stage discharge assessment in compound meandering channels discharge measurements for overbank flow were carried out in a two stage meandering channel with various bed slopes sinuosities and water depths the effect of bed slope and sinuosity on discharge was found to be significant a simple design equation for the conveyance capacity based on dimensional analysis is proposed this equation may be used to estimate the stage discharge curve in a meandering channel with overbank flow predictions of discharge using existing methods and the proposed method are compared and tested against the new measured discharge data and other available overbank data the strengths and weaknesses of the various methods are discussed

modeling of the mesoscale structure of coupled upwelling downwelling events and the related input of nutrients to the upper mixed layer in the gulf of finland baltic sea 1 a high resolution numerical study is undertaken to simulate an upwelling event along the northern coast of the gulf of finland 21 29 july 1999 which was documented well by in situ and remote measurements the simulated sequence of sst maps shows a reasonably good resemblance to that of satellite infrared imagery including both mesoscale coherent structures filaments or squirts and the whole process of post upwelling relaxation of the temperature field upwelling along the northern coast of the gulf is accompanied by downwelling along the southern coast so that two longshore baroclinic jets and related fronts are developed simultaneously when the strong westerly winds producing the upwelling downwelling weaken the longshore jets become unstable and produce transverse jets cold warm water squirts using pseudo random simulated fields of temperature and velocity of currents the apparent lateral diffusivity due to squirts is directly estimated at 500 m2 s 1 the model is also applied to estimate nutrient transport simulated phosphate concentration in the surface layer at the cold side of upwelling front is found to be about 0 3 mmol m 3 which is consistent with observations the total content of phosphorus and nitrogen in the upper 10 m layer of the gulf introduced by the upwelling event is estimated to be 387 and 36 tons respectively it follows that the upwelling event transports nutrients into the upper layer with clear excess of phosphorus n p 36 387 0 093 compared to the redfield ratio of 7 2 therefore phosphorus input caused by upwelling during summer most likely promotes nitrogen fixing cyanobacteria blooms

middle to late jurassic tectonic evolution of the klamath mountains california oregon the geochronology stratigraphy and spatial relationships of middle and late jurassic terranes of the klamath mountains strongly suggest that they were formed in a single west facing magmatic arc built upon older accreted terranes a middle jurassic arc complex is represented by the volcanic rocks of the western hayfork terrane and consanguineous dioritic to peridotitic plutons new u pb zircon dates indicate that the middle jurassic plutonic belt was active from 159 to 174 ma and is much more extensive than previously thought this plutonic belt became inactive just as the 157 ma josephine ophiolite which lies west and structurally below the middle jurassic arc was generated late jurassic volcanic and plutonic arc rocks rogue formation and chetco intrusive complex lie outboard and structurally beneath the josephine ophiolite u pb and k ar age data indicate that this arc complex is coeval with the josephine ophiolite both the late jurassic arc complex and the josephine ophiolite are overlain by the galice formation a late jurassic flysch sequence and are intruded by 150 ma dikes and sills the following tectonic model is presented that accounts for the age and distribution of these terranes a middle jurassic arc built on older accreted terranes undergoes rifting at 160 ma resulting in formation of a remnant arc back arc basin island arc triad this system collapsed during the late jurassic nevadan orogeny 150 ma and was strongly deformed and stacked into a series of east dipping thrust sheets arc magmatism was active both before and after the nevadan orogeny but virtually ceased at 140 ma

rocas verdes ophiolites southernmost south america remnants of progressive stages of development of oceanic type crust in a continental margin back arc basin

free surface profiles in river flows can standard energy based gradually varied flow computations be pursued summary is the energy equation for gradually varied flow the best approximation for the free surface profile computations in river flows determination of flood inundation in rivers and natural waterways is based on the hydraulic computation of flow profiles this is usually done using energy based gradually varied flow models like hec ras that adopts a vertical division method for discharge prediction in compound channel sections however this discharge prediction method is not so accurate in the context of advancements over the last three decades this paper firstly presents a study of the impact of discharge prediction on the gradually varied flow computations by comparing thirteen different methods for compound channels where both energy and momentum equations are applied the discharge velocity distribution coefficients specific energy momentum and flow profiles are determined after the study of gradually varied flow predictions a new theory is developed to produce higher order energy and momentum equations for rapidly varied flow in compound channels these generalized equations enable to describe the flow profiles with more generality than the gradually varied flow computations as an outcome results of gradually varied flow provide realistic conclusions for computations of flow in compound channels showing that momentum based models are in general more accurate whereas the new theory developed for rapidly varied flow opens a new research direction so far not investigated in flows through compound channels

