the cosmogenic 21ne production rate in quartz evaluated on a large set of existing 21ne 10be data abstract based on a compilation of published combined 10 be and 21 ne cosmogenic nuclide data sets from quartz samples obtained at eth zurich we assess the 21 ne 10 be p21 p10 production rate ratio with the goal to determine the 21 ne production rate p21 in quartz a variety of sliding erosion islands in a 21 ne 10 be versus 10 be diagram were evaluated to find the one that fits the data best which in turn yields the most probable p21 if the 10 be production rate is known the approach minimizes the influence of samples with a complex exposure history a best fit value for p21 p10 sp sp the 10 be fraction being produced by spallation as opposed to production by muons of 4 23 0 17 is obtained for a 10 be half life of 1 39 ma adopting a p10 sp value in quartz of 4 41 0 52 at g 1 yr 1 this yields a p21 of 18 7 2 3 at g 1 yr 1 it is possible that 2 of the 21 ne is produced by fast muons

evidence for muon induced production of 10be in near surface rocks from the congo distributions of 10be in vein quartz from a lateritic weathering profile from the congo provide evidence for significant in situ production of 10be by reactions other than neutron induced spallation after consideration of geomorphological and nuclear processes which might contribute to the observed depth variability we conclude that cosmic ray muon induced reactions are the most likely mechanism and that such reactions lead to 1 to 3 of 10be production at the surface this small muon induced component has only minor implications for the use of 10be for quantification of exposure histories of surficial rocks nevertheless the muogenic component has the potential to expand the utility of cosmogenic nuclides in examination of surficial processes overcoming some of the limitations associated with the use of the neutron produced component

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

terrestrial cosmogenic nuclides as paleoaltimetric proxies the production rates of terrestrial in situ cosmogenic nuclides depend on the altitude and can therefore be used to constrain paleoaltitudes if the history of cosmogenic nuclide production in a region can be constrained this chapter discusses the theory behind cosmogenic nuclide paleoaltimetry sampling strategies and practical limitations of the technique three exposure scenarios may allow for the calculation of past altitudes 1 exposure for a finite time period at a single elevation and without erosion or burial followed by immediate shielding from further production of cosmogenic nuclides 2 steady uplift of a surface throughout nuclide production without erosion or burial and 3 exposure of a sample without erosion or burial for a sufficient duration that the concentration of a cosmogenic radionuclide has reached equilibrium to constrain paleoelevation all exposure scenarios require independent evidence of the depth history of a sample during exposure to cosmic rays because production rates attenuate rapidly in rock depth profiles and measuring multiple nuclides allow for better constraints of parameters in paleoaltitude calculations

effects of bedrock landslides on cosmogenically determined erosion rates abstract the successful quantification of long term erosion rates underpins our understanding of landscape formation the topographic evolution of mountain ranges and the mass balance within active orogens the measurement of in situ produced cosmogenic radionuclides crns in fluvial and alluvial sediments is perhaps the method with the greatest ability to provide such long term erosion rates although deep seated bedrock landsliding is an important erosional process in active orogens its effect on crn derived erosion rates is largely unquantified we present a numerical simulation of cosmogenic nuclide production and distribution in landslide dominated catchments to address the effect of bedrock landsliding on erosion rates results of the simulation indicate that the temporal stability of erosion rates determined from crn concentrations in sediment decreases with increased ratios of landsliding to bedrock weathering rates within a given catchment area and that as the frequency of landsliding increases larger catchment areas must be sampled in order to accurately evaluate long term erosion rates in addition results of this simulation suggest that sediment sampling for crns is the appropriate method for determining long term erosion rates in regions dominated by mass wasting processes whereas bedrock surface sampling for crns may generally underestimate long term erosion rates response times of crn concentrations to changes in erosion rate indicate that climatically driven cycles of erosion may be detected but that complete equilibration of crn concentrations to new erosional conditions may take tens of thousands of years comparison of simulated crn derived erosion rates with a new data set of such rates from the nepalese himalaya underscore the conclusions drawn from the model results

large scale erosion rates from in situ produced cosmogenic nuclides in european river sediments abstract we have calculated long term erosion rates of 20 100 mm kyr from quartz contained 10be in the bedload of middle european rivers for catchments ranging from 102 to 105 km2 these rates average over 10 40 kyr and agree broadly with rock uplift incision and exhumation rates historic soil erosion rates and erosion rates calculated from the measured sediment loads of the same rivers moreover our new erosion rate estimates correlate well with lithology and relief however in the regen neckar loire and meuse catchments cosmogenic nuclide derived erosion rates are consistently 1 5 4 times greater than the equivalent rates derived from measured river loads this may be due to the systematic under representation of high magnitude low frequency transport events in the gauging records which cover less than a century alternatively the discrepancy may derive from spatially non uniform erosion and preferential tapping of deeper sections of the irradiation profile a third explanation relates the high cosmogenic nuclide derived erosion rates to inheritance of an elevated pleistocene erosion signal uncertainties associated with the cosmogenic nuclide derived erosion rate estimates are not greater than the potential errors in conventional estimates therefore the cosmogenic nuclide approach is an effective tool for rapid catchment wide assessment of time integrated rates of bedrock weathering and erosion and we anticipate its fruitful application to the quaternary sedimentary record

the erosion response to quaternary climate change quantified using uranium isotopes and in situ produced cosmogenic nuclides abstract studying how catchment erosion has responded to past climate change can help us better understand not only how landscape evolution operates but also predict the consequences of future climate change on soil resource availability recent years have seen the development of tools that allow a quantitative assessment of past changes in catchment erosion this work reviews the principles of the application of in situ produced cosmogenic nuclides and uranium isotopes to quantifying past erosion rates results highlight the role of periglacial processes and mass wasting in dictating how catchment erosion responds to climatic variability at the 10 kyr scale at the million year scale it is more difficult to untangle the role of climate and tectonics a strong coupling exists at the 10 kyr to 100 kyr scales between climatic cycles and the transfer time of regolith from source to sink this coupling reflects changes in sediment source that are either set by changes in vegetation cover at the catchment scale or by the storage of sediments on continental shelves at a larger scale although further analytical developments are required for these tools to reach their full potential existing works suggest that in the near future they will provide unprecedented quantitative insights on how soil and fluvial systems adapt to external perturbations climatic tectonic and or anthropic

tectonic significance of the lambert graben east antarctica reconstructing the gondwanan rift antarctica s lambert graben australia s north west shelf and the eastern indian peninsula all host thick fault bounded permian triassic successions these terranes were adjacent to each other in gondwana the lambert graben intersects the modern coastline strikes oblique to shelf architecture and has a geophysical signature that can be traced 1000 km inland vitrinite reflectance data from the graben margins record permian triassic infill australia s north west shelf is the relict of an intracontinental carboniferous permian rift that was infilled during the permian triassic then driven to oceanic completion during jurassic cretaceous gondwana breakup this rift was compartmentalized over length scales of 650 km corresponding to accommodation zones margin normal geophysical lineaments and long lived crustal weaknesses in eastern india similar compartmentalization is marked by extensive coal bearing graben systems gondwana reconstructions indicate that the lambert graben corresponds to the orientation and length scale of carboniferous permian rift compartmentalization the lambert graben represents an accommodation zone of a wide intracontinental rift that extended from australia s north west shelf between india and antarctica to southern africa this rift collected gondwana s thick permian triassic sedimentary blanket and rich alluvial coal deposits

late quaternary landscape evolution in the keep river region northwestern australia abstract this paper evaluates the late quaternary chronostratigraphic context of archaeological sites in the keep river region northern territory australia cosmogenic dating luminescence dating and sediment characterisation reveal sedimentary processes commencing from erosion of the escarpment and plateaux source through temporary storage in sand sheets to final deposition in alluvial floodplains erosion of the sandstone plateaux 5 mm ka 1 and escarpment faces probably 50 100 mm ka 1 provide the main sediment source for the adjacent sand sheets which have evolved over the past 100 000 years as the product of ongoing cycles of accumulation and denudation the rate of sediment accumulation is lowest near the escarpments on the low energy sediment limited sand sheets 1 and greatest near the main streams 400 mm ka 1 that have more numerous sediment sources collectively luminescence ages indicate an apparent increase in sediment accumulation rate in the sand sheets from 100 mm ka 1 in the late pleistocene to over 200 mm ka 1 in the holocene this most likely reflects enhanced monsoonal activity following postglacial marine transgression palaeosol horizons in the creek profile distinguished by sediment mottling mark potentially significant palaeoenvironmental and palaeoclimatic changes during the quaternary

holocene uplift and rapid fluvial erosion of iceland a record of post glacial landscape evolution abstract in actively deforming regions fluvial systems are strongly regulated by uplift river geometries record histories of vertical motions that can be used to examine the driving forces generating topographic relief iceland s rapidly evolving landscapes provide an opportunity to disentangle histories of uplift generated by postglacial rebound volcanism dynamic support and plate spreading broad knickzones observed along iceland s large rivers and its powerful waterfalls and deep canyons hint that regional processes have generated significant relief we combine high resolution drone photogrammetry and cosmogenic 3he dating of fluvial terraces to measure the erosional history of one of iceland s largest knickzones jokulsarglufur in the northeast part of the island progressive younging of terraces indicates knickpoint propagation rates of up to 70 cm a 1 during the last 8 ka knickpoint velocities appear to be controlled partly by toppling of basalt columns these rates were used to calibrate a model that inverts iceland s drainage networks for uplift rate histories calculated uplift and isostatic calculations indicate that rifting sub plate support and isostatic adjustment resulted in tens to hundreds of meters of regional holocene uplift our results suggest regional uplift and fluvial erosion can rapidly generate hundreds of meters of relief in post glacial landscapes

