late accretion to the moon recorded in zircon u th he thermochronometry abstract we conducted zircon u th he zhe analysis of lunar impact melt breccia 14311 with the aim of leveraging radiation damage accumulated in zircon over extended intervals to detect low temperature or short lived impact events that have previously eluded traditional isotopic dating techniques our zhe data record a coherent date vs effective uranium concentration eu trend characterized by 3500 ma dates from low 75 ppm eu zircon grains and ca 110 ma dates for high 100 ppm eu grains a progression between these date populations is apparent for intermediate 75 100 ppm eu grains thermal history modeling constrains permissible temperatures and cooling rates during and following impacts modeling shows that the data are most simply explained by impact events at ca 3950 ma and ca 110 ma and limits allowable temperatures of heating events between 3950 110 ma modeling of solar cycling thermal effects at the lunar surface precludes this as the explanation for the ca 110 ma zhe dates we propose a sample history characterized by zircon resetting during the ca 3950 ma imbrium impact event with subsequent heating during an impact at ca 110 ma that ejected the sample to the vicinity of its collection site our data show that zircon has the potential to retain 4he over immense timescales 3950 myrs thus providing a valuable new thermochronometer for probing the impact histories of lunar samples and martian or asteroidal meteorites

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

correction to cosmogenic and nucleogenic 3he in apatite titanite and zircon and anomalous cosmogenic 3he production and elevation scaling in the high himalaya earth planet sci lett 248 2006 451 461 and 265 2008 287 301

the 21ne production rate in quartz revisited abstract i have revised our earlier production rate determination of 21ne in terrestrial quartz s niedermann th graf j s kim c p kohl k marti and k nishiizumi 1994 earth planet sci lett 125 341 355 taking account of improved knowledge about the exposure age of samples used in that work and applying distinct procedures for scaling to sea level and high latitudes the corrected value of 19 0 3 7 atoms g 1 a 1 is in excellent agreement with expectations based on nuclear properties j masarik and r c reedy 1995 earth planet sci lett 136 381 395 and closely corresponds to the present day production rate in the case of substantial variations of the geomagnetic field in the past as proposed by several studies the revised value can consistently be used with suitable correction methods

cosmogenic 3he in himalayan garnets indicating an altitude dependence of the 3he 10be production ratio to investigate the potential of using cosmogenic helium in garnet as a dating tool 3hec and 10bec have been measured within garnets and coexisting quartz respectively sampled in the himalayan range at various elevations comparison and correlation of 3hec and 10bec concentrations demonstrate that cosmogenic 3he is well retained in himalayan garnets and can thus be used in this mineral to quantify precisely earth s surface processes this in the case of recently cooled orogenic samples which contain limited amounts of non cosmogenic helium for these high elevation samples the exposure ages derived from 3hec using classical scaling factors lead however to an overestimation of 3hec ages compared to 10bec ages 0 1 to 28 ky by up to a factor of 2 additionally over the samples altitude range 3000 4622 m the theoretically invariant polar 3hec 10bec production ratio 22 5 increases with increasing elevation challenging classical models of production rate evolution to explain this observation we propose a new 3hec production mechanism based on the altitudinal dependence of the energy spectrum of cosmic rays and according to which neutrons or protons resulting from a first spallation reaction within the rock tertiary particles may have sufficient energy to induce an additional in situ spallation reaction producing a second 3h or 3he but insufficient energy to produce 10be the probability of such a mechanism increasing with altitude according to these observations we propose for future and ongoing studies to use the empirically determined attenuation length of 121 g cm2 for helium production at high altitude

cosmogenic 3he and 21ne dating of biotite and hornblende stable cosmogenic isotopes such as 3he and 21 ne are useful for dating of diverse lithologies quantifying erosion rates and ages of ancient surfaces and sediments and for assessing complex burial histories although many minerals are potentially suitable targets for 3he and 21 ne dating complex production systematics require calibration of each mineral isotope pair we present new results from a drill core in a high elevation ignimbrite surface which demonstrates that cosmogenic 3he and 21 ne can be readily measured in biotite and hornblende 21 ne production rates in hornblende and biotite are similar and are higher than that in quartz due to production from light elements such as mg and al we measure 21 ne hbl 21 ne qtz 1 35 0 03 and 21 ne bio 21 ne qtz 1 3 0 02 which yield production rates of 25 6 3 0 and 24 7 2 9 at g 1 yr 1 relative to a 21 ne qtz production rate of 19 0 1 8 at g 1 yr 1 we show that nucleogenic 21 ne concentrations produced via the reaction 18 o n 21 ne are manageably small in this setting and we present a new approach to deconvolve nucleogenic 21 ne by comparison to nucleogenic 22 ne produced from the reaction 19 f n 22 ne in f rich phases such as biotite our results show that hornblende is a suitable target phase for cosmogenic 3he dating but that 3he is lost from biotite at earth surface temperatures comparison of 3he concentrations in hornblende with previously measured mineral phases such as apatite and zircon provides unambiguous evidence for 3he production via the reaction 6li n 3h 3he due to the atypically high li content in the hornblende 160 ppm we estimate that li produced 3he represents 40 of total 3he production in our samples and must be considered on a sample specific basis if 3he dating in hornblende is to be widely implemented

extraterrestrial 3he in seafloor sediments evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust orbital parameters and quaternary climate we have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the ontong java plateau western equatorial pacific ocean odp site 806 these results provide a two million year record of the burial flux of extraterrestrial 3he which we believe is a proxy for the terrestrial accretion rate of interplanetary dust particles the 3he burial flux prior to 700 ka was relatively low 0 5 pcc cm 2 kyr 1 but from 700 ka to the present the burial flux gradually increased to a value of 1 0 pcc cm 2 kyr 1 100 kyr periodicity in the 3he burial flux is apparent over the last 700 kyr and correlates with the oxygen isotope record of global climate with high 3he burial fluxes associated with interglacial periods this periodicity and phase are consistent with previous 3he measurements in north atlantic sediments although 100 kyr periodicity in 3he burial flux is in agreement with recent predictions of the accretion rate of interplanetary dust based on a model of the orbital evolution of asteroidal debris the measurements and predictions differ by one half cycle in phase nevertheless our observations suggest the terrestrial accretion rate of interplanetary dust is controlled by orbital eccentricity and or inclination relative to the solar system invariable plane such control is a necessary but not sufficient condition for the hypothesis of muller and macdonald 1995 that variations in extraterrestrial dust accretion modulates terrestrial climate with a 100 kyr period we also identify several brief 25 kyr intervals of strongly enhanced 3he burial possibly related to random and transient fluctuations in the accretion rate of asteroidal or cometary dust particles

