the role of magma mixing in the petrogenesis of mafic alkaline lavas rockeskyllerkopf volcanic complex west eifel germany the quaternary rockeskyllerkopf volcanic complex rvc comprises three spatially and temporally distinct volcanic centers that can also be distinguished on the basis of their geochemical signatures all the volcanic products in the complex are olivine basanites whose major and trace element compositions span almost the entire range defined for the west eifel field as a whole the rvc lavas have lower al2o3 na2o and y contents and higher tio2 cao k2o sc v co rb and ba than the tertiary lavas in nearby hocheifel volcanic field within the complex the oldest south east lammersdorf center sel comprises primitive lavas with an average mgo content of 11 wt and lan ybn of 29 2 the second center mauseberg has similar mgo to sel but is distinct in its much higher lan ybn of 42 2 the rockeskyllerkopf center which was erupted after a break in activity comprises lavas similar in composition to the sel center but with distinctly higher al2o3 and lower mgo contents given the lack of evidence for significant fractionation or assimilation in the rvc lavas we attribute the compositional variations within and between the centers of the rvc to be due to variations in the composition of the source region in combination with magma mixing our preferred model involves 1 5 partial melting of lree enriched mantle in the garnet stability field likely within the thermal boundary layer at the base of the lithospheric mantle these melts mixed to variable degrees with 2 4 partial melts of phlogopite spinel peridotite formed at higher levels in the modally metasomatised lithospheric mantle

stress regime strain release and geothermal implicationsregional stress field and rifting in western europe in situ stress determination is one possibility to determine stress magnitudes in the earth s crust most measurements especially in the northern alpine foreland have been carried out by using the doorstopper technique stress magnitudes are presented as excess stresses a number of sites where stresses have been determined gave sufficiently high values to statistically determine stress directions for the following tectonic blocks 1 1 western alps 2 2 their immediate foreland with the rhinegraben and 3 3 the rhenish shield bordering on the rift segment of the lower rhine embayment in discussing results of the statistical analyses of stress data it is suggested that stresses measured in the western alps have mainly a topographic origin in the alpine foreland to the north of the rhenish shield topographic stresses are superimposed on active tectonic stress considering the structural and lithological differences the foreland blocks show a different response to the same tectonic stress field which trends for 1 at about 146 this active stress field causes shear rifting in the upper rhinegraben but extensional rifting in the lower rhine embayment in the rhenish shield area only local step faults are observed in direction of 1 due to the ductile behaviour of its basement

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

mid cretaceous primitive alkaline magmatism in the northern calcareous alps significance for austroalpine geodynamics basanitic dykes local name ehrwaldite occur over a distance of at least fifty kilometres in a narrow east west trending zone within the lechtal nappe of the northern calcareous alps the dykes crosscut mesozoic sedimentary strata up to the lower cretaceous the sedimentary rocks show contact metamorphism in the immediate vicinity of the dykes the ehrwaldites vary in mineral content from olivine fo 91 87 titanian augite basanites to basanites containing also kaersutite titanian biotite and zeolites minor phases are titanian magnetite picotite llmenite carbonate and sulfides mantle derived xenoliths and xenocrysts form up to five percent of the rock bulk chemical analyses show the typical characteristics of nepheline basanites ne 11 17 wt mg number 74 78 and demonstrate that the ehrwaldites are primitive mantle derived melts trace element contents of the dykes are in excellent agreement with those for basanites and olivine nephelinites from tertiary and quaternary european provinces the same is true for the isotope characteristics of the dykes with average initial esr and end values of 8 2 and 4 7 respectively these data demonstrate similarities in the mantle source rocks and in the melting characteristics with european alkaline rocks and thus similarities in the european subcontinental mantle at different localities for the last 100 ma these data are in clear contrast with the value for the penninic suboceanic mantle geochemical constraints and piston cylinder experiments indicate a depth of origin of 80 kilometres at temperatures of at least 1250 c for the ehrwaldites potassium argon bulk rock data of petrographically different samples of the dykes from different localities yield consistent ages around 100 ma upper albian after emplacement the ehrwaldites underwent conditions of the zone of diagenesis with temperatures around 120 c which the late magmatic zeolites survived

sediment budget for salmonid spawning habitat rehabilitation in a regulated river bed elevation feature adjustments and spawning use were monitored at three chinook salmon oncorhynchus tschawytscha spawning habitat rehabilitation sites to measure project longevity in a regulated river sites enhanced with 649 1323 m 3 of gravel lost from 3 20 of remaining gravel volume annually during controlled flows of 8 70 m 3 s and 2 6 4 6 of placed material during a short duration 19 days release of 57 m 3 s the oldest site lost 50 of enhancement volume over 4 years of the mechanisms monitored gravel deflation was the greatest contributor to volumetric reductions followed by hydraulic scour spawning local scour around placed features and oversteepened slopes contributed to volumetric changes as sites matured volumetric reductions decreased sites captured as much large woody debris as was lost while complexity is an extremely important aspect of ecological function artificial production of highly diverse and complex habitat features may lead to limited longevity without natural rejuvenation d 2005 elsevier b v all rights reserved

