cause of dominance by sheetflood vs debris flow processes on two adjoining alluvial fans death valley california two large adjoining alluvial fans of the panamint range piedmont death valley california are composed of different facies assemblages deposited by contrasting sedimentary processes the anvil spring fan was built solely by water flow processes incised channel floods and sheetfloods whereas the neighbouring warm spring fan has been constructed principally by debris flows the boundary between these fans delineates a sharp provincial piedmont contact between sheetflood dominated fans to the south and debris flow dominated fans to the north factors such as climate catchment area fan area catchment relief aspect vegetation types and density and neotectonic setting are essentially identical for these two fans the key difference between them is that their catchments are underlain by dissimilar bedrock types which weather to yield distinctive sediment suites weathering of the granite and andesite of the anvil fan catchment produces significant volumes of medium to very coarse sand granules pebbles cobbles and boulders but minimal silt and clay in contrast the shale quartzite and dolomite that dominate bedrock in the warm spring catchment weather to yield a wide suite of sedimentary particles spanning from clay to boulders the abundance of mud and the unsorted character of the yielded sediment cause precipitation induced slope failures in the warm spring catchment to transform readily into debris flows this propensity is due to the low permeability of the colluvial sediment which causes added water to become trapped quickly and pore pressure to rise rapidly promoting transformations to debris flows in contrast the limited volume of sediment finer than medium sand yielded from the anvil fan catchment causes the colluvium to have high permeability this factor prevents the transformation of wet colluvium to a debris flow during hydrologically triggered slope failures instead maintaining sediment transport as entrained bed load or suspended load in a water flow

structural and rheological features of the western liaoning metamorphic core complex corridor indications for late mesozoic extension of the eastern north china craton abstract the xingcheng taili ductile shear zone and yiwulushan metamorphic core complex formed during crustal extension of the eastern north china craton the ene trending xingchegn taili sinistral ductile shear zone developed along the margins of the western liaoning metamorphic core complex corridor within upper greenschist to lower amphibolite facies grade metamorphic conditions shearing was associated with two different ductile deformation events in the yiwulushan metamorphic core complex i e 1 an earlier dextral shearing and 2 later sinistral shearing the earlier dextral ductile shear zone is mainly characterized by simple shear dominated general shear with l s and ls tectonites under upper greenschist to lower amphibolite facies conditions the orientation and fabrics of l s tectonites indicate that the later ductile deformation consists of almost equally simple and pure shear and constrains a low middle temperature sinistral shear within upper greenschist facies grade conditions the estimation of rock rheological parameters from dynamically recrystallized grain sizes of quartz indicates that the high temperature shear zone has formed under lower stress conditions and higher strain rates while opposite features exist in the lower temperature shear zone the initiation of deformation of the western liaoning metamorphic core complex corridor might have started between 136 ma and 120 ma and its termination time was at ca 100 ma the ne ene strike slip ductile deformation in the western liaoning metamorphic core complex corridor within the eastern block of the north china craton was resulted from roll back of the subducting pacific plate beneath the north china craton along the eastern asian margin during early cretaceous times

uplift of the altiplano puna plateau a view from the west 1 the western flank of the central andean plateau is a crustal scale monoclinal fold expressed in the geomorphology and in the westward tilt of fore arc basin strata data from three fore arc basins quantify the magnitude and time of displacement of the plateau system relative to the fore arc from 18 30 s to 22 s there is a single monocline strand there other authors documented 2000 m 500 m of early and middle miocene structural relief growth across small scale monoclines and our data reveal 810 m 640 m of 11 5 ma relief growth and 400 m 170 m relief growth since 5 ma across a long wavelength monoclinal fold limb this structural relief growth since 11 ma approximates the topographic relief growth between the fore arc and the altiplano plateau from 22 s to 24 s there are two subparallel long wavelength monoclines structural relief on the east side of the fore arc increased by 2840 m 2510 m during 17 10 ma and by 2320 m 1050 m since 10 ma some part of this monoclinal limb rotation led to topographic uplift of the adjacent puna plateau rotation across the western monocline could have increased the altitude of the fore arc basins by 900 m since 6 ma and may result from intense heating of the eastern margin of the cold and strong atacama lithosphere block although the wavelengths of the monoclines vary along strike and through time the monoclinal style of deformation dominated the uplift history of the eastern fore arc of the central andes throughout the neogene

predictive mapping of prospectivity and quantitative estimation of undiscovered vms deposits in skellefte district sweden mapping of mineral prospectivity and assessment of undiscovered mineral deposits both aim to delineate prospective ground for mineral exploration but the latter is usually carried out exclusive of the former we propose that the spatial distribution of known mineral deposits of the type sought is the key to link mapping of mineral prospectivity and assessment of undiscovered deposits we demonstrate this proposition in regional scale mapping of prospectivity for volcanogenic massive sulphides vms deposits and estimation of undiscovered vms endowment in the skellefte district sweden the results of analyses of the spatial distribution of known vms deposits and their spatial associations with geological features are consistent with existing knowledge of geological controls on vms mineralization in the district and we used them to define spatial recognition criteria of regional scale vms prospectivity integration of layers of evidence representing spatial recognition criteria of vms prospectivity via application of data driven evidential belief functions results in a regional scale map of prospective areas occupying 15 of the district and having fitting and prediction rates of 100 we used the map of prospective areas and proxy measures for degrees of exploration based on the spatial distribution of known vms deposits in one level prediction of undiscovered mineral endowment we obtained estimates of 709 kt undiscovered cu endowment 3190 kt undiscovered zn endowment 95 mt undiscovered ore tonnage and 48 undiscovered vms deposits these estimates are slightly ca 5 on average lower than and thus corroborated by estimates obtained via radial density fractal analysis of the spatial distribution of known vms deposits therefore mineral prospectivity mapping can be a part of mineral resource assessment if the spatial distribution of discovered deposits of the type sought is considered in both predictive modeling processes

