late miocene holocene canyon incision in the western altiplano northern chile tectonic or climatic forcing abstract major fluvial incision 600 1000 m affecting the coastal cordillera and central depression of northern chile is analysed to evaluate supposed coeval uplift of the altiplano and or climatic changes in the atacama desert the timing of the beginning of incision is constrained by the age of deposition of the central depression top in the north 18 19 s this top corresponds to fluvial gravels accumulated between 11 9 0 6 ma and 8 3 0 5 ma which are genetically related to semiarid climate and to an eastward poorly dissected parallel drainage network that developed between 15 0 0 6 and 11 2 0 6 ma thus gravel deposition ended at 11 9 11 2 ma to the south 19 20 s the central depression top corresponds to c 6 ma alluvial deposits stratigraphically determined canyon ages and knickzone locations indicate that southward dissection began later and or developed under a regime of lower erosion capacity owing to drier climate vertical incision rate evolution is compatible with eastward knickzone migration dissection required a considerable altitude difference between ancient and present day river base levels which was achieved predominantly by basin infill on an already partially elevated bedrock therefore subsequent incision would have been triggered by local semiarid climatic periods rather than by contemporaneous surface uplift exoreic canyons occur when climatic conditions in the catchments are arid semiarid whereas endoreism is developed when these conditions in catchments are hyperarid

earthquake ground motion estimation using strong motion records a review of equations for the estimation of peak ground acceleration and response spectral ordinates abstract engineering seismology is the link between earth sciences and engineering the main input of engineering seismology in engineering design are loading conditions which must satisfy certain conditions regarding their level and frequency of occurrence during the lifetime of a structure one method for estimating these loading conditions is through equations based on strong ground motion recorded during previous earthquakes these equations have a handful of independent parameters such as magnitude and source to site distance and a dependent parameter such as peak ground acceleration pga or spectral acceleration and the coefficients in the equation are usually found by regression analysis this review examines such equations in terms of data selection accelerogram processing techniques of the strong motion records used to construct the equations the characterisation of earthquake source travel path and local site used and regression techniques employed to find the final equations it is found that little agreement has been reached in the past 30 years of ground motion estimation relation studies workers have chosen their techniques based on the available data which varies greatly with geographical region also it is noted that there is a need to include more independent parameters into ground motion estimation equations if the large uncertainties associated with such equations are to be significantly reduced the data required to do this is unfortunately scarce

an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey abstract this paper presents an attenuation relationship of peak ground acceleration pga derived from turkish strong motion data for rock soil and soft soil sites and an iso acceleration map of turkey based on this relationship for the purpose among all the three component accessible records 221 records from 122 earthquakes that occurred in turkey between 1976 and november 2003 were selected the database was compiled for earthquakes with moment magnitudes m w and pga values ranging between 4 1 and 7 5 and 20 and 806 gal and distances to epicenter considered in the database were between 5 and 100 km from the regression analysis of the data an attenuation equation of pga considering rock soil and soft soil conditions was developed the pga values predicted from the equation suggested in this study and those both from a few domestic equations and some imported equations were compared in addition an iso acceleration map of turkey was constructed using the suggested attenuation equation and considering both known active faults and epicenter locations of the earthquakes that have occurred in turkey

comment on an attenuation relationship based on turkish strong motion data and iso acceleration map of turkey by ulusay et al eng geol 74 265 291 2004 b

bounds on the viscosity coefficient of continental lithosphere from removal of mantle lithosphere beneath the altiplano and eastern cordillera 1 the rapid rise of the central andean plateau between 10 and 6 8 ma implies that mantle lithosphere including eclogitized lower crust was removed from beneath the region in that time interval we infer from that removal that the average viscosity coefficient of mantle lithosphere was quite low when removal occurred using scaling laws for the growth of perturbations to the thickness of a dense layer over an inviscid substratum rayleigh taylor instability we place bounds on the average viscosity coefficient for central andean lithosphere when compared with laboratory measurements of flow laws for olivine and eclogite the allowed range of viscosity coefficients yields bounds on the temperature of 500 800 c at the moho beneath this region and suggests that mean stresses across mantle lithosphere during continental deformation are less than 50 mpa this range of temperature is comparable with if a slightly lower than we might expect for lithosphere approximately doubled in thickness and not yet equilibrated with the doubled crustal radioactivity the mean deviatoric stress is comparable to that associated with stresses that drive plates and hence shows that lithospheric material is not too strong to prevent removal of its mantle part

erosional processes topographic length scales and geomorphic evolution in arid climatic environments the lluta collapse northern chile the lluta collapse of northern chile is one of the oldest recognizable landslides 2 5 ma in a hyperarid continental setting this paper develops a conceptual landscape evolution model of the lluta collapse and analyzes the controls of mass wasting and erosion sediment transport in channels on the topographic development the data presented here imply that high relief along a topographic scarp surface fracturing elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding 2 5 ma ago a strong seismic event then possibly resulted in the displacement of ca 26 km3 of mass subsequent modification of the landslide scar occurred by backward erosion resulting in the establishment of a dendritic drainage network and the removal of an additional ca 24 km3 of material it appears that this mass was produced by mass wasting in the headwaters and exported by high concentrated debris flows in channels in addition morphometric information suggest that whereas the geometrical development of the lluta collapse has been controlled by gravitational mass wasting the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flows

balancing crustal thickening in arcs by tectonic vs magmatic means igneous intrusions were emplaced prior to and contemporaneous with horizontal shortening of the crust in the late cretaceous to late eocene magmatic arc in north chile 21 45 22 30 s temporally changing major and trace elements of magmatic rocks from this paleo arc system chronicled gradual crustal thickening prior to and substantial crustal thickening contemporaneously with crustal shortening balanced structural cross sections indicate a minimum of 9 km of arc normal shortening that occurred simultaneously with dextral arc parallel movements accounting for orogen parallel lengthening of 10 km this shortening produced 5 4 km of tectonic crustal thickening and resulted in a minimum of 42 km late eocene andean crustal thickness temporal and spatial geochemical changes diagnostic of crustal thickening indicate that the remainder 2 6 km was accommodated by basaltic underplating at or near the base of the arc crust prior to and during transpression the ratio of tectonic to magmatic crustal thickening is 2 1 whole crustal magmatic addition rates during the 12 m y duration of arc transpression are 35 km 3 per kilometer of model arc length per million years mafic underplating may have thickened the andean crust considerably but most pre neogene crustal thickening was due to discrete episodes of tectonic shortening