crystallization paths of leucite bearing lavas examples from italy the salic phases found in leucite basanites trachytes and phonolites may be used to portray crystallization in the system naalsio 4 kalsio 4 caal 2si 2o 8 sio 2 the phonolite pentahedron only two lavas have been found that contain the assemblage leucite nepheline plagioclase sanidine and liquid a natural pseudo invariant assemblage at 900 c 100 equivalent to the isobaric invariant point of the four component system the diversity of phases in this group of lavas illustrates the role of halogens in controlling their crystallization paths thus the presence of f in the leucite basanites has stabilized magnesian biotite and suppressed sanidine as has been found in other basanitic lavas brown and carmichael 1969 the presence of cl in these same lavas has induced the crystallization of sodalite which takes the place of nepheline in the groundmass however in the leucite trachytes biotite has suppressed olivine and coexists with sanidine and leucite the presence of s may produce hauyne at the expense of nepheline and in general sulphate minerals which include apatite have the role in lavas of low silica activity that pyrrhotite plays in liquids of high silica activity both pyroxenes and titaniferous magnetites in this suite of lavas are very aluminous groundmass crystals of pyroxene may have one fifth of si replaced by al other phases which occur occasionally are melanite garnet and a potassium rich hastingsite but neither ilmenite nor a sulphide mineral has been found phenocryst equilibration temperatures derived from olivine and sr rich plagioclase are generally in the range from 1 050 c to 1 150 c the high content of incompatible elements e g k ba rb f sr p in these lavas suggests that they represent a small liquid fraction from a mantle source which possibly contains phlogopite

paleointensity in the quaternary west eifel volcanic field germany preliminary results abstract preliminary paleointensity results are presented from 36 sites with virtual geomagnetic pole vgp latitudes of about 30 90 normal polarity in the quaternary west eifel volcanic field a strong correlation between vgp latitude and the earth s virtual magnetic dipole moment vdm is observed with low intensities for low vgp latitudes indicating possibly an emplacement during an excursion or event of the brunhes epoch the age distribution of the west eifel volcanics is as yet poorly known also the mean vdm value for sites with high vgp latitudes is considerably lower than the present day dipole moment of the earth

sediment transport in the cauvery river basin sediment characteristics and controlling factors abstract during the monsoon period 75 of the annual rainfall 73 of the annual water discharge and 85 of the annual sediment transport takes place in the cauvery river basin geology and river water discharge are the major natural factors controlling the sediment transport sediment transport in the cauvery river is greatly influenced by the presence of two major dams built across the river an examination of the particle size distribution of the suspended sediments shows that the less than 20 m fraction accounts for nearly 60 of the total sediment transported by the river at dam sites coarse sediments are selectively removed from the suspended load the suspended mineralogy is dominated by quartz and feldspar followed by clay minerals and carbonates clay minerals average about 30 and are dominated by the montmorillonite type the results of our study also demonstrate the importance of such sediment characteristics as particle size and mineralogy in controlling the trace metal distribution in sediments

sedimentological proof and dating of the early holocene volcanic eruption of ulmener maar vulkaneifel germany a minerogeniclayer occurs in early postglacial organic sediments from five maar lakes west eifel volcanic field germany the mineralogy and stratigraphic position of this tephra suggests that it is related to the youngest german volcano ulmener maar nearby radiocarbon dating of wood from the base of the ulmener maar tephra at two locations provide ages in agreement with an accelerator mass spectrometer 14c date for the minerogenic layer from sediments of lake holzmaar situated 13 km south west of ulmener maar the mean radiocarbon age is 9 560 years bp dating by varve chronology provides an age of 10017 years vt varve time in years before 1950 or 10 895 years corrected vt based on palynology the ulmener maar tephra was deposited at the end of the preboreal high values of natural remnant magnetization intensity typical of pyroclastic material confirm that this minerogenic layer differs in composition from other clastic deposits of the sedimentary record geochemical analyses reveal increased values of total trace elements for the laacher see tephra and ulmener maar tephra an isopach map based on thickness variations of the ulmener maar tephra at five investigated maar lakes indicates that the tephra was mainly transported to the south west

comparing different methods of bed shear stress estimates in simple and complex flow fields bed shear stress is a fundamental variable in river studies to link ow conditions to sediment transport it is however dif cult to estimate this variable accurately particularly in complex ow elds this study compares shear stress estimated from the log pro le drag reynolds and turbulent kinetic energy tke approaches in a laboratory ume in a simple boundary layer over plexiglas and over sand and in a complex ow eld around de ectors results show that in a simple boundary layer the log pro le estimate is always the highest over plexiglas the tke estimate was the second largest with a value 30 per cent less than the log estimate however over sand the tke estimate did not show the expected increase in shear stress in a simple boundary layer the reynolds shear stress seems the most appropriate method particularly the extrapolated value at the bed obtained from a turbulent pro le in a complex ow eld around de ectors the tke method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent uctuations close to the de ectors it is suggested that when single point measurements are used to estimate shear stress the instrument should be positioned close to 0 1 of the ow depth which corresponds to the peak value height in pro les of reynolds and tke shear stress copyright 2004 john wiley sons ltd

three dimensional ground motion modelling in the kachchh rift zone gujarat india abstract the strong motion dataset of the 6 april 2006 bhuj aftershock of mw5 5 from 16 three component accelerograph stations are used here to perform a detailed ground motion modelling in the kachchh rift basin first we estimate the 1 d velocity structure model down to the bedrock at 16 accelerograph sites through the genetic algorithm inversion of strong motion waveforms then a 3 d velocity structure model of the basin is constructed using the modelled 1 d velocity structure and constraints from earlier seismological vs30 estimation by ps logging and masw and seismic exploration studies in the region we modelled low frequency 0 1 1 hz ground motions excited by the 6 april 2006 event using the finite difference method fdm assuming a point source to access the robustness of the constructed velocity structure model at most of the stations the observed and simulated velocity waveforms are found to be in good agreement in terms of both amplitude and ground motion duration we also computed synthetic ground velocities at numerous locations within the basin for both the 2001 bhuj mainshock finite fault source and the 2006 aftershock point source cases using the 3 d velocity structure model for both the cases we notice significant amplifications of amplitudes and elongation of shaking at stations lying within the basin while smaller amplifications are noticed at stations away from the basin our fdm modelling for the 2001 bhuj mainshock at lower frequency

