geometrical analysis of the punta del pedron shear zone asturias spain implications related to exploration of salave gold type mineralization abstract the salave gold deposit is located at the northern end of the oscos gold belt which forms part of the asturian leonese zone of the variscan massif the gold belt and the salave deposit are genetically related to the emplacement of post kinematic granitoids which were largely controlled by variscan fracture systems a geometrical analysis following the mccoss mccoss a m 1986 simple construction for deformation in transpression transtension zones journal of structural geology 8 6 715 718 method has been utilized to discriminate the transpressional transtensional and simple shear components and the displacement vectors s vectors of the punta del pedron shear zone a contour map of the s vector orientations is consistent with the contour map of the calculated extension of the whole area and shows those shear zones where extensional and contractional components have been determined extension is higher e 15 towards the east where transtension is predominant near the salave gold deposit this deposit is located at the intersection of the extensional sinistral shear zones striking between 130 and 140 which promoted dilation and the emplacement of the salave granodiorite with the dextral shear zones striking between 070 and 080 extension was transferred to the dextral shear zones and associated 030 pinnate veins in a transtensional stage which promoted connected vein systems and localized fluid flow this gave rise to the alteration patterns of the deposit and ore deposition in an area previously affected by the mondonedo thrust system the use of this geometrical method with limitations and several assumptions discussed in the text and the analysis of the scaling properties of the vein sets in traverses can be utilized in the field to aid in mineral exploration

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

decadal warming of the coldest antarctic bottom water flow through the vema channel a decadal warming trend of antarctic bottom water flowing through the vema channel is reanalyzed our data base consists of 94 high precision full depth stations from 19 visits to the vema sill plus twelve stopovers at two additional key locations originally a long term temperature increase in the near bottom jet was noted from 1992 onward after a period of rather constant abyssal temperatures since 1972 from today s perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2 8 mk yr 1 in the following 15 years however the clearly manifested temperature rise is superimposed with fluctuations for the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water an attempt is made to trace the observed variability back to its source region in the weddell sea

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

fractal geometries of vein systems and the variation of scalingrelationships with mechanism abstract investigation of vein geometries has identified empirical relationships which allow extrapolation of outcrop scale observation to larger scales measurements of vein shapes and aspect ratios in a number of different environments demonstrate that veins follow similar empirical scaling laws to those of faults geometries of veins are easier to characterise accurately than faults because their thickness is related to the variation in displacement from zero at their tips to a maximum at their thickest point vein sizes obey the empirical relationship l kta where l length in mm t thickness in mm 20 1 this suggests that veins amplify initially by inflation and subsequently by elongation

a fractal relationship between vein thickness and gold grade in drill core from la codosera spain analysis of quartz vein thicknesses and gold grades in drill core from western spain indicates that both approximate a power law distribution suggesting an underlying fractal relationship log log plots of cumulative frequency n against vein thickness t show systematic changes in relation to gold grade the exponent d in a power law of the form n c t super d is lower for higher gold grades indicating that a greater proportion of the dilation is taking place on the thicker veins which are interpreted as providing interconnected conduits for gold bearing fluids thus monitoring the vein thickness distribution may provide a means of discriminating mineralized and barren structures in vein hosted mineral deposits

fractal analysis of a mineralised vein deposit curraghinalt gold deposit county tyrone quantitative description and prediction of vein hosted deposits using fractal statistics have been tested using data collected from the curraghinalt gold deposit sperrin mountains county tyrone n ireland goldbearing quartz veins are hosted by neo proterozoic dalradian southern highland group age psammites pelitic schists and graphitic schists veins trend e to ese and cross cut regional structures vein thickness z distributions closely approximate a power law distribution of the form n z cz d with an exponent d of 0 76 over three orders of magnitude vein spacing data approximate a log normal distribution with a mean of 2 92m numerical analysis indicates that the veins are more clustered than expected from a random distribution regions of high percentage extension and high vein density define vein clusters the vein clustering relationship may be combined with the power law thickness distribution and used in a predictive manner the data may be used to constrain the probability of intersecting veins of potentially mineable dimension

uphill facing antislope scarps in the coast mountains southwest british columbia uphill facing scarps are examined at affliction creek a glacierized area within the meager creek volcanic complex of southwest british columbia scarps occur directly downslope of tension cracks and are considered to have developed from a combination of 1 antithetic movement between partly toppled slices of rock defined by a master joint set dipping into the slope and 2 erosion of the upslope face of each tension crack leaving the downslope face prominent as an antislope scarp a kinematic test for toppling failure is described glacial erosion and rapid glacial downwasting are probable causes of toppling lichenometric data indicate significant scarp development since affliction glacier attained its maximum neoglacial dimensions about 140 yr ago dilatancy is cited as a possible mechanism for scarp stabilization

