radionuclide diffusion rates in igneous crystalline rocks abstract previous work on diffusion in geologic materials indicates that diffusion may be a significant radionuclide transport and retardation mechanism in igneous crystalline rocks a study of the pore structure of igneous rocks and theoretical and experimental diffusion was initiated in 1978 under the canadian nuclear fuel waste management program theoretical predictions of diffusion based on modifications of fick s laws and pore structure information show excellent agreement with experimental results this suggests that methods are available to predict radionuclide diffusion rates over prolonged periods of time in excess of 0 1 ma in rocks that could form the barriers required to isolate nuclear fuel waste a parameter termed diffusion radius rd has been developed which can be used to predict diffusion rates and contribute in comparing rock types in terms of their suitability for isolating nuclear fuel waste according to results obtained thus far radionuclides are not expected to travel more than a few hundred metres in a period of 0 1 ma the results also indicate that diffusion distances in gabbros are smaller than in granites on the other hand retardation effects may be greater in granites than in gabbros some pore parameters that may play an important role in predicting retardation have been identified

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

uranium thorium helium dating of apatite experience with samples from different geochemical environments abstract u he dating which during its history has been very problematic might find special application in the field of hydrothermal mineralizations where other methods generally fail the mineral apatite is a potential candidate for this method in order to shed light on various aspects of apatite dating by the u th he method two samples each from different geochemical environments plutonic pneumatolytic and hydrothermal were probed isotope dilution techniques were used for concentration analyses from which 4he model dates also called helium indices after n b keevil were calculated 4he diffusion measurements were carried out for comparison of the 4he retentivities between the samples comparisons of the apatite he indices with plausible reference ages of the sampling locations in combination with results obtained from diffusion experiments show that the u th he dating method applied to apatite yields an age of cooling rather than an emplacement age the calculated closure temperatures are similar to those obtained by the fission track method 100 c our results suggest that the high temperature apatites plutonic and pneumatolytic may be more suitable for he dating than hydrothermal apatite important criteria for the dating of apatite by u th he are the presence of moderate radionuclide concentrations tens of ppm and a minimum abundance of inclusions

on the inference of denudation rates from cooling ages of minerals abstract the inference of denudation rates from the temperature time histories of rocks is not straightforward because the geothermal gradient evolves with time as denudation advects heat towards the land surface we show that the curvature in the temperature time path recorded by an exhumed rock is strongly dependent upon denudation rate and upon the temperature of the rock before denudation began but only weakly dependent upon the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation for the case in which denudation rate is constant a systematic search of parameter space yields robust estimates of denudation rate and of the initial temperature if there is prior knowledge of the initial geothermal gradient the original depth of burial of the rock or the duration of the denudation this may be used further to limit the acceptable ranges of the other two parameters application of this procedure to two geological examples suggests that denudation rates in the nanga parbat massif are lower and less variable than previously suggested and that the inference drawn from accelerated cooling rates of accelerating denudation in the andes is incorrect

controls on the strength of coupling among climate erosion and deformation in two sided frictional orogenic wedges at steady state 1 many important insights regarding the coupling among climate erosion and tectonics have come from numerical simulations using coupled tectonic and surface process models however analyses to date have left the strength of the coupling between climate and tectonics uncertain and many questions unanswered we present an approximate analytical solution for two sided orogenic wedges obeying a frictional rheology and in a condition of flux steady state that makes explicit the nature and sensitivity of the coupling between climate and deformation we make the simplifying assumption that the wedge grows in a self similar fashion consistent with airy isostasy such that topographic taper is invariant with orogen width tectonic influx rate and climate we illustrate first how and why the form of the erosion rule matters to orogen evolution and then derive a physically based orogen scale erosion rule we show that steady state orogen width crest elevation and crustal thickness are controlled by the ratio of accretionary flux to erosional efficiency to a power dictated by the erosion process remarkably we show that for most combinations of parameters in the erosion law rock uplift rate is more strongly controlled by erosional efficiency than it is by the accretionary flux further assuming frontal accretion with no underplating the spatial distribution of erosional efficiency dictates the relative rock uplift rates on the pro wedge and retro wedge and the time averaged trajectories of rocks through the orogen the restriction to invariant frictional properties is conservative in these respects systems subject to positive feedback between erosion and rheology will exhibit even stronger coupling among climate erosion and deformation than shown here

measurement of rock elastic moduli in tension and in compression and its practical significance the moduli of deformation of rock in tension and in compression are generally assumed equal however many rocks show different deformation properties when loaded in tension and in compression thi

lateral extrusion in the eastern alps part 1 boundary conditions and experiments scaled for gravity lateral extrusion encompasses extensional collapse gravitational spreading away from a topographic high in an orogenic belt and tectonic escape plane strain horizontal motion of wedges driven by forces applied to their boundaries in the eastern alps it resulted from 1 an overall northerly compression apulia against eurasia 2 a strong foreland bohemian massif 3 lack of constraint along a lateral boundary carpathian region and 4 a previously thickened gravitationally unstable thermally weakened crust eastern alpine orogenic belt six indentation experiments reproduce lateral extrusion at lithospheric scale the models have two to four lithospheric layers with a mohr coulomb rheology for the upper and a viscous rheology for the lower crust the lithosphere rests upon a low viscosity asthenosphere a broad indenter a narrow deformable area and a weakly constrained eastern margin fullfill as closely as possible conditions in the eastern alps indentation produces both thickening in front of the indenter and escape of triangular wedges lateral variations in crustal thickness become attenuated by gravitational spreading the overall fault pattern includes domains of reverse strike slip oblique normal and pure normal faults strike slip faults in conjugate sets develop serially the narrow width of the deformable area and the strength of the foreland determine the angles between the sets gravitational spreading produces a rhombohedral pattern of oblique and pure normal faults along the unconstrained margin opposite the unconstrained margin the indenter front shows thrusts and folds intersecting with the conjugate strike slip sets a triangular indenter favors spreading high velocity of indentation favors escape high confinement limits lateral motion inhibits spreading and favors thickening lateral extrusion in the eastern alps is best modeled by 1 a weak lateral confinement 2 a broad and straight indenter 3 a narrow width of the deformable area and 4 a rigid foreland crustal thickening lateral escape and gravitational spreading all contribute to the overall deformation

rock type control on erosion induced uplift eastern swiss alps abstract there is growing evidence that quaternary rock uplift in parts of the european alps is a consequence of climate and erosion driven isostatic rebound contemporary rates of rock uplift u in the swiss alps show two distinctive dome like peak regions that attain 1 6 mm yr 1 we focus on the alpenrhein catchment and its surroundings where one of these peak regions spatially coincides with widely exposed cretaceous bundner schist and lower tertiary flysch field assessments and analyses of hillslope gradient distributions quantitatively demonstrate the low rock mass strength and high erodibility of these rocks this is reflected in mean postglacial catchment erosion rates d 4 mm yr 1 as opposed to 0 7 mm yr 1 in more resistant crystalline rocks though largely inferred from landslide and debris flow prone tributary catchments 2 the localised erosion rates in bundner schist and flysch are among the highest documented for the alps and corroborated by historic suspended sediment yields and thus export from the region we further find that the steepness of bedrock rivers the density of large landslides and d correlate with the highest values of u our observations highlight the possibility that erosion of mechanically weak bundner schist and flysch enhanced by large landslides may have contributed to regional crustal unloading and concomitant rock uplift irrespective of whether this is betraying a coupling between long term uplift and erosion modulated by rock type our findings indicate that long term 10 3 to 10 4 yr geomorphic signals contained in bedrock river steepness spatial density of large landslides and postglacial erosion rates strikingly correlate with regional gradients of historic 10 1 yr rock uplift rates

