sequestration of atmospheric co2 in a weathering derived serpentinite hosted magnesite deposit 14c tracing of carbon sources and age constraints for a refined genetic model abstract the attunga magnesite deposit is texturally and geochemically distinct from other spatially associated serpentinite hosted magnesite deposits in the great serpentinite belt new south wales australia such as the hydrothermal piedmont magnesite deposit or widespread silica carbonate alteration zones cryptocrystalline magnesite at attunga predominantly occurs in nodular masses and irregular desiccated veins that occupy pre existing cracks and pore spaces resulting from fracturing and weathering of the host rock incipient weathering of the serpentinite host rock is accompanied by a decrease in volume and the mobilisation of mgo and cao from the serpentinite pore spaces and permeability created during weathering and fracturing of the host rock provide access for co2 mgo and cao bearing meteoric waters which led to an increase of volume during carbonation sio2 is only mobilised during more advanced stages of weathering and late stage infiltration of sio2 bearing waters and precipitation of opal a lead to local silicification of the serpentinite stable carbon and oxygen isotope signatures show that nodular magnesite at attunga has formed under near surface conditions incorporating carbon from c3 photosynthetic plants and oxygen from meteoric waters radiocarbon concentrations in the magnesite preclude subducted carbonaceous sediments as the source of carbon and together with distinct stable carbon and oxygen isotope signatures indicate that magnesite at attunga precipitated from low temperature supergene fluids even though there is no direct geochemical and isotopic evidence some textural observations and field relationships for weathering derived magnesite deposits suggest the prior existence of a possibly early triassic hydrothermal magnesite deposit at attunga the presence of a pre existing magnesite deposit may entail the localised formation of the weathering derived magnesite at attunga but the predominance of weathering related textures and geochemical signatures indicate that weathering is the integral magnesite mineralisation process at attunga conventional radiocarbon ages of about 50 ka represent a maximum age constraint for the formation of the magnesite deposit during quaternary weathering a significant amount of atmospheric co2 has been sequestered via the biosphere and carbonation of serpentinite at attunga

survival of ancient landforms in a collisional setting as revealed by combined fission track and u th he thermochronometry a case study from corsica france abstractthe age of high elevation planation surfaces in corsica is constrained using new apatite u th he data field observations and published work zircon fission track apatite fission track aft data and landform stratigraphical analysis thermal modeling results based on aft and u th he data and the eocene sediments uncomformably overlapping the variscan crystalline basement indicate that present day elevated planation surfaces in corsica are the remnants of an erosion surface formed on the basement between 120 and 60 ma during the alpine collision in the paleocene eocene the variscan crystalline basement was buried beneath a westward thinning wedge of flysch and the eastern portion was overridden by the alpine nappes resetting of the apatite fission track thermochronometer suggests an overburden thickness of 4 km covering variscan corsica protected by soft sediment the planation surface was preserved in the latest oligocene to miocene times the surface was re exposed and offset by

a physical explanation of the cumulative area distribution curve a physical explanation for the behavior of the cumulative area distribution cad based on the tokunaga channel network model is given the cad is divided into three regions the first region for small areas is dependent on hillslope flow accumulation patterns and represents the catchment average of the hillslope flow accumulation in the diffusive erosion dominated areas upstream reaches of the catchment the second region represents that portion of the catchment dominated by fluvial erosion this region is well described by a log log linear power law which results from the scaling properties of the channel network the scale exponent b is highly sensitive to a parameter of the tokunaga stream numbering scheme the exponentb converges to 0 5 for higher order tokunaga networks for parameters consistent with topological random networks small networks have lower values ofb which asymptotic converges tob 0 5 as the catchment scale increase the third region reflects the lowest reaches of the channel network the scale of the catchment and is a boundary effect an explicit analytical solution to the scaling properties in the second region is derived on the basis of the tokunaga network model the cumulative distribution of drainage area is the percent age of the catchment that has an area per unit width draining through a point which is greater than or equal to a given area it is a geomorphologic measure that characterizes part of the catchment hydrology and is a measure commonly used by geo morphologists and hydrologists to characterize the scale invari ant structure of channel networks tarboton et al 1989 ro driguez iturbe et al 1992 inaoka and takayasu 1993 la barbera and roth 1994 this cumulative area distribution cad characterizes the scaling properties of drainage area the cad and its scaling properties are key components in the development of physically based models that link geomorphol ogy and hydrology perera 1997 ibbitt et al 1997 perera 1997 showed that slope of the cad in both the hillslope and channel domains is important for describing the geomorphic impact on subsurface saturation excess runoff generation using a digital elevation model dem of a catchment the drainage path through and the drainage area per unit width of each point in the catchment can be computed for a grided dem the cumulative area a is determined as the number of pixels within the catchment which have drainage area a num ber of pixels draining through greater than or equal to some specified drainage area a

optimal channel networks a framework for the study of river basin morphology optimal channel networks ocns are dendritic structures obtained by minimizing the local and global rates of energy dissipation in a continuously fed in space and time plane aggregation system reminiscent and based on the properties of the planform of three dimensional natural drainage networks geomorphological and fractal properties of ocns are known from earlier studies by the authors this paper explores further the structures derived by optimization of energy dissipation rates optimality of subnetworks and of basin shapes is investigated as a by product of competition for drainage a new perspective on the possible prediction of the width function of a basin network and hence of its hydrologic response is obtained by exploiting ocn techniques requiring only the definition of the outer boundaries of the basin the interplay between hillslope processes and the development of drainage networks is addressed aiming at the relative role and the mutual interrelations of geology and optimal organization in the structure of mature river basins also addressed is the issue of multiscaling and multifractality in the spatial organization of the network it is concluded that ocn approaches provide a comprehensive framework for the study of the morphology of geophysical structures

ni speciation in a new caledonian lateritic regolith a quantitative x ray absorption spectroscopy investigation abstract changes in ni speciation in a 64 m vertical profile of a new caledonian saprolitic lateritic regolith developed over ultramafic rocks under tropical weathering conditions were investigated by exafs spectroscopy quantitative analysis of the exafs spectra by linear combination least squares fitting lc lsf using a large set of model compound spectra showed that ni hosted in primary silicate minerals olivine and serpentine in the bedrock is incorporated in secondary phyllosilicates serpentine and fe oxides goethite in the saprolite unit and mainly in goethite in the laterite unit a significant concentration of ni up to 30 of total ni is also hosted by mn oxides in the transition laterite i e the lowest part of the laterite unit which contains large amounts of mn oxides however the amount of ni associated with mn oxides does not exceed 20 of the total ni in the overlying laterite unit this sequence of ni species from bedrock to laterite yields information about the behavior of ni during tropical weathering of ultramafic rocks the different ni distributions in phyllosilicates in the bedrock randomly distributed and in the saprolite unit clustered indicate two generations of ni bearing phyllosilicates the first which formed at higher temperature is related to serpentinization of oceanic crust whereas the second one which formed at lower temperature is associated with post obduction weathering of ultramafic rocks in addition the observed decrease in the proportion of ni hosted by mn oxides from the transition laterite to the upper lateritic horizons indicates dissolution of mn oxides during the last stages of differentiation of the lateritic regolith i e lateritization finally the ubiquitous occurrence of ni bearing goethite emphasizes the major role of this phase in ni speciation at the different weathering stages and suggests that goethite represents the major host for ni in the final tropical weathering stages of new caledonian ultramafic rocks

properties of iron oxides in some new caledonian oxisols abstract oxisols from two toposequences of new caledonia formed from peridotite consist essentially of fe oxides goethite hematite maghemite these fe oxides were characterized by their mineralogy crystal size and morphology al substitution thermal behaviour and dissolution kinetics in 6 m hcl at 25 c in one toposequence the samples were free of hematite goethite only at 1050 m above sea level whereas at lower altitudes hematite was also present al substitution was generally low due to the low al content of the peridotite except in gibbsitic samples on rocks somewhat higher in al the surface areas of goethite and hematite ranged between 50 and 150 m 2 g 1 dithionite extractable ni and cr were between 0 2 and 2 2 ni and 0 3 and 2 3 cr the hematite containing samples tended to be higher in cr and lower in ni whereas the opposite held for samples containing goethite only maghemites had a low unit cell size 8 31 8 32 instead of 8 34 8 35 a which was attributed to al substitution dehydroxylation temperature of goethites was weakly correlated with al substitution dissolution kinetics could be described by a linear form of a modified first order reaction with one straight line for samples containing goethite only and two lines for samples containing goethite plus hematite

the topography of optimal drainage basins a model for drainage networks and their associated landscapes has been developed this model is based on the minimum energy dissipation principle and an empirical relationship s q between the slope s of each link in a channel network and the mean annual discharge q that flows through it the model was studied using six different values for the exponent the surfaces of these minimum energy dissipation drainage networks appear to be more complex than simple self affine fractals the drainage basins in these optimal drainage networks have power law size area distributions with a universal exponent which is independent of the value of for the minimum energy dissipation drainage networks obtained using a particular value for the basin shapes are similar to each other an empirical relationship has also been found to relate the basins length width ratio to the value of

