relative sea level change along the slave craton coastline characteristics of archean continental rifting abstract the 2 8 ga siliciclastic dominated craton cover succession with subordinate mafic volcanic rocks at beniah lake in the slave craton has been informally referred to as the bell lake group the beniah lake succession up to 1 km thick is composed of 7 120 m thick coarsening upward cu sequences arranged with the following lithofacies architecture 1a argillite sandstone 1b mafic volcanic lithofacies 2 sandstone argillite 3a quartz arenite and 3b conglomerate lithofacies a pan slave unconformity indicating an autochthonous 2 8 to 4 013 ga basement cover relationship is present and locally well exposed the lithofacies and their arrangement are consistent with a tide influenced coastal setting whereby the change from argillite sandstone to quartz arenite lithofacies represents an initial estuary system defining transgression with a maximum flooding surface evolving into a fan delta defining progradation with a maximum regressive surface the mafic volcaniclastic lithofacies and associated pillowed flow units suggesting drowning of the siliciclastic succession coincide with a change from rift to drift tectonics as crustal attenuation facilitated magma ascent the slave wide unconformities and lithofacies contacts permit a sequence stratigraphic approach with the major slave basement quartz arenite unconformity suggestive of a 1st order sea level change coinciding with the proposed super continent break up or rifting the consistent stacking of cu sequences with capping subaqueous volcaniclastic volcanic units are considered the expression of 2nd order sea level cycles probably caused by changes of spreading rates at oceanic ridges the cu sequences and their thicknesses constitute 3rd order sea level changes and reflect the immediate response to crustal thinning time constraints for all these orders remain elusive but the hierarchy is consistent with sequence stratigraphic events the observed relative sea level change is attributed primarily to tectono eustasy where mantle dynamics caused rifting basin subsidence and mafic volcanism the latter occurred as the crust was sufficiently attenuated

amethyst bearing lava flows in the parana basin rio grande do sul brazil cooling vesiculation and formation of the geodic cavities size distribution data obtained from detailed field study of bubbles and amethyst geodes in the basaltic lava flows of the serra geral formation ametista do sul rio grande do sul brazil are used in cooling and vesiculation models to infer the origin and the formation processes of the geodic cavities coupled field observations and modelling results emphasize that 1 the formation of geodes in the studied lava flow can be explained qualitatively and quantitatively by the exsolution of magmatic gas from the supersaturated melt with no need for external surface water supply 2 the vertically elongated habits of the geodes result from higher cooling rate of the magma in contact with the accumulating bubbles and 3 the abnormal metre sized geodes with their branching habits result not only from the diffusive decompressive bubble growth but also from the coalescence of inwards progressing tubular cavities

relation between soil age and silicate weathering rates determined from the chemical evolution of a glacial chronosequence long term weathering rates rlt were determined from base cation depletion in soil profiles developed on six granitic glacial moraines varying in age from 0 4 to 297 ka in the wind river mountains wyoming weathering rates were found to decrease with soil age t according to the power law equation rlt 15 t 0 71 where rlt is in meq m 2 yr 1 and t is in ka comparable data from the literature are consistent with this function and it is similar to power law equations describing changes in laboratory weathering rates with time on the basis of our study we predict that for a catchment unaffected by anthropogenic inputs and in a steady state with respect to the organic and cation exchange pools rlt should be higher than present day weathering rates derived from stream fluxes rpd by a factor of about 3 4

petrology of serra geral parana continental flood basalts southern brazil crustal contamination source material and south atlantic magmatism the serra geral parana continental flood basalt sg cfb province in brazil is associated with the jurassic cretaceous breakup of gondwanaland and the transition of continental to oceanic magmatism during the opening of the south atlantic ocean a suite of 24 samples representative of the sg cfb in rio grande do sul southern brazil shows a compositional continuum from basalt 50 53 wt sio2 mg 60 45 to basaltic andesite to andesite rhyodacite and rhyolite 73 wt sio2 certain compositional aspects of the mafic rocks e g tio2 k2o cao zr nb zr y ti zr resemble those of basaltic dikes and flows associated with the opening of the north atlantic ocean

proterozoic continental volcanism in the belcher islands implications for the evolution of the circum ungava fold belt the belcher islands of eastern hudson bay expose a continuous sequence of early proterozoic volcanics and continental and shallow marine sedimentary rocks the volcanic rocks comprise two sequences of continental basalts the older eskimo formation and the younger flaherty formation the flows of both formations are composed of tholeiitic basalts mgo 9 wt which in each formation are divided into two groups based on the concentrations of high field strength elements both groups of eskimo flows have fractionated rare earth element ree patterns with negative nb anomalies relative to eskimo flows the flaherty flows have flatter ree profiles and higher nb contents the chemical variations observed in the eskimo flows are consistent with an assimilation fractional crystallization process involving a lower continental crust contaminant the major and most trace element trends of the flaherty flows are attributed to gabbroic crystal fractionation of two parental liquids which are interpreted to

the genesis of mid ocean ridge basalt the tholeiitic volcanics erupted at mid ocean ridges mid ocean ridge basalts or morb constitute the dominant volcanic lithology on earth analyses of tachylites from atlantic pacific and indian ocean spreading centres range widely in 100 mg mg fe2 ratios m and m varies from 70 to 30 glasses with m 55 65 are the most common variants and only a small percentage of glass analyses has m approaching 70 the latter defines the m value of basaltic melts in equilibrium with residual upper mantle source peridotites with m 88 the frequency histogram of the m values of average compositions of morb glasses at 88 ocean floor localities is similar in analysis distribution to the frequency histograms depicting variation in the m values of glasses from the various spreading centres m values and nickel contents of morb and the nature and compositions of the near liquidus phases crystallized experimentally from morb melts at elevated pressures have been applied to identify primary unfractionated melts erupted in a mid ocean ridge environment however ni abundances and high pressure phase relationships are not necessarily unique or definitive parameters of primary melts the latter are generally linked genetically with mg rich lherzolitic source rocks of pyrolite type m 90 the spectrum of m values displayed by morb glasses with a definite bias towards relatively fe rich compositions average m of approximately 600 morb glasses is 58 6 suggests that the melts may have evolved either via ferromagnesian fractionation of relatively mg rich parental melts m 70 80 or by partial melting of a heterogeneous upper mantle with variable m values or as a result of magma mixing of already fractionated melts and primitive magma batches for a number of reasons fractonation models based on the extraction of olivine or one or more of olivine plagioclase and clinopyroxene either from picritic melts m 75 or primitive basaltic melts with m 70 are questionable as prime controls of morb chemistry these include 1 the extreme rarity of quenched picritic or mg basaltic melts in ocean ridge environments 2 the lack of adequate evidence of the appropriate of necessity voluminous complementary cumulates dunites allivalites troctolites anorthosites demanded by olivine plagioclase or olivine plagioclase fractionation models and 3 the aberrent frequencies of glass m values whereby the assumed derivatives m 55 65 are much more abundant and presumably much more voluminous than the alleged parents or transitional derivatives 65 m 75 the nature of the trends of na2o cao and al2o3 in galapagos spreading centre tachylites of extended composition m 65 30 indicates the gabbroic fractionation is also unlikely to exert important controls on morb chemistry as their m values increase mid ocean ridge basalts increase in al ca ni co cr and decrease in ti mn na k and p except for al and ca these trends are similar to those displayed by upper mantle peridotites increasing in m i e becoming more refractory following one or more partial melting episodes it is suggested that at least a majority of mid ocean ridge basalts is intrinsically primary and generated by variable degrees of partial melting of heterogeneous lherzolitic upper mantle 80 m 90 with variable abundances of elements such as ti al ca and na and also depleted in large ion lithophile lil elements negative europium anomalies in the rare earth patterns of some oceanridge basalts ferrobasalts with low m are ascribed mainly to the persistence of residual plagioclase in relatively fe rich plagioclase lherzolite source rocks following low degrees of partial melting the partial melting events leading to the generation of mid ocean ridge basalts took place over a relatively modes pressure range approximately 8 15 kb which encompassed the transition of plagioclase lherzolite to spinel lherzolite this proposal appears consistent with the nature and occurrence of megacrysts xenocrysts of tschermakitic cr diopside ca43mg52fe5 olivine mg 89 91 plagioclase an92 85 and spinel fe2al60cr38 in some morb the megacryst compositions suggest that these phases represent disaggregated plagioclase peridotite or spinel lherzolite acquired by melts during their passage through the oceanic upper mantle

hierarchical patterns of physical biological associations in river ecosystems abstract the interplay of biological and physical patterns and processes within river ecosystems generates a complex matrix of interactions a challenge in interdisciplinary river science is to dissect patterns and processes in multi causal river ecosystems into hierarchical levels of organization hierarchy theory and the associated concept of scale provides a sound framework for achieving this we present two interdisciplinary case studies that demonstrate how a multi scale approach can dissect hierarchies of organization in river ecosystems the first case study examined patterns of large wood character and distribution at three scales of a hierarchy of morphological river system organization in the large lowland river murray the character and distribution of large wood was uniform at the largest reach scale 95 km length of river because stream energy conditions are relatively uniform within the reach however there was an association between lower level functional sets straight or bend sections of river and functional units 12 quadrats within each functional set and the character and distribution of large wood because stream energy differs between straight and bend morphologies and the inner and outer channel functional units thus functional sets and functional units are important levels of organization for large wood in the river murray the second case study examined the associations between macroinvertebrate assemblage distribution and environmental influences across a hierarchy of river system organization in the upland murrumbidgee river catchment we previously demonstrated that macroinvertebrate assemblages were arranged hierarchically at the region cluster within region reach within cluster and riffle within reach scales with region and reach being the strongest signatures in this study we related different scaled environmental factors collected across a hierarchy of catchment zone valley confinement reach similar stream orders and riffle scales to the region and cluster levels of macroinvertebrate distribution the hierarchical pattern of large region level and local reach level macroinvertebrate distribution was matched by a large catchment scale and local reach scale of environmental influence intermediate zone scale environmental factors and smaller riffle scale factors were not important influences thus large regions and catchments and local reaches are important levels of organization for macroinvertebrate environment associations in rivers of the upper murrumbidgee catchment both case studies support the applicability of hierarchy theory to describe the organization of physical biological associations in river ecosystems the multi scaled approach allowed the detection of levels of hierarchical organization and showed other hierarchical characteristics such as emergent properties and top down constraint bottom up influence hierarchical understanding of river ecosystem organization will enhance river conservation and management because it facilitates a holistic ecosystem perspective rather than a partial single scale single component or single discipline perspective