flow distribution in compound channels the performances of four of the most commonly used methods for discharge calculation in compound channels of varying roughness were assessed by comparison with laboratory data the four methods are based on splitting the section into main channel and floodplain subdivisions using either horizontal or vertical interfaces the accuracy of the four methods in calculating overall section discharge generally increases at greater floodplain depth and with smoother floodplains however the distribution of flow within the section is generally poorly modelled which leads to very erroneous values for momentum and kinetic energy flux

velocity distribution in compound channel flows by numerical modeling the paper examines the problem of prediction of uniform turbulent flow in a compound channel with the nonlinear k e model this model is capable of predicting the secondary currents caused by the anisotropy of normal turbulent stresses that are important features of the flow in compound channels as they determine the transverse momentum transfer the model is applied to reproduce experimental runs available in the literature the comparison shows that the model predicts with accuracy the distribution of the primary velocity component the secondary circulation and the discharge distribution the numerical results are used to search a subdivision surface between main channel and floodplain on the basis of the flow field and to compare different subdivision surfaces on the basis of the discharge distribution by a simple uniform flow formula the better subdivision surfaces as predicted by the model are the diagonal surface going from the corner between main channel and floodplain to the free surface on

hydrodynamic behavior of partly vegetated open channels the hydrodynamic response of turbulent flow in a compound wide rectangular open channel with a vegetated domain at the channel bank in a channel corner and in a floodplain to the vegetation density and diameter is discussed to this end a phenomenological model was imbedded in an algebraic stress model with the vegetation modeled as an internal resistance that exerts drag force produces energy of turbulence and interferes with its anisotropy and length scale simple suggestions for some modeling problems associated with the presence of wide vegetated domains are used to yield the three dimensional flow vorticity sources relaxation was implemented to smooth periodic behavior and dissipation correction was introduced as a coordinate invariant damping with these the results represent fully developed flow

modeling the pathways and ages of inflowing salt and freshwater in the baltic sea abstract a three dimensional eddy permitting ocean circulation model with implemented bottom boundary layer model and flux corrected transport scheme is used to calculate the pathways and ages of various water masses in the baltic sea the agreement between simulated and observed temperature and salinity profiles of the period 1980 2004 is satisfactory especially the renewal of the deep water in the baltic proper by gravity driven dense bottom flows is better simulated than in previous versions of the model based upon these model results details of the mean circulation are analyzed for instance it is found that after the major baltic inflow in january 2003 saline water passing the slupsk furrow flows directly towards northeast along the eastern slope of the hoburg channel however after the baroclinic summer inflow in august september 2002 the deep water flow spreads along the southwestern slope of the gdansk basin further the model results show that the patterns of mean vertical advective fluxes across the halocline that close the large scale vertical circulation are rather patchy mainly within distinct areas are particles of the saline inflow water advected vertically from the deep water into the surface layer to analyze the time scales of the circulation mean ages of various water masses are calculated it is found that at the sea surface of the bornholm basin gotland basin bothnian sea and bothnian bay the mean ages associated to inflowing water from kattegat amount to 26 30 28 34 34 38 and 38 42 years respectively largest mean sea surface ages of more than 30 years associated to the freshwater of the rivers are found in the central gotland basin and belt sea at the bottom the mean ages are largest in the western gotland basin and amount to more than 36 years in the baltic proper vertical gradients of ages associated to the freshwater inflow are smaller than in the case of inflowing saltwater from kattegat indicating an efficient recirculation of freshwater in the baltic sea

mesozoic cenozoic evolution of the southern patagonian andes fold and thrust belt 47 48 s influence of the rocas verdes basin inversion and onset of patagonian glaciations abstract the southern patagonian andes spa between 47 48 s are characterized by relatively high elevations 1500 4000 m and a 200 km wide largely exhumed basement domain along the backbone of the cordillera bounded by a narrow 30 km wide fold and thrust belt to the east the tectonic evolution of the spa includes widespread jurassic extension during the opening of the austral magallanes basin and the rocas verdes back arc oceanic basin rvb followed by cretaceous to cenozoic shortening although the main phases of deformation that affected this andean segment have been the focus of previous studies its finite geometry and step by step structural and kinematic evolution have not been quantitatively determined in this work we present kinematically restored cross sections showing the variable geometry trough time of the eastern basement domain and the fold and thrust belt a regional westward dipping listric decollement interpreted as formed during the jurassic extensional event was reactivated during the andean deformation constituting the main detachment surface of basement structures and the fold and thrust belt west verging faults systems are considered a consequence of inversion of north south trending extensional features as passive roof high angle west vergent faults using regional data such as field relations unconformities and existing ages to differentiate deformational stages three main phases of contractional deformation are proposed for the area starting with an aptian cenomanian phase related to inversion of the extensional depocenter in inmediate response to the closure of northernmost rvb a second miocene phase responsible for most of the shortening occurred between 18 ma and 10 ma finally the onset of glaciations and glacial erosion might have triggered out of sequence thrusting in the interior of the orogen after 7 ma