erosion of the rwenzori mountains east african rift from in situ produced cosmogenic10be 1 high relief and steep topography are thought to result in high erosion rates in the rwenzori mountains of the albert rift east africa where more than 3 km of relief have formed during uplift of the rwenzori fault block overall low denudation rates prevail we measured in situ derived cosmogenic denudation rates of 28 2 to 131 mm kyr in mountainous catchments and rates of 7 8 to 17 7 mm kyr on the adjacent low relief east african plateau these rates are roughly an order of magnitude lower than in other settings of similar relief we present an extensive geomorphological analysis and find that denudation rates are positively correlated with relief hillslope gradient and channel steepness indicating that river incision controls erosional processes in most upper headwater reaches above quaternary ela levels 4500 m a s l glacial imprinting inherited from several older and recent minor glaciation stages prevails in regions below 4500 m a s l however mild climatic conditions impede frost shattering favor dense vegetation and minimize bare rock areas and associated mass wasting we conclude that erosion of the rwenzori mountains is significantly slower than corresponding rates in other mountains of high relief due to a combination of factors extremely dense mountain cloud forest vegetation high rock strength of gneiss and amphibolite lithologies and low internal fracturing due to the extensional tectonic setting this specific combination unique to this extensional tropical setting leads to unexpected low erosion rates that cannot outpace post pliocene ongoing rock uplift of the rwenzori fault block

tectonic strain and paleomagnetism experimental investigation a porous clay rich sandstone with a natural remanent magnetisation shows complex changes in the orientation of the remanence vector when the sandstone is subjected to experimental deformation at 100 mpa room temperature and constant natural strain rates of 1 10 5 s 1 the paleomagnetic vector does not simply rotate away from the axis of compression when the rock is shortened perpendicular to bedding the remanence vector rotates toward the bedding as expected but the remanence also rotates toward bedding when the rock is shortened parallel to bedding moreover in some cases the remanence vector changes azimuth within the specimen during experimental deformation thus bedding anisotropy and the accompanying mineral fabric anisotropy are more influential than strain in controlling deflections of the paleomagnetic vector in this study this anisotropy also influences the post deformational behaviour of remanence 4 months after deformation some cores shortened perpendicular to bedding relaxed their remanence vectors back towards the pre deformational attitude whereas some other cores continued to show progressive changes intragranular recoverable elastic strains in the magnetic grains may be partly responsible for the experimentally induced deflections of remanence

deformation of remanent magnetism in a synthetic aggregate with hematite a hematite calcite aggregate bonded with portland cement is deformed triaxially at 200 mpa confining pressure and at a constant strain rate of 10 5 s 1 in some cases with a pore fluid pressure of 120 mpa this aggregate deforms in a ductile fashion at room temperature and is a good textural analog of naturally penetratively strained hematite bearing rocks the changes in inclination of an isothermal remanent magnetisation are indistinguishable from the behaviour expected of a homogeneously strained non material line rotating according to wettstein s equation this is encouraging for paleomagnetists who might wish to restore remanence in tectonically strained hematite bearing rocks an unknown combination of rigid grain rotation and intracrystalline stress must be responsible for rotation of the grains that carry remanence and thus for the changes in inclination of remanence the reason that wettstein s equation is approximately valid may be because the large aspect ratios of rigid hematite grains cause them to rotate nearly as quickly as a passive line p hydrostatic compaction wet deformation and dry deformation in that order are progressively more effective in reducing the intensity of remanence however wet deformation is more effective than dry deformation in reducing the intensity of the most coercive components presumably by spinning the finest grains in the cement matrix and scattering their individual moments p where multiple direction components of remanence are present deformation reduces the components with higher coercivities 70 mt more than those with lower coercivities in previous experiments on magnetite bearing samples the lower coercivity components were most reduced thus the natural tectonic deformation of an nrm may be expected to preserve selectively low coercivity components in hematite and high coercivity components in magnetite this may be used to predict the success of preservation of a characteristic nrm and conversely the success of overprinting by syntectonic remagnetisation

single grain cosmogenic 21ne concentrations in fluvial sediments reveal spatially variable erosion rates we evaluated the hypothesis that the spatial variation in erosion in a catchment is reflected in the distribution of the cosmogenic nuclide concentrations in sediments leaving the catchment using published data and four new 10be measurements in fluvial sediment collected from the outlets of small river catchments we constrained the spatial variability of erosion rates in the gaub river catchment in namibia we combined these catchment averaged erosion rates and the mean slope values with which they are associated in a digital elevation model dem based analysis to predict distributions of cosmogenic 21ne concentrations in the sediment leaving the gaub catchment we compared these synthetic distributions with the distribution of concentrations of cosmogenic 21ne 21nec in 32 quartz fluvial pebbles 16 21 mm collected from the catchment outlet the 21nec concentrations span nearly two orders of magnitude 2 6 160 106 atoms g and are highly skewed toward low values the dem based analysis confirms this skew the measured 21nec distribution plots within the envelope of distributions predicted for the catchment this match between measured and synthetic 21ne distributions implies that the measured distribution is a signature of the spatial variation in erosion rates

using pyroxene microphenocrysts to determine cosmogenic 3 he concentrations in old volcanic rocks an example of landscape development in central gran canaria abstract determinations of cosmogenic 3he exposure ages and erosion rates in volcanic rocks older than a few hundred thousand years are complicated by the presence of radiogenic he in addition to the magmatic and cosmogenic he in phenocryst minerals however by analysing microphenocrysts that crystallised on or immediately prior to eruption that have not trapped magmatic he the three component problem can be eliminated and accurate determinations of cosmogenic 3he made in this study we perform three experiments using pyroxene microphenocrysts in basaltic clasts in the pliocene ayacata formation breccias gran canaria that demonstrate they are free of magmatic he exposure ages and erosion rates calculated from the cosmogenic 3he concentrations are combined with a geomorphological study to produce a tentative interpretation of landscape evolution in the mountainous interior of gran canaria long term steady state erosion rates of 14 24 mm ka 1 are recorded from bedrock erosional surfaces on a high plateau headwall retreat rates for a major drainage system of 1 6 m ka 1 have been constrained from the ca 225 ka exposure age of a boulder emplaced on slopes beneath the headwall strath terraces and boulders in a small canyon system yield much younger exposure ages of 47 43 ka

methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile methods and applications of magnetic anisotropy a special issue in recognition of the career of graham j borradaile

remanence stability and magnetic fabric development in synthetic shear zones deformed at 500 c shear experiments were performed on magnetite bearing calcite aggregates to examine magnetic fabric development and remanence stability in a deforming system using elevated temperature and pressure to encourage deformation by crystal plastic processes samples composed of 1 wt pseudo single domain magnetite 1 2 m in a calcite matrix were created with either strong or weak initial fabrics and deformed in coaxial simple shear to strains up to 1 5 at constant strain rates between 6 10 5 and 1 10 4 s 1 at 500 c and confining pressure of 300 mpa samples were given weak field thermal remanent magnetizations prior to deformation demagnetization of postdeformation remanence reveals that a primary remanent magnetization can withstand deformation at pressures and temperatures approximately equivalent to greenschist facies metamorphic conditions on laboratory time scales but this stability is found to depend on the character of the predeformation fabric the origin of secondary remanence components acquired during deformation is uncertain but is likely to partially result from thermal viscous remagnetization complete postdeformation remagnetization in initially anisotropic samples appears to involve a stress softening or piezoremanent magnetization mechanism postdeformation anisotropy measurements show progressive changes in magnetic fabric strength with strain in the absence of a strong initial magnetic anisotropy magnetic fabric intensity increases linearly as a function of strain however deformation that overprinted an existing fabric results in an apparent decrease of the initial anisotropy at low strains followed by rapid increases in magnetic fabric strength with increasing strain our results underscore the important role that initial fabric can play in determining the character of deformation fabrics

experimental deformation of synthetic magnetite bearing calcite sandstones effects on remanence bulk magnetic properties and magnetic anisotropy we have quantified effects of experimental deformation on the magnetic properties of a set of synthetic calcite sandstone samples containing magnetite the deformation was carried out in a microcomputer controlled apparatus that adjusted the applied differential stress as needed to maintain a constant strain rate of 10 5 s 1 most samples were deformed under dry conditions but a few were deformed with a pore fluid present the samples deformed under dry conditions required substantially higher differential stresses macroscopically ductile shortening strains of up to 25 produced the following irreversible changes in magnetic properties 1 increased bulk coercivity remanence coercivity and mean anhysteretic remanence susceptibility 2 decreased mean low field susceptibility 3 decreases in the component of remanence parallel to shortening 4 smaller decreases for most samples in the component normal to shortening resulting in a net rotation of the remanence away from the shortening axis 5 larger decreases in the normal component in a few samples resulting in a net rotation of the remanence towards the shortening axis 6 increased magnetic anisotropy and 7 increased deformation of initial magnetic ellipsoids a comparison of data for samples deformed under dry and wet conditions higher and lower differential stresses respectively indicates that remanence reorientation and susceptibility anisotropy are controlled primarily by bulk strain i e rotation and displacement of particles whereas coercivity and anhysteretic anisotropy are controlled dominantly by microstrain or intragranular stress