calcrete fossilisation of alluvial fans in se spain the roles of groundwater pedogenic processes and fan dynamics in calcrete development abstract dryland alluvial fans developed along the northern flanks of the sierra lisbona in the north western vera basin almeria region southeast spain display negligible amounts of incision despite distal base level lowering of 30 m by the modern drainage network the fans are of early middle quaternary age and are graded to a coeval river terrace now isolated from the modern drainage network the negligible incision is due to the encasement and fossilisation of the alluvial fans by calcrete this paper explores the reasons for such fossilisation and assesses the relative importance of pedogenic and groundwater mechanisms for calcrete formation within an alluvial fan setting a single fan was selected for detailed examination the geomorphological and sedimentological features of the fan its catchment area and their relationship to the distal river terrace were documented qualitative and semi quantitative petrographic and scanning electron microscope analyses of calcrete samples collected from transects across the fan surface and within its distal top river terrace surface enabled the style pattern and relative timing of calcrete development to be assessed calcrete fabrics comprised initial micritic grain coating cements pellets and glaebular carbonate nodules with interstitial spaces infilled by equant sparite and microsparite mosaics it is proposed that the early phases of calcrete development were dominated by pedogenic processes with increasing groundwater calcretisation over time point count data indicated increased quantities of interstitial sparite and microsparite cement within near surface proximal fan calcretes and at depth across the fan suggesting that groundwater processes played a more important role in calcrete formation in these locations the contribution of groundwater to calcrete development can be best explained by the intrinsic funnelling of groundwater from the catchment through the proximal fan head area a zone where the fan gravels are thinnest calcrete fossilisation appears to have followed a reduction in the fan catchment area as a result of rockfalls and watershed stream capture which reduced water and sediment supply to the fan and enabled surface stabilization and calcrete development to take place the reduced sediment water supply combined with calcrete fossilisation appears to have protected the alluvial fans from regional base level lowering the implications of these results for existing pedostratigraphic models of calcrete development in alluvial fans are subsequently explored

a recharge model for high altitude arid andean aquifers evidence for groundwater recharge in arid zones is mounting despite early ideas that recharge was unlikely where evaporation greatly exceeded precipitation the mechanisms and magnitude of groundwater recharge in the andes and atacama desert are not well known but the subject of current research diffuse recharge is expected to be limited to high altitude areas with coarse grained soils devoid of vegetation a recharge model for this environment is developed based on a simple soil moisture budgeting technique and the calculation of actual evaporation based on empirical studies the model is run with data for the linzor basins over 4000 m elevation at 22 2 s on the west slope of the andes it is checked against independent estimates based on the chloride mass balance cmb method and flood events measured downstream in the rio salado and found to provide robust and reliable results the results indicate that irregular and volumetrically limited amounts of diffuse recharge occur at high elevations in half of all years with a tendency to cluster during la nina episodes for the linzor basins mean annual recharge is found to be equivalent to 28 mm a 1 although no recharge occurs in years with precipitation less than 120 mm and increases proportionately with annual rainfall amounts above this limit copyright 2009 john wiley sons ltd

insights on the structural control of a neogene forearc basin in northern chile a geophysical approach abstract the comprehensive study of intramountain basins located in the coastal cordillera of the continental emergent andean forearc in northern chile enables the better understanding of the nature and evolution of the upper crustal deformation during the neogene and quaternary a case study is the extensive extensional half graben alto hospicio basin the basin is cut by the coastal cliff which exposes the deformed neogene basin fill also exposed are several structural systems some of which affect quaternary surfaces the results of the integrated geophysical surveys electromagnetic transient and gravity allow us to fully constrain the geometry of the alto hospicio basin and the lithological relationship between the subsurface geological units the structural geology analysis assesses the deformation regimes affecting the faults present in the basin and surrounding area altogether evidence a change in the deformation regime from an ew extensional deformation during the miocene pliocene to a ns compression in the quaternary as is presented in this study we suggest this deformation change is related to a small change in the convergence vector orientation during the pliocene

landscape modification in response to repeated onset of hyperarid paleoclimate states since 14 ma atacama desert chile the landscape of the hyperarid atacama desert in northern chile records extremely slow change on earth s surface disputed ages for the onset of hyperaridity range from the late paleogene through the pleistocene a long term paleoclimate record is recorded in a nonmarine basin whose fill is primarily alluvial strata for this setting the primary proxies for climate state are the mineralogical and chemical composition of soil which varies across a precipitation gradient and the landforms and deposits of alluvial fans during the most recent 15 million years five climate related landscape stages are resolved for the pampa del tamarugal sedimentary basin with each successively younger stage inset lower in the local topography than its predecessor the earliest landscape stage is expressed as a set of alluvial strata inherited from a time of arid or semi arid climate ca 14 12 ma the younger four landscape stages generated a composite long lasting exposure surface predominantly hyperarid conditions have persisted since ca 12 1 ma during which four intervals of arid to semi arid climate occurred each wet interval was short lived a million years or less whereas some of the hyperarid periods were lengthy 1 5 m y the hyperarid intervals were roughly 11 5 5 ma 4 5 4 ma 3 6 2 6 ma 2 2 1 ma and repeated intervals during the last 1 m y the onset of hyperaridity ca 12 ma likely reflects the growth of the andes mountains above a climate threshold in contrast sea surface temperature variability likely has controlled atacama paleoclimate changes since the late miocene

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

sedimentology and climatic environment of alluvial fans in the martian saheki crater and a comparison with terrestrial fans in the atacama desert abstract the deflated surfaces of the alluvial fans in saheki crater reveal the most detailed record of fan stratigraphy and evolution found to date on mars during deposition of at least the uppermost 100 m of fan deposits discharges from the source basin consisted of channelized flows transporting sediment which we infer to be primarily sand and gravel sized as bedload coupled with extensive overbank mud rich flows depositing planar beds of sand sized or finer sediment flow events are inferred to have been of modest magnitude probably less than 60 m3 s of short duration and probably occupied only a few distributaries during any individual flow event occasional channel avulsions resulted in the distribution of sediment across the entire fan a comparison with fine grained alluvial fans in chile s atacama desert provides insights into the processes responsible for constructing the saheki crater fans sediment is deposited by channelized flows transporting sand through boulder sized material and overbank mudflows sand size and finer and wind erosion leaves channels expressed in inverted topographic relief the most likely source of water was snowmelt released after annual or epochal accumulation of snow in the headwater source basin on the interior crater rim during the hesperian to amazonian periods we infer the saheki fans to have been constructed by many hundreds of separate flow events and accumulation of the necessary snow and release of meltwater may have required favorable orbital configurations or transient global warming

rapid recharge of fresh water to the halite hosted brine aquifer of salar de atacama chile we document analyze and interpret direct and rapid infiltration of precipitation to the southern margin of the salar de atacama halite hosted brine aquifer during 2 intense precipitation events in 2012 2013 we present physical geochemical and stable and radioactive isotope data to detail this influx of water the two events differ distinctly in the mechanisms of recharge the 2012 event did not produce direct precipitation onto the salar surface while the 2013 event did both events are recorded by abrupt changes in head in observation wells along the halite aquifer margin spatially distributed water levels rose by over 30 cm during the larger 2013 event consistent with remotely sensed observations of surface water extent the lithium concentration and stable isotopic composition of water indicate dilution of brine and dissolution of salt with fresh water tritium measurements of precipitation surface water and groundwater all indicate modern influx of water to the halite aquifer along the southern margin we extend these observations by examining the response of the halite aquifer as a whole to precipitation events during the period of 2000 2010 this study suggests that local recharge to the aquifer during sporadic precipitation onto the halite nucleus is an important component of the modern water budget in this hyper arid environment the rapid dissolution and salinization along the southern margin of the salar halite nucleus is aided by such precipitation events contributing a modern fresh water component to the water budget of the economically valuable lithium rich brine this article is protected by copyright all rights reserved