the composite floor of the cretaceous back arc basin of south georgia part of an ophiolite sequence and pre jurassic continental basement rocks are remnants of the composite floor of the cretaceous back arc basin system on south georgia the partially preserved ophiolite consists of pillow lavas and breccias inter bedded tuffs basic and silicic dykes and occasional sills it is intruded by a composite gabbro plagiogranite pluton and smaller gabbroic plutons the basement gneisses are intruded by layered gabbros diorites granitic rocks and numerous basic dykes a migmatitic aureole surrounds the plutonic rocks which are fragmented and net veined by remobilized crustal rocks the mafic rocks of the ophiolite sequence and basement complex are geochemically similar and both formed by differentiation of a mantle derived sub alkali tholeiitic magma in a former back arc basin tectonic setting the plagiogranite and silicic dykes and lavas of the ophiolite and some of the silicic rocks within the basement formed by differentiation of the basic magma the remainder of the granitic rocks within the basement are geochemically distinct comprising remobilized basement rocks and a calc alkaline pluton of a remnant magmatic arc the back arc basin formed by emplacement of the tholeiitic magma within pre existing basement rocks up to 80 extension of the continental crust occurred prior to rifting and development of the back arc basin

a new look at the stratigraphy of the yellowknife supergroup at yellowknife n w t implications for the age of gold bearing shear zones and archean basin evolution based on recent detailed mapping a revised stratigraphic column is proposed for the rocks of the archean yellowknife supergroup in the yellowknife greenstone belt the mafic volcanic rocks of the kam formation previously thought to represent the oldest supracrustal rocks of the belt overlap remnants of an earlier volcanic sedimentary sequence here referred to as the octopus formation as its enormous thickness makes it too unwieldy to be described as a single formation the kam formation is raised to group status and subdivided into four formations it is proposed that the kam group should replace the beaulieu group in the yellowknife area the chan formation at the base of the kam group consists of multiple gabbroic intrusions that were emplaced into a carapace of pillowed flows the intrusions locally resemble sheeted mafic dyke complexes in phanerozoic ophiolites thought to represent evidence for sea floor spreading the crestaurum formation which overlies the chan formation is characterized b

a method for improved representation of dense water spreading over topography in geopotential coordinate models abstract a new technique for incorporating processes of near bottom tracer transport over sloping topography in geopotential coordinate ocean circulation models is presented it is based on a hybrid approach coupling a simple terrain following bottom boundary layer model to the standard ocean general circulation model tests in simplified configurations show enhanced downslope spreading of passive and active density tracers the method is helpful for both coarse resolution global climate studies and biogeochemical coastal modeling studies

discharge assessment in compound channel flow a series of laboratory tests were performed to measure the boundary shear stresses in a compound channel consisting of a main channel and associated shallow floodplains four different floodplain roughnesses were used from these results apparent shear stresses across three different assumed main channel floodplain interface planes vertical horizontal and diagonal were calculated the data was used with data from previous studies to derive a statistical relationship between the apparent shear stress on the vertical interface and several easily calculated parameters of the channel geometry and hydraulic characteristics the accuracies of different methods of discharge calculation were shown to be dependent upon the assumptions they make regarding the magnitude of the apparent shear stress on the particular interface chosen an apparent shear stress ratio was proposed which was found to be a useful yardstick in selecting the best method of discharge calculation for particular channel and flow conditions generally it was found that at low floodplain depths using the horizontal or diagonal interfaces gave better discharge results than the vertical

methane fluxes in marine sediments quantified through core analyses and seismo acoustic mapping bornholm basin baltic sea abstract methane is a terminal product of anaerobic degradation of organic matter in subsurface marine sediments depleted of reactive oxidants the depth and age of the sediment where sulfate is depleted determines the extent of methane production relative to the burial of organic carbon we aimed to understand how this methane production is controlled and distributed in an apparently uniform sediment basin we combined seismo acoustic surveys and geochemical analyses of sediment cores to explore the distribution of methane fluxes in brackish marine mud deposits of the bornholm basin southern baltic sea geophysical mapping revealed the depth distribution of a the thickness of the holocene organic rich mud layer overlaying organic poor postglacial clay and b the upper boundary of methane gas bubbles trapped in the holocene sediment by correlating these two parameters with the methane distributions in sediment cores from 44 stations we developed algorithms to estimate and map at high spatial resolution the diffusive methane fluxes in the 75 95 m deep and 4000 km2 large bornholm basin the two approaches termed the fgd free gas depth model and the hml holocene mud layer model yielded similar budgets for the total upwards methane flux through the sediment column in the bornholm basin about 17 ton methane c day 1 complete sulfate depletion at depth and thus onset of methane production required a minimum threshold thickness of the holocene mud layer of 4 m although the bornholm basin has an even depth contour and uniform surface sediments methane production was strongly focused in hotspots where the hml has greatest thickness this heterogeneity could not be predicted from bathymetry or from properties of the surface sediment but was related to the topography of the glacial landscape buried underneath the holocene mud blanket this demonstrates the importance of including seismo acoustic mapping of subsurface stratigraphy for the interpretation and geographic extrapolation of sediment core data for biogeochemical processes such as methane production and methane flux the two approaches which were here combined for the first time may thereby be applied to map methane production also in other coastal and shelf sediments with shallow gas and distinct holocene deposits