simple shear experiments on magnetized wax hematite samples c a e s s laboratoire de geophysique interne uniuersite de rennes 1 f 35042 rennes francereceived july 1 1991 revision accepted may 28 1992abstractwe present the results of a series of simple shear experiments on hematite bearing paraffin wax samples homogeneousand continuous deformation was obtained up to a shear strain value of y 1 4 by deforming the samples in atemperature controlled bath and at a constant strain rate of 9x10 5 s r during deformation hematite plateletsprogressively rotate which has been checked by measuring the anisotropy of magnetic susceptibility ams principalsusceptibility directions tend to parallel the corresponding principal strain directions and ams intensity increases withincreasing strain this supports the idea that the hematite population develops a preferred orientation by progressive rigidrotation within the paraffin matrix before each deformation step an isothermal remanent magnetization irm was given to the samples within ara finite strain plane the containing the shear direction and normal to the shear plane with various initial angles to theshear direction ranging from 0 to 180 after each deformation step the irm was measured it showed no deflectiontowards the a finite strain direction in contrast it did show a systematic rotation within the ara plane always in the samesense as the rotation of strain axes e g counterclockwise in sinistral shear furthermore irm deviation is of the sameorder of magnitude for each initial direction from 0 to 180 this contradicts the passive behaviour model that haspreviously been shown to hold for irm in coaxially deformed samples finally we show that in the shear strain range of ourexperiments y 0 to 1 4 the deviation of irm depends only on the shear value and not on its initial direction and thatthis deviation is equal to the rigid rotation angle of the shear strain tensor

differences in paleomagnetic interpretations due to the choice of statistical demagnetization and correction techniques kapuskasing structural zone northern ontario canada abstract the kapuskasing structural zone ksz reveals a section through the archean lower crustal granoblastic gneisses our new paleomagnetic data largely agree with previous work but we show that interpretations vary according to the choices of statistical demagnetization and field correction techniques first where the orientation distribution of characteristic remanence directions on the sphere is not symmetrically circular the commonly used statistical model is invalid fisher r a proc r soc a217 1953 295 any tendency to form an elliptical distribution indicates that the sample is drawn from a bingham type population bingham c 1964 distributions on the sphere and on the projective plane phd thesis yale university fisher and bingham statistics produce different confidence estimates from the same data and the traditionally defined mean vector may differ from the maximum eigenvector of an orthorhombic bingham distribution it seems prudent to apply both models wherever a non fisher population is suspected and that may be appropriate in any tectonized rocks non fisher populations require larger sample sizes so that focussing on individual sites may not be the most effective policy in tectonized rocks more dispersed sampling across tectonic structures may be more productive second from the same specimens mean vectors isolated by thermal and alternating field af demagnetization differ which treatment gives more meaningful results is difficult to decipher especially in metamorphic rocks where the history of the magnetic minerals is not easily related to the ages of tectonic and petrological events in this study thermal demagnetization gave lower inclinations for paleomagnetic vectors and thus more distant paleopoles third of more parochial significance tilt corrections may be unnecessary in the ksz because magnetic fabrics and thrust ramp are constant in orientation to the depth at which they level off at approximately 15 km depth with archean geothermal gradients primary remanences were blocked after the foliation was tilted to rise on the thrust ramp therefore the rocks were probably magnetized in their present orientation tilting largely or entirely predates magnetization

an improved experimental determination of cosmogenic 10be 21ne and 26al 21ne production ratios in quartz abstract the confidence in surface exposure dating and related research such as erosion rate studies or burial dating strongly depends on the accuracy and precision of the currently used production rates of in situ produced cosmogenic nuclides reducing the uncertainties of nuclide production rates by more accurate calibrations with independently dated natural rock surfaces is crucial for further improving the quantification of earth surface processes here we use surface samples from the 760 2 ka old bishop tuff in eastern california to quantify the 10 be 21 ne and 26 al 21 ne production rate ratios in quartz our determination is based on 1 measured nuclide concentrations of cosmogenic 10 be 21 ne and 26 al 2 a conservative estimate for the erosion of the tuff in the volcanic tableland area which we base on our previously published 21 ne concentrations goethals m m niedermann s hetzel r fenton c r 2009 determining the impact of faulting on the rate of erosion in a low relief landscape a case study using in situ produced 21 ne on active normal faults in the bishop tuff california geomorphology 103 401 413 and a conservative estimate for the uncertainty of the 21 ne production rate and 3 the assumption of steady state erosion other assumptions such as the applied scaling procedure the muon contribution to nuclide production or the attenuation lengths of neutrons and muons in rock do not substantially affect the results based on 13 samples the following average production rate ratios and conservative uncertainty estimates are obtained for sea level high latitude open sky and rock surface 0 249 0 009 or 0 232 0 009 for 10 be 21 ne using 10 be half lives of 1 51 and 1 39 ma respectively and 1 80 0 09 for 26 al 21 ne for an 26 al half life of 0 72 ma the 10 be 21 ne and the 26 al 21 ne production ratios are consistent with currently used production rates but the ratios are much more precise than previous determinations the resulting 26 al 10 be production ratio of 7 23 0 45 for a 10 be half life of 1 51 ma or 7 76 0 49 for a 10 be half life of 1 39 ma is high when compared to previously published values we discuss reasons for this difference amongst them the possibility that 26 al analyses in general might be compromised by artefacts affecting the stable al concentration measurements when combined with a 10 be production rate of 5 01 at g 1 a 1 for the 1 51 ma half life or 4 61 at g 1 a 1 for the 1 39 ma half life our production ratios convert to 21 ne and 26 al production rates of 20 1 and 36 2 at g 1 a 1 or 19 9 and 35 7 at g 1 a 1 respectively

cosmogenic chlorine 36 production rates in terrestrial rocks abstract chlorine 36 is produced in rocks exposed to cosmic rays at the earth surface through thermal neutron activation of 35cl spallation of 39k and 40ca and slow negative moun capture by 40ca we have measured the 36cl content of 14c dated glacial boulders from the white mountains in eastern california and in a 14c dated basalt flow from utah effective time intergrated production parameters were calculated by simultaneous solution of the 36cl production equations the production rates due to spallation are 4160 310 and 3050 210 atoms 36cl yr 1 mol 139k and 40ca respectively the thermal neutron capture rate was calculated to be 3 07 0 24 105 neutrons kg of rock 1 yr 1 the reported values are normalized to sea level and high geomagnetic latitudes production of 36cl at different altitudes and latitudes can be estimated by appropriate scaling of the sea level rates chlorine 36 dating was performed on carbonate ejecta from meteor crater arizona and late pleistocene morainal boulders from the sierra nevada california calculated 36cl ages are in good agreement with previously reported ages obtained using independent methods

attenuation length for fast nucleon production of 10be derived from near surface production profiles abstract we have measured the fast nucleon production of 10 be to depths of 2 37 m 659 g cm 2 in a granodiorite core of uniform density and composition from the mt givens pluton on the western side of the sierra nevada california at 37 14 7 n 118 53 7 w and 2286 m the data are well fit with a simple exponential decrease yielding an apparent attenuation length of 10 be production of 177 4 2 g cm 2 the shallowest data point is from a depth of 1 24 cm 3 45 g cm 2 and shows no indication of a near surface flattening of the radionuclide inventory and hence the 10 be production rate

spatial distribution of cosmogenic 10be derived denudation rates between the western tian shan and northern pamir tajikistan abstract the northward motion of the pamir mountains relative to eurasia results in uplift and shortening of the pamir and tian shan orogens the vakhsh river catchment tajikistan is situated along a thrust system in the collision zone between the northern pamir and the western tian shan in this study spatial variations in catchment wide denudation rates are reported from the vakhsh river catchment with in situ produced cosmogenic 10be and 26al of 22 samples from active river channels samples distributed along 140 km of the main vakhsh river yield denudation rates between 1 28 0 16 to 1 94 0 26 mm yr in detail samples from rivers draining the northern pamir indicate denudation rates of 1 7 mm yr and a river draining the alai valley indicates denudation rates of 1 14 0 14 mm yr in contrast rivers draining the western tian shan show increasing denudation rates from 0 18 0 02 mm yr in the west to 2 70 0 36 mm yr in the east coincident with a small increase in the fluvial normalized steepness index ksn measured 26al 10be ratios range from 5 2 to 7 6 indicating a low influence of sediment storage and reworking of partially shielded material in addition locations resampled one year later confirm previously calculated denudation rates along the main trunk analysis of in situ produced cosmogenic 10be from depth profiles collected from a sequence of terraces preserved along the main trunk of the vakhsh river indicate terrace incision starting at 3 kyr as well as paleo denudation rates ranging between 1 75 0 54 to 2 01 0 39 mm yr 2 s d errors all these results suggest consistent high denudation rates in the northern pamir block and a spatial along strike gradient in western tian shan denudation rates the most likely explanation for the spatial gradient in western tian shan and vakhsh river denudation rates is a regional gradient in tectonic rock uplift

structural implications of paleomagnetic data from pelvoux belledonne area french alps abstract paleomagnetic studies were carried out in triassic lias lavas from five new sites of the external zone of the french alps pelvoux belledonne area and compared with previous data in two sites magnetization seems to have been disturbed during alpine deformation but the paleomagnetic directions obtained in the other sites allow one to define the eastern boundary of the anticlockwise rotated taillefer block and the importance of local rotation along the aspres les corps faults the major anticlockwise rotation of taillefer is probably of ante nummulitic age but other rotations in the pelvoux belledonne area could have occurred during this same period or be of more recent age