local scour associated with angled spur dikes a series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear water overtopping flows spur dike models were angled at 45 90 and 135 to the downstream channel sidewall with contraction ratios of 0 125 and 0 250 the main goals of the experiments were to evaluate the effect of the three angles on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks the experiments showed that of the three angles tested the least erosion of the bed in the near bank region was associated with the spur dikes with 90 angles while the greatest volume of the scour hole was associated with the 135 spur dikes it was concluded that spur dikes with 135 angles showed the best potential for providing improved aquatic habitats while minimizing the potential for erosion of the channel bank

potassium rich volcanic rocks of the muriah complex java indonesia products of multiple magma sources abstract the extinct pleistocene volcano muriah situated behind the main pleistocene recent sunda magmatic arc in north central java has erupted at least two contrasted groups of lavas one group forms a well defined compositional series anhydrous series from leucite basanite to tephritic phonolite with olivine and tschermakitic clinopyroxene the main phenocrysts the other group the hydrous series includes compositionally variable tephrites and high k andesites with common plagioclase biotite and amphibole lavas of the anhydrous series are much richer in lil trace elements than the most potassic lavas of neighbouring active volcanoes but relative hfs element enrichment is less pronounced ree patterns have almost constant slopes from la 250 600 times chondrites to yb 5 10 times chondrites while those of lavas of active centres are less light enriched and show flattening in the heavy ree anhydrous series initial 87sr 86sr ratios 0 7043 0 7046 are lower than those of active centres 0 7047 0 7053 hydrous series lavas are intermediate in all these geochemical characteristics the most mafic a series leucite basanite with mg mg fe 2 0 69 140 ppm ni and 620 ppm cr was probably derived from the primary magma for the series by fractionation of only 5 wt olivine its ree pattern suggests derivation from a garnet bearing source experiments on this basanite with up to 10 olivine and 20 orthopyroxene added and in the presence of h2o and h2o co2 mixtures have shown that for all but very high magma water contents the olivine and garnet liquidus fields are widely separated by fields of phlogopite and clinopyroxene there is no liquidus field of orthopyroxene hence if magma production involved an equilibrium melting process alone the most probable sources are of garnet bearing phlogopite clinopyroxenite type alternatively this magma may represent the end product of interaction between a low k basanite magma from a garnet lherzolite source in the asthenosphere and a phlogopite bearing lherzolite zone in the lower lithosphere its production was probably related to crustal doming and extension superimposed on the dominant subduction regime hydrous series magmas may have resulted from mixing between anhydrous series magmas and high k calc alkaline basaltic to andesitic magmas more directly related to subduction processes

identification of maars and similar volcanic landforms in the west eifel volcanic field through image processing of dtm data efficiency of different methods depending on preservation state the west eifel volcanic field comprises 98 maars tuff rings and scoria rings of volcanoes younger than 700 ka digital terrain models dtms allow to automatically measure morphologic parameters of volcanic edifices such as slope angles diameters elevations floor and slope surface areas based on their morphological characteristics we subdivided the west eifel volcanoes into five morphometric groups which reflect different stages of erosion group i ii and iv comprise clear ring shaped structures the difference between these groups is that a tephra ring is well preserved in group i partially preserved in group ii and absent in group iv the original shapes of group iii maars have been lost more substantially than in groups i ii or iv but they nevertheless retain a negative shape a depression and have characteristic channel systems which can be used as search criteria maar diatremes of group v are eroded down to their feeder pipes and form hills in order to locate potential volcanic depressions that are likely to be maar volcanoes we defined common search criteria such as circular negative landforms or particular drainage system patterns for all groups except the least well preserved group v these criteria were taken as the basis for further processing of the dtm data the first processing step consisted of constructing a residual relief calculated as the difference between a filtered smoothed topographic surface and the original dtm data this identifies local topographic features we propose a method for regulating the degree of smoothing which is based on filtering of local maxima according to their distance from a surface constructed from local minima the previously defined search criteria for groups i to iv such as specific ranges of curvature slope circularity density of the drainage network were then applied to the residual relief in order to extract maar shapes not all criteria work equally well for all morphological groups combinations of multiple search criteria therefore yield the best results and efficiently identify most known maars they also separate some probable new hitherto unrecognized maars from a large number of other local depressions we also compared the erosional state of maars to their absolute ages published estimates of erosion rates for maars in the french massif central suggest a general trend of erosion rates decreasing with time elapsed since eruption however this cannot explain the strongly varying ages for maars of the same morphometric group i e similar preservation state in the west eifel volcanic field the spatial distribution of the morphometric groups shows some regularity for example strongly eroded maars are concentrated in the gerolstein area where maar density is highest whereas most well preserved maars are located east of the eifel north south depression ensd most maars affected by fluvial erosion lie near the kyll and kleine kyll streams these observations suggest differential recent uplift of the west eifel volcanic field with stronger uplift occurring west of the ensd

fluorine geochemistry of basaltic rocks from continental and oceanic regions and petrogenetic application fluorine contents in about 300 samples of various types of basalts and related rocks from continental southwestern u s a zaire deccan and south africa and oceanic regions hawaii and mid atlantic ridge between 23 n and 40 n were determined by a selective ion electrode method

space time evolution of monogenetic volcanism in the mafic garrotxa volcanic field ne iberian peninsula we reconstructed the evolution of the volcanic activity within the central garrotxa monogenetic volcanic field the youngest volcanic area of the iberian peninsula by investigating the stratigraphy of the volcanic successions and the morphology of the monogenetic eruptive centres analysis of this volcanic succession has been conducted following the unconformity bounded stratigraphic units criteria the detailed stratigraphy of the volcanic successions shows that the central garrotxa volcanic field gvf evolved through four main periods of volcanic activity synthems represented by the eruptive products of the mafic monogenetic volcanoes and associated syn eruptive reworked deposits eruptive units and by the inter eruptive deposits epiclastic units the distribution and the morphologies of the monogenetic volcanoes suggest that feeder dykes were emplaced under influence of the present stress filed and along pre existing fractures of the basement our facies analysis of the deposits and their distribution shows that migration of volcanism toward the centre of the basin was accompanied by a trend of increasing explosivity episodic hydromagmatism in central garrotxa occurred without a specific geographic locus or obvious temporal correlation finally by integrating field data with the stratigraphy extracted from water wells we determined the volume of the volcanic deposits the small average volume of products emitted during each eruptive period and the long quiescence separating them allow us to classify the gvf as a low output rate volcanic field

