experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

magmatic epidote and its petrologic significance epidote is a major magmatic mineral in tonalite and granodiorite in a belt coextensive with the mesozoic accreted terranes between northern california and southeastern alaska textural and chemical evidence indicates that epidote crystallized as a relatively late but magmatic mineral that formed through reaction with hornblende in the presence of a melt phase the observed relations concur with experimental data on crystallization of epidote from synthetic granodiorite at 8 kbar total pressure plutonic rocks bearing magmatic epidote must have formed under moderately high pressures corresponding to lower crustal depths under fairly oxidizing conditions

hydraulic geometry river sediment and the definition of bedrock channels a growing literature deals with bedrock channels erosion processes within them and their role in landscape evolution formal definitions currently in use classify channels as bedrock when alluvial cover is discontinuous or thin this is equated with a physical property of the flow using up to date erosion laws and descriptions of channel dynamics we show that existing definitions are difficult to apply and may lead to conflicting classifications we propose the definition a bedrock channel cannot substantially widen lower or shift its bed without eroding bedrock applied to channels in taiwan this leads to a different classification than previous definitions by analysing at a station hydraulic geometry of these channels we show that the classification exposes different controls of sediment effects on dynamics of channels classified as alluvial and bedrock

epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

geochronological and mineralogical constraints on depth of emplacement and ascencion rates of epidote bearing magmas from northeastern brazil calc alkalic to high k calc alkalic granitoid plutons in the borborema province northeastern brazil have been studied to constrain depth of emplacement by mineralogical and geological methods and to estimate upward magma transport rate based on partial dissolution of magmatic epidote laser probe incremental heating 40ar 39ar dating of biotite and hornblende single crystals from the neoproterozoic tavares and brejinho high k calc alkalic magmatic epidote mep bearing plutons reveals age differences of around 60 m y between these two minerals in each of these two intrusions these data suggest solidification at relatively great depth followed by prolonged cooling interval between the closure temperatures of biotite and hornblende al in hornblende barometry indicates that hornblende in several mep bearing plutons in the transversal domain of the borborema province solidified at 5 to 7 kbar whereas in the serido and macurure terranes solidification pressures range from 3 to 4 kbar partial dissolution of epidote indicates very rapid upward transport partial corrosion occurred during 15 35 years cachoerinha salgueiro terrane 10 30 years alto pajeu 15 years serido and 10 years macurure corresponding to upward transport rates of 450 1300 650 1050 1200 and 1800 m year respectively in these four terranes rapid upward magma migration in most cases was probably facilitated by diking simultaneous with regional shearing

constraints on the origin of archean trondhjemites based on phase relationships of nuk gneiss with h2o at 15 kbar we report the t x h2o phase relations for the trondhjemitic nuk gneiss which comprises the principal component of the second phase of archean 3 0 2 8 by igneous activity in the godthab region of southwestern greenland a pressure of 15 kbar was chosen to place constraints on possible protoliths for trondhjemitic melts at lower crustal depths under h2o saturated conditions a melting interval of 135 c separates the solidus at 610 c from the liquidus at 745 c h2o saturation at 15 kbar occurs at approximately 15 5 wt h2o the h2o undersaturated liquidus extends along a curved path from 745 c at 15 5 wt h2o to 1100 c at 2 h2o lower h2o contents were not investigated at low h2o contents 7 mafic residues consisting of some combination of hb ga ep and bi are possible and could correspond to amphibolitic source rocks at lower melt h2o contents 5 possible residues consist of na pl qz ga and could correspond to an earlier generation of tonalitic trondhjemitic rocks however such residues would not impart the highly fractionated ree patterns characteristic of archean trondhjemites if a first generation of tonalitic trondhjemitic melts was generated by higher pressure partial fusion of eclogite and emplaced at 55 km depth it would crystallize to an assemblage consisting almost entirely of na pl qz with highly fractionated ree patterns these rocks in turn could be partially melted to yield a second generation of trondhjemites which would inherit the highly fractionated ree patterns because neigher pl nor qz is capable of significantly fractionating hree from lree

measuring flow velocity and sediment transport with an acoustic doppler current profiler an acoustic doppler current profiler adcp measures three dimensional velocity profiles within the water column using the doppler shift principle whilst the bottom tracking function and acoustic backscatter can be used to measure bed load velocity and estimate suspended sediment concentration the adcp offers many advantages over traditional single point current meters and sediment samplers including deployment from a moving launch a single instrument for both velocity and sediment transport measurements profiles of three dimensional velocity and suspended sediment and the ability to map an entire flow field limitations of adcps include a large sampling diameter close to the bed coarse measurement of vertical velocity fragmented bottom track records a poor understanding of the relation between bottom tracking and the mechanisms of sediment transport and sensitivity of the acoustic backscatter to particle size

identifying environmental controls on the shoreline of a natural river delta river deltas form where sediment laden water debouches into a basin the spatial delineation of a delta is nontrivial and yet is fundamental to systematically evaluating fluxes across its surface here we study shoreline dynamics of the wax lake delta wld a naturally developing delta downstream of the atchafalaya river usa we demonstrate the ability to extract hydrodynamic and morphodynamic shorelines from time series of satellite imagery and topography data respectively the hydrodynamic shoreline corresponds to the traditional dry wet interface whereas we introduce the concept of a morphodynamic shoreline demarcating the topset foreset transition of a delta to quantitatively express the degree of inundation of a delta plain these shorelines enable us to assess environmental controls on inundation of the wld delta plain noting the abundance of satellite imagery whereas time series of bathymetric data from delta plains are scarce from the analysis of noaa and u s geological survey environmental data we identify the effects of river discharge tides wind and vegetation on shoreline position in particular using delft3d simulations and a simplified momentum balance we highlight the nonuniform and nonlinear effect of wind on delta plain inundation our analyses reveal that wind riverine discharge and tides significantly contribute to inundation of the wld and hence incorporating their interaction is essential to the accurate modeling of hydrodynamics and ecodynamics of the wld delta plain as well as to the dynamic shape of delta plains in general

