mafic and felsic magma interaction in granites the hercynian karkonosze pluton sudetes bohemian massif the hercynian post collisional karkonosze pluton contains several lithologies equigranular and porphyritic granites hybrid quartz diorites and granodiorites microgranular magmatic enclaves and composite and lamprophyre dykes field relationships mineralogy and majorand trace element geochemistry show that 1 the equigranular granite is differentiated and evolved by small degrees of fractional crystallization and that it is free of contamination by mafic magma 2 all other components are affected by mixing the end members of the mixing process were a porphyritic granite and a mafic lamprophyre the degree of mixing varied widely depending on both place and time all of the processes involved are assessed quantitatively with the following conclusions most of the pluton was affected by mixing implying that huge volumes 475 km of mafic magma were available this mafic magma probably supplied the additional heat necessary to initiate crustal melting part of this heat could have also been released as latent heat of crystallization only a very small part of the karkonosze granite escaped interaction with mafic magma specifically the equigranular granite and a subordinate part of the porphyritic granite minerals from these facies are compositionally homogeneous and or normally zoned which together with geochemical modelling indicates that they evolved by small degrees of fractional crystallization 520 accessory minerals played an important role during magmatic differentiation and thus the fractional crystallization history is better recorded by trace rather than by major elements the interactions between mafic and felsic magmas reflect their viscosity contrast with increasing viscosity contrast the magmatic relationships change from homogeneous hybrid quartz diorites granodiorites to rounded magmatic enclaves to composite dykes and finally to dykes with chilled margins these relationships indicate that injection of mafic magma into the granite took place over the whole crystallization history consequently a long lived mafic source coexisted together with the granite magma mafic magmas were derived either directly from the mantle or via one or more crustal storage reservoirs compatible element abundances e g ni show that the mafic magmas that interacted with the granite were progressively poorer in ni in the order hybrid quartz dioritescgranodioritescenclavesccomposite dykes this indicates that the felsic and mafic magmas evolved independently which in the case of the karkonosze granite favours a deep seated magma chamber rather than a continuous flux from mantle two magma sources mantle and crust coexisted and melted almost contemporaneously the two reservoirs evolved independently by fractional crystallization however mafic magma was continuously being intruded into the crystallizing granite with more or less complete mixing several lines of evidence e g magmatic flux structures incorporation of granite feldspars into mafic magma feldspar zoning with fluctuating trace element patterns reflecting rapid changes in magma composition indicate that during its emplacement and crystallization the granite body was affected by strong internal movements these would favour more complete and efficient mixing the systematic spatial temporal association of lamprophyres with crustal magmas is interpreted as indicating that their mantle source is a fertile peridotite possibly enriched metasomatized by earlier subduction processes

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

significance of ferrodioritic liquids in magma mixing processes a general model to explain the various igneous associations found in mixed magma intrusives and extrusives belonging to high level volcanic centres is presented this model is based on detailed mapping in the british tertiary volcanic centre on skye which suggests that basic and acid magmas were continually available throughout its development new major and trace element data from these rocks indicate that they were co genetic and that the basic magmas which combined with acid magmas to produce hybrid magmas were ferrodioritic in composition and not basaltic as had previously been thought

on the dimensions of passive ripple marks in the nearshore zone abstract it has been proven on the basis of field observations that the length and height of passive ripple marks in the nearshore zone depend primarily on the sediment grain size d as it turns out the relationships d and d may be approximated with a high degree of accuracy by the equation 17 3 d 1 22 83 5 d 1 08 in which and are expressed in centimeters and d in millimeters it follows that passive ripple dimensions together with grain size distribution of bedload can present only a minimum shear stress at a moment preceding storm damping they will never indicate the storm strength in its maximal development and it is therefore impossible to completely reconstruct the ancient conditions of wave generation by passive ripple mark parameters

caldera formation in the rum central igneous complex scotland the northern marginal zone of the rum central igneous complex in nw scotland represents part of the early felsic phase of the volcano the marginal zone is a relic of the early caldera floor and the infilling of sedimentary and igneous rocks its formation has been explored through field examination of the ring fracture system of the complex and its pyroclastic and epiclastic intracaldera facies a sequence of magmatic tumescence and chamber growth caused initial doming followed by the formation of a collapse structure without accompanying volcanism this collapse structure circular in plan is akin in origin to a salt basin formed by crustal stretching above a rising diapir we call this the proto caldera collapse breccias which represent the slumping and sliding of megablocks blocks and boulders of the torridonian sandstones which form the walls of the basin were the original infilling logs of these deposits reveal considerable variation in thickness of the breccias from 80 170 m in the complex indicating an uneven floor to the proto caldera consistent with piecemeal collapse following accumulation of up to 70 m thickness of breccia thin interbedded rhyodacitic crystal tuffs 10 30 cm record the earliest eruptions of felsic magma in the caldera caldera formation was then interrupted by a period of quiescence recorded by the presence of an epiclastic sandstone of locally several metres thickness formed by washout of fines from the breccias subsequent resurgence created a fracture pattern characteristic of doming along which rhyodacite magma rose in dykes and erupted up to perhaps 10 km3 of rhyodacitic intracaldera ignimbrites this major eruption caused further incremental subsidence of the caldera floor into a now partly emptied magma chamber mafic inclusions in the ignimbrites point to the eruption being triggered by multiple injections of basic magma into a chamber occupied by felsic magma

velocity measurements close to rippled beds in oscillatory flow the results are reported of velocity measurements in oscillatory flow over rippled beds velocities were measured with a laser doppler anemometer in both an oscillating tray rig and an oscillatory flow water channel both self formed and artificial ripples were examined in addition some measurements were made with an apparently plane bed with intense sediment motion the experimental results were compared with the predictions of kalkanis 1964 kajiura 1968 bakker 1973 1974 and sleath 1974 the closest agreement between theory and experiment was obtained with the method of sleath measurements of the eulerian drift velocities showed drift towards the adjacent ripple crest in the immediate vicinity of the bed and away from the crest further out

introduction from the british tertiary into the future modern perspectives on the british palaeogene and north atlantic igneous provinces the study of volcanic rocks and igneous centres has long been a classic part of geological research despite the lack of active volcanism the british isles have been a key centre for the study of igneous rocks ever since ancient lava flows and excavated igneous centres were recognized there in the 18th century hutton 1788 this led to some of the earliest detailed studies of petrology the starting point for many of these studies was the british palaeogene igneous province bpip formerly known as the british tertiary judd 1889 and still recognized by this name by many geologists around the globe this collection of lavas volcanic centres and sill dyke swarms covers much of the west of scotland and the antrim plateau of northern ireland and together with similar rocks in the faroe islands iceland and greenland forms a world class large igneous province this north atlantic igneous province naip began to form through continental rifting above a mantle plume at c 60 ma and subsequently evolved as north america separated from europe creating the north atlantic ocean

investigating the response of wave generated ripples to changes in wave forcing abstract wave generated ripples are macroscopic roughness elements that influence fluid flow and sediment transport for a major group of ripples orbital ripples morphology height and wavelength is set by the wave conditions in natural conditions where wave forcing is highly variable ripple morphology is frequently changing we investigate the rate of morphological change after changes in wave conditions i e wave height and period using laboratory experiments with a step change in wave forcing the adjustment time of ripple morphology to new conditions the hysteresis time scale hereafter referred to simply as hysteresis is proportional to changes in wave orbital diameter and the coefficient of proportionality differs for decreasing and increasing orbital diameter when the shields parameter is lower than a threshold 0 043 there is no change in ripple morphology or changes are extremely slow in addition we find the presence of defects irregularities from straight parallel crestlines reduces the hysteresis time scale the dependence of hysteresis on defect density implies that a larger density of defects results in faster ripple adjustment confirming previous theoretical and numerical model results

crustal assimilation during turbulent magma ascent ata new isotopic evidence from the mull tertiary lava succession n w scotland assimilation of crustal rocks with concomitant fractional crystallisation afc is a well documented phenomenon in many igneous suites but geochemical evidence from the tertiary mull lava succession suggests that in these magmas crustal contamination occurred by a distinctly different mechanism lavas from the lower half of the mull plateau group mpg can be divided into two broad sub types high 8 mgo basalts with elevated ba and k and lower mgo 8 basaltic hawaiites with lower ba and k the lower crust and most of the upper crust beneath mull is probably of lewisian age the sr nd and pb isotope compositions of local lewisian crustal samples yield the following ranges 87sr 86sr 0 71002 0 72348 143nd 144nd 0 51045 0 51058 and 206pb 204pb 14 0 14 6 ten lavas have also been analysed and yield the following ranges 87sr 86sr 0 7028 0 7042 143nd 144nd 0 51214 0 51230 and 206pb 204pb 15 1 17 9 however within this range it is predominantly the more primitive mafic compositions with elevated mg ba and k that show the lowest nd and pb and the highest sr isotope values modelling of these isotopic results in conjunction with major and trace element data show that 1 contamination by lewisian lower crustal material does occur 2 that the process involved was not one of assimilation with concomitant fractional crystallisation afc the proposed contamination process is one whereby the hottest most mgo rich magmas have assimilated acidic partial melts of lewisian lower crust during turbulent ascent ata through thin poorly connected dyke and sill like magma chambers the chemical composition of the contaminated lavas can be modelled successfully through addition of 5 acidic lewisian crust to an uncontaminated lava in contrast the more evolved magmas which probably fractionated at sub crustal levels were either not hot enough to molt significant amounts of crust or did not ascend turbulently because of their higher viscosity and so are less contaminated with crust