the temporal evolution of three magmatic systems in the west eifel volcanic field germany abstract the quaternary west eifel volcanic field is the surface expression of a mantle plume that is thought to contain 1 melt the volcanoes range in age from 0 7 ma to 10 000 yr bp and the average recurrence rate of volcanism is around 3 5 10 4 eruptions per year giving a mean time between eruptions of 2875 years assuming that the field is monogenetic the presence of mafic and ultramafic xenoliths is taken as evidence for rapid single stage emplacement of magmas at velocities around 0 5 km h however the presence of clinopyroxene that preserves evidence of polybaric crystallisation belies this simple model this study uses variations in the fo content of olivine in mantle derived xenoliths and in olivine xenocrysts enclosed in cumulate xenoliths to calculate the time scale of evolution of three volcanic centres in the eifel field core rim variations in olivine are interpreted to result from fe mg interdiffusion between it and a surrounding melt using experimental determinations of the interdiffusion coefficient and approximations of magma temperature contact times have been calculated using planar and radial diffusion models the three volcanic centres studied were meerfelder maar gemundener maar and baarley the cumulate xenoliths at meerfelder maar formed at a depth of 13 km and record a magma emplacement event at between 1 and 3 years prior to eruption two suites of mantle derived olivine clinopyroxenites record a further two events at 1 8 days and 3 h prior to eruption the final event is interpreted to record the eruption of this volcano and the 3 h contact time records the time required for transport of peridotite xenoliths from the mantle to surface giving an average emplacement velocity of around 15 km h the cumulate xenoliths at gemundener maar crystallised at depths of between 4 and 22 km there are four distinct events recorded by the zoned olivine grains in the clinopyroxene rich cumulates from this locality the maximum residence time is similar to that at meerfelder maar however in this case the final magma resided in the chamber for between 23 days and 2 7 months prior to eruption allowing enough time for any entrained peridotite xenoliths to be filtered out the cumulate xenoliths from the baarley locality record a much longer history than those at the other localities in this case initially peridotitic olivine has been completely re equilibrated over 175 years prior to eruption in common with the other two localities there is evidence of multiple intrusive events at depths up to 7 km prior to final eruption the duration of the final eruption event and the interpreted depth to source of the xenoliths indicate an emplacement velocity of around 3 km h the data derived from modelling of diffusion profiles in olivine from cumulate xenoliths indicate that the magmatic systems feeding these three volcanoes were dynamic and very short lived in addition these data can be used to place constraints on the rate of cumulate formation in subvolcanic magma chambers on the basis of the data presented here it would seem that an appreciable thickness of cumulates can form over relatively short time spans days to a few years

partial entrainment of gravel bars during floods 1 spatial patterns of bed material entrainment by floods were documented at seven gravel bars using arrays of metal washers bed tags placed in the streambed the observed patterns were used to test a general stochastic model that bed material entrainment is a spatially independent random process where the probability of entrainment is uniform over a gravel bar and a function of the peak dimensionless shear stress t of the flood the fraction of tags missing from a gravel bar during a flood or partial entrainment had an approximately normal distribution with respect to t 0 with a mean value 50 of the tags entrained of 0 085 and standard deviation of 0 022 root mean square error of 0 09 variation in partial entrainment for a given t demonstrated the effects of flow conditioning on bed strength with lower values of partial entrainment after intermediate magnitude floods 0 065 t 0 08 than after higher magnitude floods although the probability of bed material entrainment was approximately uniform over a gravel bar during individual floods and independent from flood to flood regions of preferential stability and instability emerged at some bars over the course of a wet season deviations from spatially uniform and independent bed material entrainment were most pronounced for reaches with varied flow and in consecutive floods with small to intermediate magnitudes index terms 1815 hydrology erosion and sedimentation 1821 hydrology floods 1869 hydrology stochastic processes keywords sediment transport bed material entrainment disturbance gravel bars stochastic model

determination of geomagnetic palaeointensities from the quaternary west eifel volcanic field germany summary determination of geomagnetic palaeointensities has been attempted for 418 specimens from 51 volcanic units of the quaternary west eifel volcanic field this paper describes the measuring procedure using a modification of the thellier method the analysis of the derived data points the determination of linear segments and the quality of the individual palaeointensity values calculated from the corresponding slopes according to a series of acceptance and rejection criteria finally 312 reliable individual palaeointensity results have been obtained about 73 per cent of the accepted regression lines have correlation coefficients better than 0 990 and less than 10 per cent of the accepted thellier experiments have quality factors less than 1 0 the carriers of magnetization of the west eifel volcanic rocks are titanomagnetites with a broad range of titanium contents and oxidation states in a more or less unweathered mostly foiditic rock matrix accompanying rock magnetic experiments allowed a rough classification of the specimens corresponding to the oxidation state of the titanomagnetites specimens with highly oxidized titanomagnetites have been the most successful candidates for the thellier experiments however a prediction of the suitability of the specimens for the thellier experiments by sample selection according to this classification was not always appropriate instead for most volcanic units pilot specimens were first measured to determine the suitability of a specific sample type the temperature interval from which the evaluation of palaeointensity was possible and the best laboratory field intensity to keep the slope errors of the thellier experiments to a minimum palaeointensity determination was not possible for 14 volcanic units because only unsuitable specimens were available for each of the 37 remaining volcanic units at least five successful thellier experiments have been carried out leading to a final mean palaeointensity result these 37 values have relative standard errors of between 4 and 23 per cent mostly around 10 per cent specimens with differing rock magnetic properties from the same volcanic unit yielded consistent palaeointensity values therefore all west eifel palaeointensity results have to be regarded as reliable estimates of the earth s magnetic palaeofield strength mean palaeointensities range from 7 to 62 pt with an unexpectedly large number of palaeointensity values less than 30 pt about half of the low palaeointensity values are associated with intermediate virtual geomagnetic pole latitudes which may be due to a geomagnetic excursion