a mechanistic model for river incision into bedrock by saltating bed load 1 abrasion by bed load is a ubiquitous and sometimes dominant erosional mechanism for fluvial incision into bedrock here we develop a model for bedrock abrasion by saltating bed load wherein the wear rate depends linearly on the flux of impact kinetic energy normal to the bed and on the fraction of the bed that is not armored by transient deposits of alluvium we assume that the extent of alluvial bed cover depends on the ratio of coarse sediment supply to bed load transport capacity particle impact velocity and impact frequency depend on saltation trajectories which can be predicted using empirical functions of excess shear stress the model predicts a nonlinear dependence of bedrock abrasion rate on both sediment supply and transport capacity maximum wear rates occur at moderate relative supply rates due to the tradeoff between the availability of abrasive tools and the partial alluviation of the bedrock bed maximum wear rates also occur at intermediate levels of excess shear stress due to the reduction in impact frequency as grain motion approaches the threshold of suspension measurements of bedrock wear in a laboratory abrasion mill agree well with model predictions and allow calibration of the one free model parameter which relates rock strength to rock resistance to abrasive wear the model results suggest that grain size and sediment supply are fundamental controls on bedrock incision rates not only by bed load abrasion but also by all other mechanisms that require bedrock to be exposed in the channel bed

hornblende geobarometry of the nelson batholith southeastern british columbia tectonic implications hornblende geobarometry has been applied to granitic rocks of the middle jurassic nelson batholith british columbia locally containing magmatic epidote geobarometry suggests equilibration pressu

tectonic evolution of the sergipano fold belt ne brazil during the brasiliano orogeny abstract the sergipano fold belt sfb represents the southern segment of a brasiliano age 600 ma continental collision zone which extends over ne brazil and continues into central africa as the north equatorial fold belt major sinistral transcurrent fault shear zones and thrusts separate domains with individual lithological tectonometamorphic and magmatic characteristics the principal steeply dipping strike slip zones trend east west to wnw ese lithological correlations across the shears have not proved possible which suggests that displacements were probably large but as yet are unquantified major folding and thrusting affected all the domains folds have a southerly vergence with nw se to wnw ese trends consistent with a ne sw to nne ssw shortening direction although small differences in shortening trends exist between individual domains the southernmost allochthonous domain of carbonate to clastic shelf slope sediments was subject to a single phase of folding and thrusting onto the sao francisco craton accompanied by greenschist facies metamorphism north of this domain lies the macurure domain which is separated from the southernmost allochthonous domain by the major sao miguel do aleixo transpressive shear zone polyphase deformation amphibolite facies metamorphism and massive granitic intrusion characterize this domain north of the macurure domain lie the migmatites and granites of the poco redondo domain which represent a deeper crustal level they are separated from the macurure domain by the belo monte shear a late tectonic leucogranite in the poco redondo domain yields a 600 ma rb sr isochron finally the poco redondo domain was overthrust from the north by the caninde gabbroic complex associated with carbonates pelites and amphibolites metamorphosed to greenschist and upper amphibolite facies this has previously been interpreted as an ophiolite sequence although the relative movements or absolute ages of the domains are unknown their distinct geological differences suggest that they are separate crustal blocks which underwent large lateral movement during the brasiliano collision

bulk rock and mineral chemistries and ascent rates of high k calc alkalic epidote bearing magmas northeastern brazil abstract a manifestation of the pan african brasiliano orogeny 700 550 ma in northeastern brazil was the emplacement of widespread neoproterozoic granitoids in diverse tectonic terranes among these plutons are the magmatic epidote bearing conceicao das creoulas caldeirao encantado murici and boqueirao plutons located close to the boundary between the alto pajeu and cachoeirinha salgueiro terranes the plutons are high k calc alkalic granodiorites to monzogranites with tabular k feldspar megacrysts pistacite atomic fe 3 fe 3 al in epidote in these granitoids ranges from 21 to 27 high oxygen fugacity log f o 2 19 to 13 and the preservation of epidote suggest that the magma was oxidized al in hornblende barometry indicates hornblende solidification between 6 and 8 kbar at 620 to 780 c according to the hornblende plagioclase thermometer zircon saturation thermometry attests to a near liquidus temperature range from 794 to 853 c partial corrosion of magmatic epidote in these four plutons occurred during an interval of no more than 10 30 years which corresponds to maximum magma ascent rates of 650 1000 m year diking associated with regional shearing probably facilitated rapid transport of granitic magma through hot continental crust at peak metamorphism and permitted survival of epidote that was out of equilibrium at the low pressure of final emplacement similarities between mineralogical composition chemistry and isotopic compositions end 0 60ga between 2 and 5 t dm from 1 2 to 1 3 ga 18 o values 10 v smow of these four plutons and neoproterozoic magmatic epidote bearing plutons elsewhere in northeastern brazil argue for similar metabasaltic mafic sources that had previously experienced low temperature alteration