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

a laboratory model of a replenished magma chamber abstract it has recently been suggested that periodic influxes of hot but heavy magma into the base of a basaltic magma chamber can remain isolated from the rest of the chamber while the new magma cools and crystallization proceeds when thermal equilibrium is almost complete the suspended crystals settle out and the residual less dense liquid can then mix with the fluid above in the present paper the basic fluid dynamical processes underlying this model have been investigated in laboratory experiments using aqueous solutions the lower layer was hot kno3 solution for which saturated solutions become less dense as the temperature decreases with a cold deeper layer of less dense nano3 or k2co3 above the lower layer there was strong convective transfer of heat through a sharp interface separating the layers at a rate which is predicted here drawing on previous studies carried out with oceanographic applications in mind once crystallization began non equilibrium effects became important and the observed temperatures differ somewhat from those predicted in the experiments crystals grew mainly from the bottom rather than while in suspension but this is not an essential aspect of the model the important fact is that the density of the residual liquid in the lower layer decreased until it became equal to that of the upper layer and then the interface broke down so that the two layers mixed thoroughly together leaving a layer of kno3 crystals at the base no crystallization at all occurred when the hot input liquid was forced to mix initially with the cold solution already in the chamber

petrology and geochemistry of the loch ba ring dyke mull n w scotland an example of the extreme differentiation of tholeiitic magmas the loch ba ring dyke in the tertiary igneous central complex of mull n w scotland is composed predominantly of a banded rhyolitic welded tuff the rhyolite contains numerous inclusions of dark aphanitic rock the textural relationships between the different rocks indicate rapid violent and intimate mixing during emplacement of the dyke the dark glassy component varies continuously from basaltic andesite to andesite dacite and rhyolite these glasses are enriched in feo and depleted in mgo at a given sio2 content in comparison to other tholeiitic highly differentiated volcanic rocks the rhyolite contains an average of 4 phenocrysts and is associated with the mineral assemblage plagioclase an32 to an21 sanidine or50 60 hedenbergite fayalite magnetite ilmenite apatite zircon mineral aggregates involving either plagioclase hedenbergite ilmenite or plagioclase fayalite magnetite are common but aggregates containing fayalite and hedenbergite together are scarce the dark glassy components are either phenocryst free or contain less than 0 2 phenocrysts the main phenocrysts associated with the dark glasses are plagioclase an65 an30 high calcium clinopyroxene ranging continuously from augite to pure hedenbergite pigeonite magnetite ilmenite and rare apatite zoning in minerals is generally weak or absent the plagioclase feldspar high calcium clinopyroxenes and pigeonites have similar compositional ranges to the minerals observed in the middle and upper zones of the skaergaard intrusion the mineral compositions are systematically related to sio2 content and mg number of the glasses the data demonstrate that mineral compositions and assemblages similar to the skaergaard form from silica rich andesitic to rhyolitic liquids the various mafic glasses are interpreted to have been derived from a zoned magma chamber underlying an upper layer of rhyolitic magma differentiation is attributed to fractional crystallization of the observed mineral assemblages causing sio2 enrichment and feo depletion however glasses with less than 57 sio2 have unusual compositions with very low mgo and p2o5 as well as variable al2o3 and tio2 their peculiarities could be explained by andesitic magmas assimilating cumulate mineral aggregates precipitated from more differentiated dacite and rhyolite magmas the bulk compositions of these cumulates have high feo low sio2 and negligible mgo and p2o5 it is suggested that the high density of the mineral aggregates containing fayalite hedenbergite magnetite and ilmenite caused them to settle through the zoned chamber to be assimilated by high temperature less differentiated magmas

measurement and prediction of wave generated suborbital ripples 1 experiments in a large scale wave flume using regular and irregular waves with periods between 4 s and 6 s and heights between 0 2 m and 1 55 m have examined the formation of wave generated ripples using sediment beds composed of four grain sizes d50 0 349 mm 0 329 mm 0 220 mm and 0 162 mm in a water depth of approximately 4 m estimates of wave generated ripple height and wavelength were obtained using zero down crossing analyses of bed profiles measured by acoustic means along a 4 m transect normal to the ripple crests further information pertaining to was obtained from bed images obtained using scanning sonar the analyses reported here focus on the sequence bedforms that evolved in response to stepwise increases and decreases in wave height results show that ripples for the most part are suborbital in nature and do not conform well to empirical equations used frequently to predict and values in the field on the basis of the present data two new equations for prediction of and are obtained and their use in field situations where hydrodynamic and sedimentary conditions favor development of suborbital bedforms is recommended

modeling bottom roughness in the presence of wave generated ripples 1 near bottom wave current and microtopography measurements have been obtained at the leo 15 site off the southern coast of new jersey the measurements are used in conjunction with a recently calibrated continental shelf bottom boundary layer model to refine estimates of bottom roughness for a rippled bed under combined wave and current flows in the presence of nearly two dimensional wave generated ripples application of the grant and madsen 1979 type bottom boundary layer model produces estimates of the bottom roughness felt by the current that are several times greater than established formulations for rippled beds under waves modifying one of the primary length scales in the eddy viscosity profiles returns estimates that are more consistent with the wave roughness results application of the roughness model in conjunction with a refined empirical ripple geometry model produces highly accurate estimates of measured shear velocities and apparent roughnesses during a moderate storm the demonstrated accuracy of this simple combined roughness and ripple geometry formulation reveals its utility when considering applications of coupled bottom boundary layer shelf circulation models

early mafic magmatism and crustal anatexis on the isle of rum evidence from the am mam intrusion breccia the rum igneous centre comprises two early marginal felsic complexes the northern marginal zone and the southern mountains zone along with the later central ultrabasic basic layered intrusions these marginal complexes represent the remnants of near surface to eruptive felsic magmatism associated with caldera collapse examples of which are rare in the north atlantic igneous province rock units include intra caldera collapse breccias rhyolitic ignimbrite deposits and shallow level felsic intrusions as well the enigmatic am mam intrusion breccia the latter comprises a dacitic matrix enclosing lobate basaltic inclusions 1 15 cm and a variety of clasts ranging from millimetres to tens of metres in diameter these clasts comprise lewisian gneiss torridonian sandstone and coarse gabbro detailed re mapping of the am mam intrusion breccia has shown its timing of emplacement as syn caldera rather than pre caldera as previously thought textural analysis of entrained clasts and adjacent uplifted country rocks has revealed their thermal metamorphism by early mafic intrusions at greater depth than their present structural position these findings provide a window into the evolution of the early mafic magmas responsible for driving felsic magmatism on rum our data help constrain some of the physical parameters of this early magma crust interaction and place it within the geochemical evolution of the rum centre

geometry prediction for wave generated bedforms published data on wave generated bedform geometry from field and laboratory measurements are re evaluated in terms of relative fluid orbit diameter at the bed and a wave period parameter d 8t2 laboratory bedform data shows a strong dependence on these parameters however for very small values of the period parameter typically field data there is evidence that bedform length depends only on sediment grain size the disappearance of sediment bedforms at high fluid velocities apparently occurs through a decrease in bedform height improved methods for the prediction of bedform geometry under waves are provided in graphical form and computer code