problems of scale in the modeling and interpretation of coastal dunes abstract coastal dune systems are studied at time scales from seconds to millennia and space scales from millimeters to kilometers present approaches to the study of coastal dunes make it difficult to integrate models and interpretations of these systems over these scale ranges and arrive at reasonable conclusions it is argued that identification of key controls on dune development measurement of those controls and synthesis of data describing past and present conditions and used as calibration points will improve the viability of coastal dune models theoretical and empirical advances are necessary to improve the reliability of predictions across a range of geomorphological scales attempts at linking theoretical systematic models process synoptic measurement and historical or paleoenvironmental synthetic approaches make explicit the recognition that at time scales of more than a few hours and space scales greater than a few hundred meters deterministic models become unstable vis a vis prototype environments process climatologies provide one means to link process based work with broader scaled analysis as scales increase such climatologies will become less appropriate as the data become less reliable or as the systems change or as the scales become too large relative to the process record lengths in these conditions specific data i e samples representing points in time and space become check points for calibrating models it should be possible ideally to integrate both up and down time and space scales this is not yet possible

geochemical and scintillometric characterization and correlation of amethyst geode bearing parana lavas from the quarai and los catalanes districts brazil and uruguay geochemical studies of the six lowermost lava flows of the cretaceous serra geral formation parana volcanic province in quarai brazil and artigas uruguay were combined with flow by flow field studies of structures and scintillometric profiles to establish a consistent regional stratigraphic framework over at least 100 km this greatly improves exploration capability for amethyst and agate geodes a basalt colada mata olho alegrete facies serra geral formation was the first lava to flow over the ancient botucatu desert in the region but an andesite colada catalan overstepped this basalt in many places perhaps palaeohighs four basaltic andesites complete the lava stratigraphy in this formation adding up to 300 m of lavas the stratigraphic sequence of contrasting lava compositions is 51 0 wt sio 2 in the first lava followed by 57 5 52 5 56 0 53 0 and finally 54 5 wt sio 2 overall mgo variation is between 2 and 7 wt all lavas in the two districts are low ti 2 of the gramado type the characteristic contents of most major and trace elements 124 rock samples analysed allow the ready identification of each lava contrasting rock chemistry also results in strong variation in scintillometric values 270 points measured in the field and nineteen continuous borehole profiles from bottom to top of the stratigraphy the cps values are 49 3 2 123 10 3 62 4 7 94 4 6 45 and 85 colada catalan has the structure of aa lava particularly the contorted igneous banding and autobreccias in the upper and lower crusts in some places a 2 m thick silicified sandstone layer lies on top of some coladas and silicified sandstone forms breccias with volcanic rocks geochemistry of the six lavas indicates complex evolution involving melting of lithospheric mantle injection into the crust and assimilation of crust followed by fractional crystallization this study indicates the possibility of world class deposits of amethyst geodes on the brazilian side of the border with uruguay

biogeomorphology and landscape evolution the problem of scale abstract vegetation may vary continuously and rapidly while landforms sometimes vary episodically and relatively slowly this disparity in temporal scales creates scale linkage problems in dealing with landform vegetation interactions four theoretical approaches for coping with these issues are outlined and illustrated via applications to problems arising from fieldwork on the coastal plain of north carolina the first approach the transient form ratio is used to determine whether ecosystems and geomorphic environments preserved in pleistocene stratigraphy represent stable landform ecosystem combinations which should reflect landform and vegetation responses to sea level rise the second the information criterion is applied to estimate the appropriate time steps for simulation modelling and appropriate spatial resolutions for field studies of vegetation effects on soil thickness in coastal plain uplands the abstracted systems argument the third approach is used to show that alluvial sedimentation and floodplain ecological dynamics cannot be considered independently in studies of floodplain system response to post european settlement finally ratios of relaxation times and durations suggest that changes in upland erosion regimes associated with historical devegetation are best treated as a singular perturbation in the context of quaternary landscape evolution

scale issues in weathering studies a review of the major scale issues in weathering studies reveals concerns over the fundamental spatio temporal distributions of weathering phenomena as well as issues of upscaling microscope based observations and linking different scales of observations in explanations of landform development various strategies are proposed which can be used to tackle these issues many rooted in non linear dynamical systems ideas as an initial step spatio temporal scale distributions are estimated here for weathering processes landforms and controls based on a range of empirical data two case studies of phytokarst in grand cayman and blistering and scaling of building stones are presented to illustrate the types of data that might be used to establish more convincing scale linkages in weathering investigations

rhyolites in the emeishan large igneous province sw china with implications for plume related felsic magmatism abstract in the emeishan large igneous province elip western yangtze block sw china minor amounts of silicic volcanic rocks 5 are spatially and temporally associated with flood basalts the distribution and origin of these silicic rocks are keys to understanding the processes associated with mantle plume activities in the binchuan and panzhihua areas southwestern elip there are nb ta poor and nb ta rich rhyolites nb ta poor rhyolites interlayered with basalts in the binchuan area occur in the lower part of the emeishan volcanic sequence and have a crustal origin they are characterized by negative nb ta anomalies low end t and high 87sr 86sr i values and zircon saturation temperatures 836 852 c nb ta rich rhyolites are associated with the main phase of the emeishan volcanic sequence in the binchuan and panzhihua areas and are characterized by positive nb ta anomalies oceanic island basalt oib like trace element ratios low 87sr 86sr i ratios positive end t and ehf t values and high a cnk ratios and fe s in addition they have high ga al ratios high field strength elements hfses and high zircon saturation temperatures 920 c typical of aluminous a type silicic rocks similar to the spatially distributed syenitic intrusions of the elip these nb ta rich rhyolites are best interpreted as hybrid products of crystal fractionation of high ti basaltic magmas coupled with minor crustal assimilation 6 14 on the basis of rhyolite melts and ec afc simulations the temporal and spatial distributions of these two types of rhyolite reflect various extents of thermal and mass exchange between mantle derived basaltic magma and crustal material above a mantle plume when the plume head reached the base of the western yangtze block enriched components in the lithospheric mantle were melted and the melts partially ponded near the crust mantle boundary or in the lower crust where they induced partial melting of crustal materials to form nb ta poor rhyolites during the main phase of volcanism large magma chambers and extensive plumbing systems developed due to decompressional melting of the mantle plume in this stage abundant mafic ultramafic and felsic intrusions were formed and nb ta rich rhyolites and a type granites were emplaced

epigenetic formation of amethyst bearing geodes from los catalanes gemological district artigas uruguay southern parana magmatic province abstract giant geodes up to 4 m long in the massive central portions of altered basalt lavas from the parana magmatic province southern brazil and uruguay form a world class source of amethyst and agate although the origin of the cavities has been ascribed to degassing of the lava at 1150 c field evidence is conclusive that the giant amethyst agate filled geodes were formed by hydrothermal processes at low temperatures we propose an epigenetic and hydrothermal model for the origin of giant geodes this model includes hydrothermal brecciation during an early brittle stage and the late formation of the cavities geodes in the brittle stage an overpressured aqueous fluid affected the basalt in a p t field delimited by temperatures between 100 and 150 c and vapor pressures between 1 2 and 5 5 bar the fluids were capable of lifting the roof and fracturing the host rock along new subhorizontal and subvertical fractures and breccias in the massive lava the formation of these structures occurred at shallow depths unit by unit to open the cavities dissolution of the now altered basalt to clay minerals is necessary the process is closely linked to the highest alteration grade of mineralized lavas in los catalanes gemological district dissolution processes are observed in micrometer scale in the studied basalts the primary mineralogy consisting of labradorite andesine augite pigeonite mesostasis k rich was altered during the interaction of large volumes of hot aqueous fluid with the rock the alteration of pigeonite and its replacement by smectite is observed around the cavities followed by the precipitation of amorphous silica and microcrystalline quartz in clay rich sites associated zeolites heulandite clinoptilolite fill the newly formed cavities in progressive stages of hydrothermal alteration our data indicate that the temperatures were less than 200 c and probably less than 150 c cavity formation occurred after alteration of the basalt to more than 60 vol clay minerals we thus suggest that cavities related to geode formation are of epigenetic origin

amethyst geodes in the basaltic flow from triz quarry at ametista do sul rio grande do sul brazil magmatic source of silica for the amethyst crystallizations the amethyst geodes observed in the tholeiitic basaltic flow from the triz quarry at ametista do sul rio grande do sul brazil show particular wall layering infillings with from the outside inwards celadonite chalcedony fine grained quartz and large sized amethyst crystals the primary fluid inclusions analysed in the amethyst crystals yield a 152 to 238 c crystallization temperature range the amethyst geodes are always located in the massive fracture free basaltic part of the lava flows and surrounded by a limited wall lining alteration halo the thickness of which depends on the geode radius the geochemical balances calculated from fresh to altered basalt in the geode environment indicate that the amount of sio 2 released from the alteration halo is always sufficient to produce the siliceous rims in the geodes without requirement for extraneous silica supply the results point to a volcanic origin for the amethyst geode infillings through basalt autoalteration by authigenic high temperature hydrothermal fluids these fluids can originate from 1 unmixing of volatile coumpounds from melt through pressure release 2 cooling to supercritical hydrous fluids with autoalteration of the surrounding basalt and 3 migration of the residual hot fluids from the basalt to the geodic cavities through the pressure gradient between the geodic cavity and the rock

gis based landslide susceptibility mapping using analytical hierarchy process and bivariate statistics in ardesen turkey comparisons of results and confirmations abstract the ardesen area is prone to landslides because of the climate conditions geologic and geomorphologic characteristics of the region as in previous years in 2001 due to heavy rainfall there were many landslides resulting in damage and human casualties there is still a great danger of further landslides in the region therefore it is vitally important to prepare a landslide susceptibility map of the region in this study the analytical hierarchy process ahp the statistical index wi and weighting factor wf methods were used to produce and later compare three susceptibility maps for this purpose thematic layers including landslide inventory lithology weathering slope aspect land cover distance to stream drainage density and distance to road were used in this study area 98 of landslides occurred in highly or completely weathered units lithology weathering land cover and slope data layers were found to be important factors in the study area to confirm the practicality of the three susceptibility maps were compared with a landslide activity map containing 16 active landslide zones the outcome was that the active landslide zones do not completely fit into the high and very high susceptibility classes but 81 3 of these landslide zones fall into the high and very high susceptibility zones of the ahp method while this is 62 5 in the case of wi method and 68 8 with the wf method in spite of the results obtained in this study the development of a susceptibility map is usually determined by the needs and available resources the results showed that the ahp method gave a more realistic picture of the actual distribution of landslide susceptibility than the wi and wf methods