neogene exhumation history of the bergell massif southeast central alps terra nova 25 110 118 2013 abstract the bergell pluton is an elongated plutonic body emplaced during oligocene time along the insubric line in the central alps reconstruction of its exhumation based on apatite u th he dating and one dimensional thermal modelling provides evidence for a three steps history i following initial fast exhumation from 20 25 to 17 ma slow down of the exhumation rate until 10 ma ii quiescent phase from 10 to 5 6 ma and iii an apparent increase of exhumation after 5 6 ma the decrease in exhumation rate is related with migration of thrusting south of the bergell area in the southern alps lombardic phase increase in exhumation rate after 5 6 ma is possibly related with messinian base level drop enhanced climatic variability 3 4 ma and intensification of glaciation 0 87 ma

channel changes in badlands stripping of the vegetation and soil from a 13 hectare site in virginia underlain by coastal plain sediments created a rapidly evolving badland topography two types of channels developed 1 sand bed alluvial channels were graded to transport the bed material load supplied from slope erosion with available runoff but they also generally eroded their beds slowly and 2 steeper bedrock floored channels incised rapidly in bedrock channels the erosion rate was proportional to the 4 9ths power of drainage area and the 2 3rds power of gradient these exponents are consistent with a model in which the erosion rate is proportional to the bed shear during high flows due to rapid mass wasting and reduced runoff the alluvial channels became as much as 50 steeper during the winter than the summer with an attendant yearly cycle of winter aggradation and summer entrenchment the gradients their seasonal variability and their downstream hydraulic geometry were consistent with the predictions of total load transport formulas for sand beds and high loads the hydraulic geometry of alluvial channels in the virginia badlands were similar to that on the morrison formation in the western united states

erosion driven uplift of the modern central alps abstract we present a compilation of data of modern tectono geomorphic processes in the central european alps which suggest that observed rock uplift is a response to climate driven denudation this interpretation is predominantly based on the recent quantification of basin averaged late holocene denudation rates that are so similar to the pattern and rates of rock uplift rates as determined by geodetic leveling furthermore a gps data based synthesis of adriatic microplate kinematics suggests that the central alps are currently not in a state of active convergence finally we illustrate that the central alps have acted as a closed system for holocene redistribution of sediment in which the peri alpine lakes have operated as a sink for the erosional products of the inner central alps while various hypotheses have been put forward to explain central alpine rock uplift e g lithospheric forcing by convergence mantle processes or ice melting we show with an elastic model of lithospheric deformation that the correlation between erosion and rock uplift rates reflects a positive feedback between denudation and the associated isostatic response to unloading thus erosion does not passively respond to advection of crustal material as might be the case in actively converging orogens rather we suggest that the geomorphic response of the alpine topography to glacial and fluvial erosion and the resulting disequilibrium for modern channelized and associated hillslope processes explains much of the pattern of modern denudation and hence rock uplift therefore in a non convergent orogen such as the central european alps the observed vertical rock uplift is primarily a consequence of passive unloading due to erosion

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

the influence of bedrock geology on knickpoint development and channel bed degradation along downcutting streams in south central indiana geologic controls on knickpoint development and the mechanics of channel bed degradation were eluci dated by comparison of downcutting streams in south central indiana developed in lithologically homoge neous carbonate units and layered siliciclastic strata knickpoints formed in a single lithologic unit are stepped each step consists of a knickpoint face and tread the height of each step is equal to and controlled by bed thickness spatially knickpoints in homogeneous terrain are limited to jointed strata that dip 1 upstream or 2 downstream at angles less than the channel gradient knickpoints observed in lithologically layered strata are characterized by a single step in which resistant jointed rocks overlie and protect weaker units total knickpoint relief is influenced by thickness of the weaker strata knickpoints in layered siliciclastic strata are spatially limited to bedrock reaches produced by differential rates of channel incision knickpoint distribution is also influenced by joint

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

feedbacks among climate erosion and tectonics in a critical wedge orogen the interactions among climate erosion and tectonics have long been of interest to geologists but have not yet been united into a single theoretical framework in this study representations of orographic precipitation and fluvial erosion are combined with the concept of a critical wedge orogen the idealized framework captures the basic system dynamics it also allows for a formal analysis of the precipitation and tectonic interactions in terms of feedback factors and gains and so permits a quantitative comparison of their relative strengths the constraint of self similar growth in a critical wedge orogen acts as a tectonic governor whereby changes in orogen size are strongly damped we determine that this negative tectonic feedback is stronger than the precipitation feedback which may be negative or positive depending on whether precipitation increases or decreases with orogen size for an extreme positive feedback unconstrained runaway growth is possible ultimately leading to plateau formation when orographic precipitation leads to a significant rain shadow there is a strong partitioning of rock uplift rates that favors the wet windward flank of the orogen this flank also dominates the response of the whole orogen to changes in climate or tectonic forcing except in the case where a large fraction of the eroded material is recycled into the wedge finally it is demonstrated that the response time of the orogen depends on the feedbacks and is proportional to the gain of the system

middle eocene to early miocene sedimentary evolution of the western lombardian segment of the south alpine foredeep italy the main steps of the sedimentary evolution of the west lombardian south alpine foredeep between the eocene and the early miocene are described the oldest is a bartonian carbonate decrease in hemipelagic sediments linked with an increase in terrigenous input possibly related to a rainfall increase in the alps between the middle eocene and the early chattian a volcanoclastic input is associated with an extensional tectonic regime coeval with magma emplacement in the southern central alps and with volcanogenic deposits of the european foredeep and apennines suggesting a regional extensional tectonic phase leading to the ascent of magma during late eocene to early oligocene two periods of coarse clastic sedimentation occurred probably controlled by eustasy the first during late eocene fed by a local south alpine source the second earliest oligocene in age supplied by the central alps in the chattian a strong increase in coarse supply records the massive erosion of central alps coupled with a structures growth phase in the subsurface it was followed by an aquitanian rearrangement of the alpine drainage systems suggested by both petrography of clastic sediments and retreat of depositional systems while subsurface sheet like geometry of aquitanian turbidites marks a strong decrease in tectonic activity

channel width response to differential uplift 1 the role of channel width and slope adjustments to differential uplift in rivers within actively deforming terrains remains contentious here high resolution topographic surveying of formerly antecedent outwash channels demonstrates marked changes in channel width as a primary response to differential uplift for five late quaternary alluvial paleochannels crossing small folds along the active ostler fault zone of southern new zealand nearly continuous measurements of paleochannel width and concomitant incision reveal abrupt narrowing of widths toward minimum values at channel positions coincident with the initial uplift when the magnitude of differential uplift is sufficiently small narrowing alone permits these channels to remain antecedent in the context of a unit stream power model for fluvial erosion observed limits on the magnitude of channel narrowing suggest that above some threshold amount of differential uplift continued incision requires concomitant changes in channel gradient thus when crossing small growing folds alluvial rivers simply narrow their channels whereas larger folds that demand greater incision prompt an initial narrowing followed by channel steepening

late oligocene to early miocene lateral extrusion at the eastern border of the lepontine dome of the central alps bergell and insubric areas eastern central alps 1 how the internal domain of the central alps deformed during late stages of the continental collision remains poorly understood to fill this gap in knowledge we present new data constraining the late alpine brittle and brittle ductile tectonics in oligocene intrusions of the bergell alps eastern central alps syncollisional late normal faulting is widespread at all investigated scales but part of the deformation observed is also associated with oblique slip and transcurrent displacements the faults are explained by stress permutations in space and time implying the three principal stress axes and correspond to different homoaxial states of stress of one single transtensive tectonic event motion on these faults accommodated coeval orogen parallel extension and orogen perpendicular contraction during oblique indentation by the southern alpine crust extensional and transcurrent structures likely formed by lateral extrusion of the bergell alps via distributed eastward extrusion of imbricated wedge shaped crustal blocks during the late oligocene and lower miocene a first order wedge shaped crustal block in the bergell alps is represented by three coeval segments of the periadriatic fault system namely the tonale engadine and forcola faults the eastern central segment of the alpine belt appears to have deformed during the late oligocene and lower miocene in a similar way to its extremities where lateral escape tectonics occurred at least until the upper miocene according to free boundary availabilities