sedimentology of archean greenstone belts signatures of tectonic evolution abstract stratigraphic styles in archean greenstone belts are compared to those of modern and phanerozoic depositional basins in order to test the conformity of tectonic style through time six lithological associations in greenstone belts are recognized 1 mafic ultramafic volcanic 2 calc alkaline volcanic 3 bimodal volcanic 4 quartz arenite iron formation or carbonate 5 conglomerate wacke and 6 conglomerate arenite examples of the associations are described from the kaapvaal superior and zimbabwe provinces and the pilbara block each association differs only slightly between the four regions thereby emphasizing a common tectonostratigraphic theme sedimentary rocks are a minor component of the mafic ultramafic volcanic association they were deposited in two types of volcanic basin environments one similar to barred lagoons and bays around oceanic volcanic islands and the other similar to sediment starved platforms adjacent to coalesced volcanoes in inter arc intra arc and back are basins in contrast sedimentary rocks in the calc alkaline volcanic association comprise thick wedges of epiclastic and volcaniclastic detritus deposited in elongate sedimentary basins and thick wedges of pyroclastic and volcaniclastic detritus deposited adjacent to volcanic centers sedimentary facies were identical to those of forearc trench and marine volcanoplutonic arc settings chemogenic lithofacies in both volcanic associations were deposited in shallow to deep marine waters although shallow water profiles were selectively preserved in some terrains sedimentary rocks of the bimodal volcanic association are thick wedges of siliciclastic and volcaniclastic deposits interbedded with subaerial to submarine erupted flows of komatiite basalt and rhyolite depositional environments ranged from braid plain and braid delta to coastal marine and submarine fan starved basin deposits include banded iron formation and sulfidic black shale the association is identical to that of cratonic extensional basins in arc continent and intracontinental rifts sedimentary rocks of the quartz arenite iron formation or carbonate association onlap weathered basement or bimodal volcanic association rocks depositional environments were either transitional from fluvial to siliciclastic and carbonate marginal marine to offshore pelagic hemipelagic or from inshore intrabasinal clastic and volcaniclastic to offshore pelagic hemipelagic siliciclastic deposits are supermature two tectonic sites are represented those with siliciclastic facies represent continent adjacent syn to post rift stable shelves and those dominated by banded iron formation with volcaniclastic deposits represent arc adjacent post rift stable shelves sedimentary rocks of the conglomerate wacke association are represented by thick wedges of siliciclastic or volcaniclastic sandstone with minor volcanic components these were deposited in braid plain braid delta and submarine fan environments within elongate sedimentary basins coastal plain and pelagic basin facies are also present siliciclastic detritus was derived from syndepositional magmatic and metasedimentary thrust belts two stratigraphic styles are preserved one that records a flysch like stage of deep to marginal marine environments and the other that records a molasse like stage of marginal marine to fluvial environments the association is identical to that of compressional foreland basins of arc continent collisional and compressional arc tectonic affinities the conglomerate arenite association is preserved in elongate structural basins that transgress crustal components and all other supracrustal units it is dominated by thick wedges of siliciclastic sandstone although bimodal volcanic and volcaniclastic rocks can also be present depositional environments ranged from talus and alluvial fan and braid plain to either lacustrine or coastal marine local basin margins often show lateral offsets from source terrains and vertically skewed facies patterns longitudinal facies geometries are typical the association is similar to that of strike slip collisional graben in hinterland tectonic escape and terrane accretion orogens the examples show that despite all the ramifications of secular geophysical geothermal and geochemical global change the stratigraphic style of sedimentary rocks in archean greenstone belts can be matched with modern tectonic analogues thereby emphasizing the conformity of stratigraphic style through time the inseparable link between stratigraphic and tectonic styles implies that the tectonic style of greenstone belts was not temporally unique major differences exist with regards to the chemical composition of certain magmatic and sedimentary products but these are compensated for by their constant stratigraphic function in terms of depositional processes depositional environments and tectonic sites