microstructure and porosity evolution during experimental carbonation of a natural peridotite abstract carbonation experiments t 100 200 c pco2 14 6 19 4 mpa were performed under closed system conditions on a natural peridotite from almklovdalen w norway to investigate the microstructure and porosity evolution as a function of reaction progress the unreacted samples cubes of 2 5 3 cm3 were composed mainly of forsteritic olivine 80 90 vol clinochlore orthopyroxene amphibole and chromite initial porosities were on the order of 6 8 due to the presence of abundant inter and intragranular microfractures microstructural observations after 7 42 days of experimental treatment showed that olivine was by far the most reactive phase after 7 days at 100 c no carbonate products were formed but longer reaction times produced small amounts of magnesite on the surface and within the fracture network of the peridotite cubes increasing temperatures led to faster reactions and pore space filling by magnesite in addition replacement rims up to 50 m thick composed of magnesite and amorphous silica formed around individual olivine grains the replacement began with the formation of an amorphous silica layer that retained the shapes of the initial olivine grains this layer remained permeable during the reaction as it allowed further dissolution of the underlying olivine increasing extents of carbonation were accompanied by decreasing porosities and enhanced cementation of grain boundaries about 50 of the initial porosity was closed when carbonation reached about 10 the reacted samples showed no evidence of reaction induced cracking indicating that the carbonation reaction was self limiting in our experiments these results may have important implications for the efficiency of in situ co2 sequestration in peridotites

cryogenic cave calcite from several central european caves age carbon and oxygen isotopes and a genetic model abstract cryogenic cave calcite ccc formed by segregation of solutes during water freezing was found in three central european caves this calcite type forms accumulations of loose calcite grains on cave floor the calcite grains are of highly variable crystal morphology and of sizes ranging from less than 1 mm to over 1 cm the most typical feature is their accumulation as loose uncemented crystals u series dating indicates the formation of ccc in the studied caves during several climatic oscillations of the weichselian between 61 and 36 ka bp in the chelsiowa jama jaskinia jaworznicka cave system in poland between 34 and 26 ka bp in the buml cave in the czech republic and between 26 and 21 ka bp in the stratenska jasky a cave system slovakia at the time of ccc formation the studied caves were lying in a periglacial zone detailed c and o stable isotope study of ccc samples revealed that slow water freezing under isotope equilibrium was the dominant formational process in the studied polish and czech caves significantly higher 13 c values of ccc in the stratenska jasky a cave indicate either water freezing in a more opened system with continuous co 2 escape rayleigh fractional separation or participation of another co 2 source the model of slow water freezing under isotope equilibrium is supported by isolated character of the caves having limited ventilation in contrast modern cryogenic cave calcite powders sampled directly on the ice surface of two recently iced caves in slovakia with high ventilation showed much higher 18 o and 13 c data similar to cryogenic calcites obtained in experimental rapid water freezing

on the cumulative area distribution of natural drainage basins along a coastal boundary the natural drainage network in a region is analyzed in order to investigate scaling properties and the form of the probability distribution for basin areas along a coastal boundary the horton strahler approach used in the classical description of the drainage network within a single basin is extended to a series of independent though conterminous basins with outlet to the sea assuming that a regional area ratio ra analogous to the hortonian area ratio holds for independent basins a multiplicative factor rc is also defined as the average ratio between the number of independent basins of a given order and those of order 1 the cumulative area distribution cad for drainage basins that drain along the coastal boundary is obtained as a power law in the form p a a a with log rc log ra the derived form and parameters of the cad are shown to hold for the liguria region of italy 5700 km2 in the northern mediterranean as well as for the whole continental italy 250 000 km2 the fractal dimension of the regional system encompassing all drainage areas of basins with outlet to the sea is derived in the form 1 the analytical results obtained are shown to agree with the theoretical expressions already available in the literature for optimal channel networks

incorporating 3 d parent nuclide zonation for apatite 4he 3he thermochronometry an example from the appalachian mountains the ability to constrain km scale exhumation with apatite 4he 3he thermochronometry is well established and the technique has been applied to a range of tectonic and geomorphic problems however multiple sources of uncertainty in specific crystal characteristics limit the applicability of the method especially when geologic problems require identifying small perturbations in a cooling path here we present new 4he 3he thermochronometric data from the appalachian mountains which indicate significant parent nuclide zonation in an apatite crystal using la icpms measurements of u and th in the same crystal we design a 3 d model of the crystal to explore the effects of intra crystal variability in radiation damage accumulation we describe a numerical approach to solve the 3 d production diffusion equation using our numerical model and a previously determined time temperature path for this part of the appalachians we find excellent agreement between predicted and observed 4he 3he spectra our results confirm this time temperature path and highlight that for complex u and th zonation patterns 3 d numerical models are required to infer an accurate time temperature history in addition our results provide independent and novel evidence for a radiation damage control on diffusivity the ability to exploit intra crystal differences in 4he diffusivity i e temperature sensitivity greatly increases the potential to infer complex thermal histories

morphometrics of china s loess plateau the spatial legacy of tectonics climate and loess deposition history abstract the loess plateau in china is the largest and deepest loess deposit in the world the surficial geology is dominated by quaternary loess deposits of varying thicknesses which exhibit some of the fastest erosion rates in the world although the plateau has been traditionally thought of as morphologically homogenous river network morphometrics in this area are spatially variable suggesting that landscape evolution processes across the plateau are sensitive to variability in local conditions we divided the plateau into sub basins and examined six dem derived morphometric parameters aspect ratio anisotropic coefficient variation acv bifurcation ratio concavity steepness and mean junction angle the sub basins exhibited low aspect ratios high bifurcation ratios and large junction angles relative to landscapes around the world however they varied intra regionally relative to each other through the use of principal component analysis and cluster analysis we observed specific spatial variation in morphometrics attributable to differences in climate lithology and tectonics along a nw se transect through the plateau sub basins in the elevated plateau regions are more oval with higher aspect ratios and lower acv values while those located in down dropped valley regions have smaller junction angles lower concavity and steepness index sub basins in the transition area between down dropped and elevated parts of the plateau are distinguished by their high bifurcation ratios and elongated shape we propose a conceptual model to explain the relationship between these morphometrics and the local environmental conditions

carbon dioxide fixation within mine wastes of ultramafic hosted ore deposits examples from the clinton creek and cassiar chrysotile deposits canada carbon dioxide co2 is sequestered through the weathering and subsequent mineralization of the chrysotile mine tailings at clinton creek yukon territory and cassiar british columbia canada accelerated weathering is attributed to a dramatic increase in surface area which occurs during the milling of ore we provide a detailed account of the natural process of carbon trapping and storage as it occurs at clinton creek and cassiar including mineralogy modes of occurrence methods of formation for carbonate alteration light stable isotope geochemistry and radiocarbon analysis powder x ray diffraction data were used to identify weathering products as the hydrated magnesium carbonate minerals nesquehonite mgco3 3h2o dypingite mg5 co3 4 oh 2 5h2o hydromagnesite mg5 co3 4 oh 2 4h2o and less commonly lansfordite mgco3 5h2o textural relationships suggest that carbonate precipitates formed in situ after milling and deposition of tailings samples of efflorescent nesquehonite are characterized by 13c values between 6 52 and 14 36 per mil 18o values between 20 93 and 26 62 per mil and f14c values fraction of modern carbon between 1 072 and 1 114 values which are consistent with temperature dependent fractionation of modern atmospheric co2 during mineralization samples of dypingite hydromagnesite collected from within 0 2 m of the tailings surface give 13c values between 1 51 and 10 02 per mil 18o values between 17 53 and 28 40 per mil and f14c values between 1 026 and 1 146 which suggests precipitation from modern atmospheric co2 in a soil like environment field observations and isotopic data suggest that hydrated magnesium carbonate minerals formed in two environments nesquehonite formed in an evaporative environment on the surface of tailings piles and dypingite and hydromagnesite formed in the subsurface environment with characteristics similar to soil carbonate in both cases these minerals

solving the production diffusion equation for finite diffusion domains of various shapes part 2 application to cases with alpha ejection and non homogeneous distribution of the source abstract in this paper numerical methods derived in part i chem geol 2002 are expanded to accommodate the effects of emission and zonation of u and th as relevant for u th he thermochronology expressions for the required coefficients are derived for spheres finite and infinite cylinders and rectangular blocks for parent nuclide distributions which are either uniform or have stepwise zoning we show that the effects of emission and zonation on the he retention in a nonspherical crystal of modest aspect ratio can be approximated by a sphere of identical surface to volume ratio s v if the zonation is transposed on to the sphere the currently usual correction method is to perform first a diffusive calculation without considering emission and zonation and to multiply afterward with a correction factor that has been derived originally for nondiffusive calculations our results demonstrate that more accurate calculations yield different results and that the differences are often too large to be ignored in practice especially for thermal histories that include a protracted residence in the partial retention zone the difference between the usual correction and our correction can be as high as 20 for homogeneous sources for zoned crystals the difference can be even larger