widespread extension in the core of the western alps revealed by earthquake analysis the western alps are an active collision belt whose current stress field is inhomogeneous muller et al 1992 we report new seismological data which significantly improve our knowledge of this stress field about 1600 earthquakes which occurred in the western alps during the last 10 years were precisely located and 79 new focal solutions were computed the analysis of this database shows that widespread extension affects all the internal zones of the belt to better constrain the associated stress regime six stress tensors were computed using the gephart and forsyth 1984 method they show that the current tectonics of the western alps are contrasted with close variation in the stress regime transpression to the front of the belt contrasting with extension in the core of the belt the extensional direction is radial to the arcuate geometry of the belt and bounded outboard by the former thrust of the internal zones onto the external zone suggesting extensional reactivation of this inherited crustal discontinuity such widespread extension within the inner part of an actually ongoing collision belt cannot be explained by simple collision related tectonics we propose that intrabelt buoyancy forces such as those produced by a slab retreat or slab break off interfere with the boundary forces driven by the ongoing europe africa convergence

miocene lateral extrusion in the inner western alps revealed by dynamic fault analysis 1 from early miocene to the present day the core parts of the western european alps experienced brittle extensional deformations mostly in a strike parallel direction here we present new data constraining the brittle deformation of the vanoise area french alps and a synthesis of 312 paleostress tensors in the whole arc of the internal western alps the data show a continuous change in the direction of extension from n065 simplon area to n s vanoise area and to nnw sse briancon area the abundance of orogen perpendicular 3 axes increases from the north to the south in the brianconnais area an extensional reactivation of the basal penninic thrust seems to be the origin of the e w to ne sw oriented 3 in light of these new data and the regional paleostress synthesis we propose a predominant orogen parallel extension in the internal zone as a whole this orogen parallel extension is related to the indentation rotation of the apulian microplate and to the opening of the ligurian sea during the lower middle miocene the locally observed orogen perpendicular extension is interpreted as an effect of the exhumation of the internal crystalline massifs the uplift of the external crystalline massifs and or the present day geodynamics postorogenic gravitational collapse some transcurrent tectonics older than the extension in the valais area and younger than the extension farther south is observed in the entire inner western alps strike slip movements are correlated with the apulian rotation and local permutation of stress axes

miocene paleotopography of the central alps abstract reconstructing surface elevation surface uplift and relief histories is fundamental to understanding the growth of mountain ranges to explore their topographic limits and relate these to the interplay between geodynamic and earth surface processes here we aim to quantify miocene paleoelevation of the central european alps through stable isotope paleoaltimetry the novelty of our approach which renders our analysis less sensitive to past climate change is that stable isotope proxies of identical age are analyzed from both the high internal parts of the alpine orogen and the adjacent foreland basin whereas the foreland basin was at or near sea level and traces the combined effects of upstream changes in rainfall amount and composition the high alpine site additionally records the effect of elevation on stable isotopes in precipitation we compare hydrogen isotopic ratios d in mica and chlorite that interacted with meteoric water along the simplon detachment a major normal fault that developed at high elevations with meteoric water compositions deduced from carbonate bearing paleosols of the north alpine foreland basin d values of muscovite 126 and chlorite 135 from the brittle hanging wall and of recrystallized muscovite 108 and biotite 140 from adjacent footwall mylonites provide unequivocal evidence for localized syntectonic meteoric water interaction along the simplon detachment detailed 40 ar 39 ar and fission track geochronology constrains the timing of isotopic exchange to ca 14 5 ma when the footwall mylonites passed through the ductile to brittle transition age equivalent oxygen isotope ratios 18 o measured within pedogenic carbonate from north alpine foreland paleosols that developed near miocene sea level serve as our low elevation point of reference 18 o values in these paleosols dated with ca 100 ka precision vary between 19 and 25 smow with average values of 20 at ca 14 5 ma using the relative differences between meteoric water compositions in the foreland basin and the high alpine simplon detachment our isotope data are consistent with a mid miocene minimum average elevation difference of 2350 700 500 m for the simplon region our results indicate that miocene alpine elevations were at least comparable to those of today and are likely to have acted as an important barrier to atlantic derived moisture transport into central europe and eurasia since that time

hanging valleys in fluvial systems controls on occurrence and implications for landscape evolution 1 we document and characterize hanging valleys in a fluvially eroded landscape in eastern taiwan our conceptual model for the initiation of hanging valleys builds on a recently proposed model of bedrock incision in which erosion actually becomes less efficient on very steep channel gradients if a pulse of incision in the main stem outpaces the tributary response the gradients at tributary mouths may therefore pass a threshold value beyond which erosional efficiency declines giving rise to a mismatch between trunk and tributary erosion rates this mismatch is expected at junctions with small tributaries where a step function decrease in drainage area also leads to sharp contrasts in water and sediment flux between trunk and tributary channels the occurrence of hanging valleys in actively uplifting fluvial landscapes such as the central range of taiwan suggests that the most common parameterizations of bedrock erosion which typically assume a monotonic positive correlation between channel gradient and incision rate may be violated in very steep channels in addition hanging valleys could greatly increase the response time of landscapes to tectonic perturbations since catchments above these tributary mouths will be insulated from these perturbations until a new suite of processes e g weathering and rock mass failure wear through the hanging valley lip the results of this study underscore the need for a more complete understanding of bedrock erosion processes and the incorporation of process transitions and threshold conditions into landscape evolution models

a very efficient o n implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution abstract we present a new algorithm to solve the basic stream power equation which governs channel incision and landscape evolution in many geomorphic settings the algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization it is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation which means that large time steps can be used without sacrificing accuracy in this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy

4he 3he thermochronometry using classical diffusion theory we present a mathematical technique for the determination of 4he concentration profiles in minerals this approach should prove useful for constraining the low temperature cooling histories of individual samples and for correcting u th he ages for partial diffusive loss the calculation assumes that the mineral of interest contains an artificially produced and uniform distribution of 3he obtained by proton irradiation shuster et al earth planet sci lett 217 2004 19 32 in minerals devoid of natural helium this isotope allows measurement of he diffusion coefficients in minerals with measurable radiogenic he it permits determination of 4he profiles arising during ingrowth and diffusion in nature the 4he profile can be extracted from stepwise degassing experiments in which the 4he 3he ratio is measured the evolution of the 4he 3he ratio as a function of cumulative 3he released can be compared with forward models to constrain the shape of the profile alternatively we present a linear inversion that can be used to directly solve for the unknown 4he distribution the inversion incorporates a standard regularization technique to filter the influence of random measurement errors on the solution using either approach we show that stepwise degassing data can yield robust and high resolution information on the 4he profile profiles of radiogenic he are a sensitive function of the time temperate t t path that a cooling sample experienced thus by step heating a proton irradiated sample it is possible to restrict the sample s acceptable t t paths the sensitivity of this approach was explored by forward modeling 4he profiles resulting from a range of realistic t t paths using apatite as an example results indicate that 4he profiles provide rich information on t t paths especially when the profiles are coupled with u th he cooling ages on the same sample samples that experienced only moderate diffusive loss have 4he concentration profiles that are rounded at the edge but uniform in the core of the diffusion domain such profiles can be identified by nearly invariant 4he 3he ratios after the first few to few tens of percent of 3he have been extracted by step heating we show how such data can be used to correct u th he ages for partial diffusive loss

