foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

mechano chemical interactions in sedimentary rocks in the context of co2 storage weak acid weak effects abstract due to the corrosive nature of dissolved co2 the potential short or long term alteration of rock properties represents a major issue in several sites where natural co2 circulation is observed as well as in reservoirs targeted for storage of anthropogenic co2 to date this has been primarily studied from a transport chemical perspective with laboratory evidence of microstructural modifications together with the consequences for flow properties compared to the transport chemical aspects the mechanical chemical aspects have been less investigated though it is to be expected that mechanical properties e g elastic properties failure parameters and time dependent mechanical behaviour could potentially be affected in a similar manner to hydraulic parameters yet since co2 is a weak acid the ph drop is expected to be moderate with a likely lower limit close to 4 0 the buffering of ph by calcite minerals present in most reservoirs targeted for storage may further limit the ph drop as well as confining it to a localized rock volume around the injection well this leads to the question of the magnitude and time spatial scales of chemically mediated mechanical processes during co2 sequestration the authors propose to address this issue by reviewing recent laboratory based studies restricted to sedimentary rocks namely reservoir rocks carbonate or sandstone intact or fractured caprocks and fault rocks key findings include the following 1 the short term impact on the elastic and inelastic behaviour of intact caprocks remains limited 2 shear strength weakening is likely to be respectively low and low to moderate for shale clay rich and anhydrite rich faults but without modifying slip stability in either case 3 the largest impact is located within carbonate reservoirs but with a broad range of reported responses depending on hydrodynamic conditions closed or open and on dissolution regime uniform or channelling and 4 creep experiments confirm that co2 induced dissolution may enhance long term compaction of carbonate reservoirs but the magnitude of acceleration varying from non significant to 50 times depends to a large extent on site specific conditions grain size ph temperature effective stress state etc which renders any direct extrapolation from laboratory to reservoir scale difficult finally some directions for future research studies are discussed

late cenozoic deformation and uplift of the western flank of the altiplano evidence from the depositional tectonic and geomorphologic evolution and shallow seismic activity northern chile at 19 30 s 1 we analyze the west vergent thrust system wts along the western flank of the altiplano in northern chile 18 s 21 s in our study area 19 20 s 19 50 s the wts consists of three thrust propagation monocline folds flexures developing growth strata the relative uplift accommodated by the flexures is rapid between 26 and 8 ma 0 1 mm yr diminishing to 0 02 mm yr after 8 ma approximately 2000 m of relative surface uplift was accommodated by the flexures since the late oligocene sedimentological and geomorphological analysis shows that westward tilting of the forearc occurred after 10 ma coeval with the shifting of deformation from the altiplano to the sub andean zone where the underthrusting of the brazilian craton would have resulted in crustal thickening surface uplift in the orogen and westward ductile subcrustal flow forearc tilting is accommodated by east vergent thrusts ets issued from the benioff zone beneath the central depression emerging into the western cordillera contributing 500 1400 m of surface uplift the wts connects the ets in the brittle ductile crustal transition 25 km depth continuing farther east as the altiplano low velocity zone configuring the western altiplano as a crustal scale fault bend fold forearc tilting would be caused by westward ductile flow in the lower crust pushing the rigid forearc in the ets meanwhile between 19 s and 21 s the wts accommodates dextral strike slip and 3 km of n s shortening occurred in the coastal cordillera transcurrence and strain partitioning are probably the result of slight plate convergence obliquity strong coupling within the interplate zone westward continental concavity and high elevation opposing horizontal contraction

