the role of climate in the accumulation of lithium rich brine in the central andes abstract lithium rich brine within the sub surface of the salar del hombre muerto shm salt pan in the andes of northwestern argentina has a chemical and isotopic composition which is consistent with li derived from several sources the modern halite saturated lagoon li rich salts and brines formed recently and dissolution of halite which precipitated from ancient saline lakes shm lies in the closed basin that includes part of the massive cerro galan caldera which is drained by the rio los patos which is responsible for 90 of surface runoff into the salar the low li isotope composition 3 4 of this river is consistent with significant contributions of geothermal spring water as water drains through the volcaniclastic deposits which cover a large proportion of the basin li removal as indicated by decreasing li na occurs but without significant isotope fractionation this indicates a mechanism of surface sorption onto smectite or ferrihydrite rather than li incorporation into octahedral structural sites of clays these observations suggest that conditions in this high altitude desert have limited the dilution of hydrothermal spring water as well as the formation of clay minerals which jointly have allowed the li resource to accumulate rapidly changes in climate on a multi millennial time scale specifically in the hydrologic budget have resulted in solute accumulation rates that have been variable through time and decoupled li and na fluxes inflow to the salar under modern conditions has high li na 7 9 10 3 by wt with 7 li indistinguishable from basement rocks 0 3 to 6 4 while under pluvial climate conditions the li na of the saline lake was 40 times lower than the modern lagoon 0 1 0 3 10 3 compared to 10 6 13 4 10 3 with slightly higher 7 li 6 9 to 12 3 reflecting the uptake of 6 li into secondary minerals which formed under a wetter climate

paleogene synorogenic sedimentation in the altiplano plateau and implications for initial mountain building in the central andes sedimentologic data and palynological ages from paleogene clastic deposits of the northern and central altiplano plateau suggest foreland basin development in the central andes by mid paleocene time the nonmarine potoco formation 3000 6500 m thick constitutes the majority of cenozoic basin fill the potoco overlies the santa lucia formation 50 300 m thick previously dated as mid paleocene by mammal fossils and magnetostratigraphy new geochronologic data for the potoco formation include late eocene to oligocene palynomorph assemblages recovered throughout lower to upper stratigraphic levels these ages and published 40 ar 39 ar and k ar ages from overlying upper oligocene lower miocene volcaniclastic rocks indicate 1 nondeposition or greatly reduced deposition average sediment accumulation rates 10 m m y from mid paleocene to middle eocene time top santa lucia to lowermost potoco formation followed by 2 rapid deposition average sediment accumulation rates up to 500 m m y throughout late eocene and oligocene time majority of potoco formation lithofacies and paleocurrent data confirm both depositional phases a 20 100 mthick interval of superimposed paleosols in the basal potoco supports reduced sediment accumulation and low rates of subsidence during mid paleocene to middle eocene time the overlying main body of the potoco contains facies assemblages and stratigraphic architecture dominantly nonero

late quaternary climate and hydrology of tropical south america inferred from an isotopic and chemical model of lake titicaca bolivia and peru abstract a simple mass balance model provides insight into the hydrologic isotopic and chemical responses of lake titicaca to past climatic changes latest pleistocene climate of the altiplano is assumed to have been 20 wetter and 5 c colder than today based on previous modeling our simulation of lacustrine change since 15 000 cal yr b p is forced by these modeled climate changes the latest pleistocene lake titicaca was deep fresh and overflowing the latest pleistocene riverine discharge from the lake was about 8 times greater than the modern average sufficient to allow the expansion of the great paleolake tauca on the central altiplano the lake 18o value averaged about 13 smow the modern value is about 4 2 the early holocene decrease in precipitation caused lake titicaca to fall below its outlet and contributed to a rapid desiccation of paleolake tauca continued evaporation caused the 100 m drop in lake level but only a slight 1 2 increase relative to modern in 18o of early holocene lake waters this holocene lowstand level of nearly 100 m was most likely produced by a precipitation decrease relative to modern of about 40 the lake was saline as recently as 2000 cal yr b p the timing of these hydrologic changes is in general agreement with calculated changes of insolation forcing of the south american summer monsoon