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

water surface profiles in compound channel with multiple critical depths water surface profiles measured in a laboratory compound channel that has rough floodplains and multiple critical depths are compared with computed water surface profiles obtained by numerical solution of the one dimensional equation of gradually varied flow in a form that includes a compound channel froude number manning s in is found to vary with depth in the floodplain and the interaction between the main channel and floodplain is represented as a correction to the main channel resistance coefficient outside the discharge range of multiple critical depths good agreement is demonstrated between measured and computed water surface profiles within the discharge range of multiple critical depths the measured water surface profile near a free overfall cannot be computed as a one dimensional flow because it separates into distinctly different drawdown profiles in the main channel and floodplain a method is proposed for identifying the discharge range within which multiple critical depths exist in order to identify potential problems with interpretation of water surface profiles computed by one dimensional methods in this range

magnetic properties of the bay of islands ophiolite suite and implications for the magnetization of oceanic crust rock magnetic properties opaque mineralogy and degree of metamorphism were determined for 101 unoriented samples from the north arm and blow me down massifs of the bay of islands ophiolite complex newfoundland the weathered and metamorphosed extrusive basalt samples have a weak secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin the initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation the magnetic intensity of the gabbroic samples increases as the degree of alteration increases with the highly altered upper metagabbros having an average intensity of 3 10 3 emu c3 because magnetization of the metagabbro samples is related to nonpervasive variable alteration these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies a compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer roughly 600 m thick with no contribution from a deeper source layer recognizable from these bay of islands data

turbulence modeling of flood plain flows a numerical model capable of predicting flow characteristics in a compound channel is described the model solves the continuity and momentum equations along with the transport equations of kinetic energy of turbulence and the dissipation rate closure is achieved with the aid of algebraic relations for turbulence stresses the model is capable of treating compound channels formed by regular geometrical sections of main channel and flood plain segments the width of the main channel the width of the total section the depth of flow in flood plain the total depth channel slope and boundary roughness of main channel section and flood plain section can all be varied the model predictions of total flow rate shear stress distributions around the wetted perimeter and the percentage of flow and shear force carried by the different sections were compared with published experimental data reasonable agreement between data and predictions was obtained

a two stage model for the formation of the granite greenstone terrains of the kalgoorlie norseman area western australia abstract accurate dating of granites and greenstones from the kalgoorlie norseman area shows that there is considerable overlap in time between the formation of granites and greenstones however within any given area the oldest granites are always younger than the oldest greenstones it is suggested that the long lived 100 ma thermal anomaly in the uppermost asthenosphere that gave rise to the greenstones is also responsible for regional metamorphism and widespread crustal melting leading to the production of granites the time lag between greenstone and granite formation reflects the time taken to conduct heat from the mantle to the lower crust anatexis of the lower crust produces a layer of light granitic magma that may temporarily stop the ascent of basaltic magma where this happens the basaltic magma ponds at the base of the crust supplying additional heat and accelerating the melting process eventually the granitic melt layer becomes unstable and rises within the crust areas intruded by granite become topographic highs with topographic lows forming above areas where light melt has been withdrawn from the lower crust when the topographic highs protrude above sea level they are eroded to shed sediments into the topographic lows which contain the basaltic greenstones thus the change from a basalt dominated lower greenstone succession to a sediment and felsic volcanic dominated upper whitestone sequence seen in many granite greenstone terrains results from the intrusion of granitic magma into the upper crust the crust of the kalgoorlie norseman area formed in two distinct stages separated by a time break of up to 700 ma the first stage involved the formation of primitive crust probably above subduction zones this primitive crust was characterized by low rb sr and high sm nd ratios the second stage resulted from a major change in mantle convection that produced thermal upwellings in the mantle below the continents this led to the eruption of basaltic magmas and to metamorphism and anatexis of the lower crust to produce granitic magmas melting reset the rb sr sm nd and u pb systems giving the impression that the second event which occurred at 2 7 ga was a major crust forming event it was in fact a crustal reworking process although some basalt was added to the crust at this time although the two stage history of the kalgoorlie norseman area is clearly seen in the lead isotopes and in zircons it is not readily discernible from the rb sr and sm nd systematics due to mantle like ratios of those elements in the primitive crust