long term cosmogenic 3he production rates 152 ka 1 35 ma from 40ar 39ar dated basalt flows at 29 n latitude a set of time integrated cosmogenic 3he production rates in olivines for the last 1 35 ma are presented we investigated three basaltic lava flow tops from lanzarote canary islands spain the 40ar 39ar ages determined for those basalt flows by incremental laser heating of leached groundmass samples are 152 26 ka 281 19 ka and 1 35 0 01 ma 2 three or four different olivine phenocryst samples have been analyzed from each flow for their cosmogenic 3he abundances the resulting 3he production rates in olivine at sea level at 29 latitude are 82 14 and 82 8 atoms g 1 a 1 as obtained from the 152 ka and 281 ka old flows respectively considering effects of erosion on the 1 35 ma old flow we find that the production rate of 82 8 atoms g 1 a 1 is consistent with the cosmogenic 3he production during the last 1 35 ma there appears to be a 14 discrepancy between previously published production rates derived at higher latitudes and altitudes if the scaling factors of lal are used to compare results this discrepancy is greatly reduced however if the revised scaling factors of dunai this issue are applied using the new scaling factors we derive a production rate for cosmogenic 3he in olivine at sea level and high latitudes 60 of 118 11 atoms g 1 a 1 2 the correspondingly revised value of cerling and craig and ackert et al is 123 6 atoms g 1 a 1 2 the mean value of these two calibrations is 121 6 atoms g 1 a 1 2 we suggest that the production rate of 121 6 atoms g 1 a 1 at sea level and high latitudes may be applied to the complete time range where paleomagnetic data indicate that there was no long term averaged intensity variation in the earth s magnetic field i e over the last 10 ma

measurement of ancient cosmogenic 21ne in quartz from the 28 ma fish canyon tuff colorado abstract measurement of 21 ne in quartz from the 28 ma buried fish canyon tuff of colorado yielded a maximum of 2 75 0 57 10 6 21 ne atoms g sio 2 1 above nucleogenic and modern concentrations this quantity represents cosmogenic 21 ne produced on the fish canyon tuff surface prior to the deposition of the overlying carpenter ridge tuff ancient 21 ne was isolated through the analysis and identification of 1 background 21 ne produced from particle interactions or inherited and 2 cosmogenic 21 ne produced from modern radiation multiple samples of fish canyon tuff shielded during both exposure periods 28 ma ago and in modern time yielded the background that was then subtracted from all samples likewise samples of fish canyon exposed today but well below the fish canyon carpenter ridge contact and therefore shielded 28 ma ago yielded a modern component that was also removed from all sample concentrations the presence of an ancient cosmogenic isotope in a buried surface has several potential applications including the quantification of paleoelevation paleolatitude and pre quaternary erosion rates

the isotopic composition of radiogenic helium and its use to study groundwater movement in confined aquifers abstract the 3 he 4 he ratio for radiogenic he is shown to be primarily determined by the abundance of li and neutron absorbing elements in the host formations and is almost independent of the radioelement abundance the 3 he 4 he ratios have been computed for various li contents in rock matrices with average abundances of other elements the 3 he 4 he ratio is specific for each formation and may therefore be used to study crustal diffusion of he it is shown however that both the 3he and 4he contents of continental basements are likely to exceed those of the mantle so that diffusion of mantle he through continental crust is not likely to occur changes in the 3 he 4 he ratio for dissolved he have potential for studying groundwater movement and mixing processes atmospheric he which was dissolved at recharge is progressively diluted by radiogenic he with an isotopic ratio characteristic of the aquifer as the groundwater migrates down dip mixing proportions for formation he and atmospheric he in aquifers for which there is admixture of fracture borne water and interstitially stored water can also be estimated from isotopic measurements these processes are discussed in relation to two aquifers in eastern england

geochemical processes controlling the relationship between co mn and fe in early diagenetic deep sea nodules abstract early diagenetic manganese nodules from the northeast pacific nodule belt and from the southeast pacific peru basin show primary growth features of dendritic microtextures consisting of alternating laminae of crystalline 10 amanganate a1 substance and amorphous material which is composed of an intimate mixture of ferric hydroxide silicate and mno 2 a2 substance the formation of rhythmic sequences of a1 and a2 microlayers is explained by physico chemical changes in the peneliquid sediment layer and in the microenvironment of the accreting nodule surface a upward diffusion of mn 2 in the interstitial water as a result of decay of organic matter and mn mobilization b oxidation of mn 2 and formation of 10 amanganate in the upper part of the peneliquid sediment layer leading to ph depression in the microenvironment of the nodule surface which decreases the mobility of silicate resulting in formation of a2 layers c restoration of ph and renewed precipitation of 10 amanganate based on data of 171 bulk analyses and on electron microprobe investigations interelement relationships between co mn and fe are pointed out fe and co show a significant positive correlation r 0 84 while mn and co are poorly negatively correlated r 0 21 assuming linear regression the enrichment of co within the amorphous a2 phase is attributed to specific surface adsorption and subsequent oxidation of co 2 to co 3 in the strong electric field of si 4 robust complexes of co iii and feh 2 sio 4 prevent most of the co from being available for the 10 amanganate precipitation concerning the relation between mn and fe and co respectively the highest correlation coefficients are obtained using an inverse logarithmic regression under early diagenetic conditions the concentration and precipitation of mn 2 in the interstitial water depends on the redox gradient which is controlled by the amount of decomposing organic matter the nernst equation describes the relationship as a reciprocal logarithmic function however the quantities of colloidal ferric hydroxide and of dissolved silicate are not affected by variations of the redox potential these different characteristics in the precipitation of mn and the fe and si rich colloidal phase may cause the significantly negative logarithmic correlation of mn versus fe and co respectively

anomalous cosmogenic 3he production and elevation scaling in the high himalaya the production rate of cosmogenic 3he in apatite zircon kyanite and garnet was obtained by cross calibration against 10 be in co existing quartz in glacial moraine boulders from the nepalese himalaya the boulders have 10 be ages between 6 and 16 kyr and span elevations from 3200 to 4800 m in all of these minerals 3he correlates with 10 be and is dominantly cosmogenic in origin after modest correction for non cosmogenic components 3he 10 be systematics imply apparent sea level high latitude slhl apparent production rates for 3he of 226 atoms g 1 yr 1 in zircon 254 atoms g 1 yr 1 in apatite 177 atoms g 1 yr 1 in kyanite and 153 atoms g 1 yr 1 in gamet these production rates are unexpectedly high compared with rates measured elsewhere in the world and also compared with proposed element specific production rates for apatite and zircon the data are sufficient to conclude that the 3he 10 be ratio increases with elevation if this reflects different altitudinal scaling between production rates for the two isotopes then the slhl production rates estimated by our approach are overestimates we consider several hypotheses to explain these observations including production of 3he via thermal neutron capture on 6li altitudinal variations in the energy spectrum of cosmic ray neutrons and the effects of snow cover because all of these effects are small we conclude that the altitudinal variations in production rates of cosmogenic 3he and 10 be are distinct from each other at least at this location over the last last 10 kyr kyr this conclusion calls into question commonly adopted geographic scaling laws for at least some cosmogenic nuclides if confirmed this distinction may provide a mechanism by which to obtain paleoelevation estimates