palaeoenvironmental and diagenetic control of the mineralogy of upper cretaceous lower tertiary deposits of the central palaeo andean basin of bolivia potosi area abstract a study involving mainly x ray diffraction of the mineralogy of upper cretaceous and lower tertiary deposits aroifilla chaunaca el molino santa lucia and cayara formations of the andean basin in the bolivian eastern cordillera is presented this work refines environmental reconstructions based on previous sedimentological studies in the potosi basin the results including the clay mineralogy show that the sediments were deposited in a lacustrine system which suffered large variations of water level and groundwater influence the siliciclastic sediments are characterized either by abundant feldspars or analcime suggesting a perennial volcanoclastic influence tuff layers in the santa lucia formation support this interpretation the great diversity of clay minerals identified reflects both detrital influences and diagenetic overprinting although diagenetic changes are common in this sedimentary series it is still possible to identify the nature of detrital supply illite and illite smectite mixed layer clays constitute the background clay sedimentation and reflect predominantly arid climate this had already been deduced from sedimentogical and geochemical investigations however detrital kaolinite occurs in a 40 m thick interval of the el molino formation which probably embraces the k t boundary and reflects more humid conditions further work is necessary to locate more precisely this boundary in the absence of accurate biostratigraphical markers authigenic clays are also recognized in the sandstones in the basal part of the cayara formation kaolinite developed authigenically in the tuff layers of the santa lucia formation well crystallized authigenic smectite characterizes the clay fraction in addition chlorite replaces smectite in limestones beds of the el molino formation which were deposited in evaporitic environments the clay assemblages including illite and chlorite at base of the stratigraphic column aroifilla and chaunaca formations probably results from the replacement of smectitic minerals either by chlorite or illite where depth of burial reached more than 2000 m

landscape and drainage evolution during the cenozoic in the salinas grandes basin andean plateau of nw argentina abstract endorheic basins are distinctive features of the modern andean plateau these basins record thick neogene to modern evaporite successions that are considered as the onset of internal drainage and aridity some isolated older paleogene evaporites and intermontane depocenters have been also described across the argentine puna suggesting that some degree of hydrological isolation would have pre dated the main miocene pliocene plateau uplift evaporites beds however are not conclusive evidence for endorheism given that their formation depends not only on the tectonically driven paleo drainage but also on other sensitive variables as climate and salinity of the sources here we discuss the paleo drainage evolution across the eastern puna plateau at 23 24 s combining landscape numerical modeling with seismic stratigraphy seismic observations suggest an intermontane configuration as early as the late paleogene and relief formation to the east and west basin margins using different combinations of precipitation rates our landscape models allowed us to reproduce the modern elevations observed in the study region as well as published thermochronological data our results suggest that endorheism would have started in the paleogene and would have dominated most 70 of the cenozoic basin history models show the recurrence of endorheism interrupted by intermittent phases of drainage connectivity exorheism to the east foreland in the upper half eocene and the early miocene according to these results the formation of closed basins in the puna region would have pre dated the main miocene pliocene uplift stage of the andean plateau

chronology of internal drainage development and uplift southern puna plateau argentine central andes fundamental to understanding the late cenozoic evolution of the central andes is knowledge of the age that the puna altiplano plateau became a unique tectonomorphic entity within the orogen the two attributes that define the puna altiplano are 1 its average elevation of 3 km and 2 regions of high elevation that correspond spatially to regions with internal drainage the chronology of plateau uplift to elevations similar to modern ones is equivocal owing to an inability to define the absolute elevation of the plateau surface through time however because regions of the puna altiplano have nonmarine evaporites nad because such evaporites must accumulate within regions of internal drainage the chronology of these strata elucidates when the plateau became internally drained we show that for the southern puna between lat 24 and 26 s internal drainage was established between 14 1 and 24 2 ma and probably by 15 ma these results corroborate and refine other workers inferences that the puna altiplano plateau became uplifted and paleogeographically isolated from the adjacent fore arc and foreland during middle to late miocene time

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

stratigraphy and chronology of upper cretaceous lower paleogene strata in bolivia and northwest argentina integration of sequence stratigraphy magnetostratigraphy ar ar dating and paleontology considerably advances knowledge of the late cretaceous early paleogene chronostratigraphy and tectonic evolution of bolivia and adjacent areas the partly restricted marine el molino formation spans the maastrichtian and danian 73 60 0 ma deposition of the alluvial to lacustrine santa lucia formation occurred between 60 0 and 58 2 ma the widespread erosional unconformity at the base of the cayara formation is 58 2 ma this unconformity separates the upper puca and corocoro supersequences in bolivia and is thus coeval with the zuni tejas sequence boundary of north america the thick overlying potoco and camargo formations represent a late paleocene oligocene foreland fill the onset of shortening along the pacific margin at 89 ma initially produced rifting in the distal foreland santonian campanian eastward onlapping deposits indicate subsequent waning of tectonic activity along the margin significant tectonism and magmatism resumed along the margin at 73 ma and produced an abrupt increase in subsidence rate and other related phenomena in the basin subsidence was maximum between 71 and 66 ma due to the early maastrichtian global sea level high marine waters ingressed from the northwest into this underfilled basin subsidence decreased during the late maastrichtian and was low during the danian it increased again in the latest danian for which a slight transgression is recorded and peaked in the early selandian tectonism between 59 5 and 58 2 ma produced a variety of deformational and sedimentary effects in the basin and correlates with the end of emplacement of the coastal batholith the subsequent 58 2 ma major unconformity marks the onset of continental foreland basin development which extended into andean bolivia during the late paleocene oligocene interval this basin underwent internal deformation as early as eocene time in the altiplano and cordillera oriental these early structures previously assigned to the late oligocene early miocene orogeny probably accommodated observed tectonic rotations in the eocene oligocene