measurements of cesium and strontium diffusion in biotite gneiss a significant retardation of radionuclides transported by flowing water from an underground repository can be expected if the nuclides are able to diffuse into the water filled micropores in the rock this diffusion into the pores will also increase the surface available to interactions between the nuclides in the ground water and the rock material such as sorption to calculate the retardation it is necessary to know the sorption properties and the diffusivities in the rock matrix for the radionuclides diffusion experiments with cesium and strontium in biotite gneiss samples have been performed both the transport of strontium and cesium through rock samples and the concentration profiles of cesium and strontium inside rock samples have been determined the result shows that diffusion of cesium and strontium occurs in the rock material a diffusion model has been used to evaluate the diffusivity both pore diffusion and surface diffusion had to be included in the model to give good agreement with the experimental data if surface diffusion is not included in the model the effective pore diffusivity that gives the best fit to the experimental data is found to be higher than expected from earlier measurement of iodide diffusion in the samemore type of rock material this indicates that the diffusion of cesium and strontium sorbing components in rock material is caused by both pore diffusion and surface diffusion acting in parallel less

a late miocene pliocene origin for the central himalayan inverted metamorphism abstract perhaps the best known occurrence of an inverted metamorphic sequence is that found immediately beneath the himalayan main central thrust mct generally thought to have been active during the early miocene however in situ 208 pb 232 th dating of monazite inclusions in garnet indicates that peak metamorphic recrystallization of the mct footwall occurred in this portion of the central himalaya at only ca 6 ma the apparent inverted metamorphism appears to have resulted from activation of a broad shear zone beneath the mct which tectonically telescoped the young metamorphic sequence this explanation may resolve some outstanding problems in himalayan tectonics such why the mct and not the more recently initiated thrusts marks the break in slope of the present day mountain range it also renders unnecessary the need for exceptional physical conditions e g high shear stress to explain the generation of the himalayan leucogranites

inversion of thermochronological age elevation profiles to extract independent estimates of denudation and relief history ii application to the french western alps abstract thermochronologic data collected along age elevation profiles are commonly interpreted as recording temporally variant but spatially constant exhumation rates however thermochronologic age elevation relationships are known to be perturbed by topographic effects and potential changes in relief which are neglected in the inherently 1 d interpretation commonly applied such data thus potentially record both the denudation and relief history of the sampled region but extracting this information is challenging in a companion paper we develop a methodology for rigorously interpreting thermochronologic age elevation profiles in terms of exhumation rates and relief development through time and to independently quantify the resolution of these constraints here we test this approach using a thermochronological dataset consisting of apatite and zircon fission track and u th he data collected at la meije peak in the pelvoux ecrins massif french western alps our data and models suggest a three phase exhumation history in the pelvoux ecrins massif including a pulse of rapid exhumation at 6 5 5 ma preceded and followed by more moderate rates of denudation in the order of 0 3 0 4 km myr 1 this rapid exhumation event appears to occur coevally in other external crystalline massifs in the alps but is not detected by qualitative inspection of the age elevation relationships both our synthetic results and inversion of the la meije data strongly suggest that apatite fission track age elevation relationships alone cannot resolve both denudation and relief histories independently and that multiple thermochronometers are required combining apatite fission track and u th he ages and particularly including fission track length data greatly improves the resolution of the inferred exhumation histories although denudation rates through time and the timing of rate changes are generally well resolved our data have insufficient resolution to satisfactorily constrain the relief history synthetic results reported in the companion paper suggest that the reason for this limitation is that relief increase through valley carving has been insufficient with respect to the regional denudation rates to be unambiguously extracted from the data

quantifying canyon incision and andean plateau surface uplift southwest peru a thermochronometer and numerical modeling approach incision we quantify the timing and magnitude of incision by integrating previously published ages from the valley bottom with 19 new sample ages from four valley wall transects interpretation of the incision history from cooling ages is complicated by a southwest to northeast increase in temperatures at the base of the crust due to subduction and volcanism furthermore the large magnitude of incision leads to additional threedimensional variations in the thermal field we address these complications with finite element thermal and thermochronometer age prediction models to quantify the range of topographic evolution scenarios consistent with observed cooling ages comparison of 275 model simulations to observed cooling ages and regional heat flow determinations identify a best fit history with 0 2 km of incision in the forearc region prior to 14 ma and up to 3 0 km of incision starting between 7 and 11 ma incision starting at 7 ma requires incision to end by 5 5 to 6 ma however a 2 2 ma age on a volcanic flow on the current valley floor and 5 ma gravels on the uplifted piedmont surface together suggest that incision ended during the time span between 2 2 and 5 ma these additional constraints for incision end time lead to a range of best fit incision onset times between 8 and 11 ma which must coincide with or postdate surface uplift

the mediterranean messinian salinity crisis an apennine foredeep perspective abstract owing to its expanded stratigraphic sections the apennine thrust belt offers the opportunity to better understand the evaporitic and post evaporitic messinian events a physical stratigraphic framework of messinian deposits based on facies analysis and basin wide correlation of key surfaces and sedimentary cycles is presented it is shown that the messinian apennine foredeep had marginal basins with shallow water primary evaporites and deeper basins where resedimented evaporites accumulated under relatively deep water conditions like many other mediterranean examples primary shallow water evaporites of apenninic marginal basins show evidence for subaerial exposure and erosion however the development of such an erosional surface does not correspond to the deposition of primary evaporites in the deepest part of the basin s here the unconformity can be traced towards the base of resedimented evaporites or to a level within them implying that the deeper basins of the apennine foredeep never underwent desiccation during the messinian salinity crisis but rather received the eroded marginal evaporites this fact usually overlooked raises important questions about the deep desiccation model of the mediterranean

diffusion in the matrix of granitic rock field test in the stripa mine three field experiments in granitic rock were performed at 360 m depth in a mine to investigate diffusion in the undisturbed rock matrix the results from all three experiments showed that tracers had migrated through the disturbed zone close to the injection hole and a distance into the undisturbed rock matrix these results show that it is possible for dissolved compounds to migrate into the rock matrix in its natural stress environment diffusivities and hydraulic conductivities obtained in this in situ experiment compare well with those obtained in laboratory experiments

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

cenozoic thermal evolution of the central sierra nevada california from uth he thermochronometry apatite u th he cooling ages are reported for igneous apatite samples from the central sierra nevada and compared to published apatite fission track ages and track length data from the same mineral separates helium ages are youngest at low elevations and increase systematically toward higher elevations ranging from 43 to 84 ma at yosemite valley 32 to 74 ma at kings river canyon and 23 to 75 ma at mt whitney helium ages from high elevation samples are generally concordant with corresponding fission track ages while lower elevation helium ages are substantially younger cooling histories inferred from present laboratory derived fission track annealing and helium diffusion models do not match well suggesting that either helium diffusion rates or fission track annealing rates are miscalibrated at temperatures below about 60 c for geologic exposure periods unlike the fission track results the helium data do not indicate a very low geothermal gradient in the sierra nevada during early to middle tertiary time

glacier shrinkage and modeled uplift of the alps 1 present day glacier reduction in the alps estimated from glacier inventories and induced viscoelastic response of a stratified earth s model is responsible for sizable uplift rates patches of 0 4 0 5 mm yr due to ice mass loss of largest ice complexes overprint a characteristic area of slower uplift of 0 1 0 2 mm yr signature of the phenomenon in the whole alpine chain viscous stress relaxation in the lower crust due to glacier mass loss after the end of the little ice age is expected to produce uplift rates of 0 32 mm yr leading to a total viscoelastic response up to 0 8 mm yr our predictions in the western alps show that viscoelastic response to present day glacier shrinkage forms a substantial fraction half of the observed uplift data attempts to constrain the contributions arising from active alpine tectonics and drainage must account for this uplift signal citation barletta v r c ferrari g diolaiuti t carnielli r sabadini and c smiraglia 2006 glacier shrinkage and modeled uplift of the alps geophys res lett 33 l14307 doi 10 1029 2006gl026490