an alternative isochron method for measuring cosmogenic 3he in lava flows this study evaluates an alternative isochron method designed to improve the precision and the accuracy of the measurement of cosmogenic 3he 3hec and the calibration of 3hec production rates in lava flows while the accuracy of the standard two steps routine i crushing ii melting may be affected by possible crushing induced release of matrix sited 3hec this new isochron technique does not involve the preliminary crushing step such advance is thus potentially able to improve the accuracy of 3hec determination moreover this method has the advantage to yield cosmogenic 3he concentrations using only one type of extraction technique cosmogenic 3he isochrons can be built successfully measuring the 3he and 4he concentrations of several phenocrysts replicates fused in vacuo provided that these aliquots have identical magmatic 3he 4he ratios identical 3hec concentrations and variable magmatic helium contents when plotted in the 3he 4he vs 1 4he space such a suite of data define a straight line whose intercept yield the magmatic 3he 4he mag ratio and whose slope is the cosmogenic 3he concentration the frequent addition of radiogenic 4he 4helow asterisk may be easily accounted taking advantage of a property that is characteristic of non eroded lava flows the 3hec 4helow asterisk ratio is not time dependent this radiogenic correction of the isochron slope involves the r factor whose calculation requires that the u and th abundances in the phenocrysts and the host lava be known as well as the diameter and the shape of the analyzed minerals this correction also requires that all the analyzed aliquots have identical radiogenic 4he concentration the isochron method was tested on surface samples of three quaternary basalt flows from mount etna and mauna loa aged of 6 1 8 2 0 1 and 41 3 ka the obtained data set yielded statistically robust isochrons and cosmogenic 3he concentrations that are not significantly different from those obtained with the standard method importantly for samples with high magmatic cosmogenic 3he ratio the isochron technique offers both better accuracy and precision than the standard two steps method this alternative technique should thus open new perspectives for the particularly important task of 3hec production rate calibrations from lava flow surfaces

heavy metal distributions in peru basin surface sediments in relation to historic present and disturbed redox environments abstract heavy metal distributions in deep sea surface sediments and pore water profiles from five areas in the peru basin were investigated with respect to the redox environment and diagenetic processes in these areas the 10 20 cm thick mn oxide rich and minor metal rich top layer is underlain by an increase in dissolved mn and ni concentrations resulting from the reduction of the mno 2 phase below the oxic zone the mobilised associated metals like co zn and cu are partly immobilised by sorption on clay organic or fe compounds in the post oxic environment enrichment of dissolved cu zn ni co pb cd fe and v within the upper 1 5 cm of the oxic zone can be attributed to the degradation of organic matter in a core from one area at around 22 25 cm depth striking enrichments of these metals in dissolved and solid forms were observed offset distributions between oxygen penetration and mn reduction and the thickness of the mn oxide rich layer indicate fluctuations of the mn redox boundary on a short term time scale within the objectives of the german atesepp research programme the effect of an industrial impact such as manganese nodule mining on the heavy metal cycle in the surface sediment was considered if the oxic surface were to be removed or disturbed oxygen would penetrate deep into the formerly suboxic sediment and precipitate mn 2 and metals like ni and co which are preferably scavenged by mno 2 the solid enrichments of cd v and other metals formed in post oxic environments would move downward with the new redox boundary until a new equilibrium between oxygen diffusion and consumption is reached

cosmogenic 3he and 21ne production rates calibrated against 10be in minerals from the coso volcanic field this study calibrates the production rate of cosmogenic 3 he in pyroxene olivine garnet zircon and apatite as well as 21 ne in quartz and pyroxene against the known production rate of 10 be in quartz the devil s kitchen rhyolite from the coso volcanic field in southeastern california elev 1300 m was chosen for this study due to its young age 610 ka and diverse mineral assemblage based on 10 be our two rhyolite samples have apparent exposure ages of 49 and 93 ka indicating substantial erosion after eruption combining data from the two samples we estimate sea level high latitude 3 he spallation production rates of 145 11 141 16 and 144 30 at g 1 a 1 2 for pyroxene olivine and spessartine garnet respectively for zircon and apatite we estimate apparent 3he spallation production rates of 114 8 and 149 28 at g 1 a 1 2 respectively the rates for zircon and apatite are reported as apparent production rates because we do not explicitly address the redistribution of spallation produced 3 he from adjacent minerals these estimates quantitatively account for production of 3 he from both cosmogenic and radiogenic neutron reactions on 6 li within the analyzed phases and also implanted from nuclear reactions in neighboring minerals the high u th and li content of this rhyolite provides a particularly rigorous test of this correction we estimate 21 ne production rates of 17 7 1 6 and 34 1 3 2 at g 1 a 1 2 in quartz and pyroxene fe mg 0 7 by mass respectively although high u and th contents create the potential for significant production of nucleogenic 21 ne this component is small due to the young eruption age of the rhyolite

production rate of cosmogenic 21ne in quartz estimated from 10be 26al and 21ne concentrations in slowly eroding antarctic bedrock surfaces abstract we estimated the production rate of 21ne in quartz using a set of samples from slowly eroding sandstone surfaces in the antarctic dry valleys geologic evidence as well as cosmogenic 10be and 26al concentrations indicate that i these sites have experienced millions of years of surface exposure at low erosion rates and ii steady erosion has been sustained long enough that surface 10be and 26al concentrations have reached equilibrium with the erosion rate under these conditions surface cosmogenic 21ne concentrations should be a function only of the erosion rate and the 21ne production rate as the erosion rate can be determined from 10be and 26al concentrations this allows an estimate of the 21ne production rate estimating the reference 21ne production rate on this basis with the assumption that all 21ne production is by neutron spallation yields a poor fit to measured 21ne concentrations and a systematic residual that is correlated with the erosion rate of the sample site the same steady erosion assumption with a production model that includes production by deeply penetrating muons yields a good fit both to our measurements and to similar independent measurements from an antarctic bedrock core both data sets together yield a total reference 21ne production rate of 18 3 0 4 atoms g 1 a 1 of which 0 66 0 10 atoms g 1 a 1 is due to muon interactions

growth of a manganese nodule from peru basin a radiochemical anatomy abstract attempts have been made to study the entire growth history of a manganese nodule from the northern part of peru basin in the pacific using radiochemical profiles of 230 th 232 th 227 th 230 th and 10 be 9 be combined with the observations on fe mn contents and textural variation the radiochemical data indicate that the nodule grew more or less concentrically throughout most of its existence since it formed 1 5 my ago receiving mn from both bottom water and pore water this condition appeared to have changed about 180 ky ago when the growth became asymmetric in that the top and bottom sides became fixed in their relative positions on the sea floor since then the bottom side accreted with a fast rate of close to 200 mm my apparently fueled by the supply of diagenetically remobilized mn in pore water from the sediment substrate in the meantime the top side accumulated at about 6 mm my a value which is in the normal range for deep sea nodules having their mn supplied from the hydrogenous source