two contrasting styles of interaction between basic magmas and continental crust in the british tertiary volcanic province some of the magmas that were extruded to form the 59 ma early plateau forming basalt dominated floods in the british tertiary volcanic province mixed with small amounts of sialic melt during their uprise through the continental crust while others underwent concomitant fractional crystallization and crustal assimilation magma batches of the first group originated in the uppermost asthenosphere and mostly ponded at the moho where they crystallized fractionally to form a basalt benmoreite suite the major element compositions of members of this series show that they underwent negligible further fractional crystallization between the moho and the surface nevertheless they paused long enough during their uprise to dissolve their high pressure phenocrysts and in many cases to mix with small amounts of acid melt from lower crustal granulite facies archaean lewisian leucogneisses basalts and tholeiitic andesites of the second group outcrop locally at the base of the lava piles in mull and skye their major element compositions show that they equilibrated within the upper third of the crust under conditions approximating to anhydrous 1 atm cotectic equilibria most of these lavas are in sw mull where proterozoic moine metasediments form the uppermost crust the major and trace element and isotopic compositions of the sw mull basal lavas show that they assimilated substantial amounts of moine metasediments progressively as they fractionated within the upper crust pb isotope data reveal that before their final upper crust evolution some of the sw mull basal lavas had already mixed with small amounts of lower crust acid melts

distribution and compositions of magmatic inclusions in the mount helen dome lassen volcanic center california insights into magma chamber processes abstract variations in spatial abundances compositions and textures of undercooled magmatic inclusions were determined in a glaciated pleistocene lava dome mt helen 0 6 km3 at the lassen volcanic center lvc southernmost cascades spatial variations were determined by point counting at 86 locations separated by 100 m on the dome major and trace element compositions of host rocks and inclusions at 12 locations along the flow length of the dome were obtained important results include the following 1 inclusion abundances range from 3 19 vol with the highest values generally located along the little eroded northwestern margin and flow front of the dome 2 host rock compositions are markedly uniform across the dome 65 4 0 4 wt sio2 indicating that the degree of inclusion disaggregation was uniform despite large spatial variations in inclusion abundances 3 inclusion sizes range from a maximum of 1 m across to mm sized crystal clots of phenocrysts plus adhering ca rich plagioclase microphenocrysts 4 inclusions have variable macroscopic textures indicating that partial undercooling both prior to and following entrapment in cooler dacitic host magma were important processes 5 inclusions are variably fractionated magmas with large variations in ni 79 11 ppm and cr 87 7 ppm contents that are lower than presumed mantle derived melts furthermore large ranges in incompatible trace elements indicate that inclusion compositions also reflect deep processes involving either melting of variable mantle source rocks or assimilation fractional crystallization 6 inclusions are variably mixed magmas 56 61 wt sio2 that contain up to 50 host dacitic magma 7 correlations between ni and cr contents in hosts and inclusions from individual outcrops indicate that the effect of inclusion disaggregation and magma mingling on host dacitic magma was local e g these features are interpreted to reflect protracted recharge of diverse composition mafic magmas into the base of a shallow magma reservoir containing a lower layer of compositionally evolving hybrid mafic magma and an upper layer of rhyodacitic magma complex interactions among magmas in the upper and lower layers resulted in formation of mafic inclusions by both pre and post entrapment undercooling mechanisms followed by buoyant rise and accumulation near the roof of the reservoir the main stage of inclusion disaggregation probably occurred in the conduit during eruptive ascent and largely ceased upon surface eruption we infer that endogenous growth concentrated inclusions along the margins and top of the dome as more inclusion poor dacite was progressively tapped from deeper regions of the reservoir

crustal differentiation processes at krakatau volcano indonesia anak krakatau is a basaltic andesite cone that has grown following the famous caldera forming 1883 eruption of krakatau it breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week we present new major and trace element data combined with whole rock delta o 18 sr and nd isotope data for 1883 1993 and 2002 krakatau eruptive products and the surrounding crust bombs erupted from anak krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism plastic deformation and partial melting contact metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high temperature metamorphism and incorporation at mid to upper crustal depth energy constrained assimilation and fractional crystallization modelling of whole rock data suggests that the anak krakatau magmas have a genetic relationship with the 1883 eruption products the geochemical impact of crustal contaminants on whole rock compositions is apparently small and we conclude that low levels of assimilation of a quartzo feldspathic sediment are recorded in anak krakatau magmas plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning however and are also isotopically variable with a total range in sr 87 sr 86 of 0 center dot 7043 0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry this suggests that although shallow crustal assimilation appears to have had a limited effect on whole rock chemistry a complex late stage differentiation history is recorded within the magma s cargo of crystals and xenoliths

geometry and migration characteristics of bedforms under waves and currents part 2 ripples superimposed on sandwaves this paper presents results of a series of detailed measurements of geometric and migrating characteristics of ripples superimposed upon sandwaves under the action of combined waves and currents velocity measurements within the fluid surface wave characteristics and 3d mapping of the bottom were recorded with an acoustic doppler velocimeter adv an acoustic water level sensor and a 32 composite element array of sub aquatic acoustic sensors respectively bottom records were statistically analyzed to obtain height length and migration rates of ripples experiments examined ripple heights and wavelengths for the mobility factors as defined in eq 4 and the reynolds wave number within the ranges 10 88 and 16 103 rew 5 105 respectively measured values were compared with laboratory and field data together with semi empirical and analytical formulae from the literature good correlation was obtained when plotting measured ripple length and length in dimensionless form as a function of the reynolds wave number rew under a given hydraulic condition it was observed that ripples with different geometric characteristics may coexist at different locations over the sandwave ripple steepness is presented as a function of the shields parameter although characterized with rather large scatter finally average ripple migration speed is presented as a function of the shields parameter and the mobility number

intrawave observations of sediment entrainment processes above sand ripples under irregular waves 1 measurements of intrawave sediment entrainment processes are reported above ripples under irregular waves generated in a large scale flume facility the data consist of substantive observations of small scale processes collected at high spatial and temporal resolution under irregular wave forcing typical of coastal environments acoustic measurements were made of water velocities bed forms and suspended sediment concentration over plane and rippled beds during each rippled bed experiment measurements were taken over the crests of steep sided ripples above which flow separation was considered likely to occur above the ripple crests a strong intrawave variation in the near bed suspended sediment indicative of vortex formation and shedding was observed to dominate wave half cycles where the orbital diameter was greater than 1 2 times the ripple wavelength l the irregular waves were parameterized with a significant wave height hs and a significant orbital diameter d0s thus during irregular wave conditions and over steep ripples where d0s l 1 2 vortex shedding was deemed as the dominant sediment entrainment process furthermore the percentage of wave half cycles where vortex shedding was observed was found to scale as 26 d0s l these results demonstrate for under irregular waves the existence of a clear suspended sediment structure consistent with vortex shedding previously observed under regular waves citation o hara murray r b p d thorne and d m hodgson 2011 intrawave observations of sediment entrainment processes above sand ripples under irregular waves j geophys res 116 c01001 doi 10 1029 2010jc006216

modeling of vortex ripple morphodynamics 1 a new morphology module has been developed in order to perform simulations of the bed form evolution under hydrodynamic forcing this module has been implemented into the numerical model dune2d which solves the reynolds averaged navier stokes rans equations in the boundary layer and resolves sediment transport over moving sand beds the morphology module is composed of a modified central scheme and a routine that simulates avalanches and has been successfully applied to the study of orbital ripples evolution ripple growth from a quasiflat bed have been simulated and the growth behavior has been compared to previous experimental measurements the simulated ripples reach an equilibrium state where energy damping processes avalanches compensate energy production processes flux of sediment these processes have been analyzed during ripple creation growth merging and annihilation furthermore sandy bed evolutions have been simulated with random initial bed forms in order to examine the influence of the bed history on the final solution and the wave energy dissipated during these evolutions

sand ripples under sea waves part 2 finite amplitude development in the present paper the authors formulate a theory to predict the time development of sand ripples characterised by small but finite amplitude under the action of surface gravity waves the theory is based on a weakly nonlinear stability analysis of a flat sandy bottom subject to viscous oscillatory flow the parameters of the problem namely the reynolds number of the flow and the reynolds and froude numbers of sediments are assumed to fall within a neighbourhood of the critical conditions determined in blondeaux 1990 the analysis can predict the actual ripple height wavelength and profile when flow separation is absent i e for the case of rolling grain ripples assuming sleath s 1984 criterion for separation the values of the relevant parameters at which transition from rolling grain ripples to vortex ripples occurs are predicted a comparison between theoretical findings and experimental data supports the validity of the present theory