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

internal dynamics of a paleoaccretionary wedge insights from combined isotope tectonochronology and sandbox modelling of the south central chilean forearc forearc accretionary wedges are cyclic systems in which material is frontally and or basally accreted material cycling involves underthrusting subduction underplating exhumation erosion transfer to the trench and underthrusting again in this study we present a novel tectonochronologic approach to constrain long term exhumation rates of basally accreted wedge complexes based on isotopic dating of structural features on petrological data and sandbox analogue simulations congruence between the structural inventory in nature and structures generated in scaled sandbox experiments allows detailed insights into wedge dynamics for the present day surface material of the paleoaccretionary wedge of south central chile valdivia area 40 s published u pb ages of detrital zircon place a maximum age of 278 ma for subduction prograde metamorphism at transitional greenschist to blueschist facies conditions 420 c 8 9 kbar was immediately followed by progressive penetrative deformation associated with basal accretion dated at 250 245 ma using rb sr internal mineral isochrons the accretion process involved duplex tectonics and antiformal stacking with formation of near horizontal mylonitic shear zones at around 241 ma continuous basal accretion at depth gave rise to an extensional tectonic regime at higher structural levels both semi ductile small scale extensional shear zones and post kinematic vein mineralizations yield rb sr ages of 235 ma tension gashes representing the latest isotopically dateable stage of structural evolution were formed at 210 ma at conditions of 230 c at 1 5 3 kbar as constrained by fluid inclusion data zircon fission track data indicate final cooling to below 200 c at 186 24 ma the results suggest continuous basal accretion for at least 50 ma with long term average exhumation rates of 0 6 0 2 mm a most probably outbalanced by similar long term average erosion rates changing plate boundary conditions at about 210 200 ma terminated the accretion process as evident from a dramatic decrease of exhumation rates at that time since then the paleoaccretionary wedge remained stably in place despite its delicate geotectonic position within the andean active margin the tectonochronologic approach complements thermochronologic and geomorphologic methods of exhumation research as it provides direct constraints on mass flux rates even for high temperature increments of p t trajectories

episodic development of a convergent margin inferred from structures and processes along the southern chile margin seismic reflection data acquired in the vicinity of isla mocha across the southern coast of chile image structures formed along the continental margin and reveal an episodic history of accretion nonaccretion and possibly erosion structures formed at the toe of the continental slope suggest frontal accretion of to 1 km of trench fill seismic images also reveal that a small accretionary wedge 20 30 km wide abuts the truncated continental metamorphic basement that extends seaward from beneath the shelf the small size of the accretionary wedge on three profiles examined here is not consistent with a long history of accretion with the current deformational style as current rates of frontal accretion could have accumulated all of the existing accretionary wedge in less than 1 2 m y this is a small fraction of convergence history along this margin and the current accretionary mode has not been consistently maintained in the past the isla mocha region is located between the temperate climate of central chile and the glacial climate of southern chile and climatic conditions in this region have likely fluctuated sufficiently to cause significant variation in trench sediment supply accretionary and nonaccretionary or erosional episodes are probably linked to temporal variations in trench sediment thickness as suggested by observations along the chile margin currently thick trench sediment correlates with accretion along the southern chile margin and thin trench sediment correlates with nonaccretion tectonic erosion as near the chile ridge and from the juan fernandez ridge to northern chile the isla mocha region also lies 900 1000 km north of the chile triple junction and the chile ridge lies approximately 2000 km to the west and has not yet collided and affected the margin near isla mocha this part of the precollision zone provides an excellent reference to examine the effects of chile ridge collision in the development of the chile margin the most apparent effect of subduction of the buoyant young crust of the chile ridge is a shallow trench that is nearly devoid of sediment consequently the triple junction is undergoing nonaccretion or erosion and the accretionary complex near the triple junction remains smaller than to the north or south because the current phase of rapid accretion elsewhere in the trench has bypassed the triple junction region the interplay of subduction zone processes such as trench sedimentation and ridge collision has resulted in an episodic development of the margin and produced a discontinuous record of convergence history within the accretionary wedge