mass spectrometric 3he measurement in 4he rich phases techniques and limitations for cosmogenic 3he dating of zircon apatite and titanite recent calibration studies have expanded the range of target minerals suitable for cosmogenic 3he dating to include u and th rich phases such as zircon apatite and titanite these minerals often contain large amounts of radiogenic 4he that present several analytical challenges for precise and accurate 3he determinations in this paper we document the abundance sensitivity and changes in the absolute sensitivity and time evolution of the 3he signal over a wide range of 4he pressures in a map 215 50 noble gas mass spectrometer large 50 decreases in sensitivity with 4he amount arising from space charge effects were observed but can be corrected for using an isotope dilution like technique in which 3he spike is added to a sample midway through the mass spectrometric analysis large amounts of 4he also cause the time evolution of the 3he signal to become steeper degrading precision of the initial peak height determination from the intercept taken together we find that these effects preclude reliable analysis of samples with 4he 1 mol and that 3he 4he ratios of greater than 5 10 10 are required to routinely measure 3he to better than 20 precision we present some general considerations by which to assess the probability of success of measuring cosmogenic 3he in these phases as a function of elevation exposure age and helium cooling age

the influence of radiogenic 4he on cosmogenic 3he determinations in volcanic olivine and pyroxene accurate determination of cosmogenic 3he concentrations in olivine and pyroxene phenocrysts requires knowledge of the amount of magmatic 3he also in the sample the magmatic 3he component is commonly estimated by measuring the magmatic 3he 4he ratio and assuming that all 4he is magmatic however this approach yields incorrect results if 4he produced by u and th decay is also present here we propose several strategies to account for the presence of radiogenic 4he the optimal approach depends on whether the helium closure age tc is similar to the exposure age te of the analyzed phenocrysts i when tc te which applies to uneroded lava flows the ratio of cosmogenic 3he to radiogenic 4he is constant and the correction for radiogenic helium is independent of time we provide a simple expression for a correction factor r that can be applied in this case ii in the more common case that tc te it is necessary to obtain an independent constraint on the closure age to estimate the radiogenic correction in either case a quantitative estimate of the radiogenic 4he production rate is required because of the long stopping distance of particles this production rate depends on the u and th concentrations of both phenocryst and host and also on phenocryst grain size to illustrate the magnitude and uncertainty of the necessary corrections we compiled u and th measurements on phenocrysts and whole rock samples of basalts and andesites supplemented by new measurements on hawaiian basalts and altiplano andesites our data and models suggest that some published cosmogenic 3he production rate determinations may have underestimated the true production rate by up to 5 because the presence of radiogenic 4he was not recognized similarly a recent study presenting cosmogenic 3he derived erosion rates in 4 ma hawaiian olivines probably overestimates true erosion rates by an order of magnitude or more

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

effective attenuation lengths of cosmic rays producing 10be and 26al in quartz implications for exposure age dating we have measured cosmic ray produced 10be t 1 5 my and 26al t 0 72 my as functions of depth in a core of quartz sandstone bedrock collected in south victoria land antarctica these data were used to place limits on the exposure age and erosion rate of the exposed surface and to calculate the effective attenuation lengths of cosmic rays producing these nuclides these latter results indicate that the production attenuation length for 26al is comparable to that for 10be this suggests that the production ratio 26al 10be does not vary substantially with depth in a rock and that its value at the surface of exposed rock is not strongly affected by erosional losses allowing wider use of the ratio in determining exposure ages

specific distribution of ground motion during the 1995 kobe earthquake and its generation mechanism the 1995 kobe hyogo ken nanbu earthquake mw 6 9 is the most damaging in the recent japanese history and its notable feature is that most of the damage and over 6000 casualties occurred in a narrow belt through kobe and neighboring cities the kobe hanshin area usually a fault rupture propagation generates strong ground motions along the direction of propagation and this directivity effect should be significant above the source faults and beyond its leading end however the damage zone of the kobe earthquake is migrated noticeably from the fault trace into the center of kobe city three dimensional 3 d simulations of ground motion in kobe show that this migration is due to the strong amplification and ray bending in the sedimentary basin below the city in cooperation with the multipathing effects at a basin bedrock boundary

combining 3 he cosmogenic dating with u th he eruption ages using olivine in basalt this paper presents new u th he crystallization and 3 he exposure ages on olivine for a suite of basalt samples from the snake river plain idaho the results provide the first demonstration that u th he geochronology can be successfully applied to late quaternary basalts using measurements of olivine phenocrysts as opposed to u rich minerals the approach employs abrasion to remove the outer rinds of olivine crystals to avoid problems with 4 he implantation from the groundmass and a specially designed extraction system that allows u th and he concentrations and isotopic compositions to be measured on the same olivine grains we demonstrate the viability of the u th he technique on basalts with ages of 373 ka and 3400 ka previously dated by ar ar and show that concurrent measurements of u th 4 he ages and 3 he cosmogenic exposure ages improve the accuracy of both methods the combinedu th 4 he 3 hetechniqueisappliedtoaseriesofbouldersandflowsfromboxcanyonnearhagerman idaho toevaluate the ages of the basalts and to use exposure ages to make inferences about the age and mode offormation of the canyon the u th he ages of the box canyon basalts are between 86 12 ka and 130 12 ka 1 sigma errors and suggest at least two periods of eruption the ages are similar to a ca 95 ka ar ar age previously assigned and distinguish the box canyon basalts from nearby ca 395 ka basalt exposure ages of boulders within the canyon at the mouth head and middle of box canyon are 21 1 19 3 and 48 3 ka scoured bedrock at the canyon head has an exposure age of 45 5 ka these data indicate that the canyon was carved before the