the generation of overpressure in felsic magma chambers by replenishment abstract evidence of magma mixing is common in the products of explosive felsic eruptions and it is generally accepted as a common mechanism for triggering such events in order to quantify the potential for magma mixing to trigger explosive eruptions we have developed a simple analytical model based on previous models of magma chamber replenishment which considers the injection of volatile rich mafic magma into a chamber occupied by a homogeneous volatile rich felsic magma we assume that the overpressure caused by the injection of new magma is not sufficient to trigger an eruption for which additional overpressure is required two mixing related mechanisms have traditionally been considered to have the potential to generate the additional overpressure 1 exsolution of volatiles from the felsic magma during forced convection and 2 exsolution of volatiles from the mafic magma by oversaturation during cooling and subsequent crystallization our calculations suggest that exsolution of volatiles from the felsic magma is not an effective mechanism to generate additional overpressure however significant overpressure can be achieved by volatile exsolution from the mafic magma during its cooling and crystallization the time scale between intrusion and eruption considered in our model is of the order of a few days to a few months which coincides with petrological and geophysical evidence obtained from magma mixing related eruptions we also suggest that replenishment of shallow felsic magma chambers by mafic magma in most cases does not lead to large scale mixing as eruption will occur before thermal equilibrium between the two magmas is reached so that density and viscosity contrasts between the two magmas will remain significant

geometry and grain size sorting of ripples on low energy sandy beaches field observations and model predictions there are very few field measurements of nearshore bedforms and grain size distribution on low energy microtidal beaches that experience low amplitude long period waves field observations are needed to determine grain size distribution over nearshore bedforms which may be important for understanding the mechanisms responsible for ripple development and migration additional nearshore field observations of ripple geometry are needed to test predictive models of ripple geometry ripple height length and sediment composition were measured in the nearshore of several low energy beaches with concurrent measurements of incident waves the distribution of sediment sizes over individual ripples was investigated and the performance of several models of ripple geometry prediction was tested both spatially and temporally sediment samples were collected from the crest and trough of 164 ripples the sand sized sediment was separated from the small amount generally 2 mm that was present within the sand sized fraction the ripple crests were found to be significantly coarser better sorted and more positively skewed than the troughs overall the troughs were finer than the crests but contained a greater proportion of the small fraction of sediment larger than 2 mm the field model of nielsen 1981 and the model of wiberg harris 1994 were found to be the most accurate models for predicting the wavelength of parallel ripples in the nearshore of the low energy microtidal environments surveyed the wiberg harris 1994 model was also the most accurate model for predicting ripple height temporal changes in ripple wavelength appear to be dependent on the morphological history of the bed

the record of magma chamber processes in plagioclase phenocrysts at thera volcano aegean volcanic arc greece lavas and pyroclastic rocks throughout the volcanic stratigraphy of the tertiary quaternary volcanic complex of thera in the aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures interpreted as indicative of magma mixing plagioclase zoning characteristics studied by nomarski and laser interferometry techniques establish three main categories of plagioclase i inherited plagioclase nucleated in endmember prior to initial mixing event ii in situ plagioclase nucleated in mixed or hybrid magma and iii xenocrystic plagioclase nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases depending on the composition of the lava in which they are hosted these differences reflect the contrasting effects of changes in physical chemical parameters in basic vis a vis more acidic melts during magma mixing and or influx of new magma into the subvolcanic magma chamber as well as the influence of magma chamber dynamics on plagioclase equilibration variations in bulk major and trace element abundances of thera volcanic products reflect the dominant overprint of crystal fractionation but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes consistent with compositional and textural zoning in plagioclases

wave formed sediment ripples transient analysis of ripple spectral development 1 a new method has been developed that models the changes a wave formed rippled sediment bed undergoes as it is actively evolving between two given equilibrium states due to a change in surface wave conditions the transient analysis of rippled beds has received very little attention within the literature dynamic changes within ripple parameters have implications for the estimation of flow dissipation and sediment transport by changing the bottom roughness height the method uses the spectral density function of the rippled bed and is based on a series of ripple growth and ripple transition experimental tests the ripple evolution model was developed from the well known logistic growth law fitting the general solution of the logistic nonlinear differential equation to the experimental data enabled the evolution rate of the bed to be determined for each experimental test it was concluded that there was no difference between the evolution rate determined from the ripple growth tests and the ripple transition tests this indicated that the two types of growth are special cases of the same evolution processes which is adequately modeled by the logistic growth equation a functional dependence was established between the ripple evolution rate and the shields parameter this allows the evolution rate to be estimated from flow and sediment properties the estimation of the rate at which rippled sediment beds evolve under a variable sea state has the potential to lead to significant improvements to the way ripple transition and hence bottom roughness is approximated in coastal wave models

oscillatory ripple geometry ripple geometry provides a bed roughness which governs the bed shear stress and the profile of eddy viscosity or diffusion coefficient required for the description of the sediment concentration profile or rate of sediment transport an analysis is made of ripple geometries using known tabulated laboratory and field data as well as water tunnel data obtained by the writer three different types of ripples can be identified sand light sediment and oscillating bed ripples they reflect different effects of the fluid shear stress and fluid acceleration on bed sediments it is also shown that when the bed shear stress or the amplitude of the water particle motion relative to the sediment size is small the resulting vortices are more regular with low turbulence intensity and the generated ripples are two dimensional they are called growing or vortex ripples which are strongly influenced by the amplitude of the water particle motion at the other extreme when the bed shear stress or the amplitude of the

an origin for harrisitic and granular olivine in the rum layered suite nw scotland a crystal size distribution study dendritic crystal morphologies occur in a number of igneous rocks and are thought to originate from the rapid growth of crystals yet many examples of dendritic morphologies are found in plutonic igneous rocks where cooling rates should be low results from crystal size distribution csd measurements on harrisitic olivines from rum scotland combined with estimated olivine growth rates suggest that the characteristic skeletal hopper and branching olivines of harrisitic cumulates that are up to centimetres long may have exceptionally short crystal growth times several hours to several hundreds of days this together with very low calculated nucleation densities for harrisitic olivine supports the interpretation of harrisite being a disequilibrium texture developed in response to supersaturation of the magma in olivine we propose that this supersaturation arose through undercooling of thin picrite sheets emplaced along the rum magma chamber floor beneath cooler resident magma it is envisaged that the picrite sheets were largely free of suspended olivine crystals coupled with the olivine enriched composition of the melt and the increasing cooling rate this allowed homogeneous nucleation of olivine to set in at deeper undercooling and greater olivine supersaturation than if there had been plentiful suspended olivines to act as heterogeneous nuclei the enhanced supersaturation caused rapid growth of olivine once nucleation began with skeletal and dendritic shapes it is suggested that the observed interlayered sequences of harrisite and cumulus peridotite found throughout the rum layered suite are a result of multiple episodes of harrisite crystallization resulting from picrite emplacement that alternated with periods of crystal growth and accumulation in the main body of magma at lesser degrees of undercooling

laser interferometry study of oscillatory zoning in plagioclase the record of magma mixing and phenocryst recycling in calc alkaline magma chambers iztaccihuatl volcano mexico

sand ripples under sea waves part 1 ripple formation in the present paper we formulate a predictive theory of the formation of sand ripples under sea waves the theory is based on a linear stability analysis of a flat sandy bottom subject to a viscous oscillatory flow the conditions for decay or amplification of a bottom perturbation are determined along with the wavelength of the most unstable component as a function of the reynolds number of the flow and of the froude and reynolds numbers of the sediments a comparison between theoretical findings and experimental data supports the validity of the present theory an analytical solution for viscous oscillatory flow over a small amplitude wavy bottom is determined for arbitrary values of the ratio r between the amplitude of fluid displacement and the wavelength of bottom waviness previous works by lyne 1971 and sleath 1976 who considered small or large values of r are thus extended

highest natural bed forms 1 fluid flow interacts with sedimentary beds forming waves of different kinds which are of considerable practical importance since they influence significantly the near bed flow both over and below the bed sediment transport and wave height attenuation we focus here on steep bed forms capable of producing flow separation in this case the large scale vorticity generated in the phenomenon of separation rules the process of friction which appears to be practically unaffected by sediment motion under the crests of the bed forms the mean shear force due to friction is balanced by the force that bed forms exert on the flow via pressure which can be calculated from the work of gimenez curto and corniero 2002 bed forms grow until they have a height such that friction at their troughs is negligible thus ceasing the motion of fluid and sediment this condition leads to a very simple expression for the limiting steepness which compares favorably with existing observations on bed form geometry under steady open channel flow as well as under oscillatory flow