power law vein thickness distributions and positive feedback in vein growth the thicknesses of veins of a single generation from the kodiak accretionary complex show a power law distribution with an exponent of d 1 33 this value d 1 indicates that a significant portion of the vein related extension is accommodated by the thinnest veins thick vein segments are typically confined to southeast dipping brittle ductile shear zones textural observations of veins within these zones indicate a progressive evolution from crack seal to euhedral growth of quartz with an increase over time in the duration that fractures remained open model simulations of vein thickness distributions show that a constant growth model results in a negative exponential distribution and that it is necessary to assume size proportional growth to produce a power law distribution textures and power law thickness distributions for the kodiak veins are thus consistent with an increasing time averaged growth rate as vein thickness increased comprising a positive feedback the positive feedback resulted in the progressive evolution from fractures to brittle ductile shear zones and ultimately to faults

the probable importance of snow and sediment shielding on cosmogenic ages of north central colorado pinedale and pre pinedale moraines abstract eight uncorrected 36 cl ages for pinedale boulders in north central colorado fall in the range 16 5 to 20 9 kyr 10 be age determinations on four of five boulders are in close agreement 6 difference with 36 cl determinations hypothetical corrections for snow shielding increased the 36 cl ages of pinedale boulder surfaces by an average of 12 most ages for pre pinedale bull lake boulders fall within marine isotope stage mis 5 a time when continental and sierran ice accumulations were small or nonexistent under the assumption that these boulders were deposited on moraines that formed before the end of mis 6 140 kyr bp calculations indicated that rock surface erosion rates would have had to range from 5 9 to 10 7 mm kyr 1 to produce the observed 36 cl values when compared to rates that have been documented for the past 20 kyr these erosion rates are extremely high snow shielding accounts for 0 48 of the additional years needed to shift pre pinedale dates to mis 6 this suggests that some combination of snow shielding sediment shielding or 36 cl leakage has greatly decreased the apparent ages of most pre pinedale boulders inability to account for the effects of these processes seriously hinders the use of cosmogenic ages of pre pinedale boulders as estimators of the timing of alpine glaciation

structural constraints on deep seated slope deformation kinematics abstract a significant sackung type deep seated slope gravitational deformation dsgsd was recognised for the first time by the authors in the middle part of valfurva east of bormio rhaetian alps italy the reconstruction of its kinematics age and state of activity is presented through a detailed description of its morphological geomechanical and structural features an integrated multi disciplinary approach was performed to achieve a clear comprehension of the phenomenon field surveys and aero photo interpretation were carried out in order to clarify the structural geological and geomorphological setting in which the dsgsd developed a kinematic conceptual model of the slope deformation was developed through the analysis of morpho structures of their significance and relationships with lithological markers and quaternary deposits after a geomechanical characterisation of the rock mass involved in the slope deformation numerical modelling was performed to verify the hypotheses made on kinematics and driving factors of the phenomenon the sackung affects pre permian metapelites metabasites and marbles belonging to the upper austroalpine basement of the campo nappe as well as late pleistocene and holocene glacial and rock glacier deposits the deformation started after the late wurmian age 15 000 11 000 years b p and continued until few centuries ago not excluding a present day low rate activity deformation consists in a large oblique sagging along a deep confined sliding surface associated with gravitational reactivation of pre existing late alpine and recent tectonic brittle structures leading to the formation of n s and wnw ese trending gravitational morpho structures the evolution of the wnw ese trending system resulting in asymmetric trenches led to progressive failure of the lower part of the slope during the last 10 000 years as testified by large paleo landslide accumulations and it is still in progress numerical modelling indicates post glacial unloading as the main triggering factor of the slope deformation the importance of this deep seated slope deformation is enhanced by the occurrence of the 30 mm 3 active ruinon landslide in the lower part of the slope such landslide is subjected to rapid evolution and threatens the valley floor establishing an important risk factor connected to human lives and socio economic activities