textural evidence for high grade ignimbrites formed by low explosivity eruptions parana magmatic province southern brazil abstract the parana etendeka province is a lower cretaceous huge bimodal tholeiitic volcanic province 1 million km 3 that predated the gondwana breakup its silicic portion makes up a total volume of at least 20 000 km 3 and in southern brazil it comprises the chapeco porphyritic high ti trachydacites dacites and the palmas microporphyritic aphyric low ti dacites rhyolites the widespread silicic sheets are debated in the literature because they bear similarities between lavas and high grade ignimbrites here we provide new observations and interpretations for flow units with large dark and vesicle poor lens shaped blobs surrounded by a light colored matrix the textural features macro to micro scale of these blobs are different from typical pumice and or fiamme and support a low explosivity pyroclastic origin possibly low column fountain eruptions with discharge rates high enough to produce laterally extensive high grade ignimbrites such an interpretation combined with a conspicuous absence of lithic fragments in the deposits is aligned with a lack of identified calderas in the parana etendeka province maximum timescales of crystallization associated with the juvenile blobs and estimated from csd slopes are on the order of millennia for phenocryst populations and on the order of decades for microphenocryst populations

geomorphic coupling and sediment connectivity in an alpine catchment exploring sediment cascades using graph theory through their relevance for sediment budgets and the sensitivity of geomorphic systems geomorphic coupling and sediment connectivity represent important topics in geomorphology since the introduction of the systems perspective to physical geography by chorley and kennedy 1971 a catchment has been perceived as consisting of landscape elements e g landforms subcatchments that are coupled by geomorphic processes through sediment transport in this study we present a novel application of mathematical graph theory to explore the network structure of coarse sediment pathways in a central alpine catchment numerical simulation models for rockfall debris flows and hillslope and channel fluvial processes are used to establish a spatially explicit graph model of sediment sources pathways and sinks the raster cells of a digital elevation model form the nodes of this graph and simulated sediment trajectories represent the corresponding edges model results are validated by visual comparison with the field situation and aerial photos the interaction of sediment pathways i e where the deposits of a geomorphic process form the sources of another process forms sediment cascades represented by paths a succession of edges in the graph model we show how this graph can be used to explore upslope contributing area and downslope source to sink functional connectivity by analysing its nodes edges and paths the analysis of the spatial distribution composition and frequency of sediment cascades yields information on the relative importance of geomorphic processes and their interaction however regardless of their transport capacity in the study area the analysis stresses the importance of mass movements and their interaction e g the linkage of large rockfall source areas to debris flows that potentially enter the channel network moreover it is shown that only a small percentage of the study area is coupled to the channel network which itself is longitudinally disconnected by natural and anthropogenic barriers besides the case study we discuss the methodological framework and alternatives for node and edge representations of graph models in geomorphology we conclude that graph theory provides an excellent methodological framework for the analysis of geomorphic systems especially for the exploration of quantitative approaches towards sediment connectivity

a theoretical model coupling chemical weathering rates with denudation rates uplift of the himalayas has been proposed to have locally accelerated chemical weathering thus leading to enhanced co2 sequestration and global cooling this hypothesis assumes that rapid erosion exposes fresh highly reactive minerals at earth s surface empirical studies quantifying the relationship between erosion and weathering have produced apparently conflicting results where the nature of the relationship is dependent on the weathering regime of the sampled landscapes we derive a quantitative model that defines this relationship across the range of weathering regimes from supply limited to kinetically limited conditions the model matches trends in field data collected by others and reconciles apparently conflicting results the model also demonstrates that as erosion rates increase potential increases in weathering rate from the exposure of fresher materials are offset by the decrease in the total volume of minerals exposed due to thinner regolith we conclude that the relationship between weathering and erosion is one of diminishing returns in which increases in erosion rate lead to progressively smaller increases in weathering rate indeed at the highest erosion rates weathering rates may decline the ability therefore of accelerated uplift and erosion to stimulate greater co2 sequestration may be significant in landscapes eroding at rates of 10 102 t km 2 yr 1 however where erosion rates are greater than 102 t km 2 yr 1 increases in denudation may not be matched by increases in chemical weathering finally our results suggest that watersheds with regolith thicknesses of 0 5 m will yield the greatest solute fluxes

the soil production function a brief history and its rediscovery abstract in 1877 g k gilbert reasoned that the rate at which bedrock is converted to soil reaches a maximum under an optimal soil depth that facilitates contact between bedrock and water such that freeze thaw and chemical weathering are maximised in doing so he outlined the functional dependence of soil production bedrock weathering on local soil depth however the concept of a soil production function does not appear to have been utilised until well into the following century when carson and kirkby carson m a kirkby m j 1972 hillslope form and process cambridge university press cambridge 475 pp expressed it as a notional relationship they also noted that at depths less than optimum instability exists that will either drive soil depth to the optimal weathering depth or to zero depth more recent work has also described a declining exponential soil production function in which the highest rate is at zero soil depth despite dealing with a fundamental issue in soil science viz soil formation the soil production concept has been applied mostly to landscape evolution studies the situation is ripe for its use in soil science and developments in techniques such as cosmogenic nuclides will assist this

weathering instability and landscape evolution abstract the argument in this paper is that the fundamental control on landscape evolution in erosional landscapes is weathering the possibility of and evidence for instability in weathering at four scales is examined the four scales are concerned with weathering processes allocation of weathered products the interrelations of weathering and denudation and the topographic and isostatic responses to weathering limited denudation the regolith hillslope landscape unit and landscape scales respectively the stability conditions for each model and the circumstances under which the models themselves are relevant are used to identify scale related domains of stability and instability at the regolith scale the interactions among weathering rates resistance and moisture are unstable but there are circumstances over long timescales and where weathering is well advanced under which the instability is irrelevant at the hillslope scale the system is stable when denudation is transport rather than weathering limited and where no renewal of exposure via regolith stripping occurs at the level of landscape units the stability model is based entirely on the mutual reinforcements of weathering and erosion while this should generally lead to instability the model would be stable where other external controls of both weathering and erosion rates are stronger than the weathering erosion feedbacks at the broadest landscape scale the inclusion of isostatic responses destabilizes erosion topography uplift relationships thus if the spatial or temporal scale is such that isostatic responses are not relevant the system may be stable essentially instability is prevalent at local spatial scales at all but the longest timescales stability at intermediate spatial scales is contingent on whether weathering erosion feedbacks are strong or weak with stability being more likely at shorter and less likely at longer timescales at the broadest spatial scales instability is likely although stability may be present at intermediate temporal scales if weathering erosion feedbacks are weak the distinction is important because stability is associated with convergent evolution whereby the effects of initial variations or disturbances are reduced over time as the landscape converges toward a stable equilibrium state instability by contrast indicates divergent evolution increasing differentiation over time and the persistence and growth of disturbance effects and initial variations

tectonic significance of the florianopolis dyke swarm parana etendeka magmatic province a reappraisal based on precise u pb dating abstract the first precise id tims u pb baddeleyite zircon dating of dykes representative of the main activity in the florianopolis dyke swarm parana etendeka magmatic province south brazil reveals a restricted age range 134 7 0 3 to 133 9 0 7 ma this is at least 5 ma older than indicated by previous 40 ar 39 ar stepwise heating dating and precludes a direct relationship with syn rifting magmatism connected with opening the south atlantic ocean instead as indicated by their age and geochemical signature these dykes are feeders to the nearby urubici lavas and coeval khumib lavas in etendeka these new geochronological results also cast doubt on a large 10 ma time span for the emplacement of the florianopolis dyke swarm implied by 40 ar 39 ar dates but the determination of its upper age limit still requires accurate dating of younger low volume fine grained dykes with distinct low ti chemistry crystals suitable to u pb dating were not obtained thus far from these dykes

cordierite bearing lavas from jaguarao southern brazil petrological evidence for crustal melts during early rifting of gondwana abstract the jaguarao stratoid dacites rio grande do sul brazil are limited in areal extent are comprised of about 3 2 km3 of preserved erupted material and outcrop only in areas of the region underlain by mylonitic and ultramylonitic rocks they are s type volcanic rocks containing cordierite orthopyroxene plagioclase and ilmenite as liquidus phases and partially melted granite gneiss and migmatite enclaves that are very similar to the precambrian basement rocks the jaguarao lavas have distinct geochemical signatures and sr nd isotopes with respect to other volcanic rocks of the region available geochronological data for jaguarao dacites range between 157 5 ma and 139 6 7 4 ma considering the errors the younger ages obtained for jaguarao lavas overlap the 138 128 ma age of rocks of the serra geral group and thus indicate that the dacites were erupted prior to the break up of gondwana in this region petrographic mineralogical and petrochemical data as well as the tectonic context of the jaguarao lavas suggest that magma genesis was linked at least in part to friction melts the dacitic magma was generated by partial melting reactions involving biotite breakdown in a dominantly quartz feldspathic source terrane leaving a granulite facies residue in subsurface these melts were probably generated as a consequence of crustal thinning linked to simple shear extension just prior to gondwana break up and rifting of the southern atlantic ocean

graph theory recent developments of its application in geomorphology abstract applications of graph theory have proliferated across the academic spectrum in recent years whereas geosciences and landscape ecology have made rich use of graph theory its use seems limited in physical geography and particularly in geomorphology common applications of graph theory analyses of connectivity path or transport efficiencies subnetworks network structure system behaviour and dynamics and network optimization or engineering all have uses or potential uses in geomorphology and closely related fields in this paper we give a short introduction to graph theory and review previous geomorphological applications or works in related fields that have been particularly influential network like geomorphic systems can be classified into nonspatial or spatially implicit system components linked by statistical causal relationships and spatial units linked by some spatial relationship for example by fluxes of matter and or energy we argue that if geomorphic system properties and behaviour e g complexity sensitivity synchronisability historical contingency connectivity etc depend on system structure and if graph theory is able to quantitatively describe the configuration of system components then graph theory should provide us with tools that help in quantifying system properties and in inferring system behaviour

