rare earth thhfta and large ion lithophile element variations in metabasites from the proterozoic amphibolite granulite transition zone at arendal south norway abstract the proterozoic arendal metabasites are minor intrusions which possess wholly metamorphic textures and mineral assemblages data are presented for eight selected samples chondrite normalised ree patterns are relatively flat between 10 and 20 chondrite abundances they are characterised by 1 ce n yb n n nd n 1 normalised to primordial mantle values the incompatible elements reveal variable enrichment in the large ion lithophile elements except th and low ta they are similar to many destructive plate margin basalts on a th hf ta diagram the rocks plot in a sub linear trend reflecting variation in th hf samples with high th hf ratios come from the zone of highest metamorphic grade where the host gneisses are deficient in th consequently the patterns in the metabasites could not have been produced by any secondary metamorphic fractionation or by bulk contamination by the country rocks there is no evidence for any post magmatic mobility of any of the elements except rb which is depleted in the highest grade rocks relative to their lower grade counterparts the trace element distributions are largely reflecting those of the parental magmas but consideration of bulk distribution coefficients shows how they may have been modified in some aspects e g ce n nd n by the imposition of the metamorphic mineralogies the data are consistent with a model involving a derivation from a mantle source region which had been affected by subduction related hydrous metasomatism or partial melting and b crystallisation of the magmas directly under the high grade conditions

erosional power in the swiss alps characterization of slope failure in the illgraben landslides and rockfalls are key geomorphic processes in mountain basins their quantification and characterization are critical for understanding the processes of slope failure and their contributions to erosion and landscape evolution we used digital photogrammetry to produce a multi temporal record of erosion 1963 2005 of a rock slope at the head of the illgraben a very active catchment prone to debris flows in switzerland slope failures affect 70 of the study slope and erode the slope at an average rate of 0 39 0 03 m yr the analysis of individual slope failures yielded an inventory of 2500 failures ranging over 6 orders of magnitude in volume despite the small slope area and short study period the slope failures form a characteristic magnitude frequency distribution with a rollover and a power law tail between 200 m and 1 6 106 m with an exponent of 1 65 slope failure volume scales with area as a power law with an exponent of 1 1 both values are low for studies of bedrock landslides and rockfall and result from the highly fractured and weathered state of the quartzitic bedrock our data suggest that the magnitude frequency distribution is the result of two separate slope failure processes type 1 failures are frequent small slides and slumps within the weathered layer of highly fractured rock and loose sediment and make up the rollover type 2 failures are less frequent and larger rockslides and rockfalls within the internal bedded and fractured slope along pre determined potential failure surfaces and make up the power law tail rockslides and rockfalls of high magnitude and relatively low frequency make up 99 of the total failure volume and are thus responsible for the high erosion rate they are also significant in the context of landscape evolution as they occur on slopes above 45 and limit the relief of the slope copyright 2012 john wiley sons ltd

formation of al rich titanite catisio4o caalsio4oh reaction rims on ilmenite in metamorphic rocks as a function of fh2o and fo2 abstract reaction rims of titanite on ilmenite are described in samples from four terranes of amphibolite facies metapelites and amphibolites namely the tamil nadu area southern india the val strona area of the ivrea verbano zone northern italy the bamble sector southern norway and the northwestern austroalpine otztal complex the titanite rims and hence the stability of titanite catisio4o and al oh titanite i e vuaganatite hypothetical end member caalsio4oh are discussed in the light of fh2o and fo2 buffered equilibria involving clinopyroxene amphibole biotite ilmenite magnetite and quartz in the systems cao feo fe2o3 tio2 sio2 h2o o2 cftsh and cao feo fe2o3 al2o3 sio2 h2o o2 cfash present in each of the examples textural evidence suggests that titanite reaction rims on ilmenite in rocks from tamil nadu val strona and the bamble sector originated most likely due to hydration reactions such as clinopyroxene ilmenite quartz h2o amphibole titanite and oxidation reactions such as amphibole ilmenite o2 titanite magnetite quartz h2o during amphibolite facies metamorphism or as in the case of the otztal complex during a subsequent greenschist facies overprint overstepping of these reactions requires fh2o and fo2 to be high for titanite formation which is also in accordance with equilibria involving al oh titanite this study shows that in addition to p t bulk rock composition and composition of the coexisting fluid fo2 and fh2o also play an important role in the formation of al bearing titanite during amphibolite and greenschist facies metamorphism