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

cosmogenic 3he and 10be chronologies of the late pinedale northern yellowstone ice cap montana usa cosmogenic 3 he and 10 be ages measured on surface boulders from the moraine sequence deposited by the northern outlet glacier of the yellowstone ice cap indicate that the outlet glacier reached its terminal position at 16 5 6 0 4 3 he ka and 16 2 6 0 3 10 be ka respectively concordance of these ages supports the scaled production rates used for 3 he 118 6 6 6 6 atoms g 21 y r 21 and 10 be 5 1 6 0 3 atoms g 21 y r 21 62s at high latitudes at sea level two recessional moraines upvalley from the terminal moraine have mean ages of 15 7 6 0 5 10 be ka and 14 0 6 0 4 10 be ka respectively and a late glacial flood bar was deposited at 13 7 6 0 5 10 be ka these cosmogenic chronologies identify a late pinedale glacial maximum in northern yellowstone that is significantly younger than previously thought and they suggest deglaciation of the yellowstone plateau by 14 10 be ka

the influence of suboxic diagenesis on the formation of manganese nodules in the clarion clipperton nodule belt of the pacific ocean abstract polymetallic nodules and a single fe mn crust from the clarion and clipperton zone ccz of the equatorial eastern pacific have been analyzed to determine their chemical and mineralogical compositions icp oes analyses of bulk nodules from the ccz indicate that the nodules formed under oxic diagenetic conditions with typical mn fe ratios of 4 6 ni cu values of 2 3 wt co contents of 0 12 0 17 wt however detail analyses of individual growth layers by electron microprobe analyses empa reveal much larger chemical heterogeneity of individual layers with mn fe ratios ranging from 800 two different genetic types of layers can be distinguished layer type 1 dense layer with average mn fe ratios of 1 80 average ni cu of 0 81 wt co contents of 0 30 wt hydrogenetic metal precipitation from oxic waters these layers consist of fe vernadite mno2 epitaxially intergrown with feroxyhyte feooh nanoparticles layer type 2 growth structures dendritic growth structures and dense layers with average mn fe ratios of 96 ni cu of 3 9 wt co contents of 0 08 wt and a distinct ni cu maximum of 6 51 wt at a mn fe ratio of 56 suboxic diagenetic metal precipitation from suboxic pore waters type 2 layers mainly consist of turbostratic phyllomanganates such as 10 a vernadite 7 a vernadite and todorokite are minor compounds mixed layer type 3 these layers can occur as zones of low reflectivity in the transition from layer type 1 to 2 or build up inhomogeneous growth structures of nm thin layers of low or high reflectivity the mn fe ratios of this material range between 3 and 11 ni cu of 1 4 6 wt and co contents are between 0 02 and 0 77 wt in most cases these growth structures represent a mixture of type 1 and 2 layers x ray photoelectron spectroscopy xps of the recent outermost nm layers of nodules top rim and bottom side indicates hydrogenetic accretion processes under recent oxic conditions both from seawater and pore water the mixed type ccz nodules are interpreted to consist of an oxic hydrogenetic and a suboxic diagenetic end member calculations of the proportions of the individual layer end members show that suboxic layers make up about 50 60 of the chemical inventory of the ccz nodules whereas oxic hydrogenetic layers comprise about 35 40 the remaining part 5 10 consists of incorporated sediment particles occurring along cracks and pores these results demonstrate that suboxic conditions alternate with oxic conditions during the growth of nodules in the eastern ccz this is probably due to fluctuating bioproductivity in the equatorial pacific surface waters during glacial interglacial periods which led to changing organic carbon flux to the sediment and changing oxygen consumption in near surface sediments furthermore reduced ventilation of the deep ocean during glacial periods may have led to suboxic conditions in near surface sediments our investigations prove that bulk chemistry data of whole nodules only provides an average of individual layers that build up the nodules and is inappropriate for genetic interpretation

pore water profiles and numerical modelling of biogeochemical processes in peru basin deep sea sediments abstract an extensive set of pore water profiles including o 2 no 3 no 2 nh 4 po 4 3 fe 2 mn 2 so 4 2 sio 4 4 ph and alkalinity as well as solid phase data on organic carbon content and porosity in 18 sediment cores obtained from five areas in the peru basin rv sonne 106 expedition in 1996 is presented the pore water profiles indicate that early diagenesis progresses through oxygen respiration denitrification and manganese iv reduction while the subsequent redox states iron iii reduction sulphate reduction and methanogenesis cannot be observed from the dissolved phase in these deep sea sediments a numerical diagenetic model was applied to the data in order to derive parameters such as the depositional flux of metabolizable organic matter or the bioturbation intensity that control the geochemical conditions in the deep sea floor and could not be obtained directly by measurements moreover the numerical simulations show that even those pore water no 3 profiles that decline non linearly to zero concentration are not compatible with a steady state assumption they can be explained only by transient downward progression of a nitrate front

in situ cosmogenic 10be and 21ne in sanidine and in situ cosmogenic 3he in fe ti oxide minerals abstract we report concentrations of in situ cosmogenic 10 be and 21 ne from coexisting quartz and sanidine separates and of cosmogenic 3 he in coexisting fe ti oxide minerals from ignimbritic successions of northern chile oxaya and lauca ignimbrites new mineral isotope pairs such as sanidine and fe ti oxide minerals are helpful in quantitative geomorphology for geological settings where the lithology lacks the commonly used minerals quartz pyroxene or olivine production rates in sanidine and fe ti oxide minerals were determined by normalizing nuclide concentrations to established production rates in quartz the experimentally determined production rates are compared to model production rates calculated with new cross sections for 3 he 21 ne and 10 be production from the individual target elements the mean experimental 21 ne production rate for five sanidine samples is 30 4 3 7 atoms g 1 yr 1 30 4 5 4 atoms g 1 yr 1 including the uncertainty of the 21 ne production rate in quartz p 21 ne qtz this is in excellent agreement with the modelled value of 28 3 atoms g 1 yr 1 which has an estimated uncertainty of 20 the 21 ne production rate in sanidine is thus about 50 higher than that in quartz the cosmogenic neon in sanidine is entirely released in low temperature steps 400 600 c and no signs of an interfering nucleogenic neon component were observed this is in stark contrast to quartz and makes sanidine an attractive mineral for terrestrial cosmogenic neon studies 3 he diffuses out of the sanidine structure preliminary results also indicate that sanidine is well suited for 10 be studies the mean experimental 10 be production rate from two sanidine samples is 4 45 0 38 atoms g 1 yr 1 4 45 0 42 atoms g 1 yr 1 including uncertainty of p 10 be qtz very close to the modelled value of 4 55 atoms g 1 yr 1 which has an estimated uncertainty of 20 we emphasize that 10 be and 21 ne production in sanidine is composition dependent therefore major element analyses should be carried out and production rates calculated on a sample by sample basis fe ti oxide minerals retain 3 he quantitatively experimentally derived production rates are in excellent agreement with new values derived from physical modelling the mean experimental 3 he production rate for five fe ti oxide minerals samples is 120 11 atoms g 1 yr 1 120 12 atoms g 1 yr 1 including the uncertainties of p 21 ne qtz compared to a mean modelled value of 124 atoms g 1 yr 1 which has an estimated uncertainty of 20 the variable chemical and structural composition of the solid solution lines of fe ti oxide minerals has little effect on the total 3 he production rate cosmogenic 21 ne is not produced in significant quantities in fe ti oxide minerals due to the absence of suitable target elements