distinguishing strongly rheomorphic tuffs from extensive silicic lavas high temperature silicic volcanic rocks including strongly rheomorphic tuffs and extensive silicic lavas have recently been recognized to be abundant in the geologic record however their mechanisms of eruption and emplacement are still controversial and traditional criteria used to distinguish conventional ash flow tuffs from silicic lavas largely fail to distinguish the high temperature versions we suggest the following criteria ordered in decreasing ease of identification to distinguish strongly rheomorphic tuffs from extensive silicic lavas 1 the character of basal deposits 2 the nature of distal parts of flows 3 the relationship of units to pre existing topography and 4 the type of source as a result of quenching against the ground basal deposits best preserve primary features can be observed in single outcrops and do not require knowing the full extent of a unit lavas commonly develop basal breccias composed of a variety of textural types of the flow in a finer clastic matrix such deposits are unique to lavas because the chilled base of an ashflow tuff generally does not participate in secondary flow primary pyroclastic features are best preserved there massive flow banded bases are more consistent with a lava than a pyroclastic origin lavas are thick to their margins and have steep abrupt flow fronts ashflow tuffs thin to no more than a few meters at their distal ends where they generally do not show any secondary flow features lavas are stopped by topographic barriers unless the flow is much thicker than the barrier ash flow tuffs moving at even relatively slow velocities can climb over barriers much higher than the resulting deposit lavas dominantly erupt from fissures and maintain fairly uniform thicknesses throughout their extents tuffs commonly erupt from calderas where they can pond to thicknesses many times those of their outflow deposits these criteria may also prove effective in distinguishing extensive silicic lavas from a postulated rock type termed lava like ignimbrite the latter have characteristics of lavas except for great areal extents up to many tens of kilometers these rocks have been interpreted as ash flow tuffs that formed from low boiling over eruption columns based almost entirely on their great extents and the belief that silicic lavas could not flow such distances however we interpret the best known examples of lava like ignimbrites to be lavas this interpretation should be tested through additional documentation of their characteristics and research on the boiling over eruption mechanism and the kinds of deposits it can produce flow bands flow folds ramps elongate vesicles and probably upper breccias occur in both lavas and strongly rheomorphic tuffs and are therefore not diagnostic pumice and shards also occur in both tuffs and lavas although they occur throughout ash flow tuffs and generally only in marginal breccias of lavas dense welding secondary flow and intense alteration accompanying crystallization at high temperature commonly obliterate primary textures in both thick rheomorphic tuffs and thick lavas high temperature silicic volcanic rocks are dominantly associated with tholeiitic flood basalts extensive silicic lavas could be appropriately termed flood rhyolites

effusive silicic volcanism in the parana magmatic province south brazil evidence for locally fed lava flows and domes from detailed field work abstract lava flows and dome complexes of silicic composition were identified in the lower cretaceous parana magmatic province pmp at rio grande do sul state southern brazil detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments likely representing the fissural systems that fed the three palmas type silicic units different structures indicative of effusive emplacement lava domes lobated flows sheet flows and autobreccias are very common in the study area and are probably also more abundant than previously thought in whole pmp silicic magmatism in fact effusive deposits seem predominant in the three distinct silicic units identified in the area since no remnants of pyroclastic components have been identified the vitreous dacites that make up the upper flows of the basaltic andesite to dacite barros cassal sequence are clearly effusive as indicated by their occurrence as thin sheet flows the much thicker early caxias do sul dacites occur mostly as lava flow lobes and pancake like of low to moderate viscosity and lava domes the younger high sio2 santa maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion as lobated flows formed by vesicle rich obsidian in spite of higher viscosities relative to the previous units 106 pa s it is probable that the very low h2o contents 1 wt of these rhyolite melts associated with high discharge rates resulted in an effusive nature in most to this unit

conceptualising and mapping coupled estuary coast and inner shelf sediment systems whilst understanding and predicting the effects of coastal change are primarily modelling problems it is essential that we have appropriate conceptual frameworks for 1 the formalisation of existing knowledge 2 the formulation of relevant scientific questions and management issues 3 the implementation and deployment of predictive models and 4 meaningful engagement involvement of stakeholders important progress continues to be made on the modelling front but our conceptual frameworks have not evolved at a similar pace accordingly this paper presents a new approach that re engages with formal systems analysis and provides a mesoscale geomorphological context within which the coastal management challenges of the 21st century can be more effectively addressed coastal and estuarine system mapping cesm is founded on an ontology of landforms and human interventions that is partly inspired by the coastal tract concept and its temporal hierarchy of sediment sharing systems but places greater emphasis on a hierarchy of spatial scales this extends from coastal regions through landform complexes to landforms the morphological adjustment of which is constrained by diverse forms of human intervention crucially cesm integrates open coastal environments with estuaries and relevant portions of the inner shelf that have previously been treated separately in contrast to the nesting of littoral cells that has hitherto framed shoreline management planning cesm charts a complex web of interactions of which a sub set of mass transfer pathways defines the sediment budget and a multitude of human interventions constrains natural landform behaviour conducted within a geospatial framework cesm constitutes a form of knowledge formalisation in which disparate sources of information published research imagery mapping raw data etc are generalised into usable knowledge the resulting system maps provide a framework for the development and application of predictive models and a repository for the outputs they generate not least flux estimates for the major sediment system pathways they also permit comparative analyses of the relative abundance of landforms and the multi scale interactions between them finally they articulate scientific understanding of the structure and function of complex geomorphological systems in a way that is transparent and accessible to diverse stakeholder audiences as our models of mesoscale landform evolution increase in sophistication cesm provides a platform for a more participatory approach to their application to coastal and estuarine management

the magmatic evolution at the moroccan outboard of the west african craton between the late neoproterozoic and the early palaeozoic

morphological classification of fluvial environments an investigation of the continuum of channel types abstract bedrock controlled channel systems exhibit considerable morphological variation both bedrock influenced and alluvial morphological units coexist to form a system of changing channel patterns in response to changes in the relative influence of the controlling process variables this article investigates the morphological composition of the bedrock influenced sabie river mpumalanga province south africa mapping 25 km of river channel at the scale of individual morphological units cluster and discriminant analyses define objective reach scale channel type assemblages based on morphological unit composition a number of robust clusters emerged that could be broadly classified into five channel types namely bedrock anastomosed mixed anastomosed pool rapid braided and alluvial single thread the cluster analysis revealed that these channel types fit on a continuum from bedrock dominated channels to fully alluvial systems each channel type could also be characterized by a certain set of d

shifts in the source of the parana basalts through time magmatism occurred intermittently in the parana region of south america between 240 50 ma with the peak of magmatic activity between 138 126 ma comprising the parana continental flood basalts cfb detailed chemical subdivision of the parana basalts into six units allowed stratigraphic correlations to be made implying a northward migration of magmatism following the rifting of the south atlantic however 40ar 39ar ages do not uphold the chronostratigraphic nature of such magmatic units instead they indicate a southeastwards migration major elements extrapolated to 8 wt mgo are used to investigate changes in magma type with time and are interpreted in terms of parameters such as pressure depth of melting and the nature of the source region fertile refractory and water content the oldest parana unit originated by melting at the greatest depths 90 120 km shifting to shallow levels 30 60 km for the younger units accompanying this decrease in pressure the source material undergoing partial melting became progressively more refractory in major elements and also more hydrous this hydrous metasomatism occurred after major element depletion of the lithosphere at shallow levels the data is consistent with conductive heating of a stratified source region inferred to lie within the lithospheric mantle which is relatively fertile but anhydrous at depth and also appears to be younger in age than the relatively major element refractory hydrous lithosphere at shallower depths thus the interaction of asthenosphere and lithosphere can be determined within an integrated age tectonic and thermal framework

the loch scridain xenolithic sill complex isle of mull scotland fractional crystallization assimilation magma mixing and crustal anatexis in subvolcanic conduits

petrology and k ar ages of rift related basaltic rocks offshore northern brazil 3 n tholeiitic basaltic rock in three cores from petrobras drill site aps 21 1960 2480 m depths amapa basin offshore brazil is compositionally similar to rift related basaltic rock associated with the opening of both the north and south atlantic oceans sio 2 52 54 wt k 2 o 0 7 1 3 tio 2 1 3 2 whole rock k ar ages are 185 4 183 2 and 126 5 m y if these represent crystallization ages then the older samples correspond to north atlantic tectonism as represented by the liberian dike system and the younger correlates with south atlantic rift related magmatism of which serra geral flood basalts are the best example trace and ree elements identify t type mantle source areas la sm n 2 zr nb 8 11 that feasibly were mixes of n type and p type components metasomatized or veined upper mantle these amapa basin mafic rocks document the southernmost magmatism related to north atlantic rifting as well as early mesozoic mantle source areas and processes beneath gondwanaland such

effects of physical erosion on chemical denudation rates a numerical modeling study of soil mantled hillslopes article i nfo many biogeochemical and earth surface processes depend critically on chemical weathering the immediate products of chemical weathering are present as solutes and secondary minerals in groundwater soils and streams and form the nutritional foundation for terrestrial biogeochemistry chemical weathering also contributes to physical erosion by weakening bedrock and producing easily erodible regolith and as the primary long term sink for atmospheric co2 it modulates earth s long term climate via the greenhouse effect long term chemical denudation rates on soil mantled hillslopes can be estimated from cosmogenic radionuclide crn concentrations in soil borne quartz and the enrichment of a chemically inert tracer in soil relative to its parent bedrock a technique that inherently assumes steady physical erosion over the timescale of crn accumulation we present a numerical model that computes changes in soil mineralogy and crn concentrations under time varying physical erosion rates and we use this model to assess the accuracy of the crn based technique for estimating chemical denudation rates in non steady conditions our modeling results suggest that crn based estimates of chemical denudation rates closely resemble actual chemical denudation rates averaged over the timescale of crn accumulation even during large amplitude and long period oscillations in physical erosion rates for example this model predicts that when physical erosion rates fluctuate sinusoidally by 50 of their mean over any period in time crn based estimates of chemical denudation rates should differ from actual chemical denudation rates by less than 15 our model also implies that chemical denudation rates should approach zero both when physical erosion rates approach zero because soluble minerals become depleted in the soil and when physical erosion rates approach the maximum soil production rate because soil thickness approaches zero modeled chemical denudation rates thus reach a maximum at intermediate physical erosion rates if this relationship holds in nature it implies that in rapidly eroding regions further increases in physical erosion rates e g due to increases in tectonic uplift rates may not necessarily lead to faster chemical denudation on soil mantled hillslopes published by elsevier b v

upper crustal structure of the northeast parana basin brazil determined from integrated magnetotelluric and gravity measurements eight magnetotelluric mt soundings were performed as a continuation of an earlier audiomagnetotelluric amt survey conducted in the northeastern border of the parana basin a large intracratonic basin located in central eastern south america and constituted by silurian to jurassic sedimentary rocks with lower cretaceous sill type magmatic intrusions and overlying volcanics two of the mt stations were carried out near two deep petroleum wells the remaining mt soundings were done on a profile traversing two important gravity features a positive anomaly near the border of the states of sao paulo and minas gerais and a strong trending nw se linear gradient major findings of an integrated interpretation of the mt survey and of available gravity data are as follows 1 inhomogeneities and or strong magnetization of the superficial volcanics and diabase intrusions in the paleozoic sedimentary rocks appearing to distort the mt results and 2 identification of important structural discontinuities including a possible different crustal structure beneath the parana basin compared to the region on the north a thickening of the crust toward the ne and the probable existence of a trough graben within the basin characterized by a thick accumulation of sediments and basalts