the sveconorwegian orogeny reamalgamation of the fragmented southwestern margin of fennoscandia abstract the sveconorwegian orogeny encompasses magmatic metamorphic and deformational events between ca 1140 and 920 ma at the southwestern margin of fennoscandia in recent years the tectonic setting of this nearly 200 myr long evolution has been debated with some workers arguing for collision with an unknown continent off the present day southwest coast of norway and others advocating accretionary processes inboard of an active margin recently it has been suggested that orogeny may have been gravity driven by delamination and foundering of heavy subcontinental lithospheric mantle in an intraplate setting in some ways similar to proposed sagduction processes in the archaean resolving the tectonic setting of the sveconorwegian orogen has implications for correlation with other orogens and rodinia supercontinent reconstructions and for assessments of the evolution of plate tectonics on earth from the archaean to the present here we present new mapping and geochronological data from the bamble and telemark lithotectonic units in the central and western sveconorwegian orogen the former representing a critical region separating western parts of the orogen that underwent long lived high to ultrahigh temperature metamorphism and magmatism from parts closer to the orogenic foreland that underwent episodic high pressure events the data show that the units constituting the sveconorwegian orogen most likely formed at the southwestern margin of fennoscandia between ca 1800 and 1480 ma followed by fragmentation during widespread extension between ca 1340 and 1100 ma marked by bimodal magmatism and sedimentation a summary of sveconorwegian magmatic metamorphic and depositional events in the different units shows disparate histories prior to their assembly with adjacent units the most likely interpretation of this record seems to be that episodic sveconorwegian metamorphic and deformational events in the central and eastern parts of the orogen represent accretion and assembly of these units this process most likely took place behind an active margin to the southwest that sustained mafic underplating in the proximal back arc resulting in high to ultrahigh temperature metamorphism in the western parts in this interpretation all features of the sveconorwegian orogen are readily explained by modern style plate tectonic processes and hypotheses involving some form of vertical intraplate tectonics are not supported

the partitioning of the total sediment load of a river into suspended load and bedload a review of empirical data the partitioning of the total sediment load of a river into suspended load and bedload is an important problem in fluvial geomorphology sedimentation engineering and sedimentology bedload transport rates are notoriously hard to measure and at many sites only suspended load data are available often the bedload fraction is estimated with rule of thumb methods such as maddock s table which are inadequately field tested here the partitioning of sediment load for the pitzbach is discussed an austrian mountain stream for which high temporal resolution data on both bedload and suspended load are available the available data show large scatter on all scales the fraction of the total load transported in suspension may vary between zero and one at the pitzbach while its average decreases with rising discharge i e bedload transport is more important during floods existing data on short and long term partitioning is reviewed and an empirical equation to estimate bedload transport rates from measured suspended load transport rates is suggested the partitioning averaged over a flood can vary strongly from event to event similar variations may occur in the year to year averages using published simultaneous short term field measurements of bedload and suspended load transport rates maddock s table is reviewed and updated long term average partitioning could be a function of the catchment geology the fraction of the catchment covered by glaciers and the extent of forest but the available data are insufficient to draw final conclusions at a given drainage area scatter is large but the data show a minimal fraction of sediment transported in suspended load which increases with increasing drainage area and with decreasing rock strength for gravel bed rivers whereby in large catchments the bedload fraction is insignificant at 1 for sand bed rivers the bedload fraction may be substantial 30 50 even for large catchments however available data are scarce and of varying quality long term partitioning varies widely among catchments and the available data are currently not sufficient to effectively discriminate control parameters

a demonstration of the importance of bedload transport for fluvial bedrock erosion and knickpoint propagation we provide field evidence for the role of bedload in driving fluvial incision and knickpoint propagation using aerial photographs field surveys and hydrological data we constrain the incision history of a bedrock gorge 1200 m long and up to 20 m deep cut by da an river in western taiwan this reach of the river experienced 10 m of uplift during the 1999 chi chi earthquake for five years following the earthquake bedload was prevented from entering the uplift zone the knickpoint was static and little incision took place bedload transport across the uplift zone resumed in 2004 initiating extremely rapid incision with 620 m of knickpoint propagation and up to 20 m of downcutting by 2008 this change highlights the relative inefficiency of suspended sediment and the dominant role of bedload as a tool for fluvial erosion and knickpoint propagation once bedload tools became available knickpoint propagation was influenced by geological structure lithology and drainage organization in particular a change in dip of the sandstone beds at the site caused a decrease of knickpoint propagation velocity copyright 2012 john wiley sons ltd

age relationships in the proterozoic high grade gneiss regions of southern norway reply to discussion and comment by weis and demaiffe

dating topography of the sierra nevada california using apatite u th he ages the upward motion of rock masses relative to the earth s surface has been documented for most of the main mountain belts using thermochronological and petrological techniques more fundamental to the physical processes of mountain building however is the motion of the earth s surface itself which remains elusive here we describe a technique for estimating the age of topographic relief by mapping the low temperature thermal structure imparted by river incision using the ages of apatites determined from their uranium thorium and helium contents the technique exploits horizontal variations in temperature in the shallow crust that result from range normal river drainages because cooling beneath ancient river valleys occurs earlier than beneath intervening ridges our results from the sierra nevada california indicate that two of the modern transverse drainages the kings and the san joaquin had developed deep canyons by the late cretaceous period suggesting that the high topography of the range is 50 60 million years older than generally thought

