analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers sloping coastal aquifers in reality are ubiquitous and well documented steady state sharp interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the dupuit forchheimer approximation specifically analytical solutions based on the constant flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone analytical solutions for the constant head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant flux inland boundary it is found that for the constant flux inland boundary the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types despite that the geometry of the bottom confining layer determines the location of the interface tip this is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary so the shape of the bed below the interface is irrelevant to the interface position moreover developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable density flow numerical modelling analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer this article is protected by copyright all rights reserved

crossing the several scales of strain accomplishing mechanisms in the hinterland of the central andean fold thrust belt bolivia depictions of structures at outcrop regional and tectonic scales enforce horizontal shortening and vertical thickening as the predominant style of deformation at all scales within the hinterland of the central andean fold thrust belt outcrop scale structures document a progression of strain that created 1 flexural slip folds 2 fold flattening via axial planar cleavage 3 vertical stretching via boudinage and late stage faulting and finally 4 kink folding these examples of intraformational deformation are generally concentrated just beyond the tip lines of thrust faults where fault propagation folds and related structures are well developed fault propagation folding accommodated the accrual of strain indicated by outcrop scale structures while the structures themselves indicate how deformation developed within each individual fold fault propagation fold geometries at a regional scale emerge from the construction of regional balanced cross sections the sections were drawn with careful attention to 1 known map relationships 2 field inspection of key contacts 3 bedding orientation data 4 local seismic control and 5 principles of balance the pervasive ese wnw shortening and vertical elongation seen at the outcrop and regional scales developed during the formation of the central andean backthrust belt in the hinterland of the andes the central andean backthrust belt is a large scale west vergent thrust system along the western side of the eastern cordillera in the generally east vergent andean fold thrust belt of bolivia strain accrual within this west verging zone of deformation is proposed to be a taper building mechanism that allowed the fold thrust belt to continue propagating eastward

a correction factor to account for mixing in ghyben herzberg and critical pumping rate approximations of seawater intrusion in coastal aquifers 1 the classic ghyben herzberg estimate of the depth of the freshwater saltwater interface together with the dupuit approximation is a useful tool for developing analytical solutions to many seawater intrusion problems on the basis of these assumptions strack 1976 developed a single potential theory to calculate critical pumping rates in a coastal pumping scenario the sharp interface assumption and in particular this analytical solution are widely used to study seawater intrusion and the sustainable management of groundwater resources in coastal aquifers the sharp interface assumption neglects mixing and implicitly assumes that salt water remains static consequently this approximation overestimates the penetration of the saltwater front and underestimates the critical pumping rates that ensure a freshwater supply we investigate the error introduced by adopting the sharp interface approximation and we include the effects of dispersion on the formulation of strack 1976 to this end we perform numerical three dimensional variable density flow simulations we find that strack s equations can be extended to the case of mixing zone if the density factor is multiplied by an empirically derived dispersion factor 1 t b 1 6 where t is transverse dispersivity and b is aquifer thickness we find that this factor can be used not only to estimate the critical pumping rate but also to correct the ghyben herzberg estimate of the interface depth its simplicity facilitates the generalization of sharp interface analytical solutions and good predictions of seawater penetration for a broad range of conditions

kinematic restoration of contractional basement structures using thermokinematic models a key tool for petroleum system modeling in this paper we demonstrate a workflow for constructing kinematic restorations in complex foothill areas devoid of growth strata and other indicators for the chronology of deformation our initial reconstructions utilize thermochronometric data a well documented structural geometry and a first order conversion of exhumation rates into tectonic rates we then utilize models obtained from the new in house developed software fetkin to build a first version of the thermokinematic restoration the fetkin approach is geared primarily toward testing and further calibration and refinement of the kinematic restoration based on the extent to which the model result agrees with thermochronometric data from the study area in the form of both discrete ages and inverse modeled time temperature envelopes this analysis also provides rates of shortening and time temperature paths throughout the model space that can be used to make first order predictions of when different source rocks entered the oil window these capabilities are demonstrated in a pilot case study along a cross section in the colombian eastern cordillera the improved confidence in the reconstruction that this technique provides allows us to show increasing shortening rates in this part of the andes during the neogene reaching up to 5 mm yr 0 20 in yr by the pliocene and constrain the timing of generation from the most important oil kitchens for the eastern cordillera llanos basin petroleum system this approach therefore proves to be a useful method for creating high resolution and high fidelity kinematic restorations

a reporting protocol for thermochronologic modeling illustrated with data from the grand canyon apatite u th he and fission track dates as well as 4he 3he and fission track length data provide rich thermal history information however numerous choices and assumptions are required on the long road from raw data and observations to potentially complex geologic interpretations this paper outlines a conceptual framework for this path with the aim of promoting a broader understanding of how thermochronologic conclusions are derived the tiered structure consists of thermal history model inputs at level 1 thermal history model outputs at level 2 and geologic interpretations at level 3 because inverse thermal history modeling is at the heart of converting thermochronologic data to interpretation for others to evaluate and reproduce conclusions derived from thermochronologic results it is necessary to publish all data required for modeling report all model inputs and clearly and completely depict model outputs here we suggest a generalized template for a model input table with which to arrange report and explain the choice of inputs to thermal history models model inputs include the thermochronologic data additional geologic information and system and model specific parameters as an example we show how the origin of discrepant thermochronologic interpretations in the grand canyon can be better understood by using this disciplined approach

evolutionary cycles during the andean orogeny repeated slab breakoff and flat subduction tectonomagmatic similarities between the modern chilean flat slab region and pre neogene magmatic episodes suggest that they represent analogues to flat subduction evolutionary patterns in each magmatic suite include i increasing la yb ratios and sr and nd isotopic enrichment through time ii eastward migration of magmatism after periods of transpressional transtensional intra arc deformation and iii subsequent termination and virtual absence of main arc activity for 5 10 myr these patterns may reflect slab shallowing followed by flat subduction and thickening of the overlying crust if repeated they require interchanging episodes of slab steepening increasing convergence rates force slab kinking and eventual failure of the oversteepened slab followed by rebound of the slab tip owing to lack of further slab pull flat subduction and termination of subduction related magmatism rapid subduction leads to shallow overriding of the detached slab fragment eclogitization of the gradually steepening slab tip at depth and subsequent slab pull permits asthenospheric corner flow and subduction related magmatism

revised deformation history of the central andes inferences from cenozoic foredeep and intermontane basins of the eastern cordillera bolivia 1 investigation of cenozoic deformation sediment accumulation and provenance in the eastern cordillera of bolivia at 17 21 s indicates major shortening 60 140 km and foredeep development followed by limited internal shortening and intermontane basin development contrasting histories of shortening deposition sediment dispersal and detrital composition distinguish a formerly extensive paleogene foredeep exposed along an eastern belt of synclines from a zone of principally neogene intermontane basins in the central eastern cordillera new 40ar 39ar ages of 25 17 ma for interbedded tuffs reveal latest oligocene early miocene accumulation in intermontane basins at rates 80 m myr several times lower than andean foredeeps although poorly dated foredeep evolution probably coincided with middle eocene oligocene deformation and denudation in adjoining regions to the west a mid cenozoic transition from foredeep to intermontane conditions may be attributable to emplacement of a basement involved tectonic wedge beneath the eastern cordillera in this interpretation wedge emplacement drove flexural foredeep subsidence from roughly 40 to 25 ma whereas subsequent accumulation occurred in localized internally drained basins in elevated intermontane areas regardless of the regional subsurface structural geometry 40ar 39ar ages define a 25 21 ma onset of intermontane sedimentation that signifies the termination of major upper crustal shortening over large parts of the eastern cordillera and possibly the age of initial shortening in the interandean and subandean zones to the east in contrast to several popular models the revised tectonic history presented here suggests significant pre neogene shortening in the eastern cordillera and underscores the large uncertainties in estimates of long term shortening rates in the andes

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

the growth of the central andes 22 s 26 s we synthesize geologic observations with new isotopic evidence for the timing and magnitude of uplift for the central andes between 22 s and 26 s since the paleocene to estimate paleoelevations we used the stable isotopic composition of carbonates and volcanic glass combined with another paleoelevation indicator for the central andes the distribution of evaporites paleoelevation reconstruction using clumped isotope paleothermometry failed due to resetting during burial the andes at this latitude rose and broadened eastward in three stages during the cenozoic the fi rst in what is broadly termed the incaic orogeny ended by the late eocene when magmatism and deformation had elevated to 4 km the bulk 50 of what is now the western and central andes the second stage witnessed the gradual building of the easternmost puna and eastern cordillera starting with deformation as early as 38 ma to 3 km by no later than 15 ma the proximal portions quadej email arizona edu quade j dettinger m p carrapa b decelles p murray k e huntington k w cartwright a canavan r r gehrels g and clementz m 2015 the growth of the central andes 22 s 26 s in decelles p g ducea m n carrapa b and kapp p a eds geodynamics of a cordilleran orogenic system the central andes of argentina and northern chile geological society of america memoir 212 p 277 308 doi 10 1130 2015 1212 15 for permission to copy contact editing geosociety org 2014 the geological society of america all rights reserved on january 15 2015 memoirs gsapubs org downloaded from

pumping management of coastal aquifers using analytical models of saltwater intrusion 1 analytical models of saltwater intrusion in coastal aquifers of finite size are developed and utilized in an optimization methodology for determining the optimal pumping rates the models are based on the sharp interface approximation and the ghyben herzberg relation the governing equations are expressed in terms of a single potential and are solved analytically using the method of images to account for the aquifer boundaries the analytical models consider ambient flow and surface recharge the results are compared to numerical simulations indicating a good match as the number of images is increased the objective of optimization is to maximize the total pumping from the aquifer and a set of constraints protect the wells from saltwater intrusion the constraints are expressed using the analytical saltwater intrusion models two different constraint formulations are investigated the toe constraint formulation protects the wells from saltwater intrusion by not allowing the toe of the interface to reach the wells this formulation results in a nonlinear optimization problem which is solved using sequential quadratic programming sqp the potential constraint formulation on the other hand protects the wells by maintaining a potential at the wells larger than the toe potential this formulation results in a linear optimization problem which is solved using the simplex method several simulation runs indicate that the optimal solution is very sensitive to variations of recharge rates hydraulic conductivity heterogeneities etc the linear programming formulation besides being computationally simpler provides a safer solution than the nonlinear formulation

