparison of the queensborough complex with proterozoic and phanerozoic igneous complexes suggests that it represents a partially preserved crustal section of a mesoproterozoic ophiolite in addition the rocks of the queensborough complex are petrographically and geochemically similar to those of the vavilov basin which occurs in the deepest part of the tyrrhenian sea by analogy with this neogene back arc basin we suggest that the central metasedimentary belt which contains the queensborough complex formed by attenuation of the continental crust the complex is preserved along a suture and is interpreted as having formed during the collision of a continental island arc with the continental margin of laurentia the characteristics and preservation of the queensborough mafic ultramafic complex are very similar to those of many phanerozoic ophiolites and suggest that mesoproterozoic thermotectonic processes are also similar to those presently operating

proterozoic subduction and terrane amalgamation in the southwestern grenville province canada evidence from ultrapotassic to shoshonitic plutonism a late grenvillian 1089 1076 ma subduction regime followed by terrane amalgamation is postulated as the paleoenvironment of a 400 km long belt of potassium rich alkaline and shoshonitic plutons in the central metasedimentary belt of the southwestern grenville province canada emplacement of the plutons postdates the regional metamorphism in the country rock but predates major shear zones that form a structural boundary for the plutonic belt the extent timing and magmatic affinities of the suite delineate the gatineau domain within the current mont laurier terrane of quebec and are compelling evidence for the allochthonous nature of the elzevir terrane and its extension eastward to rideau lake in ontario and northward into the gatineau domain the belt trends northeast the emplacement ages are younger to the southeast and the magmatic affinities are those of island arc ultrapotassic to shoshonitic rocks this is interpreted to reflect the existence of a southeast dipping northeast trending subduction zone beneath the combined elzevir gatineau terrane between 1089 and 1076 ma subsequent to subduction amalgamation of the elzevir terrane to the other terranes formed the central metasedimentary belt which then accreted and collided with the allochthonous polycyclic belt these events provide evidence that the ottawan orogeny commenced at ca 1090 ma in the central metasedimentary belt a modern analogue of this plutonism and its tectonic setting may have been the magmatism and arc continent collision and subduction setting of the sunda are indonesia

the spatial distribution of coarse surface grains and the stability of gravel river beds previous studies of surface particle structures in gravel bed rivers in particular coarse grain clusters conclude that these bedforms increase bed stability and reduce sediment transport rates however few studies have quantitatively analysed the effect of the surface distribution of coarse grains in isolation or arranged into distinct bedforms on particle entrainment focussing on descriptions of bedform formation and mechanical behaviour a novel image analysis technique was employed that allowed recognition of coarse grains and calculation of particle cluster areas under laboratory conditions increasing discharges were applied to a unimodal sand gravel bed the size class containing the d90 size was painted in ultraviolet paint image analysis software was used to identify this size class on digital images of the bed surface taken under ultraviolet light both the total surface area occupied by ultraviolet grains and the area of accumulations of connected grains were related to the threshold shear stress for entrainment as discharge magnitude increased coarse grains actively grouped together forming fewer larger accumulations of coarse particles lower values of critical bed shear stress occurred for beds with higher degrees of clustering beds are more stable when coarse grains are distributed more evenly over the bed surface this implies that using bed surface composition as a descriptor of bed resistance to entrainment may need to be complemented by a descriptor of the spatial distribution of the coarsest grains

multiprofile discharge estimation in the tidal reach of yangtze estuary abstractwith the advent of acoustic doppler current profiler adcp the velocity profile method or index velocity method based on a single profile or a fixed depth cell has been recommended for estimating discharge in tidal reaches however in large tidal reaches with a width of nearly 6 km and cross sectional variability of flow such as yangtze estuary these methods are not accurate enough for the discharge estimation therefore an improved method named the multiprofile method is proposed in this paper the method includes four main steps 1 calculating the cross sectional area a with stage data by considering the transverse slope 2 calculating the depth mean velocity u at each fixed adcp 3 establishing the u u model with the multiprofile us and estimating the cross sectional mean velocity u 4 estimating the final discharge through u multiplied by a the proposed method was tested at the xuliujing section of the yangtze estuary the result shows that the multiprofile method averagely imp