origin and development of theater headed valleys in the atacama desert northern chile morphological analogs to martian valley networks abstract understanding planetary landforms including the theater headed valleys box canyons of mars usually depends on interpreting geological processes from remote sensing data without ground based corroboration here we investigate the origin and development of two mars analog theater headed valleys in the hyperarid atacama desert of northern chile previous workers attributed these valleys to groundwater sapping based on remote imaging topography and publications on the local geology we evaluate groundwater sapping and alternative hypotheses using field observations of characteristic features strength measurements of strata exposed in headscarps and estimates of ephemeral flood discharges within the valleys the headscarps lack evidence of recent or active seepage weathering such as spring discharge salt weathering alcoves or vegetation their welded tuff caprocks have compressive strengths multiple times those of the underlying epiclastic strata flood discharge estimates of cubic meters to tens of cubic meters per second derived using the manning equation are consistent with the size of transported clasts and show that the ephemeral streams are geomorphically effective even in the modern hyperarid climate we interpret that headscarp retreat in the quebrada de quisma is due to ephemeral flood erosion of weak miocene epiclastic strata beneath a strong welded tuff with erosion of the tuff facilitated by vertical jointing the quebrada de humayani headscarp is interpreted as the scar of a giant landslide maintained against substantial later degradation by similar strong over weak stratigraphy this work suggests that theater headed valleys on earth and mars should not be attributed by default to groundwater sapping as other processes with lithologic and structural influences can form theater headscarps

late quaternary hydrological and ecological changes in the hyperarid core of the northern atacama desert 21 s abstract the hyperarid core of the atacama desert possesses important reserves of fossil or ancient groundwater yet the extent and timing of past hydrologic change during the late quaternary is largely unknown in situ and or short distance transported leaf litter deposits abound along relict fluvial terraces inserted within four dry and unvegetated valleys that drain into the endorheic basin of pampa del tamarugal pdt 21 s 900 1000 m one of the largest and economically important aquifers in northern chile our exceptional archive offers the opportunity to evaluate the response of low elevation desert ecological and hydrological systems to late quaternary climate variability three repeated expansions of riparian wetland ecosystems and perennial rivers occurred along the southernmost pdt basin between 17 6 14 2 ka 12 1 11 4 ka and from 1 01 0 71 ka both early and late archaic archaeological artefact are present in clear association with our fossil riparian wetland assemblages which suggests that these palaeoenvironmental changes facilitated past human occupations in the hyperarid core of the atacama desert using modern analogues we estimate that these ecological and hydrological changes were triggered by a threefold increase in rainfall along the headwaters of what are presently inactive canyons comparisons with other regional palaeoclimatic records from the central andes indicate that these changes were synchronous with the widespread pluvial stages now termed the central andean pluvial event cape 17 5 14 2 ka and 13 8 9 7 ka in addition we summarize new evidence for perennial runoff riparian ecosystems and a major human settlement during the latest holocene our findings clearly show that local hydrological changes in the pdt were coupled with precipitation variability in the adjacent eastern highlands during the late quaternary the long term dynamics of low elevation desert ecological and hydrological systems are likely driven by changes in moisture sources with one source tied to the amazon region n ne mode and the other to the gran chaco region se mode we conclude by linking enso like variability and moisture variations over the gran chaco to the three major regional scale recharge events over the last 18 ka in the pdt basin we conclude by asserting that an important portion of the groundwater resources in the pdt is indeed fossil inherited from past pluvial events we recommend that the relationship between ancient recharge together with palaeoclimate records of past headwater rainfall fluctuations should be incorporated into future water balance models and evaluation of groundwater potential in northern chile

groundwater recharge through an alluvial fan in the atacama desert northern chile mechanisms magnitudes and causes the chacarilla fan in the atacama desert is one of several formed in the late miocene at the foot of the pre andean cordillera overlying the large complex pampa tamarugal aquifer contained in the continental clastic sediments of the fore arc basin the pampa tamarugal aquifer is a strategic source of water for northern chile but there is continuing doubt over the resource magnitude and recharge during january 2000 a 1 in 4 year storm in the andes delivered a 34 million m3 flash flood to the fan apex where c 70 percolated to the underlying aquifers groundwater recharge through the fan is calculated to be a minimum of 200 l s or 6 of the long term catchment rainfall these figures are supported by hydrochemical data that suggest that recharge may be 9 of long term rainfall isotopic data suggest groundwater less than 50 years old is transmitted westward through the permeable sheetflood sediments of the fan overlying the main aquifer analysis of this and other events shows that the hydrological system is non linear with positive feedback the magnitude of groundwater recharge is dependent on climatic variations antecedent soil moisture storage and changes in channel characteristics long term declines in groundwater level may partly result from climatic fluctuations and the causes of such fluctuations are discussed copyright 2002 john wiley sons ltd

the precordilleran fault system of chuquicamata northern chile evidence for reversals along arc parallel strike slip faults abstract the chilean precordillera situated between the longitudinal valley and the western cordillera of northern chile was the site of the andean magmatic arc from the late cretaceous to the eocene oligocene boundary magmatism came to an end during the incaic tectonic phase 38 ma which caused arc normal shortening and the development of longitudinal dextral strike slip faults precordilleran fault system this magmatic arc tectonism is also related to the formation of the chuqicamata porphyry copper ore deposit as well as of other important deposits of this type in the precordillera structural investigations in and around the chuqicamata open pit mine have shown that wrench tectonics determined the kinematics of the area the n s striking west fissure which separates a 35 ma old non mineralised pluton to the west from a central late paleozoic basement ridge containing the mineralization became a sinistral fault along with other parallel faults in the area the central part is separated from similar paleozoic rocks to the east by the messabi este fault and a narrow faulted and sheared syncline of mesozoic cenozoic sediments this fault bears structures indicating dextral movements which probably are of an age that is similar to the mylonites 34 8 ma in the western pluton the dextral movements preceded the sinistral shear thus the fault system of chuqicamata displays a reversal of arc parallel shear movements according to the orientation of quartz veins in the mineralized body it is presumed that the sense of displacement of these strike slip motions reversed when mineralization started at about 32 ma during this time the stress field must have changed fundamentally the incaic phase dextral transpression is supposed to have been induced by the oblique vector of plate motion the following sinistral transtension corresponds to a time of reduced convergence rate and possibly reduced plate coupling as however the vector of plate motion remained unchanged during that time oblique subduction cannot be used as an argument for arc parallel sinistral shear movements