ordovician bimodal volcanism in sw wales geochemical evidence for petrogenesis of the silicic rocks rhyolitic lavas pyroclastic and high level intrusive rocks form an important component of a bimodal tholeiitic basalt rhyolite association of early ordovician llanvirn age exposed in north pembrokeshire on ramsey island in the fishguard area and on mynydd preseli in the same region a 400 m thick tholeiitic layered differentiated sill the st david9s head intrusion considered to be co genetic with this association comprises a series of units ranging from basic olivine orthopyroxene bearing gabbros through intermediate granophyric gabbro to acidic aplite compositions consideration of the major and trace element concentrations in these various intrusive units suggests that they are related largely through a crystal fractionation process the principal fractionating phases were clinopyroxene and plagioclase feldspar with olivine and orthopyroxene in the more mafic compositions substantial fe ti oxide and minor apatite in the intermediate compositions and minor apatite and titanite in the most evolved compositions a comparison between the composition of a typical aplite from the st david9s head intrusion and compositions of the various silicic rocks from the bimodal suites in north pembrokeshire suggests these latter rocks have also been derived from a more basic tholeiitic magma via crystal fractionation potential parental magmas are the various basaltic lavas and related doleritic intrusions of the fishguard volcanic complex however certain silicic lavas and intrusions from the porth maen melyn area appear not to have been derived from a tholeiitic parental magma but rather have a calc alkaline type chemistry similar to older lavas of the trefgarn volcanic group exposed a short distance to the south of fishguard these findings support the contention that large volume silicic units in bimodal associations can be derived by crystal fractionation despite the obvious geochemical discontinuity and the apparently anomalous volume relationships commonly present

geomorphic controls of soil spatial complexity in a primeval mountain forest in the czech republic abstract soil diversity and complexity is influenced by a variety of factors and much recent research has been focused on interpreting or modeling complexity based on soil topography relationships and effects of biogeomorphic processes we aimed to i describe local soil diversity in one of the oldest forest reserves in europe ii employ existing graph theory concepts in pedocomplexity calculation and extend them by a novel approach based on hypothesis testing and an index measuring graph sequentiality the extent to which soils have gradual vs abrupt variations in underlying soil factors and iii reveal the main sources of pedocomplexity with a particular focus on geomorphic controls a total of 954 soil profiles were described and classified to soil taxonomic units stu within a 46 ha area we analyzed soil diversity using the shannon index and soil complexity using a novel graph theory approach pairwise tests of observed adjacencies spectral radius and a newly proposed sequentiality index were used to describe and quantify the complexity of the spatial pattern of stus this was then decomposed into the contributions of three soil factor sequences sfs i degree of weathering and leaching processes ii hydromorphology and iii proportion of rock fragments six reference soil groups and 37 second level soil units were found a significant portion of pedocomplexity occurred at distances shorter than the 22 m spacing of neighbouring soil profiles the spectral radius an index of complexity of the pattern of soil spatial adjacency was 14 73 to which the individual sfs accounted for values of 2 0 8 0 and 3 5 respectively significant sequentiality was found for degree of weathering and hydromorphology exceptional overall pedocomplexity was particularly caused by enormous spatial variability of soil wetness representing a crucial soil factor sequence in the primeval forest moreover the soil wetness gradient was partly spatially correlated with the gradient of soil weathering and leaching suggesting synergistic influences of topography climate hydro geology and biomechanical and biochemical effects of individual trees the pattern of stony soils random in most respects resulted probably from local geology and quaternary biogeomorphological processes thus while geomorphology is the primary control over a very locally complex soil pattern microtopography and local disturbances mostly related to the effects of individual trees are also critical considerable local pedodiversity seems to be an important component of the dynamics of old growth mixed temperate mountain forests with implications for decreasing pedodiversity in managed forests and deforested areas

least action principle equilibrium states iterative adjustment and the stability of alluvial channels the energy based least action principle lap has proven to be very successful for explaining natural phenomena in both classical and modern physics this paper briefly reviews its historical development and details how in three ways it governs the behaviour and stability of alluvial rivers first the lap embodies the special stationary equilibrium state of motion and so its incorporation with the principle of energy conservation explains why so many optimizing hypotheses have been proposed in fluvial geomorphology second the variational approach underlying the lap provides a more straightforward and simpler fuzzy object orientated method for solving river regime problems than do the various complex newtonian formulations third it is shown that in fluvial systems with surplus energy the surplus can be expended with slope and or channel geometry adjustments with the degree of channel geometry adjustment quantified by the dimensionless numbers f for depth dominated adjustment and h for width depth dominated adjustment different planforms are preferred at different energy levels with h providing a quantitative measure of the flow s efficiency for moving sediment in rivers with insufficient energy the interactions of endogenous and exogenous factors are shown to be capable in certain circumstances of achieving a stationary equilibrium condition which acts as the attractor state importantly this study describes how iterative changes enable systems to achieve such a stable equilibrium copyright 2007 john wiley sons ltd

relationships between crustal contamination and crystallisation in continental flood basalt magmas with special reference to the deccan traps of the western ghats india the upper part of the deccan traps sequence bushe to mahabaleshwar formations shows a statistically significant tendency for the most mafic lavas to be the most contaminated by crustal materials this is the reverse of the relationship shown by suites evolving by contamination accompanied by fractional crystallisation afc the observed correlations e g between mg number and sr isotope initial ratios are partly an accidental consequence of the fact that the most mafic lavas are more abundant in the lower part of the sequence while contaminant availability declines in the upper part it is probable however that the correlations are augmented by increased contamination of hotter magma batches during ascent through dykes a process during which fractional crystallisation is suppressed by magmatic turbulence the absence of afc relationships suggests that most of the contamination took place during the ascent stage rather than in a magma chamber other continental flood basalt provinces such as the parana and etendeka do show afc relationships and it is speculated that this may be a result of magma chamber contamination coupled with flow rates which prevent contamination during ascent

coccolith evidence for instabilities in surface circulation south of iceland during holocene times abstract the coccolith based micropaleontological investigation of an exceptionally thick deep sea holocene sediment core was conducted in order to document the pattern and timing of surface circulation changes south of iceland over the gardar contour drift during the last 12 000 years fluctuations in bulk carbonate content at the core location are primarily driven by the coccolith fraction the observed overall correlation between bottom flow speed as given by the sortable silt mean size index and the bulk coccolith concentration abundance g dry sediment suggests that the accumulation of this fine carbonate fraction is as a first order controlled by processes of sediment redistribution by bottom current the down core variations in coccolith assemblage structure species indicate that changes in properties of surface waters south of iceland occurred as two distinct steps at ca 11 2 and 6 ka the onset of north atlantic drift water influence over the gardar drift after 11 2 ka was associated with excess export flux of coccolith carbonate in the vicinity of an active frontal system the period from 10 to 6 ka saw the progressive warming of the study area which culminated between 6 and 7 ka cooling of the surface waters after 6 ka as indicated changes in the relative abundances of the dominant coccolith species took place in two phases the present hydrological regime being only established after a last cooling step between 3 5 and 2 8 ka these long term reorganisations of the surface hydrology are interpreted as the response of the north atlantic to the combined force of the solar insolation and the waning laurentide ice sheet millennial scale perturbations of the surface hydrology are documented by changes in accumulation of the species emiliania huxleyi these successive decreases in the export fluxes of e huxleyi exhibit a distinct millennial pacing in phase with previously recorded holocene advection of cool ice bearing waters from the greenland iceland seas to the british islands from a clear analogy with the most recent extreme variation in global ocean climate we argue that mechanisms responsible for these observed millennial scale perturbations might be found in long term modulations of the atmospheric processes associated with the north atlantic oscillation nao

inherited vs acquired complexity in east texas weathering profiles complexity in weathering profiles may reflect variability in the parent material and or complex feedback relationships within regolith weathering systems because regolith formation modifies or destroys the parent material it is difficult to determine the extent to which variability in the weathering profile is inherited as opposed to created by the weathering processes the state probability function spf designed to model the spatial pattern of transitions in system states is applied to complex weathering profiles formed in glauconitic materials in east texas to address this issue the weathering profile is remarkably complex with units ranging from unweathered parent material to highly modified weathering products similar to those found in the bt horizons of the overlying rhodic paleudalf there is a very general vertical sequence with more weathered material near the top and less weathered material near the bottom however the pattern is quite irregular highly weathered units are found everywhere except at the base of the study section and much less developed units are found throughout though the spf indicates a high degree of spatial complexity the value never approaches or exceeds that which would be expected in a random vertical sequence of weathering horizons variation inherited from the parent material would produce spf values greater than that for a random sequence the complex patterns in the east texas regolith are thus attributable primarily to feedbacks within the weathering system and indicate that the complexity is dominantly acquired whatever anisotropy there may have been in the parent material has been magnified and overprinted by complex interactions within the weathering system

synchronization and scale in geomorphic systems abstract geomorphic systems consist of coupled subsystems with traits of small world networks swn characterized by tightly connected clusters of components with fewer connections between the clusters geomorphic systems based on scale hierarchies often exhibit a connected caveman small world network ccswn structure swns are efficient for linking a large number of components with a relatively small number of links but effects of ccswn structure on synchronization and scale linkage have not been examined synchronization is analyzed via graph theory and applied to 1 relationships among three levels of form process interaction in stream channels 2 hierarchical relationships of weathering systems at scales from weathering profiles to landscapes and 3 interactions in fluviokarst systems at the scale of flow processes and of landscape evolution relationships among system components are represented as simple unweighted graphs the largest eigenvalue of the adjacency matrix spectral radius reflects the critical coupling strength required to synchronize the system the second smallest eigenvalue of the laplacian of the adjacency matrix algebraic connectivity is a measure of the synchronizability in all examples both are much less than the maximum for networks of the same number of nodes the sparseness of the networks is the major contributor to the low synchronization but the specific pattern of connections wiring is also significant where ccswn structures arise naturally they help explain how geomorphic effects are transmitted between disparate scales in the absence of obvious scale linkage where ccswns are an option for representation of geomorphic systems in models and data structures they will not improve scale linkage despite the efficiency of swns in other respects methods developed here can be applied to evaluating alternative spatial data structures or mapping strategies which either increase synchronization supporting a lumping or aggregation approach or decrease synchronization indicating disaggregation or splitting into scale hierarchies

a revised chemo chrono stratigraphic 4 d model for the extrusive rocks of the parana igneous province abstract the statistical analysis of a lithogeochemical database from whole parana igneous province pip containing 5974 outcrop and drillhole samples stresses natural gaps separating sio2 zr tio2 and p2o5 in high and low values their combination delimits 16 chemical types which have been adopted to classify a sub set of extrusive rocks with