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

structure and cenozoic kinematics of the eastern cordillera southern bolivia 21 s 1 the eastern cordillera is a main morphotectonic unit of the central andes in southern bolivia it is predominantly composed of ordovician sedimentary rocks as thick as 10 km revision of the ordovician stratigraphy and new structural fieldwork resulted in detailed balanced cross sections improved estimates of crustal shortening and a new kinematic model for the eastern cordillera new estimates of total shortening in the eastern cordillera are up to 95 km 41 44 higher than previous estimates and sufficient to thicken the andean crust to its present state between the eastern foreland and the magmatic arc after initial tertiary uplift at 58 ma first thrusts developed in the middle eocene to early oligocene 40 30 ma exhuming the central part of the eastern cordillera tectonic shortening culminated in late oligocene and early miocene time 25 20 ma when west facing thrust systems developed in the central and western part of the eastern cordillera thrusting terminated in the western part by the end of the early miocene and middle miocene tectonic activity was restricted to minor strike slip faulting in the central part thrusting remained active until the late miocene by 10 ma shortening in the eastern cordillera essentially ceased kinematic fault analyses indicate clockwise rotation of the shortening direction from nne ssw or ne sw in eocene early oligocene time over e w to wnw ese or even nw se in late oligocene to middle miocene time nevertheless wnw ese directed shortening and subvertical extension predominate sinistral oblique motion on many thrusts probably reflects plan view flexural slip in the clockwise rotating southern limb of the bolivian orocline it is proposed that space problems in the oroclinal hinge slowed the rotation there and caused decoupling of the still rotating south limb along ne trending transfer zones

salar de atacama basin a record of compressional tectonics in the central andes since the mid cretaceous the salar de atacama basin lies in the inner fore arc of northern chile topographically and structurally it is a first order feature of the central andes the sedimentary fill of the basin constrains the timing and extent of crustal deformation since the mid cretaceous we have studied good exposures along the western edge of the basin and have correlated them with seismic reflection sections and data from an exploration well throughout most of its history the basin developed in a foreland setting during periods of thin skinned and thick skinned thrusting growth strata provide evidence for coeval sedimentation and thrust motions during mid cretaceous paleogene and neogene times pre neogene deformation was significant in the basin and in surounding areas of the early central andes models that attempt to explain the current thickness of the central andes should consider late cretaceous and paleogene shortening as well as the more obvious neogene and quaternary shortening

the influence of burial heating on the u th he system in apatite grand canyon case study article history thermochronological data can constrain the cooling paths of rocks exhumed through the uppermost 1 2 km of earth s crust and have thus been pivotal in illuminating topographic development over timescales 0 1 ma however in some cases different methods have led to conflicting conclusions about timing of valley scale exhumation here we investigate the case of western grand canyon usa where different thermochronological datasets have been interpreted to record very different timings of canyon incision 70 ma versus 5 ma we present a method to assess key assumptions in these constraints and demonstrate that burial heating conditions of basement rocks in the mesozoic can result in incomplete annealing of radiation damage in apatite in turn this has a dramatic effect on the temperature sensitivity of the apatite u th he system and its ability to record post burial exhumation the possibility of incomplete annealing resolves the apparent conflict in time temperature paths inferred over the last 70 ma although it requires temperatures during burial that are lower than predicted by apatite fission track data a refinement of parameters that prescribe the kinetics of damage annealing and related control on 4 he diffusivity in apatite would account for this discrepancy specifically if alpha recoil damage anneals at a lower rate than fission tracks at a given temperature these effects will be important for any application of the apatite u th he system in geologic settings that experienced prolonged residence 10 ma between 50 150 c the approaches developed here provide means to assess these effects

high level surfaces plateau uplift and foreland development bolivian central andes newly dated tertiary strata in the bolivian central andean plateau and synthesis of the tertiary record in the adjacent subandean fold thrust belt constrain the age of deformation in both regions age of deformation within the plateau is determined by dated crosscutting relations associated with a regionally extensive high level surface known as the san juan del oro surface new 40 ar 39 ar dates on undeformed strata above the high level surface preclude significant upper crustal shortening within the eastern cordillera after 10 ma tertiary strata within the adjacent subandean region demonstrate that formation of the fold thrust belt occurred after 10 ma on the basis of these data we propose a two stage model of late cenozoic andean growth that links plateau uplift to the development of the fold thrust belt in the first stage early plateau uplift occurred in response to widespread compressional deformation of the plateau eastern cordillera and altiplano during the second stage beginning after 10 ma upper crustal deformation within the plateau terminated and the subandean fold thrust belt developed crustal scale eastward thrusting along the eastern margin of the eastern cordillera drove subandean folding and thrusting the eastern cordillera served as the bulldozer for the deforming subandean wedge

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

early cenozoic uplift of the puna plateau central andes based on stable isotope paleoaltimetry of hydrated volcanic glass uplift of the central andes is largely thought to have occurred during the past 10 m y based on paleoaltimetry studies from the altiplano of bolivia however the spatio temporal uplift history may not be uniform across the central andes we present new stable isotopic results from the salar de antofalla salina del fraile and arizaro basin on the puna plateau 24 26 s of northwestern argentina samples of volcanic glass give d paleowater values and modeled paleoelevations that indicate an elevated 4 km puna plateau since ca 36 ma with limited

groundwater pumping in head controlled coastal systems the role of lateral boundaries in quantifying the interface toe location and maximum pumping rate summary the current study explores quantitatively the impact of lateral impermeable boundaries on groundwater pumping in head controlled coastal systems based on the potential theory and the image well superposition method we compare the interface toe location and maximum pumping rate among three scenarios that assume s1 an infinite domain width and a finite domain length s2 a finite domain width and length and ss an infinite domain width and length focusing exclusively on boundary effects the upstream freshwater discharge is assumed the same for all scenarios regardless of the variation in domain size it is found that the impact from both inland and lateral boundaries could play a significant role on the interface toe location and maximum pumping rate defined as the maximum allowable pumping rate that will not lead to pumping saltwater depending on sizes of domain length and width since the impacts of inland fixed head boundary and lateral impermeable boundaries are contrary on the maximum interface toe location defined as the farthest inland point of the interface toe under pumping condition and maximum pumping rate they can be offset under certain critical conditions such that the results of the two quantitative indictors i e the maximum interface toe location and maximum pumping rate in s2 are close to those in ss in particular a linear equation is derived to reflect the relationship between the domain width and length under such critical conditions and expressed as l 0 87 w 0 62 w 1 or l 1 5 in which w and l are the domain width and length normalized by the distance between the coastline and pumping well when l 0 87 w 0 62 the impact from lateral overcomes that from inland producing a larger maximum interface toe location and a lower maximum pumping rate than those in ss when l w 0 62 by contrast the impact from inland exceeds that from lateral and hence resulting in a smaller maximum interface toe location and a higher maximum pumping rate it is expected that the results developed in the current study could support the design of numerical models and 3d laboratory experiments as well as the assessment of domain size impact on pumping in head controlled coastal groundwater systems

tectonics and climate of the southern central andes the history of the southern central andes including the world s second largest plateau and adjacent intermontane basins and ranges of the eastern cordillera and the northern sierras pampeanas of argentina and bolivia impressively documents the effects of tectonics and topography on atmospheric circulation patterns the development of orographic barriers and their influence on erosion and landscape evolution at various timescales protracted aridity in the orogen interior has facilitated the creation and maintenance of the puna altiplano plateau contraction and range uplift filling of basins and possibly wholesale uplift of the plateau increased gravitational stresses in the orogen interior which caused the eastward migration of deformation into the foreland and successive aridification the uplift of the andean orogen has also had a far reaching influence on atmospheric and moisture transport patterns in south america this is documented by the onset of humid climate conditions on the eastern side of the andes in late miocene time which was coupled with the establishment of dramatic precipitation gradients perpendicular to the orogen and changes in tectonic processes in the andean orogenic wedge