cordierite gedrite rocks from the central metasedimentary belt boundary thrust zone grenville province ontario mesoproterozoic metavolcanic rocks with affinities to the composite arc belt cordierite gedrite rocks in the southern grenville province occur near the base of the central metasedimentary belt boundary thrust zone interpreted by some as a crustal suture between the 1 29 1 24 ga composite arc belt and 1 4 ga rocks of laurentia major and trace element compositions of these rocks are consistent with volcanic protoliths that range in composition from basalt to dacite these cordierite gedrite rocks have low cao average 1 2 wt and major element and oxygen isotope ratios suggestive of hydrothermal alteration before metamorphism rare earth element ree compositions also indicate igneous protoliths although some ree patterns have been modified by local melt extraction the trace element compositions of cordierite gedrite rocks and neodymium isotope systematics are similar to those of metavolcanic rocks in the composite arc belt and are consistent with the extension of the composite arc belt to the base of the boundary thrust zone

archean metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 2 mobility of trace elements and petrogenetic constraints qualitative evaluation of altered mafic pillows from the rouyn noranda district of the abitibi metavolcanic belt reveals that for low grade metamorphism the high field strength elements hfs zr y ti and the rare earth elements ree are immobile however where alteration is extreme the ree elements are leached and redeposited by carbonate rich and k rich metasomatic fluids whilst zr y and zr ti remain unchanged rubidium ba and to a lesser extent sr are mobile at all levels of alteration however provided certain filters are applied the original geochemical values of the lavas for the alkaline elements the hfs elements and the ree can be defined the geochemical variations thus identified for the volcanic series of the rouyn noranda district are ascribed to a combination of contamination and fractional crystallization of a primitive tholeiitic magma

boundary shear in smooth and rough channels a series of flume experiments are reported in which the walls and bed were differentially roughened normal depth flow set and measurements made of the boundary shear stress distribution an empirically derived equation is presented giving the percentage of the shear force carried by the walls as a function of the breadth depth ratio and the ratio between the nikuradse equivalent roughness sizes for the bed and the walls the results are compared with other available data for the smooth channel case and some disagreements noted the systematic reduction in the shear force carried by the walls with increasing breadth depth ratio and bed roughness is illustrated further equations are presented giving the mean wall and bed shear stress variation with apsect ratio and roughness parameters although the experimental data is somewhat limited the equations are novel and thought to indicate the general behavior of such open channel flows with some success

sharbot lake terrane and its relationships to frontenac terrane central metasedimentary belt grenville province new insights from u pb geochronology the sharbot lake terrane of the central metasedimentary belt in ontario comprises marbles minor tholeiitic basalts and siliciclastic rocks metamorphosed at low to moderate degrees and is intruded by several suites of mafic to felsic plutons gabbroic and associated monzogranitic phases of the lavant complex in northwestern parts of the terrane yield ages of 1224 2 ma for zircon and monazite and 1221 1211 ma for titanite the wolf grove structure a gneissic domain in the northeastern part of the area was migmatized and intruded by granites at 1168 ma prior to its tectonic juxtaposition on amphibolites and marbles of the sharbot lake terrane correlative events recorded by gneiss quartzite and marble from carleton place farther east stress the strong affinity of the wolf grove structure with rocks of the frontenac terrane the 1156 2 ma posttectonic maberly stock intrudes rocks near the boundary zone between the frontenac and sharbot lake terranes suggesting that the two terranes were linked by

the central metasedimentary belt grenville province as a failed back arc rift zone nd isotope evidence abstract nd isotope data are presented for granitoid orthogneisses from the central metasedimentary belt cmb of the grenville province in order to map the extent of juvenile grenvillian age crust within this orogenic belt that is composed mostly of older crustal terranes the data reveal a 150 km wide belt of juvenile crust in ontario but this belt contains a block of pre grenvillian crust containing the elzevir pluton which yields an estimated crustal formation age of 1 5 ga the recognition of an older block within the cmb has profound implications for its structure and tectonic evolution because it implies that juvenile grenvillian crust apparently forming a wide ne sw belt is in fact distributed in two narrower segments with approximately n s strike we suggest that the cmb comprises an en echelon series of ensimatic rift segments created by back arc spreading behind a continental margin arc these rift segments extend southwards in the subsurface into the northeastern unites states the rift segments contain abundant marble outcrops consistent with marine incursion into the rift zone and these deposits also continue northwards into a marble domain of the cmb in quebec however crustal formation ages in the latter domain are largely pre grenvillian implying that the quebec rift segment was ensialic hence we interpret the cmb in ontario and quebec as the northern termination of a failed back arc rift zone