geochemical evolution of the tertiary mull volcano western scotland the early tertiary mull volcano western scotland is one of the most dissected and best exposed igneous complexes of the north atlantic province the new and published geochemical data enable us to chart the magmatic evolution of the mull volcano from the oldest lavas through the intrusive rocks of three overlapping igneous centres to the youngest dykes in this study we identify four successive magma types within the remnant volcano the earliest type the mull plateau group comprises mildly alkaline basaltic rocks with steep chondrite normalized rare earth element ree patterns this type is succeeded within the lava succession and dyke swarm by the coire gorm magma type with essentially flat chondrite normalized ree patterns a third magma type represented within the lava and dykes the central mull tholeiites is more depleted in incompatible trace elements than the preceding types and has flat to lree depleted chondrite normalized patterns the major intrusions and cone sheets of mull centre 1 and early centre 2 belong to this magma type midway through the igneous activity associated with centre 2 the magma type changed to become more alkalic and more enriched in incompatible trace elements this magma type the late mull type is found to persist through the cone sheets and major intrusions of centre 3 to the youngest dykes these changes in magma composition were related to variations in the mantle source and depth of partial melting beneath mull and or differences in the efficiency of melt pooling before ascent through the lithosphere with the exception of the early staffa magma sub type part of the mull plateau group the location of magma chambers in which the bulk of contamination occurred changed with time from deep lower crustal lewisian gneiss to shallow upper crustal moine schist intermediate members of the plateau group and the late mull magma type are enriched in fe ti and p relative to the central mull tholeiites we attribute this difference to the more alkalic nature of these suites lower fo2 and the formation of fe3 p complexes in the magma the intermediate rocks were important in magma mixing processes with two types of mixing identified on mull 1 cryptic mixing between basalts and low fe intermediate magmas typified by lavas and early basic cone sheets of the central mull tholeiite magma type 2 observable mingling between rhyolitic magmas and high fe intermediate magmas of the late mull type shown by the mixed magma bodies of the glen more and loch ba ring dykes the main factor in determining which type of mixing occurred appears to have been the density contrast between the various magmas it may safely be maintained that mull includes the most complicated igneous centre as yet accorded detailed examination anywhere in the world bailey et al 1924 memoir of the geological survey of great britain scotland hmso edinburgh 1924

pre eruptive magma mixing in ash flow deposits of the tertiary rum igneous centre scotland the northern marginal zone of the rum igneous centre is a remnant of an early caldera and its infill it is composed of intra caldera breccias and various small volume pyroclastic deposits overlain by prominent rhyodacite ash flow sheets of up to 100 m thickness the ash flows were fed from a feeder system near the caldera ring fault and intrusive rhyodacite can locally be seen grading into extrusive deposits a variety of features suggest that the ash flows were erupted from a magma chamber that contemporaneously hosted felsic and mafic magmas i chilled basaltic inclusions in rhyodacite ii formerly glassy basaltic to andesitic enclaves with fluid fluid relationships iii feldspars with thick reaction rims enclosed in the basaltic to andesitic inclusions yet with cores chemically resembling those of the rhyodacite iv trace element compositions of the rhyodacite and the mafic enclaves form a mixing line between the end member rhyodacite and basalt compositions additionally textural and chemical features in the rhyodacite feldspar phenocrysts are consistent with magma mixing v feldspars with resorption embayments cutting through internal zonation of the crystals vi complexly zoned crystals with sieve textured zones that are overgrown with euhedral zones vii oscillatory zonation of feldspar phenocrysts in the rhyodacite showing sharp increases in anorthite an 10 followed by gradual decrease in an content an 4 this evidence points to eruption of ash flows from a felsic magma chamber that was periodically replenished by injection of mafic magma diffusional mixing between the two magmas was permitted by temperature and compositional differences but was slow due to the contrast in viscosities and densities the fe ti p enriched basic magma that replenished the chamber was degassing on entering the lower temperature environment and soon equilibrated thermally followed by chemical exchange between the two end member magmas this process formed hybrid andesite enclaves enriched in trace elements beyond that caused by simple mixing implying trace element diffusion in addition to bulk mixing eruption was caused by replenishment with and degassing of the basic magma and the chamber partially evacuated while the process of hybridisation was underway the erupted products record magma mixing by chamber replenishment blending of two magmas and elemental exchange in the magma chamber and also physical mingling in the eruptive conduit

a model that helps explain sr isotope disequilibrium between feldspar phenocrysts and melt in large volume silicic magma systems feldspar phenocrysts of silicic volcanic rocks are commonly in sr isotopic disequilibrium with groundmass in some cases the feldspar is more radiogenic and in others it is less radiogenic several explanations have been published previously but none of these is able to accommodate both senses of disequilibrium we present a model by which either more or less radiogenic feldspar or even both within a single eruptive unit can originate the model requires a magma body open to interaction with biotite and feldspar bearing wall rock magma is incrementally contaminated as wall rock melts incongruently biotite preferentially melts first followed by feldspar such melting behavior which is supported by both field and experimental studies first contaminates magma with a relatively radiogenic addition followed by a less radiogenic addition feldspar phenocrysts lag behind melt groundmass of volcanic rock in incorporating the influx of contaminant thus resulting in sr isotopic disequilibrium between the crystals and melt the sense of disequilibrium recorded in a volcanic rock depends on when eruption quenches the contamination process this model is testable by isotopic fingerprinting of individual feldspar crystals for a given set of geologic boundary conditions specific core to rim sr isotopic profiles are expectable moreover phenocrysts that nucleate at different times during the contamination process should record different and predictable parts of the history initial results of sr isotopic fingerprinting of sanidine phenocrysts from the taylor creek rhyolite are consistent with the model more tests of the model are desirable

origin of mafic enclaves from the taihang mesozoic orogen north china craton abstract the origin of mafic enclaves in intermediate and felsic granitoids has long been debated in this paper petrological and geochemical analyses whole rock geochemistry nd sr and zircon in situ hf isotopic compositions are used to address this controversial issue mafic enclaves in the taihang felsic plutons north china craton are fine grained and show typical magmatic textures they occur as rounded to ellipsoidal globules and are sometimes highly elongated without solid state deformation due to stretching within the partially crystallized convective felsic magma such occurrence suggests that the mafic enclaves and host rocks represent two co existing compositionally distinct magmas the mafic enclaves contain abundant hydrous phases hornblende and biotite and show the reaction relationship of clinopyroxene being rimmed by hornblende they also contain plagioclase xenocrysts showing compositional and textural disequilibrium in terms of nd hf isotopes mafic enclaves have end t values of 10 to 15 and host rocks have lower values as a whole 13 to 18 zircons from a single enclave show a large variation in hf isotopic compositions ehf t 5 to 20 a model is proposed whereby an evolved basaltic magma first mixed with a granitic magma of crustal origin at depth and then the mixed magma broke up into discrete globules upon entering the felsic magma chamber forming enclaves by convective motion or forceful injection in the host felsic magma this was followed by a double mechanical transfer of plagioclase crystals at the contact of the two magmas and by the diffusion of mobile elements e g si alkalis p y yb pb from felsic magma to enclave forming magma

spatial and temporal structures of suspension and transport over megaripples on the shore face megaripples of 0 10 0 15 m height and 0 75 0 9 m wavelength occurred under swell wave activity on a macrotidal beach in southern cornwall england megaripples are relatively common features on the shore face in wave dominated environments although their occurrence is not well predicted by bed form models of the four bed form models examined clifton 1976 mogridge et al 1994 nielsen 1981 wiberg and harris 1994 only that of clifton 1976 predicted the formation of megaripples the average suspended sand concentration profiles measured using acoustic backscatter differed considerably in absolute magnitude and vertical gradient depending on whether the measurements were made over the crest or trough of the bed form the temporal structure of the suspension also varied with position relative to the megaripple utilizing the motion of the bed form beneath the instruments patterns of suspension over the megaripple were calculated as a function of the phase of the wave sand transport was computed from the cospectra of the suspended concentration with an electromagnetic current meter at 10 cm from the seabed transport was dominantly at the infragravity frequencies and was consistently directed offshore while the transport associated with the swell waves was smaller and varied with position over the megaripple the motion of the megaripple itself was toward the shore