late mesozoic to paleogene stratigraphy of the salar de atacama basin antofagasta northern chile implications for the tectonic evolution of the central andes abstract the salar de atacama basin the largest pre andean basin in northern chile was formed in the early late cretaceous as a consequence of the tectonic closure and inversion of the jurassic early cretaceous tarapaca back arc basin inversion led to uplift of the cordillera de domeyko cd a thick skinned basement range bounded by a system of reverse faults and blind thrusts with alternating vergence along strike the almost 6000 m thick upper cretaceous to lower paleocene sequences purilactis group infilling the salar de atacama basin reflects rapid local subsidence to the east of the cd its oldest outcropping unit tonel formation comprises more than 1000 m of continental red sandstones and evaporites which began to accumulate as syntectonic growth strata during the initial stages of cd uplift tonel strata are capped by almost 3000 m of sandstones and conglomerates of western provenance representing the sedimentary response to renewed pulses of tectonic shortening which were deposited in alluvial fan fluvial and eolian settings together with minor lacustrine mudstone purilactis formation these are covered by 500 m of coarse proximal alluvial fan conglomerates barros arana formation the top of the purilactis group consists of maastrichtian danian alkaline lava and minor welded tuffs and red beds cerro totola formation 70 64 ma k ar deposited during an interval of tectonic quiescence when the el molino yacoraite late cretaceous sea covered large tracts of the nearby altiplano puna domain limestones interbedded with the totola volcanics indicate that this marine incursion advanced westwards to reach the eastern cd slope cd shortening in the late cretaceous was accompanied by volcanism and continental sedimentation in fault bounded basins associated to strike slip along the north chilean magmatic arc to the west of the cd domain indicating that oblique plate convergence prevailed during the late cretaceous oblique convergence seems to have been resolved into a highly partitioned strain system where margin parallel displacements along the thermally weakened arc coexisted with margin orthogonal shortening associated with syntectonic sedimentation in the salar de atacama basin a regionally important early paleocene compressional event is echoed in the salar de atacama basin by a distinctive angular unconformity which separates paleocene continental sediments from purilactis group strata the basin also records the eocene early oligocene incaic transpressional episode which produced renewed uplift in the cordillera de domeyko and triggered the accumulation of a thick blanket of syntectonic gravels loma amarilla formation

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

pattern formation at the ocean surface sargassum distribution and the role of the eddy field positively buoyant organisms such as the macroalga sargassum and the cyanobacterium trichodesmium often form surface accumulations visible in satellite imagery that have lateral scale separation of tens of kilometers and cannot be explained by langmuir circulation here we discuss the accumulation of floating materials in the ocean in presence of meso and submesoscale activity using high resolution simulations of the ocean mesoscale in both idealized a 3 dimensional box where coherent eddies are forced by small scale winds and realistic domains western gulf of mexico where extensive concentrations of floating sargassum have been recorded in satellite images we show that the distribution of tracers at the ocean surface departs rapidly from that observed a few tens of meters below it such distribution does not resemble that observed for passive tracers in quasi geostrophic turbulence the strong divergence and convergence zones generated at the surface by ageostrophic processes in the submesoscale range are responsible for the creation of areas where the floating material accumulates floating particles are expelled from the core of mesoscale eddies and concentrate in convergence regions in patterns comparable to the ones observed through the satellite images in light of those results sargassum and or trichodesmium may provide a useful proxy to track convergence divergence processes resulting from ageostrophic processes at the ocean surface

apatite triple dating and white mica 40ar 39ar thermochronology of syntectonic detritus in the central andes a multiphase tectonothermal history we applied apatite u pb fission track and u th he triple dating and white mica 40 ar 39 ar thermochronology to syntectonic sedimentary rocks from the central andean puna plateau in order to determine the source area geochronology and source sedimentary basin thermal histories and ultimately the timing of multiple tectonothermal events in the central andes apatite triple dating of samples from the eocene geste formation in the salar de pastos grandes basin shows late precambrian devonian apatite u pb crystallization ages eocene apatite fission track aft and eocene miocene u th he ca 8 47 ma cooling ages double dating of cobbles from equivalent strata in the arizaro basin documents early eocene 46 2 3 9 ma and cretaceous 107 6 7 6 109 5 7 7 ma aft and eocene oligocene ca 55 30 ma u th he ages thermal modeling suggests relatively rapid cooling between ca 80 and 50 ma and reheating and subsequent diachronous basin exhumation between ca 30 ma and 5 ma the 40 ar 39 ar white mica ages from the same samples in the salar de pastos grandes area are mainly 400 350 ma younger than apatite u pb ages suggesting source terrane cooling and exhumation during the devonian early carboniferous together these data reveal multiple phases of mountain building in the paleozoic and cenozoic basin burial temperatures within the plateau were limited to

a geophysical and geochemical approach for seawater intrusion assessment in the acquedolci coastal aquifer northern sicily vertical electrical sounding ves surveys and chemical analyses of groundwater have been executed in the coastal plain of acquedolci northern sicily with the aim to circumscribe seawater intrusion phenomena this urbanized area is representative of a more general problem interesting most of mediterranean littoral areas where intensive overdraft favors a heavy seawater intrusion through the coastline aquifer resistivity seems decisively to be conditioned by the chlorine and magnesium content in the main aquifer of the region schlumberger ves together with piezometric and chemical physical information of groundwater allowed us to perform hydrogeological and geophysical elaborations to propose the occurrence of a relatively narrow belt marked by fresh salt water mixing in the considered plain pollution risk studies have been already realized by authors with the proposal to identify by parametric and synthetic zoning of significant hydrogeological elements the most vulnerable sectors in detail an intrinsic vulnerability mapping has been already performed applying the well known sintacs system this paper intends to give in this sector of sicily an example of integration of different methodologies showing the role of geophysics to describe the degradation of aquifers on the whole as well as to assess their pollution risk better

tectonic inversion in the santa barbara system of the central andean foreland thrust belt northwestern argentina 1 the santa barbara system sbs of northern argentina is a 400 km long segment of the subandean foreland thrust belt it is characterized by predominantly west verging relatively high angle thrust faults many of these faults are reactivated normal faults from one branch of a complex cretaceous to paleogene rift system heteroaxial folding in parts of the sbs is probably due to a slight component of range parallel dextral strike slip motion acting on preexisting faults striking north and ne during inversion regional balanced cross sections along two transects across the northern sbs indicate that the major faults flatten into a detachment in the basement at about 10 km depth neogene e w contraction in the sbs is of the order of 21 26 km rift extension is not very well constrained but was probably less than 10 km the structural style of the sbs differs from the thin skinned subandean thrust belt to the north and from the large wavelength sierras pampeanas basement uplifts to the south the changes between the different styles are sharp and coincide with the northern and southern boundaries of the rift in the foreland suggesting that crustal or lithospheric heterogeneities exert an overriding control on foreland structural style

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

uplift of the central andean plateau and bending of the bolivian orocline the topography of the central andes can be considered the primary tectonic signal of late cenozoic mountain building in an arid region where the effects of uplift and magmatism are little obscured by denudation the spatial coverage of the topographic signal is more complete than that for sparsely sampled geological and geophysical data a color coded image of digitized topography between 12 s and 37 s highlights the altiplano puna one of the world s most remarkable plateaus and reveals important physiographic clues about the formation of that major feature the topographic data combined with information on structure magmatism seismicity and paleomagnetism support a simple kinematical model for the late cenozoic evolution of the central andes the model does not require collisional effects or enormous volumes of intrusive additions to the crust but instead calls upon plausible amounts of crustal shortening and lithospheric thinning the model interrelates andean uplift a changing geometry of the subducted nazca plate and a changing outline in map view of the leading edge of the south american plate crustal shortening has accommodated convergence between the chilean peruvian forearc and the south american foreland the altiplano puna plateau can be constructed by a combination of crustal shortening and thickening and lithospheric thinning above a shallow dipping 20 30 subducted plate the seawardly concave bend of western south america the bolivian orocline was enhanced but not completely produced by an along strike variation in the amount of late cenozoic shortening maximum shortening in bolivia both produced the widest part of the plateau and increased the seaward concavity of the bolivian orocline the along strike variations of shortening are hypothesized to result from corresponding along strike variations in the width of a weakened zone in the overriding plate weakening occurs above the wedge of asthenosphere located between the subducted and overriding plates hence the width of the zone of weakening depends upon the dip of the subducted plate two types of shortening are recognized 1 a widespread basin and range laramide like shortening that characterizes modem activity in the sierras pampeanas and late miocene deformation of the altiplano puna and 2 on the eastern side of the cordilleras and plateau an east verging foreland fold thrust belt in which the underthrust foreland compresses and thickens the ductile lower crust and produces a plateau uplift of the upper crust the second type of shortening can be applied to plio quaternary deformations throughout the central andes but with a substantial narrowing of the region of plateau uplift in peru and south of 28 s a proposed monoclinal flexure of the upper crust on the western side of the plateau uplift explains the remarkably simple and regular morphology of the main western slope of the central andes the monocline is located above the tip of the asthenospheric wedge between the converging plates it is postulated to occur above the western limit of lower crustal thickening in the regions of horizontal subduction the monocline can be associated with a late miocene asthenospheric wedge tip

pathways and processes associated with the transport of groundwater in deltaic systems summary rivers are considered to be the primary means driving hydrological and geochemical fluxes between the continents and the ocean however it is unclear how well surface water fluxes represent total fluxes or whether more diffuse subterranean fluxes of river water to the coastal ocean occur this question is important in light of research demonstrating that submarine groundwater discharge sgd is important for geochemical and hydrological fluxes here we examine the pathways and potential magnitude of the role that sgd plays in the mississippi river delta mrd the largest delta in north america we present multiple independent lines of evidence demonstrating a hydrological connection between the mississippi river mr and the mrd evidence includes hydrological budgets demonstrating downstream water losses from the mr which are unexplained and are of the same magnitude as water sources to adjacent coastal bays of the mrd well data indicating a correlation between groundwater height and the stage of the mr and excess 222 rn inventories exceeding that expected from in situ production implying an advective i e groundwater source to coastal bays sgd likely flows from the mr to its delta via paleochannels and other buried sand bodies seismic data indicates that such features are common whereas resistivity data suggest the intrusion of low salinity water to coastal bays adjacent to the river these results may be applicable to other deltas worldwide as many of the world largest rivers have deltas with numerous abandoned distributaries that could act as conduits for groundwater