the geochemistry and petrogenesis of k rich alkaline volcanics from the batu tara volcano eastern sunda arc mineralogical major and trace element and isotopic data are presented for leucite basanite and leucite tephrite eruptives and dykes from the batu tara volcano eastern sunda arc in general the eruptives are markedly porphyritic with phenocrysts of clinopyroxene olivine leucite plagioclase biotite set in similar groundmass assemblages these k rich alkaline volcanics have high concentrations of large ion lithophile lil light rare earth lre and most incompatible trace elements and are characterized by high 87sr 86sr 0 70571 0 70706 and low 143nd 144nd 0 512609 0 512450 compared with less alkaline volcanics from the sunda arc they also display the relative depletion of ti and nb in chondrite normalized plots which is a feature of subalkaline volcanics from the eastern sunda arc and arc volcanics in general chemical and mineralogical data for the batu tara k rich rocks indicate that they were formed by the accumulation of variable amounts of phenocrysts in several melts with different major and trace element compositions the compositions of one of these melts estimated from glass inclusions in phenocrysts is relatively fe rich 100 mg mg fe2 48 51 and is inferred to have been derived from a more primitive magma by low pressure crystal fractionation involving olivine clinopyroxene and spinel mg rich mg 90 and cr rich up to 1 7 wt cr2o3 zones in complex oscillatory zoned clinopyroxene phenocrysts probably also crystallized from such a magma the marked oscillatory zoning in the clinopyroxene phenocrysts is considered to be the result of limited mixing of relatively evolved with more primitive magmas together with their phenocrysts along interfaces between discrete convecting magma bodies

radius rapid particle analysis of digital images by ultra high resolution scanning of thin sections radius is a newly developed particle size measurement technique based on evaluation of digital images of thin sections analyses are performed with sub millimetre sample resolution and are thus designed to work on a single lamina of laminated sediments the method covers grain sizes from medium silt to coarse sand the application contains pattern recognition modules that allow the detection of typical particle distributions of loess organic detritus turbidites and tephra layers cutting and hiding effects of particles on thin sections are corrected by empirical correction matrices the calculated analysis results are compared with manually counted and measured samples to calibrate the application settings the method can be applied to all fine grained clastic sediments particularly to laminated lake sediments

methodological sensitivity of morphometric estimates of coarse fluvial sediment transport abstract the estimation of fluvial sediment transport rate from measurements of morphological change has received growing recent interest the revival of the morphological method reflects continuing concern over traditional methods of rate determination but also the availability of new survey methods capable of high precision high resolution topographic monitoring remote sensing of river channels through aerial digital photogrammetry is a potentially attractive alternative to labour intensive ground surveys however while photogrammetry presents the opportunity to acquire survey data over large areas data precision and accuracy particularly in the vertical dimension are lower than in traditional ground survey methods this paper presents results of recent research in which digital elevation models dems have been developed for a reach of a large braided gravel bed river in scotland using both digital photogrammetry and high resolution rtk gps ground surveys a statistical level of change detection is assessed by comparing surfaces with independent check points the methodological sensitivity of the annual channel sediment budget 1999 2000 to the threshold is presented results suggest that while the remote survey methods employed here can be used to develop qualitatively convincing moderate precision dems of channel topography rmse 0 21 m the remaining errors imply significant limits on reliable change detection which lead to important information losses tests at a 95 confidence interval for change detection show that over 60 of channel deposition and 40 of erosion may be obscured by the lower level of precision associated with photogrammetric monitoring when compared to ground survey measurements this bias reflects the difficulty of detecting the topographic signature of widespread but shallow deposition on bar tops

estimating local bed shear stress from velocity observations replicate velocity observations using conventional equipment under typical field conditions are used to evaluate the precision of different methods for estimating local boundary shear stress from velocity measurements the bed shear velocity u can be estimated within 3 using the depth averaged velocity in the vertically averaged logarithmic velocity profile to be accurate this method is limited to relatively simple flow geometries which may be expected to have the appropriate velocity structure estimates of u made using a single near bed velocity observation are less precise by a factor of 3 because of the larger uncertainty associated with a single observation accuracy of this method requires appropriate flow conditions only near the bed so it may be applied in a wider range of flow conditions including spatially variable flow estimates of u from the slope of the near bed velocity profile are the least precise and require the most restrictive flow conditions for accuracy but offer the advantage that they may be made without independent knowledge of the bed roughness different methods for estimating roe should be useful in judging the precision of estimates made under similar conditions these estimates of precision together with considerations of convenience and model accuracy provide the basis for select ing the most appropriate or advantageous method for different conditions and purposes

on the controls of oxygen fugacity in the generation and crystallization of peralkaline melts the formation of peralkaline melts is generally recognized to be related to enrichment of the mantle in sodium or potassium during a metasomatic event that predated magma generation the wide range in mineral assemblages mineral compositions and fluid compositions in peralkaline melts are to a large extent a function of the sodium potassium content of these mantle metasomatizing fluids which also governs redox conditions we propose that sodic fluids will reduce the mantle assemblage by depleting ferric iron from garnet to form the aegirine component in pyroxene in contrast potassic fluids would oxidize the mantle assemblage by extracting al2o3 from the garnet to make phlogopite we suggest that during differentiation of peralkaline melts once fe ti oxides have been depleted from the assemblage simple crystallization reactions of common solid phases such as aegirine or arfvedsonite control the oxygen fugacity by equilibria such as