boundary layer dynamics and sediment transport under storm and non storm conditions on the scotian shelf abstract near bed measurements of waves currents seabed responses and ripple migration rates were obtained using an instrumented tripod at a water depth of 39 m on the scotian shelf during the winter of 1992 93 these data and the grant and madsen s 1986 grant w d madsen o s 1986 the continental shelf bottom boundary layer annu rev fluid mech 18 265 305 combined flow boundary layer model are used to examine wave current interaction various sediment dynamic thresholds and sediment transport on an exposed high energy continental shelf the seabed was found to be rippled for most time of the deployment and thus the ripple enhanced combined skin friction shear velocity had to be used to determine the initiation of bedload transport under combined flows this indirectly indicates adequate predictions of the skin friction shear velocities inside the wave boundary layer by the grant and madsen model at high transport stages bedload roughness must be added to the grain size roughness to obtain a transportrelated combined shear velocity in order to predict correctly the onsets of saltation suspension and sheet flow transports otherwise the initiation of suspended load transport and the total sediment transport rates will be severely under estimated the comparison between the prediction by the grant and madsen 1986 model and the calculation of a quadratic stress law suggests that the total current shear velocity was enhanced by a factor of 2 3 due to the wave current interaction during storms while the apparent bottom roughness was increased by more than an order of magnitude the non linear coupling between waves and currents also causes a 20 increase of the combined skinfriction shear velocity inside the wave boundary layer this non linear coupling is most important when waves and currents are roughly equal in magnitude and the angles between them are less than 30 four sediment transport formulae were tested while the engelund hansen total load and yalin bedload methods did not perform well the einstein brown and bagnold formulae were found to respectively give reasonable predictions of the bedload and total load sediment transport rates under the observed combined flow conditions the predicted sediment transport direction is also in good agreement with the observed ripple migration direction the gsc sediment transport model sedtrans92 predicts that the net daily transport rates during the storms reached 822 kg m 1 day 1 and were 2 3 orders of magnitude higher than the non storm transport suggesting the dominance of storm processes in sediment transport on the scotian shelf these values are in good agreement with the results from sand tracer experiments conducted in this region we thus conclude that sedtrans92 can properly simulate boundary layer dynamics and sediment transport on continental shelves

occurrence and orientation of anorbital ripples in near shore sands dimensional and of the anorbital type l0 d50 524 to 535 d0 d50 4300 to 25 000 with 7 6 cm mean wavelength in 150 mm median diameter sand the ripple crests were typically aligned perpendicular to the incident sea and swell direction specifically about 60 of the normals to the crests differ from wave direction by less than 5 and more than 90 by less than 10 during rapid changes in wave direction however ripple orientation adjustment lagged the wave direction by o 1 h ripple reorientation occurred piecewise along the crests with new crest segments sometimes bridging two or more old segments the 1 h reorientation time scale is longer by several orders of magnitude than the adjustment time based on theoretical bed load transport rate and the ripple volume as a possible explanation we suggest that a significant fraction of the transport more than 90 bypasses the ripples during orientation adjustment through large angles

pyroclastic rocks in the cnapan breaca felsite rhum the cnapan breaca felsite sheet contains strongly devitrified pyroclastic rocks including welded tuffs these indicate formation in a high level surficial or sub volcanic environment the gross structure and lithological associations of the sheet are similar to those of some ignimbrites these observations support a resurgent caldera model for the evolution of the rhum centre and raise some doubts about previous interpretations of the felsite breccia association on the island

unified view of sediment transport by currents and waves i initiation of motion bed roughness and bed load transport attention is given to the properties of sediment beds over the full range of conditions silts to gravel in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed high quality bed load transport data sets are identified and analyzed showing that the bed load transport in the sand range is related to velocity to power 2 5 the bed load transport is not much affected by particle size the prediction of bed roughness is addressed and the prediction of bed load transport in steady river flow is extended to coastal flow applying an intrawave approach simplified bed load transport formulas are presented which can be used to obtain a quick estimate of bed load transport in river and coastal flows it is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions the proposed model is fully predictive in the sense that only the basic hydrodynamic parameters dep

magma mixing and crustal recycling recorded in ternary feldspar from compositionally zoned peralkaline ignimbrite a gran canaria canary islands miocene ignimbrite a on gran canaria contains three compositional endmember fiamme types two rhyolites and one trachyte each of which crystallized distinct feldspar various textural and compositional criteria are interpreted as reflecting a complex scenario within the magma chamber in which the crystals formed about 25 30 of the feldspar phenocrysts contain evidence for magma mixing in the form of 1 partial to severe dissolution resorption rims 2 distinct zones of drastically different compositions and 3 overgrowth textures on formerly resorbed crystals four major types of zoning in the oligoclase to anorthoclase feldspars of ignimbrite a include a normal and a reversely zoned type and two complexly zoned types the feldspars with normal and reverse zonation show only minor compositional amplitudes between individual zones ab or 4 whereas the complexly zoned types show compositional differences between zones of up to 18 mol ab and 20 mol or and are commonly associated with an internal dissolution surface complex zoning with large compositional amplitudes and dissolution textures is taken as evidence of crystal movements within the magma and across compositional boundaries between magma batches a multiple step cycle model involving growth and transport of a crystal into another magma batch and its return to the original host magma is suggested by the data moreover feldspars from one rhyolite compositional group are found to be substantially elevated in 18o suggesting an input of a high 18o component to this rhyolite the other endmember rhyolite appears to be related to the endmember trachyte by mainly crystal fractionation of anorthoclase feldspar this observation is consistent with trace element and rare earth element concentrations for the magma endmembers and their feldspars where contamination led to a depletion in incompatible trace elements and light rare earth elements in the contaminated rhyolite and its feldspar phenocrysts we suggest that the combination of textural and compositional variation in ternary feldspar of peralkaline rhyolitic systems is well suited to reconstruct dynamic processes such as magma mixing and contamination in evolving rhyolitic magma chambers

magma ascent along a major terrane boundary crustal contamination and magma mixing at the drumadoon intrusive complex isle of arran scotland the composite intrusions of drumadoon and an cumhann crop out on the se coast of the isle of arran scotland and form part of the larger british and irish palaeogene igneous province a subset of the north atlantic igneous province the intrusions shallow level dykes and sills comprise a central quartz feldspar phyric rhyolite flanked by xenocryst bearing basaltic andesite with an intermediate zone of dark quartz feldspar phyric dacite new geochemical data provide information on the evolution of the component magmas and their relationships with each other as well as their interaction with the crust through which they travelled during shallow crustal emplacement the end member magmas mixed isotopic evidence shows that both magmas were contaminated by the crust prior to mixing the basaltic andesite magma preserves some evidence of contamination within the lower crust whereas the rhyolite mainly records upper crustal contamination the highland boundary fault divides arran into two distinct terranes the neoproterozoic to early palaeozoic grampian terrane to the north and the palaeozoic midland valley terrane to the south the drumadoon complex lies within the midland valley terrane but its isotopic signatures indicate almost exclusive involvement of grampian terrane crust therefore although the magmas originated at depth on the northern side of the highland boundary fault they have crossed this boundary during their evolution probably just prior to emplacement

response of sand ripples to change in oscillatory flow ripples take time to evolve to a new equilibrium state in response to a change in wave generated oscillatory flow the paper presents results from flow tunnel experiments designed to examine oscillatory flow transient ripple processes under controlled full scale laboratory conditions the experiments include study of the growth of ripples from flat bed and the evolution of existing ripples to new equilibrium ripples in response to a step change in the flow in general ripples evolve through a combination of two main processes i from a flat bed or from a bed consisting of ripples that are smaller than the equilibrium ripples through a combination of slide and merge ii from a bed consisting of ripples that are larger than the equilibrium ripples through a combination of split and merge the experimental results show that equilibrium ripple geometry is independent of initial bed morphology while the time to reach equilibrium is largely independent of the initial bed and the equilibrium ripple size the time to reach equilibrium depends strongly on the mobility number and a new empirical equation relating mobility number and the number of flow cycles to equilibrium is proposed this equation is combined with a simple exponential function for ripple height growth or decay to produce a new empirical model for ripple height evolution which gives a reasonably good overall agreement with the measurements the model is based on experiments involving one sediment size only and further work is needed to develop the model for other sand sizes