atmospheric carbon sequestration in ultramafic mining residues and impacts on leachate water chemistry at the dumont nickel project quebec canada abstract passive carbon mineralization in ultramafic mining residues which allows the sequestration of co2 through carbonate precipitation is one of the options being considered to limit the accumulation of anthropogenic co2 in the atmosphere the dumont nickel project dnp will generate approximately 1 7 gt of utramafic mining residues over 33 years of production and the mine will release about 127 700 tonnes of co2 each year using two experimental cells filled with ultramafic waste rock ec 1 and milling residues ec 2 the impacts of carbon mineralization on leachate water quality were studied and the quantity of sequestered carbon was estimated hydrotalcite supergroup minerals aragonite artinite nesquehonite dypingite and hydromagnesite precipitated through atmospheric weathering while the inorganic carbon content of the weathered mining waste increased from 0 1 wt to 4 0 wt which indicates active co2 sequestration the leachate water sampled at the bottom of the experimental cells is characterized by an alkaline ph 9 5 a high alkalinity 90 to 750 mg l and a high concentration of magnesium 50 750 mg l which is typical from weathering of ultramafic rocks in a system open to co2 since 2012 the chemical composition of the leachate water has evolved seasonally these seasonal variations are best explained by 1 climatic variations over the year and 2 increased carbonate precipitation between may and july increased carbonate precipitation decreased the alkalinity and magnesium concentrations in the leachate water and produced pore waters which were undersaturated with respect to carbonate minerals such as artinite and hydromagnesite carbonate precipitation thus self limits carbon sequestration through a negative feed back loop the carbon sequestration potential of the dnp residues is also influenced by the hydrogeological properties of the residues in cell ec 2 a high liquid solid ratio which limits carbonate precipitation was maintained by the hydrogeological properties since 2011 an estimate of 13 kg of atmospheric co2 has been sequestered in the milling residues ec 2 which corresponds to a mean rate of 1 4 0 3 kgco2 tonne year using this mean rate the 15 mt of tailings produced each year during the planned 33 years of mining operation could potentially sequester 21 000 tonnes of co2 per year by passive carbon mineralization about 16 of the 127 700 tonnes of co2 annually emitted by the planned mining operation

subarctic physicochemical weathering of serpentinized peridotite abstract frost weathering is effective in arctic and subarctic climate zones where chemical reactions are limited by the reduced availability of liquid water and the prevailing low temperature however small scale mineral dissolution reactions are nevertheless important for the generation of porosity by allowing infiltration of surface water with subsequent fracturing due to growth of ice and carbonate minerals here we combine textural and mineralogical observations in natural samples of partly serpentinized ultramafic rocks with a discrete element model describing the fracture mechanics of a solid when subject to pressure from the growth of ice and carbonate minerals in surface near fractures the mechanical model is coupled with a reaction diffusion model that describes an initial stage of brucite dissolution as observed during weathering of serpentinized harzburgites and dunites from the feragen ultramafic body fub se norway olivine and serpentine are effectively inert at relevant conditions and time scales whereas brucite dissolution produces well defined cm to dm thick weathering rinds with elevated porosity that allows influx of water brucite dissolution also increases the water saturation state with respect to hydrous mg carbonate minerals which are commonly found as infill in fractures in the fresh rock this suggests that fracture propagation is at least partly driven by carbonate precipitation dissolution of secondary carbonate minerals during favorable climatic conditions provides open space available for ice crystallization that drives fracturing during winter our model reproduces the observed cm scale meandering fractures that propagate into the fresh part of the rock as well as dm scale fractures that initiate the breakup of larger domains rock disintegration increases the reactive surface area and hence the rate of chemical weathering enhances transport of dissolved and particulate matter in the weathering fluid and facilitates co2 uptake by carbonate precipitation our observations have implications for element cycling and co2 sequestration in natural gravel and mine tailings

modeling relative frost weathering rates at geomorphic scales abstract frost damage is a powerful agent of geomorphic change cracks can grow when the ice pressure in pores reaches a threshold that depends on matrix properties and crack geometry mineral surfaces that are preferentially wetted by liquid water rather than ice are coated by premelted liquid at a pressure that is lower than the ice pressure because this pressure difference increases as the temperature cools when the ice pressure is effectively pinned at the cracking threshold temperature gradients induce gradients in liquid pressure that draw water towards colder temperatures porosity increases and frost damage accumulates in regions where water supplies crack growth to apply this understanding over the large spatial and temporal scales that are relevant to evolving landscapes we develop a simple model that tracks porosity changes our central assumption is that frost damage is correlated with porosity increases under conditions where frost cracking takes place accordingly we account for the permeability reductions with decreased temperature that accompany ice growth along porous pathways and derive general expressions for the porosity change through time at particular depths as well as the total porosity increase through all depths beneath a point at the ground surface over the time during which cracking occurs each year to illustrate the resulting patterns of frost weathering we consider a general case in which the permeability has a power law dependence on temperature and the annual surface temperature variation is sinusoidal we find that the degree of frost damage generally decreases with depth except at localized depths where damage is elevated because the rock spends longer times near the threshold for cracking leading to enhanced water supply in comparison with neighboring regions the magnitude of the net expansion that results from porosity changes at all depths beneath the ground surface is increased for seasonal thermal cycles with larger amplitudes with a broad maximum centered on a mean annual temperature near the threshold required for crack growth warmer mean annual temperatures lead to less damage because of the reduction in time during which it is cold enough for cracking whereas colder mean annual temperatures are accompanied by reduced water supply due to the temperature dependence of permeability all of the controlling parameters in our model are tied explicitly to physical properties that can in principle be measured independently which suggests promise for informing geomorphic interpretations of the role of frost weathering in evolving landforms and determining erosion rates

u th he dating of apatite a potential thermochronometer abstract we found a gem quality crystal of durango fluorapatite to have a 4he content consistent with complete retention of radiogenic helium since its formation at about 31 ma isothermal heating and step heating analysis reveal 4he loss to occur systematically by volume diffusion at low temperatures the linear low temperature portion of the diffusion data yields an activation energy of 38 5 8 1 kcal mol and a frequency factor of in d 0 a 2 16 4 2 8 sec 1 corresponding to a closure temperature of 105 c 30 c cooling rate 10 c m y it appears that u th he dating of apatite might represent a useful new thermochronometer with a range similar to that of fission track dating of apatite from these results we infer that a number of the too young u th he dates reported in the literature on minerals such as zircon and magnetite may in fact represent valuable records of the low temperature thermal history of their host rocks

in situ carbonation of peridotite for co2 storage the rate of natural carbonation of tectonically exposed mantle peridotite during weathering and low temperature alteration can be enhanced to develop a significant sink for atmospheric co2 natural carbonation of peridotite in the samail ophiolite an uplifted slice of oceanic crust and upper mantle in the sultanate of oman is surprisingly rapid carbonate veins in mantle peridotite in oman have an average 14c age of 26 000 years and are not 30 95 million years old as previously believed these data and reconnaissance mapping show that 104 to 105 tons per year of atmospheric co2 are converted to solid carbonate minerals via peridotite weathering in oman peridotite carbonation can be accelerated via drilling hydraulic fracture input of purified co2 at elevated pressure and in particular increased temperature at depth after an initial heating step co2 pumped at 25 or 30 c can be heated by exothermic carbonation reactions that sustain high temperature and rapid reaction rates at depth with little expenditure of energy in situ carbonation of peridotite could consume 1 billion tons of co2 per year in oman alone affording a low cost safe and permanent method to capture and store atmospheric co2

neocrystallization or cooling 40ar 39ar ages of white micas from low grade mylonites abstract 40 ar 39 ar data for white micas from quartzite mylonites from a thrust system are evaluated with respect to whether the minerals record cooling ages or alternatively ages of deformation induced neocrystallization to address these interpretations three types of information are needed 1 the effective diffusion length scale controlling volume diffusion of argon in white micas 2 an estimate of the diffusion parameters for volume diffusion of argon and 3 the thermal history completely recrystallized quartzites exhibit smooth grain size distributions for white micas with good exponential or power law fits suggesting that the grains grew under similar conditions the microstructures indicate that the grains grew over a narrow range in time near the end of the deformation history measured grain size distributions provide a maximum limit for the diffusion length scale thermal histories are estimated by 40 ar 39 ar diffusion experiments on k feldspars using the multi diffusion domain method of lovera lovera o m richter f m harrison t m 1989 the 40 ar 39 ar thermochronometry for slowly cooled samples having a distribution of diffusion domain sizes j geophys res 94 17917 17935 these results are consistent with the expected temperature time path for the thrusting environment and predict maximum temperatures of 250 350 c during the time span recorded by the white micas experimentally and empirically calibrated diffusion parameters for white micas are applied to a cylindrical diffusion geometry to explore the question of cooling ages versus neocrystallization ages forward modeling of the passage of the white micas through the closure window for argon diffusion using the thermal histories derived from the k feldspars indicates that the white micas record neocrystallization rather than cooling and supports the idea that the white micas record the timing of when ductile deformation ceased

low temperature thermochronology and thermokinematic modeling of deformation exhumation and development of topography in the central southern alps new zealand 1 apatite and zircon u th he and fission track ages were obtained from ridge transects across the central southern alps new zealand interpretation of local profiles is difficult because relationships between ages and topography or local faults are complex and the data contain large uncertainties with poor reproducibility between sample duplicates data do form regional patterns however consistent with theoretical systematics and corroborating previous observations young neogene ages occur immediately southeast of the alpine fault the main plate boundary structure on which rocks are exhumed partially reset ages occur in the central southern alps and older mesozoic ages occur further toward the southeast zircon apparent ages are older than apatite apparent ages for the equivalent method three dimensional thermokinematic modeling of plate convergence incorporates advection of the upper pacific plate along a low angle detachment then up an alpine fault ramp adopting a generally accepted tectonic scenario for the southern alps the modeling incorporates heat flow evolving topography and the detailed kinetics of different thermochronometric systems and explains both complex local variations and regional patterns inclusion of the effects of radiation damage on he diffusion in detrital apatite is shown to have dramatic effects on results geometric and velocity parameters are tuned to fit model ages to observed data best fit is achieved at 9 mm a 1 plate convergence with pacific plate delamination on a gentle 10 se dipping detachment and more rapid uplift on a 45 60 dipping alpine fault ramp from 15 km depth thermokinematic modeling suggests dip slip motion on reverse faults within the southern alps should be highest 22 km from the alpine fault and much lower toward the southeast