contrasting nature of deformation along an intra arc shear zone the liquine ofqui fault zone southern chilean andes abstract the liquine ofquifault zone lofz cuts the patagonian batholith and the modern volcanic arc of southern chile for ca 1000 km the rock fabric along three transects of the lofz combined with new and published geochronological data suggest marked differences in the nature and timing of deformation along strike in the liquine transect 39 s a 1 km wide northeast striking subvertical mylonitic zone shows north plunging stretching lineations this mylonitic zone has been juxtaposed by high angle reverse faulting against a nearly undeformed miocene granitoid metamorphic assemblages and microstructures in the mylonites indicate greenschist facies conditions and sinistral reverse displacement deformation pre dates a 100 2 ma undeformed porphyritic dike hornblende 40ar 39ar mean age in the reloncavi transect 41 42 s deformation in cretaceous and miocene plutons is predominantly brittle kinematic analysis of two fault populations yields compressional and dextral strike slip stress regimes interpreted as late miocene in age in the hornopiren transect 42 43 s a 4 km wide mylonitic zone developed in plutons and wallrocks shows subhorizontal stretching lineations and dextral displacement a single fault population overprinting the mylonites supports a dextral strike slip stress regime available u pb k ar and 40ar 39ar dates on deformed cenozoic plutons and wallrock range from 9 to 13 ma on hornblende and from 6 to 3 ma on biotite microstructures and mineral assemblages indicate that the youngest ductile fabrics in the plutons formed at greenschist facies similar to the biotite ar closure temperature subparallel magmatic and solid state fabrics combined with geochronology suggest that dextral displacement was continuous during emplacement and cooling of the plutons dextral oblique subduction of the nazca plate beneath western south america has driven long term intra arc deformation at the southern andes plate boundary zone ridge collision in turn has favored dextral displacement at the leading edge of the continent since the pliocene

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

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

carbon dioxide injection and resultant alteration of the weber sandstone rangely field colorado 1 geologic interpretations made during the current enhanced oil recovery project at rangely field rio blanco county colorado have shown the relationships between alteration of reservoir mineralogy and texture changes in produced water composition and increased problems with oil production the bottom hole ph of weber brine has decreased from approximately 7 5 to 4 5 since the initiation of co 2 injection into the pennsylvania permian weber sandstone in the central portion of the field much of the weber is partially cemented with carbonate minerals including ferroan calcite and ferroan dolomite with authigenic clay minerals predominately illite and mixed layer smectite illite also present these minerals are affected by the lowered ph of the co 2 flood changes in the chemistry of produced water are associated with alteration of reservoir mineralogy the co 2 flood has caused substantial increases in the concentrations of iron calcium and magnesium in the produced brine from the dissolution of carbonate cements and perhaps authigenic clays and detrital feldspars produced water from some wells has experienced large changes in barium and sulfate concentrations an increase in bromide concentration indicates that previously segregated portions of the reservoir which contained very saline original formation brine have been accessed by the carbonated water hypotheses based on the water chemistry changes were confirmed in core flood experiments these experiments also indicated that there was no net change in permeability following co 2 injection

orographic precipitation and the relief of mountain ranges 1 the influence of climate on the relief of mountain ranges has long been supposed but has received little quantitative investigation the simplified system of a longitudinal river profile in a bedrock channel coupled to a physically based model of orographic precipitation is used to explore how orographically influenced patterns of precipitation affect the relief of fluvially sculpted mountain ranges it is shown that the impact on the orography depends on the nature of the precipitation regime significant changes in relief also occur for imposed temperature changes of realistic magnitude although the ability of the relief to respond to any given change depends sensitively on its response time and the timescale of the forcing

quaternary glaciations of the southern andes abstract the southern andes comprise the southernmost portion of the andean cordillera beginning at the edge of the puna altiplano lat 27 s and ending at isla de los estados lat 55 s the late cainozoic glacial record of these mountains spans the interval from the late miocene to the present and is one of the most complete to be found anywhere in the world this has arisen for several reasons i the conterminous mountain ice cap extended to the piedmont zone on both flanks of the range where the sedimentary and morphological record has been well preserved ii periodic volcanism mainly from monogenetic fissure eruptions of basalt east of the range and from central tephra producing cones along the mountain crest has provided opportunity for the preservation and radiometric dating of interbedded glacial deposits iii a tectonically induced interval of stream incision in the mid pleistocene and simultaneous uplift has preserved glacial sediments on interfluves iv in the chilean lakes region west of the mountains late quaternary glaciers terminated in a well vegetated landscape thus creating scope for radiocarbon dating of interbedded and incorporated organic materials consequently the last glaciation in the llanquihue area of chile is one of the best dated sequences in south america thus the llanquihue glaciation is proposed as the south american equivalent of the wisconsin and weichsel glaciations of north america and north west europe respectively