field techniques for measuring bedrock erosion and denudation bedrock erosion rates in natural landscapes are usually slow of the order of millimeters per year or less and sophisticated techniques have been developed to measure them different techniques have proved to be valuable depending on the spatial and temporal scale on which information is needed on the environment and on the scientific question that is asked here we give an overview of the various methods that have been developed we introduce their working principles and outline their advantages and disadvantages further we provide comprehensive references to relevant literature both on the methods and on scientific examples of their application 2016 the authors earth surface processes and landforms published by john wiley sons ltd

anomalously low temperature orthopyroxene spinel and sapphirine occurrences in metasediments from the bamble amphibolite to granulite facies transition zone south norway possible evidence for localized action of saline fluids a reply the question has been raised whether isolated granulite facies islands which occur throughout the amphibolite facies of the regional amphibolite to granulite facies transition zone in the central part of the bamble sector southern norway are the result of prograde or retrograde metamorphism we have studied one of these islands the sapphirine granulites at hauglandsvatn despite the preponderance of amphibolite facies assemblages in the surrounding rocks and the small scale of distribution of the granulite facies assemblages the current assemblage is considered to be prograde and has developed at the expense of biotite in the regional main foliation leaving relict biotite separated from quartz by a continuous corona of orthopyroxene and k feldspar other high temperature low ah2o reactions resulted in the formation of spinel corundum albite oligoclase symplectites at the expense of biotite and sillimanite the symplectites have partially been replaced by symplectites of tiny blue sapphirine

what controls partial melting in migmatites the layers of six stromatic migmatites from northern western and central europe display small but systematic chemical and mineralogical differences at least five of these migmatites do not show any signs of largescale metamorphic differentiation metasomatism or segregation of melts it is concluded therefore that the compositional layering observed in most of the investigated migmatites is due to compositional differences inherited from the parent rocks almost isochemical partial melting seems to be the most probable process transforming layered paragneisses metavolcanics or schists into migmatites the formation of neosomes is believed to be caused by higher amounts of partial melts formed due to higher amounts of water moving into these layers the neosomes have less biotite and more k feldspar if k feldspar is present at all than the adjacent mesosomes these differences are small but systematic and seem to control the access of different amounts of water to the various rock portions petrographical observations chemical data and theoretical considerations indicate a close relationship between rock composition rock deformation transport of water partial melting and formation of layered migmatites

the influence of deformation on the formation of axial planar leucosomes and the segregation of small melt bodies within the migmatitic napperby gneiss central australia in the napperby gneiss central australia a distinctive group of elongate leucosomes occurs along the axial planes of mesoscopic crenulations that have harmonic two dimensional kink band like geometries the leucosomes truncate a fabric defined by biotite quartz k feldspar plagioclase sillimanite and are chiefly composed of k feldspar and quartz with or without plagioclase they are characterized by accessory garnet or aggregates of intergrown ilmenite and magnetite produced during the melting reactions bi plag q sill g ksp melt and bi plag q ru ilm mt ksp melt the absence of garnet and intergrown ilmenitemagnetite aggregates in the gneiss surrounding the crenulation zones indicates that these melting reactions preferentially occurred in the deformation zones in spite of a homogeneous distribution of reactant phases in the gneiss this means that strain partitioning and partial melting are coupled processes in which the garnet and ilmenite magnetite producing melt reactions initially occurred in high strain zones where the melting reaction activation energy was first overstepped this was a consequence of an additional strain induced matrix free energy component on top of the temperature effect once reaction product nucleation had occurred the deformation zones became the sites for continued melting which was energetically favoured over nucleating garnet and ilmenite magnetite elsewhere the melt reactions producing garnet and ilmenite magnetite resulted in the formation of grain supported leucosomes with a higher melt component than the surrounding gneiss and the leucosomes were therefore relatively incompetent in a differential stress field diffusional processes will cause elongation of the leucosome in a plane normal to 1 parallel to the axial planes of folds if sufficient melting has occurred an interconnected leucosome network will result creating a potentially important buoyancy driven melt drainage system in the napperby gneiss interconnected leucosome bearing crenulation zones are mostly vertical which is an ideal orientation for buoyancy driven diffusive melt migration however melt segregations remained small due to a melt impermeable lithological boundary overlying the gneiss