palaeomagnetism of the cordillera de la costa northern chile evidence for local forearc rotation abstract palaeomagnetic studies of lower jurassic to lower cretaceous volcanic plutonic and sedimentary rocks from the cordillera de la costa of northern chile indicate that there has been no significant latitudinal movement of northern chile since early cretaceous times a palaeomagnetic pole for the cordillera de la costa 63 s 187 e 95 7 7 was derived from combining the results of three studied units the la negra formation jurassic volcanics jurassic lower cretaceous granodioritic plutons and the e1 way formation hauterivian marine carbonates together with the coloso formation lower cretaceous red beds comparison with a cretaceous reference pole for the stable shield area of south america 87 s 235 e 95 2 4 indicates that 24 7 of clockwise rotation has taken place possible mechanisms for the rotation of the andean forearc in this area have been examined in relation to the kinetics of the subducting nazca and over riding south american plates the cordillera de la costa has been subjected to both compressional and extensional tectonics since the lower cretaceous major eastwardly directed thrusting in mid cretaceous and early tertiary times possibly associated with a period of oblique subduction of the nazca plate contributed to the accretion of the cordillera to the main forearc rotation may have occurred during this process in oligo miocene and later tertiary times extensional faulting possibly associated with roll back of the nazca plate led to the reactivation of the atacama fault zone and the formation of oblique extension faults in the cordillera de la costa structural rotation associated with this phase of extension could equally explain the observed palaeomagnetic results

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

sidewall ripouts in strike slip faults abstract distinctive splay fault configurations in wallrocks associated with pseudotachylyte bearing strike slip fault structures at three different localities are recognized as sidewall ripouts sidewall ripout structures occur as asymmetric doubly tapered fault bounded lenses or slabs adjacent to a dominant planar fault surface scallop shaped lens ripouts develop in isotropic or weakly anisotropic host rocks and elongate slab ripouts develop in strongly anisotropic host rocks the tapered ends of these structures consist of leading contractional p type ramp structures at a low angle to the dominant planar fault surface and trailing extensional r or x type ramp structures at higher angles to the dominant fault surface the formation of ripout structures is attributed to transient variations in the coefficient of friction that cause adhesion between fault surfaces leading to rupture of the sidewalls ripouts are interpreted as large outcrop scale examples of adhesive wear during rupture of the sidewalls developed along planar fault surfaces during slip the asymmetry of the ripout structures in these exposures allows their use as a kinematic indicator where the narrow tapered leading end points in the direction of movement of the ripout lens or slab during adhesion to the opposing fault block wall

perennial stream discharge in the hyperarid atacama desert of northern chile during the latest pleistocene abstract a large fraction of the vital groundwater in the atacama desert of northern chile is likely composed of fossil or ancient reserves that receive little or no recharge in today s hyperarid climate here we present evidence for latest pleistocene perennial streamflow in canyons from the hyperarid core of the atacama desert in northern chile fluvial terraces in the pampa del tamarugal pdt basin 21 s contain widespread fossil wood in situ roots and well preserved leaf litter deposits indicative of perennial surface flow currently absent in these channels nineteen radiocarbon dates on these deposits from four separate drainages within this endorheic basin indicate ages from 16 380 to 13 740 cal yr bp synchronous with paleolake tauca on the bolivian altiplano and other regional evidence for wetter conditions during the latest pleistocene groundwater fed riparian ecosystems and associated fluvial deposits abound today in the absence of direct rainfall in northern atacama canyons with perennial discharge our relict riparian ecosystems from the pdt basin are indicative of conditions similar to these northern canyons given that discharge was higher than present during this time we propose that these deposits represent the most important groundwater recharge events of the last 18 000 years a lesser recharge event occurred during the holocene when phreatophytic trees also grew in these drainages between 1 070 and 700 cal yr bp during the medieval climatic anomaly taken together our evidence lends further support for gradient changes in the equatorial pacific as a major driver of hydrologic change in the atacama on both centennial and millennial time scales central andes hyperaridity riparian ecosystems late quaternary fluvial terraces

alluvial fan and wetland interactions evidence of seasonal slope wetlands from the silurian of south central wales uk distal environs of the ludlow age trichrug formation from south central wales uk detail deposition on the outer fringe of an ephemeral debris flow dominated alluvial fan debrites and subordinate sheetflood deposits are interbedded with sporadic thin sandstone dominated heterolithic units deposited in shallow ephemeral ponds in the axial valley the latter slope wetland system fringed the permeable alluvial fan deposits being maintained by streamflow precipitation and ground water recharge a prolonged high water table is indicated by low chroma intervals interpreted as the result of gleying a variety of redoximorphic indicators including colour mottling and ferricrete concretions are evidence of iron mobilization and concentration associated with a seasonally fluctuating water table the slope wetlands were colonized periodically by skolithos generating organisms most likely to have been arthropods the widespread occurrence of redoximorphic indicators and ferricrete contrasts markedly with calcrete vertisols in penecontemporaneous continental deposits lower old red sandstone of the region it is likely that the alluvial fan toe area was the site of a wetland depression which maintained a high though fluctuating water table in contrast the alluvial channel reaches of the surrounding drainage network were significantly better drained with floodplains prone to wetting and drying and vertisol palaeopedogenesis

climatic and geomorphic interactions on alluvial fans in the atacama desert chile abstract alluvial fan surfaces in the atacama desert of northern chile preserve evidence of recent precipitation driven surface flows determining the hydrologic characteristics of these flows is important for understanding the effects of rare yet significant storms in the region flow reconstruction runoff analysis and comparison with climatological data yield surface activation recurrence intervals of 1 20 years for three small fans and their associated catchments proximal to iquique and antofagasta chile modeled discharges provide minimum constraints on the precipitation rates required to resurface fans in the hyper arid region and suggest that relatively short lived and intense precipitation events 1 3 h 4 mm h 1 are capable of producing surface flows that mobilize and transport the largest grains found in channelized portions of the fan surface the results of this study provide an indication of the ability of a particular storm event i e precipitation rate to activate a geomorphic surface and contribute to our understanding of the controls on surface evolution in hyper arid environments