the recent fault scarps of the western alps france tectonic surface ruptures or gravitational sackung scarps a combined mapping geomorphic levelling and 10be dating approach abstract in the western alps some recent scarps were previously interpreted as surface ruptures of tectonic reverse and normal faults that agree with microseismicity and gps measurements our analysis shows that in fact there are hundreds of recent scarps up to 30 m high and 2 1 km long with only pure normal motions they share the same characteristics as typical sackung scarps the scarps are mainly uphill facing parallel to the ridge crests and the contour lines they are relatively short less than 2 1 km with respect to tectonic fault ruptures and organized in swarms they cut screes and relict rock glaciers with a slow commonly 1 mm year average slip rate in the aiguilles grives massif these sackung scarps clearly express the gravitational toppling of sub vertical bedding planes in hard rocks in contrast the belledonne outer crystalline massif exhibits scarps that stem from the gravitational reactivation of conjugate tectonic faults the recent faults extend to about 1600 m beneath the rognier ridge crest but are always above the valley floor the main scarp swarm is 9 2 km long and constitutes the largest sackung ever described in the western alps 10 be dating of a scarp and offset surfaces shows that 4 m slip may have occurred rapidly in less than 3800 years sometimes between the end of the glaciation and 8800 1900 years ago this dating together with the location of some faults far from the deep glacial valleys suggests that sagging might have been triggered by strong earthquakes during a post glacial period of probably enhanced seismicity the belledonne and synclinal median faults just beneath the rognier sackung could have been the sources of this seismicity

simple constructions for deformation in transpression transtension zones abstract a simple geometrical construction is demonstrated for determining the orientations of the principal axes of the infinitesimal strain ellipsoid in tectonic zones where boundaries obliquely converge or diverge the construction may also be used to determine the relative magnitudes of the principal axes and the ellipsoid shape for infinitesimal and finite transpressional transtensional strains the analysis leads to a tightening of the definitions of the loosely used terms compression wrench and extension applications of the simple construction and convenient graphical solution are illustrated by brief examples

examination of surface exposure ages of antarctic moraines using in situ produced 10be and 26al concentrations of 10be t12 1 5 106 y and 26a1 t12 0 72 106 y have been determined by accelerator mass spectrometry ams in a suite of quartz samples taken from sandstone boulders in several moraines in arena valley a dry valley adjacent to the taylor glacier in the quatermain mountains southern victoria land east antarctica these isotopes are produced in surficial quartz by cosmic ray spallation of o and si the concentrations in these samples ranged from 6 1 105 to 3 0 107 at g 1 for 10be and from 9 4 106 to 1 2 108 at g 1 for 26a1 depending upon the extent of exposure at the surface analyses of 10be in several samples from a single moraine at altitudes ranging from 1300 to 1650 m permitted an estimation of the air attenuation pathlength of cosmic ray neutrons the value of 142 96 41 g cm 2 is consistent with other published values production rates of 17 6 4 at g 1 y 1 for 10be and 113 54 16 at g 1 y 1 for 26a1 at 1300 m and 87 s and a 26al 10be production ratio of 6 5 1 3 1 3 were calculated from the data these values correspond to sea level production rates at high geomagnetic latitude of 6 4 at g 1 y 1 and 41 7 at g 1 y 1 for 10be and 26a1 respectively consistent with determinations based on 11 ky glacially polished surfaces in the sierra nevada in california these production rates imply exposure ages for the various moraines ranging from 50 ky to 2 5 my in accordance with other geological evidence the 10be and 26al ages of these rocks compare favorably with those found using a similar dating method based on in situ production of 3he examination of the 3he concentrations in conjunction with the present data set yields an estimate of 3he production of 230 8540 at g 1 y 1 corresponding to 85 31 15 at g 1 y 1 at sea level this is lower than previously reported values of 240 60 at g 1 y 1 and 190 at g 1 y 1 scaled to sea level and high geomagnetic latitude based respectively on volcanic flows less than 2000 years old at low latitude and samples collected from 14 400 year old volcanic flows this discrepancy is likely due to diffusive losses which may become significant up to 50 for surface exposure ages on the order of 2 0 my nevertheless the general correlations among the three isotopes suggest that 3he does not suffer gross losses through diffusion