contrasting sources and p t crystallization conditions of epidote bearing granitic rocks northeastern brazil o sr and nd isotopes abstract the 618 ma curral de cima tonalite and 577 ma lourenco monzodiorite northeastern brazil are magmatic epidote bearing plutons that carry ferrohornblende biotite titanite and epidote major trace and isotope chemistry suggests that the major magmas of the two plutons followed similar differentiation trends but derived from source rocks that differed in age and isotopic composition the mineral phases of the curral de cima tonalite the presence of amphibole rich clots and juvenile component average end 3 55 point to an i type source for these rocks these data and high calculated 18 o w r 10 0 for the tonalite and high 18 o value for a clot 9 3 argue that the clots are fragments of a metabasaltic source rock that has been hydrothermally altered at a low temperature in contrast average calculated 18 o w r for the lourenco monzodiorite 7 8 87 sr 86 sr 0 7083 end 14 6 and t dm 1 92 ga these data are compatible with a long crustal residence time of lower crust amphibolites source epidote in the curral de cima pluton crystallized close to the nno buffer and hornblende chemistry due to al reequilibration yielded sub solidus temperature and pressure in contrast in the lourenco pluton epidote crystallized close to the hm buffer and al in hornblende points to near solidus solidification 685 c around 4 4 kbar this study confirms that magmatic epidote in granitic plutons can crystallize at pressures lower than 5 5 kbar under higher f o 2 as experimentally foreseen rapid magma transportation through hot continental crust during the peak of metamorphism in early stages of an orogenic cycle prevents epidote dissolution

eastern mississippi delta late wisconsin unconformity overlying transgressive facies sea level and subsidence abstract analysis of 92 engineering core logs located in the balize sector of the eastern mississippi delta focuses on the late wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon this major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin observations emphasize lithofacies distributions of the latest pleistocene sediments underlying the unconformity the late pleistocene to early holocene transgressive facies and the immediately overlying deltaic deposits maps and a cross section compiled with this information highlight the critical relation between lithofacies distributions and late wisconsin sea level oscillations core analysis reveals that the transgressive facies comprises distinct environments of deposition offshore to onshore findings identify criteria to determine the approximate position of the shoreline at the late wisconsin maximum sea level lowstand and at the extent of early holocene maximum marine inundation in the balize complex mapping of lithologies along the late wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high resolution seismic profiles an estimate of long term averaged land subsidence suggests lowering of at least 1 mm year near the shelfedge during the past 18 000 years this mapping also refines sea level response models for the mississippi delta including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other recent marine deltas and in older stacked deltaic sequences

autogenic erosional surfaces in fluvio deltaic stratigraphy from floods avulsions and backwater hydrodynamics erosional surfaces set the architecture of fluvio deltaic stratigraphy and they have classically been interpreted in terms of changes in boundary conditions such as climate tectonics and base level allogenic forces intrinsic dynamics of sedimentary systems autogenic dynamics can also create a rich stratigraphic architecture and a major knowledge gap exists in parsing the relative roles of autogenic versus allogenic processes emerging theoretical and experimental work suggests that backwater hydrodynamics play an important role in driving transient channel incision in river deltas even those experiencing net aggradation here we identify and quantify two autogenic mechanisms that produce broad erosional surfaces in fluvio deltaic stratigraphy namely floods and avulsions using a simple mass balance model for single threaded delta channel systems we show that flood induced scours begin near the shoreline and avulsion induced scours begin at the avulsion site and both propagate upstream over a distance that scales with the backwater length bed slope and bed grain size we also develop scaling relationships for the maximum scour depths arising from these mechanisms which are functions of characteristic flow depth and formative flood variability we test our theoretical predictions using a flume experiment of river delta evolution governed by persistent backwater hydrodynamics under constant relative sea level results indicate that autogenic dynamics of backwater mediated deltas under conditions of constant base level can result in stratigraphic surfaces and shoreline trajectories similar to those often interpreted to represent multiple sea level cycles our work provides a quantitative framework to decouple autogenic and allogenic controls on erosional surfaces preserved in fluvio deltaic stratigraphy

mineralogy geochemistry and petrology of neoarchean ferroan to magnesian granites of carajas province amazonian craton the origin of hydrated granites associated with charnockites abstract 2 75 to 2 73 ga old granitic intrusions associated with coeval charnockitic rocks were emplaced in the northern domains of the carajas province the vila jussara suite was recognized recently and its geologic mineralogical and geochemical characteristics are presented in this paper and compared with the data available in the literature on the estrela complex serra do rabo and igarape gelado granites and planalto suite monzogranites and syenogranites are dominant in most units but in the igarape gelado granite and vila jussara suite granodiorites and tonalites are also relatively abundant the main mafic phases in all these granitoids are amphibole potassian hastingsite with subordinate magnesiohastingsite 0 95 fe fe mg 0 47 and biotite 0 88 fe fe mg 0 52 with rare occurrence of clinopyroxene relict crystals magmatic epidote of pistacite component from 26 to 31 occurs only in the vila jussara suite the rocks of estrela serra do rabo and planalto units contain only ilmenite generally with coronas of titanite or ilmenite associated with magnetite and are essentially reduced ferroan granites whole rock feot feot mgo 0 89 that evolved at low f o 2 fmq 0 5 the igarape gelado granite needs additional studies but it is formed apparently by reduced ferroan and oxidized ferroan granites the vila jussara suite is also composed of reduced ferroan granites that are similar to those of the other granite units however it has additionally oxidized ferroan and magnesian granitoids which contain magnetite ilmenite as the main fe ti oxide phase and evolved respectively at moderate f o 2 nno 0 5 and at comparatively higher f o 2 nno to nno 1 the magmas of these granites were formed at temperatures 900 c and derived from a heterogeneous dominantly reduced and tholeiitic granulitic crust locally varying to oxidized and calc alkaline in composition plagioclase orthopyroxene clinopyroxene and fe ti oxides were the main phases in the melt residues and the liquids were enriched in ba zr y and ree except for eu but not in sr compared to their sources the magmas should have relatively high water content 4 wt the magmatic evolution was strongly influenced by partial melting processes the different varieties of the vila jussara suite are not linked by fractional crystallization and derived from distinct magmas the neoarchean granites of the carajas province were emplaced in a collisional tectonic setting they are syntectonic granites that were deformed and sometimes intensely recrystallized during their emplacement and subsequent subsolidus cooling the magmas were generated in the crust at pressures of 800 to 1000 mpa and emplaced at pressures of 200 to 500 mpa the studied granitoids are similar geochemically to the ferroan and magnesian groups of charnockites the magnesian variety of the vila jussara suite is similar to the pyroxene free granitoids of the neoarchean matok pluton of the collisional limpopo belt the neoarchean granites of carajas are hydrated granites emplaced at comparatively higher crustal levels when compared with the matok pluton