stable isotopic and geochemical identification of groundwater evolution and recharge sources in the arid shule river basin of northwestern china stable isotopic dvsmow and 18ovsmow and geochemical signatures were employed to constrain the geochemical evolution and sources of groundwater recharge in the arid shule river basin northwestern china where extensive groundwater extraction occurs for agricultural and domestic supply springs in the mountain front of the qilian mountains the yumen tashi groundwater ytg and the guazhou groundwater gzg were ca hco3 ca mg hco3 so4 and na mg so4 cl type waters respectively total dissolved solids tds and major ion mg2 na ca2 k so42 cl and no3 concentrations of groundwater gradually increase from the mountain front to the lower reaches of the guazhou basin geochemical evolution in groundwater was possibly due to a combination of mineral dissolution mixing processes and evapotranspiration along groundwater flow paths the isotopic and geochemical variations in melt water springs river water ytg and gzg together with the end member mixing analysis emma indicate that the springs in the mountain front mainly originate from precipitation the infiltration of melt water and river in the upper reaches the lateral groundwater from the mountain front and river water in the middle reaches are probably effective recharge sources for the ytg while contribution of precipitation to ytg is extremely limited the gzg is mainly recharged by lateral groundwater flow from the yumen tashi basin and irrigation return flow the general characteristics of groundwater in the shule river basin have been initially identified and the results should facilitate integrated management of groundwater and surface water resources in the study area copyright 2015 john wiley sons ltd

discrimination of fluvial and eolian features on large ignimbrite sheets around la pacana caldera chile using landsat and srtm derived dem abstract satellite images and ground based observations were used to investigate the morphology and origin of valleys and ridges across large ignimbrite provinces around la pacana caldera n chile we studied 12 separate sites that included five different ignimbrite units that range in age from 5 6 0 5 ma to 1 35 0 15 ma over 400 features from within these study sites were quantified study sites typically have dimensions of 25 35 km measurements were made using landsat tm etm and srtm derived dem and shaded relief images morphological measurements were made of the ridges and channels including the direction of regional slope length orientation and gradient of each feature a classification of the different ignimbrite erosion influences resulting in varying landscape morphologies identified 4 landscape types fluvial eolian modified and complex we conclude that the most prevalent features are fluvial derived channels but the most distinctive are linear wind derived ridges the orientation of these ridges suggests that strong uni directional winds from the northwest have been constant over a long period of time 1 my

fabrics and geochronology of the taibai ductile shear zone implications for tectonic evolution of the qinling orogenic belt central china abstract the taibai ductile shear zone affecting the northern margin of the taibai granitic pluton which emplaced in the north qinling orogenic belt is crucial to understand the amalgamation and post collision history between the north china block and the south china block the shear sense indicators and the kinematic vorticity numbers 0 42 0 59 suggest that the taibai shear zone is an elongating general shear zone involving both sinistral shear and pure shear components the quartz lattice preferred orientations mainly indicate the activation of prism a slip system combined with rhomb a slip to prism a slip system the dynamic recrystallization of quartz is accommodated by sub grain rotation and bulging recrystallization while plagioclase mainly displays bulging recrystallization these characteristics suggest that the mylonites have experienced ductile shear deformation under greenschist facies conditions at temperatures of 400 550 c zircons from granitic mylonite yield upper and lower intercept ages of 425 4 ma and 144 1 ma respectively suggesting the protolith of the mylonite crystallized at ca 425 ma and was involved into a hydrothermal activity at ca 144 ma muscovite 40ar 39ar dating of the mylonite sample yield a plateau age of 346 5 ma and an inverse isochron age of 344 4 ma constraining the ductile shear deformation occurring during the early carboniferous time we suggest that the taibai shear zone was formed by ne sw oblique compression with top to the nw shear sense during the early carboniferous time following the n s shortening caused by collision between the north china block and south china block along the shangdan suture at ca 400 ma

mesozoic fault systems deformation and fault block rotation in the andean forearc a crustal scale strike slip duplex in the coastal cordillera of northern chile abstract in this paper we discuss the evolution and tectonic significance of the mesozoic trench parallel fault systems which affected the coastal cordillera and their relation to magmatism and crustal rotation the oldest extensional fault system separates basement from rift related late triassic and younger sedimentary units this system i subsequently developed into a wider extensional fault system which acted as the locus of magma ascent and emplacement of the coastal batholith during much of the jurassic to earliest cretaceous period this extensional fault system defined the forearc sliver during this period and was the consequence of a retreating subduction boundary during the early cretaceous c 132 125 ma the kinematics of this fault system changed to transtension ii and accommodated a major component of left lateral strike slip motion the principal fault being the atacama fault zone along which plutons continued to be emplaced the final phase of pluton emplacement within the coastal cordillera appears to be c 106 ma after which this magmatic arc and fault system was abandoned an late cretaceous arc and fault system iii developed some 20 ma later and located some 50 km to the east in what is now the central valley of northern chile this paper seeks to show that the coastal cordillera was deformed as a whole by this late cretaceous fault system iii which formed a crustal scale left lateral transpressional duplex during this deformation the thermally weakened crust was dissected into a series of large scale blocks bounded by nw trending left lateral strike slip faults which merge into a nne ssw fault zone which forms the eastern boundary to the duplex we term this eastern boundary zone the central valley fault zone cvfz and this together with the nw trending faults defines the duplex system which we refer to as a whole as the coastal cordillera fault system ccfs iii we have traced the ccfs duplex between 25 s and 29 s and suspect that it continues northward the timing of the deformation is constrained to be post 106 ma the age of coastal cordillera arc abandonment and pre tertiary based on the deformation and pluton emplacement in and along the central valley fault zone palaeomagnetic data from the fault bound blocks within the ccfs duplex indicate 35 45 of post early cretaceous clockwise rotation with no substantial latitudinal motion we suggest that the observed fault kinematics of the ccfs are consistent with this crustal scale duplex model where rotations would have occurred in response to left lateral transpression

combined use of tracer approach and numerical simulation to estimate groundwater recharge in an alluvial aquifer system a case study of nasunogahara area central japan summary in this study we simulate the spatial and temporal distribution of groundwater recharge in an alluvial aquifer system in the nasunogahara area of japan natural stable isotopes 18 o d were considered as additional calibration targets in a numerical model the reliability of the model outputs was further validated by comparing the results from the numerical simulation and an independent tracer approach the results indicated that the calibrated model can effectively simulate the spatial and temporal characteristics of the contribution ratios of recharge sources to groundwater in the nasunogahara area however the tracer approach i e end member mixing analysis provided more reliable results at point scale particularly for the estimated contribution ratios of paddy field water the precipitation in the nasunogahara area is the major recharge source its mean contribution ratio is 58 for a one year period over the entire alluvial fan river seepage is significant in the upstream area of the alluvial fan and the contribution ratio of river waters along the river channels in the upstream area increases during the wet season paddy field water is a highly important recharge source in the midstream and downstream areas of the alluvial fan and the contribution ratio of paddy field water obviously increases from dry season to wet season because of irrigation this study demonstrates that combined use of the tracer approach and numerical simulation with stable isotopes as additional calibration targets can eliminate their respective limitations and can assist in better understanding the groundwater recharge mechanism in alluvial aquifer systems