sr isotopic evidence for ion exchange buffering in tropical laterites from the parana brazil sr isotopes have been measured in laterite sequences and in associated waters from the region of ribeirao preto parana basin brasil in order to characterize the water rock interactions corresponding to the successive stages of weathering of these continental flood basalts we analyzed detailed sections of concentric rims of alteration in ball shaped spheroids developed around cores of fresh basalts waters were also analyzed on the different types of facies in this region unaltered basalts thick weathered profiles of lateritic material and surrounding sandstones the results show that a major part of the initial sr is removed from the basalt during the earliest stages of weathering within the narrow grey rims surrounding the unweathered core radiogenic sr is also leached from hydrothermal minerals located in basalt fractures or disseminated in the basalt groundmass at this early stage very high water rock ratios of at least 100 000 are calculated for this process from the sr 87 sr 86 in the related waters a general trend of increasing sr 87 sr 86 ratios is observed in the increasingly weathered facies inner yellow cortexes red kaolinitic soils and matrices and in their related waters the very high sr 87 sr 86 ratios of the red kaolinitic horizons probably result from isotopic exchange with radiogenic rainwaters or sandstone waters and also from the presence of residual or neoformed radiogenic minerals budget calculations as well as experimental leaching of kaolinite samples suggest that significant amounts of radiogenic sr can be leached from these facies during weathering thus the kaolinitic facies of tropical laterite profiles are able first to trap strontium from surficial waters then to provide radiogenic sr to the waters that weather the fresh basalts at the weathering front therefore the thick weathered horizons must be considered as a natural cation exchange layer that play an active role in the weathering process

geochemical stratigraphy of lavas and fault block structures in the ametista do sul geode mining district parana volcanic province southern brazil abstract the parana volcanic province is the world s largest producer of amethyst geodes mostly from the ametista do sul mining district 20 by 30 km in southern brazil the description of the lava flows in the ametista do sul mining district and adjacent areas combined with flow by flow geochemistry and scintillometry defines the stratigraphy of the flows nine flows were identified in the ametista do sul region and four additional flows were identified in the frederico westphalen region totalizing 13 flows in the stratigraphy of the ametista do sul mining district six of the flows belong to pitanga magma type more than 3 wt tio 2 which occur at the base of the local stratigraphy and the other seven flows belong to paranapanema magma type 2 3 wt tio 2 at the top of the stratigraphy the amethyst bearing geodes occur in the uppermost three pitanga flows known as veia alta main producer veia do meio and veia baixa these flows were highly altered more than 60 vol to clay minerals by a low temperature alteration process the massive presence of clay minerals is an important component that controls the rheology of the rock transforming the basalt into a very low grade smectite and celadonite metabasalt two paranapanema flows coogamai and linha alta from ametista do sul were identified in a lower position at the base of the section in frederico westphalen which were correlated using scintillometry and flow by flow geochemistry in addition veia alta and veia do meio flows were also identified in lower positions compared to ametista do sul thus the identification of these flows in different places with different elevations is an evidence of the presence of downthrown blocks in a fault block structure lowering the stratigraphy more than 200 m to the west in four steps the tectonic patterns that generate this structure are three nw strike lineaments the identification of the coogamai flow at the base of the frederico westphalen region suggests that the veia alta geode hosting flow is below the ground or below the elevation of 250 m in this region these evidences show that the fault block structure is controlling vertically the deposit of amethyst bearing geodes and is of major significance in the exploration for new amethyst geode deposits in the region

flow and fragmentation patterns in the silicic feeder system and related deposits in the parana etendeka magmatic province sao marcos south brazil voluminous silicic volcanic products from the paran etendeka magmatic province are exposed in the southern brazil a regional synformal structure torres syncline controls a tick sequence of these units in the region of sao marcos rio grande do sul parallel to the axis of torres syncline a nw se trending zone constituted by the alignment of complex structures was interpreted as the feeding system of silicic volcanism characterized as fissural through a combination of field mapping and determination of fractal dimension fd we have identified and described distinct intermingled morphological domains one related to flow processes and one related to fragmentation processes vertical flow directions in this zone exhibit two preferential directions nw ranging from n272 degrees to n 355 degrees and ne varying from n20 degrees to n85 degrees the systematic repetition and crosscutting relations of domains point towards a cydicity of flow and fragmentation processes in this zone this feeder system intrudes previous basaltic and silicic volcanic rocks the later being composed by banded deposits interpreted as rheoignimbrites and proximal volcanic breccias this set is overlapped by hybrid deposits lava flows and finally massive deposits the silicic volcanism can be summarized at an early pyrodastic stage characterized by rheoignimbrites and proximal volcanic breccias a transition between explosive and effusive events is suggested by the occurrence of hybrid deposits which gradually give place to lobated lavas local alternation with new possibly rheoignimbritic deposits suggests oscillatory fragmentation processes at the conduit related to decompression and volatiles ex solution in an effective permeable system

an ams study of different silicic units from the southern parana etendeka magmatic province in brazil implications for the identification of flow directions and local sources abstract in the southern portion of the parana etendeka magmatic province in brazil extensive silicic dacite rhyolite deposits occur at the top of a sequence of low ti pahoehoe to rubbly basalts the internal architecture of the silicic deposits and their eruptive style as well as the location of their sources are still unsatisfactorily known in an attempt to provide independent evidence for flow directions in deposits previously characterized as effusive and test the hypothesis of local sources we carried out anisotropy of magnetic susceptibility ams studies on the two main silicic units caxias do sul dacites and santa maria rhyolites with the best exposures in an area previously mapped in detail magnetic anisotropies were determined on oriented cylindrical specimens from a total of 28 sites rock magnetism properties indicate that pseudo single domain magnetite carries the fabrics and the remanence magnetic fabrics were determined by applying anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanent magnetization aarm both ams and aarm tensors are coaxial indicating that the ams fabric is not affected by the effect of magnetite single domain grains magnetic data from several dacitic coulees caxias do sul unit indicate flows from se to nw the location and spatial distribution of these lavas support the hypothesis of local sources aligned along a ne sw trend these data are in agreement with the alignments of structures dome shaped hills observed in field work and dem images on the other hand magnetic data obtained in santa maria rhyolites indicate that flow directions in two different areas are distinct towards nw ne and w suggesting that they derived from different emission centers so regarding the silicic volcanism in the studied region our data do not support the model which classifies the entire silicic volcanism of the province as extensive rheomorphic pyroclastic deposits released from a central conduit in contrast we propose the occurrence of local volcanic events implying in the existence of different sources possibly characterized by local emission centers

parameter free delineation of slope units and terrain subdivision of italy abstract quantitative geomorphological and environmental analysis requires the adoption of well defined spatial domains as basic mapping units they provide local boundaries to aggregate environmental and morphometric variables and to perform calculations thus they identify the spatial scale of the analysis grid cells typically aligned with a digital elevation model are the standard mapping unit choice a wiser choice is represented by slope units irregular terrain partitions delimited by drainage and divide lines that maximise geomorphological homogeneity within each unit and geomorphological heterogeneity between neighbouring units adoption of slope units has the advantage of enforcing a strong relation with the underlying topography absent in grid cell based analyses but their objective delineation is still a challenge a given study area admits different slope unit maps differing in number and size of units here we devise an objective optimisation procedure for slope units suitable for study areas of arbitrarily large size and with varying terrain heterogeneity we applied the new approach to the whole of italy resulting in a map containing about 330 000 slope unit polygons of different sizes and shapes the method is parameter free due to objective optimisation using a morphometric segmentation function and the map is readily available for general purpose studies a cluster analysis of slope units properties compared with terrain elevation slope drainage density and lithology confirmed that the terrain partition is geomorphologically sound we suggest the use of the slope unit map for different terrain zonations including landslide susceptibility modelling hydrological and erosion modelling geo environmental ecological forestry agriculture and land use land cover studies requiring the identification of homogeneous terrain domains facing distinct directions

keweenaw hot spot geophysical evidence for a 1 1 ga mantle plume beneath the midcontinent rift system the proterozoic midcontinent rift system of north america is remarkably similar to phanerozoic rifted continental margins and flood basalt provinces like the younger analogues the volcanism within this older rift can be explained by decompression melting and rapid extrusion of igneous material during lithospheric extension above a broad asthenospheric thermal anomaly which the authors call the keweenaw hot spot great lakes international multidisciplinary program on crustal evolution seismic reflection profiles constrain end member models of melt thickness and stretching factors which yield an inferred mantle potential temperature of 1 500 1 570c during rifting combined gravity modeling and subsidence calculations are consistent with stretching factors that reached 3 or 4 before rifting ceased and much of the lower crust beneath the rift consists of relatively high density intruded or underplated synrift igneous material the isotopic signature of keweenawan volcanic rocks presented in a companion paper by nicholson and shirey this issue is consistent with the model of passive rifting above an asthenospheric mantle plume

divergent evolution in fluviokarst landscapes of central kentucky central kentucky is characterized by a mixture of karst and uvial features typically manifested as mosaic of karst rich channel poor krcp and channel rich karst poor crkp environments at the regional scale the location and distribution of krcp and crkp areas are not always systematically related to structural lithological topographic or other controls this study examines the relationship of krcp and crkp zones along the kentucky river gorge area where rapid incision in the last 1 5 million years has lowered local base levels and modi ed slopes on the edge of the inner bluegrass plateau at the scale of detailed eld mapping on foot within a 4 km2 area the development of karst and uvial features is controlled by highly localized structural and topographic constraints and can be related to slope changes associated with retreat of the kentucky river gorge escarpment a conceptual model of karst uvial transitions is presented which suggests that minor localized variations are suf cient to trigger a karst uvial or uvial karst switch when critical slope thresholds are crossed copyright 2004 john wiley sons ltd

the columbia river basalts between 17 million and 6 million years ago 200 000 square kilometers of the american northwest were flooded by basaltic lava that erupted through fissures in the crust up to 150 kilometers long larger individual eruptions covered over a third of the columbia plateau in a few days the lavas represent partial melts of the earth s mantle that were only slightly modified by near surface upper crustal processes the abundant chemical and mineralogical data now available offer an opportunity to study mantle composition and the processes involved in the evolution of the earth s crust