re computing palaeopoles for the effects of tectonic finite strain abstract the pre messinian limestone cover 58 8 ma to the troodos ophiolite 88 ma of southern cyprus is penetratively strained as shown by ubiquitous magnetic fabrics and in many sites stylolitic cleavage these define a gently n dipping foliation and an n plunging extension south vergent folding and thrusting is well known in very localized whereas the bulk of the strained limestone cover dips gently south disturbed by faulting the magnetic fabrics and stylolitic cleavage define the axes of finite strain in all sites studied and the calcite matrix was suitably ductile to permit the original palaeomagnetic directions to be de strained assuming continuum behaviour the optimum de straining 30 40 shortening in a flattening strain is compatible with the stylolitic cleavage development restores bedding to the near horizontal and restores the characteristic remanent magnetization vectors chrms to concentrated symmetrical fisherian distributions the strain corrected chrms yield more reasonable palaeopole locations for the lefkara and pakhna limestone and more uniform micro plate rotation rates corrected palaeopoles reveal a relatively uniform anticlockwise rotation of the troodos plate since the creation of the late cretaceous 88 ma ocean lithosphere it did not accelerate during the deposition of the limestone cover as required by palaeopoles calculated from data not corrected for finite strain but turned at 1 5 ma 1 since 58 ma

controls on denudation rates in tectonically stable mediterranean carbonate terrain using cosmogenic isotopes and solute load analysis we quantify chemical weathering solutional erosion and denudation rates over variable time scales in a tectonically stable moderate relief carbonate terrain soreq drainage judea hills israel located in a semihumid mediterranean climate long term 10 4 yr denudation rates were calculated from 36 cl concentrations in 51 bedrock and sediment samples bedrock samples range in elevation 340 850 m hillslope gradient 0 30 and mean annual precipitation map 500 630 mm and vary in soil cover thickness 0 75 cm mg ca ratio 0 0 1 0 mol clay mineral contents 0 6 wt and mechanical strength 41 58 schmidt hammer rebound units soil pco2 values at a single location during the course of 1 yr range between 0 4 and 9 0 mmol mol 1 average long term denudation rate of exposed bedrock samples is 21 7 mm k y 1 field observations and 36 cl measurements indicate that soil pockets undergo cycles in the rate of deepening and that over 10 5 yr time scale average denudation rates beneath soil pockets are similar to those of exposed bedrock sediment samples yield even higher denudation rates which are probably anthropogenically induced but could also indicate that the sediment source is soil pockets long term denudation rates are decoupled from hillslope gradient elevation and rock strength denudation rates show a positive correlation with present day map values exhibit a complex relation with rock mg content and show a weak correlation with clay content annual chemical weathering rates were calculated from modern day solute load measured in waters of perched springs and the regional carbonate aquifer our results indicate that on annual decadal and 10 4 yr time scales chemical weathering and denudation are controlled by carbonate dissolution while mechanical processes are far less signifi cant overlap between the distributions of hco3 concentrations measured in runoff springs and the regional aquifer water suggests that chemical weathering focuses at the bedrock surface and therefore is comparable with solutional denudation this result is in contrast to the features of ancient fl uvial and colluvial activity steep nonconcave hillslopes and stream profi les and knickzones in the streams preserved in the present landscape such features were formed in response to mid pleistocene uplift and could have been preserved due to a decrease in stream power following the formation of subsurface drainage and the lowering in abrasive clast supply that followed the stabilization of hillslopes in the drainage long term denudation rates calculated from exposed bedrock samples are higher by factor of 1 4 relative to annual contemporary chemical weathering rates increased precipitation by a similar factor averaged over the last glacial and present interglacial can explain this difference

landscape disequilibrium on 1000 10 000 year scales marsyandi river nepal central himalaya in an actively deforming orogen maintenance of a topographic steady state requires that hillslope erosion river incision and rock uplift rates are balanced over timescales of 10 5 10 7 years over shorter times 10 5 years hillslope erosion and bedrock river incision rates fluctuate with changes in climate on 10 4 year timescales the marsyandi river in the central nepal himalaya has oscillated between bedrock incision and valley alluviation in response to changes in monsoon intensity and sediment flux stratigraphy and 14 c ages of fill terrace deposits reveal a major alluviation coincident with a monsoonal maximum ca 50 35 ky bp cosmogenic 10 be and 26 al exposure ages define an alluviation and reincision event ca 9 6 ky bp also at a time of strong south asian monsoons the terrace deposits that line the lesser himalayan channel are largely composed of debris flows which originate in the greater himalayan rocks up to 40 km away the terrace sequences contain many cubic kilometers of sediment but probably represent only 2 8 of the sediments which flushed through the marsyandi during the accumulation period at f10 4 year timescales maximum bedrock incision rates are f7 mm year in the greater himalaya and f1 5 mm year in the lesser himalayan mahabarat range we propose a model in which river channel erosion is temporally out of phase with hillslope erosion increased monsoonal precipitation causes an increase in hillslope derived sediment that overwhelms the transport capacity of the river the resulting aggradation protects the bedrock channel from erosion allowing the river gradient to steepen as rock uplift continues when the alluvium is later removed and the bedrock channel re exposed bedrock incision rates probably accelerate beyond the long term mean as the river gradient adjusts downward toward a more equilibrium profile efforts to document dynamic equilibrium in active orogens require quantification of rates over time intervals significantly exceeding the scale of these millennial fluctuations in rate d 2003 elsevier b v all rights reserved

experimental deformation of two component irm in magnetite bearing limestone a model for the behaviour of nrm during natural deformation abstract experimental room temperature triaxial deformation at 200 mpa 2 kbar and at a controlled strain rate of 10 5 s 1 is performed on three limestones with magnetic behaviour dominated by single domain magnetite permanent deformation is achieved mainly by twinning of calcite isothermal remanent magnetisation irm in the samples is reduced in magnitude especially when parallel to compressive stress the decrease in magnitude correlates slightly better with peak stress than with strain in accord with previous work in uniaxial tests indicating the role of stress in deformational demagnetisation remanences have their vector plots condensed after deformation particularly in the range 0 30 mt a two component irm is used as a simple model of a multi component natural remanent magnetisation nrm the resultant vector is deflected by the action of stress towards whichever components are least reduced by deformation in the case of magnetite bearing rocks this appears to be the most coercive components in the case of a natural deformation it is predicted that the effects of stress at any stage should be to remove progressively any low coercivity components added to an nrm by remagnetisation during tectonism especially those parallel to compressive stress

nature and timing of quaternary glaciation in the himalayan tibetan orogen abstract much effort has been made in recent years to define the timing and extent of quaternary glaciation throughout the himalayan tibetan orogen these studies are challenging because of the logistical and political inaccessibility of the region and the inherent problems associated with the application of numerical dating techniques nevertheless the studies are providing abundant evidence for significant glacial advances throughout the last several glacial cycles and are beginning to accurately define the extent and timing of glaciation in selected regions studies are showing that himalayan tibetan glaciers in arid regions during the last glacial cycle reached their maximum extent early in the cycle and that global last glacial maximum glacier advances were significantly less extensive however along the more monsoonal influenced greater himalaya there is increasing evidence to suggest that glaciation was more extensive later in the last glacial cycle but this has yet to be fully assessed in addition the new studies are showing that throughout most himalayan tibetan regions significant glacier advances occurred during the lateglacial and early holocene with minor advances in some regions during the mid holocene the still relatively poor chronological control in the himalayan tibetan orogen however makes it difficult to construct correlations across the region and with regions elsewhere in the world this in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation across the himalayan tibetan orogen and to quantify paleoclimate change in this high altitude subtropical region the lateglacial and holocene glacial records however are particularly well preserved in several himalayan tibetan regions glacial successions such as these have the greatest potential to be examined in detail using newly developing numerical dating and geomorphic and sedimentologic methods to derive high resolution terrestrial records of glaciation that will help in paleoclimatic reconstruction for high altitude subtropical regions

cosmogenic 10be production rate calibrated against 3he in the high tropical andes 3800 4900 m 20 22 s abstract many geomorphologic applications notably glacier chronologies require improvements in both the precision and the accuracy of the cosmogenic dating tool of particular importance is the need to better constrain the spatial variability of the cosmogenic nuclides production rates at high elevation and low latitudes one strategy that can be adopted for this is to couple absolute calibrations from independently dated surfaces with cross calibration studies performed by measuring several cosmogenic nuclides in the same rock in the present study we report the highest elevation 4800 m cross calibration published to date comprising measurements of cosmogenic 3 he and 10 be in cogenetic pyroxene and quartz the samples were collected from six dacitic moraine boulders exposed from 32 to 65 ka at 4820 m on the flanks of the uturuncu volcano 22 s 67 w southern lipez bolivia the samples yield a remarkably tight cluster of 3 he 10 be production ratios with a weighted mean of 33 3 0 9 1 this production ratio is undistinguishable within uncertainties from the 3 he 10 be production ratio of 32 3 0 9 determined in the same mineral pair at low elevation 1333 m by amidon et al 2009 these results agree at the 1 level and suggest that any hypothetical increase of the 3 he 10 be production ratio in pyroxene and quartz is likely to be lower than 5 over this elevation range 1000 5000 m moreover the production ratio is almost insensitive to the li content of the pyroxene 20 to 50 ppm li suggesting that the cosmogenic thermal neutron production of 3 he is very low in this setting the high elevation 3 he 10 be production ratio is used in combination with a local determination of the 3 he production rate in the high central altiplano 3800 m blard et al 2013 to establish a local 10 be production rate of 30 0 1 4 at g 1 yr 1 at 3800 m and 20 s after scaling to sea level high latitude with the time dependent lal stone model this yields a 10 be production rate in quartz of 3 63 0 17 at g 1 yr 1 importantly this rate can be used for high precision geomorphologic dating for example for determining glacial chronologies 1 4 through 10 be dating of moraines in the high tropical andes any inaccuracy attached to the scaling model is canceled out when the calibration site is located close to the dated object the same experiment was also undertaken in pyroxene and plagioclase from two andesitic boulders from the tunupa volcano moraines exposed at 3800 m and 4200 m a 3 he 10 be production ratio of 35 9 1 3 1 is obtained for this mineral pair indicating that the 10 be production rate in plagioclase is about 8 lower than in quartz