denudation rates and a topography driven rainfall threshold in northern chile multiple cosmogenic nuclide data and sediment yield budgets abstract the quantification of geomorphic process rates on the outcrop and the orogen scale is important to describe accurately the interaction between the relative effects of erosion tectonics and climate on landscape evolution we report single and paired cosmogenic nuclide 10 be 26 al and 21 ne derived erosion rates and exposure ages on hillslope interfluves from the tectonically active western central andes that show a distinct spatial variation a positive correlation of erosion rates with elevation and present day rainfall rates is observed erosion rates at lower altitudes the hyperarid coastal cordillera and the western escarpment with the northern part of the atacama desert are extremely low and of the order of 10 100 cm my nominal exposure ages 1 6 my in contrast erosion rates at higher altitudes the semiarid western cordillera range up to 4600 cm my nominal exposure ages 0 02 0 1 my this latter average long term bedrock erosion rate record suggested to be coupled to an orographically controlled pattern of rainfall is also reflected in the pattern of denudation rates derived from a short term decadal record of limited sediment yield data specifically denudation rates calculated from sediment flux data are of a similar order of magnitude as erosion rates deduced from long lived cosmogenic nuclides from bedrock hillslope interfluves of the western cordillera nevertheless the production and the supply of sediment from the western andean slope are very limited analysis of multiple cosmogenic nuclides allows simultaneous determination of erosion rates and exposure ages but also reveals complex exposure histories of non bedrock samples such as boulders or amalgamated clast samples notably this study shows that saturation of nuclides usually assumed in studies where only a single nuclide is analyzed is rather the exception than the rule as revealed by erosion island plots constant erosion that started much later than the formation age of the rocks or episodic erosion by spalling can partially explain non steady state concentrations and more complicated exposure scenarios furthermore the use of multiple nuclides with different half lives allowed us to infer that no significant variations in long term erosion rates have occurred and that at the western escarpment erosion rates have been low and constant for most of the late neogene nevertheless the time intervals necessary to reach steady state concentrations for cosmogenic nuclides can be quite different from those needed for landscapes to reach steady state

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

incised channels and gully erosion in northern iberian peninsula controls and geomorphic setting abstract gully erosion has scarcely been reported in the cantabrian cordillera northern iberian peninsula even though this phenomenon is relatively frequent in this mountain range a total of 133 permanent channels with evidences of gully erosion have been mapped in a 71 8 km2 study area on the northern slope of this mountain range the underlying ordovician unit comprises quartzite sandstone and slate which are partially mantled by different surficial deposits the relief is fairly steep with average slopes of 27 and hillsides with level drops of the order of 700 m and generally vegetated by atlantic heaths a result of the degradation suffered by the natural vegetation following forest fires the mapped channels present different morphological features shallow and deep channels some of them with associated ravines and are usually related to headcut in first and second order pre existing channels although some of them are located on unchanneled hillsides with no evidence of pre existing channels moreover lower reaches of first and second order channels are often incised into bedrock a field description and morphometric study has been carried out on channels affected by gully erosion based on their cartography digital terrain models and several layers of thematic mapping this study describes some of the relations between relief factors the type of substratum and the development of gully erosion i there are robust correlations between morphometry relief and erosion intensity and ii gullying is strongly influenced by the presence of a deep regolith the erosion forms observed and the described relations suggest that gully development is associated to landsliding processes which are ultimately controlled by ground water movement through a porous regolith regional uplift and deforestation are argued to be the most likely causes of channel incision and gullying

counterclockwise rotation of late eocene oligocene fore arc deposits in southern peru and its significance for oroclinal bending in the central andes the results of a paleomagnetic study along the fore arc of southern peru 15 18 s and northern chile 18 19 s are reported from middle to late miocene ignimbrites 7 sites late oligocene to early miocene ignimbrites 72 sites paleogene sediments 20 sites and mesozoic and paleocene volcanics and intrusions 31 sites comparison of locality mean directions with expected paleomagnetic directions indicates vertical axis rotations ranging from 5 2 11 3 clockwise to 55 6 7 0 counterclockwise spatially the magnitude of counterclockwise rotations increases northward from 0 within the chilean fore arc south of 18 30 s to 45 north of 16 30 s in southern peru paleomagnetic rotations recorded in paleogene red beds decrease from late eocene to late oligocene whereas miocene ignimbrites display no evidence of rotation these new results confirm that the rotations recorded in the fore arc of southern peru were acquired at least before 15 ma and probably before 25 ma and thus prior to the late neogene shortening of the sub andes the onset of major andean shortening in the eastern cordillera during the latest eocene earliest oligocene is interpreted to have triggered the bending of the peruvian fore arc the region of the peruvian fore arc with the largest rotations appears to be the fore arc counterpart of the abancay deflection a remarkable ne sw offset in the axis of the eastern cordillera induced by a major regional preorogenic structure we underline that the abancay deflection should be seen as the northwestern boundary and therefore as a key element of the bolivian orocline

tectonic rotations within the bolivian altiplano implications for the geodynamic evolution of the central andes during the late tertiary paleomagnetic results from 61 sites in tertiary red beds and volcanic rocks from the bolivian andes allow quantification of tectonic rotations within the altiplano domain a total of 16 sites were also obtained in lower miocene ignimbrites that cover the forearc of the north chilean andes near arica in the southern altiplano lipez region a local clockwise rotation of up to 38 is recorded in lower miocene volcanic rocks farther north near the salar de uyuni there is no evidence of significant rotations counterclockwise rotations are observed in the northern altiplano the largest counterclockwise rotation 28 is found in eocene oligocene red beds tiwanaku formation along the eastern border of the corque syncline middle miocene sediments located within the center of the corque basin record a counterclockwise rotation of only 10 about 200 km north of the corque basin eocene oligocene sedimentary rocks near the locality of viacha record only 10 counterclockwise rotation paleomagnetic results in lower miocene ignimbrites from the forearc near the arica bend do not show evidence for late cenozoic rotation of the forearc these new results suggest that the 20 to 25 counterclockwise rotation of the southern peruvian forearc occurred prior to the miocene anisotropy of magnetic susceptibility ams data show a magnetic fabric mostly controlled by bedding but slight ams lineations are found almost parallel to the major regional structural trends such as fold axes the apparent relationship between tectonic rotations ams lineations and structural trends suggests that rotations occured after or during the final stage of folding paleomagnetic data obtained in paleozoic rocks show evidence of clockwise rotation of the southern sub andean ranges tectonic rotations during the neogene are mostly localized on the eastern side of the central andes the curvature of the occidental margin near arica was likely acquired prior to the last stage of andean deformation although the magnitude of the rotations may vary from one locality to the other there is a consistent pattern showing counterclockwise rotations to the north and clockwise to the south a large scale regional mechanism is needed to explain this pattern of tectonic rotations within the central andes we propose a model in which along strike segmentation of the andean foreland and indentation of the altiplano by a curved forearc are the major factors controlling tectonic rotations within the altiplano eastern cordillera and sub andean ranges