evaluation of the impact of co2 co contaminant gas aqueous fluid and reservoir rock interactions on the geologic sequestration of co2 lowering the costs of front end processes e g separation in the geologic sequestration of co2 can dramatically lower the overall costs one possible approach is to sequester less pure co2 waste streams that are less expensive or require less energy to separate from flue gas or a coal gasification process etc the objective of this research is to evaluate the impacts of co2 itself as well as an impure co2 waste stream on geologic sequestration using reaction progress models reactive transport simulators and analogous reactive transport experiments run in a plug flow reactor specifically we are investigating the potential for co injecting the sox nox and h2s present in coal fired waste streams along with the co2 we present here the results of reactive transport simulations made to investigate the long term impact of dissolved co2 h2s and so2 on carbon sequestration in the frio fm tx the results suggest that addition of relatively large amounts of h2s to a co2 injection should not adversely impact injectivity or sequestration compared to the injection of co2 alone the co injection of so2 however could produce significantly different results if conditions are such that so2 can oxidize to sulfate in the long term the simulations suggest that carbonate mineral formation can sequester a significant fraction of the injected carbon through the formation of calcite magnesite and dawsonite

climatic and ecologic changes during miocene surface uplift in the southern patagonian andes abstract the up to 4 km high southern patagonian andes form a pronounced topographic barrier to atmospheric circulation in the southern hemisphere westerlies and cause one of the most drastic orographic rain shadows on earth geologic data imply that this climatic pattern has been established or significantly enhanced during miocene surface uplift of this andean segment we report evidence for important climatic and ecologic changes in the eastern foreland of the patagonian andes that appear to be the result of this uplift to provide constraints on miocene plant ecosystems and precipitation in the eastern leeward foreland of the patagonian andes we determined carbon and oxygen isotope values of pedogenic carbonate nodules from a 500 m thick section of the continental santa cruz formation the age of these deposits was constrained by ar ar dating of intercalated tuffs which range from 22 to 14 ma at 16 5 ma the 13 c values increase by 3 the 18 o values decrease by 2 and the scatter in the oxygen isotope data increases significantly we interpret these changes as the consequence of 1 km surface uplift in this andean segment from the 18 o values and increased aridity to its east from the 13 c values and the increased scatter in the 18 o values sediments overlying the santa cruz formation are very limited in extent and volume and dominated by coarse conglomerates related to pleistocene and older glaciations it thus seems that by 14 ma deposition in the eastern foreland of the southern patagonian andes had essentially ceased as the result of rain shadow formation

mesozoic to quaternary continental margin dynamics in south central chile 36 42 s the apatite and zircon fission track perspective zircon and apatite fission track data provide constraints on the exhumation history fault activity and thermal evolution of the south central chilean active continental margin 36 s 42 s which we use to assess the tectonic and geomorphic response of the margin to the andean subduction regime several domains with different exhumation histories are identified the coastal cordillera is characterized by uniform and coherent exhumation between late triassic 200 ma and late miocene times with surprisingly slow average rates of 0 03 0 04 mm a thermal anomalies related to late cretaceous and early miocene magmatism have regionally modified fission track age patterns the upper cretaceous thermal overprint is of previously unrecognized significance and extent in the coastal cordillera south of 39 s with the exception of a local but distinct pliocene to recent exhumation period in the high relief cordillera nahuelbuta segment between 37 s and 38 s cenozoic overall exhumation in the coastal cordillera was very slow the sedimentary record shows that uplift and subsidence here was episodic with low amplitudes and durations this rules out large scale long term cenozoic accretion trench parallel tilting and tectonic erosion processes in the forearc the main andean cordillera shows markedly greater long term exhumation rates than the coastal cordillera and at 39 s a steep exhumation gradient to the south long term average pliocene to recent exhumation rates of 1 to 2 mm a in the liquine area 39 45 s are almost an order of magnitude more rapid than average paleogene to recent exhumation near lonquimay 38 30 s and farther north while no imprint of the intra arc liquine ofqui fault zone on the exhumation pattern is evident long term exhumation rates decrease from the crest of the andes toward the western foothills exhumation gradients correlate with climatic gradients suggesting a causal link to the variable intensity of late miocene to pleistocene glacial erosion