sr and nd isotope evidence for successive crustal contamination of slieve gullion ring dyke magmas co armagh ireland the palaeogene slieve gullion igneous centre in southern armagh northern ireland consists of a layered central intrusive complex surrounded by a prominent and slightly older ring dyke that intrudes both lower palaeozoic sedimentary rocks and the caledonian newry granodiorite pluton 452 ma the ring dyke comprises two major rock types porphyritic felsite and porphyritic granophyre we analysed both ring dyke lithologies both types of country rock and a local palaeogene basalt dyke sample for sr and nd isotopes trace element and whole rock data for this suite suggest that there are two distinct groups of both felsite and granophyre one si rich and one si poor most likely representing two magmas from a zoned chamber and their mushy chamber wall equivalents mcdonnell et al 2004 isotope data show the low si rocks to be higher in radiogenic sr than the high si rocks which is inconsistent with a simple afc scenario of increasing sediment assimilation with higher degrees of differentiation however using morb type basalt as a starting composition the low si ring dyke rocks can be modelled through afc with lower palaeozoic sedimentary rock as the contaminant the decreasing 87 sr 86 sr trend from low si to high si dyke rocks in turn represents a second stage of contamination selective assimilation of the most fusible portions of newry granodiorite which is lower in radiogenic sr than the local sedimentary rocks appears to be the most plausible solution the sr and nd data are consistent with a at least a two stage contamination history during upper crustal residence and storage whereby fractionating magmas of basaltic and intermediate composition are contaminated by local sedimentary rocks giving rise to rhyolite magmas that experience additional shallow contamination by newry granodiorite and b a zoned rhyolite magma chamber where high si magma is stored in the upper part of the chamber where crystallization and crustal contamination are most extensive

unifying large and small wave generated ripples 1 frequently in field and laboratory studies of wave generated bed forms on beds of sandy sediments both large and small wave generated ripples lwrs and swrs are observed and in some situations may be superimposed upon one another the present paper examines relationships between measured wave conditions and the geometry of lwrs and swrs and shows that existing empirical equations used to predict the dimensions of swrs perform badly for lwrs to address this problem relationships found between ripple geometry and the wave reynolds number are used as the basis for new expressions for prediction of ripple height wavelength and steepness that improve the accuracy of existing approaches for both lwrs and swrs the present results indicate strongly that swrs and lwrs are related and their superposition in certain conditions reflects the time lag between the response of the bed to changing hydrodynamic conditions they must be considered therefore when estimating the total bed roughness in a range of practical engineering and numerical modeling applications

contrasting styles of hurricane irene washover sedimentation on three east coast barrier islands cape lookout north carolina assateague island virginia and fire island new york abstract storm surge and wind driven waves generated by hurricane irene which made landfall on the u s east coast on august 27 2011 resulted in overwash of sandy barrier islands from north carolina to new york state overwash has significant impacts on barrier island geomorphology it represents a sediment pathway into island interiors a component of island sediment budgets and can cause considerable aggradation of backshore surfaces important for potentially offsetting the effects of rising sea level this study describes the morphology texture and microfossil content of hurricane irene washover deposits at three contrasting barrier island sites cape lookout north carolina assateague island virginia and fire island new york at all three sites run up overwash occurred wherein waves were sufficient to overtop parts of the beach system and transport sediment inland however at fire island overwash was restricted by a higher elevational threshold to low spots in the beach system coinciding with pre existing breaches in foredunes the result was the formation of isolated thinner low volume washover fans at assateague island and cape lookout lower elevational thresholds allowed waves to overtop longer continuous sections of beach systems resulting in the formation of laterally continuous thicker larger volume washover terraces overall the deposits lacked consistent trends in thickness and texture such as thinning and fining inland reflecting a progressive reduction in overwash competence thickness and texture of the deposits were both spatially variable and probably reflect infilling of low points on the former surface and the influence of beach and foredune sediment sources all the washover deposits were essentially barren of foraminiferal microfossils supporting the textural evidence that the adjacent beach and foredunes were the predominant sediment sources

bed forms created by simulated waves and currents in a large flume 1 the morphology and evolution of bed forms created by combinations of waves and currents were investigated using an oscillating plate in a 4 m wide flume current speed ranged from 0 to 30 cm s maximum oscillatory velocity ranged from 20 to 48 cm s oscillation period was 8 s except for one run with 12 s period and the median grain size was 0 27 mm the angle between oscillations and current was 90 60 or 45 at the end of each run the sand bed was photographed and ripple dimensions were measured ripple wavelength was also determined from sonar images collected throughout the runs increasing the ratio of current to wave i e oscillatory velocity decreased ripple height and wavelength in part because of the increased fluid excursion during the wave period increasing the ratio of current to waves or decreasing the angle between current and waves increased the three dimensionality of bed forms during the runs ripple wavelength increased by a factor of about 2 the average number of wave periods for evolution of ripple wavelength to 90 of its final value was 184 for two dimensional ripples starting from a flat bed bed form orientations at the end of each run were compared to four potential controlling factors the directions of waves current maximum instantaneous bed shear stress and maximum gross bed form normal transport mgbnt the directions of waves and of mgbnt were equally good predictors of bed form orientations and were significantly better than the other two factors

deterministic coastal morphological and sediment transport modeling a review and discussion 1 modern coastal ocean modeling systems are now capable of numerically simulating a variety of coastal and estuarine problems and can thus provide useful information for managing coastal zones here we review state of the art eulerian implementations of bottom up sediment transport and morphological change in coastal ocean hydrodynamic models in order to investigate the fate of suspended sediment in coastal and estuarine waters as well as the evolution of sea or river beds sediment dynamics need to be represented at a scale relevant to the numerical discretized solution and significant effort is devoted to parameterize sediment processes we discuss boundary layer hydrodynamics and the computation of the bed shear stress we also focus on approaches used to represent near bed processes such as bed load transport and sediment erosion and deposition sediment diffusivities settling velocities and cohesive processes such as flocculation all have an impact on suspended sediment throughout the water column we then describe the implementation of process parameterizations in coastal hydrodynamic models explicitly reviewing five widely used systems the approaches implemented in these coastal models may present distinct strengths and shortcomings with regard to some important issues for coastal zones both numerical and physical while these detailed limitations need to be considered as part of model assessment more general issues also hinder present state of the art models in particular sediment transport is inherently highly empirical which is further compounded by issues arising from turbulence closure schemes we conclude by suggesting some possible directions toward improving sediment dynamics understanding and coastal scale predictive ability

observations of wave generated vortex ripples on the north carolina continental shelf 1 sand ripples with wavelengths between 0 5 and 3 m were observed on the bottom across the u s east coast continental shelf off north carolina during three side scan sonar surveys in september and december 1999 ripples were present in about 75 of the survey images in particular in regions with coarser sediments analysis of surficial sediment samples shows that median grain diameters range from 0 1 to 4 7 mm with large variations on the inner shelf over distances 1 km the observed ripple properties are consistent with wave generated vortex ripples analysis of concurrent wave observations indicates that the ripple crests were aligned perpendicular to the average direction of near bottom wave induced motions during preceding events that were sufficiently energetic to mobilize surficial sediments furthermore the ripple wavelengths proportionality to near bottom wave orbital excursions is consistent with wave formed vortex ripples these findings support the hypothesis that the observed strong attenuation of waves across the shelf resulted from form drag over large vortex ripples

experimental and textural constraints on mafic enclave formation in volcanic rocks abstract we have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at southwest trident volcano alaska andesite enclaves are present throughout the four dacite lava flows produced by the eruption and resemble mafic enclaves commonly found in other volcanic rocks our experiments replicate the pressure temperature time path taken by enclave forming andesite magma as it is engulfed in dacite during magma mixing pressure and temperature information for the andesite and dacite are from coombs et al contrib mineral petrol 140 2000 99 118 the andesite was annealed at 1000 c and then cooled to 890 c at rates of 110 c h 1 10 c h 1 and 2 c h 1 once cooled to 890 c andesite was held at this lower temperature from times ranging from 1 to 40 h the andesite that was cooled at the slower rates of 2 c h 1 and 10 c h 1 most resembles enclave groundmass texturally and compositionally based on simple thermal calculations these rates are more consistent with cooling of the andesite groundmass below an andesite dacite interface than with cooling of enclave sized spheres if enclaves do crystallize as spheres post crystallization disaggregation must occur calculations using the melts algorithm ghiorso and sack contrib mineral petrol 119 1995 197 212 show that for incoming andesite to become less dense than the dacite 34 volume of its groundmass must crystallize to undergo 18 volume vesiculation these values are similar to those determined for southwest trident enclaves thus such crystallization may lead to flotation of enclaves and be a viable mechanism for enclave formation and dispersal the residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments decompression experiments on southwest trident dacite suggest an average ascent rate for the eruption of 2 3 mpa h 1 an andesite experiment that was cooled and then decompressed at this rate contains melt that matches that of the natural enclaves it is apparent that decompression ascent induced crystallization occurs in enclaves but not in the form of microlites as happens in the dacite host due either to insufficient residence time at chamber temperatures or to the pre existing microphenocrysts which act as sites for new growth