stable isotope based paleoaltimetry abstractthe quantitative estimation of paleoaltitude has become an increasing focus of earth scientists because surface elevation provides constraints on the geodynamic mechanisms operating in mountain belts as well as the influence of mountain belt growth on regional and global climate the general observation of decreasing 18o and 2h values in rainfall as elevation increases has been used in both empirical and theoretical approaches to estimate paleoelevation these studies rely on the preservation of ancient surface water compositions in authigenic minerals to reconstruct the elevation at the time the minerals were forming in this review we provide a theory behind the application of stable isotope based approaches to paleoaltimetry we apply this theory to test cases using modern precipitation and surface water isotopic compositions to demonstrate that it generally accords well with observations examples of the application of paleoaltimetry techniques to himalaya tibet and the andes are discussed

ephemeral gully erosion in southern navarra spain abstract ephemeral gully erosion is a common type of water erosion in the loamy soils formed on the miocene marls of southern navarra a study has been conducted to describe the different types of ephemeral gullies and to determine their origin evolution and importance as sediment sources three main types were identified according to their origin classic ephemeral gullies formed within the same field where runoff starts drainage ephemeral gullies collecting the runoff from another upstream area and discontinuity ephemeral gullies due to some abrupt slope change in the landscape during 2 consecutive years of normal precipitation ephemeral gully erosion has caused significant soil losses locally over 2 66 kg m 2 yr 1 which is above tolerable levels in each year one short and intense rainfall event has been responsible for almost all soil losses from ephemeral gullies the main cause of gully formation is the lack of any proper waterway for conveying water excess conventional tillage practices provoked gully occurrence while the maintenance of stubble or vegetation cover completely prevented their formation although farmers refill gullies every year they reappear at the same position if no preventive measures are taken early winter has been the most critical period for gully formation when the soil is wetter and the surface cover is scarce but a strong summer thunderstorm also caused severe gully erosion in unprotected soils two simple topographic indices based on the area and the slope of the watersheds are useful to describe total soil losses

assessing the age of relief growth in the andes of northern chile magneto polarity chronologies from neogene continental sections the andes of northern chile currently experience a phase of relief rejuvenation as indicated by valleys that are 1000 m dissected into pediplains however it has been unclear when this phase of relief enhancement started this paper discusses the use of palaeomagnetic chronologies from four sections in the taracapa region northern chile to assess this age the sections are located in distal and proximal positions sediment accumulation occurred between c 22 5 and 8 7 5 ma with a hiatus that possibly spans a time interval between c 19 5 and 11 ma the magnetic polarity chronologies suggest a preferred age between 8 0 and 7 5 ma for the time when relief growth started in proximal positions however alternative correlations suggest an age of 8 5 ma in addition the palaeomagnetic data reveal no rotation of the analysed strata suggesting a minimum age of c 22 5 ma for the tectonic block rotation south of the arica deflection

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

late miocene increase in precipitation in the western cordillera of the andes between 18 19 s latitudes inferred from shifts in sedimentation patterns modern climate in the andes is characterized by strong n s decreasing trends in precipitation rates here we use stratigraphic records to show that this pattern has been established since as early as 12 11 ma at least on the western andean margin of northern chile the stratigraphic architecture on the western andean margin documents a transition between 19 20 s latitude where matrix supported debris flow deposits shift to fluvial conglomerates between 12 11 ma the deposition of fluvial sediments has been maintained to the present north of 19 20 s while the occurrence of post 11 ma aeolian sand matrix supported breccias with conglomerate interbeds south of these latitudes implies ongoing sedimentation with less water and thus under drier conditions we relate these changes to the tectonic development of the andes existing palaeoclimate models suggest that an elevated plateau deflects the andean jet towards the south thereby focusing moisture from the equatorial atlantic to the northeastern flanks of the altiplano in addition the formation of the eastern andean foothills most likely intercepted moisture transport and shifted it farther to the east thereby keeping the western andean margin dry south of 19 20 s latitudes the sedimentological data support a strong linkage between orographic precipitation and stratigraphy whereby central andean deformation controls the distribution of available moisture on the western flank through a combination of orographic precipitation and deflection of air masses

uplift of the western altiplano plateau evidence from the precordillera between 20 and 21 s northern chile 1 we present a quantitative reconstruction of uplift of the western flank of the altiplano plateau central andes one of the largest monoclines on the earth on the basis of an analysis of tectonic structures syntectonic deposits and geophysical data uplift occurred on a west vergent slowly propagating system of high angle reverse faults merging into a joint detachment that ramps down to midcrustal levels below the plateau edge the upper ramps determine local fold geometries while the lower ramp controls large scale surface tilting and uplift at 20 s this fault system was active between 30 ma and 5 10 ma with maximum shortening rates of 0 22 mm yr between 17 and 10 ma it generated some 2600 m of surface uplift with only minor shortening of 3000 m its activity was largely synchronous to eruption of large volume ignimbrites from a midcrustal source geophysical data indicate that the fault system localized deformation at the boundary between a cool strong forearc crust and a presumably fluid rich and or partially molten zone underneath the plateau area the systematic relation between crustal melting and shortening with uplift at the western plateau margin can be traced along most of the plateau flank with a stepwise decrease in age of deformation and magmatism toward the south indicating discontinuous addition of plateau segments crustal thickening to as much as 70 km from westward underthrusting in the back arc parts of the plateau isostatically compensated the tectonic surface uplift and monocline formation with respect to a stable forearc which only reacted with minor tilting