timing and nature of alluvial fan and strath terrace formation in the eastern precordillera of argentina abstract sixty eight 10 be terrestrial cosmogenic nuclide tcn surface exposure ages are presented to define the timing of alluvial fan and strath terrace formation in the hyper arid san juan region of the argentine precordillera this region is tectonically active and numerous fault scarps traverse quaternary landforms the three study sites marquesado strath complex loma negra alluvial fan and carpinteria strath complex reveal a history of alluvial fan and strath terrace development over the past 225 ka the marquesado complex q3 m surface dates to 17 3 ka whereas the loma negra q1 ln q2 ln q3 ln q4 ln and q5 ln surfaces date to 24 3 ka 48 2 ka 65 13 ka 105 21 ka and 181 29 ka respectively the carpinteria complex comprises eight surfaces that have been dated and include the q1 c 23 3 ka q2 c 5 5 ka q3a c 25 12 ka q3b c 29 15 ka q4 c 61 12 ka q5 c 98 18 ka q6 c 93 18 ka and q7 c 212 37 ka 10 be tcn depth profile data for the loma negra alluvial fan complex and carpinteria strath terrace complex as well as osl ages on some carpinteria deposits aid in refining surface ages for comparison with local and global climate proxies and additionally offer insights into inheritance and erosion rate values for tcns 10 10 4 10 be atoms g of sio 2 and 5 m ma 1 respectively comparison with other alluvial fan studies in the region show that less dynamic and older preserved surfaces occur in the carpinteria and loma negra areas with only younger alluvial fan surfaces preserved both to the north and south these data in combination with that of other studies illustrate broad regional agreement between alluvial fan and strath terrace ages which suggests that climate is the dominant forcing agent in the timing of terrace formation in this region

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

effect of progressive deformation on remanent magnetization of permian redbeds from the alpes maritimes france abstract the relationships among the anisotropy of magnetic susceptibility the finite strain and the characteristic remanent magnetization chrm have been investigated in deformed red sediments from the alpes maritimes in southeast france the magnetic properties of these rocks are due to hematite the finite strain is known from field studies of the shapes and orientations of green reduction spots and from optical microscopy and x ray texture goniometry studies of chlorite and illite the strain data permit a classification of the magnetic results according to four main stages of progressive deformation in the compaction stage magnetic anisotropy is flattened in the bedding due to compactional loading the chrm directions approximate to a fisherian distribution about a mean value close to the known permian direction for the region as deformation proceeds pencil structure first develops and the anisotropy is characterized by a prolate pattern with maximum axis parallel to the subhorizontal azimuth of the pencil structure and fold axes with increasing deformation the magnetic susceptibility ellipsoid becomes oblate and finally triaxial at these stages of high deformation the anisotropy patterns show that the hematite grain orientations are strongly influenced by the cleavage the remanence directions in deformed rocks do not correspond to a fisher distribution and eventually deviate strongly from permian directions these results show that paleomagnetic vectors are affected by the distortional strains which accomodate shape change in the rock simple tilt correction without compensation for the strain would yield incorrect paleopole positions an attempt has been made to compensate for the effects of deformation by regarding the remanent vector as a passive marker march 1932 equations for strain removal were applied to the remanence in two ways 1 a using strain data directly obtained in the field for each site and 2 b by converting the magnetic susceptibility anisotropy of each sample to a corresponding finite strain value correcting for the finite strain by both methods improves the within site grouping of paleomagnetic vectors in strongly deformed rocks strain removal assuming the march model results in overcorrection of the remanent magnetization data in low strain regions distortion may produce mechanical rotation of the hematite particles but recrystallization may alter the deformation mechanism in regions of high strain the limits of applicability of the passive marker treatment could not be tested adequately in the deformed red sediments of the alpes maritimes

the effect of magnetic anisotropy on paleomagnetic directions in high grade metamorphic rocks from the juiz de fora complex se brazil the juiz de fora complex is mainly composed of granulites and granodioritic migmatite gneisses and is a cratonic basement of the ribeira fold belt which was formed during the last stage of brasiliano orogeny samples widely distributed over the studied region se brazil rio de janeiro state were collected for paleomagnetic and magnetic anisotropy determinations after measurement of anisotropy of low field magnetic susceptibility ams the same specimens were submitted to both alternating field for anisotropy of remanent magnetization arm determinations and thermal demagnetization for paleomagnetic analyses demagnetization processes allowed isolating an eastern steep positive inclination characteristic remanent magnetization chrm direction from the rocks the studied specimens are strongly heterogeneous at sample scale regarding the amount of magnetic minerals even for specimens from the same core rock magnetism indicates that there is a complex mixture of magnetic minerals with both low and high coercivity which are associated with coarse grained titano magnetite and either fine grained titano magnetite or titanohematite grains respectively these magnetic minerals are responsible for both remanent direction and magnetic anisotropies even though for some specimens paramagnetic minerals are the carriers of ams fabric the chrm direction found for the rocks should represent the cooling phase of the brasiliano event in the area and it was acquired after the magnetic fabric was formed the ams and arm fabrics are coaxial and tectonic in origin and compare favorably with the mesoscopic scale fabrics in the adjacent areas however arm measurements have reached only low coercivity grains and it could be determined in few specimens then only an estimate of arm effect on chrms correction is shown the rocks are strongly magnetically anisotropic 50 and foliated the paleomagnetic directions from each specimen within a site tend to approach its ams or arm foliation kmax kint or armmax armmin plane these directions were corrected specimen by specimen from the sites taking into account the pole of ams or arm foliation kmin or armmin and the value of the degree of anisotropy p results show that even for specimens with high p the angular difference between corrected and uncorrected magnetization direction may be insignificant if the geomagnetic field at the time of acquired magnetization was approximately parallel to the magnetic foliation of the specimens our data set suggests that ams is a powerful tool to correct the chrm deviation from paleofields in rocks with complex magnetic mineralogy such as those from the juiz de fora complex

measurements of past ice sheet elevations in interior west antarctica a lateral moraine band on mount waesche a volcanic nunatak in marie byrd land provides estimates of past ice sheet surface elevations in west antarctica helium 3 and chlorine 36 surface exposure ages indicate that the proximal part of the moraine up to 45 meters above the present ice surface was deposited about 10 000 years ago substantially later than the maximum ice extent in the ross embayment the upper distal part of the moraine may record multiple earlier ice sheet high stands a nonequilibrium ice sheet model predicts a delay of several thousand years in maximum ice levels at mount waesche relative to the maximum ice extent in the ross sea the glacial geologic evidence coupled with the ice sheet model indicates that the contribution of the ross sea sector of the west antarctic ice sheet to holocene sea level rise was only about 3 meters these results eliminate west antarctic ice as the principle source of the large meltwater pulse during the early holocene

remanent magnetism and ductile deformation in an experimentally deformed magnetite bearing limestone abstract a limestone with pseudo single domain psd pure magnetite is given an isothermal remanent magnetization irm samples are deformed triaxially at 200 mpa 2 kbar confining pressure at room temperature and at a strain rate of 10 5 s 1 the limestone deforms in a ductile manner by twinning to produce sufficiently homogeneously strained specimens up to about 20 shortening the uniform saturation irm rotates away from the shortening axis approximately by an amount expected for the homogeneous strain of a non material line marker hydrostatic compaction alone shows that this is time dependent and compatible with progressive damage of the ferrimagnetic grains strain produces an increase in coercivity of the magnetite an increase in its saturation remanence and an increase in its anisotropy of magnetization with respect to irm these observations are compatible with reduction in effective grain size and change of shape of magnetite experimental deformation reduces the intensity of magnetisation chiefly by the removal of low coercivity components of remanence when there is a pure irm vector

erosion rates and mechanisms of knickzone retreat inferred from 10be measured across strong climate gradients on the northern and central andes western escarpment escarpment edge deep gorges and distinct knickzones in river profiles characterize the landscape on the western escarpment of the andes between 5 s and 18 s northern peru to northern chile th

a paleomagnetic study of tectonically deformed red beds of the lower glarus nappe complex eastern switzerland a paleomagnetic study at 15 sites 315 samples in permo triassic red beds of the helvetic nappes of eastern switzerland isolated stable characteristic and secondary remanent directions thermal demagnetization and isothermal remanent magnetization experiments suggest pigmentary hematite carries the characteristic direction secondary directions are scattered but may have been acquired during the alpine deformation in the oligocene and miocene the characteristic directions also show large between site scatter anisotropy of magnetic susceptibility indicates that the hematite grains are flattened within the slaty cleavage and that there is a north south lineation this anisotropy pattern implies that the magnetic grains were realigned by the alpine deformation it is not possible to explain the characteristic remanent magnetization deviations on a site by site basis but the site mean directions are streaked along a great circle the down dip direction of which is approximately parallel to the regional fold axes 60 20 this spread could be explained by a penetrative simple shear deformation associated with the nappe internal deformation