application of x ray micro computed tomography in u th he thermochronology abstract a practical issue in determining a u th he age is the correction factor f he that accounts for potential he loss due to alpha ejection during the decay of u and th located in the outer 20 m of a mineral grain an accurate determination of f he is affected by the accuracy of measurements made by individual observers and the need for a subjective assessment of crystal morphology relative to an ideal crystal shape other issues include the presence of latent mineral inclusions or fracture planes that are potential pathways for helium loss these issues are potentially most important for detrital grains where grain shape and transparency have been affected by weathering we used x ray micro computed tomography microct analysis to objectively and quantitatively address these problems using traditional microscopy four workers with considerable experience in u th he studies independently examined the same set of apatite and zircon grains and reported f he values that agree to within 4 and 9 respectively these same grains were then imaged and measured using microct to obtain x y z dimension surface area s and volume v data f he values calculated using the microct s v differed by up to 24 as compared to microscope based f he determinations the largest discrepancies occurred in small grains with deviations from ideal hexagonal tetragonal dipyramidal grain morphology a significant advantage of microct scans is the ability to computationally excise the outer 20 m layer from the grain via a 3d erosion procedure the effective f he is proportional to eroded v original v and objectively accounts for the daughterless parent component in each grain independent of morphology and without the need for microscopic measurements the effective f he determined by triple erosion is up to 6 smaller than that derived using traditional microscopy methods microct can also be successfully used prior to analysis to reveal internal fractures mineral and fluid inclusions to 1 m resolution via density and elemental contrasts and to provide accurate volume measurements for the calculation of u and th concentrations in single grains

late cenozoic cooling history of the central menderes massif timing of the buyuk menderes detachment and the relative contribution of normal faulting and erosion to rock exhumation abstract based on new thermochronological data and 10be derived erosion rates from the southern part of the central menderes massif aydin block in western turkey we provide new insights into the tectonic evolution and landscape development of an area that undergoes active continental extension fission track and u th he data reveal that the footwall of the buyuk menderes detachment experienced two episodes of enhanced cooling and exhumation assuming an elevated geothermal gradient of 50 c km the first phase occurred with an average rate of 0 90 km myr in the middle miocene and the second one in the latest miocene and pliocene with a rate of 0 43 km myr the exhumation rates between these two phases were lower and range from 0 14 to 0 24 km myr depending on the distance to the detachment cosmogenic nuclide based erosion rates for catchments in the aydin block range from 0 1 to 0 4 km myr the similarity of the erosion rates on both sides of the aydin block northern and southern flank indicate that a rather symmetric erosion pattern has prevailed during the holocene if these millennial erosion rates are representative on a million year timescale they indicate that apart from normal faulting erosion in the hanging wall of the buyuk menderes detachment fault did also contribute to the exhumation of the metamorphic rocks

power law distributions of discharge mass and energy in river basins river networks constitute dissipative systems with many spatial degrees of freedom previous work by mandelbrot 1983 and bak et al 1987 1988 1990 suggests that such systems will follow power law distributions in their mass and energy characteristics it is shown that this is the case for river networks where the exponent in the distribution p x x x is approximately equal to 0 45 and 0 90 for discharge and energy respectively in the case of several networks analyzed in north america when these variables are calculated for each individual link throughout the drainage network an explanation of the values of is offered based on the fractal structure of rivers and on principles of energy expenditure in river basins

climatically versus tectonically forced erosion in the alps thermochronometric constraints from the adamello complex southern alps italy abstract we apply u th sm he dating and fission track thermochronometry of apatites to the adamello complex located in the southern european alps our goal is to constrain exhumation rates since the miocene in particular to determine whether the increase in sedimentation documented in the foreland basins since 5 ma is recorded in cooling rates of the southern alps thermochronometry provides a cooling rate for rocks which can be converted to an exhumation rate through thermal modeling thereby quantifying the amount of rock exhumed at different time scales apatite fission track and u th sm he analyses all record miocene ages we find no evidence for an increase in exhumation rate during the plio pleistocene the results of our exhumation rate estimates and tectono geomorphic modeling suggest that unroofing during thrust propagation of the southern alps in the late miocene drove most of the exhumation while changes in relief mainly associated with plio pleistocene climate change likely did not affect the adamello complex the findings from this study combined with other studies highlight that there appears to be a gradient across the alps with more intensive plio pleistocene erosion in the western and central alps compared to the eastern and southern alps

fractal structures as least energy patterns the case of river networks natural drainage networks like river basins exhibit fractal and multifractal properties this work shows that these properties evolve from arbitrary initial conditions by minimizing the local and global rates of energy expenditure in the system this suggests that many fractal structures may arise as a natural consequence of least energy dissipation requirements

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

peridotite dissolution and carbonation rates at fracture surfaces under conditions relevant for in situ mineralization of co2 abstract whereas the dissolution of pure single phases e g olivine and other mafic minerals has been the focus of many studies no investigation has been reported on the progress of reactions at and within polymineralic transgranular fracture surfaces cutting peridotites we document experiments that address the evolution of dissolving peridotite surfaces and the rates of dissolution and carbonation reactions that occur at these surfaces under both open and closed system conditions relevant for in situ co2 sequestration the results of experiments conducted under quasi open system conditions on solid samples of peridotite whose surfaces were taken as an analogue of free fracture surfaces demonstrate apparent rates of olivine dissolution at the free surfaces that are equivalent to or upwards of 100 times greater than those determined for pure olivine under similar conditions this increase in apparent olivine dissolution rate is ascribed to fluid penetration along grain boundaries and veins which resulted in increased accessibility of reactive olivine surface area apparent dissolution rates under closed system conditions where serial olivine dissolution and magnesite precipitation take place are 1 order of magnitude slower owing to changes in fluid composition and ph in both of these reaction environments it is apparent that serpentinized veins and mineral grain boundaries within the peridotite allowed fluids to penetrate the rock and to promote the release of divalent metals and silica from within the sample or simulated fracture walls these results indicate that the microstructure of free fracture surfaces exerts a dominant control on peridotite dissolution and carbonation rates relative to the proportion of highly reactive minerals that compose such ultramafic rock the rapid dissolution we observe under open system conditions implies that co2 mineralization may be viable in open systems if the composition of injected fluids can be maintained at or near the initial composition fracture clogging that results from precipitation and fluid phase ph changes in closed systems however can drastically limit peridotite carbonation

sequestration of atmospheric co2 in chrysotile mine tailings of the woodsreef asbestos mine australia quantitative mineralogy isotopic fingerprinting and carbonation rates since closure of the woodsreef asbestos mine located in the great serpentinite belt gsb new south wales australia extensive carbonate rich crusts have formed by recessive weathering of fine grained material on the surface of the tailings pile a relationship exists between the mode of carbonate occurrence the mineralogy and the isotopic fingerprint of carbonates from the tailings pile vertical carbonate crusts covering most of the tailings predominantly consist of the hydrated mg carbonate hydromagnesite mg5 co3 4 oh 2 4h2o which has precipitated from evaporating meteoric waters incorporating atmospheric co2 as reflected in high 18o 13c and f14c signatures respectively low and variable concentrations of magnesite dolomite and calcite represent bedrock carbonate which has formed during alteration of the serpentinite bedrock before mining and is characterised by moderately high 18o low 13c and f14c a signature typical for weathering derived magnesite deposits in the gsb the carbonate fraction of deep cement samples collected from 70 to 120 cm below the surface representing the bulk tailings material at depth predominantly consists of pyroaurite mg6fe2 co3 oh 16 4h2o and despite stable isotope signatures similar to bedrock contains significant radiocarbon this indicates that pyroaurite forming under different conditions as hydromagnesite may represent an additional trap for atmospheric co2 in the woodsreef mine tailings the distribution of carbonates and quartz together with the absence of isotopic mixing trends between bedrock carbonate and atmospheric derived carbonate strongly indicates that dissolution and re precipitation of bedrock carbonate is not a dominant process in the woodsreef tailings the cations for carbonate formation are instead derived from the dissolution of serpentine minerals lizardite and chrysotile and brucite the internal standard method and the reference intensity method have been used with x ray diffraction data to estimate the abundance of the two major carbonate minerals hydromagnesite and pyroaurite respectively considering the formation of hydromagnesite on the outer surface of the tailings pile alone or together with formation of pyroaurite within the tailings pile we conclude that between 1400 and 70 000 t of atmospheric co2 have been sequestered in the mine tailings since closure of the mine 29 a ago carbonation rates of 27 g c m 2 y 1 and 1330 g c m 2 y 1 are significantly higher than background rates of co2 uptake by chemical weathering and demonstrate the potential of passive carbonation of mine tailings as a cost and energy effective alternative for storage of co2 in carbonate minerals