geomorphology and geochronology of sackung features uphill facing scarps in the central spanish pyrenees abstract the paper analyses uphill facing scarps and associated troughs developed in the oversteepened slopes of two neighbouring glacial valleys in the central spanish pyrenees previous studies of sackung landforms in the pyrenees have argued for deglacial unloading as the genetic mechanism but this causal and temporal relationship has not been proved due to the lack of chronological data the antislope scarps in the two studied locations vallibierna and estos are developed in palaeozoic metasedimentary rocks parallel to the contour lines and the structural grain occur in the intermediate sector of the hillslope and are up to 0 5 km long and several meters high a trench was excavated in a sackung trough fill in each of the valleys in order to gain information about their chronology and genesis charcoal from the lowermost unit in vallibierna provided an age of 5 9 cal ka for the sackung and extrapolation of the three dates obtained in estos indicates that the trough formed ca 7 6 7 8 cal ka deglaciation of the studied sectors of the valleys occurred between 16 and 13 ka the time lag of 5 ka suggests that glacial erosion and the subsequent debutressing of the oversteepened valley walls created slopes predisposed to sackung development but did not initiate the movement seismic shaking is proposed as a probable triggering factor this hypothesis although supported by the sudden deformation event recorded by a failure plane exposed in vallibierna trench and by the seismic and neotectonic activity of the area cannot be proved due to the lack of chronological information about paleoearthquakes

columbia mountain landslide late glacial emplacement and indications of future failure northwestern montana usa abstract the well preserved and undissected columbia mountain landslide which is undergoing suburban development was studied to estimate the timing and processes of emplacement the landslide moved westward from a bedrock interfluve of the northern swan range in montana usa onto the deglaciated floor of the flathead valley the landslide covers an area of about 2 km2 has a toe to crown height of 1100 m a total length of 3430 m a thickness of between 3 and 75 m and an approximate volume of 40 million m3 deposits and landforms define three portions of the landslide from the toe to the head they are i clast rich diamictons made up of gravel sized angular rock fragments with arcuate transverse ridges at the surface ii silty and sandy deposits resting on diamictons in an internally drained depression behind the ridges and iii diamictons containing angular and subangular pebble to block sized clasts some of which are glacially striated in an area of lumpy topography between the depression and the head of the landslide drilling data suggest the diamictons cover block to slab sized bedrock clasts that resulted from an initial stage of the failure the landslide moved along a surface that developed at a high angle to the ne dipping thinly bedded metasediments of the proterozoic belt supergroup the exposed slope of the main scarp dips 30 37 w a hypothetical initial rotational failure of the lower part of a bedrock interfluve may have transported bedrock clasts into the valley the morphology and deposits at the surface of the landslide indicate deposition by a rock avalanche sturzstrom derived from a second stage of failure along the upper part of the scarp the toe of the columbia mountain landslide is convex west in planview except where it was deflected around areas now occupied by glacial kettles on the north and south margins landsliding therefore occurred during deglaciation of the valley while ice still filled the present day kettles available chronostratigraphy suggests that the 1 km thick glacier in the region melted before 12 000 14c years bp within 3000 years of the last glacial maximum deglaciation and hillslope failure are likely causally linked failure of the faceted interfluve was likely due tensile fracturing of bedrock along a bedding normal joint set shortly after glacial retreat from the hillslope open surficial tension fractures and grabens in the swan range are limited to an area above the crown of the landslide movement across these features suggests that extensional flow of bedrock sackung is occurring in what remains of the ridge that failed in the columbia mountain landslide the fractures and grabens likely were initiated during failure but their morphologies suggest active extension across some grabens continued movement of bedrock above the crown may result in future mass movements from above the previous landslide scarp landslides sourced from bedrock above the scarp of the late glacial columbia mountain landslide which could potentially be triggered by earthquakes are geologic hazards in the region

scaling factors for the rates of production of cosmogenic nuclides for geometric shielding and attenuation at depth on sloped surfaces abstract the decrease in rates of production of cosmogenic nuclides occurs because of shielding of cosmic rays by mountains sloped surfaces and local rock formations that block them when a large part of the sky is blocked this correction is large and requires detailed model calculations this paper considers three geometries a rectangular obstruction a triangular obstruction and a sloped surface other geometries can be considered as a combination of these the results are presented in terms of formulas and graphs so that the reader can easily apply them to common field situations any use of cosmogenic nuclides in the study of geomorphic processes or forms must consider factors that introduce variations in the production of nuclides