landscape response to tectonic forcing digital elevation model analysis of stream profiles in the mendocino triple junction region northern california the topographic evolution of orogens is fundamentally dictated by rates and patterns of bedrock channel incision quantitative field assessments of process based laws are needed to accurately describe landscape uplift and denudation in response to tectonics and climate we evaluate and calibrate the shear stress or similar unit stream power bedrock incision model by studying stream profiles in a tectonically active mountain range previous work on emergent marine terraces in the mendocino triple junction region of northern california provides spatial and temporal control on rock uplift rates digital elevation models and field data are used to quantify differences in landscape morphology associated with along strike northwest to southeast changes in tectonic and climatic conditions analysis of longitudinal profiles supports the hypothesis that the study area channels are in equilibrium with current uplift and climatic conditions consistent with theoretical calculations of system response time based on the shear stress model within uncertainty the profile concavity of the trunk streams is constant throughout the study area 0 43 as predicted by the model channel steepness correlates with uplift rate these data help constrain the two key unknown model parameters the coefficient of erosion k and the exponent associated with channel gradient n this analysis shows that k cannot be treated as a constant throughout the study area despite generally homogeneous substrate properties for a reasonable range of slope exponent values n best fit values of k are positively correlated with uplift rate this correlation has important implications for landscape evolution models and likely reflects dynamic adjustment of k to tectonic changes due to variations in orographic precipitation and perhaps channel width sediment load and frequency of debris flows the apparent variation in k makes a unique value of n impossible to constrain with present data

climate and tectonic controls on glaciated critical taper orogens abstract in this work we present the results of a new analytical model that examines the coupling between glacial erosion and orogen development surface processes are assumed to be glacially dominated and tectonic activity is controlled by critical wedge mechanics in these circumstances we find that orogen width is strongly dependent on both the rate of accretion and on the rate of precipitation the orogen size is linked to tectonic and climate changes via proportionality constants the orogen width scales with the rate of accretion to between the 2 3rd and 2nd powers and with the rate of precipitation to the 1 3rd and 5 4th powers the value of the proportionality constants varies with the taper angle and the relative rates of ice deformation and sliding in all cases the sensitivities are higher than those calculated for fluvially eroding critical wedge orogens analytical solutions are supported by the results of a numerical flow line model the flow line model further predicts that uplift rates will be highest at and just below the equilibrium line altitude if glacial ablation is largely a calving process rock uplift in the wedge will be strongly focused towards the toe the predicted response time of glaciated orogens to changes in climate and tectonic forcing is dependent upon the constants of erosion the rheology and the rate of precipitation these analyses predict that actual orogens have variable e folding response times for example approximately 1 5 myr for the southern alps of new zealand and the olympic mountains of washington state and approximately 5 5 myr for the european alps

a test of the effectiveness of pore scale fluid flow simulations and constitutive equations for modelling the effects of mineral dissolution on rock permeability abstract macro scale transport properties of rocks such as permeability are bulk parameters combining the contributions of various properties only properly defined at the pore scale since pore scale processes are known to modify the rock properties it is legitimate to ask if constitutive equations based on macro scale properties e g porosity permeability formation factor etc can properly describe their effect in a previous experimental study lamy chappuis et al 2014 we found that the effect of mineral dissolution on permeability could be much higher than predicted by such semi empirical constitutive equations here we directly solve pore scale fluid flow in high resolution 2 5 m 3d models of a rock s geometry before and after mineral dissolution in order to evaluate permeability and how it is changed this methodology is limited by the resolution of the micro ct images used to define the rock geometry which leads to significant overestimates of absolute permeability but it does produce a much closer match to the change in permeability due to mineral dissolution than the constitutive equations this is possible because the dissolution features which enhance permeability are large enough to be adequately resolved and produce a significant change in permeability