geomorphic evidence for post 10 ma uplift of the western flank of the central andes 18 30 22 s 1 the western andean mountain front forms the western edge of the central andean plateau between 18 5 and 22 s latitude the mountain front has 3000 m of relief over 50 km horizontal distance that has developed in the absence of major local neogene deformation models of the evolution of the plateau as well as paleoaltimetry estimates all call for continued large magnitude uplift of the plateau surface into the late miocene i e younger than 10 ma longitudinal river profiles from 20 catchments that drain the western andean mountain front contain several streams with knickpoint bounded segments that we use to reconstruct the history of post 10 ma surface uplift of the western flank of the central andean plateau the generation of knickpoints is attributed to tectonic processes and is not a consequence of base level change related to pacific ocean capture eustatic change or climate change as causes for creating the knickpoint bounded stream segments observed minor valley filling alluvial gravels intercalated with the 5 4 ma carcote ignimbrite suggest uplift related river incision was well under way by 5 4 ma the maximum age of river incision is provided by the regionally extensive approximately 10 ma el diablo altos de pica paleosurface the river profiles reveal that relative surface uplift of at least1 km occurred after 10 ma

fault related folding drainage network evolution and valley incision during the neogene in the andean precordillera of northern chile abstract we describe neogene drainage network development before during and after regional folding in the precordillera of the andes of northern chile 18 19 s the drainage network developed on an extensive regular erosional surface formed on oligocene miocene ignimbrites oxaya formation the folding affecting the rocks of the precordillera is represented by the oxaya anticline oa which trends n to nw is 50 km long and 30 km wide the fold is gentle west vergent and has resulted in an uplift of the hinge zone by up to 850 m it formed by the propagation on its western border of a subvertical east dipping blind reverse fault ausipar fault af the folding occurred in the middle late miocene essentially between 11 7 0 7 and 10 7 0 3 ma its maximum duration was 2 my two phases of drainage development are recognised in the precordillera an initial lower middle miocene 19 12 ma parallel drainage network is well preserved and synchronous with fluvial and lacustrine sedimentation in the central depression the network was poorly structured and attained maximum incision of to 250 50 m the minimum long term rate of incision was 36 7 m my folding generated the progressive abandonment and fossilisation of the initial parallel drainage network which became trellissed and concentrated in a few deeply incised valleys in the anticline hinge the lluta and azapa main valleys present a total incision of 1650 50 and 1605 50 m respectively whereas the cardones valley presents 595 50 m during folding river incision at the fold hinge was equal to or greater than the amplitude of the folding which is 790 50 m in the lluta valley and 715 50 m in the azapa valley consequently the long term rate of synfolding incision was much greater than 395 25 lluta valley and 358 25 m my azapa valley the cardones valley was fossilised approximately in the middle of the folding after folding 11 to 0 ma the incision in the lluta and azapa rivers was 610 100 and 640 100 m and with a rate of 56 9 and 58 9 m my respectively the postfolding incision rate is approximately twice than of the prefolding incision rate this implies an acceleration of valley incision since the late miocene which is considered as consequence of regional uplift of the andean forearc

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

paleosurfaces paleoelevation and the mechanisms for the late miocene topographic development of the altiplano plateau abstract we construct a topographic datum across the central andes between 18 s and 22 s using extensive well preserved paleosurfaces that span the entire range this datum combined with estimates of topographic change from paleoaltimetry in the altiplano and geomorphic relief generation estimates from the plateau flanks allow us to reconstruct the paleo topography of the range at 10 ma using the 10 ma topography we explore which geophysical processes can create the observed topographic change over the

late cainozoic rotation of the peruvian western cordillera and the uplift of the central andes abstract a palaeomagnetic study was carried out in the region of lima peru on 55 sites 564 cores of middle cretaceous to late miocene age distributed along three northeast southwest transverses which cross the western cordillera of the central andes over the entire studied area the results consistently yield westerly declinations corresponding to post cretaceous and post eocene counterclockwise rotations with respect to stable south america of 16 6 and 13 7 8 1 respectively when compared to the ill defined reference poles of this continent these new results are in good agreement with previous ones from the central peruvian andes and support the model recently proposed for the uplift of the andean cordillera

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

trench parallel shortening in the northern chilean forearc tectonic and climatic implications in the central andes the frictional coupling between south america and the subducting nazca plate occurs beneath the coastal cordillera of northern chile one of the most distinctive characteristics of the coastal cordillera is a suite of ew topographic scarps located between 19 and 21 6 s latitude these scarps are associated with predominantly south dipping reverse faults that have almost pure dip slip and produce shortening parallel to the plate boundary limited geochronology as well as more regional studies indicate that the scarps formed during the late miocene and early pliocene though some show activity extending into the quaternary in several areas the scarps dammed local drainages producing internally drained basins that accumulated evaporites this relationship indicates that the coastal cordillera was probably moister during the late miocene and pliocene than it is today and also indicates that the coastal cordillera has been significantly uplifted or that the coastal escarpment of northern chile has advanced significantly eastward since the pliocene the limited latitudinal extent of the ew scarps and their location symmetrically about the axis of topographic and wadati benioff zone symmetry suggest that they owe their origin to the concave seaward shape of the continental margin due to prior formation of the bolivian orocline

evolution of the west andean escarpment at 18 s n chile during the last 25 ma uplift erosion and collapse through time abstract the geological record of the western andean escarpment warp reveals episodes of uplift erosion volcanism and sedimentation the lithological sequence at 18 s comprises a thick pile of azapa conglomerates 25 19 ma an overlying series of widespread rhyodacitic oxaya ignimbrites up to 900 m thick ca 19 ma which are in turn covered by a series of mafic andesite shield volcanoes between 19 and 12 ma the surface of the oxaya ignimbrites evolved into a large monocline on the western slope of the andes a giant antithetically rotated block oxaya block 80 km 20 km formed on this slope at about 10 12 ma and resulted in an easterly dip and a reversed drainage on the block s surface morphology topography and stratigraphic observations argue for a gravitational cause of this rotation a secondary gravitational collapse 50 km3 extending 25 km to the west occurred on the steep western front of the oxaya block alluvial and fluvial sediments 11 2 7 ma accumulated in a half graben to the east of the tilted block and were later thrust over by the rocks of the escarpment wall indicating further shortening between 8 and 6 ma flatlying upper miocene sediments