enhanced co2 mineral sequestration by cyclic hydraulic fracturing and si rich fluid infiltration into serpentinites at malentrata tuscany italy abstract the magnesite deposits of malentrata tuscany italy were derived from serpentinite silicification carbonation of the ligurian ophiolite and represent a natural analogue of in situ co 2 mineral sequestration carbonation of magnesium silicate minerals e g serpentine olivine at temperatures below 200 c is an exothermal process involving incorporation of carbon dioxide into stable carbonates e g magnesite dolomite serpentinites at malentrata were transformed to a brownish friable rock characterized by the occurrence of opal chromian montmorillonite fe rich magnesite and minor iron sulfides and oxides widespread lenses of cohesive rocks occur within the altered serpentines resulting from the complete silicification of the protolith the pervasive alteration of serpentinite was accompanied by the formation of a network of magnesite and dolomite veinlets and large magnesite dolomite veins along major structures field observations petrography and mineral chemistry define the following crystallization sequence in the major veins i early microgranular fe poor magnesite ii comb textured fe rich magnesite and dolomite cementing the early brecciated magnesite vein infill and iii late quartz chalcedony and rare opal in the cavities the mineral assemblage observed both in veins and in host rock is indicative of low temperature hydrothermal alteration driven by si and co 2 rich fluids under relatively low ph conditions pervasive and cyclic hydraulic fracturing maintained a high structural permeability during the whole hydrothermal event creating conduits for the input and output fluids the concomitant presence of co 2 and silica in the fluid enhanced the congruent dissolution of serpentine and hampered immediate carbonate deposition the mg bearing solutions were focused out of the reactor zone and promoted massive carbonate veining along the main structural discontinuities this two steps reaction dissolution of serpentinite followed by carbonate precipitation outside the reacting volume seems to be very efficient and provide new insights on in situ and ex situ induced mineral carbonation and its industrial applications

u th he thermochronometry mapping 3d geometry using micro x ray tomography and solving the associated production diffusion equation u th he ages reflect the combined effects of he particles loss due to diffusion and he ingrowth due to radioactive decay of u and th series furthermore the particles are emitted with sufficient kinetic energy that they can travel in theory up to 20 m and as a result particles may be ejected beyond the crystal edges to circumvent this problem a correction factor must be applied which is essentially based on the geometry of the crystals farley k a wolf r and silver l 1996 the effect of long alpha stopping distances on u th he dates geochimica et cosmochimica acta 60 4223 4229 this strongly limits the application of the technique to crystals of appropriate geometries we present here a method to compute the effects of ejection for u th he dating by taking into account the 3d morphology of individual crystals determined with micro x ray tomography we also develop a model which solves the diffusion equation for the crystals that have been imaged we then couple this model with an inversion algorithm to extract the range of thermal histories that the rocks may have experienced this technique is applied to detrital samples from rocks collected in the southern alps of new zealand a region of high exhumation rate

co2 sequestration and extreme mg depletion in serpentinized peridotite clasts from the devonian solund basin sw norway the conglomerates of the solund devonian basin of sw norway contain numerous locally up to 20 vol peridotitic clasts with concentric mm to 10 cm thick zones of varying red to black color the peridotite clasts show a clear alteration related textural evolution the least altered rocks are partly serpentinized peridotites showing a typical mesh texture with veins of serpentine magnesite and ni rich magnetite surrounding olivine fo91 relicts and its mg depleted clay like alteration product deweylite assemblage in the more advanced ophicarbonate stage the mesh cells contain calcite silica and are surrounded by talc in the final stage quartz calcite and hematite dominate the mineralogy and occur together with minor amounts of chromite talc cr chlorite and cr hydroandradite in tandem with this textural evolution is a decrease in mgo from 40 to 2 5 wt and a cao increase from 1 to 35 wt all peridotite clasts are characterized by high cr and ni concentrations the chemistry and the textural evolution show that the clasts formed by an extreme mg mobilization from the peridotite with development of secondary porosity and subsequent precipitation of calcite mgo removed from the clasts after burial is in part consumed by replacement reactions in the sediment matrix around the clasts where mg free minerals e g almandine are replaced by mg bearing minerals e g talc calculated apparent 87 sr 86 sr ratios of the clasts at 385 ma 0 7124 0 7139 corresponding to the inferred age of sediment deposition and incipient clast alteration indicate interaction with diagenetic basinal fluids we explain the reaction history as a three stage process involving a partial serpentinization of olivine in an oceanic environment b breakdown of olivine relicts to the deweylite assemblage resulting in mobilization of mgo under near surface conditions in a tropical devonian climate and c further mg mobilization and replacement of the deweylite assemblage by calcite and quartz after diagenesis sedimentary basins with abundant weathered peridotite represent potential sites for a permanent co2 storage by formation of calcite in a low temperature environment 2010 elsevier ltd all rights reserved

forsterite dissolution and magnesite precipitation at conditions relevant for deep saline aquifer storage and sequestration of carbon dioxide the products of forsterite dissolution and the conditions favorable for magnesite precipitation have been investigated in experiments conducted at temperature and pressure conditions relevant to geologic carbon sequestration in deep saline aquifers although forsterite is not a common mineral in deep saline aquifers the experiments offer insights into the effects of relevant temperatures and pco2 levels on silicate mineral dissolution and subsequent carbonate precipitation mineral suspensions and aqueous solutions were reacted at 30 c and 95 c in batch reactors and at each temperature experiments were conducted with headspaces containing fixed pco2 values of 1 and 100 bar reaction products and progress were determined by elemental analysis of the dissolved phase geochemical modeling and analysis of the solid phase using scanning electron microscopy infrared spectroscopy and x ray diffraction the extent of forsterite dissolution increased with both increasing temperature and pco2 the release of mg and si from forsterite was stoichiometric but the si concentration was ultimately controlled by the solubility of amorphous silica during forsterite dissolution initiated in deionized water the aqueous solution reached supersaturated conditions with respect to magnesite however magnesite precipitation was not observed for reaction times of nearly four weeks magnesite precipitation was observed in a series of experiments with initial solution compositions that simulated extensive forsterite dissolution the precipitation of magnesite appears to be limited by the process of nucleation and nucleation requires a critical saturation index between 0 25 and 1 14 at 95 c and 100 bar pco2 magnesite precipitation is fastest in the presence of an initial magnesite seed although magnesite precipitates do form on the surfaces of forsterite particles the presence of the forsterite surface does not significantly accelerate magnesite precipitation relative to solid free systems

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

accounting for long alpha particle stopping distances in u th sm he geochronology 3d modeling of diffusion zoning implantation and abrasion in apatite u th he thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production thermally activated volume diffusion and the ejection of he caused by long alpha stopping distances these processes are further complicated by zonation of u th and sm within the grain and implantation of 4he from neighboring u th sm bearing minerals we use a refined version of the 3d monte carlo diffusion code of gautheron and tassan got 2010 to simulate the interplay between ejection and diffusion with or without zonation ejection and abrasion for a suite of thermal histories we examine the phenomenon of over correction produced by the alpha ejection correction parameter ft or fzac for homogeneous or heterogeneous eu repartition by comparing the raw measured and ft or fzac corrected ages for a number of scenarios to the ejection free age aef which we define as the age that would be obtained if alpha ejection had not occurred or equivalently if the stopping distance was zero we show that the use of ft or fzac corrected ages generally reproduces the ejection free age to within typical u th he uncertainties 8 even for zoned apatites we then quantify the effect of alpha implantation on u th he ages showing that implantation from a single external source with modest relative u or th enrichment can generate as much as 50 excess he for more extreme cases where an apatite is surrounded by multiple external sources the measured age can be 300 of that determined from an isolated crystal while abrasion of the outer 20 25 m can significantly reduce the age dispersion for rapidly cooled samples slowly cooled samples can still retain 10 30 excess he the removal of the rim of the crystal reduces the thermal information from very low temperatures 40 c and introduces additional technical complications and biases and should therefore be used with caution overall we demonstrate that although zonation and implantation may not be routinely determined we now have the 3d modeling capability to fully investigate and constrain the causes of age dispersion within a sample leading to significant improvement in our ability to interpret u th he data

modeling of the temperature sensitivity of the apatite u th he thermochronometer apatite u th he apparent ages will generally reflect residence for extended periods at temperatures where helium is neither quantitatively retained nor lost by diffusion to characterize the response of apatite he ages to thermal histories involving partial he retention we explored solutions to the he production diffusion equation under thermally static conditions the analytical solution to this equation coupled with published diffusivity data demonstrates that the zone of partial he retention extends from about 40 c to 85 c this zone lies at temperatures 35 c cooler than the analogous fission track partial annealing zone he ages within the partial retention zone ultimately achieve a balance between he production and loss yielding a steady state age both the ultimate age and the time it takes to achieve this age are temperature dependent for example an apatite held at 75 c equilibrates to an age of 2 ma after 17 myr regardless of whether equilibrium is approached from a higher or a lower initial he age for representative dynamic thermal histories we evaluated apatite he ages using a numerical solution to the ingrowth diffusion equation the results illustrate the sensitivity of he ages to various geologic histories and are useful for understanding he age elevation relationships and for testing time temperature paths derived from apatite fission track length distributions in addition although he diffuses rapidly from apatite at shallow crustal temperatures modeling of ambient temperature fluctuations indicates that he ages are nearly unaffected by surficial processes