clinopyroxene zoning patterns in the young alkali basalts of hungary and their petrogenetic significance in the upper pliocene during the final phase of igneous activity within the pannonian basin alkali basalts were erupted their occurrences are restricted to two main regions in hungary 1 transdanubia 2 nograd county the clinopyroxene phenocrysts of these rocks are zoned titanaugites which often have distinctive colourless or green cores two kinds of green cores can be distinguished 1 olive green cores fassaitic augite and fassaite and 2 grassgreen cores salite and ferrosalite both types of green cores are comparatively iron rich and they occur only in the basalts of nograd county the olive green fassaites probably precipitated from relatively evolved melts which have been mixed into their present host magmas whereas the grassgreen salites and ferrosalites are xenocrysts derived probably from upper mantle rocks the clinopyroxene zoning patterns suggest that after being generated by small degree partial melting in the mantle the transdanubian basalts ascended to the surface with little or no modification en route whereas those of nograd county had a more complex evolution in which fractionation at depth and magma mixing played an important role

metasomatised lower crustal and upper mantle xenoliths from north queensland chemical and isotopic evidence bearing on the composition and source of the fluid phase a diverse range of ultramafic and mafic granulite xenoliths from cone 32 north queensland display mineralogical and chemical evidence for enhanced fluid activities in the lowermost crust and uppermost mantle metasomatism of spinel lherzolite garnet and spinel websterite and garnet granulite produced variable amounts of amphibole mica locally resulting in development of hornblendite as the end product of reaction between spinel websterite and c o h fluids in contrast associated felsic and 2 pyroxene granulite xenoliths have remained relatively unaffected the garnet granulites and spinel websterites are interpreted as products of underplating of the lower crust by cenozoic magmatic activity whereas nd sr isotope systematics for the 2 pyroxene and felsic granulite xenoliths suggest that they may be of proterozoic age the development of amphibole and mica in the mafic and ultramafic xenoliths was accompanied by increases in tio2 na2o k2o a12o2 sr ba zr nb lree and fe2o3 feo and decreased mgo sio2 cr and ni virtually anhydrous spinel websterite xenoliths have 87sr86sr and 143nd144nd almost identical to amphibole rich variants and hornblendite and very similar values to the host nepheline mugearite and an amphibole megacryst the chemical and isotopic data suggest that the metasomatism is a relatively young feature caused by oxidized fluids exsolved from alkaline magmas similar to the host as they ascended through the lithosphere this style of metasomatism is considered a relatively localized phenomenon which is unlikely to provide an important contribution to the source regions of alkali basaltic magmas

sediment transport processes in pool riffle sequences this paper reviews the published data for sediment transport in pool riffle sequences which suggests that a velocity or shear stress reversal hypothesis does not explain all of the published evidence of sediment transport this conclusion is explored in more detail using observations of sediment transport from the regulated river north tyne sediment transport rates at discharges of 30 per cent bankfull are initially highest on riffles as discharge increases sediment transport rates in pools rise sharply and values locally exceed those on riffles tracing experiments using a combination of magnetic and painted tracers are used to show the downstream dispersal of fine and coarse sediments through the pool riffle sequence coarser particles experience longer transport paths and faster virtual rates of travel in pools during bankfull floods analysis of entrainment data reveals evidence for additional restraint operating on riffles and causing higher dimensionless entrainment thresholds an appraisal of the possible mechanisms controlling sediment entrainment transport and deposition in pool riffle sequences is made which reveals evidence for the operation of a combination of hydraulic sedimentological and interactive processes a descriptive model of sediment transport processes in pool riffle sequences is presented

geochemical and petrographic characteristics of potassium rich pyroclastic and lava samples from vulsini volcano roman magmatic region italy abstract pyroclastic deposits are the dominant eruptive product at vulsini and at other potassic volcanoes in the roman magmatic region central italy geochemical data from 139 k rich undersaturated vulsinian samples are used in the first systematic study of both pyroclastic and lava eruptions from a large volcano in this region the pyroclastic samples span the complete range of rock chemistries however compared to the lavas they are concentrated in the more evolved products and thus significantly enlarge the erupted volume of phonolitic and trachytic magma the pumice and lava major and trace element trends generally form a continuum consistent with a fractionated sequence of k rich magmas as follows leucite basanite mg rich leucitite leucitite tephritic leucitite leucite phonolite leucite trachyte saturated trachyte olivine is conspicuous in the primitive basanitic pumice and lava samples and is also present in the less evolved tephritic leucitites clinopyroxene crystallizes at all stages of magma evolution along with leucite plagioclase mica opaque oxides and sanidine leucite phenocrysts are prominant in the intermediate to more evolved compositions particularly in the leucite phonolites where they form large macrophenocrysts sanidine is a significant phenocryst phase in the more evolved samples particularly in the evolved pumices where it dominates the modal assemblage in these samples increasing rb and rapidly decreasing sr and ba as well as reducing k2o na2o ratios are linked to sanidine fractionation high ni contents 250 ppm high mg numbers 78 and forsteritic olivine fo92 suggest that the basanitic pumice and lava magmas had a mantle origin through partial melting similarly mg rich leucitites are also inferred to be mantle partial melts on the basis of high k cao rb and f concentrations and high k na cao mgo low k rb and high di ol ratios found in the primary basanites and leucitites the mantle source is inferred to be rich in phlogopite and clinopyroxene by comparison with various purported primary alkaline magmas the vulsinian primary magmas show considerable enrichment of k rb and th while other elements such as nb zr sr p and ti are significantly depleted thus suggesting a decoupling between these groups of incompatible elements in the mantle beneath vulsini variable nb th ratios are a feature of vulsinian magmas and such variations along with the relative decoupling of incompatible elements are linked to metasomatic processes and the development of a phlogopite and clinopyroxene enriched mantle