optimal annual operation of a coastal aquifer optimal annual operation of a coastal aquifer is determined by using a multiple objective linear programing model based on a multicell model of the aquifer and a network representation of the hydraulic distribution system the decision variables are pumping and or recharge quantities in each cell four objective functions are based on 1 a desired ground water surface map 2 a desired location of the sea water fresh water interface toe in each coastal cell 3 a desired concentration map of a selected conservative contaminant and 4 minimization of the energy for pumping and recharge an approximate linearized expression of the location of the interface has been developed to enable the use of linear programing as the optimization method a trade off procedure is employed for identifying the most desirable solution the model is applied to a segment of the coastal aquifer in israel a 44 km strip along the coast with a width of 7 to 15 km and results are discussed

subandean thrust and fold belt of northwestern argentina geometry and timing of the andean evolution the subandean ranges of northwestern argentina are an active thin skinned fold and thrust belt the main detachment level in silurian shales dips 2 3w and all the major east verging faults detach from it important intermediate detachment levels in the devonian shales generate lift off structures and the decoupling of the lower and upper structural levels the subandean thrust belt has a minimum shortening of about 60 km 36 at about 2240 latitude the deformation started at about 8 5 9 ma with the uplift of the el pescado range and the formation of an important back thrust at the cinco picachos range fault generation gets young to the east the pintascayo range uplift started at 7 6 ma while the baja orn range uplift began at about 6 9 ma these two ranges continued growing simultaneously until at least 4 7 ma at san antonio range fault movement began at approximately 4 4 ma and the aguarage uplift started at about 2 7 ma an important stage dominated by out of sequence movements spans from about 4 5 ma to present for both proposed models of shortening the quaternary rates of shortening between 8 and 11 mm yr coincide well with global positioning system results from the area the hydrocarbon generation and migration is contemporaneous with the deformation enhancing the possibilities of hydrocarbon entrapment in the area

management of coastal aquifers based on nonlinear optimization and evolutionary algorithms abstract a method of assessing the optimum pumping rates of coastal aquifers based on nonlinear optimization and evolutionary algorithms ea is developed the objective is to maximize the total pumping rate while protecting the wells from sea water intrusion the formulation of the constraints is based on numerical simulation of the freshwater flow equations the simulation model is based on the sharp interface and the ghyben herzberg approximation and is applicable to unconfined aquifers and steady state flow the single potential formulation of water resour res 12 1976 1165 is followed and the governing equations are solved numerically using finite differences the numerical model can handle aquifers of complex shapes nonuniform hydraulic conductivity nonuniform distribution of surface recharge etc the constraints are nonlinear with respect to the decision variables resulting in a nonlinear optimization problem two optimization methods are investigated specifically sequential quadratic programming sqp and evolutionary algorithms ea sqp requires less computer time than ea but can get stuck on local optimum solutions the simulation and optimization methodology is applied to a real unconfined coastal aquifer in the greek island of kalymnos for determining the optimal pumping rates while protecting the wells from sea water intrusion

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

seismic and field evidence for selective inversion of cretaceous normal faults salta rift northwest argentina abstract northwestern argentina was the site of the continental salta rift in cretaceous to paleogene time the salta rift had a complex geometry with several subbasins of different trends and subsidence patterns surrounding a central high fault trends in the rift were extremely variable there is evidence of normal and or transfer faults trending n ne e and se it is not clear if all these faults were active at the same time indicating a poorly defined extension direction or if they formed in different non coaxial extension phases in either case their trends were very likely influenced by preexisting fault systems beginning in early eocene time the rift basins were superseded by andean foreland basins and later became caught in the andean thrust deformation propagating eastward resulting in the inversion of rift faults due to their different orientations not all faults were equally prone to reactivation as thrusts n to nne trending faults were apparently most strongly inverted probably often to a degree where the traces of their normal fault origin have become obliterated we present seismic evidence of moderately inverted n trending faults in the tres cruces basin and field examples of preserved e trending normal faults however reactivation sometimes also affects faults trending approximately parallel to the main neogene shortening direction indicating short term deviations from the general pattern of neogene thrust deformation these pulses of orogen parallel contraction may be linked to the intermittent activity of oblique transfer zones

hercynian deformation and metamorphism in the cordillera oriental of southern bolivia central andes abstract in southern bolivia the very thick ordovician siliciclastic rocks of the cordillera oriental show folds and a slaty cleavage of pre cretaceous age these deformations had previously been attributed to either the late ordovician ocloyic or to the late devonian to early carboniferous eohercynian chanic orogenies now we present k ar age determinations from phyllosilicates of the ordovician slates which have been interpreted in relation to illite crystallinity data high anchizonal to epizonal metamorphism is indicated for most of the investigated samples the majority of the samples have provided ages within the 320 290 ma interval late carboniferous to early permian indicating a late hercynian orogeny traces of synchronous orogenic processes are known from different parts of the central andes this points to late hercynian orogenic activities in that region

highly variable nutrient concentrations in the northern gulf of mexico abstract the distribution of surface nutrients along the salinity gradient in the mississippi atchafalaya river outflow region was examined during four cruises including two simultaneous cruises conducted in the northern gulf during the summer of 2010 and 2011 and in late spring of 2012 the new extensive data set covers the salinity gradient from 11 to 37 psu practical salinity unit in a year of extraordinarily high river discharge 2011 with few samples from a year of average 2010 and below average 2012 river outflow the overall surface concentrations of nitrate nitrite orthophosphate and silicate are compared to those recorded in cruises spanning the 1985 2009 interval using monte carlo simulations to test the statistical significance we found that surface orthophosphate and nitrate nitrite concentrations are approximately three and two fold smaller respectively in the 2010 2012 period compared to the previous years changes in silicate concentrations were in most cases not significant and their assessment complicated by different measurement techniques and potential preservation artifacts the weighted river loading of these nutrients was on the other hand very high in the latest period when samples mostly covered 2011 the well known negative correlation between nutrient concentrations and salinity at the ocean surface is confirmed in the most recent data the area surrounding the mississippi river mouth is characterized by inorganic n p ratios greater than 30 1 that decrease to values typically less than 10 1 at about 100 km from of the mouth overall our analysis suggests that surface nutrient concentrations in the northern gulf of mexico cannot be described with any good accuracy by a linear model based on river discharge alone

how significant is the slope of the sea side boundary for modelling seawater intrusion in coastal aquifers application of numerical models is a common method to assess groundwater resources the versatility of these models allows consideration of different levels of complexity but the accuracy of the outcomes hinges upon a proper description of the system behaviour in seawater intrusion assessment the implementation of the sea side boundary condition is of particular importance we evaluate the influence of the slope of the sea side boundary on the simulation results of seawater intrusion in a freshwater aquifer by employing a series of slope variations together with a sensitivity analysis by varying additional sensitive parameters freshwater inflow and longitudinal and transverse dispersivities model results reveal a multi dimensional dependence of the investigated variables with an increasing relevance of the sea side boundary slope for seawater intrusion decrease of up to 32 submarine groundwater discharge zone reduction of up to 55 and turnover times increase of up to 730 with increasing freshwater inflow or dispersivity values

the kinematic history of the central andean fold thrust belt bolivia implications for building a high plateau this paper presents a model for the kinematic evolution of the central andean plateau based on balanced cross sections across the bolivian andes the proposed model links the formation of the andean plateau to the development of the andean fold thrust belt through the creation and propagation of two large basement mega thrusts support for large basement involved thrust sheets is found in significant steps in both the topography and the exposed structural elevation of the andean fold thrust belt the structurally highest basement thrust raised folds and faults in predominantly lower paleozoic rocks of the eastern cordillera with respect to tertiary rocks in the broad internally drained basin of the altiplano to the west and east verging folds and faults in upper paleozoic rocks of the interandean zone to the east the interandean zone was in turn raised both structurally and topographically with respect to the frontal folds and faults of the fold thrust belt the subandean zone by a second structurally lower basement thrust sheet thus these two megathrusts divide the andean fold thrust belt into four areas of markedly different structural elevations the eastern cordillera can be further subdivided into two zones of west and east vergent folds and thrusts shortening accommodated by the fold thrust belt can be divided among these tectono structural zones and linked to shortening accommodated by the inferred basement megathrusts the proposed kinematic model suggests that the eastward propagation of the structurally highest basement thrust fed 105 km of slip into the eastern cordillera along east vergent and west vergent faults this structure also fed 90 km of eastward slip into the interandean zone the initiation and eastward propagation of a lower basement thrust structurally elevated the interandean zone with respect to the foreland while feeding 65 km of slip into the subandean zone out of sequence basement thrusting to the west is proposed to have elevated the western edge of the plateau and accommodated 40 km of shortening within the altiplano total cumulative shortening within the cover rocks of the andean fold thrust belt 300 330 km can be balanced by an equivalent amount of shortening along two basement megathrusts to the first order the eastern margin of the central andean plateau defined by the 3 km topographic contour is contiguous with the leading edge of the upper basement megathrust this relationship between the basement highs and the physiographic boundaries of the andean plateau suggests that extensive megathrust sheets involving strong rocks such as crystalline basement or quartzite play an important role in the formation of the central andean plateau and a similar link between megathrust sheets and plateaus may be found in other orogens