chronology stratigraphy and hydrological modelling of extensive wetlands and paleolakes in the hyperarid core of the atacama desert during the late quaternary abstract the halite encrusted salt pans salars present at low elevations in the hyperarid core of the atacama desert in northern chile are unique features of one of the driest and possibly oldest deserts on earth here we show that these landscapes were shallow freshwater lakes and wetlands during the last glacial period and formed periodically between 46 9 ka and 7 7 ka the moisture appears to have been sourced from increased andean runoff and most of our chronologies for these deposits were coeval with the central andean pluvial event 17 5 14 2 ka and 13 8 9 7 ka but we also find evidence for older as well as slightly younger wet phases these environments supported a diverse hygrophytic halophytic vegetation as well as an array of diatoms and gastropods using a regional hydrological model we estimate that recharge rates from 1 5 to 4 times present were required to activate and maintain these wetlands in the past activation in the late pleistocene was part of a regional enhancement of water resources extending from the andes downstream and through riparian corridors to the lowest and most arid portions of the desert itself this fundamentally unique environment was encountered by the earliest human explorers in the region and most likely facilitated migration and encampments on a landscape that at present lacks macroscopic life on its surface

recharge to groundwater in the turi basin northern chile an evaluation based on tritium and chloride mass balance techniques summary the turi basin contains an unconfined phreatic aquifer within the toconce formation volcano sedimentary sequence that passes eastwards under the quaternary volcanic chain and outcrops in the altiplano the phreatic aquifer is floored by impermeable welded miocene ignimbrites precipitation captured by the volcanic edifices infiltrates through high permeability soils to recharge the phreatic aquifer the hydrochemistry of the groundwater in the phreatic aquifer shows little evidence of mixing with geothermal water and therefore approximates to a closed system tritium values demonstrate that recharge is occurring under current climatic conditions and takes around 40 years to pass 10 km from recharge areas on the slopes of the volcanoes and the altiplano to the center of the basin the chloride mass balance technique has been used to quantify precipitation recharge at 15 500 m3 d 1 this is significantly less than the flow through the phreatic aquifer 58 000 86 000 m3 d 1 calculated from its physical properties and the difference is interpreted to be due to subsurface inflow through the toconce formation from the altiplano the results of this study have wider application throughout the andean hydrological environment of northern chile

stress and strain analysis of interlayer slip from fractures and minor folds by terrestrial laser scanning data abstract fracture geometry in folded strata is fundamental to stress and strain analysis and outcrop reservoir analogues the well exposed tian mu anticline which consists of interlayered micrite limestone and cherty limestone was studied in order to reveal interlayer slip mechanisms and stress and strain impacts of derived fractures and minor folds by using terrestrial laser scanning lidar data the minor folds occurring predominantly within flexible micrite limestone layers are closely related to interlayer slip and are largely affected by the lithology the secondary structures were probably formed at different times during past folding processes it is necessary to separate different joint sets and secondary folds and to then judge their ages separately this results in implications for joint research more importantly it is necessary to consider the overall strain of the primary fold or a larger area when researching the strain variations

stretch in shear zones implications for section balancing abstract the stretch s of a line in a zone of general shear deformation is given by s wsin sin where the shear zone s final to initial width ratio is w and the line s inclination to the zone boundary is before deformation and after for the special cases of simple shear and pure shear s sin sin and s2 sin 2 sin 2 respectively fisher s and sorby s formulae may be combined in a form appropriate to general shear strain cot rcot where r is the axial ratio of the irrotational component of deformation and is the shear strain for simple shear and pure shear the equation reduces to cot cot and tan rtan respectively these relationships may be used to estimate strain in exposed faulted strata or to restrict the possible geometries of inferred fault ramps in balanced geological cross sections

climatic controls on diffuse groundwater recharge in semiarid environments of the southwestern united states 1 although there is no diffuse groundwater recharge at many semiarid sites evidence for diffuse recharge exists at some locations where mean annual precipitation is much less than mean annual potential evapotranspiration particularly where soils are coarse and rainfall variable is substantial we investigate the climatic controls on diffuse recharge using a one dimensional variably saturated flow model the model is driven by a stochastic parameterization of climate that includes storm size distribution and seasonality of precipitation p and potential evapotranspiration pet constrained by data from 536 weather stations in the southwestern united states storm size distribution and seasonality determine the frequency and duration of intervals when p exceeds pet which controls the flux of water past the root zone for coarse soils climates with large infrequent storms yield recharge when exceeds 0 4 compared with 0 7 for a typical climate recharge through fine soils is insensitive to storm size and occurs at 0 8 seasonality has a stronger influence on recharge than storm size distribution and the effects are similar for coarse and fine soils recharge is relatively insensitive to rainfall seasonality in contrast the typical pet annual cycle lowers of the recharge threshold by 0 3 the relative timing of p and pet maxima is critical recharge occurs at values that are lower by 0 2 when the rainy season occurs during winter instead of summer over the range of climate and soils examined values at the recharge threshold varied from 0 2 to 0 7 therefore and alone are insufficient to predict where recharge will occur

mapping of prospectivity and estimation of number of undiscovered prospects for lode gold southwestern ashanti belt ghana in the southwestern part of the ashanti belt the results of fractal and fry analyses of the spatial pattern of 51 known mines prospects of mostly lode gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales intersections of nne and nw trending faults were likely predominantly involved in local scale structural controls on lode gold mineralisation whilst nne trending faults were likely predominantly involved in district scale structural controls on lode gold mineralisation the results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area the applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines prospects results in a one level prediction of 37 undiscovered lode gold prospects the applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines prospects result in an estimate of 40 undiscovered lode gold prospects the study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits

controls on mineral deposit occurrence inferred from analysis of their spatial pattern and spatial association with geological features in this paper point pattern analysis fractal analysis and fry analysis were employed to study the spatial pattern of known occurrences of mineral deposits of the type sought whereas distance distribution method was applied to study the spatial associations between various geological features and known occurrences of mineral deposits of the type sought in the aroroy district philippines the results of the applications of these spatial analytical techniques support a conceptual model of district scale mechanism of geologic controls on low sulphidation epithermal au mineralization which involves a more or less regular mesh of interlinked zones of extension faults fractures at and or around intersections of nnw and nw trending strike slip faults fractures integration of spatial evidential data layers representing these structural controls and surficial geochemical anomalies via knowledge guided application of data driven evidential belief functions results in delineation of prospective areas occupying about 25 of the district in which there is about 70 likelihood of undiscovered occurrences of low sulphidation epithermal au deposits

polar mohr constructions for strain analysis in general shear zones abstract the polar mohr diagram is a useful tool for strain analysis in general shear zones polar mohr diagrams for general shear zones can be constructed with the following measured data a the stretches of two line markers which were originally perpendicular to each other b the ratio of their stretches and the principal directions c the stretches in the shear direction and in the principal direction and d the stretches in any two directions with these diagrams the angle between eigenvectors v can be obtained and the kinematic vorticity number w k in the shear zone and the ratio of pure shear rate e to simple shear rate during deformation can be computed with the formulae w k cos v and w k cos cot 2e

the great atacama flood of 2001 and its implications for andean hydrology in february 2001 widespread flooding occurred throughout the atacama desert of northern chile and southern peru it was particularly severe in the rio loa basin where roads and bridges were disrupted and the town of calama inundated the instantaneous peak flow in the rio salado a tributary of the rio loa reached 310 m3 s 1 an order of magnitude higher than any previously recorded event the flood is estimated to have a return period of 100 200 years and is shown to have been caused by intense long duration rainfall in the western cordillera associated with la nina the surface water response is typical of arid areas and highly dependent on antecedent conditions but is quite different in perennial and ephemeral catchments ephemeral flood flows suffer high transmission losses recharging phreatic aquifers perennial rivers have lower runoff coefficients but baseflow levels remained high after the event for several months due to bank storage rebound and interflow extremely high energies of 3000 w m 2 were generated by the floods in the cordillera becoming less in the precordillera and downstream erosion and sediment transport were consequently highest in the upper and middle reaches of the rivers with mixed erosion deposition in the lowest reach the new insights gained from the interpretation and quantification of this event have important implications for palaeoenvironmental analysis hazard management water resource evaluation and the palaeohydrological evolution of the andes copyright 2005 john wiley sons ltd

strain and kinematic analysis in general shear zones we present a unifying theory for the development and distribution of strain markers and kinematic indicators in zones of general shear and thus provide a framework in which data previously considered contradictory may be understood rigid and deformable porphyroclast systems including and complex grains are potential indicators of both strain and flow the shapes and distribution of such porphyroclast systems may be used to distinguish among different tectonic regimes general shear is divided into two fields sub simple shear in which the rotational component of the strain is less than that for simple shear and super simple shear in which the rotational component is greater than for simple shear sub simple shear may involve narrowing or broadening of shear zones super simple shear regimes are possible in local regions such as the vicinities of deformable porphyroclasts but must be enclosed by regimes of sub simple shear the polar mohr constructions for finite deformation and flow are useful to analyze general shear in theory the hyperbolic net is employed for practical plotting of real data and derivation of the kinematic vorticity number wn this number represents the relative contributions of pure and simple shear in steady flow in nature deformation is thought to build up and decay by processes that may invalidate the assumption of constant flow regime we therefore introduce the concept of accelerating deformation and analyze the implications of non steady flow for the shearing histories of deformed objects

paleomagnetism of mesozoic rocks from the central andes of southern peru importance of rotations in the development of the bolivian orocline a paleomagnetic study has been undertaken in jurassic volcanics and cretaceous intrusions from coastal southern peru a secondary magnetization in the jurassic volcanics was identified at 21 sites from three main localities along the southern coast of peru mean virtual geomagnetic pole 59 5 n 190 1 e k 111 95 3 0 this secondary magnetization was acquired during a tectonomagmatic event that may be related to the emplacement of the peruvian coastal batholith and or to the first andean phase of compressional deformation in late cretaceous if we assume that the remagnetization is of late cretaceous age a regional counterclockwise rotation of about 20 is recorded by the forearc of southern peru from 16 s to 18 s primary remanent magnetizations recorded by the volcanics and the batholith reveal a more complex tectonic history of block rotations counterclockwise rotations of 50 to 80 are documented near the localities of chala eight sites ocona two sites and arequipa four sites preliminary results based on three sites of late permian to early triassic sediments from northern bolivia also show a large counterclockwise rotation the observed differences between the primary and the secondary magnetization indicate that large block rotations occurred prior to the acquisition of the secondary magnetization perhaps this first episode of deformation partially structured the andean chain in the central andes and induced an incipient orocline during the cenozoic a differential shortening along the chain gave the present day shape of the bolivian deflection and resulted in a counterclockwise rotation of the forearc system by about 20 as indicated by the remagnetization

structures kinematic analysis rheological parameters and temperature pressure estimate of the mesozoic xingcheng taili ductile shear zone in the north china craton abstract the ne to ene trending mesozoic xingcheng taili ductile shear zone of the northeastern north china craton was shaped by three phases of deformation deformation phase d 1 is characterized by a steep generally e w striking gneissosity it was then overprinted by deformation phase d 2 with ne sinistral shear with k feldspar porphyroclasts forming a subhorizontal low angle stretching lineation on a steep foliation during deformation phase d 3 lateral motion accommodated by ene sinistral strike slip shear zones dominated associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle to shallow crustal levels in some parts the older structures have been in turn overprinted by late stage sinistral d 3 shearing finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid l s tectonites near plane strain simple shear dominated general shear during d 3 deformation is probably of general significance the quartz c axis textures indicate prism gliding with a dominant rhomb slip and basal slip system formed mainly at low middle temperatures mineral deformation behavior quartz c axis textures quartz grain size and the kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 c dislocation creep is the main deformation mechanism at a shallow crustal level fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self similarities differential stresses deduced from dynamically recrystallized quartz grain size are at around 20 39 mpa and strain rates in the order of 10 12 to 10 14 s 1 this indicates deformation of granitic rocks in the xingcheng taili ductile shear zone at low strain rates which is consistent with most other ductile shear zones hornblende plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca 3 5 kbar and temperatures of 400 500 c within greenschist facies conditions the main d 3 deformation of the ene trending sinistral strike slip ductile shearing is related to the roll back of the subducting pacific plate beneath the north china craton