eifel maars quantitative shape characterization of juvenile ash particles eifel volcanic field germany abstract the eifel region in western central germany is the type locality for maar volcanism which is classically interpreted to be the result of explosive eruptions due to shallow interaction between magma and external water i e phreatomagmatic eruptions sedimentary structures deposit features and particle morphology found in many maar deposits of the west eifel volcanic field wevf in contrast to deposits in the east eifel volcanic field eevf lack the diagnostic criteria of typical phreatomagmatic deposits the aim of this study was to determine quantitatively the shape of wevf and eevf maar ash particles in order to infer the governing eruption style in eifel maar volcanoes the quantitative shape characterization was done by analyzing fractal dimensions of particle contours 125 250 m sieve fraction obtained from scanning electron microscopy sem and sem micro computed tomography sem micro ct images the fractal analysis dilation method and the fractal spectrum technique confirmed that the wevf and eevf maar particles have contrasting multifractal shapes whereas the low small scale dimensions of eevf particles eppelsberg green unit coincide with previously published values for phreatomagmatic particles the wevf particles meerfelder maar pulvermaar and ulmener maar have larger values indicating more complex small scale features which are characteristic for magmatic particles these quantitative results are strengthening the qualitative microscopic observations that the studied wevf maar eruptions are rather dominated by magmatic processes the different eruption styles in the two volcanic fields can be explained by the different geological and hydrological settings found in both regions and the different chemical compositions of the magmas

roman lava quarries in the eifel region germany geochemical data for millstone provenance studies roman millstones of assumed eifel origin were produced and exported in huge quantities to many parts of roman europe and can be used as tracers for trade patterns in roman times this study presents for the first time a raw material centred geochemical definition of the 13 well known roman basaltic lava quarries in the quaternary east and west eifel volcanic fields the aim is to find a way to characterize the individual exploitation sites precisely by means of their geochemical composition and to recommend a standard procedure for further millstone provenance analysis based on major and trace element composition analyses by xrf a differentiation of each quarry is achieved by using a combination of geochemical discrimination and cluster and discriminant analysis therefore for provenance analysis of a unknown millstone sample the following procedure is recommended 1 geochemical discrimination to check if it actually belongs to the volcanic eifel quarries 2 cluster analysis to check to which quarry or cluster of quarries the millstone can be affiliated and 3 discriminant analysis to assign the sample to its quarry of origin with a certain confidence

friction angle measurements on a naturally formed gravel streambed implications for critical boundary shear stress we report the first measurements of friction angles for a naturally formed gravel streambed for a given test grain size placed on a bed surface friction angles varied from 10o to over 100o friction angle distributions can be expressed as a function of test grain size median bed grain size and bed sorting parameter friction angles decrease with increasing grain size relative to the median bed grain size and are a systematic function of sorting with lower friction angles associated with poorer sorting the probability distributions of critical shear stress for different grain sizes on a given bed surface as calculated from our friction angle data show a common origin but otherwise diverge with larger grains having narrower and lower ranges of critical shear stresses the potential mobility of a grain as defined by its probability distribution of critical shear stress may be overestimated for larger grains in this analysis because our calculations do not take into account the effects of grain burial and altered near bed flow fields

geochemical evidence for holocene palaeodischarge variations in lacustrine records from the westeifel volcanic field germany schalkenmehrener maar and meerfelder maar various chemical elements fe mn u mo can be transported in both dissolved and solid form and then deposited into lakes geochemical profiles of these elements in lacustrine records are therefore potential palaeoclimatic proxies since there should be a positive correlation between discharge from the catchment and dissolved element input flux rates for the dissolved input of uranium ul t and the total allochthonous minerog enic deposit were calculated for an annually laminated sediment record from the lake schalkenmehrener maar smm calculated ul t values were critically examined with the help of monitoring data hydrochemistry soil chemistry from the modern meerfelder maar mfm catchment the calculated ul t profile and the variation of varve thickness show a corresponding pattern the palaeoproductivity of lake smm with respect to diatomaceous matter was clearly controlled by the discharge from the catchment the deposition rate of allochthonous minerogenic matter which received significant

structure and evolution of the rockeskyllerkopf volcanic complex west eifel volcanic field germany the rockeskyllerkopf volcanic complex rvc comprises three overlapping monogenetic volcanic centers southeast lammersdorf sel mauseberg m and rockeskyllerkopf rkk each volcanic center comprises proximal wall deposits with a well defined crater wall unconformity and crater fill deposits that partially to completely cover the outer crater wall the sel center is a phreatomagmatic tuff ring composed of lithic rich tephra deposited by pyroclastic falls and surges the second center mauseberg with its crater to the northwest of the sel center is predominantly magmatic topographic and outcrop patterns suggest that this center may have formed a series of overlapping scoria cones along a n s trending fissure the youngest center rkk which lies on a poorly developed palaeosol within the earlier mauseberg deposits comprises a well developed proximal crater wall sequence this sequence of magmatic likely strombolian fall and grain avalanche deposits passes upward into a crater fill sequence that comprises variably welded bombs the final eruptions in the center were massive lava flows that were ponded within the rkk crater ar ar age dating of reequilibrated fragments of phlogopite megacrysts in the sel lavas indicates volcanic activity began at 474 39 ka literature k ar dates for the youngest lava flows in the rkk center give ages of 360 60 to 470 ka our interpretation of the age data and the presence of the poorly developed palaeosol between the mauseberg and rkk centers indicates that volcanism in the rvc began around 470 ka with the eruption of the sel and mauseberg centers followed a few thousand years later by the eruption of the rkk center