zircon dating and mineralogy of the mokong pan african magmatic epidote bearing granite north cameroon we present the mineralogy and age of the magmatic epidote bearing granite composing most of the mokong pluton in the central africa orogenic belt north cameroon this pluton intrudes neoproterozoic 830 to 700 ma low to high grade schists and gneisses poli maroua group and is crosscut or interleaved with bodies of biotite granite of various sizes the pluton is weakly deformed in its interior but solid state deformation increases toward its margins marked by narrow mylonitic bands trending nne ssw the magmatic epidote granitic rocks are classified as quartz monzodiorite granodiorite monzogranite and syenogranite they are medium to coarse grained and composed of k feldspar plagioclase biotite amphibole epidote magnetite titanite zircon apatite in these granites the pistacite component atomic fe 3 fe3 al in epidote ranges from 16 to 29 high oxygen fugacity log o2 14 to 11 and the preservation of epidote suggest that the magma was oxidized al in hornblende barometry and hornblende plagioclase thermometry indicate hornblende crystallization between 0 53 and 0 78 gpa at a temperature ranging from 633 to 779 c zircon saturation thermometry gives temperature estimates ranging from 504 to 916 c the latter being obtained on samples containing inherited zircons u pb geochronology by la icp ms on zircon grains characterized by magmatic zoning yields a concordia age of 668 11 ma 2 the mokong granite is the only known occurrence magmatic epidote in cameroon and is an important milestone for the comparison of the central africa orogenic belt with the brasiliano fold belt where such granites are much more abundant

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

emplacement petrological and magnetic susceptibility characteristics of diverse magmatic epidote bearing granitoid rocks in brazil argentina and chile abstract magmatic epidote mep bearing granitoids from five neoproterozoic tectonostratigraphic terranes in northeastern ne brazil early palaeozoic calc alkalic granitoids in northwestern nw argentina and from three batholiths in chile have been studied the elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was probably the major mechanism of emplacement textures reveal that in many cases epidote underwent partial dissolution by host magma and in these cases may have survived dissolution by relatively rapid upward transport by the host magma in plutons where such a mechanism is not evident unevenly distributed epidote at outcrop scale is armoured by biotite or near solidus k feldspar aggregates which probably grew much faster than epidote dissolution preventing complete resorption of epidote by the melt al in hornblende barometry indicates that in most cases amphibole crystallized at p 5 kbar kyanite bearing thermal aureoles surrounding plutons that intruded low grade metamorphic rocks in ne brazil support pluton emplacement at intermediate to high pressure mep show overall chemical variation from 20 to 30 mol mole percent pistacite ps and can be grouped into two compositional ranges ps20 24 and ps27 30 the highest ps contents are in epidotes of plutons in which hornblende solidified under p 3 0 10 3 si typical of magnetite series granitoids crystallized under higher oxygen fugacity in ne brazil argentina and chile it seems that mep is more common in precambrian to palaeozoic ilmenite series granitoids while its occurrence in magnetite series granitoids is more restricted to mesozoic to tertiary granitoids

the unregenerate sao rafael pluton borborema province northeastern brazil abstract the late neoproterozoic sao rafael pluton located in the serido belt of the borborema geologic province northeastern brazil is an unfoliated metaluminous epidote bearing high k calc alkalic granitoid three facies are present in its northern lobe i a dominant massive granite to quartz monzonite porphyritic facies containing microcline phenocrysts ii subordinate fine grained facies similar to the porphyritic facies except lacking amphibole that crop out as inselbergs serras and iii rare pillows of microgranular mafic enclaves mmes that are present within the porphyritic facies chemical analyses include 19 bulk rock data and 33 microprobe data of epidote and amphibole beginning with bulk chemistry and postulated mineral compositions an iterative procedure of solving matrices characterizes a rock sample derived information includes i identifying what minerals are present ii their relative abundances and iii their chemical compositions even for minerals such as biotite or amphibole with complexly variable compositions calculated mineral compositions are compatible with microprobe data the matrix solutions further indicate alternative mineral assemblages and the compositions of phantom minerals that could have existed in the magma source although absent in the pluton they establish that olivine but not clinopyroxene was a possible phantom mineral and that mmes are of unrelated magmatic origin according to matrix analysis amphibole in an outer zone of the porphyritic facies is solely of neoformed origin whereas amphibole in an inner zone of the porphyritic facies is of mixed origin partly neoformed and partly residual i e xenocrystic patchy amphibole derived from mmes a qualified geothermometer provides tsolidus 730 6 c for the outer subfacies and a qualified geobarometer provides p 0 78 0 06 kbar amphibole in mmes crystallized at depth at p 3 3 kbar corroded epidote attests to the pressure sensitive instability of that mineral during rapid ascent decompression cathodoluminescence reveals complexly structured zircons with magmatic overgrowths and inherited cores 207pb 206pb ages of inherited components cluster at 2 0 ga and 2 4 ga these ages being prominent in the local basement oscillatory zoned magmatic components yield a concordia upper intercept age of 580 9 ma interpreted as the age of igneous crystallization values of 18o in zircon are only slightly higher than 18o in mantle like zircon at 0 58 ga ehf in magmatic zircon was notably unradiogenic 22 to 26 indicating a magma source in old continental crust as adduced by ages of inherited zircon a u pb titanite date is around 0 55 ga for the rb sr and sm nd whole rock systems isotopic inheritance from the magma protolith is so extreme and variable that isochrons are actually scatterchrons that provide no useable age information rb sr cooling ages of biotite are 498 1 ma most sm nd depleted mantle ages lie in the range of 2 6 0 13 ga sao rafael magma was unregenerate not isotopically homogenized when emplaced