style and history of andean deformation puna plateau northwestern argentina topographically the puna plateau of northwestern argentina is the southern continuation of the bolivian altiplano its thickening and consecutive uplift result from the andean orogeny to better constrain the structural style and its progressive development we have studied field data topographic and satellite imagery balanced cross sections seismic reflection data kinematic analysis of fault slip data anisotropy of magnetic susceptibility ams paleomagnetic data and apatite fission track aft data across the puna plateau precambrian and paleozoic basement ranges bounded by high angle reverse faults dips 60 alternate with cenozoic intermontane basins major thrusts trend nne ssw and do not show a preferred vergence intermontane basins have various degrees of symmetry depending on the geometries and attitudes of associated thrusts as well as on the magnitudes of their offsets there is a close correlation between the surface expression of a basin and the amount of internal deformation a line balanced cross section of the puna at 25 s has yielded a cenozoic shortening of 10 15 in a direction subperpendicular to the orogen by kinematic analysis of cenozoic fault slip data we have obtained principal directions of strain rate across the puna shortening axes are subhorizontal and trend on average wnw ese n110 stretching axes are subvertical and intermediate axes are subhorizontal and trend on average nne ssw strain ellipsoids are dominantly of plane strain type and they represent dip slip thrusting from paleomagnetic and ams data shortening axes form a radial pattern around the eastern edge of the central andes the pattern is attributed to an inhomogeneous stress field reflecting the eastward convex shape of the central andean thrust front from the history of burial and uplift andean shortening reached the northeastern part of the puna in the late eocene and the adjacent eastern cordillera in the late eocene or early oligocene this shortening was presumably due to the incaic phase of the andean orogeny in the eastern part of the orogen the onset of shortening was probably guided by preexisting paleozoic and mesozoic structures so that andean deformation propagated unevenly eastward

global lithium resources relative importance of pegmatite brine and other deposits abstract previous studies of the availability of lithium for use in batteries to power electric vehicles evs have reached the generally encouraging conclusion that resources are sufficient to meet growing demand for the remainder of the 21st century however these surveys have not looked past estimates of lithium resource to the geological constraints on deposit size and composition that will allow the resources to be converted to reserves from which lithium can be produced economically in this survey we review the relevant geological features of the best characterized pegmatite brine and other types of lithium deposits and compare their potential for large scale long term production the comparison shows that the average brine deposit 1 45 mt li is more than an order of magnitude larger than the average pegmatite deposit 0 11 mt li and that brine deposits especially the large atacama chile and uyuni bolivia deposits have a much larger total lithium resource 21 6 mt li brine deposits clearly have a much greater capacity for large scale long term production than do pegmatite deposits however individual brine deposits differ considerably and successful production from one deposit does not necessarily assure success at others conversion of brine resources to reserves will depend on the degree of compartmentalization of brine reservoirs the extent to which brine can be recovered without dilution from recharge waters and degradation of salt bearing reservoir rock and whether other constituents of the brines including potassium magnesium bromine and boron restrict processing or the capacity of production to respond to changes in demand for lithium despite their smaller size and total estimated resource 3 9 mt pegmatites will remain of interest because of their wider geographic distribution and consequently lesser susceptibility to supply disruptions and their more lithium dominant compositions which might allow more flexible response to market changes some deposits will be amenable to large scale mining but significant production might also come from selective underground mining of small deposits in areas with low labor costs even the largest pegmatite deposits such as those at greenbushes australia and manono kitolo democratic republic of congo have estimated resources that are similar to only an average brine deposit for this reason continuous long term production from pegmatites will require extensive exploration and discovery of new pegmatite deposits and districts two other types of lithium deposits unusual rocks and unusual fluids have also received attention deposits consisting of rocks and minerals that are enriched in lithium by interaction with brines and hydrothermal solutions including the large jadar serbia and king valley usa deposits have estimated resources of about 3 4 mt li unusual brines in oilfields and the salton sea geothermal field usa contain an estimated 2 mt li both of these deposit types will require new processing methods but are likely to become important because of their lithium dominant compositions and relatively large size the total lithium resource in these deposits 31 1 mt li far exceeds estimated lithium demand of up to 20 mt li including consideration for recycling in all markets through 2100 the difference between these two estimates should be vied largely as a challenge rather than a comfort evaluation of the economic extractability of these resources will require large investments and result in only partial success if prices provide sufficient encouragement and exploration is sustained however lithium resources should be available for the next century