thermochronometer record of central andean plateau growth bolivia 19 5 s 1 quantifying the timing magnitude and rates of exhumation and deformation across the central andes is a prerequisite for understanding the history of plateau rise we present 23 new apatite and zircon fission track thermochronometer samples to chronicle the exhumation and deformation across the entire 500 km andean fold thrust belt at 19 5 s in bolivia exhumation and deformation are constrained with inverse thermal modeling of the thermochronometer data regional stratigraphy geothermal gradients and mass deficits inferred from a balanced section results suggest the following 1 initial exhumation of the eastern cordillera ec fore thrust and back thrust belts began in the late eocene to early oligocene 27 36 ma and continued in a distributed manner in the late oligocene to early miocene 19 25 ma interandean zone ia exhumation began 19 22 ma followed by a third pulse of exhumation 11 16 ma in the ec back thrust belt and initial cooling in the westernmost subandes sa 8 20 ma finally exhumation propagated eastward across the sa during the late mio pliocene 2 8 ma 2 exhumation magnitudes are spatially variable and range from maximums of 8 km in the ec fore thrust belt to average values of 4 7 km across the ec 2 5 3 km in the altiplano 4 6 km in the ia and 3 km in the sa 3 exhumation rates range from 0 1 to 0 2 mm a in the ec from 0 1 to 0 6 mm a in the ia and from 0 1 to 0 4 mm a to locally 1 4 mm a or more in the eastern sa we synthesize similar constraints with sediments throughout bolivia and characterize plateau development by 1 distributed deformation throughout the altiplano and ec regions from 20 to 40 ma with minor deformation continuing until 10 ma 2 contemporaneous cessation of most ec deformation and exhumation of the ia 20 ma implying establishment of the modern plateau width with significant but unknown crustal thickness and elevation shortly thereafter by 15 20 ma and 3 dominantly eastward propagation of deformation from the ia since 20 ma with minor out of sequence deformation in the central to eastern sa

accounting for long alpha particle stopping distances in u th sm he geochronology 3d modeling of diffusion zoning implantation and abrasion in apatite u th he thermochronology the helium distribution in a crystal is a function of the simultaneous processes of radiogenic production thermally activated volume diffusion and the ejection of he caused by long alpha stopping distances these processes are further complicated by zonation of u th and sm within the grain and implantation of 4he from neighboring u th sm bearing minerals we use a refined version of the 3d monte carlo diffusion code of gautheron and tassan got 2010 to simulate the interplay between ejection and diffusion with or without zonation ejection and abrasion for a suite of thermal histories we examine the phenomenon of over correction produced by the alpha ejection correction parameter ft or fzac for homogeneous or heterogeneous eu repartition by comparing the raw measured and ft or fzac corrected ages for a number of scenarios to the ejection free age aef which we define as the age that would be obtained if alpha ejection had not occurred or equivalently if the stopping distance was zero we show that the use of ft or fzac corrected ages generally reproduces the ejection free age to within typical u th he uncertainties 8 even for zoned apatites we then quantify the effect of alpha implantation on u th he ages showing that implantation from a single external source with modest relative u or th enrichment can generate as much as 50 excess he for more extreme cases where an apatite is surrounded by multiple external sources the measured age can be 300 of that determined from an isolated crystal while abrasion of the outer 20 25 m can significantly reduce the age dispersion for rapidly cooled samples slowly cooled samples can still retain 10 30 excess he the removal of the rim of the crystal reduces the thermal information from very low temperatures 40 c and introduces additional technical complications and biases and should therefore be used with caution overall we demonstrate that although zonation and implantation may not be routinely determined we now have the 3d modeling capability to fully investigate and constrain the causes of age dispersion within a sample leading to significant improvement in our ability to interpret u th he data

detrital zircon u pb ages provide provenance and chronostratigraphic information from eocene synorogenic deposits in northwestern argentina paleogene clastic sedimentary rocks in the puna plateau of northwestern argentina contain valuable information about the timing and location of early mountain building in the central andes because these rocks generally lack tuffaceous facies only paleontological ages have been available we present u pb ages from detrital zircons in the conglomeratic eocene geste formation of the central puna plateau the zircon ages indicate that the geste formation was derived from nearby high relief ranges composed of ordovician metasedimentary rocks a small population of ca 37 35 ma grains also confirms the late eocene stratigraphic age of the geste formation and suggests that u pb detrital zircon ages may provide a new tool for determining depositional ages and provenance of widespread paleogene deposits in the central andes

the changing face of the deep colonization of the early ordovician deep sea floor puna northwest argentina abstract an upper tremadocian deep sea ichnofauna from the chiquero formation of puna northwest argentina represents a link between ediacaran and cambrian microbial mat dominated ecosystems and younger ordovician deep marine trace fossil assemblages this ichnofauna is preserved at the base of thin bedded turbidites formed in the lobe fringe of a back arc deep sea fan while ediacaran cambrian deep marine trace fossils are typically linked to matground grazing and feeding microbial textures in the chiquero formation are rare and not associated with trace fossils morphologic patterns e g radial trace fossils and networks of the chiquero ichnofauna indicate the onset of novel trophic types recording trapping of microorganisms and bacterial farming however in comparison with younger ordovician deep sea ichnofaunas graphoglyptids are relatively rare poorly diverse and geometrically simpler this study indicates that the early ordovician was a pivotal point in the ecology of deep sea infaunal communities this upper tremadocian ichnofauna records the arrival of the agronomic revolution to the deep sea comparisons with slightly older and younger deep sea ichnofaunas demonstrate that the colonization of the deep sea was a protracted process spanning the early paleozoic lagging behind colonization of nearshore and offshore substrates

aptian to recent compressional deformation foothills of the neuquen basin argentina abstract the neuquen basin lies in north western patagonia on the eastern foreland of the andes it formed as a rift basin in the early mesozoic and contains some 5000 m of triassic to aptian sediment mainly marine as a result of andean orogeny the western edge of the basin now forms part of the foothills we describe some of the main compressional structures drawing on surface and sub surface data we argue that regional eastward dips are due to west verging thrust displacements on the andacollo loncopue fault system during a late cretaceous peruvian phase aptian to campanian continental sediment accumulated in a retro arc foreland basin which was mainly of flexural origin nevertheless more than 1500 m of late cretaceous sediment accumulated in the footwall of the east verging agua amarga thrust the peruvian phase was responsible also for transpressional reactivation of a rift transfer zone the huincul arch the incaic phase eocene was responsible for north westerly trending folds and thrusts reactivation of cretaceous thrusts abundant andesitic lavas and high level intrusions and a swarm of north easterly trending bitumen dykes the quechua phase miocene to recent produced northerly trending folds and thrusts and a miocene foreland basin containing some 1000 m of basalt lava flows structures that formed during the incaic and quechua phases are broadly compatible with the history of convergence at the pacific margin of south america as deduced from plate reconstructions

effects of u th rich grain boundary phases on apatite helium ages abstract single grain apatite u th sm he ages he ages from non detrital samples sometimes show larger dispersions than can be explained by known sources of age dispersion such as grain size radiation damage parent zonation fracturing or intracrystalline inclusions we present observations and model age bias effects of an additional source of apatite he age dispersion observed in some cases u th rich grain boundary phases gbps precipitated on apatite crystal surfaces apatite grains from several samples with dispersed apatite he ages are coated or partially coated by reddish orange gbps rich in fe u and th these gbps are heterogeneous in thickness grain coverage and composition and have effective u concentrations eu up to 1000 ppm these phases may have large effects on the bulk eu and 4he compositions of apatite grains and can produce significant he age biases the direction and magnitude of this age bias is primarily a function of four factors 1 the host grain s size 2 the gbps thickness and eu relative to the host grain 3 the timing of gbp formation relative to the cooling age of the host grain and 4 whether the gbps are preserved and analyzed with the grain during he dating some of the most severe effects occur when gbps formed before or near the time of the apatite cooling age but were lost just prior to analysis for example during mineral separation in this case gbps of commonly observed thicknesses 1 10 m with eu 2 10 times that of the host apatite grain implant enough 4he into typical sized apatite grains to produce hundreds of percent positive age biases in contrast when u th rich gbps are preserved and analyzed with apatite grains the resulting he ages can be negatively biased though the heterogeneity variable preservation and ambiguous formation ages of gbps preclude a general quantitative and practical solution to this problem our model demonstrates that observed age dispersions in some samples are consistent with the effects of u th rich grain boundary phases and illustrates the conditions under which and by how much they will bias he ages