current subsidence rates due to compaction of holocene sediments in southern louisiana 1 relative contributions of geologic and anthropogenic processes to subsidence of southern louisiana are vigorously debated of these shallow sediment compaction is often considered dominant although this has never been directly observed or effectively demonstrated quantitative understanding of subsidence is important for predicting relative sea level rise storm surge flooding due to hurricanes and for successful wetland restoration despite many shallow borings few appropriate stratigraphic and geotechnical data are available for site specific calculations we overcome this by determining present compaction rates from monte carlo simulations of the incremental sedimentation and compaction of stratigraphies typical of the holocene of southern louisiana this approach generates distributions of present compaction rates that are not expected to exceed 5 mm yr but may locally locations with present subsidence rates greater than the predicted maximum probable shallow compaction rates are likely influenced by additional processes

epidote phenocrysts in dacitic dikes boulder county colorado epidote ps21 crystallized early as elongate phenocrysts in late cretaceous rhyodacitic dikes in the vicinity of ward boulder county colorado other unusual phenocryst phases are garnet gr17 24 and muscovite in a xenolith containing kyanite corundum biotite and plagioclase magmatic garnet grew as a rim around xenocrystic pyrope rich py37 garnet the xenolith was derived from a granulite facies zone not represented at the present day erosion surface which is composed of upper amphibolite facies cordierite and sillimanite bearing gneisses the dike magmas were fed not from an immediately underlying batholith but from a magma chamber at a depth corresponding to a pressure of 8 13 kilobars phenocrysts cystallized in the temperature range 800 to 700 c under h2o and o2 activities greater than normal for silicic magmas this occurrence shows convincingly not only that epidote can be magmatic but that it is a possible early crystallization phase in silicic magmas

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

pluton accommodation at high strain rates in the upper continental crust the example of the central extremadura batholith spain abstract emplacement in the tensional bridge of a stepped dextral shear zone system is proposed for the central extremadura batholith spain the country rocks show a pervasive anisotropy that conditioned the style of the structures developed as a consequence of the transference of displacement from the stepped shear zones to the releasing area the kinematic evolution of the resulting megakink fold provided the volume increase necessary for the granite emplacement thermal and kinematic models suggest that the growth of individual plutons took place in periods of no more than several hundred to a few thousand years fast strain rates 10 10 10 11 s 1 must concentrate in local structures e g initiation of kink folds even in zones deforming as a whole under typical strain rates 10 14 1 s 1 granite plutons might be used as strain rate gauges for syn plutonic structures

origin of miarolitic pegmatites in the konigshain granite lusatia abstract in this study we examine an interesting occurrence of miarolitic pegmatites in the konigshain granite of the lusatia region of the bohemian massif this granite is characterized by the extensive development of micro sized miarolitic pegmatites typically with diameters of 5 to 15 mm irregularly distributed through its upper levels and larger miarolitic pegmatites up to 1 m in the uppermost levels this granite also shows evidence of varied forms of transport of extremely volatile rich residual melts fluids in the form of more or less discrete inter granular melt bodies and associated magmatic quartz veins formed in tectonic fissures together these provide evidence for the origin of miarolitic pegmatites both in the specific case of konigshain and more generally our evidence suggests that miarolitic pegmatites form from volatile and alkali rich residual melts ranging from 10 to 50 h 2 o far more than typical granitic melts but far more silicate components than aqueous fluids or vapor suggested by some authors using melt inclusions in quartz from the aplitic and graphic granite zones in miarolitic pegmatites in the konigshain granite we show that two different inclusion populations are present we provide evidence that the first inclusion population are those related to the primary granite at the level of intrusion and the second were trapped during the re crystallization of the granite wall rocks by silicate rich supercritical fluids moving through the solid crystal framework with a porosity 0 see clarke et al 2013 our results show that a significant volume fraction of the miarolitic pegmatites was not created by a pegmatite forming fluid but formed in situ by re crystallization of wall rocks triggered by highly reactive volatiles exsolved from the pegmatite forming melts evidence is also presented which suggests the nature and speed of emplacement of the konigshain granite this evidence may explain the unusual form and abundance of miarolitic pegmatites in the studied area and may have application to similar occurrences thus there is a mixture of features which are applicable to miarolitic pegmatites in general and others which help separate the overriding processes from the variations produced by local or regional chemical or tectonic characteristics

experimental constraints on bar migration through bends implications for meander wavelength selection the bed of an initially straight channel often deforms into a series of migrating alternate bars that can cause bank erosion and the development of periodic planform curvature which is often expressed as a meandering channel trace the planform curvature in turn leads to topography similar to alternate bars but stationary with respect to the meander the migration of alternate bars over this steady topography may lead to interactions influencing meander initiation and wavelength selection we studied these interactions in flume channels with bends of various lengths and angles and having various width to depth ratios in channels whose wavelength was equal to the length of bars in straight channels nearly eight channel widths bars migrated through sine generated channels with angles up to 10 the critical bend angle was smaller for channels of longer wavelength and smaller width to depth ratio migration was nonuniform and bars temporarily stalled when in phase with the curvature induced topography leading to amplification of the topography flow against an opposing bank can lead to such a strong boundary shear stress divergence that migration of the bars is prevented because sediment that otherwise would have led to bar migration is scoured from the bar front we propose that the amplification of bar pool topography in bends where free alternate bars are stalled enhances scour of the bank which leads to selection of a meander wavelength equal to that of the alternate bars