size fractions resulting from an aggregate stability test interrill detachment and transport aggregate stability is a soil characteristic often linked with soil erodibility but this relationship is generally empirical the aggregate size distribution is a recognized factor in uencing crust characteristics and transport during interrill erosion events this parameter was used in this work in order to improve the understanding of the relationship between aggregate stability and erodibility a second aspect of this study was to investigate the size selectivity of interrill erosion processes i e breakdown detachment by splash and transport by overland ow this experimental work was based on rainfall simulations and aggregate stability tests which were performed using two different soils a clay loam slightly sensitive to erosion and a more susceptible silt loam size distributions of soil fragments either produced by aggregate stability tests or detached by splash or transported by runoff were measured by both wet sieving and laser diffraction sizer analysis the clay loam is particularly stable and has coarse breakdown products with mean weight diameters larger than 1400 m aggregate breakdown is more ef cient for the silt loam and leads to ner soil fragments with mean weight diameters between 229 and 380 mm for the more stable soil the clay loam splash rate and sediment concentration are respectively two and six times lower and less time variable than for the silt loam for the two soils detachment by splash and short distance transport are size selective interrill erosion processes this selectivity leads to the enrichment of silt and clay fractions of the eroded aggregates in comparison with the breakdown products the low erodibility of the more stable soil is in accordance with results of aggregate stability tests copyright 2004 john wiley sons ltd

granite magma formation transport and emplacement in the earth s crust the origin of granites was once a question solely for petrologists and geochemists but in recent years a consensus has emerged that recognizes the essential role of deformation in the segregation transport and emplacement of silica rich melts in the continental crust accepted petrological models are being questioned either because they require unrealistic rheological behaviours of rocks and magmas or because they do not satisfactorily explain the available structural or geophysical data provided flow is continuous mechanical considerations suggest that far from being geologically sluggish granite magmatism is a rapid dynamic process operating at timescales of or 100 000 years irrespective of tectonic setting

late miocene to early pliocene paleohydrology and landscape evolution of northern chile 19 to 20 s abstract northern chile s forearc lies in the hyperarid atacama desert the northern portion 150 km of the forearc basin known as the central depression contains perennial streams that drain to the pacific ocean through canyons that are deeply incised within a pediplain however during the late miocene and early pliocene a lake existed in the western part of the central depression between 19 3 s and 19 7 s indicating a forearc geomorphic landscape and paleohydrologic regime distinct from the present one for approximately 2 ma this lake was large 375 km2 and deep up to 120 m the catchment area sourcing the lake covered an area of 2900 5200 km2 new 40ar 39ar ages of volcanic ashes intercalated with the lake deposits and the overlying fluvial deposits indicate that lacustrine diatomite rich deposition had begun by 10 86 0 04 ma and the final stage of incision of a canyon through the lake deposits is younger than 3 04 0 03 ma additional published age constraints demonstrate that the expanse of the lake shrunk shortly after 9 ma yet the water balance in the western sector of the basin permitted lacustrine diatomite deposition until more recently than 6 4 ma even after the sediment hydrology balance shifted from balanced fill to overfilled a near surface groundwater table led to accumulation of salt pan salar evaporites until more recently than 3 5 ma the existence of a large deep lake is consistent with but not conclusive evidence for a wetter than modern climate in the catchment region during the late miocene the ultimate demise of the paleolake system is attributed to a kilometer scale decline of the base level of drainages downstream of the paleolake this study takes advantage of the unique characteristic of the drainage profiles in the study region a spatial separation between areas of deep incision east and west of a prominent knickzone to evaluate three end member scenarios of landscape evolution that could explain the base level fall event s the sedimentological stratigraphic and geomorphological data best fit the interpretation that forearc tectonic uplift and tectonically driven coastal retreat both contributed to base level fall

massive middle miocene gypsic paleosols in the atacama desert and the formation of the central andean rain shadow abstract the central andes of south america are one of the highest and broadest mountain ranges on earth and have a profound influence on climate in the southern hemisphere yet the timing of andean uplift and its subsequent impact on atmospheric circulation is not well known here we use fossil soils from along an 800 km transect 19 25 s in the atacama desert of northern chile to identify the initiation of extreme aridity along the west coast of south america and infer a minimum age for the development of the central andean rain shadow paleosols record the onset of extreme aridity at the boundary between the middle and late miocene 12 10 ma lower miocene 24 20 ma soils are chemically weathered and contain soil carbonate indicative of a vegetated landscape and semi arid climate in contrast gypsum dominates massive 2 5 m thick upper middle miocene soils that formed on a hyperarid landscape devoid of vegetation the development of extreme hyperaridity is linked to the formation of the central andean rain shadow through the divergence of oxygen isotope values oxygen isotope values of lower miocene soil carbonates in the atacama desert 5 0 1 1 vpdb and central andes 7 8 1 are similar indicating no or a limited rain shadow by 15 mya however 18 o values of soil carbonate differ by 8 with values of soil carbonate in altiplano paleosols getting lower due to uplift while soil carbonate values in the atacama desert get higher due to aridity therefore by 15 mya there is clear evidence for a rain shadow from the central andes by the latest middle miocene ca 12 10 ma paleosols in the altiplano decreased to 11 8 1 0 while soils in the atacama desert increase to 1 5 4 5 this almost 14 divergence in the 18 o values of soil carbonate for soils only 250 km apart is evidence of a strong central andes rain shadow effect in place during the late middle miocene 12 10 ma

slow cenozoic uplift of the western andean cordillera indicated by cosmogenic 3he in alluvial boulders from the pacific planation surface to determine the mechanisms responsible for mountain belt growth it is important to accurately establish the timing of surface uplift here we exploit the altitude control on the production rate of in situ cosmogenic nuclides to test the hypothesis that the andes was uplifted in the late miocene high concentrations of in situ cosmogenic 3he 3hecos have previously been measured in alluvial boulders on the western flank of the central andes northern chile evenstar et al 2009 these are consistent with deposition soon after formation of the surface 13 14 ma we have modeled the accumulation of cosmogenic 3he in several different surface uplift scenarios and compared them to the measured concentrations the measured 3hecos concentrations are too high to be produced by late miocene uplift and imply that the western flank of the andean cordillera attained a substantial part of its current elevation prior to 14 myr ago

consistency of geologic and geodetic displacements during andean orogenesis displacement and convergence rates inferred from gps and marine magnetic data suggest that this trend may be continuing at present hence an increasing fraction of convergence is being absorbed by mountain building this change may reflect increased plate coupling due to decreased sediment supply younger subducting lithosphere or increased normal stress at the interface from the effects of uplift index terms 8102 tectonophysics continental contract orogenic belts 8157 evolution of the earth plate motions past 3040 8158 evolution of the earth plate motions present and recent 3040 8099 structural geology general or miscellaneous