apatite u th he thermochronometry using a radiation damage accumulation and annealing model helium diffusion from apatite is a sensitive function of the volume fraction of radiation damage to the crystal a quantity that varies over the lifetime of the apatite using recently published laboratory data we develop and investigate a new kinetic model the radiation damage accumulation and annealing model rdaam that adopts the effective fission track density as a proxy for accumulated radiation damage this proxy incorporates creation of crystal damage proportional to production from u and th decay and the elimination of that damage governed by the kinetics of fission track annealing the rdaam is a version of the helium trapping model hetm shuster d l flowers r m and farley k a 2006 the influence of natural radiation damage on helium diffusion kinetics in apatite earth planet sci lett 249 148 161 calibrated by helium diffusion data in natural and partially annealed apatites the chief limitation of the hetm now addressed by rdaam is its use of he concentration as the radiation damage proxy for circumstances in which radiation damage and he are not accumulated and lost proportionately from the crystal by incorporating the rdaam into the hefty computer program we explore its implications for apatite u th he thermochronometry we show how u th he dates predicted from the model are sensitive to both effective u concentration eu and details of the temperature history the rdaam predicts an effective he closure temperature of 62 c for a 28 ppm eu apatite of 60 m radius that experienced a 10 c ma monotonic cooling rate this is 8 c lower than the 70 c effective closure temperature predicted using commonly assumed durango diffusion kinetics use of the rdaam is most important for accurate interpretation of u th he data for apatite suites that experienced moderate to slow monotonic cooling 1 0 1 c ma prolonged residence in the helium partial retention zone or a duration at temperatures appropriate for radiation damage accumulation followed by reheating and partial helium loss under common circumstances the rdaam predicts u th he dates that are older sometimes much older than corresponding fission track dates nonlinear positive correlations between apatite u th he date and eu in apatites subjected to the same temperature history are a diagnostic signature of the rdaam for many but not all thermal histories observed date eu correlations in four different localities can be explained with the rdaam using geologically reasonable thermal histories consistent with independent fission track datasets the existence of date eu correlations not only supports a radiation damage based kinetic model but can significantly limit the range of acceptable time temperature paths that account for the data in contrast these datasets are inexplicable using the durango diffusion model the rdaam helps reconcile enigmatic data in which apatite u th he dates are older than expected using the durango model when compared with thermal histories based on apatite fission track data or other geological constraints it also has the potential to explain at least some cases in which u th he dates are actually older than the corresponding fission track dates

pumping optimization in saltwater intruded coastal aquifers this paper investigates the hydraulic issues of pumping well optimization in saltwater intruded coastal aquifers the well field includes freshwater outflow pumping wells and a recharge canal the objective is to maximize the total pumping rate subject to the constraint of no intrusion of the saltwater front into the wells analytical solutions are presented for one well two well and one well with recharge canal problems for problems involving multiple pumping wells a structured messy genetic algorithm is used to search for the optimal solution

sediment accumulation on top of the andean orogenic wedge oligocene to late miocene basins of the eastern cordillera southern bolivia a large volume of tertiary synorogenic sediment accumulated on top of the eastern cordillera of southern bolivia as the andean orogenic wedge was shortened thickened and uplifted oligocene to upper miocene strata were deposited in five basins that were separated by active north trending fold thrust structures of the then frontal part of the orogenic wedge these coarse grained deposits recorded accumulation in the most proximal sector of the andean foreland basin system the wedge top depozone analyses of depositional systems sediment dispersal patterns and clast provenance of 0 6 2 3 km thick oligocene to upper miocene wedge top successions demonstrate that faultpropagation and fault bend folds commonly isolated individual basins while serving as primary sediment sources growth strata which formed by progressive fold limb rotation indicate thrust fault displacement and related folding concurrent with deposition alluvial fans defined most basin margins whereas braided streams or small lakes occupied basin axes diagnostic stratigraphic units confined to individual basins suggest that streams were rarely able to cut across growing folds to connect adjacent basins growth strata and crosscutting and onlapping relationships between contractional structures and wedge top strata delineate the chronology of fold thrust deformation in the eastern cordillera five new 40 ar 39 ar dates and previously published k ar dates ranging from 30 to 8 ma define an oligocene phase of west vergent backthrusting followed by primarily east vergent thrusting during miocene time timing of displacement on two east vergent thrusts is determined by 40 ar 39 ar ages of tuffs within adjacent growth strata sequences of the tupiza formation conglomerate 16 14 0 06 ma and oploca formation 13 33 0 15 ma 15 7 2 4 ma these ages combined with basin depositional histories demonstrate synchronous and out of sequence thrust displacement during miocene shortening upper crustal contractional deformation and wedge top deposition terminated in the eastern cordillera during late miocene time as the thrust front propagated eastward into the subandean zone continued thrust front migration produced the present day configuration in which eastern cordillera wedge top basins originally developed above the toe of the orogenic wedge at relatively low elevations are now 250 km west of the active thrust front and at 3 km elevation the modern wedge top depozone overlies the active frontal part of the orogenic wedge and consists of strata in thrustbounded subandean zone basins and sediment overlying blind structures beneath the westernmost chaco plain in general wedge top deposits become highly susceptible to erosional recycling as the orogenic wedge propagates forward and the wedge surface is uplifted nevertheless eastern cordillera wedge top deposits have been preserved for 10 30 m y in southern bolivia such long term preservation may reflect the inability of drainage systems to remove sediment mass from this low precipitation region of the central andes retention of sediment mass within the orogenic belt may promote critical thrust wedge conditions in which propagation of the thrust front is favored

plateau style accumulation of deformation southern altiplano 1 employing surface mapping of syntectonic sediments interpretation of industry reflection seismic profiles gravity data and isotopic age dating we reconstruct the tectonic evolution of the southern altiplano 20 22 s between the cordilleras defining its margins the southern altiplano crust was deformed between the late oligocene and the late miocene with two main shortening stages in the oligocene 33 27 ma and middle late miocene 19 8 ma that succeeded eocene onset of shortening at the protoplateau margins shortening rates in the southern altiplano ranged between 1 and 4 7 mm yr with maximum rates in the late miocene summing rates for the southern altiplano and the eastern cordillera we observe an increase from eocene times to the late oligocene to some 8 mm yr followed by fluctuation around this value during the miocene prior to shutoff of deformation at 7 8 ma and transfer of active shortening to the sub andean fold and thrust belt shortening inverted early tertiary graben and half graben systems and was partitioned in three fault systems in the western central and eastern altiplano respectively the east vergent fault systems of the western and central altiplano were synchronously active with the west vergent altiplano west flank fault system from these data and from section balancing we infer a kinematically linked western altiplano thrust belt that accumulated a minimum of 65 km shortening evolution of this belt contrasts with the eastern cordillera which reached peak shortening rates 8 mm yr in between the above two stages hence local shortening rates fluctuated across the plateau superimposed on a general trend of increasing bulk rate with no trend of lateral propagation this observation is repeated at the shorter length and time scales of individual growth structures that show evidence for periods of enhanced local rates at a timescale of 1 3 myr we interpret this irregular pattern of deformation to reflect a plateau style of shortening related to a self organized state of a weak crust in the central south american back arc with a fault network that fluctuated around the critical state of mechanical failure tuning of this state may have occurred by changes in plate kinematics during the paleogene initially reactivating crustal weak zones and by thermal weakening of the crust with active magmatism mainly in the neogene stage

preserved extensional structures in an inverted cretaceous rift basin northwestern argentina outcrop examples and implications for fault reactivation 1 during the cretaceous eocene interval a system of intracontinental rift basins the salta group rift evolved in northwestern argentina individual segments of the rift later suffered different degrees of inversion during cenozoic shortening the tres cruces subbasin on the west side of the eastern cordillera was strongly deformed being now part of a thick skinned thrust belt with a predominantly n s structural trend on its eastern border tilting due to folding and thrusting and subsequent erosion have produced exceptional outcrops of preserved east trending extensional structures including half grabens rollover anticlines and extensional fault propagation folds farther west the synrift succession is only intermittently exposed although the interference of north and east trending structures as well as peculiar dome shaped anticlines with spur like extensions suggest that north and east trending cretaceous faults were reactivated particularly near their intersections compilation of published data and analysis of our new data focused on the salta rift indicates three main factors favoring the contractional reactivation of normal faults dip angles lower than approximately 60 especially for faults striking roughly normal to contraction strikes no closer to the contraction direction than approximately 30 and low downdip fault curvatures occasional dip slip reactivation of east trending faults does not match the present and long term andean stress regimes and presents an unresolved problem

an updated crustal thickness map of central south america based on receiver function measurements in the region of the chaco pantanal and parana basins southwestern brazil

mine water hydrogeology and geochemistry this book is a collection of keynote reviews and detailed case studies covering the principal areas of active research and state of the art industrial practice in the field of mine water management it addresses both issues of water quantity such as the impact of iongwall mining on the piezometry and hydraulic properties of overlying aquifers and water quality spanning an array of sites from deep coal mines to open pit base metal mines as well as a wealth of hybrid integrated studies in which hydrogeological and geochemical aspects are considered and managed together the papers presented in this book are intended for practicing geologists and engineers involved in the management of active and abandoned mine sites all over the world it is also of interest to academic geoscientists and students with interests in low temperature aqueous geochemistry and the hydrogeology of complex quasi karstic groundwater flow systems

replenishing an unconfined coastal aquifer to control seawater intrusion injection or infiltration in this study we compare the performances of well injection and pond infiltration in controlling seawater intrusion in an unconfined coastal aquifer through two scenario groups 1 a single injection well vs an elliptic infiltration pond and 2 an injection extraction well pair system vs an elliptic infiltration pond extraction well system comparison is based on quantitative indicators that include the interface toe location saltwater volume and maximum net extraction rate for scenario 2 we introduce a method to determine the maximum net extraction rate for cases where the locations of stagnation points cannot be easily derived analytical analysis shows that the performances of injection and infiltration are the same provided that the pond shape is circular the examination of scenario group 1 suggests that the shape of the infiltration pond has a minor effect on the interface toe location as well as the reduction in the saltwater volume given the same total recharge rate the investigation of scenario group 2 indicates by contrast that the maximum net extraction rate increases significantly with the increasing ratio of b to a where a and b are semi axes of the ellipse parallel and perpendicular to the coastline respectively specifically for a typical aquifer assumed an increase of 40 is obtained for the maximum net extraction when b a increases from 1 200 to 200 despite that the study is based on a simplified model the results provide initial guidance for practitioners when planning to use an aquifer recharge strategy to restore a salinized unconfined coastal aquifer