formation of internally drained contractional basins by aridity limited bedrock incision 1 low internal relief aridity and internal drainage characterize the puna altiplano plateau and the tibetan plateau and the tarim basin structurally these areas are reverse fault bounded terrains with intervening wedge top basins that store thick accumulations of sediment for millions of years orographic barriers along the margins of these basins are oriented normal to moisture bearing winds resulting in regional aridity the combination of this aridity rapid shortening and uplift rates and resistant exposed lithologies coincides with the location of these internally drained basins we hypothesize that these large internally drained areas persist indefinitely when uplift overwhelms the fluvial systems and defeats the channel network to test this hypothesis we developed models of channel defeat to examine the threshold conditions required to fragment the channel network the results of these models suggest that low erodibility rocks moderate to high uplift rates and low precipitation favor defeat of orogen traversing channels most coupled tectonic landscape development models prevent the development of internal drainage and so may overestimate the voracity of erosion in regimes that favor internal drainage profoundly influencing predicted orogenic growth patterns

early to middle tertiary foreland basin development and the history of andean crustal shortening in bolivia a 2 5 km thick succession of tertiary strata in the eastern cordillera of southern central bolivia consists of predominantly fluvial and lacustrine deposits the age of the base of the succession is middle paleocene and its upper part which is erosionally truncated is probably late oligocene early miocene the lower 50 130 m of the succession consists of interbedded fluvial sandstone and mudstone including minor paleosols of the santa lucia formation these strata are overlain by up to 50 m of pervasively pedogenically altered mudstone and sandstone in the upper part of the santa lucia formation and lower part of the impora formation that may represent much of late paleocene eocene time above the paleosol zone is a thin zone 10 m of lacustrine carbonate and clastic rocks in the uppermost impora formation and this in turn is overlain by a 2000 m thick upward coarsening succession of clastic fluvial deposits in the cayara camargo and suticollo formations paleocurrent data indicate that fluvial channels that deposited the santa lucia impora and cayara formations flowed mainly westward whereas channels responsible for the camargo and suticollo formations flowed generally eastward modal sandstone petrographic data show a long term evolution from subarkosic during santa lucia deposition to quartz arenitic during impora and cayara deposition to sublitharenitic during camargo and suticollo deposition compositions we argue that the lithofacies and sediment accumulation history of this succession are most consistent with deposition in an eastward migrating foreland basin system e mail decelles geo arizona edu critical to this interpretation is the zone of extreme stratigraphic condensation in the lower impora formation the inferred upper paleocene eocene part of the succession the abrupt decrease in sediment accumulation represented by this zone is difficult to reconcile with the leading alternative model in which continuous postrift thermal subsidence resulted in a gradual continuous decay of early tertiary sediment accumulation rates stratigraphic condensation is however consistent with passage of the forebulge through the region an interpretation that also can be reconciled with the record of foreland basin development in the altiplano to the west and gross sediment accumulation patterns in the subandean zone and modern foreland basin to the east simple flexural modeling and palinspastic reconstruction of the complete cenozoic migration history of the foreland basin system suggest that 1000 km of foreland lithosphere has been underthrust westward beneath the andean orogenic belt at the latitude of southern bolivia the amount of middle and lower crust that would have been added to the andean infrastructure is sufficient to explain the present crustal thicknesses in bolivia