cosmic ray exposure dating with in situ produced cosmogenic 3he results from young hawaiian lava flows in an effort to determine the in situ production rate of spallation produced cosmogenic 3 he and evaluate its use as a surface exposure chronometer we have measured cosmogenic helium contents in a suite of hawaiian radiocarbon dated lava flows the lava flows ranging in age from 600 to 13 000 years were collected from hualalai and mauna loa volcanoes on the island of hawaii because cosmic ray surface exposure dating requires the complete absence of erosion or soil cover these lava flows were selected specifically for this purpose the 3 he production rate measured within olivine phenocrysts was found to vary significantly ranging from 47 to 150 atoms g 1 yr 1 normalized to sea level although there is considerable scatter in the data the samples younger than 10 000 years are well preserved and exposed and the production rate variations are therefore not related to erosion or soil cover data averaged over the past 2000 years indicate a sea level 3 he production rate of 125 30atoms g 1 yr 1 which agrees well with previous estimates the longer record suggests a minimum in sea level normalized 3 he production rate between 2000 and 7000 years 55 15atoms g 1 yr 1 as compared to samples younger than 2000 years 125 30 atoms g 1 yr 1 and those between 7000 and 10 000 years 127 19atoms g 1 yr 1 the minimum in production rate is similar in age to that which would be produced by variations in geomagnetic field strength as indicated by archeomagnetic data however the production rate variations a factor of 2 3 0 8 are poorly determined due to the large uncertainties in the youngest samples and questions of surface preservation for the older samples calculations using the atmospheric production model of o brien 1979 35 and the method of lal and peters 1967 11 predict smaller production rate variations for similar variation in dipole moment a factor of 1 15 1 65 because the production rate variations archeomagnetic data and theoretical estimates are not well determined at present the relationship between dipole moment and production rate will require further study precise determination of the production rate is an important uncertainty in the surface exposure technique but the data demonstrate that it is feasible to date samples as young as 600 years of age providing that there has been no erosion or soil cover therefore the technique will have important applications for volcanology glacial geology geomorphology and archaeology

physico chemical mechanisms of weathering processes and corresponding models of dynamics of mineral zonality evolution abstract the peculiarities of weathering processes involving duration slow change of ambient conditions isothermality as well as proceeding in open systems permit to study these processes in a steady state approach d c i d t 0 where ci is concentration of intermediates and t is time the most typical quasi stationary processes for a water rock system are 1 non equilibrium step surface reaction of primary mineral dissolution and 2 non equilibrium step secondary mineral precipitation these respectively determine two extreme mechanisms of mineral formation 1 pseudomorphous replacement and 2 dissolution transfer crystallization besides non stationary weathering processes are known it is the case when a process is controlled by diffusion through a layer of secondary minerals which have been deposited on the surface of the primary mineral a mathematical model of weathering dynamics of feldspar with its metasomatic replacement by clay minerals is presented numerical simulation led to the prediction of mineral zonality development along the weathering profile at any time

evidence for 5 ma paleo exposure of an eocene miocene paleosol of the bohnerz formation switzerland we obtained u th he formation ages and cosmogenic 3he concentrations for pisoliths from a paleosol of the bohnerz formation siderolithic of central europe the paleosol is exposed in the almenbuhl quarry near lohn canton schaffhausen switzerland the paleosol consists of red clay of 3 4 m thickness developed on deeply weathered jurassic limestone and overlain by early miocene conglomerates the u th he formation ages of the pisoliths are between 50 ma and 8 ma with most ages being older than 17 ma there is a sharp decline in the frequency of ages at the time of burial of the paleosol at 17 ma these ages are inconsistent with the previous assumption that the bohnerz formation formed in a cretaceous to early eocene laterite in a tropical climate we propose that the bohnerz formation more closely resembles terra rossa soils which do not require a tropical climate to form the 3he concentration in the pisoliths is roughly constant with depth throughout the paleosol at 300 matoms g we interpret this as the result of soil convection during cosmic ray exposure the minimum exposure duration at the surface of the paleosol is 5 ma a simple model of soil convection shows that the true exposure duration of the paleosol is approximately 10 20 ma these results indicate that the clay soils of the bohnerz formation were continuously exposed at the surface for millions of years since the paleosol was covered by conglomerate since 17 ma the 3he measured here was produced by cosmic ray exposure before burial cosmogenic 3he concentrations measured in fine grained soil iron oxides 1 m are similar to those measured in pisoliths this might indicate that fine grained iron oxides are retentive to helium and might be used for studying the formation and cosmic ray exposure of modern soils and paleosols

using in situ produced cosmogenic isotopes to estimate rates of landscape evolution a review from the geomorphic perspective the application of in situ produced cosmogenic isotopes to problems in geomorphology has increased rapidly over the past decade at least 57 papers and numerous abstracts have been published since the mid 1980s when the first mass spectrometric measurements of terrestrially produced cosmogenic isotopes were made taken at face value these studies provide quantitative information about rates of landscape evolution and landform age however the significance of calculated erosion rates and exposure ages depends strongly on the models used to interpret isotopic data the validity of assumptions inherent to these models and the geologic surroundings in which the samples were collected this paper attempts to place cosmogenic isotope studies in a geomorphic context by reviewing fundamentals of the method and evaluating the validity of assumptions under which these data have been interpreted at present the establishment of high precision cosmogenically based glacial and alluvial chronologies is stymied by the evolution of geomorphic surfaces the erosion of rock from sampled boulders the potential for isotope inheritance from previous exposure and the uncertainty of isotopic measurements uncertainties in isotope production rates and the observed variability of exposure ages on individual geomorphic surfaces limit the confidence with which cosmogenic ages can be correlated reliably with those obtained by other techniques estimation of erosion rates at single points on the landscape gives useful small scale information extrapolation of these rates over longer time and larger spatial scales is less sure and most likely biased toward lower erosion rates by die inadvertent selection of resistant sample sites however because erosion rates are so poorly constrained at present even estimates to within a factor of 2 may be of significant value to geomorphologists and tectonicists

cosmogenic 3he production rate in ilmenite and the redistribution of spallation 3he in fine grained minerals cosmogenic nuclide surface exposure dating and erosion rate measurements in basaltic landscapes rely primarily on measurement of 3he in olivine or pyroxene however geochemical investigations using 3he have been impossible in the substantial fraction of basalts that lack separable olivine or pyroxene crystals or where such crystals were present but have been chemically weathered fine textured basalts often contain small grains of ilmenite a weathering resistant mineral that is a target for cosmogenic 3he production with good he retention and straightforward mineral separation but with a poorly constrained production rate here we empirically calibrate the cosmogenic 3he production rate in ilmenite by measuring 3he concentrations in basalts with fine grained 20 m cross section ilmenite and co existing pyroxene or olivine from the columbia river and snake river plain basalt provinces in the western united states the concentration ratio of ilmenite to pyroxene and olivine is 0 78 0 02 yielding an apparent cosmogenic 3he production rate of 93 6 7 7 atom g 1 yr 1 that is 20 30 greater than expected from prior theoretical and empirical estimates for compositionally similar minerals the production rate discrepancy arises from the high energy with which cosmic ray spallation reactions emit tritium and 3he and the associated long stopping distances that cause them to redistribute within a rock fine grained phases with low cosmogenic 3he production rates like ilmenite will have anomalously high production rates owing to net implantation of 3he from the surrounding higher 3he production rate matrix semi quantitative modeling indicates implantation of spallation 3he increases with decreasing ilmenite grain size leading to production rates that exceed those in a large grain by 10 when grain radii are 150 m the modeling predicts that for the ilmenite grain size in our samples implantation causes production rates to be 20 greater than expected for a large grain and within uncertainty resolves the discrepancy between our calibrated production rate theory and rates from previous work the redistribution effect is maximized when the host rock and crystals differ substantially in mean atomic number as they do between whole rock basalt and ilmenite