controls on the patterns of topography and erosion rate in a critical orogen 1 we solve for the steady state patterns of erosion rate and topography in a critical wedge to understand the mutual adjustment of tectonics erosion and topography in the absence and presence of spatial variations in precipitation rate we consider steady state systems in which tectonics favors a critical topographic form assumed to be the mean elevation across the range and in which surface erosion by rivers and hillslopes operates on a two dimensional landscape we find that 1 a nonuniform critical topographic form implies a nonuniform pattern of ridge valley relief and hence a nonuniform pattern of erosion rate and 2 when the system is forced by local variations in precipitation rate maintenance of the critical topographic form requires a local response of rock uplift that greatly dampens changes in topography we apply these concepts to the western side of the olympic mountains of washington state where mean elevation ridge valley relief and precipitation rates increase from the coast to the topographic crest of the range we find that the main control on the erosion rate pattern is the pattern in mean elevation and the amount of precipitation in contrast the pattern of precipitation is only a minor control as a whole our work demonstrates an approach for developing the theoretical context that is necessary for interpreting spatial associations between patterns in topography precipitation and erosion in natural orogens

present day geodynamics in the bend of the western and central alps as constrained by earthquake analysis summary the contrasted tectonics of the western central alps is examined using a synthesis of 389 reliable focal mechanisms the present day strain regime is mapped and interpolated for the entire alpine belt based on a newly developed method of regionalization the most striking feature is a continuous area of extension which closely follows the large scale topographic crest line of the alpine arc thrusting is observed locally limited to areas near the border of the alpine chain a majority of earthquakes within the alps and its forelands are in strike slip mode stress inversion methods have been applied to homogenous subsets of focal plane mechanisms in order to map regional variations in stress orientation the stress state is confirmed to be orogen perpendicular both for 3 in the inner extensional zones and 1 in the outer transcurrent transpressional zones extensional areas are well correlated with the part of the belt which presents the thickest crust as shown by the comparison with the bouguer anomaly and the average topography of the belt in the northwestern swiss alps extension is also correlated with currently uplifting zones these observations and our strain stress analyses support a geodynamic model for the western alps in which the current activity is mostly a result of gravitational body forces earthquakes do not provide any direct evidence for ongoing convergence in the alpine system but a relationship with ongoing activity of complex block rotations of the apulian microplate cannot be ruled out

tracer transport in fractured crystalline rock evidence of nondiffusive breakthrough tailing extended tailing of tracer breakthrough is often observed in pulse injection tracer tests conducted in fractured geologic media this behavior has been attributed to diffusive exchange of tracer between mobile fluids traveling through channels in fractures and relatively stagnant fluid between fluid channels along fracture walls or within the bulk matrix we present a field example where tracer breakthrough tailing apparently results from nondiffusive transport tracer tests were conducted in a fractured crystalline rock using both a convergent and weak dipole injection and pumping scheme deuterated water bromide and pentafluorobenzoic acid were selected as tracers for their wide range in molecular diffusivity the late time behavior of the normalized breakthrough curves were consistent for all tracers even when the pumping rate was changed the lack of separation between tracers of varying diffusivity indicates that strong breakthrough tailing in fractured geologic media may be caused by advective transport processes this finding has implications for the interpretation of tracer tests designed to measure matrix diffusion in situ and the prediction of contaminant transport in fractured rock

the use of autoradiography in determining the distribution of radionuclides sorbed on thin sections of plutonic rocks from the canadian shield abstract autoradiography coupled with classical petrographic techniques has been used to determine the distribution of radionuclides sorbed under oxic conditions onto rock thin sections representative of the four major types of plutons in the canadian shield to determine which minerals are most effective in removing radionuclides from aqueous solutions kodak spectroscopic and ilford k 5 nuclear emulsion plates were investigated the ilford film was found to give higher resolution and required a shorter exposure time than the kodak film sorption was found to be negligible on quartz and strongest on the mafic minerals the pyroxenes micas hornblende and opaques and on alteration minerals chlorite and sphene precipitation of am and pm was observed indicating that for actinides and rare earths experimentally obtained static sorption coefficients may reflect precipitation as well as sorption and must be used with caution in modelling studies

tectonic control on the late stage exhumation of the aar massif switzerland constraints from apatite fission track and u th he data 1 we examine the hypothesis that pliocene exhumation of the external massifs in the central alps is controlled by climatic change new thermochronological data from the western gastern aar massif are used to investigate the timing extent and reasons for neogene exhumation our data reveal that exhumation was constant with 0 5 km ma over the last 10 ma in the north in the southern part exhumation was of the same order until 3 5 ma but then increased gradually toward the south to values of up to 1 2 km ma resulting in overall northward tilting of the western aar massif we explain this accelerated exhumation in the south after 3 5 ma mainly by tectonic denudation in the footwall of the rhone simplon fault and discuss changes in deep crustal configuration which may have triggered south directed normal faulting we propose that the rhone river was structurally trapped by the rhone simplon normal fault zone which additionally enhanced erosion in the southern section of the aar massif climatic forcing may have an impact in the very late stage of exhumation due to alpine glaciation in the late pliocene

active deformation in the eastern swiss alps post glacial faults seismicity and surface uplift abstract post glacial tectonic faults in the eastern swiss alps occur as single lineaments clusters of faults or extensive fault zones consisting of several individual faults aligned along the same trend the orientation of the faults reflects the underlying lithology and the pre existing structures joints pervasive foliations within these lithologies most post glacially formed faults in the area around chur which undergoes active surface uplift of 1 6 mm year trend e w and cut across alpine and glacial features such as active screes and moraines additionally there are nnw and ene striking faults reactivating pervasive alpine foliations and shear zones based on a comparison with the nodal planes of recent earthquakes e w striking faults are interpreted as active faults because of very short rupture lengths and mismatches of fault location with earthquake distribution magnitude and abundance the faults are considered to be secondary faults due to earthquake shaking cumulative deformation in post or interseismic periods or creep and not primary earthquake related faults the maximum of recent surface uplift rates coincides with the youngest cooling of the rocks according to apatite fission track data and is therefore a long lived feature that extends well into pre glacial times isostatic rebound owing to overthickened crust or to melting of glacial overburden cannot explain the observed surface uplift pattern rather the faults earthquakes and surface uplift patterns suggest that the alps are deforming under active compression and that the aar massif basement uplift is still active in response to ongoing collision

rock uplift and erosion rate history of the bergell intrusion from the inversion of low temperature thermochronometric data the bergell intrusion european alps was one of the first locations where thermochronometry was used to resolve changes in erosion rate yet relating these changes to variations in climate or in local tectonics remains challenging one approach that enables changes in erosion rate to be related to changes in climate or rock uplift rate is to utilize landscape evolution models as topographic response to these forcing parameters is unique furthermore low temperature thermochronometric systems have the potential to resolve topography through time and thus topographic response we present new u th he data for samples collected across 2 km of relief from the bergell the ages range from 2 to 16 ma and define an age elevation with an apparent exhumation rate of 0 1 km myr in order to infer erosion rates we use a thermokinematic model to solve the heat equation in the crust track material points through time and predict thermochronometric data paleo topography and erosion rate are parameterized using the stream power model we find that rock uplift rates were 0 4 km myr from 25 to 20 ma and subsequently decreased to 0 05 km myr this results in a gradual decrease in erosion rate from rates of 0 4 to 0 1 km myr a recent increase in rock uplift rate at 4 ma to 0 6 km myr is required to explain the youngest ages and high topographic relief