magmatic interactions as recorded in plagioclase phenocrysts of chaos crags lassen volcanic center california the silicic lava domes of chaos crags in lassen volcanic national and mingling of this material into the silicic host these processes park contain a suite of variably quenched hybrid basaltic andesite are commonplace in some orogenic magma systems and may be magmatic inclusions the inclusions represent thorough mixing elucidated by isotopic microsampling and analysis of the plagioclases between rhyodacite and basalt recharge liquids accompanied by some crystallizing from them mechanical disaggregation of the inclusions resulting in crystals mixing into the rhyodacite host preserved by quenching on dome emplacement sr sr ratios 0 7037 0 7038 of the inclusions are distinctly lower than those of the host rhyodacite

ripple morphology under oscillatory flow 1 prediction 1 recent laboratory and field experiments have shown the inability of existing oscillatory flow ripple predictors to accurately predict both ripple size and ripple planform geometry however at this time only partial adaptations of these predictors have been proposed to account for the observed discrepancies with new experimental data the present work starts by presenting a comprehensive data set compiled from 27 literature studies and our own experimental data which are presented in a companion paper dimensional analysis is used both to clarify the importance of the different variables involved in the development of ripples and to generate the basic dimensionless framework for the study of ripple morphology under oscillatory flow several ripple size and planform geometry predictors are contrasted against the compiled data set afterward a new ripple wavelength and height predictor and a new planform geometry predictor are proposed which overcome several of the limitations found in the earlier formulations the new predictors emphasize the existence of local and global sediment transport mechanisms over a ripple bed each of them acting at different scales in particular sediment size is found to have an important effect on the size and geometry of bed forms that can be generated by oscillatory flows

sand ripples generated by regular oscillatory flow abstract the prediction of ripple geometry is a necessary precursor to the prediction of sand transport under waves for ripple regime conditions the paper begins with a comparison of four existing methods for predicting the geometry of sand ripples generated by oscillatory flow the comparison points to substantial differences between ripple dimensions predicted by the methods especially for field scale conditions ripple geometry experiments carried out in a large oscillatory flow tunnel are then described the experiments involved a range of sand sizes and sinusoidal and asymmetric flows with periods and velocities typical of field conditions comparison of measured and predicted ripple geometries leads to the recommendation that the method of mogridge davies and willis be used to predict ripple geometry for field scale oscillatory flows the nielsen method yields good predictions of ripple length but the rapid fall off in ripple steepness predicted by the nielsen method at high mobility number is not supported by the measurements the lengths and heights of symmetric ripples produced by sinusoidal flows are found to be similar to the lengths and heights of asymmetric ripples produced by equivalent asymmetric flows three dimensional ripples occur with fine sand in long period flows typical of field conditions the dimensions of these ripples cannot be predicted using methods developed for two dimensional ripples previously suggested criteria for predicting the occurrence of three dimensional ripples fail when tested against a wide range of flow and sand conditions the occurrence of three dimensional ripples and the effects of ripple and flow history on ripple geometry require further research

wave formed sand ripples at duck north carolina a recently developed acoustic multiple transducer array was utilized to measure small scale bed forms in the nearshore and inner shelf regions at duck north carolina two populations of wave formed ripples were observed short wave ripples swr with heights ranging from 3 mm to 2 cm and lengths ranging from 4 to 25 cm and long wave ripples lwr with heights ranging from 3 mm to 6 cm and lengths ranging from 35 to 200 cm the swr were only present sometimes and their presence or absence was determined by a critical value of the near bed mobility number the swr were highly dynamic sometimes flattening during wave groups and reforming over several incident wave periods the lwr in contrast were almost always present they were longer and lower relief than predicted by models or generally observed previously both swr and lwr were often observed to migrate shoreward but were rarely observed to migrate seaward the dimensions of the swr when they were present were predictable by the nielsen 1981 model or the wiberg and harris 1994 model to within approximately a factor of 2

basaltic pillow mounds in the vinalhaven intrusion maine the vinalhaven intrusion is a dominantly granitic pluton of probable devonian age located on vinalhaven island and adjacent islands maine it consists of four main units coarse grained granite fine grained granite a gabbro diorite unit consisting of interlayered mafic hybrid and granitic rocks and a heterogeneous granitic unit the gabbro diorite unit occurs along the south and east coast of the island as a sheet like body hundreds of meters to more than 1 km thick that dips beneath the central granitic units and rests on heterogeneous granitic rocks that form the base of the intrusion and are exposed on islands to the southeast load cast and pipe structures at the bases of mafic sheets indicate that the gabbro diorite unit represents a sequence of basaltic injections that ponded on crystal rich mush at the base of a silicic magma chamber and variably interacted with overlying crystal poor granitic magma the pluton therefore represents a fossilized silicic magma chamber that was periodically replenished by basaltic magma near the base of the gabbro diorite unit some basaltic injections produced large mounds up to more than 10 m high and 100 m wide of tightly packed meter scale chilled basaltic pillows tubes and sheets in a granitic matrix the mounds appear to represent flow fronts of basaltic injections that entered and ponded on the floor of a silicic magma chamber although physical conditions differ significantly these plutonic pillow mounds appear to share many characteristics with submarine pillow basalts and lava flows

dating the onset of volcanism at the rum igneous centre nw scotland major volcanic activity on the isle of rum commenced with the eruption of thick 100 m intra caldera rhyodacite ash flow sheets fed from steep sided feeder conduits in the proximity of the main ring fault twenty plagioclase phenocrysts of the rhyodacite were analysed using single crystal 40 ar 39 ar laser dating yielding a mean apparent age of 60 83 0 27 ma mswd 3 65 on an age v probability plot the feldspars do not however show a simple gaussian distribution but a major peak at 60 33 0 21 ma and two smaller shoulders at c 61 4 ma and 63 ma these older ages are interpreted to represent recycled and largely re equilibrated feldspars the age peak at 60 33 0 21 ma is interpreted to represent the intrusion and eruption age of the rhyodacites this new age constraint overlaps with that for the ultrabasic intrusion implying that the latter was already forming at depth and supplying necessary heat during the early felsic activity phase and quickly thereafter migrated upwards to shallow structural levels and intruded the volcano9s earlier deposits combined with previously published ages these new age data highlight an extremely rapid succession of events at the rum centre the whole sequence occurring in potentially

lateral versus vertical emplacement in shallow level intrusions the slieve gullion ring complex revisited recent studies on shallow level arcuate intrusions have identified numerous examples of horizontal mineral fabrics these are commonly interpreted as reflecting considerable lateral flow during magma emplacement thus querying established semi vertical ring dyke models we question the recent lateral emplacement model proposed for the palaeocene slieve gullion ring complex ne ireland where the absence of steep fabrics in parts of the ring complex has been used to support a shallow semi horizontal sheet intrusion mechanism we argue that such simple flow models cannot be applied to explosive ring fissure eruptions and that fabric data alone do not warrant rejection of the ring dyke model moreover the apparent absence of steep intrusive contacts along the intrusion s perimeter is readdressed and we present numerous examples of outcrops 27 with steep sided geometries the camlough breccias are reinterpreted as the product of gas driven tuffisites injected along the active ring fault rather than of purely tectonic origin crucially the porphyritic microgranite and porphyritic rhyolite ring dyke rocks exhibit geochemical and petrographic signatures of contamination by the geographically restricted palaeozoic newry granodiorite and are best explained through crustal interaction vertically beneath the ring complex subsequently these silicic magmas rose into ignimbrite feeders along a caldera ring fault system that was emplaced into near surface vent filling breccias