exhumation history of the aydin range and the role of the buyuk menderes detachment system during bivergent extension of the central menderes massif western turkey the central menderes massif western turkey is a prominent example of symmetrical exhumation of a core complex it comprises the bozda and aydin ranges which represent the footwalls of the north dipping gediz detachment and the south dipping buyuk menderes detachment respectively in contrast to the gediz detachment the role of the buyuk menderes detachment during late cenozoic extension and exhumation of the central menderes massif is less well resolved here we present results from structural and geological mapping as well as new fission track and u th he data to show that two low angle normal faults contributed to the exhumation of the aydin range our data indicate that the sustained activity of the buyuk menderes detachment since the early miocene is followed by the onset of faulting along the previously unrecognized demirhan detachment which is situated in the hanging wall of the buyuk menderes detachment in the latest miocene pliocene thermokinematic modelling of cooling ages from the footwalls of the buyuk menderes and demirhan detachments yielded exhumation rates of c 0 5 and c 0 4 km ma 1 respectively apatite fission track ages from the demirhan detachment indicate a slip rate of c 2 km ma 1 during the pliocene high angle normal faulting along the modern buyuk menderes graben commenced in the quaternary supplementary material further results of thermal history modelling are available at https doi org 10 6084 m9 figshare c 4392905

a theoretical model of the fracture of rock during freezing we present a mathematical model for the breakdown of porous rock by the growth of ice within cracks the model is founded upon well established principles of fracture mechanics and recent advances in soil physics ijong with the assumption that progressive crack growth results from water migrating to ice bodies in cracks much as water migrates to ice lenses in freezing soil our model predicts crack growth rates compatible with empirical data calculations for a granite and a marble indicate that sustained freezing is most effective in producing crack growth when temperatures range from 4 c to 15 c at higher temperatures thermodynamic limitations prevent ice pressure from building up sufficiently to produce significant crack growth at lower temperatures the migration of water necessary for sustaining crack growth is strongly inhibited in hydraulically open systems in which pore water pressure remains near atmospheric pressure during the freezing process crackgrowth rates during continuous cooling will generally be greatest at low rates of cooling less than 0 1 0 5 c h at higher rates of cooling the influx of water to growing cracks is significantly inhibited the model delineates clearly the role of material parameters elastic moduli fracture mechanical properties grain size and shape and crack size environmental conditions temperature temperature gradient water pressure and time in frost damage to rocks our calculations along with recent experimental work on water migration in freezing rocks fukuda 1983 lead us to question the widely accepted importance of two phenomena freezing of water in sealed cracks and freeze thaw cycling in the fracture of rock exposed to natural freezing conditions

influence of crystal size on apatite u th he thermochronology an example from the bighorn mountains wyoming near surface tectonic and geomorphic processes involve cooling of rocks through low temperatures 50 200 c because rates of helium diffusion in apatite titanite and zircon are sensitive to temperature variations in this range uranium thorium helium thermochronometry u th he dating is well suited to establishing the timing and rates of these processes in the geologic record however because fractional loss of he is controlled by crystal size such that larger crystals retain a larger fraction of radiogenic he u th he ages must vary not only with thermal history but also with crystal size here we present crystal size correlated he ages from co existing apatites from the bighorn mountains wyoming that range from 100 to 350 ma these correlations are a sensitive indicator of the rock s thermal history in a temperature range below the system s nominal closure temperature t c 70 c for apatite and are consistent with a thermal history involving residence in the upper 2 3 km of crust since the precambrian with maximum temperatures of 65 80 c just prior to laramide orogenic exhumation the influence of crystal size on he ages will be most apparent in rocks where temperatures have been in the range of partial he retention for long periods of time 30 70 c for 10 7 years in such cases accurate interpretation of u th he ages must incorporate the effect of crystal size and this method may provide insights to thermal histories of rocks in previously inaccessible low temperature ranges

low temperature thermochronology of anticosti island a case study on the application of conodont u th he thermochronology to carbonate basin analysis abstract the ordovician to silurian carbonate succession preserved on anticosti island is a near continuous record of the changing depositional and tectonic history of the early paleozoic laurentian margin these strata are a prime natural laboratory to test the applicability of conodont apatite u th he thermochronology cahe for carbonate basin analysis in a setting with a well understood burial history and abundant paleotemperature constraints we report 63 cahe dates from seven samples collected from two boreholes x ray micro computed tomography xr ct was used to assess individual conodont element size volume and alpha ejection correction cahe dates are negatively correlated with effective uranium concentration eu with single conodont dates enigmatically older than the age of deposition to conodont dates as young as 2 7 0 2 ma we rationalize this dispersion as a product of several factors including diagenetic processes and pervasive conodont crystalline porosity and permeability additionally one basement and two sandstone samples were collected for apatite and zircon u th he ahe zhe and apatite fission track aft thermochronology in the precambrian basement zhe dates range from 581 7 46 5 ma to 761 2 60 9 ma n 4 and ahe dates range from 26 7 1 6 to 48 4 2 9 ma n 4 ahe dates from two lower ordovician sandstones n 8 are positively correlated with eu increasing from 13 7 0 8 ma to 105 2 6 3 ma over a range of 186 ppm eu thermal history modeling of these data suggests two plausible thermal histories both of which are novel as they imply that far field effects related to the opening of the atlantic ocean have influenced the thermal history of anticosti island ultimately these data highlight the complexities associated with and necessity of low temperature thermochronology in carbonate basins

reaction assisted hierarchical fracturing during serpentinization abstract hierarchical fracture patterns are the result of a fracturing process that successively divides rocks into smaller domains in a 2d outcrop section such fracture patterns are characterized by four sided domains and t junctions where new fractures stop growing at right angles to pre existing fractures here we describe fracturing of mm to dm thick serpentinized orthopyroxenite dykes in a dunite matrix from the leka ophiolite complex in nord trondelag norway the fracturing process is driven by volume changes associated with the serpentinization of the dunites during this process the orthopyroxenite dykes are extended by the expanding dunite and undergo considerable fracturing the resulting fracture patterns are hierarchical the cumulative distributions of fracture lengths show a scaling behavior that lies between a log normal and power law fractal distribution this is consistent with a simple fragmentation model in which domains are divided according to a top hat distribution of new fracture positions within unfractured domains reaction assisted hierarchical fracturing is also likely to be responsible for other structures commonly observed in serpentinized ultramafic rocks including the mesh textures observed in individual olivine grains and the high abundance of rectangular domains at a wide range of scales this mechanism may provide first order controls on fluid migration rates in a wide variety of geological settings

fluvial fan deltas linking channel processes with large scale morphodynamics 1 alluvial fan deltas are built by aggrading and avulsing river channels a numerical model of flow and sediment transport in channels is combined with a condition for channel avulsion to describe evolution of the fan surface the model combines elements of two recent approaches 1 diffusional models of depositional basin filling which describe the evolution of overall morphology and 2 cellular models of channel evolution which provide simplified descriptions of channel dynamics here the cellular formulation is used simply as a template for discretizing a standard set of equations describing flow and sediment transport within channels the basic formulation is thus grid invariant and the results are in actual rather than arbitrary time and length scales the model captures the interaction between microscale channel morphodynamics including converging and diverging flow and avulsion and morphodynamics at the macroscale fan it provides a starting point for the study of a wide range of topics including the three dimensional stratigraphy of fan delta deposits and the response of fan deltas to engineering activities

use of a landscape simulator in the validation of the siberia catchment evolution model declining equilibrium landforms this paper presents a study to test the ability of the current generation of landscape evolution models to correctly predict landscape form from measured erosion processes landscapes generated by the siberia landscape evolution model were compared to experimental model landscapes in declining equilibrium the model simulations were compared using geomorphologically and hydrologically significant parameters comparisons of the simulated landscapes with the experimental landscapes were carried out using the hypsometric curve width function cumulative area distribution and area slope relationship these comparisons demonstrate that siberia can correctly simulate the experimental model landscape at declining equilibrium the simulation showed sensitivity to the spatial distribution of the rainfall particularly with respect to hypsometry using the correct measured distribution of rainfall was necessary rather than using a spatially uniform rainfall distribution the results also highlighted the importance of digital terrain map dtm error in deriving geomorphic statistics the observed landform had a consistently larger width function than the simulation only when the simulations were corrupted with elevation errors with statistical properties of the errors in the experimental landscape dtm as measured by photogrammetry did the observed and simulated width functions match

garnets within geode like serpentinite veins implications for element transport hydrogen production and life supporting environment formation geochemical micro environments within serpentinizing systems can abiotically synthesize hydrocarbons and provide the ingredients required to support life observations of organic matter in microgeode like hydrogarnets found in mid atlantic ridge serpentinites suggest these garnets possibly represent unique nests for the colonization of microbial ecosystems within the oceanic lithosphere however little is known about the mineralogical and geochemical processes that allow such unique environments to form here we present work on outcrop scale vein networks from an ultramafic massif in norway that contain massive amounts of spherulitic garnets andradite which help to constrain such processes vein andradite spherulites are associated with polyhedral serpentine brucite ni fe alloy awaruite and magnetite indicative of low temperature 200 c alteration under low fo2 and low asio2 aq geochemical conditions together with the outcrop and micro scale analysis geochemical reaction path modeling shows that there was limited mass transport and fluid flow over a large scale once opened the veins remained isolated closed system forming non equilibrium microenvironments that allowed upon a threshold supersaturation the rapid crystallization seconds to weeks of spherulitic andradite the presence of polyhedral serpentine spheres indicates that veins were initially filled with a gel like protoserpentine phase in addition massive fe oxidation associated with andradite formation could have generated as much as 600 mmol h2 aq per 100 cm3 vein although no carboneous matter was detected the vein networks fulfill the reported geochemical criteria required to generate abiogenic hydrocarbons and support microbial communities thus systems similar to those investigated here are of prime interest when searching for life supporting environments within the deep subsurface