the vilalba gold district a new discovery in the variscan terranes of the nw of spain a geologic fluid inclusion and stable isotope study abstract this work defines the vilalba gold district a new gold region in the nw of spain comprising three mineralized areas castro de rei valina azumara and arcos and two different types of mineralization 1 w au skarn in castro de rei and 2 au as ag pb zn cu sb vein disseminated mineralization in valina azumara and arcos mineralization is mainly hosted by impure limestone and black slates lower cambrian and spatially related to variscan and late variscan structures rhyolite dikes occur in arcos 299 6 ma and castro de rei both consisting of peraluminous high potassium and calc alkaline rocks these dikes represent the fractionated expression of unexposed post tectonic granitoids located at depth the castro de rei area exhibits a contact aureole with biotite cordierite and calc silicate hornfels prograde skarn consists of garnet pyroxene quartz wollastonite and scheelite the retrograde alteration took place in two stages and mainly consists of amphibole epidote zoisite quartz calcite chlorite and sulfides gold mineralization in the skarn occurs as invisible gold in sulfoarsenides and as electrum related to bi te s minerals the mineralization of valina azumara and arcos comprises two stages the first consists of as rich pyrite and arsenopyrite with invisible gold the second stage mainly consists of base metal sulfides and ag pb zn cu sb sulfosalts hydrothermal fluids involved in the skarn formation are low salinity up to 6 6 wt nacl eq aqueous carbonic fluids h2o co2 ch4 n2 evolving into aqueous fluids during the last stage of gold mineralization stable isotope geochemistry indicates the importance of a magmatic fluid in the early stages 18osmow from 7 5 to 11 34scdt from 2 7 to 5 9 that evolved through interaction with host rocks and mixing with metamorphic and or meteoric fluids the 34scdt values 7 8 10 9 of second retrograde stage sulfides suggest the incorporation of 34s enriched from host rocks in valina azumara and arcos the fluid inclusion and isotope studies indicate similar hydrothermal fluids to those associated with the second retrograde skarn stage taking into account the fluid inclusion study and mineral geothermometry an attempt was made to determine the p t conditions of ore formation the prograde skarn of castro de rei formed at temperatures and pressures ranging from 520 to 560 c and from 1 7 to 2 5 kb the mineralization of valina azumara formed at minimum p t conditions of 1 7 kb and 355 c the estimated temperatures for the arcos mineralization are similar to those of valina azumara up to 383 c but at lower pressures we propose the model of intrusion related gold systems irgss to explain the mineralizations of the vilalba gold district in this model the castro de rei skarn and the valina azumara mineralization represent a proximal and a distal deposit respectively relative to an unexposed granitoid situated at depth we also consider arcos as a distal deposit in relation to another unexposed granitoid located further south in the district

beryllium 10 dating of the duration and retreat of the last pinedale glacial sequence accurate terrestrial glacial chronologies are needed for comparison with the marine record to establish the dynamics of global climate change during transitions from glacial to interglacial regimes cosmogenic beryllium 10 measurements in the wind river range indicate that the last glacial maximum marine oxygen isotope stage 2 was achieved there by 21 700 700 beryllium 10 years and lasted 5900 years ages of a sequence of recessional moraines and striated bedrock surfaces show that the initial deglaciation was rapid and that the entire glacial system retreated 33 kilometers to the cirque basin by 12 100 500 beryllium 10 years

cosmogenic 10be dating of a sackung and its faulted rock glaciers in the alps of savoy france sackungs are the largest gravitational deformation observed in mountains they are characterized by the long term slowness of the movements but their mechanism is still not well understood nowadays cosmic ray exposure cre dating methods allow dating the morphologic structures involved in sackung and can contribute at the understanding of their origin in the alps the 5 3 km long arcs sackung initiated during the activity of rock glaciers three samples from these faulted rock glaciers provide their first cre ages and show that at 2000 m elevation these block accumulations moved during the younger dryas and stopped in early holocene six 10be ages of fault scarps show that the arcs sackung lasted only a few thousand years and stopped at about 8462 432 10be yr they also reveal that deformation migrated upslope in agreement with a mechanism of flexural toppling of vertical layers this unique and long gravitational event characterized by migration of the deformation does not support earthquake shaking as triggering mechanism for individual faults it shows that in the upper isere valley slope deformation was delayed of several thousand years after glacial debuttressing and is not anymore active despite its fresh morphology