magma flow within the tavares pluton northeastern brazil compositional and thermal convection crystallization coupled with gravity removal of depleted interstitial melt has long been recognized as a mechanism of magma differentiation similarly heat released by synplutonic basaltic magma intrusions has long been recognized as capable of driving convection in granite chambers direct evidence of these processes has seldom been described in granites in the tavares pluton we mapped a number of melt extraction structures from pores of a crystal liquid mush an effectively solid magma where crystals form an interconnected skeleton and a variety of flow structures such as 1 meter scale tear or mushroom shaped blobs representing within chamber diapirs 2 meter scale ellipsoids representing frozen thermal plumes of granite driven by heat released from disrupted diorite intrusions and 3 ladder dikes and snail structures representing cross sections of several superposed cylindrical magma channels possibly feeders of diapirs and plume heads a fundamental feature of the structures in the tavares pluton is that they are well delineated by mafic schlieren developed at active channel margins we postulate a new model for the origin of marginal schlieren which combines shear flow sorting and melt escape from the flowing magma into an effectively solid surrounding mush extraction structures representing melt extraction from mush pores into melt pockets and schlieren representing regions where melt escaped into surrounding mush pores are both favored by magmas that form an interconnected solid framework at low crystal fractions 50 because these mushes are ductile and permeable favorable magmas are those with a high wetting angle between melt and solid 60 and a propitious crystal size and shape distribution we propose a model of compositional and thermal convection that accounts for all described structures

a 20th century acceleration in global sea level rise 1 multi century sea level records and climate models indicate an acceleration of sea level rise but no 20th century acceleration has previously been detected a reconstruction of global sea level using tide gauge data from 1950 to 2000 indicates a larger rate of rise after 1993 and other periods of rapid sea level rise but no significant acceleration over this period here we extend the reconstruction of global mean sea level back to 1870 and find a sea level rise from january 1870 to december 2004 of 195 mm a 20th century rate of sea level rise of 1 7 0 3 mm yr 1 and a significant acceleration of sea level rise of 0 013 0 006 mm yr 2 this acceleration is an important confirmation of climate change simulations which show an acceleration not previously observed if this acceleration remained constant then the 1990 to 2100 rise would range from 280 to 340 mm consistent with projections in the ipcc tar

mississippi delta subsidence primarily caused by compaction of holocene strata coastal subsidence causes sea level rise shoreline erosion and wetland loss which poses a threat to coastal populations this is especially evident in the mississippi delta in the southern united states which was devastated by hurricane katrina in 2005 the loss of protective wetlands is considered a critical factor in the extensive flood damage the causes of subsidence in coastal louisiana attributed to factors as diverse as shallow compaction and deep crustal processes remain controversial current estimates of subsidence rates vary by several orders of magnitude here we use a series of radiocarbon dated sediment cores from the mississippi delta to analyse late holocene deposits and assess compaction rates we find that millennial scale compaction rates primarily associated with peat can reach 5mm per year values that exceed recent model predictions locally and on timescales of decades to centuries rates are likely to be 10 mm or more per year we conclude that compaction of holocene strata contributes significantly to the exceptionally high rates of relative sea level rise and coastal wetland loss in the mississippi delta and is likely to cause subsidence in other organic rich and often densely populated coastal plains

bedform transport rates for the lowermost mississippi river 1 new methods of data collection and processing are developed to provide quantitative reach scale measurements of bedform transport mass within the tidally influenced mississippi river a multibeam swath profiler was used to collect daily bathymetry over a range of water discharges and bed elevation changes induced by dune migration are measured these values are coupled with bulk physical properties of the bed sediment to constrain mass flux and annual bedform transport is estimated at 2 2 x 10 6 metric tons mt the total annual sand flux from the mississippi river calculated by combining measured bedform transport rates and suspended sediment flux is estimated to be 20 x 10 6 mt survey data also provide information about the spatial distribution of dunes across the channel bottom straight reach segments are commonly mantled by dunes for the entire cross section while bends are typically areas of focused scour devoid of bedforms presumably any sediments associated with migrating dunes are propelled into suspension within bends before redepositing in the subsequent straight reach movement via suspension is therefore an important component for the downriver transport of bed materials in the lower mississippi river

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

constraints on rates of granitic magma transport from epidote dissolution kinetics epidote is stable only at high pressure in granitic magmas but is found in magmas crystallized at shallow crustal levels this observation suggests qualitatively that magma transport is sufficiently rapid to prevent complete epidote resorption experimental measurements of epidote dissolution showed that the presence of epidote implies that magma transport from the deep crust in these systems was rapid and that the transport was by dikes rather than diapirs

the arsikere granite of southern india magmatism and metamorphism in a previously depleted crust abstract the arsikere granite is a small diapiric potassic pluton intruded into archean gneisses of the western part of the dharwar craton of southern india a rb sr age of 2563 ma indicates that the granite was formed during a period of granulite development at lower crustal levels at least to the south of the dharwar craton schist belts in the craton were metamorphosed to greenschist or amphibolite facies at this time but gneisses underwent no isotopic or other geochemical effects the arsikere granite contains quartz oligoclase highly perthitic alkali feldspar originally precipitated as a single phase f rich biotite plus primary epidote fluorite and f rich muscovite sphene forms large euhedrons which incorporate nearly all of the ti in the rock leaving pure magnetite as the only opaque phase equilibration parameters include temperatures of 700 from feldspars f o 2 10 12 bar biotite and opaques and f oh 10 3 biotite nearby schist belts were metamorphosed at 5 kbar pressure at the same time as granite emplacement if the granite was emplaced at 5 kbar the magma could not have been water saturated perthite an initial 87 sr 86 sr ratio of 0 7021 in the arsikere granite is too low for the magma to have formed by partial melting of rocks with the rb sr ratios of gneisses currently exposed in the craton apparently the magma formed in a lower crust that had been depleted in rb and probably other lithophilic elements several hundred million years earlier at this time the craton also became water poor and inert to further geochemical activity such as resetting isochrons during later metamorphism