range imaging a new method for high resolution topographic measurements in small and medium scale field sites topographic measurements are essential for the study of earth surface processes three dimensional data have been conventionally obtained through terrestrial laser scanning or photogrammetric methods however particularly in steep and rough terrain high resolution field measurements remain challenging and often require new creative approaches in this paper range imaging is evaluated as an alternative method for obtaining surface data in such complex environments range imaging is an emerging time of flight technology using phase shift measurements on a multi pixel sensor to generate a distance image of a surface its suitability for field measurements has yet not been tested we found ambient light and surface reflectivity to be the main factors affecting error in distance measurements low reflectivity surfaces and strong illumination contrasts under direct exposure to sunlight lead to noisy distance measurements however regardless of lighting conditions the accuracy of range imaging was markedly improved by averaging multiple images of the same scene for medium ambient lighting shade and a light coloured surface the measurement uncertainty was approximately 9 mm to further test the suitability of range imaging for field applications we measured a reach of a steep mountain stream with a horizontal resolution of approximately 1 cm in the focal plane of the camera allowing for the interpolation of a digital elevation model on a 2 cm grid comparison with an elevation model obtained from terrestrial laser scanning for the same site revealed that both models show similar degrees of topographic detail despite limitations in measurement range and accuracy particularly at bright ambient lighting range imaging offers three dimensional data in real time and video mode without the need of post processing therefore range imaging is a useful complement or alternative to existing methods for high resolution measurements in small to medium scale field sites copyright 2012 john wiley sons ltd

observations on the role of lithology in strath terrace formation and bedrock channel width field observations from western washington and eastern tibet indicate a strong lithologic influence on strath terrace formation and highlight the response of bedrock channel width to spatial gradients in bedrock erodibility and or rock uplift rates measurements of local bedrock bed and bank erosion rates together with observations of the role of weathering processes on erosion of siltstones and sandstones illustrate a mechanism that underlies a conceptual model that predicts a strong lithological control on strath terrace formation direct measurements of bedrock erosion rates in lithologies susceptible to accelerated erosion upon sub aerial exposure show that lateral rates of bedrock bank erosion can substantially exceed vertical incision below the perennial flow level due to an asymmetry in erodibility between perennially submerged rock and rock exposed to cyclic wetting and drying on bedrock channel walls under such conditions the rapid weathering mediated lowering of bedrock exposed above baseflow promotes development of a beveled bedrock platform that could become a strath terrace upon abandonment in contrast to previous studies channel widths measured across a substantial gradient in lithology slope and long term erosion rates in eastern tibet do not follow conventional relations where channel width scales as a power law function of drainage area instead as they flow across a zone of rapid uplift these channels systematically narrow relative to the predicted width extrapolated from traditional power law relations field studies from a wide range of geological settings and lithologies support the interpretation that in general strath terraces tend to be more extensive in rivers flowing over weak sedimentary rock and tend to be poorly developed and or preserved where rivers flow over hard erosion resistant rock

a novel method for measuring the timing of bed erosion during debris flows and floods 1 we describe a novel channel bed erosion sensor and the first results of its usage the sensor is based on a resistance chain built into a column of 5 cm tall cylindrical aluminum elements the timing and change in resistance as elements are removed from the column are logged outside of the channel five sensor columns were placed in the illgraben torrent bed prior to the start of the 2008 flow season before the first debris flow event 0 1 m of sediment was deposited by small flood events during the 16 june 2008 debris flow this layer was eroded and erosion was therefore first measured 44 min after front arrival and took place progressively over the next 12 min the results at the erosion sensors are consistent with measurements over the entire reach using traditional surveying methods and data from the adjacent debris flow monitoring station provide a basis for interpretation the main limitation is that this sensor records only the rate and timing of the maximum bed erosion and cannot be used to determine deposition and subsequent erosion within a given event

halogen geochemistry of fluid during amphibolite granulite metamorphism as indicated by apatite and hydrous silicates in basic rocks from the bamble sector south norway abstract the halogen chemistry of apatites biotites amphiboles and titanites from metabasites in the proterozoic bamble sector amphibolite granulite facies transition zone norway has been studied to gather data on the behaviour of halogens during original magmatism and subsequent metamorphism three groups of apatites could be recognized 1 f oh apatites with more than 50 mole f and virtually no cl 2 f oh apatites with up to 15 mole of cl 3 cl rich apatites with up to 6 73 wt cl the latter are the most cl rich metamorphic apatites ever reported the f contents of coexisting biotite do not follow this division but their cl contents do log z sfnc hf z sfnc h 2 o values for the coexisting fluid phase calculated from biotite are slightly lower than those calculated from apatite log z sfnc hcl z sfnc h 2 o values in the coexisting fluid phase calculated from biotite are substantially higher than those calculated from apatite the log z sfnc hf z sfnc h 2 o reflects the composition of the peak metamorphic fluid phase the apatites show three types of patterns of f contents 1 w shaped 2 rimward increasing and 3 rimward decreasing pattern 2 reflects progressive metamorphism pattern 3 is thought to reflect growth starting near peak metamorphism and going on during retrograde dilution of the peak metamorphic fluid by a newly introduced aqueous one some apatites show local resorption effects along cracks no regional trend in calculated log z sfnc hf z sfnc h 2 o values is present as different from other granulite terrains the bamble biotites and amphiboles from granulite facies samples do not have higher halogen contents as those from the amphibolite facies area the samples show that halogen bearing fluids were controlled at a very restricted scale during peak as well as retrograde metamorphism