constraints on the timing of debris covered and rock glaciers an exploratory case study in the holar area northern iceland abstract eighteen samples for 36cl cosmic ray exposure cre dating were taken from glacially polished bedrocks moraine boulders fossil active rock glaciers and debris covered glaciers in fremri grjotardalur and holadalur cirques in the vi inesdalur hofsdalur and he insdalur valleys close to holar village in the trollaskagi peninsula northern iceland boulder sampling was preceded by a study of the boulder stability with the twofold aim of ensuring that the surfaces to be sampled were stable enough for the reliable application of cre dating and to better understand the relation between the glacier dynamics and exposition history the results show that the glaciers which occupy the valleys in trollaskagi began their retreat around 16 ka later the glaciers advanced again around 11 ka within the cirques and small moraines were formed thereafter these small glaciers retreated and evolved into rock glaciers as debris from paraglacial processes accumulated on the glacier surface the fronts of these rock glaciers stabilized definitively shortly after their formation and became eventually fossil after the melting of their internal ice new rock glaciers and debris covered glaciers formed afterwards which still have internal ice at present although their current dynamics are mostly related to subsidence the stabilization of these rock glaciers and debris covered glaciers is dated to the period between 7 and 3 ka although they may have been reactivated during cold neoglacial periods this research demonstrates the potential interest in applying cre dating methods to debris covered glaciers and rock glaciers to determine their origin evolution and phase of cessation of internal movement until they finally lost their internal ice and became fossil

in situ produced 10be measurements at great depths implications for production rates by fast muons in situ cosmogenic 10be values have been used to investigate a brazilian quartz vein from the surface to a depth of 15 m at depths greater than 1000 g cm2 deep enough for neutron induced reactions to be insignificant there is only a slight decrease in 10be concentration with increasing depth our results are consistent with deep production of 10be by a mechanism presumably induced by fast muons with an attenuation length of 5300 950 g cm2 and a contribution of 0 65 0 25 to the total surface production results are compared with values from the literature and implications of this re evaluation are discussed

chronological constraints on processes leading to large active landslides abstract cosmic ray exposure dating of gravitational scarps along a slope nesting a presently active landslide la clapiere landslide tinee valley argentera massif se france reveal successive periods of gravitational destabilization an initial gravitational destabilization at 10 3 0 5 10 be ka occurs more than 3000 yr after the end of the last deglaciation of the tinee valley dated in the studied area from stoss and lee topography sampled along the tinee and its tributary rabuons valleys a second gravitational destabilization is well constrained at 7 1 0 5 10 be ka through the dating of two gravitational scarps although coincidental with the so called climatic optimum other local or regional triggering factors may be invoked a third evidenced gravitational destabilization occurred 2 3 0 5 10 be ka ago this study thus demonstrates that in situ produced cosmogenic 10 be allows establishing the chronology of gravitational destabilization leading to present major active landslides however in the present case deciphering between the various possible triggering factors will necessitate similar studies on other landslides inside the alpine arc

fractal analysis of sn w mineralization from central iberia insights into the role of fracture connectivity in the formation of an ore deposit sampling of late hercynian quartz veins from central iberia has demonstrated a power law distribution of vein thickness which changes systematically from unmineralized to mineralized sites these changes are related to the connectivity of the underlying vein networks and hence their potential role in sn w mineralizing processes simple percolation models are used to explain these changes thus the analysis of vein thickness distribution provides an additional guide to prospecting in vein systems

cosmogenic chlorine 36 from calcium spallation calcium is a major target element for cosmogenic 36cl production consequently 36cl rapidly reaches detectable levels in minerals such as calcite and calcium feldspar exposed at the earth s surface spallation of calcium isotopes typically accounts for 80 90 of 36cl production in these minerals with subsidiary contributions from negative muon capture by 40ca and thermal neutron capture by 35cl to provide a basis for surface exposure dating we have calibrated cosmogenic 36cl production in calcium feldspar from the 17 300 year old tabernacle hill basalt at an altitude of 1445 m and an effective geomagnetic latitude of 40 9 the calcium spallation rate is 152 11 atoms g ca 1 a 1 the corresponding rate at sea level and high latitude is estimated at 48 8 3 4 atoms g ca 1 a 1 the muon capture rate used to derive these values is 8 8 2 2 atoms g ca 1 a 1 at the tabernacle hill site scaled from a value of 4 8 1 2 atoms g ca 1 a 1 at sea level and high latitude the calcium spallation rate determined in this study is in excellent agreement with previous whole rock calibration measurements at tabernacle hill when these are recalculated with respect to the absolute timescale the calibration of 36c1 production from calcium underpins development of an exposure dating technique for calcite due to its high calcium content the 36cl production rate in calcite is higher than in any other common rock forming mineral measurement of 36cl in calcite with an accelerator mass spectrometric detection limit of 5 103 atoms per gram allows dating of limestone surfaces exposed for periods ranging from 102 106 years alternatively erosion rates from less than 1 to greater than 1000 m per year can be determined in the case of eroding karst surfaces though the 36cl production rate is lower in calcium feldspar than in calcite measurements on this mineral will provide a useful means of dating young basalt lavas