new temporal constraints on the rotation of the peruvian central andes obtained from paleomagnetism new paleomagnetic data from middle eocene to middle miocene volcanic and plutonic formations of the western cordillera of central peru document a counterclockwise rotation of 11 7 4 this rotation similar to previous results reported for the northern peruvian margin is post middle miocene in age it is thus coeval with the acceleration of the andean uplift and supports isacks model

the oxaya anticline northern chile a buckle enhanced by river incision a prominent structure in the western escarpment of the andes of northern chile is the oxaya anticline dissected at the culmination by 1500 m deep valleys the distribution of fault and fold structures indicates that the anticline could represent a simple buckle buckling thus appears to have accommodated crustal shortening in the plate overriding the subducting plate between the trench and the western cordillera cross cutting relationships between structures and dated strata indicated that the time interval of enhanced buckling coincides with the period when rates of valley formation were enhanced we thus propose that the formation of this anticline was enhanced by fluvial incision which is consistent with the results of published theoretical models

a neogene giant landslide in tarapaca northern chile a signal of instability of the westernmost altiplano and palaeoseismicity effects abstract giant landslides which usually have volumes up to several tens of km 3 tend to be related to mountainous reliefs such as fault scarps or thrust fronts the western flank of the precordillera in southern peru and northern chile is characterized by the presence of such mega landslides a good example is the latagualla landslide 19 15 s composed of 5 4 km 3 of miocene ignimbritic rock blocks located next to the moquella flexure a structure resulting from the propagation of a west vergent thrust blind fault that borders the precordillera of the central depression the landslide mass is very well preserved allowing reconstitution of its movement and evolution in three main stages the geomorphology of the landslide indicates that it preceded the incision of the present day valleys during the late miocene given the local geomorphological conditions 8 9 ma ago morphology slopes and probably a high water table large magnitude earthquakes could have provided destabilization forces enough to cause the landslide on the other hand present seismic forces would not be sufficient to trigger such landslides therefore the hazard related to them in the region is low

variability in erosion rates related to the state of landscape transience in the semi arid chilean andes we quantify erosion rates in the higher sectors of the huasco valley in the main cordillera of the semi arid andes of chile using elevation differences between three successive geomorphic markers pediments and paleo valleys and the present day valley available ar ar ages of neogene pediments are used to estimate mean erosion rates for the three periods 16 to 13 my 13 to 8 my and following 8 my the landscape of the huasco valley is in a transient state as indicated by well preserved pediment surfaces in interfluves valleys deeply incised by fluvial and glacial erosion and scarped head valleys that represent the current knickzones higher erosion rates 45 75 m my are calculated for the more recent period 8 my during which deep incision developed compared to previous periods 6 31 m my quantitative data indicate that glaciers had a much higher erosional capability than fluvial activity in the higher sectors of the main cordillera comparison with erosion rates calculated in other drainage basins of the chilean andes suggests that the variability of erosion rates depends on the landscape s transient erosive state the landscape s geomorphologic response to the uplift of the main cordillera results in the retreat of a knickzone for which retreat velocity depends on precipitation rate pattern and glacial erosion intensity copyright 2011 john wiley sons ltd

assessment of the interrill and rill contributions to total soil loss from an upland field plot abstract govers g and poesen j 1988 assessment of the interrill and rill contributions to total soil loss from an upland field plot geomorphology 1 343 354 erosion measurements were carried out on an upland field plot in the loam region of belgium the sediment being detached by splash on interrill areas is transported to the channel system mainly by interrill wash over the entire 7500 m field plot rill and gully erosion is more important than interrill erosion however the relative importance of interrill erosion varies in time and in space due to changes of the interrill surface characteristics and the activation of sidewall and gullying processes in the channel network these factors should be taken into account in a realistic rill interrill erosion model introduction at present few available field data permit the separation of rill and or gully and interrill contributions to sediment removal from arable land the scarcity of this type of field data is a major factor inhibiting the validation and fur ther development of recently developed physi cally based models describing upland erosion by water e g foster 1982 rose et al 1983 knowledge of the contribution of rill and inter rill processes to total soil loss has also some practical interest if the ratio between rill and interrill erosion were known even approxi mately it would be possible to obtain a quick estimate of total erosion by making a volumet ric recording of rill patterns plot measure

interactions between soil properties and moisture content in crust formation runoff and interrill erosion from tilled loess soils soil surface seals and crusts resulting from aggregate breakdown reduce the soil infiltration rate and may induce erosion by increasing runoff the cultivated loess areas of northwestern europe are particularly prone to these processes surface samples of ten tilled silty loamy loess soils ranging in clay content from 120 to 350 g kg 1 and in organic carbon from 10 to 20 g kg 1 were packed into 0 5 m2 plots with 5 slopes and subjected to simulated rainfall applied at 30 mm h 1 the 120 minutes rainfall events were applied to initially field moist soil air dried soil and rewetted soil to investigate the effect of soil moisture content prior to rainfall runoff and eroded sediments were collected at 5 minutes intervals aggregate stability of the soils was assessed by measuring particle size distribution after different treatments all soils formed seals runoff rates were between 70 and 90 by the end of the rainfall event for field moist plots there were large differences between soil runoff rates for the air dried and rewetted plots interrill erosion was associated with runoff and sediment concentration in runoff readily reached a steady state value measurements of aggregate stability for various treatments were in good agreement with sealing runoff and erosion responses to rainfall runoff and erosion were lower for air dried plots than for field moist plots and were either intermediate or lowest for rewetted plots depending on soil characteristics soils with a high clay content had the lowest erosion rate when they were rewetted whereas the soil with a high organic carbon content had the lowest erosion rate in air dry conditions the results indicate the complexity of the effect of initial moisture content and the interactions between soil properties and climate

observed and modelled distributions of channel and gully heads with examples from se spain and belgium abstract in soil erosion by overland flow sediment discharge is driven by discharge and gradient against the resistance of the soil and vegetation the form of the relationship which is taken as a sum of power law terms may then be inferred from several data sources 1 ephemeral gully head location 2 permanent channel head location 3 slope profile form 4 consistency with evolutionary models and 5 erosion plot data the paper focuses on 1 to 4 in order to understand how far these data constrain the form of the dependence on discharge and gradient field data from mapping a set of ephemeral gully heads after storms show a weak inverse relationship between channel head gradient and catchment area which flattens towards an upper threshold gradient of about 25 these relationships are compared with those theoretically obtained for a range of sediment transport laws which have been previously used and which are analysed to forecast both overall slope profile form and the location of stream heads the theory predicts that the location of ephemeral gully heads produced in a single storm will differ from the long term average stream head location there is a fairly good relationship between theoretical and observed locations associated with the form of the sediment transport law for a single event the location depends on storm magnitude which cannot be well defined from the data sets creating a spread of data with an envelope curve defined for the largest events the empirically acceptable sediment transport equations have also been used to analyse families of slope profiles in a small area and used within a landscape evolution model to generate landscapes which are compatible with those observed in the field and provide confirmation of the long term viability of the expressions obtained to forecast the direction style and rates of landscape evolution in response to land use or climate drivers