direct measurement of channel erosion by debris flows illgraben switzerland 1 the timing and magnitude of channel bed erosion by three debris flows was measured in 2008 at the illgraben catchment switzerland using a scour sensor which consisted of a vertical array of erodible sensor elements during the largest debris flow sediment was entrained progressively and stepwise at the flow head within 20 s after front arrival and onset of erosion started before maximum values for flow height and normal and shear stress measured nearby were reached erosion in one of the two smaller debris flows also occurred at the head of the flow but the magnitude of erosion was at the detection limit for the sensor for the other small debris flow we were not able to determine the timing of erosion due to the presence of a sediment layer covering the sensors measurements of pressure fluctuations along the channel sidewall which are produced by interparticle collisions within the flow indicate that the entrainment of sediment is coincident with the largest mean and fluctuating pressures suggesting that interparticle collisions may drive the erosion process at the front of debris flows after erosion at the head of the debris flows sediment was deposited on top of the erosion sensor columns indicating that the bed was reworked to a larger depth than directly visible at the surface after the event observations from elsewhere along the channel support our measurements of the magnitude of net debris flow erosion and indicate that significant erosion can be expected on debris fans when the flow is confined to a channel debris flow entrainment and subsequent bulking of the flow influence the flow dynamics and therefore should be considered in debris flow models and hazard assessment

sveconorwegian granulite facies metamorphism of polyphase migmatites and basic dikes south norway migmatites in the nelaug krossvatnet ubergsmoen area in the amphibolite facies part of the bamble sector were intruded by the ubergsmoen augen gneiss uag and by younger basic dikes both are critical time markers and show that the area underwent two phases of deformation and migmatization during the gothian orogeny 1600 1500 ma before emplacement of the augen gneiss and four subsequent phases of deformation during the sveconorwegian event 1200 950 ma accompanied by amphibolite facies metamorphism and a minor third migmatization mineral assemblages in the basic dikes and in the migmatites indicate local granulite facies conditions resulting from lowered ah 2 o at nearly constant temperature of approx 750 circ c at 8 7 kb it is suggested that this sveconorwegian granulite facies overprinting was due to the introduction of fluids released during the crystallization of another charnockitic magma at a deeper level

comparative oxygen barometry in granulites bamble sector se norway oxygen fugacities have been estimated for the high grade portion of the bamble granulite facies terrane se norway using both titaniferous magnetite ilmenite and orthopyroxene titaniferous magnetite quartz oxygen barometers the two oxygen barometers show good agreement for samples indicating high titaniferous magnetite ilmenite temperatures whereas agreement is poor for low temperature samples oxygen fugacities estimated from titaniferous magnetite ilmenite are considerably lower than those estimated from orthopyroxene titaniferous magnetite quartz this discrepancy increases with a decrease in temperature which appears to reflect preferential resetting of the hematite content in the ilmenite grains without much alteration of the more numerous titaniferous magnetite or orthopyroxene grains the mean temperature for the non reset samples 795 60 c 1 agrees well with temperatures obtained from garnet orthopyroxene k d exchange thermometry in the same region 785 60 c 1 most non reset o

bedload transport measurements at the erlenbach stream with geophones and automated basket samplers in the erlenbach stream a pre alpine steep channel in switzerland sediment transport has been monitored for more than 25 years near the confluence with the main valley river stream flow is monitored and sediment is collected in a retention basin with a capacity of about 2000 m3 the basin is surveyed at regular intervals and after large flood events in addition sediment transport has been continuously monitored with piezoelectric bedload impact and geophone sensors since 1986 in 2008 2009 the measuring system in the erlenbach stream was enhanced by installing an automatic system to obtain bedload samples movable metal baskets are mounted on a rail at the downstream wall of the large check dam above the retention basin and they can be moved automatically into the flow to take bedload transport samples the wire mesh of the baskets has a spacing of 10 mm to sample all sediment particles coarser than this size which is about the limiting grain size detected by the geophones the upgraded measuring system permits to obtain bedload samples over short sampling periods and to measure the grain size distribution of the transported material and its variation over time and with discharge the analysis of calibration relationships for the geophone measuring system confirms findings from very similar measurements which were performed until 1999 with piezoelectric bedload impact sensors there is a linear relationship between impulse counts and bedload mass passing over the sensors findings from flume experiments are used to discuss the most important factors which affect the calibration of the geophone signal the bedload transport rates as measured by the moving baskets are among the highest measured in natural streams with values of the order of several kilograms per meter per second copyright 2012 john wiley sons ltd