eocene exhumation and basin development in the puna of northwestern argentina 1 the puna is part of the larger puna altiplano plateau also known as the central andean plateau characterized by high elevation low relief and aridity located in the central andes of bolivia and argentina tertiary sedimentary rocks preserved within the puna contain a unique archive of information regarding the paleogeography depositional environments and timing of sediment source exhumation during the early stages of andean mountain building the eocene geste formation in the salar de pastos grandes area within the central puna of northwestern argentina consists of deposits that are the result of confined to unconfined flows in a sandy to gravelly braided fluvial system and alluvial fans proximal to the source terrane paleocurrent data document an overall eastward flow direction up section coarsening of the geste formation suggests that topographic relief in the source area increased through time possibly owing to enhanced tectonic activity and source terrane unroofing sandstone petrography and conglomerate clast count data document quartzose and phyllitic compositions typical of ordovician rocks preserved just west of the salar de pastos grandes area paleocene eocene detrital apatite fission track age populations p1 35 52 ma p2 52 65 ma of the geste formation and their consistent trends up section suggest moderate to rapid 0 4 mm a to 1 mm a exhumation of western sediment sources during the early to mid tertiary stages of andean mountain building sedimentation rates increase up section from 0 1 mm a to 1 mm a our data when combined with other structural stratigraphic and seismic evidence from surrounding regions suggest that the geste formation was deposited in response to crustal shortening and resulting erosion and sedimentation which started as early as cretaceous in the chilean cordillera de domeyko and in the salar de pastos grandes area by eocene time the geste formation could be interpreted either as a local wedge top accumulation on the eastward propagating central andean orogenic wedge or as a local intermontane basin the similarities between wedge top deposits preserved in bolivia and eocene deposits in northwestern argentina south of 25 s lead us to favor the wedge top scenario for the geste formation if correct this implies that the deformation front of the andean orogenic wedge incorporated both thin and thick skinned structures as it migrated possibly unsteadily from the cordillera de domeyko during the cretaceous paleocene to areas within the puna and eastern cordillera by mid late eocene time contemporaneously a regional scale foreland basin system developed over an along strike distance of at least 650 km

paleozoic to early cenozoic cooling and exhumation of the basement underlying the eastern puna plateau margin prior to plateau growth 1 constraining the pre neogene history of the puna plateau is crucial for establishing the initial conditions that attended the early stage evolution of the southern extent of the andean plateau we apply high to low temperature thermochronology data from plutonic rocks in northwestern argentina to quantify the paleozoic mesozoic and early tertiary cooling history of the andean crust u pb crystallization ages of zircons indicate that pluton intrusion occurred during the early mid ordovician 490 470 ma and the late jurassic 160 150 ma lower temperature cooling histories from40ar 39ar analyses of k feldspar vary substantially basement rocks underlying the western puna resided at temperatures below 200 c 6 km depth since the devonian 400 ma in contrast basement rocks underlying the southeastern puna were hotter 200 300 c throughout the paleozoic and jurassic and cooled to temperatures of 200 c by 120 ma the southeastern puna basement records a rapid cooling phase coeval with active extension of the cretaceous salta rift at 160 100 ma that we associate with tectonic faulting and lithospheric thinning the northeastern puna experienced protracted cooling until the late cretaceous with temperatures 200 c during the paleocene higher cooling rates between 78 and 55 ma are associated with thermal subsidence during the postrift stage of the salta rift and or shortening related flexural subsidence accelerated cooling and deformation during the eocene was focused within a narrow zone along the eastern puna eastern cordillera transition that coincides with paleozoic mesozoic structural and thermal boundaries our results constrain regional erosion induced cooling throughout the cenozoic to have been less than 150 c which implies total cenozoic denudation of 6 4 km

exhumation history of the southern altiplano plateau southern bolivia constrained by apatite fission track thermochronology 1 although the structural geometry of the cenozoic altiplano puna plateau in the central andes is well defined the temporal evolution of this contractile deformation is poorly constrained to address this shortcoming we used apatite fission track thermochronology aft to quantify the cooling and exhumation history along a transect at 21 s in southern bolivia through the deformed intermontane altiplano basin the doubly vergent thrust belt of the eastern cordillera and the inner foreland thrust belt east of the plateau interandean zone thermal history modeling combined with published balanced cross sections and stratigraphic data constrain exhumation histories exhumation started during the late eocene 40 36 ma in the central eastern cordillera possibly due to bivergent thrusting and cretaceous rift structure inversion during the early oligocene 33 27 ma exhumation spread across the study area as the current boundary thrusts of the eastern cordillera were activated the inner west vergent thrust system became active in irregular order until circa 20 ma whereas the east vergent interandean thrust belt formed by eastward propagating deformation since circa 30 ma plateau exhumation continued at 0 2 mm yr until shortening terminated by 11 7 ma shortening within the plateau since circa 30 ma did not evolve by lateral accretion of thrust wedges the propagating deformation style is spatially confined to the foreland thrust belt which initiated coeval to plateau deformation interandean zone but propagated mainly after circa 10 ma subandean zone early oligocene plateau wide tectonically driven exhumation suggests that subduction related processes had already thermally weakened the continental lithosphere prior to the 27 25 ma onset of volcanic activity