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

jurassic to palaeogene tectono magmatic evolution of northern chile and adjacent bolivia from detrital zircon u pb geochronology and heavy mineral provenance heavy mineral provenance data presented in this article reinforce evidence for significant late palaeogene deformation and relief formation along the western margin of the central andean plateau late eocene oligocene onset of molasse type sedimentation records initial range uplift strikingly different basement sources of sediments deposited to the east and west of the late palaeogene range indicate that initial relief development was governed by a bivergent thrust system significantly higher sediment accumulation rates to the east of the range compared to the west suggest that the generated relief acted already as an effective orographic barrier at that time higher precipitation and denudation along the eastern slope facilitated deeper erosion of the trust belt

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

scale of relief growth in the forearc of the andes of northern chile arica latitude 18 s the stream profiles of rivers of northern chile reveal two graded segments separated by 20 km long knickzones their formation was initiated in the late miocene in response to surface uplift of the western flank of the altiplano this phase of uplift that was coeval with the shift of deformation from the altiplano to the sub andean zone caused relief to grow at the scale of the whole drainage basin above and beneath these knickzones the presence of braided channels and the absence of erosion on adjacent pediplains suggest no substantial modification in the local relief the knickzones however show bedrock channels and fluvial dissection rates have exceeded erosion rates on adjacent pediplains by two orders of magnitudes hence the data imply that the only geomorphic recorders of relief growth are the knickzones that currently transpose the effects of the late miocene phase of surface uplift from the coast to the altiplano

ephemeral gully erosion in northwestern spain this study aimed to describe types of ephemeral gullies and to determine their origin evolution and importance as sediment sources in a coruna province northwest spain ephemeral gullies and or rills have been measured in a representative sample of medium textured soils most prone to crusting developed over basic schist this sample consisted of 11 small sites ranging from 0 63 to 7 34 ha a case study of concentrated rill gully erosion in a 0 47 ha catchment with coarse textured soils developed over granite was also reported the mean slope of the sites studied ranged from 6 1 to 16 8 main periods when soil surface was poorly covered were late spring maize seedbeds and late autumn early winter grassland and winter cereal seedbeds case studies where fields were left bare in winter were also investigated soil incision and channel formation were observed even with relatively low rainfall intensities when the soil surface was sealed but also after a single short intense rainfall event on recently tilled surfaces concentrated erosion took place mainly on seedbeds and newly tilled soils in late spring and by autumn or early winter but gullies also appeared in other seasons when the soil surface was left bare in most of the cases studied ephemeral gully erosion caused significant soil losses ranging between 2 and 5 m3 ha for a single season to locally over 25 m3 ha gully development was significantly affected by agricultural operations such as lineal elements often acting as initial axes of concentrated erosion main gullies tended to reappear at the same position

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

sedimentology based reconstructions of paleoclimate changes in the central andes in response to the uplift of the andes arica region between 19 and 21 s latitude northern chile we focus on the sedimentological record of the middle miocene to modern deposits in the andes of northern chile between 19 and 21 s these sediments deposited at the western escarpment of the central depression indicate successively more moisture on the western margin of the altiplano and the western cordillera where the sources are at the pacific coast 20 ma old exposure ages and salic gypsisols reflect an existing and ongoing hyperarid climate we interpret the increased divergence of climates between the coast and the altiplano as consequence of the andean rise to elevations higher than approximately 2 500 m a s l when the topography of the altiplano was sufficiently high and areally extensive to attract atlantic moisture accordingly the inferred general increase in run off was closely coupled with the uplift of the andes if the steady rise model applies in case that the rapid rise model for andean uplift is correct the inferred changes in sediment transport would have occurred independently of uplift requiring an alternative yet unknown driver

fold and thrust belt structures and strike slip faulting at the se margin of the salar de atacama basin chilean andes 1 a tectonic reinterpretation is reported for the southeastern margin of the salar de atacama basin of northern chile detailed structural mapping revealed the presence of an east vergent thin skinned fold and thrust belt affecting oligocene miocene paciencia group rocks and the overlying plio pleistocene volcanic rocks along strike segmentation of the main fold implies local foreland influence on footwall ramp geometry leading to local thrust sheet rotation to the east the adjacent western slope of the western cordillera displays two different structural domains probably controlled by preexisting basement structures the southern domain comprises two n s oriented sigmoidal belts of linear arranged pressure ridges indicating left lateral transpression in contrast the northern domain is characterized by east vergent fold and thrust belt structures and reactivated nw se striking sinistral strike slip faults governing clockwise block rotations an indenter driven deformation model is proposed to explain sinistral transpression and clockwise block rotations around vertical axes this variant of a small block rotation mechanism is discussed in the context of oroclinal bending of the central andes emphasizing the significance of ancient structures in controlling rotations

concentrated flow erosion as a main source of sediments in galicia spain knowledge of soil loss rates by water erosion under given climate soil topography and management conditions is important for establishing soil conservation schemes in galicia a region with atlantic climatic conditions in spain field observations over the last decade indicate that interrill rill and ephemeral gully erosion may be an important sediment source the aim of this work was to assess concentrated erosion rates describe types of rills and ephemeral gullies and determine their origin evolution and importance as sediment sources soil surface state and concentrated flow erosion were surveyed on medium textured soils developed over basic schists of the ordenes complex series coruna province spain from 1997 to 2006 soil surface state was characterized by crust development tillage features and roughness degree soil erosion rate was directly measured in the field concentrated flow erosion took place mainly on seedbeds and recently tilled surfaces in late spring and by autumn or early winter during the study period erosion rates were highly variable and the following situations could be distinguished a no incision or limited rill incision i e below 2 mg ha 1 year 1 b generalized rill and ephemeral gully incision in the class of mean values between 2 5 and 6 25 mg ha 1 year 1 this was the most common erosion pattern and c heavy erosion as observed during an extremely wet winter period between october 2000 and february 2001 with erosion figures that may be about ten orders of magnitude higher up to 55 60 mg ha 1 year 1 therefore low values of soil losses are dominant but also large values of rill and ephemeral gully erosion occurred during the study period copyright 2009 john wiley sons ltd