model for calculating bed load transport of sediment a bed load transport model based on the mechanics of sediment moving by saltation yields predicted values of bed load flux as a function of boundary shear stress grain diameter and density the parameters required to calculate bed load transport particle velocity bed load sediment concentration and the height of the bed load layer can all be determined from our model which computes sequences of trajectories of individual saltating grains as well as the concentration of moving grains that the flow can support the latter is related to the momentum the accelerating grains extract from the flow predicted curves of bed load transport vs boundary shear stress agree well with transport data collected by gilbert meyer peter iet al n and the waterways experimental station measured shear stress was corrected for pressure drag when bed forms were present comparison of predicted bed load transport with common bed load equations reveals considerable similarity among the relationships the best agreement with the data is produced by relationships in which the transport rate vanishes as the shear stress approaches the critical shields number as in our model and yalin s equation

the geochemical nature of the igneous rocks of the sharbot lake domain central metasedimentary belt ontario two bimodal mafic silicic suites of igneous rocks the sharbot lake volcanic rocks and the lavant igneous complex are identified geochemically in the sharbot lake domain of the central metasedimentary belt in ontario and their genesis and thermotectonic environment are evaluated the sharbot lake volcanic rocks comprise a series of basalts characterized by light rare earth element lree depletion and relatively high concentrations of fe2o3 tio2 mno v and y together with rhyolites and silicic pyroclastic rocks they are intruded by rocks of the lavant igneous complex which comprises tholeiitic gabbros characterized by lree enrichment and low concentrations of fe2o3 tio2 mno v and y and granitoid rocks the trace element signatures of the mafic rocks of the sharbot lake volcanic sequences are most like those of back arc tholeiitic basalts and those of the lavant igneous complex are comparable to those of low k tholeiitic basalt suites the trace element signatures of the silicic rocks ass

archean mafic metavolcanics from the rouyn noranda district abitibi greenstone belt quebec 1 mobility of the major elements reply in a suite of archean mafic pillows from the rouyn noranda region of quebec s abitibi greenstone belt including both tholeiitic and calc alkaline varieties spanning the prehnite pumpellyite to upper greenschist metamorphic facies three types of alteration can be defined i chlorite epidote actinolite ii chlorite epidote and iii chlorite sericite the number of mineral phases decreases as a result of progressive hydration from type i to type iii alteration albitization resulting from substitution of in calcic plagioclase is highly variable in type i alteration but in types ii and iii the plagioclase is totally albitized and in some cases silicified chloritization is closely linked to increasing hydration and ca leaching with mgo and feo substituting for cao in ferromagnesian minerals calcium was mobilized and carried by solutions as evidenced by the variable concentration of epidote at the margins of pillows this calcium leaching generated an excess of al2o3 with respect to the combine

kinematical and rheological evolution of a crustal scale ductile thrust zone central metasedimentary belt grenville orogen ontario reply the central metasedimentary belt boundary thrust zone is a 10 km thick 200 km long stack of crystalline thrust sheets enclosed by an anastomosing network of ductile thrust zones formed at mid