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

oligocene range uplift and development of plateau morphology in the southern central andes 1 the puna altiplano plateau in south america is a high elevation low internal relief landform that is characterized by internal drainage and hyperaridity thermochronologic and sedimentologic observations from the sierra de calalaste region in the southwestern puna plateau argentina place new constraints on early plateau evolution by resolving the timing of uplift of mountain ranges that bound present day basins and the filling pattern of these basins during late eocene miocene time paleocurrent indicators sedimentary provenance analyses and apatite fission track thermochronology indicate that the original paleodrainage setting was disrupted by exhumation and uplift of the sierra de calalaste range between 24 and 29 ma this event was responsible for basin reorganization and the disruption of the regional fluvial system that has ultimately led to the formation of internal drainage conditions which in the salar de antofalla were established not later than late miocene upper eocene oligocene sedimentary rocks flanking the range contain features that suggest an arid environment existed prior to and during its uplift provenance data indicate a common similar source located to the west for both the southern puna and the altiplano of bolivia during the late eoceneoligocene with sporadic local sources this suggests the existence of an extensive longitudinally oriented foreland basin along the central andes during this time citation carrapa b d adelmann g e hilley e mortimer e r sobel and m r strecker 2005 oligocene range uplift and development of plateau morphology in the southern central andes tectonics 24 tc4011 doi 10 1029 2004tc001762

a very efficient o n implicit and parallel method to solve the stream power equation governing fluvial incision and landscape evolution abstract we present a new algorithm to solve the basic stream power equation which governs channel incision and landscape evolution in many geomorphic settings the algorithm is highly efficient because computation time increases linearly with the number of points used to discretize the landscape and is ideally suited to parallelization it is also unconditionally stable because it uses an implicit scheme for the time integration of the landscape evolution equation which means that large time steps can be used without sacrificing accuracy in this paper we describe the algorithm and present results that demonstrate its efficiency and accuracy

middle eocene deformation and sedimentation in the puna eastern cordillera transition 23 26 s control by preexisting heterogeneities on the pattern of initial andean shortening the quebrada de los colorados formation at the north end of calchaqui valley in salta province northwest argentina preserves evidence of syndepositional deformation since the middle eocene ca 40 ma that includes 1 an angular unconformity with the underlying salta group paleogene and 2 internal unconformities and changes in vertical facies succession and provenance its fossil record mammalian notoungulates middle eocene is correlatable to the casa grande formation which also unconformably overlies the salta group both units record middle eocene deformation along the eastern border of the puna plateau and outline previous fi rst order mechanical heterogeneities related to the cretaceous rift basin border along the western margin of the puna eocene deformation coincides with thermal magmatic arc and mechanical basin inversion heterogeneities thus the distribution of eocene deformation followed an irregular pattern as a consequence of the heritage of preexisting heterogeneities

cenozoic foreland basin system in the central andes of northwestern argentina implications for andean geodynamics and modes of deformation 1 cenozoic strata in the central andes of northwestern argentina record the development and migration of a regional foreland basin system analogous to the modern chaco parana alluvial plain paleocene lower eocene fluvial and lacustrine deposits are overlain by middle upper eocene hypermature paleosols or an erosional disconformity representing 10 15 myr this supersol disconformity zone is traceable over a 200 000 km2 area in the andean thrust belt and is overlain by 2 6 km of upward coarsening eastward thinning upper eocene through lower miocene fluvial and eolian deposits middle miocene pliocene fluvial lacustrine and alluvial fan deposits occupy local depocenters with contractional growth structures paleocurrent and petrographic data demonstrate westerly provenance of quartzolithic and feldspatholithic sediments detrital zircon ages from cenozoic sandstones cluster at 470 491 522 544 555 994 and 1024 1096 ma proterozoic mesozoic clastic and igneous rocks in the puna and cordillera oriental yield similar age clusters and served as sources of the zircons in the cenozoic deposits arc derived zircons become prominent in oligo miocene deposits and provide new chronostratigraphic constraints sediment accumulation rate increased from 20 m myr during paleocene eocene time to 200 600 m myr during the middle to late miocene the new data suggest that a flexural foreland basin formed during paleocene time and migrated at least 600 km eastward at an unsteady pace dictated by periods of abrupt eastward propagation of the orogenic strain front despite differences in deformation style between bolivia and northwestern argentina lithosphere in these two regions flexed similarly in response to eastward encroachment of a comparable orogenic load beginning during late paleocene time