mafic potassic lavas of the quaternary west eifel volcanic field major and trace element analyses for 103 volcanoes of the quaternary west eifel volcanic field show the lavas to be dominantly primitive mgo 7 wt and potassic na2o k2o 1 the rocks are divided into 1 a foidite f suite volumetrically dominant and consisting of four types leucitites and nephelinites melilite bearing foidites olivine free foidites sodalite bearing melilite free foidites and 2 a younger olivine nephelinite and basanite onb suite concentrated in the southeastern part of the field dominantly cpx phyric f suite magmas differ from the dominantly ol phyric onb suite mainly in higher k2o na2o and cao al2o3 ratios higher rb cu h2o co2 and lree concentrations and slightly lower sr ni and y contents most magmas have fractionated small amounts of olivine clinopyroxene and minor phlogopite systematic compositional variations within volcanoes or volcano groups are rare five more differentiated volcanoes 2 tephrites 3 phonolites occur in the center of the field their magmas are interpreted to have formed by fractionation within crustal magma chambers

mesozoic and cenozoic evolution of the central european lithosphere the upper crust of central europe preserves a mosaic of tectonic blocks brought together by the caledonian and variscan orogenies the lower crust in contrast appears to have undergone extensive reworking the flat moho across broad areas and the absence of contrasts in seismic properties across tectonic boundaries suggest that the moho and lower crust are effectively younger than the upper crust the evolution of the mantle lithosphere below the moho has been particularly difficult to constrain in this paper we use seismic geological and geochemical evidence to show that central europe s mantle lithosphere has evolved continuously throughout the mesozoic and cenozoic eras with episodes of lithospheric thinning causing surface uplift and volcanism and lithospheric thickening subsidence and sedimentation high resolution surface wave tomography reveals a strong spatial correlation between locations of recent basaltic volcanism and currently thin lithosphere we infer that intraplate volcanism further back in the geological past is also an indication of lithospheric thinning at the time the north central europe s lithosphere was thus thinned at the time of the permian volcanism with its subsequent post permian cooling and thickening causing the subsidence and sedimentation in the north german and neighboring basins this explains the presence of permian volcanics atop presently thickened lithosphere south of these basins lithospheric thinning evidenced by seismic data is associated with the volcanism of the central european cenozoic igneous province and surface uplift thin lithosphere here also correlates spatially with high melting rates high silica contents high temperatures and shallow magma generation this synthesis highlights the dynamic nature of the lithosphere asthenosphere boundary beneath central europe and more generally phanerozoic continents the boundary s depth varies in time its deepening lithospheric cooling and thickening causes subsidence and sedimentation its shallowing lithospheric thinning by thermal erosion or delamination is marked with uplift and intraplate volcanism

composition and isotopic constraints on the petrogenesis of alkaline arc lavas lihir island papua new guinea the sio2 undersaturated lavas from lihir island papua new guinea like most arc lavas are highly enriched in sr ba k rb and cs and depleted in hf ta nb and ti relative to ocean floor basalts and oceanic island basalts these alkali rich lavas have arc trace element signatures and nd sr and pb isotopic systematics however they are not a product of present day subduction as this volcanism has tapped mantle which was enriched by prior subduction episodes the narrow range of pb 206pb 204pb 18 74 18 76 and nd 143nd 144nd 0 51297 0 51304 isotopic compositions suggest a cogenetic origin for these lavas during the fractionation of the primitive lihir lavas elements normally considered incompatible i e the light rare earth elements lree rb th and p have high bulk solid melt partition coefficients 0 15 1 5 relatively higher partition coefficients during forma tion of the evolved lavas produced crossing rare earth element ree patterns and primitive lavas have higher incompatible elements abundances than evolved lavas this results from 1 changes in the amount of apatite in the fractionating assemblage and 2 the abnormal partitioning of trace elements into apatite microphenocrysts which nucleate at the crystal liquid interface of rapidly growing clinopyroxene phenocrysts the lihir lavas have lower alkali sr ba k rb cs and lree abundances than other tabar feni lavas they are derived from a less enriched mantle source rather than by a higher degree of melting of a source similar to that of the other islands the similarity of sm nd ratios of these undersaturated arc lavas to those of tholeiitic and calc alkaline arc lavas and the moderate chondrite normalized la yb la ybcn 3 7 indicates that there has been limited enrichment of the lree relative to the heavy ree during generation of the arc modified source mantle the alkaline nature of these lavas reflects their generation in a tensional tectonic environment from a fossil arc mantle region that has undergone extreme arc enrichment of alkali and alkaline earth elements during two earlier subduction episodes

regional stress field and rifting in western europe abstract baumann h 1981 regional stress field and rifting in western europe in j h illies editor mechanism of graben formation tectonophysics 73 105 111 in situ stress determination is one possibility to determine stress magnitudes in the earth s crust most measurements especially in the northern alpine foreland have been carried out by using the doorstopper technique stress magnitudes are presented as excess stresses a number of sites where stresses have been determined gave sufficiently high values to statistically determine stress directions for the following tectonic blocks 1 western alps 2 their immediate foreland with the rhinegraben and 3 the rhenish shield bordering on the rift segment of the lower rhine embayment in discussing results of the statistical analyses of stress data it is suggested that stresses measured in the western alps have mainly a topographic origin in the alpine foreland to the north of the rhenish shield topographic stresses are superimposed on active tectonic stress considering the structural and lithological differences the foreland blocks show a different response to the same tectonic stress field which trends for 1 at about 146 this active stress field causes shear rifting in the upper rhinegraben but extensional rifting in the lower rhine embayment in the rhenish shield area only local step faults are observed in direction of 1 due to the ductile behaviour of its basement

late pleistocene eifel eruptions insights from clinopyroxene and glass geochemistry of tephra layers from eifel laminated sediment archive sediment cores