the geochemistry and tectonic significance of pre metamorphic minor intrusions of the central metasedimentary belt grenville province canada abstract more than 250 samples collected from dykes and sills intruded into the grenville supergroup have been analysed by xrf techniques for their major and trace element contents the ree contents of 43 of the samples have been determined by inaa using these data the rocks have been identified and placed in seven suites each characterized by its own trace element signature there are four tholeiitic suites the low zirconium suite which comprises a bimodal series of basalts and minor dacites the intermediate zirconium suite which is made up of basalts andesites dacites and rhyolites the high zirconium suite consisting of high iron basalts and rare highly fractionated tholeiites which comprise basalts characterized by high mg number high ni and cr contents and with strongly fractionated trace element patterns in addition a calc alkaline suite made up of basalts and andesites a transitional suite of andesites and trachyandesites and an ultra potassic suite of leucitites have been identified on chondrite normalized multi element plots all of the suites show negative nb and ti anomalies similar ranges of rock types with similar anomalies occur within volcanic arcs and back arc basins formed at collisional plate margins where the nb and ti anomalies are interpreted as subduction signatures and also in some continental flood basalt sequences in which the anomalies are commonly suggested to result from crustal contamination the geology of the central metasedimentary belt leads us to favour an interpretation in which the minor intrusions were emplaced in supracrustal rocks deposited upon attenuated continental crust in a back arc basin during a collisional orogeny

comparisons of sidewall correction of bed shear stress in open channel flows when investigating sediment transport in laboratory open channel flows it is often necessary to remove sidewall effects for computing effective bed shear stress previous sidewall correction methods are subject to some assumptions that have not been completely verified and different values of the bed shear stress may be obtained depending on the approach used in making sidewall corrections this study provides a quantitative assessment of the existing correction procedures by comparing them to a new sidewall correction model proposed in this study the latter was derived based on the shear stress function and equivalent roughness size for both rigid and mobile bed conditions which were obtained directly from experimental measurements the comparisons show that the einstein correction formula and the vanoni and brooks method generally predict relatively lower and higher bed shear stresses respectively while the williams empirical function leads to more scatter this study also demonstrates that the widely used vanoni and brooks approach can be well approximated by a simple formula derived based on the blasius resistance function the sidewall effects when removed in the different ways would consequently affect the presentation of the bedload function experimental results of bedload transport when plotted as the dimensionless transport rate against the dimensionless shear stress with the latter being corrected using the present model exhibit less scatter than those associated with the previous procedures

discharge estimation from h adcp measurements in a tidal river subject to sidewall effects and a mobile bed horizontal acoustic doppler current profilers h adcps can be employed to estimate river discharge based on water level measurements and flow velocity array data across a river transect a new method is presented that accounts for the dip in velocity near the water surface which is caused by sidewall effects that decrease with the width to depth ratio of a channel a boundary layer model is introduced to convert single depth velocity data from the h adcp to specific discharge the parameters of the model include the local roughness length and a dip correction factor which accounts for the sidewall effects a regression model is employed to translate specific discharge to total discharge the method was tested in the river mahakam representing a large river of complex bathymetry where part of the flow is intrinsically three dimensional and discharge rates exceed 8000 m3 s 1 results from five moving boat adcp campaigns covering separate semidiurnal tidal cycles are presented three of which are used for calibration purposes whereas the remaining two served for validation of the method the dip correction factor showed a significant correlation with distance to the wall and bears a strong relation to secondary currents the sidewall effects appeared to remain relatively constant throughout the tidal cycles under study bed roughness length is estimated at periods of maximum velocity showing more variation at subtidal than at intratidal time scales intratidal variations were particularly obvious during bidirectional flow conditions which occurred only during conditions of low river discharge the new method was shown to outperform the widely used index velocity method by systematically reducing the relative error in the discharge estimates

deep structure beneath lake ontario crustal scale grenville subdivisions lake ontario marine seismic data reveal major grenville crustal subdivisions beneath central and southern lake ontario separated by interpreted shear zones that extend to the lower crust a shear zone bounded transition between the elzevir and frontenac terranes exposed north of lake ontario is linked to a seismically defined shear zone beneath central lake ontario by prominent aeromagnetic and gravity anomalies easterly dipping wide angle reflections and fractures in paleozoic strata we suggest the central lake ontario zone represents crustal scale deformation along an elzevir frontenac boundary zone that extends from outcrop to the south shore of lake ontario seismic images from lake ontario and the exposed western central metasedimentary belt are dominated by crustal scale shear zones and reflection geometries featuring arcuate reflections truncated at their bases by apparent east dipping linear reflections the images show that zones analogous to the interpreted grenville front tectonic zone are al