submesoscale impacts on horizontal and vertical transport in the gulf of mexico 1 impacts of submesoscale processes on transport are investigated numerically in an energetic mesoscale flow with an ocean model run at two horizontal resolutions 1 and 5 km the focus is the northwestern gulf of mexico where the loop current eddies are surrounded by smaller vortices by increasing the horizontal resolution the number and strength of submesoscale eddies and vorticity filaments within the mixed layer increase dramatically and with them the vertical velocities inside the coherent eddies and at their peripheries increased vertical velocities for increasing resolution are associated to near inertial motions and they are not limited to the mixed layer but are found at all depths horizontal velocities on the contrary are similar lagrangian isobaric tracers are deployed close to the surface and at 100 m and three dimensional neutrally buoyant particles are released close to the surface at the base of the mixed layer and at 100 m the modeled horizontal dispersion curves for each deployment depth are independent of the kind of particles and of horizontal resolution close to the ocean surface however convergence zones generated by submesoscale ageostrophic motions and resolved at 1 km resolution influence the details of the tracer distributions vertical dispersion increases by several folds for increasing resolution at all depths explored with the largest differences found close to the surface therefore submesoscales processes play a fundamental role in driving vertical transport in eddy dominated flows both within and below the mixed layer for times comparable to the eulerian time scale

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

the importance of apatite composition and single grain ages when interpreting fission track data from plutonic rocks a case study from the coast ranges british columbia abstract fission track results determined from granitic rocks exposed within the coast ranges of british columbia indicate that significant variations in apatite chemistry may occur in small plutonic rock samples to test ages determined earlier by parrish using the population method of fission track dating new apparent apatite ages were completed using the external detector method so that single grain ages could be generated in most cases the new apatite ages were similar to the earlier ones within 2 however in many cases it was found that individual samples contained significant variations in single grain apatite ages microprobe analyses showed the spread in ages were directly related to variations in apatite chemistry such that chlorine rich apatites retained older ages than fluorine rich grains examination of the single grain age data suggested that the spread in single grain ages provided information which constrained the thermal history of the sample and that distributions of single grain ages reflected the temperatures at which they resided during cooling these results suggest that it is important to generate more than a few single grain fission track ages when dating apatite from granitic rocks since variations in the chlorine concentration in apatite grains may exist in kg sized granitic rock samples therefore it is no longer a valid assumption that each apatite grain separated from a small granite sample will have a similar chlorine concentration and in future apatite fission track studies of granitic terrains it is important to recognize that the apatite composition might be heterogeneous when interpreting results

cretaceous to middle cenozoic exhumation history of the cordillera de domeyko and salar de atacama basin northern chile

a review of deformation pattern templates in foreland basin systems and fold and thrust belts implications for the state of stress in the frontal regions of thrust wedges aesthetically appealing thrust systems and related large scale anticlines in both active and fossil foreland fold and thrust belts and the economic potential associated with the m have captured the interest of structural geologists for many decades as a consequence a large amount of data on sub seismic deformation patterns from thrust related an ticlines is available in the literature we provide a review of deformation pattern templates from fi eld data in foreland fold and thrust belts and show that the most frequent tre nds of sub seismic syn orogenic deformation structures hosted in km scale thrust related folds frequently and pa radoxically indicate a syn th rusting strike slip stress fi eld con fi guration with a near vertical 2 and a sub horizontal 3 rather than a contractional one where the latter is expected to be the vertical principal axis of the stress ellipsoid this a pparent inconsistency between sub seismic syn orogenic deformation structures and stress fi eld orientation is here named the 2 paradox field data support a possible expla nation of the paradox provided by the major role played by i nherited early orogenic extensional deformation struc tures on thrust fault nucleation nucleation of major thru sts and their propagation is facilitated and driven by the positive inversion and linkage of the early orogenic sub s eismic extensional inheritance developed in the foreland basin this process eventually leads to the development of l argereversefaultzonesandcanoccurbothincontractional and strike slip stress fi eld con fi gurations

pressure solution and coble creep in rocks on 5 november 1976 the tectonic studies group of the geological society held a lively discussion meeting at imperial college on the subject of pressure solution and coble creep deformation mechanisms may be divided into three broad categories 1 cataclastic processes 2 intracrystalline processes involving dislocations 3 diffusive mass transfer processes we are concerned here with group 3 processes flow by diffusive mass transfer of matter from grain boundaries which are subjected to high normal stress to less highly stressed grain boundaries if the diffusion is predominantly through the grain the process is termed nabarro herring creep whereas if it is predominantly around grain boundaries the flow is termed coble creep in general grain boundary sliding must occur to accommodate the grain shape changes due to diffusion for these processes to proceed at rates which are detectable the temperature must be at a large fraction of the absolute melting temperature of the material geologists have long recognized in low grade metamorphic rocks textures in dicative of deformation by diffusive mass transfer even over the relatively long time available for geological deformations at the low temperatures concerned solid state diffusivities would be too slow to account for the observed strains it is therefore inferred that the rate of diffusive mass transfer is enhanced by the presence of an intergranular fluid film hence the use of the term pressure solution to describe the process thus coble creep and pressure solution are similar in that they both involve intergranular diffusion the meeting was intended to

chlorophyll dispersal by eddy eddy interactions in the gulf of mexico 1 a lagrangian analysis of the transport and dispersal of plumes observed in satellite derived ocean color images was conducted using a data assimilating model of the gulf of mexico the interaction between pervasive cyclonic and anticyclonic eddies in the gulf generated advective paths that connect remote shelf regions these paths aligned remarkably well with the plume events recorded with the chlorophyll a ocean color product from seawifs two such events were studied in one event material was transported in a thin strip between the northern wall of the loop current and an adjacent cyclone connecting the eastern campheche shelf off the yucatan peninsula and south florida shelves the other event began off the louisiana shelf break as a small plume traced by chlorophyll and then developed into a long and thin feature which meandered to the shelf break off the northern yucatan peninsula moving between a large anticyclone and several adjacent cyclones these results indicate that inter eddy advection plays a crucial role in developing the ocean color patterns observed in the satellite ocean color data

development of drain hole design optimisation a conceptual model for open pit mine slope drainage system with fractured media using a multi stage genetic algorithm high rainfall in equatorial regions leads to high groundwater levels or pore pressures and a high risk of landslides on the slopes of open pit mines hindering mining operations to lower the groundwater level surrounding a slope a drainage system is needed a drain hole is a part of a drainage system which utilises gravity to drain groundwater drain hole installation in fractured media requires the determination of the number location length and other parameters of the drain holes drain holes are frequently installed in uniform configurations or in layouts with uniform spacing which are often ineffective and uneconomical as some holes are not in the right positions or directions within the fractured media this paper attempts to develop a conceptual model of an optimised configuration of drain holes by setting the drain hole parameters or decision variables such as number location and length in such a way that it produces the most effective and efficient outcome by maximising groundwater lowering and minimising cost the optimisation is supported by the multi stage genetic algorithm method in combination with a groundwater simulator hereafter called the multi stage gwsim ga so method the procedure of the conceptual model will be further developed and used as a framework in the groundwater management of fractured media of an open pit mine slope

transition from basement involved to thin skinned thrusting in the cordillera oriental of southern bolivia the eastern flank of the central andes in southern bolivia and northern argentina is underlain by a fold and thrust belt of neogene age it comprises an external thin skinned segment with basal detachment in silurian shales subandean ranges and an internal segment where units as deep as precambrian metasedimentary and igneous rocks are involved in thrusting eastern cordillera oriental between the cordillera oriental and the subandean ranges an intermediate segment interandean zone intervenes north of the argentinian bolivian border 22 s the structure of the interandean zone is characterized by folded and thrust faulted cambrian to triassic strata balanced cross sections across the western subandean ranges the interandean zone and the eastern cordillera oriental are based on previously available data and recent field work they suggest that the geological structure can be interpreted in terms of two major basement involved thrusts here referred to as interandean and subandean thrusts the more internal interandean thrust caused the development of broad basement anticlines in the eastern cordillera oriental however at shallower levels its displacement was accommodated by thin skinned folding and thrusting in the interandean zone in sequence activation of the subandean thrust uplifted the interandean zone on top of an imbricate basement sheet and caused the development of the thinskinned subandean ranges farther east published radiometric data and subsidence history of the subandean foreland basin suggest that the interandean thrust was active between about 10 ma and 5 ma the subandean thrust is still active southward displacement transfer from the subandean thrust onto the interandean thrust and a southward dipping lateral ramp of the interandean thrust result in the gradual transition from the interandean zone north of 22 s to the cordillera oriental of northern argentina a similar but larger scale transfer may be involved in the southern termination of the thin skinned subandean ranges of argentina at 23 s shortening in the western part of the thrust belt is of the order of 80 90 km total shortening in the eastern andean thrust belt from the undeformed foreland to the eastern margin of the cordillera oriental is 140 150 km