lithospheric thermal regimes in europe abstract the heat flow pattern of europe derived from more than 8000 observations is dominated by a general northeast to southwest increase in geothermal activity which is the consequence of the tectonic evolution of the whole continent this paper reviews the history of the geothermal mapping of europe and describes the recently compiled set of geothermal maps of europe surface heat flow is correlated with the age of the last tectonothermal event with the near surface heat production and with the crustal thickness deep temperature distributions within the crust lithosphere are calculated for 1 d 2 d and simple 3 d models characteristic temperature depth curves are given for some of the major tectonic provinces and the results of various techniques are compared the value of the crustal heat contribution is assessed and a regional moho heat flow pattern is proposed the mohorovicic discontinuity is clearly not an isothermal surface neither is the heat flow from below the crust constant

symmagmatic folding of the base of the bergell pluton central alps abstract evidence for magmatic submagmatic and solid state deformation in tonalite granodiorite and country rocks found at the deep seated floor 22 26 km of the bergell pluton demonstrates that final emplacement and crystallization occurred during regional deformation of the pluton and the underlying country rocks after northward emplacement over the country rocks but before complete crystallization the floor of the pluton was folded during simultaneous n s shortening and e w stretching this is evidenced by synmagmatic folds with e w striking nearly vertical axial planes and by regional east plunging stretching lineations in the country rocks which are parallel to the regional scale fold axes and the magmatic mineral lineations in the pluton opposite senses of shear from the well foliated occasionally mylonitic contact suggest that deformation was mostly accomplished by pure shear synmagmatic deformation is related to late stage n s shortening of the alpine orogen and shows that the still partially molten pluton responded to low differential stress very much like the country rocks deformed in the solid state at high temperatures post emplacement tilting associated with backthrusting along the insubric mylonites led to the exposure of the pluton s floor at its present day western margin

incision and channel morphology across active structures along the peikang river central taiwan implications for the importance of channel width river morphology and dynamics are strongly influenced by active tectonics we report channel dynamics for the peikang river which flows through the hsuehshan range in central taiwan using a digital elevation model and field surveys we constrain channel morphology for an 90 km stretch of river to calculate unit stream power and boundary shear stress along the river path incision rates are estimated with optically stimulated luminescence dating of sand deposited on strath terraces we find a strong correlation between unit stream power shear stress and incision rate but only if variation in channel width is considered a calibrated river incision rule implies river incision rates of 9 13 5 mm yr upstream of the meiyuan and tili faults and suggests that one or both of these structures are presently active our results indicate that the shuilikeng fault is also actively deforming as incision rates increase to 6 10 mm yr across it compared to 1 4 mm yr in adjacent reaches prominent narrowing across the shuilikeng fault and the absence of significant gradient variation indicate that channel width is a first order morphological adjustment to differential incision only when the channel width to depth ratio reaches a minimum does the channel slope significantly adjust to local changes in base level as is the case upstream of the meiyuan and tili faults

fluvial incision and tectonic uplift across the himalayas of central nepal the pattern of fluvial incision across the himalayas of central nepal is estimated from the distribution of holocene and pleistocene terraces and from the geometry of modern channels along major rivers draining across the range the terraces provide good constraints on incision rates across the himalayan frontal folds sub himalaya or siwaliks hills where rivers are forced to cut down into rising anticlines and have abandoned numerous strath terraces farther north and upstream in the lesser himalaya prominent fill terraces were deposited probably during the late pleistocene and were subsequently incised the amount of bedrock incision beneath the fill deposits is generally small suggesting a slow rate of fluvial incision in the lesser himalaya the terrace record is lost in the high range where the rivers are cutting steep gorges to complement the terrace study fluvial incision was also estimated from the modern channel geometries using an estimate of the shear stress exerted by the flowing water at the bottom of the channel as a proxy for river incision rate this approach allows quantification of the effect of variations in channel slope width and discharge on the incision rate of a river the determination of incision rates requires an additional lithological calibration the two approaches are shown to yield consistent results when applied to the same reach or if incision profiles along nearby parallel reaches are compared in the sub himalaya river incision is rapid with values up to 10 15 mm yr it does not exceed a few millimeters per year in the lesser himalaya and rises abruptly at the front of the high range to reach values of 4 8 mm yr within a 50 km wide zone that coincides with the position of the highest himalayan peaks sediment yield derived from the measurement of suspended load in himalayan rivers suggests that fluvial incision drives hillslope denudation of the landscape at the scale of the whole range the observed pattern of erosion is found to closely mimic uplift as predicted by a mechanical model taking into account erosion and slip along the flat ramp flat geometry of the main himalayan thrust fault the morphology of the range reflects a dynamic equilibrium between present day tectonics and surface processes the sharp relief together with the high uplift rates in the higher himalaya reflects thrusting over the midcrustal ramp rather than the isostatic response to reincision of the tibetan plateau driven by late cenozoic climate change or late miocene reactivation of the main central thrust

cosmogenic 10be derived denudation rates of the eastern and southern european alps denudation rates from cosmogenic 10be measured in quartz from recent river sediment have previously been used in the central alps to argue that rock uplift occurs through isostatic response to erosion in the absence of ongoing convergence we present new basin averaged denudation rates from large rivers in the eastern and southern european alps together with a detailed topographic analysis in order to infer the forces driving erosion denudation rates in the eastern and southern alps of 170 1 400 mm ky 1 are within a similar range to those in the central alps for similar lithologies however these denudation rates vary considerably with lithology and their variability generally increases with steeper landscapes where correlations with topographic metrics also become poorer tertiary igneous rocks are associated with steep hillslopes and channels and low denudation rates whereas pre alpine gneisses usually exhibit steep hillslopes and higher denudation rates molasse flysch and schists display lower mean basin slopes and channel gradients and despite their high erodibility low erosion rates exceptionally low denudation rates are also measured in permian rhyolite which has high mean basin slopes we invoke geomorphic inheritance as a major factor controlling erosion such that large erosive glaciers in the late quaternary cold periods were more effective in priming landscapes in the central alps for erosion than in the interior eastern alps however the difference in tectonic evolution of the eastern and central alps potentially adds to differences in their geomorphic response their deep structures differ significantly and unlike the central alps the eastern alps are affected by ongoing tectonic influx due to the slow motion and rotation of adria the result is a complex pattern of high mountain erosion in the eastern alps which has evolved from one confined to the narrow belt of the tauern window in late tertiary time to one affecting the entire underthrust basement orogenic lid and parts of the southern alps today

upper mantle structure beneath the alpine orogen from high resolution teleseismic tomography 1 to understand the evolution of the alpine orogen knowledge of the actual structure of the lithosphere asthenosphere system is important we perform high resolution teleseismic tomography with manually picked p wave arrival times from seismograms recorded in the greater alpine region the resulting data set consists of 4199 relative p wave arrivals and 499 absolute p wave arrivals from 76 teleseismic events corrected for the contribution of the alpine crust to the travel times the three dimensional 3 d crustal model established from controlled source seismology data for that purpose represents the large scale alpine crustal structure absolute p wave arrival times are used to compute an initial reference model for the inversion tests with synthetic data document that the combination of nonlinear inversion high quality teleseismic data and usage of an a priori 3 d crustal model allows a reliable resolution of cells at 50 km 50 km 30 km hence structures as small as two cells can be resolved in the upper mantle our tomographic images illuminate the structure of the uppermost mantle to depth of 400 km along strike of the alps the inversion reveals a high velocity structure that dips toward the se beneath the adriatic microplate in the western and central alps in the eastern alps we observe a northeastward dipping feature subducting beneath the european plate we interpret this feature in the western and central alps as subducted mainly continental european lower lithosphere for the east we propose that parts of the vardar oceanic basin were subducted toward the ne forcing continental adriatic lower lithosphere to subduct northeastward beneath the european plate