emplacement of polygeneration pegmatites in relation to sveco norwegian contractional tectonics examples from southern norway abstract recent studies have demonstrated that there is a strong link between sites of concentrated magmatism and crustal deformation zones magmatism is often described as being syn kinematic where one or more increments of intrusion punctuate deformation with successive generations of injections being progressively deformed pegmatite formation in the mesoproterozoic of south norway has been considered as post kinematic in nature relative to sveconorwegian grenvillian deformation 1 13 ga to 0 85 ga during accretion of the sw margin of baltica this paper presents structural observations from mapping of some pegmatites in the bamble terrane of south norway demonstrating that the pegmatites are structurally related to sveconorwegian fold geometries associated with peak metamorphism at approximately 1 14 ga and are kinematically related to overthrust geometries associated with the initial overthrusting phase of the porsgrunn kristiansand fault when the bamble terrane docked with the underlying telemark terrane local fold geometries suggest a strain regime where the maximum contractional axis is sub horizontal and oriented nw se consistent with the regional kinematics the pegmatites display a systematic deformation pattern consistent with deformation in the isoclinal fold limbs pegmatites are also deformed into asymmetric antiformal folds above reverse shear structures and are also cut by these structures thus showing a thrust geometry the undeformed pegmatites are emplaced in sub horizontal fractures and suggests sub horizontal contractional axis related to overthrusting which is identical to the strain regime of the folding the evidence suggests that the pegmatites are syn tectonic and were injected into reverse shear related fractures deformation was progressive and incremental with longer periods of ductile deformation at low strain rate punctuated by shorter periods of fracturing and pegmatite injection at high strain rate this work therefore implies an intimate spatial and temporal relationship between deformation and magmatism during crustal accretion on the western margin of fennoscandia

bedload transport measurements with impact plate geophones comparison of sensor calibration in different gravel bed streams indirect bedload transport measurements have been made with the swiss plate geophone system in five gravel bed mountain streams these geophone sensors record the motion of bedload particles transported over a steel plate mounted flush with the channel bed to calibrate the geophone system direct bedload transport measurements were undertaken simultaneously at the erlenbach in switzerland a moving basket sampler was used at the fischbach and ruetz streams in austria a helley smith type bedload sampler provided the calibration measurements a bunte type bedload trap was used at the rofenache stream in austria at the nahal eshtemoa in israel reid type slot bedload samplers were used to characterize the response of the geophone signal to bedload particles impacting on the plate geophone summary values were calculated from the raw signal and stored at one second intervals the number of impulses i e the number of peaks above a pre defined threshold value of the geophone output signal correlated well with field measured gravel transport loads and was found to be a robust parameter the relations of impulses to gravel transport loads were generally near linear but the steepness of the calibration relations differed from site to site by comparing the calibration measurements from the different field sites and utilizing insights gained during preliminary flume experiments it has been possible to identify the main factors that are responsible for site specific differences in the calibration coefficient the analysis of these calibration measurements indicates that the geophone signal also contains some information about the grain size distribution of bedload copyright 2013 john wiley sons ltd

cosmic ray production rates of 10be and 26al in quartz from glacially polished rocks we have studied the concentrations of 10be and 26al in quartz crystals extracted from glacially polished granitic surfaces from the sierra nevada range these surfaces were identified with the glacial advance during the tioga period 11 000 years ago our measurements yield the most accurate estimates to date for the absolute production rates of these nuclides in sio2 due to cosmic ray nucleons and muons for geomagnetic latitudes 43 8 44 6 n and altitudes 2 1 3 6 km the estimates are relatively free from uncertainties in snow cover since we studied a suite of rock surfaces inclined 0 75 with respect to the horizontal the principal uncertainty arises due to the lack of a precise date for the glacial retreat event about 10 the 26al 10be ratio at production 6 0 is determined more accurately since the exposure age of the samples is 2 orders of magnitude smaller than the mean lives of the two nuclides production rates of 10be and 26al in quartz at other latitudes and altitudes in the troposphere can be determined from the present measurements by scaling using the known altitude and latitude dependence of cosmic ray fluxes of nucleons and negative muons knowledge of the production rates of these nuclides is a prerequisite for their application in erosion and geomorphological studies