the influence of natural radiation damage on helium diffusion kinetics in apatite abstract stepwise degassing diffusion experiments on 39 different apatite samples using radiogenic 4he and proton induced 3he reveal a range in closure temperature tc from 50 to 115 c for a cooling rate of 10 c myr there is no correlation between helium diffusion and apatite chemistry including f cl ratio but the closure temperature is positively correlated with the radiogenic 4he concentration 4he in each sample we argue that 4he is a proxy for a sample s natural exposure to actinide radioactivity below the closure temperature and that helium diffusion in apatite is impeded by radiation induced damage to the apatite structure the kinetics must therefore be an evolving function of time measured diffusivities thus reflect a snapshot in time and cannot alone be applied to the thermochronometric interpretation of a given sample the effect of radiation damage on helium diffusion appears to far exceed other known controls on helium diffusivity including grain size our diffusion data are well described by a previously proposed quantitative model that consists of two arrhenius relations one for volume diffusion through undamaged mineral structure and one for release of helium from radiation damage traps the unknown parameters in this trapping model were determined from the diffusion experiments and allow us to develop a tentative mathematical function that relates diffusivity to temperature and 4he by inserting this function into a 4he production diffusion model we have explored how these results affect the interpretation of apatite u th he thermochronometry the model predicts that the effective 4he closure temperature of apatite will vary with cooling rate and effective u concentration eu and may differ from the commonly assumed tc of 70 c by up to 15 c the 4he partial retention zone will look similar to previous expectations but its depth will depend on accumulation time and on eu most notably samples subjected to reheating after accumulation of substantial radiation damage will be more retentive than previously expected these predictions are consistent with recent observations of unexpected apatite u th he ages in some settings

coupled simulation optimization model for draining confined aquifer via underground boreholes to prevent water inrush of coal mines in north china groundwater drainage is commonly applied by coal mines to prevent water inrush from confined aquifers underlying coal seams which can also cause environmental problems the previous research has proposed dual factor and triple factor models to manage water resources in coal mines however three features of draining confined water via underground boreholes have not been sufficiently considered the geological heterogeneity workface relocation and draining principle of underground boreholes this paper aims to incorporate the three features into an optimization model for underground borehole draining a novel mathematical model was proposed that included the three features a workflow framework was proposed to conduct the optimization based on gis and a coupled simulation optimization approach an algorithm was designed and a c program was developed to couple feflow with a modified genetic algorithm to search for the optimal solution the application to the liangbei coal mine indicates that the aquifer has been over drained about 69 and 36 of the water could be saved in the first two stages the total draining rate significantly changes with the workface relocation the boreholes located at the headwaters and closer to the workface that are mined now or in the next stage usually have higher rates than other boreholes the distribution of the draining rates is also related to the workface geometry and the aquifer anisotropy the optimization should be repeated as new monitoring data are acquired

submesoscale dynamics in the northern gulf of mexico part iii lagrangian implications abstractfour numerical simulations are used to characterize the impact of submesoscale circulations on surface lagrangian statistics in the northern gulf of mexico over 2 months february and august representative of winter and summer the role of resolution and riverine forcing is explored focusing on surface waters in regions where the water column is deeper than 50 m whenever submesoscale circulations are present the probability density functions pdfs of dynamical quantities such as vorticity and horizontal velocity divergence for eulerian and lagrangian fields differ with particles preferentially mapping areas of elevated negative divergence and positive vorticity the stronger the submesoscale circulations are the more skewed the lagrangian distributions become with greater differences between eulerian and lagrangian pdfs in winter lagrangian distributions are modestly impacted by the presence of the riverine outflow while increasing the model resolution from submesoscale permitting to sub

groundwater dewatering optimization in the shengli no 1 open pit coalmine inner mongolia china impacted by groundwater faults lithology and other factors the slope of the shengli no 1 open pit coalmine has been in a state of instability among these factors groundwater in the quaternary aquifer is considered primary thus an optimum design for dewatering well pumping rates is presented in this paper a two dimensional groundwater simulation model is built to characterize the groundwater flow of the study area a steady state model was applied to the observed data head and discharge to verify and calibrate the groundwater model the pilot point method with a regularization option provided by parameter estimation was used to identify the hydraulic conductivity field afterward a groundwater optimization model is integrated with the calibrated simulation model to realize groundwater dewatering optimization in the studied open pit coalmine and an optimization method called modified pareto dominance based real coded genetic algorithm is adopted taking into account the safety of the mine slope and dewatering wells seepage discharge is added to objective function and the maximum aquifer saturated thickness is set as the constraint condition in the optimization model the results indicate that the dewatering optimization procedure developed in this paper can serve as a useful template and framework for solving mining related water problems

the ages and tectonic setting of the faja eruptiva de la puna oriental ordovician nw argentina abstract the ordovician faja eruptiva de la puna oriental is a magmatic predominantly intrusive belt in the puna of northwestern argentina with a n s extension of ca 400 km scarce isotope geochemical ages and biostratigraphic data on some of the folded faja eruptiva country rocks assign the magmatism either to the lower and lower middle ordovician or to the latest ordovician interpretations of origin and tectonic framework of the faja eruptiva are controversial and vary between arc back arc and collisional orogenic settings we present high resolution la icp ms u pb age and hf isotope data on zircons from 10 plutonic samples covering the magmatic belt along a length of 200 km in the northern argentinian puna the xenocrystic and magmatic zircon age data have a wide spread between 2700 ma and 440 ma concordia and weighted mean age data document protracted magmatism in two phases between 480 and 460 ma and between 453 and 444 ma and constrain the time of the last intrusions at 444 3 ma and at 445 2 ma thus defining this last and main phase of intrusion at 444 ma ehf t values define a main vertical trend centered at 500 ma with ehf t values between 3 and 16 indicating significant mixing of juvenile early paleozoic melts with paleoproterozoic crustal components a second trend is formed by zircons with ages between 1 1 ga and c 500 ma and predominantly positive ehf values between 8 and 3 and originates in juvenile mantle compositions between 1 6 and 1 1 ga the spread of the zircon and hf data document that the faja eruptiva intrusives have experienced large scale contamination by the hosting crustal basement it follows that the basement of the puna is formed either by the upper proterozoic lower cambrian puncoviscana formation as an erosional product of the proterozoic orogenic belts of sw amazonia or that the puna including its puncoviscana basement is underlain by a crust shaped by these orogenies the main intrusive event at 444 ma has been linked to the ocloyic orogeny in the late ordovician the plutons intruded very likely in a sinistral strike slip regime after the main folding phase of the ocloyic orogeny had deformed the ordovician sedimentary country rocks

deformation history of the puna plateau central andes of northwestern argentina abstract two tectonic shortening events created the first order structural characteristics of the puna plateau one in the paleozoic and a second during the andean orogeny in the cenozoic to constrain the structural characteristics and timing of andean deformation in the puna plateau we focus on differentiating these two shortening events and provide cooling ages apatite fission track and apatite u th he to determine the amount of andean exhumation on the hanging wall of major cenozoic faults two contrasting expressions of shortening are documented in ordovician strata strain requires four stages folding flattening through cleavage formation low angle faulting and local distributed shear in the mesozoic and cenozoic strata shortening is expressed as reverse faults fault propagation folds and dipping panels dissimilarities reflect different p t conditions and amount of strain as structures in the ordovician rocks require higher temperatures and strain than andean structures in the mesozoic and cenozoic strata furthermore local cretaceous aft cooling ages in pervasively cleaved ordovician rocks reveal these rocks did not reach temperatures compatible with cleavage formation during the andean event lastly our data show a middle eocene to oligocene exhumation history that supports an overall continuous development of the andean thrust belt in the puna plateau since the early cenozoic

growth and fragmentation of the andean foreland basin during eastward advance of fold thrust deformation puna plateau and eastern cordillera northern argentina 1 the fault bounded cianzo basin represents a cenozoic depocenter between the puna plateau and eastern cordillera of northern argentina analysis of fold thrust relationships nonmarine sedimentation and detrital provenance at 23 24 s helps constrain the origin interconnectedness and subsequent uplift and exhumation of the cianzo basin a potential analog for intermontane hinterland basins in the andes structural mapping reveals a plunging syncline within the 6000 m thick upward coarsening cenozoic clastic succession in the shared footwall of the n striking e directed cianzo thrust fault and transverse ne striking hornocal fault growth strata within upper miocene levels indicate syncontractional accumulation adjacent to the hornocal fault measured stratigraphic sections show upsection changes from 1 paleosol rich distal fluvial sandstones 400 m paleocene eocene santa barbara subgroup to 2 braided fluvial sandstones and mudstones 1400 m upper eocene oligocene casa grande formation to 3 distributary fluvial megafan sandstones and conglomerates 3300 m upper oligocene miocene rio grande formation to 4 alluvial fan conglomerates 1600 m upper miocene pisungo formation the 40ar 39ar geochronological results for interbedded tuffs indicate continuous rio grande deposition from at least 16 34 0 71 to 9 69 0 05 ma sandstone petrographic results define distinct upsection trends in lithic and feldspar content potentially distinguishing the western cordillera magmatic arc from puna eastern cordillera thrust belt sources in addition to growth stratal relationships and 40ar 39ar ages conglomerate clast compositions reflect distinct lithologic differences constraining activation of the cianzo thrust and coeval reverse slip on the reactivated inverted hornocal fault finally detrital zircon u pb ages paleocurrents and facies patterns distinguish local from distal sources revealing a systematic forelandward eastward advance of eocene through upper miocene fold thrust deformation