a calculated petrogenetic grid for the system k2o feo mgo al2o3 sio2 h2o with particular reference to contact metamorphosed pelites a petrogenetic grid is presented for the system kfmash k o feo mgo a1 0 sio h o including biotite muscovite k feldspar chlorite chloritoid staurolite cordierite garnet ortho amphibole orthopyroxene spinel andalusite sillimanite kyanite quartz and corundum with h o in excess which was calculated using the computer program thermocalc and the powell and holland internally consistent thermodynamic dataset by removing the normal constraint of having quartz in excess both quartz bearing and quartz absent equilibria are shown quartz absent equilibria are particularly relevant at high t and low p conditions because of their common occurrence at these conditions the calculated mineral assemblage and mineral compositional variations in terms of femg and fe mg siall exchange vectors are broadly compatible with observations on natural rocks particularly when non kfmash components are taken into account

mineralogy and geothermobarometry of magmatic epidote bearing dikes front range colorado epidote phenocrysts ps 19 24 in laramide age porphyritic dacite dikes in the front range of colorado prove that epidote can crystallize directly from a magma the dikes are high k calc alkaline dacites and rhyodacites sio 2 64 70 phenocryst assemblages consist of combinations of epidote plagioclase an 53 19 biotite fe 3 fe total 0 25 mg mg fe 2 0 42 0 55 quartz aluminous amphibole al total 2 4 3 0 per formula unit igneous garnet and 2 6 gros 13 27 spess 2 13 pyr 7 26 alm 51 60 igneous muscovite and sanidine holocrystalline aphanitic groundmasses consisting mainly of quartz plagioclase and alkali feldspar comprise 60 75 of the dike rocks and require that epidote grew early in the crystallization sequence petrographic and microprobe data distinguish three types of magmatic epidote phenocrysts with different petrogenetic connotations implied by each type type i epidote occurs as euhedral phenocrysts up to 8 mm long with low content of allanite component thermobarometric calculations provide empirical evidence that epidote is stable in silicic calc alkaline magmas at high total pressure high water content and high oxygen fugacity the dacitic magmas originated by partial melting at temperatures above 800 c temperatures 50 c ranged from 800 to 880 c during early phenocryst growth down to 620 to 670 c during groundmass crystallization phenocrysts formed at pressures between 7 2 1 0 and 12 2 0 kbar oxygen fugacity was within the magnetite stability field at two log units 1 0 below the hematite magnetite buffer h 2 o fugacity calculations give values ranging from 3 4 to 16 kbar depending on how annite activity in biotite is modeled the occurrences of types i and iii epidote combined with geobarometry give a minimum pressure of epidote stability in the dike magmas of 8 0 1 0 kbar these results agree with experimental evidence and with conditions inferred for the crystallization of magmatic epidote in large cordilleran plutons phenocrysts in the dikes were preserved in conditions outside their stability limits by rapid emplacement and quenching in shallow level dikes

channel dynamics sediment transport and the slope of alluvial fans experimental study a b s t ra c t we present the results of an experimental study of alluvial fan sedimentation under conditions of constant inflow water discharge qw sediment supply qso and median grain size d the study was designed to complement and test a recently formulated model of alluvial fan sedimentation and to emphasize the interactions between and controls on flow channelization and equilibrium fan slope flow channelization and fan sedimentation were studied under conditions of nearly steady uniform aggradation steady conditions were achieved by imposing a steadily rising base level just in balance with the average sediment aggradation rate experimental inflows covered a wide range of conditions allowing examination of the effects of variations in qw q so and d in both bedload and suspension dominated environments experimental results were most consistent with an expanding flow channel model key experimental findings successfully and quantitatively predicted by the expanding flow theory include 1 straight to slightly concave radial profiles of bedload dominated fans 2 distinctly convexo concave profiles of suspension dominated fans 3 a strong inverse relationship between qw and fan slope 4 a strong but secondary relationship between q so and fan slope and 5 near independence of d and fan slope so long as transport stage is high and bedload transport dominant however potential scale effects in the experiments arose from reduced flow reynolds numbers and incorrect geometric scaling of channel widths no confident conclusions regarding the debate over the relative importance of sheetfloods and braided channel flows can be drawn from the experimental data extrapolation to field scale is best accomplished through appropriate application of the theoretical model herein confirmed against experimental data

sand as a stable and sustainable resource for nourishing the mississippi river delta dams have starved the lower mississippi river of sediment over recent decades suggesting that the drowning of the delta is inevitable analysis of the rivers suspended sediment load and morphodynamic modelling suggest that the amount of sand essential for land building has not significantly decreased since dam construction with sand remaining available for several centuries

age origin and cooling history of the coronel joao sa pluton bahia brazil received april 2 2002 accepted august 8 2004advance access publication october 22 2004in north east brazil archean and paleoproterozoic cratonic blocksare enclosed within a network of brasiliano age 0 7 0 55ga metasedimentary foldbelts the unfoliated coronel joa o sa grano diorite pluton which contains magmatic epidote and stronglyresorbed clinopyroxene intrudes the sergipano foldbelt zirconsyield a concordant u pb crystallization age of 625 2ma titanite ages are approximately 621ma discordant zircons suggestinheritance from at least two magma sources of ages 2 2ga model calculations based on diffusion parameters andrb sr isotope data from separated minerals indicate that the plutoncooled ata rate of 36 c myr whole rock element compositionsandinitialsr ndisotopic compositionsthat areheterogeneous onalllength scales suggest magma mixing trace element concentrationsand nd isotope data argue against a contribution from a contem poraneous mantle derived magma values of magmatic e