growth of granite greenstone terranes at convergent margins and stabilization of archean cratons abstract archean granite greenstone terranes represent juvenile continental crust formed in a variety of plate tectonic settings and metamorphosed through a complex series of structural and magmatic events most archean granite greenstone terranes appear to have acquired their first order structural and metamorphic characteristics at convergent plate margins where large accretionary wedges similar in aspect to the chugach makran and altaids grew through offscraping and accretion of oceanic plateaux oceanic crustal fragments juvenile island arcs rifted continental margins and pelagic and terrigenous sediments buoyant slabs of parts of archean oceanic lithosphere may have been underplated beneath these orogens forming thick crustal roots characterized by interleaving between the depleted slabs and undepleted asthenosphere back stepping of the subduction zones after accretion of plateaux and arcs caused the arcs magmatic fronts to migrate trenchward through the accretionary wedges dehydration of the subducting slabs hydrated the mantle wedges below the new arcs and generated magmas sanukitoid suite in the mantle wedge whereas other magmas tonalite trondhjemite granodiorite or ttg suite appear to have been generated by melting of hot young subducted slabs eventual collision of these juvenile orogens with other continental blocks formed anatectic granites then thickened the crust beyond its ability to support its own mass which initiated gravitational collapse and decompressional release of syn to late tectonic granitoids from wedges of fertile mantle trapped between underplated oceanic lithospheric slabs and aided in the cratonization of the granite greenstone terranes deeply penetrating structural discontinuities such as shear zones and sutures provided pathways for fluids and granitoids to migrate into the mid and upper crust forming ore deposits and plutons most preserved granite greenstone terranes have been tectonically stable since the archean and form the cratonic interiors of many continents

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

variations in the degree of crustal extension during formation of a back arc basin abstract ophiolite complexes in southern chile represent the remnants of the mafic portion of the floor of a cretaceous back arc basin which widened markedly from north to south over a length of 600 km detailed field and geochemical studies of ophiolites in the northern sarmiento complex and southern tortuga complex extremities of the originally wedge shaped back arc basin floor indicate significant north south differences in the mode of emplacement of basaltic magmas into the pre existing continental crust during the formation of the basin in the northern narrow extremity of the original basin mafic melts intruded into the continental crust over a diffuse zone causing extensive remobilization and reconstitution of the sialic continental crust in the southern wider part of the original basin mafic magmas appear to have been emplaced at a localized oceanic type spreading centre the observed north south variations resulted in formation of back arc floor with crustal characteristics ranging from intermediate between continental and oceanic to typically oceanic these variations are interpreted as representing different stages of evolution of a back arc basin which formed due to a subtle interplay between subduction induced back arc mantle convection and the release of stress across the convergent plate boundary possibly related to ridge subduction prior to the release of stress heat transferred from mantle diapirs to the base of crust caused widespread silicic volcanism in south america with the release of stress mantle derived melts erupted to the surface along structural pathways resulting in extensive basaltic volcanism in a linear belt behind the island arc and the cessation of silicic volcanism initially basaltic magmas intruded the continental crust over a diffuse region causing reconstitution of sialic crustal rocks progressive localization of the zone of intrusion of mafic magmas from the mantle eventually resulted in the development of an oceanic type spreading centre observations in southern chile and elsewhere suggest that variability in horizontal stress across a convergent plate boundary may be the overriding factor in determining the regional response of continental crust to subduction induced back arc convection and hence the mechanism of emplacement into the crust of mafic mantle melts the various lithologies observed in southern chile could also be expected to form during the opening phase of major ocean basins and to currently underlie atlantic type continental margins

stratigraphic record across a retroarc basin inversion rocas verdes magallanes basin patagonian andes chile the mesozoic evolution of the andean cordillera of southern patagonia is recorded in two formations that are now part of the fold thrust belt the zapata formation and the punta barrosa formation extension in the ultima esperanza region began in the late jurassic with deposition of the marine volcaniclastic tobifera formation and eventually resulted in the full fledged oceanic rocas verdes basin the zapata formation was deposited over a time span of 50 m y in an irregular basin ultimately bordered by an early cretaceous arc to the west it is characterized by interbedded shale and siltstone mostly deposited in shallow water and in areas of oceanic crust emplacement also as deep water hemipelagic deposits sediments of the zapata formation were derived initially from local oceanic upwarps and tobifera highs and later from the ande sitic cover of the juvenile arc and or exhumed oceanic crust the paucity of sandstone in the zapata formation in the ultima esperanza region indicates a highly irregular basin partitioned by prominent horsts with sand deposition confined to sub basins closer to the arc changes in depositional regimes and sediment dispersal patterns related to the onset of andean contraction and formation of the magallanes foreland basin are recorded by sediments of the overlying punta barrosa formation this formation records the evolution of a fold thrust belt on the basis of the multimodal mineralogical and geochemical character of its sandstone and shale the presence of an arc is indicated but nearby andean metamorphic terranes are more significantly represented in punta barrosa sediments stratigraphic details across the zapata and punta barrosa formations indicate that deformation and development of a proto andean cordillera in southern south america was initiated in the late mesozoic and involved conspicuous crustal shortening