an inversion approach to assimilation and fractional crystallisation processes a numerical inversion program has been developed to investigate isotope and trace element variations in suites of related rocks in terms of assimilation and fractional crystallisation processes major element compositions constrain the degree of fractionation and the program may be used to calculate the isotope and trace element composition of either the crustal contaminant or of the parental magmas once the contaminant is known the ratio of the rate of assimilation to the rate of fractional crystallisation and the bulk partition coefficients can be varied with changes in magma composition the approach is illustrated with a suite of calc alkaline rocks from the cerro galan centre in nw argentina and a suite of continental flood basalts from the southern parana in brazil both exhibit striking increases in 87sr 86sr with increasing sio2 consistent with progressive contamination during differentiation within the continental crust in detail both suites contain a subset of samples which have undergone relatively little contamination and a subset characterised by relatively high sio2 and 87sr 86sr reflecting larger crustal contributions individual samples within the more contaminated subset can be modelled in terms of assimilation with fractional crystallisation afc processes although no clear progressively contaminated liquid lines of descent are preserved at both cerro galan and the southern parana the associated dacites and rhyodacites appear to have similar compositions to the crustal contaminants thus the inversion program has been used to investigate the amount of contamination the relationship between the amount of contamination and the amount of crystals removed by fractional crystallisation and the isotope and trace element contents of the parental magmas prior to afc the latter are estimated to have had 87sr 86sr 0 7055 and 143nd 144nd 0 51256 at cerro galan and 0 7090 and 0 51226 respectively in the southern parana

palaeomagnetism and k ar ages of the south west african basalts and their bearing on the time of initial rifting of the south atlantic ocean summary palaeomagnetic and isotopic results from the kaoko lavas hoachanas basalts and dolerite sills of south west africa indicate that the upper triassic lower jurassic stormberg flows of south africa may have extended into sw africa and that younger igneous events of lower cretaceous age were simultaneous with the serra geral volcanism in brazil five analyses on three samples of the keetmanshoop sills gave k ar ages between 178 4 and 199 4 ma four analyses of two samples of the hoachanas basalts gave ages between 161 3 and 173 2 ma and eight analyses of five samples of kaoko basalt gave ages between 110 4 and 128 2 ma the components of remanent magnetization rm used to compute palaeomagnetic pole positions for the kaoko lavas 48 n 93 w a95 3 and for the hoachanas basalts 61 n 106 w a95 7 are stable to alternating field af and thermal demagnetization correlation on a pre drift map and on a map reconstructed for 112 ma bp before present between the palaeomagnetic poles from the kaoko and serra geral lavas suggests that the south atlantic had not opened appreciably by 112 ma bp cretaceous pole positions for s america and africa on a map reconstructed for 80 ma bp are also discussed

the mount pavagadh volcanic suite deccan traps geochemical stratigraphy and magmatic evolution abstract the patterns of eruption and dispersal of flood basalt lavas on the surface or as magmas in dykes and sills within the crust determine the volcanological and stratigraphic development of flood basalt provinces this is a geochemical and sr isotopic study of lavas of varied compositions that outcrop around mount pavagadh 829 m deccan traps an important outlier north of the main basalt outcrop most of the 550 m thick exposed section at pavagadh is made up of subalkalic basalts rich in the incompatible elements particularly nb ba and sr picrite and rhyolite dacite flows also occur the latter capping the sequence the relatively high initial 87sr 86sr ratios up to 0 7083 and chemical characteristics of the rhyolitic rocks of pavagadh are consistent with a small but significant involvement of the granitic basement crust in their genesis an assimilation fractional crystallization afc model involving the picrite lava and either a southern indian or a western indian granite as the contaminant explains the geochemical and sr isotopic variation in the basalts and the rhyolites quite well a systematic comparison of the basaltic lavas with binary plots normalized multielement patterns and discriminant function analysis to the well established lava stratigraphy of the western ghats 400 500 km to the south precludes any chemical genetic relationships between the two basalts exposed in sections closer to pavagadh 150 200 km in the toranmal navagam and barwani mhow areas have several flows with some similar chemical characteristics however the pavagadh sequence is significantly different from all of these sequences geochemically petrogenetically and in magnetic polarity to be considered independently built this result is significant in terms of eruptive models for the deccan traps as it is increasingly apparent that there were separate but possibly coeval eruptive centers with their own distinctive chemistries developed in various areas of this vast province

historical contingency in fluviokarst landscape evolution abstract lateral and vertical erosion at meander bends in the kentucky river gorge area has created a series of strath terraces on the interior of incised meander bends these represent a chronosequence of fluviokarst landscape evolution from the youngest valley side transition zone near the valley bottom to the oldest upland surface this five part chronosequence not including the active river channel and floodplain was analyzed in terms of the landforms that occur at each stage or surface these include dolines uvalas karst valleys pocket valleys unincised channels incised channels and cliffs smaller features such as swallets and shafts also occur landform coincidence analysis shows higher coincidence indices ci than would be expected based on an idealized chronosequence ci values indicate genetic relationships common causality among some landforms and unexpected persistence of some features on older surfaces the idealized and two observed chronosequences were also represented as graphs and analyzed using algebraic graph theory the two field sites yielded graphs more complex and with less historical contingency than the idealized sequence indeed some of the spectral graph measures for the field sites more closely approximate a purely hypothetical no historical contingency benchmark graph the deviations of observations from the idealized expectations and the high levels of graph complexity both point to potential transitions among landform types as being the dominant phenomenon rather than canalization along a particular evolutionary pathway as the base level of both the fluvial and karst landforms is lowered as the meanders expand both fluvial and karst denudation are rejuvenated and landform transitions remain active

further constraints on the temporal evolution of the oslo rift from precise u pb zircon dating in the siljan skrim area abstract precise u pb ages have been obtained from zircon and baddeleyite in plutonic rocks from the siljan skrim area in the vestfold graben segment in the south western part of the permian oslo rift in addition common lead data from feldspars in the same rocks are presented the measured common pb compositions of the feldspars are used to correct for initial common pb in the zircons the common pb data indicate that u has been present in the feldspars since the time of crystallisation probably in a late magmatic volatile phase in fluid inclusions the siljan skrim area comprises two intrusive complexes the northern skrim mykle complex consists of two large composite intrusive bodies the skrim larvikite and the mykle ekerite the southern siljan hvarnes complex consists of a series of monzonitic to syenitic intrusions which are nested in a systematic way indicating decreasing emplacement age from east to west u pb zircon ages range from 281 2 0 6 ma 2 to 279 8 0 7 ma for three samples from the northern part of the siljan skrim area and from 278 5 0 8 ma to 277 3 0 8 ma for four samples from the southern part of the area the geochronological data suggest that large amounts of magma were emplaced within very short time spans i e less than 2 ma for each of the two complexes the high precision of the u pb age results allows discrimination between intrusive activity in the northern and southern parts of the siljan skrim area and suggests that emplacement of magmas was episodic

volcanic clasts in silurian conglomerates of the midland valley hagshaw hills inlier scotland and their meaning for caledonian plate tectonics 34 igneous clasts of predominantly rhyolitic composition of the parishholm and hareshaw conglomerate silurian hagshaw hills inlier midland valley scotland have been analysed for major and trace element contents the geochemical composition of the clasts indicates different source areas firstly some clasts are derived from rhyolites of a within plate setting peralkaline rhyolites of oceanic islands or continental rifts and secondly other clasts are derived from calc alkaline to high k rhyolites such rhyolites erupt mainly above convergent plate boundaries but occur also in continental areas of crustal extension both conglomerates were shed from the direction of the southern uplands into the midland valley since no calc alkaline rhyolites are known in the southern uplands a volcanic terrane should have been situated during the silurian in the area where the southern uplands lie now the geotectonic character of this terrane cannot unequivocally be identified with the help of the trace element data of the clasts therefore several models are discussed

the critical role of climate and saprolite weathering in landscape evolution landscapes evolve in response to external forces such as tectonics and climate that influence surface processes of erosion and weathering internal feedbacks between erosion and weathering also play an integral role in regulating the landscapes response our understanding of these internal and external feedbacks is limited to a handful of field based studies only a few of which have explicitly examined saprolite weathering here we report rates of erosion and weathering in saprolite and soil to quantify how climate influences denudation by focusing on an elevation transect in the western sierra nevada mountains california we use an adapted mass balance approach and couple soil production rates from the cosmogenic radionuclide crn 10be with zirconium concentrations in rock saprolite and soil our approach includes deep saprolite weathering and suggests that previous studies may have underestimated denudation rates across similar landscapes along the studied climate gradient chemical weathering rates peak at middle elevations 1200 2000 m averaging 112 3 9 7 t km 2 y 1 compared to high and low elevation sites 46 8 5 2 t km 2 y 1 measured weathering rates follow similar patterns with climate as those of predicted silica fluxes modeled using an arrhenius temperature relationship and a linear relationship between flux and precipitation furthermore chemical weathering and erosion are tightly correlated across our sites and physical erosion rates increase with both saprolite weathering rates and intensity unexpectedly saprolite and soil weathering intensities are inversely related such that more weathered saprolites are overlain by weakly weathered soils these data quantify exciting links between climate weathering and erosion and together suggest that climate controls chemical weathering via temperature and moisture control on chemical reaction rates our results also suggest that saprolite weathering reduces bedrock coherence leading to faster rates of soil transport that in turn decrease material residence times in the soil column and limit soil weathering copyright 2009 john wiley sons ltd

structures and lithofacies of inferred silicic conduits in the parana etendeka lip southernmost brazil abstract extensive silicic units in the parana etendeka lip have been long interpreted as pyroclastic density currents rheomorphic ignimbrites derived from the messum complex in namibia in recent literature however they have been characterized as effusive lava flows and domes in this paper we describe structures and lithofacies related to postulated silicic lava feeder conduits at mato perso sao marcos and jaquirana cambara do sul areas in southern brazil inferred conduits are at least 15 25 m in width and the lithofacies include variably vesicular monomictic welded and non welded breccias in the margins to poorly vesicular banded spherulitic and microfractured vitrophyres in the central parts flat lying coherent vitrophyres and massive obsidian are considered to be the subaerial equivalents of the conduits large scale regional tectonic structures in southern brazil include the ne sw aligned porto alegre suture leao and acotea faults besides the antas lineament a curved tectonic feature accompanying the bed of antas river south of the antas lineament smaller scale nw se lineaments limit the exposure areas of the inferred conduits ne sw and subordinate nw se structures within this smaller scale lineaments are represented by the main postulated conduit outcrops and are parallel to the dominant sub vertical banding in the widespread banded vitrophyre lithofacies upper lava flows display flat lying foliation pipe like and spherical vesicles and have better developed microlites petrographic characteristics of the silicic vitrophyres indicate that crystal poor magmas underwent distinct cooling paths for each inferred conduit area the vitrophyre chemical composition is defined by the evolution of trachydacitic dacitic vitrophyres with 62 65 wt sio 2 to rhyodacite and rhyolite with 66 68 wt sio 2 the more evolved rocks are assigned to the latest intrusive grey vitrophyre outcropping in the center of the conduits degassing pathways formed during fragmentation and fracturing episodes within the conduits may have helped to inhibit the explosivity of the eruptions based on the documented lithofacies architecture we attribute the source of the silicic lava flows in the studied localities to tectonic controlled local conduits rather than pyroclastic density currents from distant vent areas