deglaciation and landscape history around annapurna nepal based on 10be surface exposure dating abstract the high himalaya is a key area for tectonic geomorphological and climate studies because of its extreme relief and location at the transition zone between areas with abundant monsoonal precipitation and the arid semiarid tibetan plateau we present 10be surface exposure ages on 22 boulders from the annapurna area in nepal the ages improve understanding of the late quaternary landscape history and the geomorphological processes operating in this part of the himalaya although our study is reconnaissance in nature it highlights the importance of catastrophic events such as landslides and debris flows for denudation of high mountains holocene exposure ages for the dhampu chooya landslide 4 1 0 6 ka and for 600 m of alluviation in kali gandaki valley 2 1 0 6 ka for example indicate the frequent occurrence and extent of catastrophic events and their implications for natural hazards we also offer an explanation for the differences in late quaternary glacial chronologies at closely spaced study sites in the nepal himalaya topographically controlled and spatially variable precipitation in the himalaya determines the sensitivity of glaciers to changes in temperature and precipitation accordingly some glaciers advanced in phase with northern hemisphere ice sheets whereas others reached their maximum extent at times of increased monsoonal precipitation during marine isotope stage 3 and the early holocene

experimental strain of isothermal remanent magnetization in ductile sandstone abstract a macroscopically ductile sandstone to which a homogeneous isothermal remanent magnetization irm was applied has been deformed at 150 mpa confining pressure and constant strain rate of 10 5 s 1 hydrostatic compaction does not produce a deflection of the irm vector although it is reduced in intensity pure shear producing shortening in the range 2 to 35 steadily reduces the intensity of magnetization but also homogeneously rotates the remanence vector toward the plane of flattening the amount of rotation is slightly less than that expected for a non material line undergoing homogeneous strain deformation selectively removes weakly coercive components of remanence as revealed by alternating field af demagnetization during deformation a weak deformational viscous remanent magnetization dvrm is acquired from the pressure vessel this is different from a conventional viscous remanent magnetization vrm in that it is not acquired when the specimen is subject to hydrostatic confining pressure alone even for periods three times longer than the longest deformation test

strain removal applied to paleomagnetic directions in an orogenic belt the permian red slates of the alpes maritimes france abstract detailed investigations of relationships between strain and directions of characteristic remanent magnetization chrm have been conducted on the permian red series of the alpes maritimes france the analysis of the results obtained by structural and paleomagnetic studies on 14 sites leads to the following observations in most sites the mean direction of the strain shortening axis is close to the expected permian paleomagnetic direction in this case we observe a large scatter of the chrm directions within each site which is interpreted as an increase of an initial dispersion due to strain moreover this dispersion more or less increases with strain intensity in other cases where the angle between the shortening axis and the paleomagnetic direction is high the whole population is deflected towards the cleavage xy plane these observations lead us to assume a material line like behaviour of the chrm vectors and consequently an attempt has been made to recalculate these directions by strain removal these calculations give positive results at two levels 1 a statistically significant improvement in the clustering of the within site distributions and 2 after tilt correction using unstrained bedding planes a significant improvement in the clustering of the between site distribution the formation mean direction after strain removal is in good agreement with known permian results for stable europe

paleoremanence dispersal across a transpressed archean terrain deflection by anisotropy or by late compression the quetico belt is an archean metasedimentary terrain sandwiched between greenstone subprovinces a single regional schistosity is subparallel to magnetic foliation defined by anisotropy of low field magnetic susceptibility ams and anisotropy of anhysteretic remanence aarm aligned micas are the primary cause of ams aligned pyrrhotite is the sole cause of aarm each magnetic subfabric is due to minerals that grew in overlapping intervals in the strain history their slight obliquity may be due to crystallization during noncoaxial strain magnetic fabric ellipsoids suggest varying severity of flattening very strong flattening on the northern boundary less severe on the southern boundary and least severe in the interior the interior and the southern boundary of the belt stretched horizontally and the shortening direction varies gradually from ns in the north to nnw in the south the paleomagnetic record carried by pyrrhotite shows characteristic remanences dispersed around a great circle subparallel to the regional schistosity and magnetic foliations late stress effects rotated paleoremanences into this pattern we discount deflection of the paleofield by anisotropy the pattern of dispersal indicates uniaxial oblate flattening of the region with nnw sse shortening late in the metamorphic cooling history 300 c this postdates schistosity ams and aarm fabrics but it is controlled by the same kinematic pattern

deformation and magnetic fabrics in ductile shear zones a review abstract the anisotropy of magnetic susceptibility ams is a well established petrofabric tool for indicating relative strain and microstructural character and has been validated on various rock types and different structural settings the magnetic susceptibility of a rock k depends primarily on the nature and abundance of magnetic minerals the physical arrangement and lattice preferred orientation of these magnetic minerals give rise to magnetic anisotropy the ams scalar parameters most commonly used to constrain strain include the corrected degree of anisotropy p 1 a proxy for fabric intensity and the shape factor 1 t 1 an indicator of the magnetic fabric symmetry prolate vs oblate a number of studies have shown that a positive correlation generally exists between p and strain thus the ams shows a great potential as a tool for examining deformation in geologic structures characterized by large strain gradients such as shear zones however a number of caveats exist i the increase of p with strain cannot be solely attributed to deformation because p also increases with k regardless of deformation ii strain across shear zones is typically heterogeneous and is often localized in units of different lithology thus making the separation of the lithological and strain controls on ams difficult also deformation is commonly accompanied by mineral segregation or fluid rock interaction that induces changes in magnetic mineralogy iii even if the undeformed lithology was uniform across a shear zone variations in strain rate or temperature may result in different deformation mechanisms hence the relationship between p and strain depends strongly on both the mineral carriers of ams and on deformation mechanisms and iv the ams is unable to resolve composite fabrics such as those resulting from s c structures where minerals on the c and s planes respectively contribute to ams

stochastic processes of soil production and transport erosion rates topographic variation and cosmogenic nuclides in the oregon coast range landscapes in areas of active uplift and erosion can only remain soil mantled if the local production of soil equals or exceeds the local erosion rate the soil production rate varies with soil depth hence local variation in soil depth may provide clues about spatial variation in erosion rates if uplift and the consequent erosion rates are sufficiently uniform in space and time then there will be tendency toward equilibrium landforms shaped by the erosional processes soil mantle thickness would adjust such that soil production matched the erosion previous work in the oregon coast range suggested that there may be a tendency locally toward equilibrium between hillslope erosion and sediment yield here results from a new methodology based on cosmogenic radionuclide accumulation in bedrock minerals at the base of the soil column are reported we quantify how soil production varies with soil thickness in the southern oregon coast range and explore further the issue of landscape equilibrium apparent soil production is determined to be an inverse exponential function of soil depth with a maximum inferred production rate of 268 m ma 1 occurring under zero soil depth this rate depends however on the degree of weathering of the underlying bedrock the stochastic and large scale nature of soil production by biogenic processes leads to large temporal and spatial variations in soil depth the spatial variation of soil depth neither supports nor rejects equilibrium morphology our observed catchment averaged erosion rate of 117 m ma 1 is however similar to that estimated for the region by others and to soil production rates under thin and intermediate soils typical for the steep ridges we suggest that portions of the oregon coast range may be eroding at roughly the same rate but that local competition between drainage networks and episodic erosional events leads to landforms that are out of equilibrium locally and have a spatially varying soil mantle copyright 2001 john wiley sons ltd

effects of tectonic deformation on the remanent magnetization of rocks paleomagnetic investigations have usually been impossible in deformed rocks because of the effects of distortion on the remanent magnetization vector deformation produces a magnetic anisotropy in rocks which can deflect the remanence away from the minimum susceptibility axis however the assumption that the intersection points of great circles joining these two directions represent an improved estimate of the undisturbed remanence is invalid because the amount of the deflection of each remanence is not really known anisotropy of magnetic susceptibility ams provides a quantitative basis for strain determination the principal axes of the magnetic anisotropy ellipsoid have the same directions as those of the strain ellipsoid a linear relationship between the normalized principal susceptibility differences and the logarithmic strains has been found in several rock types if the correlation method used is valid ams observations can be used to establish the magnitudes and directions of the principal strains strain modifies bedding planes and realigns the grains that carry magnetic remanence compensation for deformation requires application of a modified bedding tilt correction and correction of the remanent vector for distortional strain the effects of strain on bedding can be corrected using passive marker theory attempts to compensate for distortional strain by treating the remanent vector as a passive marker have proved inconclusive during deformation linear and planar elements deflect away from the axis of maximum shortening the passive marker correction shifts the remanent vectors toward the local shortening axis for the site and reduces the directional scatter tests of the passive marker method in strongly deformed rocks resulted in a remanence distribution dominated by the shortening axis directions the passive marker model becomes inapplicable when the deformation results in recrystallization of the rock matrix