petrology geochemistry and tectonic implications of volcanics dredged from the intersection of the yap and mariana trenches abstract rocks dredged from the forearc very close to the intersection of the yap and mariana trenches include a suite of highly depleted arc tholeiites and several samples of transitional to slightly alkaline basalt the tholeiites range from magnesian quartz tholeiites with 0 46 0 6 tio2 to andesites with up to 62 sio2 and 8 2 feo all show pronounced lree depletion and have very low contents of ba and sr they are postulated to have been produced by partial melting of upper mantle peridotite residual after morb extraction following influx of hydrous fluids from the subducted slab while these fluids were responsible for small enrichments in ba k rb and sr in melts generated lree were not involved in the metasomatism and the strong lree depletion probably reflects the unmodified depleted source peridotite the second lava suite includes slightly ne normative ti augite bearing basalts with convex upward ree patterns showing slight lree depletion la sm n 0 76 the chemical features of these basalts support affinities with basalts erupted during the earliest stages of backarc basin opening a k ar age on one sample 7 8 1 3m y is in good agreement with the initial opening of the mariana trough the tectonic significance of the dredged arc tholeiite suite is less obvious a k ar age of10 8 0 4 my on one andesite and the occurrence of similar lavas in dredges from at least 300 km along the length of the yap arc suggest that subduction was occurring beneath the yap arc in the late miocene after overthrusting of the yap greenschist allochthon and while calc alkaline arc magmatism was occurring further north on the west mariana ridge we suggest that the depleted arc tholeiites in dredge 1438 were generated by abnormally shallow melting of upper mantle beneath the yap forearc following subduction beneath this area of young hot sorol trough crust these arc tholeiites represent a magma type transitional between more typical arc tholeiites e g tongan and high mg andesites and boninites

multiple mantle sources during island arc magmatism u pb and hf isotopic evidence from the kohistan arc complex pakistan this paper presents high precision u pb ages and initial hf isotopic compositions of zircon from mafic to felsic rocks of the kohistan arc complex pakistan three magmatic pulses tapping geochemically different reservoirs are distinguished partial melting of mantle with morb type isotopic characteristics generated 99 92 ma old magmas plutonism around 85 ma tapped a more fertile mantle source most likely consisting of a 600 ma old metasomatically enriched mantle or of mantle contaminated by an old sedimentary component 82 ma old felsic peraluminous dykes have morb type isotopic compositions considered to be inherited from remelting earlier magmas in the deep base of the arc the isotopic results demonstrate several and rather rapid changes in melt source region during arc development they also show that there was subordinate continental influence and negligible importance of slab components for the hf budget during the generation of the kohistan arc complex

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

influence of attenuated lithosphere and sediment loading on flexure of the deep water magallanes retroarc foreland basin southern andes flexural subsidence in foreland basins is controlled by applied loads such as topography water sediment and subcrustal forces and the mechanical properties of the lithosphere we investigate the controls on subsidence observed within the upper cretaceous magallanes retroarc foreland basin of southern south america to evaluate the impact of lateral variations in flexural rigidity due to late jurassic extension conventional elastic models cannot explain the observed basin deflection and thick accumulation of deep water cenomanian turonian basin strata however models in which the lithosphere has been previously thinned and deflects under topographic and sedimentary loads successfully reproduce regional subsidence patterns results satisfy paleobathymetric observations in the magallanes basin and suggest that lithospheric thinning is necessary to produce both long wavelength and deep subsidence during late cretaceous basin evolution results indicate that elastic thickness decreases westward from 45 25 km in the distal foreland to 37 15 km beneath the foredeep these findings are consistent with a westward reduction in crustal thickness associated with the jurassic extensional history of the patagonian lithosphere our results also show that sediment loading exerts an important control on regional deflection patterns and promotes a wider region of subsidence and reduced forebulge uplift we propose that lateral variations in mechanical properties and large sediment loads restrict depocenter migration and may cause the foredeep to remain fixed for prolonged periods of time these findings confirm that loading of thinned lithosphere imposes different mechanical controls on the flexural profile and have potential implications for other retroarc foreland basins characterized by earlier extensional histories

evidence for archean ocean opening and closing in the southern slave province archean mafic volcanic and plutonic rocks of the cameron and beaulieu river greenstone belts outcrop in the southern slave structural province of the canadian shield lower portions of the greenstone belts have ophiolitic characteristics but young felsic units may represent superimposed arc magmatism the greenstone belts are separated from older circa 2 7 3 2 ga quartzo feldspathic gneisses of the sleepy dragon complex by a regional decollement zone patterson lake structural complex consisting of deformed mafic volcanic rocks thin slivers of gneiss ultramafic rocks and banded iron formation mixed in a highly deformed phyllonitic and phacoidally cleaved metapelitic matrix high synmetamorphic strains are indicated by abundant intrafolial folds transposed layering rare sheath folds and by the parallelism of elongated primary features and metamorphic mineral lineations the patterson lake structural complex is similar to melanges of phanerozoic mountain belts adjacent quartzo feldspathic gneisses are strongly mylonitized the melange and deeper mylonites formed when the greenstone belts were emplaced as thrust sheets wildflysch shed from tips of emergent thrusts was in part incorporated into the basal melange as the allochthon overrode its own detritus continued compression involved the basement in the deformation uplifting the sleepy dragon complex in a structural culmination mantled by the imbricated greenstone stack late granodioritic to granitic intrusions formed regional thermal aureoles which overprint earlier metamorphic fabrics