production of 3he in crustal rocks by cosmogenic thermal neutrons accurate determination of cosmogenic 3he concentrations in minerals has to account for nucleogenic 3he produced from the reaction of thermalized neutrons with 6li thermal neutrons from the cosmic ray cascade are typically not considered however in exposed basalts and granites the flux of cosmogenic thermal neutrons ctn is generally 10 200 times higher than the thermal neutron flux produced by n reactions in the rock with the absolute values dependent on composition and geographic location the reaction of ctn with li can account for 5 50 of the cosmogenic 3he in minerals in typical granitiod rocks depending on the li content and distribution and petrography of the rock and may be considerably higher in special cases in basalts this contribution is usually lower 1 5 6 but may still warrant consideration the strong depth dependence of ctn produced 3he in rock may be used to assess erosion of landforms similar to ctn produced 36cl however as 3he is stable it has the potential to extend the useful time range to older surfaces

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

constraints on the loss of matrix sited helium during vacuum crushing of mafic phenocrysts vacuum crushing is an efficient technique to selectively release the mantle derived helium component trapped within olivine and pyroxene phenocrysts however contrary to previous assumptions recent studies have shown that this method may liberate significant matrix sited cosmogenic 3 he 3 he c or radiogenic 4 he 4 he because this loss may bias both the determination of magmatic 3 he 4 he ratios and the accuracy of 3 he c measurements it is essential to understand what mechanism is responsible and under what conditions matrix helium loss is manifest to address this question olivines and pyroxenes with various amounts of matrix sited 3 he from 10 7 to 10 11 at g 1 were crushed in air or in vacuum using several crushing devices sample temperature was controlled during each crushing experiment and ranged from 25 to 325 c the resulting powders were then sieved to obtain several homogeneous grain fractions ranging between 300 m the 3 he c concentrations measured in each fraction clearly show that significant 3 he c loss 20 affects only the finest fraction 10 m and importantly only under hot conditions here t 300 c even the smallest fractions 10 m quantitatively retain matrix sited 3 he c when crushed under cold conditions t 25 c regardless of the duration and energy of crushing these results invalidate the model previously proposed by yokochi r marty b pik r and burnard p 2005 high 3 he 4 he ratios in peridotite xenoliths from sw japan revisited evidence for cosmogenic 3 he released by vacuum crushing geochem geophys geosyst 6 doi 10 1029 2004gc000836 that involved spallation tracks and implied that the magnitude of loss was mainly controlled by the grain size moreover new diffusion experiments were carried out to constrain the diffusivity of matrix sited helium in crushed olivines when used to model diffusive 3 he c loss as a function of grain size during crushing these new data predict the observed release fairly well therefore we conclude that temperature enhanced volume diffusion is one of the main mechanisms controlling the release of 3 he c during crushing for future applications special attention should thus be paid to control the grain size the crushing duration and the temperature of the sample

cosmogenic 3he production rate in the high tropical andes 3800 m 20 s implications for the local last glacial maximum abstract to improve both precision and accuracy of cosmic ray exposure dating methods there is a crucial need of calibration sites constraining the production rate of cosmogenic isotopes this is particularly true in the high tropical area where existing scaling models present significant discrepancies this study presents a new calibration site for cosmogenic 3he located at 3800 m in the tropical altiplano 19 9 s 67 6 w on the southern flank of the tunupa volcano in the vicinity of the salar de uyuni it consists in a fluvio glacial outwash that is stratigraphically bracketed by two successive lacustrine shorelines these shorelines are well dated by 14c and u series dating n 57 allowing determination of the age of the boulder field at the surface of the delta at 15 3 0 5 ka 1 eleven andesitic boulders were sampled on this fluvio glacial surface and the cosmogenic 3he contents of their pyroxene phenocrysts and amphiboles was analyzed the nucleogenic contribution from 6li capture is well constrained by determining the u th sm 4he age of these rocks this correction is minimal combined with the absolute dating of the delta these 3hec data yield a local production rate of 999 38 1 at g 1 yr 1 at 3800 m and 19 89 s after scaling with the time dependent scaling scheme of stone 2000 this result yields a rate of 121 5 1 at g 1 yr 1 at high latitude and sea level this new calibration is the highest among the existing global dataset it will thus permit the establishment of new robust glacial chronologies in the high tropics with an uncertainty lower than 5 at 1 such precision may have important implications in paleoclimatology notably because it will allow comparison with other well dated paleoclimatic archives including this new data the updated global 3hec production rate is 122 15 at g 1 yr 1 using the time dependent scaling of stone 2000 the new site specific 3hec production rate is used here to refine glacier fluctuations on cerro tunupa confirming that the local last glacial maximum was synchronous with the lake tauca highstand 15 5 ka data also suggest that a dramatic glacial retreat occurred at about 15 ka few hundred years before the lake tauca regression synchronously with the onset of the bolling allerod

active tectonics within the nw and se extensions of the pambak sevan syunik fault implications for the present geodynamics of armenia this study analyzes the active tectonics within the northwestern and southeastern extensions of the pambak sevan syunik fault pssf a major right lateral strike slip fault cutting through armenia quantifying the deformations in terms of geometry kinematics slip rates and earthquake activity using cosmogenic 3he osl irsl and radiocarbon dating techniques reveal different behaviors between the two regions within the northwestern extension in the region of amasia the pssf bends to the west and splits into two main wnw ese trending reverse faults defining a compressional pop up structure we estimate an uplift rate and a shortening rate of 0 5 0 1 mm y and 1 4 0 6 mm y respectively this suggests that most of the 2 mm y right lateral movement of the pssf seems to be absorbed within the amasia pop structure within the southeastern extension the pssf shows signs of dying out within the tsghuk volcano region at the southernmost tip of the syunik graben there the tectonic activity is characterized by a very slow ns trending normal faulting associated with a slight right lateral movement slip rates analyses i e vertical slip rate ew stretching rate at 90 to the fault and right lateral slip rate of 0 2 mm y 0 1 mm y and 0 05 mm y respectively lead to the conclusion that the right lateral movement observed further north along the pssf is mainly transferred within other active faults further west within the karabagh hagari fault or other structures further northwestwards comparing our slip rates with those estimated from gps data suggests that most of the deformation is localized and seismic at least within the tsghuk region the geometrical and kinematic pattern observed within the two terminations of the pssf suggests that the fault and its surrounding crustal blocks are presently rotating anticlockwise as also observed within the gps velocity field this is consistent with the recent kinematic models proposed for the caucasus kura south caspian region and brings a new insight into the present geodynamics of armenia