geomorphological explanation of the long profile of the lower mississippi river abstract concavity in the long profile of rivers has traditionally been explained through the concept of grade in which the slope declines downstream as a response to changing discharge bed material size and sediment transport applying this concept to particular river systems has however proved problematic the long profile reflects spatially distributed form process feedbacks between all aspects of channel morphology operating at a range of poorly defined time and space scales and in the presence of natural controls in many river systems process form dynamics are further complicated by engineering interventions which add additional extrinsic controls and constrain the range of intrinsic dynamics in this paper the 1974 75 long profile of the lower mississippi river is examined at three scales the regional the reach and the sub reach pool crossing scales a combination of curve fitting zonation algorithms and empirical classification techniques are used to show that although the long profile of the lower mississippi river is concave at the largest scale the profile is characterised by discontinuities shorter trends and zonal variations in the amplitude and wavelength of pool crossing morphology these characteristics are a response to morphological and bed material changes relating to a range of physical geological tectonic tributary input and engineering controls despite its apparent simplicity and correspondence to a graded condition the long profile of the lower mississippi river is actually a complex and scale dependent morphological property at best the concave river profile is therefore a property which emerges from several scales of process form interaction at worst it is no more than an artefact arising from the application of over simplified curve fitting techniques disclosure of the nature of the long profile thus requires the application of a variety of analytical techniques as well as geomorphological explanations which are themselves scale dependent and which consider the interaction of natural processes and the history of engineering intervention

the response of subaqueous dunes to floods in sand and gravel bed reaches of the dutch rhine the branches of the river rhine in the netherlands characterized by a sand gravel bed in the upstream part and a sand bed in the downstream part of the river system show migrating dunes especially during floods in the last 20 years these dunes have been studied extensively high resolution echo sounding measurements of these dunes made with single and multibeam equipment were analysed for three different sections of the rhine river system during several floods this analysis was done to quantify the growth decay and migration rates of the dunes during floods in addition the migrating dunes were used to calculate bedload transport rates with dune tracking the results of dune growth and decay and migration rate are shown to be very different for the various sections during the various floods and these differences are related to differences in grain size of the bed and to differences in the distribution of discharge over the main channel and the floodplain the relations are used to show that the growth and migration rate of dunes and the calculated bedload transport rates during the rising stage of a flood wave can be predicted from the mobility of the bed material with simple power relations

estuarine controls on fine grained sediment storage in the lower mississippi and atchafalaya rivers observations of the lower mississippi river channel in 1999 2003 with side scan and subbottom seismic profilers multibeam bathymetry core radiotracers 7be 137cs 210pb and 234th and water column profiles of fluid and suspended sediment properties are utilized to constrain the timing location and intensity of the seasonal storage of fine grained sediments in the estuarine channel reach below venice louisiana unlike earlier studies that suggested little or no estuarine sedimentation was taking place in the river the present study demonstrates that the river channel above the head of passes seasonally stores as much as 10 of the annual suspended sediment discharge during periods of falling to low mississippi water discharge associated with salt stratification in the channel thalweg mud deposits are up to 3 2 m thick with 7be derived sediment deposition rates of up to 8 9 mm day water column profiling and 234th 7be ratios suggest that 1 particles are transported and settled mainly as flocs and 2 riverine flocs are settling through the strong salt wedge halocline and are protected from re erosion by the salt stratification with onset of the spring freshet and the corresponding seaward retreat of the saltwater wedge the entire volume of fine grained material stored in the lower river except in low freshet years is remobilized and transported to the gulf of mexico in the turbid freshwater plume this tidal hysteresis strongly influences the timing of sediment supply to the ocean high turbidities in the shelf plume during rising water discharge spikes of 1 to 2 week duration are the product of local channel floor remobilization as well as increased supply from the drainage basin pulsed resupply of sediments and the pore water products of early diagenesis potentially have major implications for issues such as continental margin carbon budgets and coastal eutrophication companion surveys conducted in the lowermost 12 km reach of the atchafalaya distributary of the mississippi show no evidence of saltwater wedge intrusion at low discharge or seasonal fine grained sediment storage likely due to the shallow 7 m river mouth sill that impedes the upstream movement of gulf water

dike transport of granitoid magmas thermal and fluid dynamical analyses suggest that for viscosities and density contrasts spanning the range considered typical for many calc alkalic granitoids dike ascent is a viable mechanism for the transport of large volumes of granitoid melt through the continental crust we present calculations showing that a granitoid melt with calculated viscosity of the order of 10 6 pa s and a density contrast between magma and crust of 200 kg m 3 can be transported 30 km through the crust in 1 month corresponding to a mean ascent velocity of 1 cm s using analysis modified from numerical studies of the flow of basaltic magmas in dikes we also present an expression that allows the calculation of the critical minimum dike or fault width required for granitic magma to ascend without freezing for all reasonable estimates of cordilleran granitoid viscosity and density contrast the critical dike width is determined to be between 2 and 7 m calculated peak batholith filling rates are orders of magnitude greater than mean cavity opening rates based on estimated fault slippage which is consistent with chemical evidence for intermittent supply of magma pulses

groundwater flow to a well in a layered porous medium 1 steady flow analytical solutions of steady multiple aquifer problems usually assume the flow of groundwater to be essentially horizontal in aquifers and vertical in aquitards these assumptions yield formulae that are economical to evaluate the simplifications however ask for a theoretical check this paper is dealing with the derivation of an analytical formula that may serve as such it considers steady flow of groundwater to a partially screened well in a layered porous medium both horizontal and vertical flow components are taken into account