surface uplift uplift of rocks and exhumation of rocks uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges rates of uplift of the surfaces of mountain ranges have not however been quantified sufficiently well that they provide useful constraints on those processes many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift and provide no information whatsoever on the rates of surface uplift

wearing down wearing back and gorge extension in the long term denudation of a highland mass quantitative evidence from the shoalhaven catchment southeast australia the long standing issue of the dominance of scarp retreat versus summit lowering in the denudation of a highland mass is investigated with supporting evidence provided by tertiary basalts throughout the shoalhaven catchment in southeast australia both of these forms of denudation are found to be insignificant compared to the role of fluvial gorge extension over the last 30 m y headward advancement of the shoalhaven gorge has been occurring at approximately 15 times the rate of major escarpment retreat 250 times the average rate of summit lowering and over 500 times the rate of interfluve consumption these estimates show that the headward erosion of gorges is the most important process denuding the highlands in the shoalhaven region and possibly elsewhere in the highlands of eastern australia over the long term the highlands in this region will become considerably more dissected well before they decrease substantially in height or are narrowed this conclusion has important implications for models p

u th pb and 230th 238u disequilibrium isotope systematics precise accessory mineral chronology and melt evolution tracing in the alpine bergell intrusion in order to investigate the potential of combined th u pb isotope and 230th 238u disequilibrium systematics for tracing magmatic crystallization and melt evolution conventional high resolution single crystal tims techniques have been applied to zircon titanite and fragments of geochemically characterized growth zones of allanite these minerals were extracted from a single tonalite specimen collected from the feeder zone of the tertiary bergell pluton southern steep belt s switzerland n italy the isotopic results document an extended history of crystallization and melt evolution of at least 5 ma with well resolved zircon ages defining an early interval of 33 0 to 32 0 ma followed by crystallization of zoned allanite from 32 0 to 28 0 ma and formation of magmatic epidote possibly as late as 26 ma trace and major element patterns in zoned allanite closely mirror melt evolution characterized by increase of u concentration and sharp decrease of th and lree reflecting early crystallization of phases low in u and in particular the dominating control by allanite precipitation preservation of substantial quantities of excess 206pb derived from initial excess 230th in all analyzed allanite grains indicates that their isotopic systems have not been reset by loss of radiogenic pb during prolonged residence at magmatic conditions and regional metamorphic cooling and that the measured sequence of 208pb 232th dates translates into a real age sequence major loss of radiogenic pb from compositionally zoned allanite by volume diffusion would have resulted in a data pattern grossly different from the observed one as demonstrated by numerical modeling of 232th 208pb 238u 230th 206pb isotopic evolution the results therefore suggest closure temperatures 700 c for magmatic allanite quantification of 230th 238u disequilibrium relationships reveals a smooth initially steep decrease of th u in the magma from values of 2 9 at 32 0 ma to 0 1 at 28 0 ma in equilibrium with sequential allanite zoning comparison of calculated th u magma with measured total rock th u 0 79 requires fractional crystallization of allanite at an early stage this process of removal of allanite and thus th from the melt was operative at least until 31 5 ma providing an upper limit for the time of emplacement of the studied magma batch the fact that bulk zircon and a large part of allanite crystallization predate emplacement cautions against equating ages determined on refractory minerals from deep seated plutons with intrusion ages the persistence of magmatic conditions over a period of 5 ma concentrated in a narrow collision zone between the european and the african plate has been a major controlling factor for the oligocene evolution of the adjacent insubric fault the main tectonic lineament of the alps being active from late cretaceous to miocene times

pre glacial topography of the european alps we present a topographic reconstruction of the european alps prior to quaternary glaciation based on the assumption that this topography was a steady state fluvial landscape eroding according to a stream power law but with spatially variable channel steepness we find high pre glacial channel steepness in the western alps and on the harder rocks of the basement and metamorphic nappes while lower values are often associated with weaker alpine flysch deposits the reconstructed pre glacial river network also provides an estimate of distribution and magnitude of glacial erosion and associated isostatic adjustment suggesting an increase of valley scale topographic relief and decrease of mean elevation throughout glaciation

two and three dimensional thermal modeling of a low angle detachment exhumation history of the simplon fault zone central alps 1 two alternative models have been proposed to explain footwall exhumation along major low angle detachments 1 crustal scale exhumation along a detachment fault that maintained a low dip angle or 2 exhumation along a high angle fault passively rotated by isostatic rebound rolling hinge model these proposed models were tested against a well documented example of a low angle detachment fault in the european central alps the simplon fault zone sfz an extensive thermochronological data set provides the basis for 2 and 3 d thermokinematic models pecube coupled with a stochastic inversion algorithm the neighbourhood algorithm model results establish that the thermochronological pattern is better reproduced by a low angle detachment that maintained a 30 dip rather than by a rolling hinge model although a range of histories involving either steady state or variable exhumation rates is possible the preferred model of highest probability is for a variable rate with the fault zone initiated at 18 5 2 5 ma and active until the present day footwall exhumation was relatively fast until 14 5 1 5 ma 1 4 mm yr 1 this enhanced sfz footwall exhumation is similar in timing and kinematics to orogen parallel extension reported throughout the alpine orogen after 14 5 ma sfz footwall exhumation continued at a reduced rate 0 7 mm yr 1 until 4 ma the subsequent increase to 1 mm yr 1 reflects enhanced regional erosion rates across both footwall and hanging wall after circa 4 ma from 0 35 0 15 mm yr 1 to 0 70 0 15 mm yr 1 probably in response to climate changes during the pliocene

the sedimentary record of the exhumation of a granitic intrusion into a collisional setting the lower gonfolite group southern alps italy abstract the clastic wedge of the gonfolite lombarda group glw accumulated during oligocene miocene times in the southern alps foreland basin formed on the southern inner side of the alpine belt it represents the depositional counterpart of the exhumation and erosion of the central alps metamorphic magmatic units among the central alps units the tertiary bergell intrusion tbi is one of the principal sources of pebbles occurring within the glw geochronologic data both from intrusive pebbles and present day outcrops of intrusive rocks document the rapid uplift history of the glw source area the lower gonfolite clastic wedge como conglomerate and val grande sandstone formations oligocene early miocene has been investigated through the study of sandstone and conglomerate petrology for detecting the effects in the sedimentary record of this collision related event the main results are i sandstone petrology of the como conglomerate records an evolution from feldspatholithic to feldspathic sandstones ii the related q f f l ratios suggest an evolution from a mixed plutonic metamorphic to a mainly plutonic source iii consistently conglomerate petrology records a progressive increase of plutonic pebbles from nearly 0 50 of the total a corresponding decrease of metamorphic clasts from nearly 80 to nearly 50 and the disappearance of cover rock fragments considering the high relief short transport setting of the glw clastic routing system these values probably resemble the real proportions of such rocks in the gonfolite catchment area during the aquitanian the return to a metamorphic rich source is recorded both by sandstones and conglomerates at the top of the como conglomerate and in the val grande sandstone this last signal is interpreted as the result of the reorganisation of the gonfolite source area possibly related to the northward shift of the main alpine divide