cosmogenic neon and helium at reunion measurement of erosion rate abstract we report analyses of both helium and neon for olivine separates from a drill core at an altitude of 2330 m in oceanite at piton de la fournaise volcano we show for the first time that cosmogenic 21 ne like cosmogenic 3 he decreases exponentially with core depth we obtain an attenuation length of 165 6 g cm 2 1 for cosmogenic 21 ne identical to the value found previously for cosmogenic 3 he alone 1 for each depth in the core the measured amount of cosmogenic 21 ne is about 13 lower than predicted based on the high precision k ar age of 65 200 2000 yrs 1 2 and this result is attributed to erosion assuming a constant erosion rate we derive a value of 3 5 1 7 mm yr 1 from the 21 ne data the same order of magnitude as the value obtained from cosmogenic 3 he at haleakala 1 3 this work highlights the important potential of both cosmogenic helium and neon for measuring in situ exposure ages and erosion rates

progressive glacial retreat in the southern altiplano uturuncu volcano 22 s between 65 and 14 ka constrained by cosmogenic 3he dating this work presents the first reconstruction of late pleistocene glacier fluctuations on uturuncu volcano in the southern tropical andes cosmogenic 3he dating of glacial landforms provides constraints on ancient glacier position between 65 and 14 ka despite important scatter in the exposure ages on the oldest moraines probably resulting from pre exposure these 3he data constrain the timing of the moraine deposits and subsequent glacier recessions the uturuncu glacier may have reached its maximum extent much before the global lgm maybe as early as 65 ka with an equilibrium line altitude ela at 5280 m then the glacier remained close to its maximum position with a main stillstand identified around 40 ka and another one between 35 and 17 ka followed by a limited recession at 17 ka then another glacial stillstand is identified upstream during the late glacial period probably between 16 and 14 ka with an ela standing at 5350 m this stillstand is synchronous with the paleolake tauca highstand this result indicates that this regionally wet and cold episode during the heinrich 1 event also impacted the southern altiplano the ela rose above 5450 m after 14 ka synchronously with the bolling allerod

cosmogenic 3he in igneous and fossil tooth enamel fluorapatite igneous fluorapatite samples from a suite of six granitic rocks from the transantarctic mountains have high 3he concentrations to 5 10 9 atoms g 1 and high 3he 4he ratios to 9 10 7 these values are far higher than those found in several hundred igneous apatites from elsewhere around the world and are higher than can be attributed to nuclear reactions on 6li this 3he is almost certainly derived from cosmic ray reactions in rocks with high exposure ages at high latitude and elevation several samples of fossil tooth enamel fluorapatite from the turkana basin of kenya are similarly rich in 3he with up to 1 10 7 atoms 3he g 1 and 3he 4he ratios up to 4 10 6 again this 3he is most logically attributed to cosmic ray reactions provided that cosmogenic 3he like radiogenic 4he is quantitatively retained in fluorapatite under earth surface conditions routine 3he exposure dating of this common phase may be possible based on its chemical composition the 3he production rate in fluorapatite is about 100 atoms g 1 yr 1 at sea level and high latitude using this rate the apatites from the transantarctic mountains have apparent exposure ages of 0 5 6 2 myr in agreement with values elsewhere in the range the fossil tooth enamel samples have apparent exposure ages ranging from a few up to 130 kyr such high exposure ages suggest some of these fossils may be lag deposits with a very long residence time at or near the earth s surface 3he exposure ages can provide insights to the depositional and reworking history of enamel bearing fossils at present the major limitations to 3he exposure dating of fluorapatite are purification of sufficient amounts of material and measurement of small amounts of 3he in the presence of large quantities of 4he in addition further work is necessary to establish the nucleogenic 3he background in fluorapatite

cosmogenic and nucleogenic 3he in apatite titanite and zircon cosmogenic 3he was measured in apatite titanite and zircon and cosmogenic 21 ne in quartz at 13 depth intervals in a 2 7 m long drill core in a miocene ignimbrite from the altiplano of bolivia all three 3he depth profiles as well as the 21 ne profile attenuate exponentially with depth indicating that both of these isotopes are cosmogenic in origin with no significant contribution from other sources the attenuation lengthscale for 3he production of 180 11 g cm 2 is consistent with expectations for neutron spallation and is identical to that found for the cosmogenic 21 ne in quartz by normalizing the measured 3he concentrations to 21 ne and using the independently known cosmogenic 21 ne production rate the apparent cosmogenic 3he production rates in apatite titanite and zircon were respectively found to be 112 97 and 87 atoms g yr at sea level and high latitude the formal uncertainty on these estimates is 20 2 and arises in equal parts from uncertainties in the measured 3he 21 ne ratios and the uncertainty in the 21 ne production rate however an additional factor affecting the apparent 3he production rate in these phases arises from the long stopping range of spalled 3he and tritium which decays to 3he because all three accessory phases have higher mean atomic number than major rock forming minerals they will have lower 3he production rates than their surroundings as a consequence the long stopping ranges will cause a net implantation of 3he and therefore higher apparent production rates than would apply for purely in situ production thus these apparent production rates apply only to the specific grain sizes analyzed analysis of sieved zircon aliquots suggests that a factor of 2 increase in grain size from 50 to 100 m cross section yields a 10 decrease in apparent production rate while this effect warrants further study the grain sizes analyzed here are typical of the accessory phases commonly encountered so the apparent rates provide an appropriate starting place for surface exposure dating using 3he in these minerals

mass spectrometric identification of cosmic ray produced neon in terrestrial rocks with multiple neon components studies of cosmic ray produced nuclides in terrestrial rocks are expected to provide important geomorphological and glaciological information such as surface exposure ages erosion rates and extent of glacial cover in the case of the stable nuclide21ne the cosmic ray produced component may represent but one of several components and a component resolution based on three isotope correlations is essential we developed analytical techniques which permit accurate corrections for all interfering ions we show for our modified nier source that corrections for doubly charged species based on constant charge state ratios are not satisfactory the improved techniques permit isotopic studies of 106 atoms of21ne the spallation ratio 22ne 21ne c from si was calibrated using a quartz separate from an allan hills sandstone and yields a value of1 243 0 022 this ratio is expected to be essentially constant for terrestrial quartz samples and should be useful in component resolutions the stepwise release of ne at increasing temperatures shows that cosmic ray produced ne is released from quartz at rather low temperatures this permits an estimate of the activation energy for ne diffusion in quartz 90 10 kj mol