architecture kinematics and exhumation of a convergent orogenic wedge a thermochronological investigation of tectonic climatic interactions within the central st elias orogen alaska abstract the kinematics and architecture of orogenic systems along the leading edges of accreting terranes may be heavily influenced by climate but little research has been devoted to the long term effects of glacial erosion on orogenesis here we use low temperature apatite and zircon u th he and fission track thermochronometry along with subsidiary structural relationships and seismicity to develop a new architectural model of the st elias orogen in southern alaska which is one of the best examples of a glaciated orogenic wedge worldwide these data illustrate that the orogen consists of a deformational backstop on the leeward flank and a rapidly deforming and eroding thin skinned fold and thrust belt on the windward flank a structure beneath the bagley ice field separates these distinct deformational domains which we propose is a backthrust that makes the orogen doubly vergent thermochronometry within the orogenic wedge suggests that denudation and deformation are strongly influenced by glacial erosion long term exhumation at rates of up to 4 mm yr is concentrated within a narrow zone along the windward flank where glacier equilibrium lines intersect the orogenic wedge the onset of enhanced glaciation also coincided with a marked acceleration in exhumation across the orogenic wedge accelerated backthrust motion and a major shift in deformation away from the north american yakutat terrane suture chugach st elias fault we propose that accelerated glacial erosion forced the redistribution of strain along the backthrust and an en echelon array of forethrusts that lie beneath the zone of heaviest glaciation which in turn are systematically truncated by the backthrust this focusing of deformation matches predictions from analytical models of orogenic wedges and implies a high degree of coupling between climate and tectonics in this glacially dominated orogen

influence of amorphous silica layer formation on the dissolution rate of olivine at 90 c and elevated pco2 for mitigating against rising levels of atmospheric co2 carbonation of m2 bearing silicates has been proposed as a possible option for sequestering co2 over long time spans due to its rapid far from equilibrium dissolution rate and its widespread occurrence in mafic and ultramafic rocks olivine has been suggested as a potentially good candidate for achieving this goal although the efficacy of the carbonation reaction still needs to be assessed with this as a goal the present study aims at measuring the carbonation rate of san carlos olivine in batch experiments at 90 c and pco2 of 20 and 25 mpa when the reaction was initiated in pure water the kinetics of olivine dissolution was controlled by the degree of saturation of the bulk solution with respect to amorphous silica this yet unrecognized effect for olivine was responsible for a decrease of the dissolution rate by over two orders of magnitude in long term 45 days carbonation experiments with a high surface area to solution volume ratio sa v 24 600 m 1 the final composition of the solution was close to equilibrium with respect to sio2 am independent of the initial concentration of dissolved salts nacl and naclo4 ranging between 0 and 1 m and with an aqueous mg si ratio close to that of olivine no secondary phase other than a ubiquitous thin 40 nm si rich amorphous layer was observed these results are at odds with classic kinetic modeling of the process due to experimental uncertainties it was not possible to determine precisely the dissolution rate of olivine after 45 days but the long term alteration of olivine was indirectly estimated to be at least 4 orders of magnitude slower than predicted taken together these results suggest that the formation of amorphous silica layers plays an important role in controlling the rate of olivine dissolution by passivating the surface of olivine an effect which has yet to be quantified and incorporated into standard reactive transport codes

experimental study of the carbonation of partially serpentinized and weathered peridotites abstract carbonation of partially serpentinized and weathered peridotites was studied experimentally under hydrothermal conditions t 200 c p co 2 130 180 bars experiments were performed in a closed system using whole rock drill core samples height 1 cm diameter 1 cm as starting material the initial samples were composed mainly of meshwork serpentine relicts of primary olivine and an olivine weathering product deweylite assemblage two types of solutions each with a total salt content corresponding to that of average seawater 35 g l dissolved salts were used 1 a na ca cl solution 12 5 g l cacl2 22 5 g l nacl and 2 a nacl solution 35 g l nacl after 15 25 days of experimental treatment the samples were partly covered with carbonates in addition noticeable carbonation reactions had occurred below the sample surfaces within zones with thicknesses up to 250 m in the na ca cl solution both the olivine relicts and the deweylite assemblage were partly replaced by calcite along the surrounding serpentine veins however the extent of calcitization was found to be considerably larger for the deweylite assemblage than for the olivine bulk fluid analyses show an increase in the mg and si concentrations with reaction time in the nacl solution the deweylite assemblage was partly dissolved resulting in large voids within the reaction zone in contrast the olivine was replaced by magnesite under the conditions of our experiments the meshwork serpentine was not reactive but aided fluid infiltration into the rock samples the experimentally produced microtextures closely resemble those found in natural examples our study elucidates the mechanisms by which carbonates form in ultramafic rocks under relatively high p co 2 t conditions and particularly in the presence of ca bearing aqueous solutions the existence of a serpentine meshtexture and the presence of weathering products formed from primary mg silicates may have significant beneficial effects on in situ co2 mineral sequestration in ultramafic rocks

in situ sequestration of atmospheric co2 at low temperature and surface cracking of serpentinized peridotite in mine shafts abstract the investigation of carbonate formation at low temperature during weathering of ultramafic rocks has become increasingly important as it represents an analog study for a cost efficient carbon disposal strategy here we present new insight into carbonate formation under subarctic surface conditions obtained from extensively carbonated chromite mine shafts in the feragen ultramafic body e norway carbonation proceeded by formation of mm to cm thick carbonate surface coatings on the serpentinized peridotite host rock the surface coatings consist in most cases of pure lansfordite mgco 3 5h 2 o and sometimes nesquehonite mgco 3 3h 2 o heavy o and c isotopes are strongly enriched in the carbonate coatings relative to drip water samples from the mines and water samples from subaerial ponds the major element composition of the water samples reveal that infiltrating rainwater reacts rapidly with the peridotite mainly due to brucite dissolution within the mines discharging alkaline water forms thin films on walls and ceilings that evaporate upon circulation of cold dry air in mines with only one opening the carbonation is limited to the entrance area in mines with a more efficient air circulation due to multiple entrances carbonation is found throughout the mine evaporation of the mine water results in lansfordite saturation and precipitation and is accompanied by a rayleigh type distillation effect causing enrichment of the heavy c and o isotopes in the liquid from which the carbonates precipitate formation of the carbonate coatings involved fragmentation of the underlying serpentinite substrate fragmentation proceeded by subcritical cracking i e by a combination of substrate weakening due to brucite dissolution and stress build up due to lansfordite precipitation in fractures close to the surface reaction induced fracturing represents a positive feedback mechanism as it creates additional reactive surface area during the carbonation mining operations in the area ceased in the mid 1920s indicating that the described carbonation occurs on a time scale relevant for the disposal of anthropogenic co 2

drainage basin perimeters a fractal significance abstract drainage basin boundaries are irregular curves with many scales of crenulation defying precise measurement of basin perimeter richardson divider analysis of six drainage basin outlines from southern indiana and of an additional six from larger u s basins suggests that basin boundaries are fractal or near fractal shapes although the basins differ significantly in physiography the fractal dimension values obtained fit within the narrow range 1 06 1 12 indicating that while basins may differ greatly in overall shape they are very similar in terms of smaller scale boundary irregularity techniques of measuring basin perimeter should be modified in recognition of these facts the consistent fractal or near fractal geometric characteristics of basin boundaries give a basis for extrapolation of perimeter values to appropriate levels of resolution for most basin morphometry applications however the objective should be to make comparison among basins using measurements taken at the same degree of resolution relative to basin size rather than identical resolution

formation of gravel pavements during fluvial erosion as an explanation for persistence of ancient cratered terrain on titan and mars abstract in many terrestrial channels the gravel bed is only transported during rare floods threshold channels and rates of erosion are very slow in this paper we explore how coarse debris delivered to channels on mars and titan from erosion may inhibit further erosion once a coarse gravel channel bed develops portions of the equatorial region of titan are fluvially eroded into banded crenulated terrain some of which contains numerous circular structures that are likely highly degraded large impact craters surviving from the late heavy bombardment no mechanism that can chemically or physically break down ice likely the most important component of titans crust has been unambiguously identified this paper examines a scenario in which fluvial erosion on titan has largely involved erosion into an impact generated megaregolith that contains a modest component of gravel sized debris as the megaregolith is eroded coarse gravel gradually accumulates as a lag pavement on channel beds limiting further erosion and creating a dissected but largely inactive or senescent landscape similar development of gravel pavements occur in ancient mountain belts on earth and partially explain the persistence of appreciable relief after hundreds of millions of years likewise coarse gravel beds may have limited the degree to which erosion could modify the heavily cratered terrains on mars particularly if weathering were largely due to physical rather than chemical weathering processes in a relatively cold and or arid environment