apatite 4he 3he and u th he evidence for an ancient grand canyon the grand canyon is one of the most dramatic features on earth yet when and why it was carved have been controversial topics for more than 150 years here we present apatite 4he 3he thermochronometry data from the grand canyon basement that tightly constrain the near surface cooling history associated with canyon incision 4he 3he spectra for eastern grand canyon apatites of differing he date radiation damage and u th zonation yield a self consistent cooling history that substantially validates the he diffusion kinetic model applied here similar data for the western grand canyon provide evidence that it was excavated to within a few hundred meters of modern depths by 70 million years ago ma in contrast to the conventional model in which the entire canyon was carved since 5 to 6 ma

field instrumentation for high resolution parallel monitoring of bedrock erosion and bedload transport river incision is fundamental in shaping the earth s surface in mountainous regions with steep river beds fluvial bedrock erosion by bedload transport is an important mechanism forming channels however there are only a few complete field datasets that can be used to improve process understanding and evaluate erosion models especially at the process scale to provide a simultaneous dataset of hydraulics bedload transport and bedrock erosion at high temporal and spatial resolution a new measuring device has been installed in the erlenbach a gauged stream in the swiss pre alps in this stream bedload transport rates can be calculated from surveying deposits and from geophone plate sensors and bedload transport samples can be taken directly by an automated moving basket system to measure bedrock erosion rates simultaneously two natural stone slabs were mounted flush with the channel bed in a steel frame hosting various measurement devices force sensors below the slabs record normal stress and shear stress at a point erosion rates on the slab surfaces are continuously measured at sub millimetre precision at three locations on each slab in addition the slab topography is monitored following erosive flood events in this article i the erosion scale device is described ii data resolution and data quality is assessed by means of tests and event data and iii the first transport event is discussed the erosion scales are confirmed to provide data at high spatio temporal resolution for process analysis the preliminary data show evidence for the tools effect in bedrock erosion the bedrock slabs can be exchanged to obtain measurements for catchments with different lithologies for comparison copyright 2014 john wiley sons ltd

bedload hysteresis in a glacier fed mountain river sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before counterclockwise hysteresis or after clockwise hysteresis the peak of bedload hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions respectively hysteresis has been mainly explored for the case of suspended sediment transport but it was rarely reported for bedload transport in mountain streams this work focuses on the temporal variability of bedload transport in an alpine catchment saldur basin 18 6 km2 italian alps where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0 5m long steel pipe runoff dynamics are dominated by snowmelt in late spring early summer mostly by glacier melt in late summer early autumn and by a combination of the snow and glacier melt in mid summer the results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin on the contrary counterclockwise hysteresis tend to be more frequent during late glacier melting period possibly due to the time lag needed for sediment provided by the glacial and peri glacial area to be transported to the monitoring section however intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis thus indicating the activation of different sediment sources these results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams

evidence of transient topographic disequilibrium in a landward passive margin river system knickpoints and paleo landscapes of the new river basin southern appalachians the upper new river basin of the southern appalachian mountains a major tributary of the modern ohio river represents the unglaciated headwaters of the tertiary teays river system of eastern north america dating of relict fluvial gravels have suggested that new river incision may be outpacing lowering of the surrounding uplands but physical evidence of transient topographic disequilibrium has yet to be identified we use focused topographic analysis of the upper new river basin to delineate a perched low relief paleo landscape that is experiencing transgressive dissection due to incision by the new river and its tributaries accelerated incision has decoupled hillslopes from the drainage network generating knickpoints which represent the boundary between remnants of the paleo landscape and actively adjusting topography downstream steepening of hillslopes downstream of knickpoints suggests dynamic headward migration which along with knickpoint occurrence throughout the drainage network is inconsistent with the development of fixed stream profile convexities atop strike extensive geologic contacts in the absence of tectonic forcing we favor a climatically forced drop in external base level as driver of the incision pattern we observe plio pleistocene glacial damming and diversion of the teays river to form the modern ohio river lowered regional base level for the study area potentially forcing the paleo landscape developed during the teays era to adjust to the modern drainage pattern the upper new river may therefore represent the potential for glacially driven drainage rearrangement to drive transient topographic evolution hundreds of kilometers away from the ice margin long after the disappearance of ice sheets copyright 2013 john wiley sons ltd