towards the identification of scaling relations in drainage basin sediment budgets abstract drainage basin sediment budgets concern inputs storages and outputs of sediments and solutes through monitored cross sections at the mouth of basins or at the base of individual slopes the question under consideration is whether and to what extent it is possible to transfer knowledge from one spatial scale to another the answer hinges on the question of scale invariance of a individual processes of sediment and solute transfer and b aggregate sediment budgets scale invariance of a number of hydrologic parameters has been established but in general with a few exceptions geomorphic parameters are subject to scale distortion by inference but not yet established by experimental or field evidence scale invariance of sediment budgets is improbable there is therefore a priority to explore scaling relations in sediment budgets so as to determine the precise extent of scale distortion that is present in this paper five ways of identifying scaling relations in drainage basin sediment budgets are identified 1 a fractal approach 2 a theory hierarchy approach 3 a non linear dynamic systems approach 4 a panarchy approach and 5 a hybrid approach there are no a priori bases for selection of any one of these approaches until further field research and modeling of sediment and solute fluxes has been completed

sediment connectivity in the high alpine valley of val muschauns swiss national park linking geomorphic field mapping with geomorphometric modelling abstract the efficiency of sediment routing through mountain sediment cascades is controlled by the connectivity of hillslopes to the main river system a lack of connectivity may cause long term sediment storage and exclude large fractions of a basin from the sediment routing for several thousand years here we studied sediment dynamics in a small formerly glaciated valley in the swiss alps to characterise the sediment connectivity to the stream we calculated a morphometric index using a gis algorithm the modelling results were tested against a field based geomorphic mapping of sediment storages which were evaluated with respect to their state of de coupling in accordance to the field diagnostics the modelling results indicate very well that the present day sediment flux is conditioned by the glacial valley morphometry inherited through pleistocene glaciation especially in the upper hanging valleys the connectivity index is reduced noticeably due to the glacial cirque morphology based on the field mapping 30 of the hillslope sediment cascades are interrupted and 20 of the storage boundaries are currently affected by a lack of material transfer as a consequence 29 of the basin surface is currently disconnected from the main river nevertheless the gis algorithm overestimates the connectivity within the basin because it fails to calculate decoupling between neighbouring pixels in digital terrain models dtms around 35 of the basin surface which has been mapped in the field as being decoupled is related to relative high connectivity our study highlights the potential of morphometric gis modelling for studying sediment connectivity but additionally emphasises the indispensability of geomorphic field mapping for a holistic understanding of mountain cascading systems

petrogenesis of rhyolites and trachytes from the deccan trap sr nd and pb isotope and trace element evidence trachytes and rhyolites from salsette island north of bombay have distinctive trace element and isotope features which mark them out from typical crustal melts their highly incompatible trace element and sr nd and pb isotope ratios are similar to those of the associated deccan flood basalts thus the rhyolites and trachytes are closely related to the basalts and a striking compositional gap between 50 and 65 sio2 suggests that the high sio2 rocks evolved by 10 15 partial melting followed by variable amounts of fractional crystallisation the source material could have been basalt within the deccan trap or related gabbroic rocks in deep crustal sill complexes the rhyolites yield an rb sr whole rock age of 61 5 1 9 ma with a slightly high initial 87sr 86sr 0 7085 18 it is argued that crustal extension provides a suitable regime for the generation of acid magmas by partial melting of associated basic rocks

origin of deccan trap lavas evidence from combined trace element and sr nd and pb isotope studies abstract geochemical and isotope results are presented from a new study of the most southern basalts in the deccan trap india three chemical formations are recognised two of which can be correlated with the established stratigraphy in mahabaleshwar and imply a regional southerly dip of 0 06 over a distance of 250 km in detail sr isotope variations within the ambenali and mahabaleshwar formations can be shown to reflect three distinct end members which provide new constraints for petrogenetic models pb isotope data for selected basalts exhibit a wide range with 206 pb 204 pb 16 87 22 45 and a linear correlation on a pb pb diagram the least contaminated ambenali basalts plot within the pb array and interaction with mantle lithosphere involves a shift to less radiogenic pb whereas contamination with crust is characterised by more radiogenic pb unlike the karoo and parana continental flood basalt provinces only four flow units within the southern deccan appear to contain a significant contribution from mantle lithosphere the mahabaleshwar and ambenali formation basalts exhibit a striking negative pb sr isotope trend which is presently regarded as one of the features of interaction with shallow level lithospheric mantle it further suggests that basalts from the walvis ridge kerguelen and ninetyeast ridge all remobilised such shallow level material and that the deccan basalts which were not affected by crustal contamination reflect interaction between asthenospheric material similar to t type morb but related to the reunion hotspot and continental mantle lithosphere of the indian plate

the interaction of plume heads with compositional discontinuities in the earth s mantle the effects of compositional discontinuities of density and viscosity in the earth s mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique three specific problems are considered 1 a plume head rising away from a deformable interface 2 a plume head passing through an interface and 3 a plume head approaching the surface of the earth for the case of a plume attached to a free surface the calculated time dependent plume shapes are compared with experimental results two principal modes of plume head deformation are observed plume head elongation or the formation of a cavity inside the plume head the inferred structure of mantle plumes namely a large plume head with a long tail is characteristic of plumes attached to their source region and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high to low viscosity region as a rising plume head approaches the upper mantle most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle if the plume head moves from a high to low viscosity region the plume head becomes significantly elongated and for the viscosity contrasts thought to exist in the earth could extend from the 670 km discontinuity to the surface plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry the dynamic surface topography induced by plume heads is bell shaped when the top of the plume head is at depths greater than about 0 1 plume head radii as the plume head approaches the surface and spreads the dynamic topography becomes plateau shaped the largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical and the surface expression of these stresses is likely to be dominated by radial extension as the plume spreads compressional stresses on the surface are produced beyond the edges of the plume consequently extensional features will be produced above the plume head and may be surrounded by a ring of compressional features

hotspots basalts and the evolution of the mantle the trace element concentration patterns of continental and ocean island basalts and of mid ocean ridge basalts are complementary the relative sizes of the source regions for these fundamentally different basalt types can be estimated from the trace element enrichment depletion patterns their combined volume occupies most of the mantle above the 670 kilometer discontinuity the source regions separated as a result of early mantle differentiation and crystal fractionation from the resulting melt the mid ocean ridge basalts source evolved from an eclogite cumulate that lost its late stage enriched fluids at various times to the shallower mantle and continental crust the mid ocean ridge basalts source is rich in garnet and clinopyroxene whereas the continental and ocean island basalt source is a garnet peridotite that has experienced secondary enrichment these relationships are consistent with the evolution of a terrestrial magma ocean

the age origin and tectonics of the grao para group and associated rocks serra dos carajas brazil archean continental volcanism and rifting the grao para group which is host to the large serra dos carajas fe deposits is located in the eastern part of the central brazil shield ssw of belem brazil it is composed of a lower sequence of metavolcanic rocks a middle sequence of iron formation carajas formation and an upper sequence of mixed metavolcanic and metasedimentary rocks the grao para group is overlain by an unnamed sedimentary dominantly sandstone unit and unconformably overlies the older xingu complex the lower metavolcanic sequence of the grao para in the region of the serra norte fe deposits is bimodal with dominant metabasalts metabasaltic andesites and metatrachyandesites and subordinate 10 15 metarhyolitic tuffs and flows most of the metavolcanic rocks are at low to medium metamorphic grade with more intense metamorphism and deformation along the northern contact with the xingu complex the thickness of the metavolcanic section is not known but may be 4 6 km the mafic metavolcanic rocks are enriched in rb ba and k with respect to oceanic basalts and basalts of greenstone belts and are relatively depleted in th sr ta ti and p the mafic rocks also show an enrichment in lrees with flat hree patterns the hrees are correlated with mg number u pb zircon analyses of the metarhyolites from the grao para group yield an age of 2758 39 ma rb sr wholerock analyses of the mafic rocks yield an isochron with an age of 2687 54 ma with an initial ratio of 0 7057 0 0010 the results indicate a late archean age of volcanism in the grao para group much older than previously thought rb sr results from the metarhyolites have been partially reset yielding an age 2497 62 ma sm nd analyses from the grao para metavolcanic rocks were too scattered to yield an isochron but nd values relative to chur at 2758 ma indicate values similar to depleted mantle at this time although with some scatter the trace element data and the sr and nd isotopic results from the mafic rocks are consistent with contamination of mantle derived melts by significant but variable amounts of diverse older continental crust the stratigraphy geochemical and isotopic compositions show that the grao para group originated on extending older continental crust during the archean an age terrane boundary must exist between this archean continental terrane and the apparently ensimatic early proterozoic greenstone belts of the northern amazonian craton similarities to other sequences e g the fortescue group australia suggest that similar tectonic settings were widespread at this time many major iron formations were deposited within these environments indicating significant iron formation development on sialic crust in the late archean u ph zircon analyses from the serra dos carajas granite which intrudes the unnamed sedimentary unit overlying the grao para group yield an age of 1820 49 ma in agreement with previous age determinations this age is similar to the ages for the uatuma supergroup volcanic and shallow plutonic rocks which occur throughout the amazonian craton

causal loop analysis of coastal geomorphological systems as geomorphologists embrace ever more sophisticated theoretical frameworks that shift from simple notions of evolution towards single steady equilibria to recognise the possibility of multiple response pathways and outcomes morphodynamic modellers are facing the problem of how to keep track of an ever greater number of system feedbacks within coastal geomorphology capturing these feedbacks is critically important especially as the focus of activity shifts from reductionist models founded on sediment transport fundamentals to more synthesist ones intended to resolve emergent behaviours at decadal to centennial scales this paper addresses the challenge of mapping the feedback structure of processes controlling geomorphic system behaviour with reference to illustrative applications of causal loop analysis at two study cases 1 the erosion accretion behaviour of graded mixed sediment beds and 2 the local alongshore sediment fluxes of sand rich shorelines these case study examples are chosen on account of their central role in the quantitative modelling of geomorphological futures and as they illustrate different types of causation causal loop diagrams a form of directed graph are used to distil the feedback structure to reveal in advance of more quantitative modelling multi response pathways and multiple outcomes in the case of graded sediment bed up to three different outcomes no response and two disequilibrium states can be derived from a simple qualitative stability analysis for the sand rich local shoreline behaviour case two fundamentally different responses of the shoreline diffusive and anti diffusive triggered by small changes of the shoreline cross shore position can be inferred purely through analysis of the causal pathways explicit depiction of feedback structure diagrams is beneficial when developing numerical models to explore coastal morphological futures by explicitly mapping the feedbacks included and neglected within a model the modeller can readily assess if critical feedback loops are included