87sr 86sr of calcium sulfate in ancient soils of hyperarid settings as a paleoaltitude proxy pliocene to quaternary constraints for northern chile 19 5 21 7 s

neogene paleomagnetism and oroclinal bending of the central andes of bolivia geophysical and tectonic evidence suggests that the principal vertical axis bending of the bolivian orocline is a late cenozoic event related to subduction and andean uplift to further test this hypothesis paleomagnetic data are presented from miocene basins within the altiplano and cordillera oriental of bolivia located in the presumed southern limb of the orocline to factor out potential vgp data samples were collected from sedimentary sections spanning at least 0 5 m y new paleomagnetic data are presented for two sites i e gerdas 21 s latitude 16 15 ma and quehua 20 s latitude 13 7 ma in conjunction with previously published paleomagnetic results from middle to late tertiary rocks from bolivia and peru spanning some 16 of latitude 6 22 s a consistent pattern of oroclinal development is as follows significant counterclockwise rotation about 15 20 in the northern limb negligible rotation in the axis at the latitude of the arica deflection and significant clockwise rotation about 15 20 in the southern limb although these paleomagnetic data could represent independent mesoscale 102 to 104 km2 block rotations the preferred interpretation is that they confirm the hypothesis that a significant portion about 30 40 of the oroclinal bending occurred during the late cenozoic using the unit mean paleomagnetic declinations in the well dated sections minimum rates of oroclinal bending during the late cenozoic are calculated to range from 0 6 m y to 1 7 m y the remaining 15 20 of observed curvature of the orocline probably resulted from an earlier phase of andean deformation or may represent the shape of the ancestral andes

cenozoic stratigraphic development in the north chilean forearc implications for basin development and uplift history of the central andean margin abstract analysis of the cenozoic stratigraphic development of the forearc of northern chile between 18 s and 23 30 s allows constraints to be placed on the timing and nature of basin formation and the uplift history of the central andes chronostratigraphic charts have been constructed from 20 lithostratigraphic sections distributed throughout the forearc sections were taken from the longitudinal valley central depression calama basin salar de atacama precordillera and the western flank of the western cordillera correlation and timing of events is largely based on the presence of dated volcanic horizons in all the studied sections three chronostratigraphic units are defined based upon the presence of regional unconformities deposition of the late eocene to early miocene chronostratigraphic unit 38 19 ma commenced across an irregular unconformity surface between 38 and 30 ma with alluvial fan and fluvial sediments derived from the east interbedded with rhyolitic ignimbrites aggradation after 25 ma resulted in development of a large broad basin over much of northern chile that expanded eastwards through onlap onto basement deposition terminated around 19 ma with the development of an angular unconformity over much but not all of the study area during deposition of the early to late miocene chronostratigraphic unit 18 10 ma emergent volcanic source areas to the east provided catchments for large fluvial systems that drained westwards into endorheic ephemeral lacustrine basins fold growth affected sedimentation restricting accommodation space to small intra thrust basins in the precordillera and localised disruption and unconformity development in the longitudinal valley the late miocene to present day chronostratigraphic unit 10 0 ma followed the development of a regional angular unconformity at 10 ma sedimentation was restricted to a series of thrust bounded endorheic basins in both the central depression and the precordillera sourced from the east with volcanic activity limited to the periodic eruption of extensive ignimbrite sheets alluvial fan fluvial and lacustrine sedimentation dominated within the endorheic basins from 8 to 3 ma after development of a regional unconformity at 3 ma a change to isolated evaporite sub basins took place in the central depression with small lacustrine basins developed along the flank of the western cordillera the scale and grain size recorded in the sedimentary systems indicates that a substantial source area was located in the present day area of the western cordillera by 30 ma and that this has persisted to the present day this area also shed material eastwards into the altiplano the presence of such a topographic feature by 30 ma suggests that a significant proportion of andean uplift had occurred prior to the late miocene this important uplift phase should be incorporated into any model of andean uplift the evidence from the basin fill succession suggests that sediments accumulated in a basin developed in front of a broad monocline between 38 and 19 ma and that a transition to a thrust bounded foreland style basin took place after the development of the unconformity at 19 ma

seismic hazard map of turkey using the deterministic approach abstract because the instrumental records of turkey are far from being satisfactory for modeling the seismic hazard using the probabilistic approach an attempt was made in this study to accomplish it through the deterministic way in this regard all active faults of turkey small and large were evaluated together to obtain major fault systems then the procedure suggested by wells and coppersmith bull seismol soc am 4 1994 975 applied to those faults to obtain the maximum magnitude earthquake that they can generate to do this it was assumed that 1 3 of the total fault length would rupture to yield the maximum earthquake following that seven different attenuation relationships of the strong ground motion were utilized to calculate the maximum horizontal ground accelerations for the whole turkey at 0 2 intervals using the computer model tumdes written in basic programming language the computed peak ground acceleration pga values were contoured and the iso acceleration map based on sadigh et al seismol res lett 1 1997 180 relationship was selected as the new seismic hazard map of turkey on which the seismic zonations were determined as following pga 0 3 g zone 1 0 3 g

andean growth and monsoon winds drive landscape evolution at sw margin of south america abstract in the atacama desert the driest place on earth located at the subduction margin of the andes the landscape evolves very slowly and changes in tectonic or erosion processes remain for a long time in the memory of topography at latitude 19 30 s a threshold between exoreic and endoreic drainage regimes is clearly associated with the latitudinal gradient imposed by the modern monsoon carrying humidity from the atlantic and disposed obliquely over catchments draining the andes to the pacific we summarize the geomorphic geological and climatic data in the threshold area we then use these data to constrain numerical experiments of drainage evolution data and experimental results are consistent with the development of a flat low energy morphology close to sea level interrupted at 10 ma by tectonic uplift prevailing to the present suggesting trench ward relief growth by incorporation of the coastal atacama region to the andes mountain belt