andean growth and the deceleration of south american subduction time evolution of a coupled orogen subduction system article i nfo present day orography at the andean margin is a result of isostasy tectonic accretion and erosional processes the resulting excess mass of the andes gives rise to frictional stresses on the seismogenic plate interface that resist the sinking of the subducting slab into the upper mantle thus subduction rates should be sensitive to the time dependent dynamics of a back arc orogen as well as erosional or accretional processes that affect orogen growth here we develop a two dimensional coupled orogen slab model that allows for the prediction of orogen size and plate motion in response to both tectonic and erosional forcing we find that the frictional force exerted by the orogen on the subducting slab grows quadratically with orogen width and that the frictional resistance typically balances 10 50 of the slab pull force the time evolution of the coupled orogen subduction zone system is largely controlled by the rate of orogen growth which is controlled by the rate of convergence and the erosivity of the climate state in the case of the andean margin our models show that miocene aridification leads to reduced erosion increased orogen growth greater frictional resistance to subduction and ultimately to a 50 reduction in the convergence rate between the nazca and south american plates

the origin of brines and salts in chilean salars a hydrochemical review abstract northern chile is characterized by a succession of north south trending ranges and basins occupied by numerous saline lakes and salt crusts collectively called salars fossil salt crusts are found to the west in the extremely arid central valley while active salars receiving permanent inflows fill many intravolcanic basins to the east in the semiarid cordillera sea salts and desert dust are blown eastward over the cordillera where they constitute an appreciable fraction of the solute load of very dilute waters salt content evaporative concentration of inflow waters leads to sulfate rich or calcium rich near neutral brines alkaline brines are almost completely lacking the alkalinity calcium ratio of inflow waters is lowered by the oxidation of native sulfur reducing alkalinity and the deposition of eolian gypsum increasing ca concentration theoretically so4 rich inflow waters and their derived so4 rich brines should be found in the intravolcanic basins of the cordillera because of the ubiquity of native sulfur while ca rich brines should prevail in sedimentary basins where ca rich minerals are abundant this relation is perfectly observed in the salar de atacama the largest in chile however several salars located within the volcanic cordillera belong to the ca rich group inflows and brines may have acquired their ca rich composition in pleistocene time when their drainage basins were mainly sedimentary later on recent lava flows and ignimbrites covered the sedimentary formations underground waters may have kept their early sedimentary signature by continuous recycling however the weathering of volcanic rocks tend to slowly shift the water compositions from the ca rich to the so4 rich type

rise of the andes the surface uplift of mountain belts is generally assumed to reflect progressive shortening and crustal thickening leading to their gradual rise recent studies of the andes indicate that their elevation remained relatively stable for long periods tens of millions of years separated by rapid 1 to 4 million years changes of 1 5 kilometers or more periodic punctuated surface uplift of mountain belts probably reflects the rapid removal of unstable dense lower lithosphere after long term thickening of the crust and lithospheric mantle

processes of oscillatory basin filling and excavation in a tectonically active orogen quebrada del toro basin nw argentina intramontane basins may act as important sediment storage areas serve as recorders of the history of deformation record syntectonic deposition and document the evolution of climatic conditions during deposition we document the timing cyclicity and processes that led to the filling and reexcavation of the intramontane quebrada del toro basin in nw argentina geomorphic and geologic observations indicate that the basin was filled with sediment that has been subsequently excavated at least two times in the last 8 m y the last filling and excavation cycle occurred within the last 0 98 m y and has led to the deposition and removal of 61 4 km 3 of material from the basin leading to a basin wide averaged minimum denudation rate of 0 16 mm yr aggradation within the basin took place due to channel steepening of the downstream fluvial system that connects the intramontane basin to the foreland this portion of the fluvial system is actively incising through an uplifting bedrock zone we use observations within the toro to test a quasi physically based model of channel aggradation behind a rising base level that rises due to downstream channel steepening our work shows that the bedrock incision rate constant required to reproduce conditions observed within the toro basin is consistent with values measured independently in similar rock types therefore in intramontane basins that experience similar processes of filling and evacuation this model may be used to assess the relative importance of tectonic rock uplift bedrock resistance to fluvial incision and climate in determining the geomorphic and sedimentologic history of these basins

discharge discharge variability and the bedrock channel profile long term bedrock incision is driven by daily discharge events of variable magnitude and frequency with ineffective events below an incision threshold we explore theoretically how this short term stochastic behavior controls long term steady state incision rates and bedrock channel profiles combining a realistic frequency magnitude distribution of discharge with a deterministic detachment limited incision model in which incision rate is a power function of basal shear stress above a critical shear stress our model predicts a power law relationship between steady state slope and drainage area consistent with observations the exponent of this power law is independent of discharge mean and variability while the amplitude factor which controls mountain belt relief is a power law function of mean runoff with an exponent of 0 5 and a complex function of runoff variability in accordance with evidence that incision occurs between 6 and 20 of time in rapidly incising rivers 1 mm yr our model predicts that channel steepness is virtually insensitive to runoff variability runoff variability can only decrease channel steepness for very slow incision rates and or weak lithologies the relationship between channel steepness and incision rate is always a power law whose exponent depends on the channel cross sectional geometry and runoff variability this contradicts models neglecting discharge stochasticity in which the steepness incision scaling is set by the incision law exponent our results suggest that changes in climate variability cannot explain an increase in bedrock incision rates during the late cenozoic within the context of a detachment limited model