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

paleoproductivity evolution off central chile from the last glacial maximum to the early holocene a geochemical and paleontological reconstruction of paleoproductivity upwelling intensity and sea surface temperature sst off central chile at 35 s geob3359 3 reveals marked changes from the last glacial maximum lgm through the early holocene surface water productivity was determined by the interaction between the atmospheric the southern westerlies and oceanographic the antarctic circumpolar current acc systems from the lgm through early termination i ti the northward shift of the climate zones during the lgm brought the acc as the main macronutrient source closer to the geob3359 3 sst lowered and surface water productivity and accumulation rates of biogenic components enhanced with the poleward return of the southern westerlies and the acc the subtropical high pressure system became the dominant atmospheric component southward till 35 s during the late ti and early holocene and caused surface water productivity to increase through enhanced upwelling

uplift of the western margin of the andean plateau revealed from canyon incision history southern peru we explore canyon incision history of the western margin of the andean altiplano puna plateau in the central andes as a proxy for surface uplift u th he apatite data show rapid cooling beginning at ca 9 ma and continuing to ca 5 1 ma in response to incision a minimum of 1 0 km of incision took place during that interval the youngest apatite date and a volcanic fl ow perched 125 m above the present valley fl oor dated at 2 261 0 046 ma 40 ar 39 ar show that an additional 1 4 km of incision occurred between ca 5 1 and 2 3 ma thus we infer that a total of at least 2 4 km or 75 of the present canyon depth was incised after ca 9 ma u th he zircon data collected along the same transect imply that the western margin of the plateau was warped upward into its present monoclinal form rather than uplift being accommodated on major surface breaking faults

late quaternary precessional cycles of terrigenous sediment input off the norte chico chile 27 5 s and palaeoclimatic implications abstract the palaeoclimatic conditions during the last glacial maximum lgm of southern south america and especially latitudinal shifts of the southern westerly wind belt are still discussed controversially longer palaeoclimatic records covering the late quaternary are rare a particularly sensitive area to late quaternary climatic changes is the norte chico northern chile because of its extreme climatic gradients small shifts of the present climatic zonation could cause significant variations of the terrestrial sedimentary environment which would be recorded in marine terrigenous sediments to unveil the history of shifting climatic zones in northern chile we present a sedimentological study of a marine sediment core geob 3375 1 from the continental slope off the norte chico 27 5 s sedimentological investigations include bulk and silt grain size determinations by sieving atterberg separation and detailed sedigraph analyses additionally clay mineralogical parameters were obtained by x ray diffraction methods the 14c dated core covering the time span from approximately 10 000 to 120 000 cal yr b p consists of hemipelagic sediments terrigenous sedimentological parameters reveal a strong cyclicity which is interpreted in terms of variations of sediment provenance modifications of the terrestrial weathering regimes and modes of sediment input to the ocean these interpretations imply cyclic variations between comparatively arid climates and more humid conditions with seasonal precipitation for northern chile 27 5 s through the late quaternary the cyclicity of the terrigenous sediment parameters is strongly dominated by precessional cycles for the palaeoclimatic signal this means that more humid conditions coincide with maxima of the precession index as e g during the lgm higher seasonal precipitation for this part of chile is most likely derived from frontal winter rain of the southern westerlies thus the data presented here favour not only an equatorward shift of this atmospheric circulation system during the lgm but also precession controlled latitudinal movements throughout the late quaternary precessional forcing of latitudinal movements of the westerly atmospheric circulation system may be conceivable through teleconnections to the northern hemisphere monsoonal system in the atlantic ocean region

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

average pleistocene climatic patterns in the southern central andes controls on mountain glaciation and paleoclimate implications abstract despite elevations of 5000 6800 m modern glaciers occur along the southern puna plateau and the northern sierras pampeanas in the southern central andes the modern snowline rises from 5100 m in sierra aconquija to 5800 m in the puna as a result of a westward decrease in precipitation from 450 to less than 100 mm yr during the pleistocene these arid highlands experienced multiple cirque and valley glaciation that likely postdate the last interglacial period although lack of age control prevents an absolute chronology glaciation in the puna and along the eastern puna edge produced a 300 m pleistocene snowline psl depression while in the sierras pampeanas the psl depression was at least 900 m the greater psl depression in the sierras pampeanas is best explained by a combination of cooling and increase of easterly moisture whereas the psl depression in the puna appears more sensitive to moisture increases than temperature previously glaciations in this region have been explained by increa