precambrian multi stage crustal evolution in the bamble sector of south norway pb isotopic evidence from a sveconorwegian deep seated granitic intrusion abstract the precambrian ubergsmoen augen gneiss in the bamble sector of south norway is a dry syntectonic charnockitic intrusion which was emplaced at amphibolite to granulite facies conditions in the sveconorwegian orogeny 1120 ma the present day 206 pb 204 pb and 207 pb 204 pb ratios show restricted variation 206 pb 204 pb 17 566 17 938 207 pb 204 pb 15 459 15 590 in whole rocks and 206 pb 204 pb 17 159 17 350 207 pb 204 pb 15 451 15 487 in feldspar whereas the 208 pb 204 pb ratio has a wider range of variation in whole rocks 36 571 42 200 but not in feldspars 36 487 37 054 these values reflect a 238 u 204 pb of 2 6 since the sveconorwegian and a variable th u ratio 2 20 at the time of final u pb differentiation homogenization of the pb isotopes was imperfect the data therefore do not allow pb pb isochron dating but are well suited for model calculations the isotopic evolution of pb can be reproduced by a three stage model involving 1 a mantle stage ending at 1 9 1 6 ga 2 extraction of a crustal precursor at 1 9 1 6 ga and differentiation of a lile enriched component 14 22 and 3 anatexis igneous differentiation emplacement and subsequent metamorphism at 1 12 ga the granitic intrusion acquired its low u pb ratio by magmatic differentiation processes rather than by fluid induced u loss at high grade metamorphic conditions

rapid pliocene exhumation of the central greater caucasus constrained by low temperature thermochronometry 1 constraining the timing of onset and rates of deformation within the greater caucasus mountains is key to understanding their role in accommodating deformation across the arabia eurasia orogen we present new low temperature thermochronometric constraints on the cenozoic thermal evolution of the central greater caucasus that elucidate a three phase cooling history between 50 and 30 ma cooling within the range was negligible in oligocene time cooling rates throughout the range increased to 4 c myr these rates remained constant until the early pliocene time when they increased again reaching 25 c myr along the axial part of the range rates and timing of oligocene exhumation are consistent with previous results from the western greater caucasus and are proposed to result from onset of subduction of the greater caucasus back arc basin rapid exhumation of the greater caucasus beginning in pliocene time contrasts with previously reported thermal histories for other portions of the range pliocene exhumation of the central greater caucasus appears to be tectonically driven and coincides with widespread evidence for a major reorganization of the arabia eurasia plate boundary we hypothesize that this exhumation and regionally observed plate reorganization results from the collision of the lesser caucasus with eurasia completing the subduction of oceanic lithosphere across this segment of the arabia eurasia plate boundary

large floods alluvial overprint and bedrock erosion depending on their behaviour during extreme floods streams can be divided into two distinct classes which derive from a simple threshold model of transport dynamics flood cleaning streams erode during high flows and deposit during small and medium flows flood depositing streams deposit during high flows and erode during small and medium flows using published descriptions of the geomorphic effects of large floods rivers with a wide range of drainage areas and other characteristics are classified as either flood cleaning or flood depositing in bedrock channels this behaviour can lead to a feedback effect the overprint effect between sediment transport processes and bedrock erosion which can modulate long term bedrock erosion rates the overprint effect arises when alluvium covers the bedrock and typical alluvial channel forms e g meandering or braiding patterns armour layers or bedforms develop which influence sediment transport rates this effect may accelerate or decelerate sediment export from a reach causing increased or decreased long term bedrock erosion rates the overprint effect is illustrated using field data from the erlenbach switzerland and its implications for channel dynamics and bedrock erosion are discussed copyright 2012 john wiley sons ltd

monazite trumps zircon applying shrimp u pb geochronology to systematically evaluate emplacement ages of leucocratic low temperature granites in a complex precambrian orogen although zircon is the most widely used geochronometer to determine the crystallisation ages of granites it can be unreliable for low temperature melts because they may not crystallise new zircon for leucocratic granites u pb zircon dates therefore may reflect the ages of the source rocks rather than the igneous crystallisation age in the proterozoic capricorn orogen of western australia leucocratic granites are associated with several pulses of intracontinental magmatism spanning 800 million years in several instances shrimp u pb zircon dating of these leucocratic granites either yielded ages that were inconclusive e g multiple concordant ages or incompatible with other geochronological data to overcome this we used shrimp u th pb monazite geochronology to obtain igneous crystallisation ages that are consistent with the geological and geochronological framework of the orogen the u th pb monazite geochronology has resolved the time interval over which two granitic supersuites were emplaced a paleoproterozoic supersuite thought to span 80 million years was emplaced in less than half that time 1688 1659 ma and a small meso to neoproterozoic supersuite considered to have been intruded over 70 million years was instead assembled over 130 million years and outlasted associated regional metamorphism by 100 million years both findings have consequences for the duration of associated orogenic events and any estimates for magma generation rates the monazite geochronology has contributed to a more reliable tectonic history for a complex long lived orogen our results emphasise the benefit of monazite as a geochronometer for leucocratic granites derived by low temperature crustal melting and are relevant to other orogens worldwide