uplift of the central andes of nw argentina associated with upper crustal shortening revealed by multiproxy isotopic analyses this study contributes to the uplift history of the andes which has received increasing attention in recent years because of its implications for geodynamic models and climate feedbacks shortening resulting in crustal thickening and removal of gravitationally unstable mantle lithosphere has been proposed to control deformation and uplift of cordillera type orogenic systems such as the puna plateau of the central andes and its eastern margin the eastern cordillera we present new clumped isotope 47 18o and 2 data from carbonate nodules marlstone spring deposits and volcanic ashes from the puna plateau and eastern cordillera of nw argentina when combined with other geological evidence our data indicate that the puna plateau was near its present elevation since at least 10 ma whereas the eastern cordillera rose 1 5 km between 14 and 7 ma this history of uplift correlates with active shortening in the eastern cordillera and with incorporation of a regional foreland into the propagating orogenic wedge our study suggests that the elevation of the puna plateau changed little during the miocene pliocene whereas the margin experienced significant uplift associated with active deformation and crustal thickening

andean uplift and climate change sedimentological data indicate that a semi arid arid climate prevailed across the central andes from 15 ma to 4 ma between 4 and 3 ma a switch to hyperaridity occurred along the western margin of south america palaeoaltitude data suggest that a substantial proto central andean mountain range was in place between 15 and 9 ma these data support the idea that the andean rain shadow existed by 15 ma and that it reinforced the pre existing climatic regime rather than changing it the change to hyperaridity in western south america is attributed to a combination of global climate cooling and enhanced upwelling of the humboldt current generated by closure of the central american seaway between 3 5 and 3 ma and not to the andean rain shadow

giant evaporite belts of the neogene central andes large volumes of continental evaporites accumulated within the central andes during neogene uplift of the altiplano puna plateau and development of the andean volcanic arc halite and gypsum are dominant minerals along with local and economically important borates playa conditions have existed since ca 15 ma halite and borate deposition has occurred for the past 7 to 8 m y evaporites formed in salar environments e g playa lakes and are characterized by complex mineral assemblages occurrence zonation and geochemistry evaporite deposition was controlled by volcanism geothermal activity closed drainage and climate these andean deposits and their controls differ from evaporites in other continental and marine environments

on the incorporation of drains into three dimensional variably saturated groundwater flow models subsurface drains are important features in many problems involving shallow groundwater flow and have generally been represented in two dimensional numerical models by specifying hydraulic head or fluid flux at one or more nodes in the computational grid here we describe a new approach for representing drains in three dimensional variably saturated flow models the method is based on a one dimensional flow equation for the drain which is analogous to a one dimensional open channel flow equation the numerical contributions to the system of global equations from the one dimensional discretized equation are added to the three dimensional porous medium contributions the inclusion of drain flow by this technique is readily adaptable to any three dimensional numerical simulator the accuracy of the method is demonstrated by comparing results obtained with the new method to steady state and transient results presented by fipps et al 1986 the numerical formulation naturally accommodates flow in heterogeneous media and demonstrates excellent mass balance illustrative examples are presented which highlight the usefulness of the algorithm for studying the influence of drains in problems involving subsurface effluent disposal in heterogeneous aquifers and agricultural land drainage the method will have application to many studies involving water and contaminant movement in drained soils

sedimentary aspects and paleoenvironmental evolution of a rift basin salta group cretaceous paleogene northwestern argentina the rift history of the salta basin is related to the evolution of the central andes and to the activity of the pacific margin owing to its geographic location sedimentation occurred from the neocomian to the paleogene with deposits reaching up to 5 000 m in thickness paleoenvironmental analysis reveals an evolutionary history controlled by tectonic and climatic changes isolated grabens characterized the early synrift stage differential subsidence provoked distinct environments in the southern and northern subbasins in the southern subbasins alluvial fan fluvial fan and lacustrine deposits prevail whilst in the northern subbasins eolian and fluvial environments dominate during the maastrichtian two major factors controlled the basin fill the decrease in tectonic subsidence and a relative sea level rise as recorded in south america an extensive and shallow atlantic marine ingression installed a carbonate system coincident with mainly humid conditions until the danian until the middle eocene the fluvial and lacustrine environmental evolution of the sag basin was controlled especially by the alternation of temperate with dry and humid periods paleontological records reflect these climatic changes and show their relationship to the sedimentation regime