symmetry randomness and process in the structure of branched channel networks the branched structure of channel networks has a primary impact on the spatial distribution of elevation water and life across earth s surface from the hillslope to the continental scale and is also observed on other planets however the link between this dendritic multiscale structure and the erosional processes that sculpt it has remained elusive for more than six decades in fact many topologic measures fail to distinguish natural networks from those generated by random walks here we show that a fundamental multiscale topologic symmetry is ingrained into the structure of these networks and reflects the equal elevation drop spanned by flows that split at the drainage divide and meet again downslope we demonstrate that this symmetry distinguishes random walk networks from natural ones captures the temporal evolution of these networks and divulges information about the processes that shape them

quantifying rates of detachment faulting and erosion in the central menderes massif western turkey by thermochronology and cosmogenic 10be exhumation of rocks in extensional tectonic settings results from a combination of normal faulting and erosion but the relative contribution of these processes has rarely been quantified here we present new low temperature thermochronological data and the first 10 be based catchment wide erosion rates from the boz dag region in the central menderes massif which has experienced nne ssw extension since the miocene the slip rate of the shallow dipping gediz detachment fault which defines the northern flank of the boz dag block is 4 3 3 0 1 2 mm a 1 as constrained by zircon u th he ages of c 4 2 ma in the footwall apatite and zircon u th he and fission track ages from the northern flank of the boz dag block yield exhumation rates of 0 6 2 km ma 1 beneath the gediz detachment whereas those on the southern flank are only 0 2 0 6 km ma 1 erosion of catchments on the northern and southern flanks proceeds at rates of 80 180 and 330 460 mm ka 1 respectively this marked contrast is a combined effect of the topographic asymmetry of the boz dag block and differences in rock erodibility if these erosion rates persisted in the past rock exhumation on the northern flank occurred predominantly by tectonic denudation whereas rocks on the southern flank were mainly exhumed by erosion

is the drainage network a fractal sierpinski space the most common approach to extract the channel network from digital elevation models is to specify a threshold area s which is the minimum area required to drain to a point within which a channel forms this threshold area is usually specified arbitrarily although it is recognized that different threshold areas will result in substantially different channel networks for the same basin this paper studies the effects of s which is also the scale of observation on scaling and morphometric properties such as the number of sources and the areas of source basins and lateral basins the gardon basin located in southern france was extensively studied the results indicate that morphometric properties vary considerably with s and that the spatial distribution of source basins can be considered as a fractal sierpinski space a simple model based on the procedure similar to the sierpinski carpet construction is proposed to explain empirical relations between the number of source areas and the threshold s the model presents a new approach to estimate basin fractal properties and defines new indices to characterize the spatial distribution of first order basins this methodology is useful for hydrologists and geomorphologists dealing with river networks and spatial patterns of various basin properties such as vegetation soil soil moisture and human activities

environmental controls of frost cracking revealed through in situ acoustic emission measurements in steep bedrock 1 frost cracking the breakdown of rock by freezing is one of the most important mechanical weathering processes acting on earth s surface insights on the mechanisms driving frost cracking stem mainly from laboratory and theoretical studies transferring insights from such studies to natural conditions involving jointed bedrock and heterogeneous thermal and hydrological properties is a major challenge we address this problem with simultaneous in situ measurements of acoustic emissions used as proxy of rock damage and rock temperature moisture content the 1 year data set acquired in an alpine rock wall shows that 1 liquid water content has an important impact on freezing induced rock damage 2 sustained freezing can yield much stronger damage than repeated freeze thaw cycling and 3 that frost cracking occurs over the full range of temperatures measured extending from 0 down to 15 c these new measurements yield a slightly different picture than previous field studies where ice segregation appears to play an important role

the hydromagnesite playas of atlin british columbia canada a biogeochemical model for co2 sequestration abstract anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide co2 through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals the hydromagnesite mg5 co3 4 oh 2 4h2o playas of atlin british columbia canada provide a natural model to examine mineral carbonation on a watershed scale at near surface conditions co2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals the purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for co2 sequestration with emphasis on microbial processes that accelerate mineral carbonation regions with ultramafic bedrock such as atlin represent the best potential sources of feedstocks for mineral carbonation elemental compositions of a soil profile show significant depletion of mgo and enrichment of sio2 in comparison to underlying ultramafic parent material polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years upon retrieval the cube surfaces as seen using scanning electron microscopy had been colonized by bacteria that were associated with surface pitting degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium rich bedrock at atlin stable carbon isotopes of groundwater from a well situated near a wetland in the southeastern playa indicate that 12 of the dissolved inorganic carbon has a modern origin from soil co2 the mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments 1 the wetland characterized by biologically aided precipitation of carbonate minerals from waters concentrated by evaporation 2 isolated wetland sections that lead to the formation of consolidated aragonite sediments and 3 the emerged grassland environment where evaporation produces mounds of hydromagnesite examination of sediments within the southeastern playa wetland suggests that cyanobacteria sulphate reducing bacteria and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals the atlin site as a biogeochemical model has implications for creating carbon sinks that utilize passive microbial geochemical and physical processes that aid in mineral carbonation of magnesium silicates these processes could be exploited for the purposes of co2 sequestration by creating conditions similar to those of the atlin site in environments artificial or natural where the precipitation of magnesium carbonates would be suitable given the vast quantities of mg rich bedrock that exist throughout the world this study has significant implications for reducing atmospheric co2 concentrations and combating global climate change

variable late neogene exhumation of the central european alps low temperature thermochronology from the aar massif switzerland and the lepontine dome italy 1 several recent studies proposed an important increase in exhumation rate in the western european alps since circa 5 4 ma in order to assess potential spatial differences in exhumation histories we present new apatite fission track aft and apatite u th he ahe ages from the central aar massif guttannen area switzerland and the western lepontine dome formazza area italy internal u th zoning in apatites explains alpha ejection corrected ahe ages that are older than the corresponding aft ages in this study a qualitative interpretation of aft and ahe age elevation relationships suggests a two phase 9 7 and 5 3 ma exhumation scenario affecting the central alps with a stronger expression of the pliocene signal in the formazza area however a quantitative evaluation of exhumation scenarios using the 3 d heat equation solver pecube highlights the existence of several other likely scenarios casting doubt on the validity of a qualitative interpretation of the age elevation relationships in formazza scenarios suggested by quantitative modeling include continuous denudation at a rate of 750 m ma and a one step exhumation rate change from 300 to 1000 m ma at 5 ma in guttannen they include continuous denudation at a rate of 400 m ma with valley deepening and two periods of higher exhumation rate increasing from 300 to 700 m ma repeatedly at 9 7 and at 5 3 ma contingent upon further flexural isostatic modeling the magnitude of exhumation recorded in the axial region of the alps since circa 5 ma does not appear sufficient to solely explain the denudation recorded in the north alpine foreland basin

frost weathering and rockwall erosion in the southeastern swiss alps long term 1994 2006 observations abstract rates and processes of frost weathering in the alps were investigated by visual observations of intensively shattered rocks continuous monitoring of frost wedging and rock temperatures in bedrock and measurements of rockfall activity rapid frost weathering of hard intact rocks occurs along lakes and streams where seasonal freezing promotes ice segregation in the rock otherwise rocks require pre existing weakness or a long exposure period for intensively shattered automated monitoring shows that crack opening occurs at three scales including small opening accompanying short term frost cycles slightly larger movements during seasonal freezing and occasional large opening originating from refreezing of snow melt water during seasonal thawing the opening events require at least partial water saturation in the crack the repetition of crack opening frost wedging results in permanent opening and finally debris dislocation debris collections below fractured rockwalls show that pebble falls occur at an average rate of about 0 1 mm a 1 with significant spatial and inter annual variations occasional large boulder falls significantly raise the rockwall erosion rates controlled by such factors as the joint distribution in the bedrock repetition of annual freeze thaw cycles and extraordinary summer thaw

fracture initiation during volume increasing reactions in rocks and applications for co2 sequestration abstract volume increasing processes in rocks can induce various types of fractures such as hierarchical domain division of the unreacted material and spalling of the reacted material the mechanism responsible for the selection of a particular fracture type is generally not known we study such deformations and fracture mechanisms in a simplified system with a range of numerical techniques and find that sharpness of reaction fronts and magnitude of volume increase are the main parameters controlling which fracture type forms spalling dominates when there is sharp reaction fronts and large magnitude of volume change otherwise we get mainly domain dividing fractures increasing reaction front sharpness and magnitude of volume change also increases the fracture density and we argue that the change in fracture density can be important for the viability of in situ co 2 sequestration in ultramafic rock

solving the production diffusion equation for finite diffusion domains of various shapes part i implications for low temperature u th he thermochronology abstract we propose an accurate fast and easy to use method to derive numerical solutions for production diffusion equations for finite diffusion domains of various shapes and arbitrary cooling histories previous studies provide solutions for spheres infinite cylinders and infinite sheets we extend this range and provide solutions for finite bodies i e finite cylinders and rectangular blocks of any aspect ratio this approach is important as recently it has become clear that for example the physical grain is the diffusion domain for he diffusion in apatite and titanite j geophys res 105 2000 2903 geochim cosmochim acta 63 1999 3845 we discuss the use of the new approach for forward modelling u th he production diffusion in apatite taking results with finite cylinders as a good approximation for apatite crystals it is found that approximating instead with spheres or infinite cylinders having the same radius yields differences in calculated ages that can easily be as large as 20 35 the relative differences are most pronounced in thermal histories that spend significant time at or near the closure temperature on the other hand reasonable agreement is found with spheres having the same surface to volume ratio