tectonic and climatic controls on the spatial distribution of denudation rates in northern chile 18 s to 23 s determined from cosmogenic nuclides in the arid region of northern chile the environmental conditions are favorable for measuring tectonic and climatic influences on catchment denudation rates in the absence of vegetation previous studies of denudation rates from cosmogenic 10be and 26al concentrations are limited to single drainages in this study we examine catchment to orogen scale spatial variation in denudation rates between 18 23 s in the coastal and western cordilleras of northern chile 10be and 26al data were obtained from 33 catchments to examine the relative roles of tectonics and climate on catchment averaged denudation rates at broader scales we examine whether denudation rates and orogen topography reflect the 3d plate geometry of the region cosmogenic nuclide derived denudation rates range from 0 4 0 5 to 20 6 1 5 m myr in the coastal cordillera and from 1 4 0 7 to 168 0 19 8 m myr in the western cordillera the controls on the denudation rates are evaluated using a statistical factor analysis of ten selected catchment parameters denudation rates indicate a strong linear relationship with channel steepness indices but insignificant correlations and covariation with mean annual precipitation rates drainage area stream order mean elevation mean local relief mean basin slope and analyzed grain size of the sampled sediments moreover denudation rates are better correlated with tectonic controls at catchment scale than orogen scale plate tectonics in the western and coastal cordillera

the competition between coastal trace metal fluxes and oceanic mixing from the 10be 9be ratio implications for sedimentary records at an ocean margin site 37 s offshore chile we use the meteoric cosmogenic 10be 9be ratio to trace changes in terrestrial particulate composition due to exchange with seawater we analyzed the marine authigenic phase in surface sediments along a coast perpendicular transect and compared to samples from their riverine source we find evidence for growth of authigenic rims through coprecipitation not via reversible adsorption that incorporate an open ocean 10be 9be signature from a deep water source only 30 km from the coast overprinting terrestrial 10be 9be signatures together with increasing 10be 9be ratios particulate bound fe concentrations increase which we attribute to release of fe rich pore waters during boundary exchange in the sediment the implications for the use of 10be 9be in sedimentary records for paleodenudation flux reconstructions are the following in coast proximal sites the authigenic record will likely preserve local riverine ratios unaffected by exchange with seawater whereas sites beneath well mixed seawater will preserve global flux signatures

catchment wide denudation rates at the margin of ne tibet from in situ produced cosmogenic 10be terra nova 23 42 48 2011 abstract we present denudation rates for catchments in the qilian shan and two mountain ranges in its foreland which differ markedly in elevation and catchment morphology catchments with mean slope angles below 25 yield 10be derived denudation rates 200 mm ka 1 and have narrow and symmetric slope frequency distributions which become broader as the mean slope angle increases denudation rates for catchments with mean hillslope angles steeper than 25 range from 100 to 800 mm ka 1 field observations suggest that these higher and more variable rates are the result of erosion by bedrock landslides which contribute to mass transport on the hillslopes six catchments aligned along the mountain front of the central qilian shan have reached threshold values of slope and relief these basins also show remarkably similar slope frequency distributions with negative skewness and a pronounced peak at a slope angle of 30 35 we hypothesize that these catchments have attained an erosional steady state

quantifying sediment transport on desert piedmonts using 10be and 26al in situ produced 10 be and 26 al measured in 40 sediment samples collected from the iron and granite mountain piedmonts eastern mojave desert provide a unique view of piedmont modification processes and process rates over the 10 3 to 10 5 year time scale cosmogenic nuclide based models suggest that the iron and granite mountains generate 0 11 0 13 and 0 082 0 097 m 3 of sediment per year per meter of rangefront respectively the sediment moves down the piedmont in an active transport layer atl which is 20 to 30 cm thick based on visual observations measurements of depth to a buried b horizon cosmogenic nuclide data and maximum ephemeral channel depths sediment in this layer is well mixed vertically and horizontally on the 10 2 year time scale indicating that the small ephemeral channels which dominate the piedmont surface migrate quickly interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the piedmont at rates between 17 21 and 38 45 m ma 1 until the late pleistocene epoch when a discontinuity to markedly lower nuclide activities in the isotopically well mixed active transport layer suggests that deposition stopped a significant change in piedmont behavior nuclide activities in 10 amalgamated surface samples each collected along a different 4 km long transect increase steadily away from the mountain front thus we infer that sediment is uniformly dosed by cosmic rays as it is transported down the iron and granite mountain piedmonts interpretive models suggest that long term average sediment speeds down the iron and granite mountain piedmonts are a few decimeters to a meter per year d 2002 published by elsevier science b v

late proterozoic reconstructions of north west scotland and central canada magnetic fabrics paleomagnetism and tectonics red beds dominate the stoer group and the unconformably overlying torridon group having accumulated between 1400 and 1000 ma in a rift of the hebridean foreland the sequences were weakly strained and shortened e w and each underwent successive diagenetic changes which altered their magnetic properties and caused their different characteristic post depositional magnetizations anisotropy of magnetic susceptibility ams reveals an n s vertical tectonic foliation superimposed on the bedding planar ams sub fabric the tectonic ams sub fabric was isolated by comparing normalized and non normalized mean tensors of multiple specimens the n s vertical ams tectonic foliation postdates warps of bedding thus the high susceptibility minerals including those carrying palaeomagnetic signals re oriented or recrystallized after deposition and diagenesis thus characteristic remanence vectors chrm were acquired long after deposition first in the stoer group then in the torridon chrms were isolated for 143 stoer specimens and 94 torridon specimens using two cycles of low temperature demagnetization followed by at least 12 steps of thermal demagnetization for the stoer group two structurally integral groups of sites yield mean magnetizations of 317 0 43 1 95 11 3 n 49 and 309 9 52 1 95 10 6 n 23 some stoer specimens bear a torridon age overprint 133 3 525 95 9 6 n 19 the younger torridon group yields 138 4 52 2 95 7 4 n 42 134 9 45 5 95 16 0 n 15 and 134 4 55 1 95 11 3 n 19 from three structurally integral clusters of sites these late chemical magnetizations postdate bedding warps faults and tectonic ams fabrics they do not warrant local rigid body tilt corrections however we restored the chrm directions for the regional post cambrian eastwards tilt which affected the entire foreland from the lewisian basement to the overlying proterozoic strata paleopoles calculated from the strata s restored vectors were rotated into laurentian coordinates for comparison with canadian proterozoic palaeopoles the stoer group was magnetized in a normal polarity geomagnetic field whereas the torridon group was magnetized in a reversed polarity epoch however both sequences include at least one polarity transition indicating long duration chemical magnetizations successfully averaging secular variation at a minimum red bed magnetization processes exceeded 0 1 ma and may have encompassed several million years during stoer group magnetization the hebridean craton was at paleolatitudes of 26 44 n when the torridon group magnetized it was at 23 27 s accepting published ages this defines a minimum southward latitudinal displacement rate of 27 40 km ma restored stoer group paleopoles lie in the present day north central pacific ocean 190e 25n corresponding to the laurentian apwp dated at between 1090 and 1109 ma torridon group paleopoles lie in the south central pacific 210e 25s near the poorly documented 900 ma southernmost part of the laurentian apwp

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

quaternary history and landscape evolution of a high altitude intermountain basin at the western end of the himalayan tibetan orogen waqia valley chinese pamir abstract quaternary valley fills and landforms in the waqia valley of the chinese pamir were examined using geomorphic mapping geomorphic and sedimentological analysis of landforms and sediments and cosmogenic 10be surface exposure dating six sets of moraines m 1 to m 6 are identified and date to the penultimate or an older glacial cycle m 1 penultimate glacial cycle m 2 early last glacial and probably marine oxygen isotope stage mis 4 m 3 mis 2 m 4 late glacial m 5 and early holocene m 6 younger moraines are also present but these were not examined in detail alluvial fans and outwash river terraces are present throughout the valley four surfaces on alluvial fans and river terraces were dated to 580 ka t 1 120 ka t 2 100 ka t 3 and 70 ka t 4 large landslide and lacustrine deposits are common within the valley fills and represent periods of major slope instability and possible damming of drainages glacial processes dominate the western side of the valley landsliding is the leading process on its eastern side defining the nature and timing of landform formation in this valley highlights the punctuated nature of landform evolution in the himalaya and tibet and provides a framework for considering the abundant valley fill successions elsewhere in the orogen

atmospheric scaling of cosmogenic nuclide production climate effect 1 absorption of cosmic rays by atmospheric mass varies temporally due to a redistribution of atmospheric pressure by ice sheets during glaciations the compression and expansion of the atmosphere due to cooling and warming and changes in katabatic winds near large ice masses these atmospheric processes can result in changes in production rates of cosmogenic nuclides which when integrated over long exposure durations may result in 0 to 5 adjustments in site production rates depending on location combining a ccm3 model with imbedded ice sheets for 20 ka we show that production rates changes relative to today are greatest at high elevations 6 7 at 5 km altitude due to atmospheric compression from decreased temperature production rates at specific times for sites near ice sheet margins can be reduced more than 10 due to a combination of katabatic winds draining off the ice sheet margins and atmospheric cooling nunatak settings may be significantly affected by the climate effect due to persistent glacial atmospheric conditions atmospheric variability may explain some of the disparities among cosmogenic nuclide production rate calibrations

scaling factors for production rates of in situ produced cosmogenic nuclides a critical reevaluation abstract new scaling factors are presented describing the altitude and latitudinal dependence of production rates for in situ produced cosmogenic nuclides the new factors incorporate the influence of the non dipole contributions to the geomagnetic field on the cosmic ray flux the currently used scaling factors of lal earth planet sci lett 104 1991 424 439 are based on the assumption of a dipole field the overall strategy used in deriving the new scaling factors is however very similar to that of lal and relies on the same and or similar nuclear data in this reevaluation data are only used if the effective geomagnetic parameters inclination horizontal field strength can be reconstructed for the time of measurement the absorption free pathlengths for cosmic rays selected for this study are based on observational data at altitudes relevant for exposure age dating sea level to 7000 m at sea level and latitudes between 20 and 40 the new factors are up to 18 lower and at high altitudes more than 30 higher than those of lal in addition to accounting for the influence of the effective geomagnetic field and providing more applicable estimates of the new factors also allow for correction for the significant deviations from the standard pressure altitude relationship that exist in the atmosphere 10