thermochronological constraints on the multiphase exhumation history of the ivrea verbano zone of the southern alps abstract the ivrea verbano zone of the western southern alps nw italy exposes a well preserved tilted section across the lower continental crust making it a key region for studying deep crustal and exhumation processes this paper refines the cooling and exhumation history of the ivrea verbano zone using k ar dating of mica and illite rich fault gouges as well as zircon fission track and u th he thermochronology the adjacent strona ceneri zone sesia lanzo zone and lower penninic nappes are included in the study to derive a broader picture of the low temperature history of the area in the strona profile of the ivrea verbano unit the biotite k ar zircon fission track and u th he geochronometers show well preserved but unusually wide partial retention zones the youngest ages representing the formerly deepest position are situated along the insubric line the main foliation of the ivrea verbano zone is vertical the exhumation of the ivrea verbano zone which section has a horizontal position on the surface now took place in three steps during jurassic time the ivrea verbano zone was exhumed to a shallow to mid crustal position by continental scale extension in this displacement the pogallo line probably played a dominant role the studied section occupied an oblique position with a calculated angle of ca 15 to 23 in the jurassic later the ivrea verbano zone experienced a minor cooling event in the late eocene 38 ma zircon fission track ages that was probably related to thrusting and erosion the final exhumation towards the surface took place in the mid miocene as documented by the ca 14 ma zircon u th he ages and a 12 8 ma k ar fault gouge age the magnitude and the high rate of final exhumation suggest orogen parallel extension as a driving force which is widespread in the alps in the lower to middle miocene and is most probably connected to orogenic collapse

messinian climate change and erosional destruction of the central european alps at the end of the miocene the european alps ceased outward expansion and tectonic uplift and exhumation shifted into the orogen interior this shift is consistent with a change from orogenic construction to orogenic destruction reflecting an increase in the ratio of erosional flux to accretionary flux the coincidence of this change with an increase in sediment yield from the alps suggests a climate driven increase in erosional flux the timing of deformation and sediment release from the southern alps indicates that the tectonic change occurred synchronous with the last phase of the messinian salinity crisis we attribute the increase in erosional flux to a climatic shift to wetter conditions throughout europe likely augmented by the base level fall that occurred during the mediterranean dessication this climate change is represented in the stratigraphic record by the lago mare deposits of the mediterranean salinity crisis

a simple method for in situ u th he dating this paper presents a significantly simplified method for in situ u th he dating removing the need to know any absolute concentrations this is done by calculating the normalised u th and he concentrations of a conventionally dated calibration standard from its measured th u ratio and known u th he age and scaling these concentrations to the raw u th and he signals of the sample the th u ratio of the standard can be determined from its measured 208pb 206pb ratio removing the need to use nist glass as a reference material we introduce an la icp ms based method to correct for variable ablation depths between the standard and the unknown using the strength of the ablated 29si signal finally we propose a pseudo depth profile method to assess the effects of compositional zoning on the accuracy of in situ u th he data the effectiveness of the proposed method has been demonstrated on three samples of gem quality sri lanka zircon which yield ages that are in agreement with previously published conventional u th he measurements

are the alps collapsing abstract orogenic collapse is a process that transfers gravitational potential energy from regions of high potential energy to regions of lower potential energy this transfer is classically considered to be accomplished by extension in the orogenic core and by synchronous shortening in foreland regions of the orogen not all extensional features in collisional mountain belts need however reflect orogenic collapse normal faulting thrust faulting and strike slip faulting are all active in different parts of the alps today and reflect complex local responses to ongoing europe adria convergence the western alps is the only area today where extension and shortening radial to orogen trend occur synchronously and where orogenic collapse may be an important process elsewhere in the alps normal faults are oriented at a high angle to orogen trend and were primarily active in oligocene and miocene time most present day activity in the central and eastern alps is on strike slip faults that are accommodati

detrital geochronology of unroofing magmatic complexes and the slow erosion of oligocene volcanoes in the alps abstract tectonic reconstructions and quantitative models of landscape evolution are increasingly based on detailed analysis of detrital systems since the definition of closure temperature in the 1960s mineral ages of low temperature geochronometers are traditionally interpreted as the result of cooling induced by erosion whose rate is a simple unique function of age patterns such an approach can lead to infer paradoxically high erosion rates that conflict with compelling geological evidence from sediment thickness in basins this indicates that tectonic and landscape models that solely interpret mineral ages as due to cooling during exhumation may not be valid here we propose a new approach that takes into account the effects of both crystallization and exhumational cooling on geochronometers from u pb on zircon to fission tracks on apatite we first model the mechanical erosion of an unroofing magmatic complex and the resulting accumulation and burial of the eroded units in reverse order in the basin detrital mineral ages follow a regular pattern downsection some mineral ages such as e g u pb ages of zircons cluster around the magmatic age i e the crystallization of the magma its value is constant along the stratigraphic column in the sedimentary basin we refer to this behavior as stationary age peak some other mineral ages such as e g apatite fission track ages are often younger than the magmatic age when they vary smoothly with depth they define a moving age peak which is the only possible effect of undisturbed cooling during overburden removal and can therefore be used to calculate an erosion rate the predictions of our model were tested in detail on the extremely well studied bregaglia bergell orogenic pluton in the alps and on the sedimentary succession derived from its erosion the gonfolite group the consistency between predicted and observed age patterns validates the model our results resolve a long standing paradox in quantitative modelling of erosion sedimentation namely the scarcity of sediment during apparently fast erosion starved basins are the observational baseline and modelling must be tuned to include a correct analysis of detrital mineral geochronology in order to reconcile perceived discrepancies between stratigraphical and geochronological information in addition our data demonstrate that volcanoes were active on top of the growing oligocene alps this study illustrates rigorous criteria for detrital mineral geochronology that are applicable to any geological setting including magmatic arcs and collision orogens and provides fundamental interpretive keys to solve complex puzzles and apparent paradoxes in geological reconstructions

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

experimental channel response to tectonic uplift 1 we have performed a series of experiments to investigate the relationship between channel geometry and tectonic forcing in steady state landscapes at various uplift rates the experimental setup consists of uniformly uplifted silica paste eroded by artificial rainfall in this setup erosional landscapes evolve by growth and amalgamation of incisions which organize into a drainage network whose dynamics are a function of the interaction between vertical channel cutting hillslope erosion and sediment transport high precision 0 5 mm pixel size digital elevation models were constructed using a stereogrammetric camera system from this data channel bed slope was found to be independent of discharge and position on the experimental surface and to increase linearly with uplift rate geometric parameters of the flow such as channel width or depth could not be observed directly during the experiments using laminar flow equations for the mean flow velocity these parameters were back calculated and relationships to the imposed substrate uplift rate were derived channel width cross sectional area and wetted perimeter decrease with increasing uplift rate to a limit value hydraulic radius and flow depth increase slightly and flow velocity increases approximately linearly with increasing uplift rate these results are qualitatively consistent with recent field surveys and highlight the importance of channel width and slope variations in accommodating channel response to variable rock uplift rates

modeling transport of cesium in grimsel granodiorite with micrometer scale heterogeneities and dynamic update of kd transport and retardation of cesium in grimsel granodiorite taking into account heterogeneity of mineral and pore structure was studied using rock samples overcored from an in situ diffusion test at the grimsel test site the field test was part of the long term diffusion project ltd designed to characterize retardation properties diffusion and distribution coefficients under in situ conditions results of the ltd experiment for cesium showed that in diffusion profiles and spatial concentration distributions were strongly influenced by the heterogeneous pore structure and mineral distribution in order to study the effect of heterogeneity on the in diffusion profile and spatial concentration distribution a time domain random walk tdrw method was applied along with a feature for modeling chemical sorption in geological materials a heterogeneous mineral structure of grimsel granodiorite was constructed using x ray micro computed tomography x ct and the map was linked to previous results for mineral specific porosities and distribution coefficients kd that were determined using c 14 pmma autoradiography and batch sorption experiments respectively after this the heterogeneous structure contains information on local porosity and kd in 3d it was found that the heterogeneity of the mineral structure on the micrometer scale affects significantly the diffusion and sorption of cesium in grimsel granodiorite at the centimeter scale furthermore the modeled in diffusion profiles and spatial concentration distributions show similar shape and pattern to those from the ltd experiment it was concluded that the use of detailed structure characterization and quantitative data on heterogeneity can significantly improve the interpretation and evaluation of transport experiments