flow interaction of meandering river with floodplains a series of laboratory test results are presented concerning the boundary shear stress shear force and discharge characteristics of compound meandering river sections composed of a rectangular main channel and one or two floodplains disposed off to its sides five dimensionless parameters are used to form equations representing the total shear force percentage carried by floodplains a set of smooth and rough sections is studied with an aspect ratio varying from 2 to 5 apparent shear forces on the assumed vertical diagonal and horizontal interface plains are found to be different from zero at low depths of flow and change sign with an increase in depth over the floodplain a variable inclined interface is proposed for which apparent shear force is calculated as zero equations are presented giving proportion of discharge carried by the main channel and floodplain the equations agree well with experimental and river discharge data using the variable inclined interface the error between the measured and calculated discharges for the meandering compound sections is found to be the minimum when compared with that using other interfaces

the open boundary condition in the united kingdom fine resolution antarctic model abstract the united kingdom fine resolution antartic model fram project it a community program to study the southern ocean central to this is an eddy resolving three dimensional primitive equation ocean general circulation model the open boundary condition at the northern boundary is described here the boundary condition is based on that of stevens 1990

simulated halocline variability in the baltic sea and its impact on hypoxia during 1961 2007 1 salinity and halocline depth variations in the baltic sea during 1961 2007 are studied using a three dimensional ocean circulation model significant interannual and interdecadal variations in the halocline depth are found together with distinct periods characterized either by shallow 1970 1975 or deep halocline 1990 1995 the model simulation indicates that the mean top layer salinity in the baltic sea is mainly controlled by the accumulated river runoff while the mean below halocline salinity in the baltic proper which comprises bornholm and gotland basins is more dependent on the low pass filtered zonal wind stress with cutoff period of 4 years henceforth called the mean zonal wind stress the halocline depth and stratification strength in the baltic sea are significantly affected by the mean zonal wind stress while the impact of runoff is smaller the ventilation of the halocline from bottom layers is stronger during the shallow and from surface layers during the deep halocline period due to changes in ventilation variations in halocline depth systematically affect bottom oxygen concentrations on seasonal and decadal but not on interannual time scales for instance a deeper halocline reduces hypoxic oxygen concentration in bottom water below 2 ml l and anoxic anoxic conditions in bottom water areas and increases the bottom oxygen concentrations in the gulf of finland but decreases them in the deeper parts of the baltic proper model results suggest that due to undersampling during 1961 2007 mean hypoxic and anoxic areas calculated from observed profiles are underestimated by 41 and 43 respectively

stratigraphic and provenance variations in the early evolution of the magallanes austral foreland basin implications for the role of longitudinal versus transverse sediment dispersal during arc continent collision resolving the role of longitudinal versus transverse sediment dispersal in ancient sedimentary basins is paramount for understanding filling history and the timing of source area exhumation the southern patagonian andes provide a unique opportunity for constraining these relationships because upper cretaceous shallow and deep marine strata that record the longitudinal filling history of the magallanes austral foreland basin are exposed along a 500 km outcrop belt new stratigraphic sedimentologic and facies analyses of the cenomanian aged lago viedma formation indicate a protracted phase of a dominantly shoreface and foreshore depositional setting at the northern end of the basin austral basin sector whereas 200 km to the south age equivalent strata of the punta barrosa formation are characterized by southward flowing deep water fan systems new sandstone compositional data from both formations are rich in intermediate volcanic grains and suggest an undissected to transitional volcanic arc source however detrital zircon populations from the shallow marine lago viedma formation are dominated by arc sources 126 75 ma whereas deep water strata of the punta barrosa formation contain much greater abundances of jurassic 199 161 ma and pre jurassic 200 ma ages this indicates that deep water fan systems were not linked to a shelfal sediment dispersal system by a simple northward point source model despite consistent southward directed paleocurrents in deep water strata time transgressive provenance variations continue southward along strike where lithostratigraphic equivalents in the ultima esperanza and fuegian sectors of the basin contain a mix of arc and pre jurassic metamorphic basement sources and a paucity of jurassic ages we interpret these along strike provenance variations to be the result of significant local sediment contributions from transverse sources the influence of transverse tributaries during the early history of the magallanes austral foreland basin suggests that the diachronous onset of coarse clastic deposition in the basin was likely due to the progressive delivery and initiation of more locally derived coarse clastic sediment we attribute this to southward progressing thrust belt development associated with progressive north to south collision or suturing of the parautochthonous patagonian arc with attenuated continental crust of south america