quantitative resolution of the debate over antiquity of the central australian landscape implications for the tectonic and geomorphic stability of cratonic interiors we report the first measure of long 100 myr and short 1 myr term denudation rates from key geologically stable landforms in the davenport range central australia these landforms have previously been assigned a cambrian age which arguably places them amongst the oldest persistent landforms on the continent if not on earth our results from combined apatite fission track thermochronology and in situ cosmogenic radionuclide analyses using 10 be and 26 al show that while average exhumation rates are low the denudation history for this cratonic region is incompatible with extreme sub aerial longevity and long term tectonic and geomorphic stability our revised model for the landscape evolution of this region is consistent with one of maximum burial prior to and during the mesozoic followed by a phase of kilometre scale exhumation that was largely complete by the beginning of the cainozoic we suggest that a similar process of burial and exhumation has probably been responsible for the sub aerial preservation of seemingly ancient landforms elsewhere in australia

elevation dependence of cosmogenic 36cl production in hawaiian lava flows abstract we measured an elevation profile of cosmogenic 36cl in two well preserved lava flows on mauna kea hawaii 19 8 n 155 5 w in order to directly constrain the elevation dependence of cosmogenic nuclide production rates the flows are vertically extensive hawaiites erupted at 40 1 0 6 and 62 2 1 0 ka from point vents on the upper flanks of mauna kea the average paleo cutoff rigidity a measure of geomagnetic shielding of cosmic rays for these flows is 11 gv and their paleo elevation range is 2100 3700 m production of 36cl is dominated by neutron reactions with the high energy 39k n x and 40ca n x mechanisms accounting for nearly half of the 36cl production and the low energy reaction 35cl n responsible for the remaining half production by negative muons is small at the elevations of our samples accounting for less than 2 of the total production in the lowest elevation samples the elevation dependence of 36cl production measured in these lava flows is described by an effective attenuation length of 138 5 g cm 2 this result is close to the value of 140 g cm 2 determined from neutron monitor surveys of high energy nucleon fluxes but significantly below the value of 149 g cm 2 determined from measurements of low energy neutrons the predicted atmospheric attenuation length for these lava flows incorporating both high and low energy mechanisms is 144 g cm 2 the good agreement between the 36cl elevation profile and cosmic ray surveys validates the use of neutron flux measurements to scale 36cl production rates when production by muons is negligible

moraine preservation and boulder erosion in the tropical andes interpreting old surface exposure ages in glaciated valleys cosmogenic dating provides a long awaited means of directly dating glacial deposits that pre date the last glacial cycle although the potential benefits of longer chronologies are obvious the greater uncertainty associated with older cosmogenic ages may be less readily apparent we illus trate the challenges of developing and interpreting a long chronology using our data from the peruvian andes we used surface exposure dating with cosmogenic radionuclides crns 10 be and 26 al to date 140 boulders on moraines in valleys bordering the junin plain 11 s 76 w in central peru our chronology spans multiple glacial cycles and includes exposure ages greater than 1 million years which indicate that long term rates of boulder erosion have been very low interpreting the chronology of moraines for glaciations that predate the last glacial cycle is complicated by the need to consider boulder erosion and exhumation surface uplift and inheritance of crns from pre vious exposure intervals as an example we recalculate exposure ages using our boulder erosion rates 0 3 0 5 metres per million years and estimated surface uplift rates to emphasise both the chal lenges involved in interpreting old surface exposure ages and the value of chronological data even with large uncertainties when reconstructing the palaeoclimate of a region copyright 2005 john wiley sons ltd

strain and magnetic remanence abstract experimental data may be compatible with the hypothesis that a single direction of magnetic remanence rotates as a rigid marker with strains up to 40 shortening in coaxial perfect flattening x y z detailed agreement with the passive line model is relatively poor for the specimens in which remanance is carried by magnetite however for this range of strains the differences with the passive line model wettstein s equation are so slight that the latter model may be more easily employed to de strain or restore deformed remanance to its original attitude in the case of hematite bearing remanences the differences between the passive line and rigid marker model are even smaller because of the higher aspect ratios of grains of hematite therefore it is suggested that wettstein s equation may be safely used to restore remanence after even higher strains where the remanence is carried by hematite

seismic hazard reappraisal from combined structural geology geomorphology and cosmic ray exposure dating analyses the eastern precordillera thrust system nw argentina because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture paleoseismological estimation of their associated seismic hazard is a difficult task to improve the seismic hazard assessments in the andean foreland of western argentina san juan province this paper proposes a novel approach that combines structural geology geomorphology and exposure age dating the eastern precordillera of san juan is probably one of the most active zones of thrust tectonics in the world we concentrated on one major regional active reverse structure the 145 km long villic um pedernal thrust where this methodology allows one to 1 constrain the quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes 2 analyse the geometry and the geomorphic characteristics of the villic um pedernal thrust and 3 estimate uplift and shortening rates through determination of in situ produced 1 0 be cosmic ray exposure cre ages of abandoned and uplifted alluvial terraces from a structural point of view the villic um pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique n40 e trending fault branches along the three segments inversion of fault slip data shows that the development of the eastern precordillera between 31 s and 32 s latitude is dominated by a pure compressive reverse faulting stress regime characterized by a n110 10 e trending compressional stress axis 1 a geomorphic study realized along the 18 km long las tapias fault segment combined with cre ages shows that the minimum shortening rate calculated over the previous 20 kyr is at least of the order of 1 mm yr 1 an earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation this analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three times greater than the shortening rate we determined for the las tapias fault i e 3 mm yr 1 suggesting that the san juan region may have experienced a seismic crisis during the 20th century moreover the ramp that controls the development of the eastern precordillera appears to be one of the main seismic sources in the san juan area particularly the 65 km long villic um las tapias segment a first order evaluation of the seismic hazard parameters shows that this thrust segment can produce a maximum earthquake characterized by a moment magnitude of 7 3 0 1 and a recurrence interval of 2 4 1 5 kyr this part of the villic um pedernal ramp may have ruptured during the ms 7 4 1944 san juan earthquake producing very few surface ruptures and only distributed flexural slip deformation on to the neogene foreland bedding planes between the eastern precordillera and pie de palo

using hilltop curvature to derive the spatial distribution of erosion rates 1 erosion rates dictate the morphology of landscapes and therefore quantifying them is a critical part of many geomorphic studies methods to directly measure erosion rates are expensive and time consuming whereas topographic analysis facilitates prediction of erosion rates rapidly and over large spatial extents if hillslope sediment flux is nonlinearly dependent on slope then the curvature of hilltops will be linearly proportional to erosion rates in this contribution we develop new techniques to extract hilltop networks and sample their adjacent hillslopes in order to test the utility of hilltop curvature for estimating erosion rates using high resolution 1 m digital elevation data published and new cosmogenic radionuclide analyses in the feather river basin california suggest that erosion rates vary by over an order of magnitude 10 to 250 mm kyr 1 hilltop curvature increases with erosion rates allowing calibration of the hillslope sediment transport coefficient which controls the relationship between gradient and sediment flux having constraints on sediment transport efficiency allows estimation of erosion rates throughout the landscape by mapping the spatial distribution of hilltop curvature additionally we show that hilltop curvature continues to increase with rising erosion rates after gradient limited hillslopes have emerged hence hilltop curvature can potentially reflect higher erosion rates than can be predicted by hillslope gradient providing soil production on hilltops can keep pace with erosion finally hilltop curvature can be used to estimate erosion rates in landscapes undergoing a transient adjustment to changing boundary conditions if the response timescale of hillslopes is short relative to channels

landscape development in an hyperarid sandstone environment along the margins of the dead sea fault implications from dated rock falls in this study we explored the spatial and temporal relations between boulders and their original in situ locations on sandstone bedrock cliffs thiswas accomplished bycombining field observations withdating methods using cosmogenicisotopes 10 be and 14 c and optically stimulated luminescence osl our conclusions bear both on the landscape evolution and cliff retreat process in the hyperarid region of timna and on the methodology of estimating exposure ages using cosmogenic isotopes we recognize three discrete rock fall events at 31 ka 15 ka and 4 ka in this hyperarid region the most plausible triggering mechanism for rock fall events is strong ground acceleration caused by earthquakes generated by the nearby dead sea fault dsf our record however under represents the regional earthquake record implying that ongoing development of detachment cracks prior to the triggering event might be slower than the earthquake cycle cliff retreat rates calculated using the timing of rock fall events and estimated thickness of rock removed in each event range between 0 14 m ky 1 and 2 m ky 1 when only full cycles are considered we derive a more realistic range of 0 4 m ky 1 to 0 7 mk y 1 these rates are an order of magnitude faster than the calculated rate of surface lowering in the area we conclude that sandstone cliffs at timna retreat through episodic rock fall events that preserve the sharp imposing landscape characteristic to this region and that ongoing weathering of the cliff faces is minor a 10 20 difference in the 10 be concentrations in samples from matching boulder and cliff faces that have identical exposure histories and are located only a few meters apart indicates that cosmogenic nuclide production rates are sensitive to