late mesozoic intracontinental deformation at the northern margin of the north china craton a case study from the kalaqin massif southeastern inner mongolia china abstract the east asian continent underwent intense crustal shortening thickening and following large scale lithospheric extension in the late mesozoic due to multiple plate convergence how to respond to the multiple plate convergence in the north china craton remains enigmatic here we undertaken structural measurements and fault kinematic analysis of the kalaqin massif in the northern part of the north china craton ncc together with new geochronological results delineate two stages of intracontinental deformation in the area 1 ne sw striking ductile sinistral shearing ds at 150 135 ma and subsequent 2 nw se ductile brittle extensional deformation de at 135 110 ma based on electron backscatter diffraction ebsd analysis of quartz c axis fabric and the characteristics of dynamically recrystallized quartz and feldspar we estimate that ductile deformation during ds and de occurred at temperatures of 400 700 c i e greenschist amphibolite facies conditions kinematic vorticity analysis shows that ds deformation was characterized by vorticity values wk of 0 72 0 87 average 0 793 corresponding to general shear with a dominant simple shear component somewhat lower vorticity values of 0 45 0 92 average 0 698 during de event indicate a dominant pure shear component we suggest that ds reflected the regional ne striking sinistral shearing represented by the tan lu fault zone combined with contemporaneous dextral transpression along the e w striking chifeng kaiyuan fault and fengning longhua fault these structures constituted a regional conjugate strike slip system in the northern edge of the ncc ds event was likely associated with the episode b of the yanshanian movement which might result from the subduction of the paleo pacific plate beneath east asia and the closure of the mongol okhosk ocean the subsequent de represents the destruction of the ncc during the early cretaceous which was likely influenced by the roll back of the paleo pacific plate and post orogenic extensional collapse of the mongol okhotsk belt

multiscale analysis of the summertime precipitation over the central andes precipitation over the central andes in south america exhibits a marked annual march with most of the rainfall concentrated during the austral summer season december february when the atmospheric circulation favors the uplifting of moist air from the lowlands to the east of the mountain range within its rainy season the central andes experiences week long rainy and dry episodes the large scale and local conditions during these episodes are investigated using satellite imagery reanalyzed atmospheric fields and in situ data despite the deep layer of conditional instability prevalent during most summertime afternoons deep convection can occur only on those days in which the mixing ratio within the local boundary layer exceeds some threshold 7gk g 21 yielding saturation of near surface air parcels rising more than 600 m above ground convective cloudiness anomalies over the central andes extend southeastward and tend to be concurrent with anomalies of opposite sign over the eastern part of the continent rainy dry episodes are also associated with anticyclonic cyclonic anomalies centered over subtropical south america that extend through the depth of the troposphere accompanied by easterly westerly wind anomalies over the central andes these anomalies are presumably forced by planetary waves originating in the southern hemisphere extratropics to gain insight into the regional processes linking the large scale and local conditions the pennsylvania state university national center for atmospheric research mesoscale model version 5 2 was used to simulate contrasting rainy and dry episodes the most marked and relevant differences are the strength and extent of diurnally varying flow over the eastern slope of the andes during the rainy simulation strong easterly winds reach the upper part of the slope by midmorning initiating an intrusion of warm and moist air high ue air originating in the eastern lowlands into the central andes in the dry case the moisture transport from the east is restricted to the eastern slope of the andes and the central andes is flooded by low ue air from the western foothills that cannot support deep convection even in the presence of localized updrafts the momentum balance based on the model output indicates that turbulent momentum mixing from aloft determined by the large scale anomalies of the upper level flow into the convective boundary layer is the leading term causing the differences in the daytime upslope flow and hence moisture transport over the upper part of the eastern side of the andes between rainy and dry simulations

sources sinks and long term cycling of iodine in the hyperarid atacama continental margin abstract the atacama region in northern chile hosts the driest desert on earth and is the world s premier iodine production province the origin of iodine enrichment in atacama is controversial and fundamentally different processes have been invoked over the years that involve marine eolian and more recently deep sedimentary fluid and groundwater sources as a result of the very limited geochemical iodine data in atacama and the western south american margin the origin of iodine enrichment in this region still remains elusive in this study we present a comprehensive survey of iodine concentrations and isotopic ratios 129i i of different reservoirs in the atacama desert of northern chile including nitrate soils supergene copper deposits marine sedimentary rocks geothermal fluids groundwater and meteoric water nitrate soils along the eastern slope of the coastal cordillera are found to have mean iodine concentrations of at least three orders of magnitude higher than the mean crustal abundances of 0 12 ppm with a mean concentration of 700 ppm soils above giant copper deposits in the central depression are also highly enriched in iodine 100 s of ppm range and cu iodide and iodate minerals occur in the supergene enrichment zones of some of these deposits further east in the precordillera jurassic sedimentary shales and limestones show above background iodine concentrations the latter averaging 50 ppm in the southern portion of the study area the highest iodine concentrations in fluids were measured in groundwater below nitrate soils in the coastal range 3 5 10 ppm and in geothermal waters 1 3 ppm along the volcanic arc although highly variable the iodine isotopic ratios 129i i of jurassic marine sedimentary rocks 300 600 10 15 nitrate soils 150 1500 10 15 and waters 215 10 15 are consistently low

geomorphological controls on soil fertility of semi arid alluvial fans a case study of the joghatay mountains northeast iran abstract alluvial fans are ideal locations to examine the effect of geomorphic processes and landforms on the soil characteristics the rate of soil development and fertility differs between active surfaces exposed to aggradation and old or relict surfaces subject to degradation the aim of this research is to evaluate the effect of landforms and processes on soil fertility based on the studies on three alluvial fans of different ages relict old and young a total of 36 soil samples were collected from these three alluvial fan surfaces the samples were gathered from different locations of fans apex and toe and landforms gully beds interfluves swales and bars and for each sample nine variables including soil texture acidity ph electrical conductivity ec total neutralizing value tnv available phosphorus ap available potassium ak total nitrogen tn total organic carbon toc and hydraulic conductivity k were measured the results show that the values of tnv ap ak tn and toc increase as clay increases in the relict and old fans the values of tnv toc tn ap ak clay and silt are higher in the interfluves than in the gully beds also in the relict and old fans the rates of clay silt toc tn and ap are higher in the apexes than in the toes in the young fan the values of most variables are higher in the toe compared to the apex the wide and relatively flat interfluves of the apex of old and relict fans have soils that are more fertile compared to the extensively entrenched surfaces of relict and old fan toes with relatively steep sloped interfluves the less fertile soils in the apex of young fan can be attributed to its coarse textured soils and also to repeated flooding and depositional processes overall this study reveals that geomorphological landforms and processes such as aggradation and degradation play an important role in the spatial variation of soil fertility