tracing the impact of glacial interglacial climate variability on erosion of the southern andes sediment accumulation rates of well dated primarily terrigenous marine sediments collected along the chilean continental margin were used to infer erosion rates of the southern andes and the adjacent coastal cordillera compared to the holocene sediment supply to the margin and thus erosion were substantially enhanced during the last glacial when continental rainfall in the region was higher major changes in precipitation forcing to the southern andes on such glacial interglacial time scales appear to be transferred to offshore sedimentation rates by a fixed relation these data show that marine archives can make it possible to trace variability in erosion at adjacent continents on time scales to 10 3 yr a much better resolution than provided by commonly used methods such as thermochronometry or seismic studies

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

two phase flow properties of a sandstone rock for the co2 water system core flooding experiments and focus on impacts of mineralogical changes the two phase flow characterization co2 water of a triassic sandstone core from the paris basin france is reported in this paper absolute properties porosity and water permeability capillary pressure relative permeability with hysteresis between drainage and imbibition and residual trapping capacities have been assessed at 9 mpa pore pressure and 28 c co2 in liquid state using a single core flooding apparatus associated with magnetic resonance imaging different methodologies have been followed to obtain a data set of flow properties to be upscaled and used in large scale co2 geological storage evolution modeling tools the measurements are consistent with the properties of well sorted water wet porous systems as the mineralogical investigations showed a nonnegligible proportion of carbonates in the core the experimental protocol was designed to observe potential impacts on flow properties of mineralogical changes the magnetic resonance scanning and mineralogical observations indicate mineral dissolution during the experimental campaign and the core flooding results show an increase in porosity and water absolute permeability the changes in two phase flow properties appear coherent with the pore structure modifications induced by the carbonates dissolution but the changes in relative permeability could also be explained by a potential increase of the water wet character of the core further investigations on the impacts of mineral changes are required with other reactive formation rocks especially carbonate rich ones because the implications can be significant both for the validity of laboratory measurements and for the outcomes of in situ operations modeling

climatic influences on profile concavity and river incision 1 longitudinal profiles of alluvial and bedrock rivers are typically concave up and the precise shape of their concavity is known to integrate tectonic climatic and channel grain size distribution factors we isolate climatic hydrologic effects on profile concavity through a spatial analysis of large watersheds with mixed bedrock alluvial trunk channels spanning a steep climatic hydrologic gradient in a tectonically stable landscape forty watersheds on the eastern american high plains were selected to minimize variability in base level relief vegetation rock type and drainage area we calculate stream concavity by two complementary methods an area normalized stream concavity index sci and the slope of a line regressed through log log plot of channel slope and basin area the sci and covary more importantly a positive correlation exists between profile concavity and climatic hydrologic factors such as precipitation intensity and peak annual discharge however modeled profile steepness has no correlation to climate or watershed hydrology we conclude that in tectonically stable settings higher intensity rainfall and greater mean annual precipitation lead to more concave profiles we do not have data to know if the concavity changes reflect primarily bedrock or alluvial grain size processes but generally a doubling of rainfall intensity on the high plains leads to a tripling in concavity manifest as tens of meters of incision such climatically influenced profile concavity could explain some of the often cited late cenozoic incision and increase in local relief for the high plains and rocky mountains traditionally ascribed to tectonics

changes in the hypsometric curve through mountain building resulting from concurrent tectonics and denudation abstract the stages of geomorphic development of mountains have sometimes been explained based on strahler s diagram of hypsometric curves although the japanese mountains are young they do not follow his diagram hypsometric curves simulated using empirical laws deduced from the japanese mountains indicate that mountain building resulting from concurrent tectonics and denudation does not produce convex curves but concave and or s shaped curves the hypsometric curve of a mountain changes from a concave curve to an s shaped curve in accordance with the increase in mountain altitude the succession of the hypsometric curve during concurrent tectonics and denudation is the reverse of strahler s diagram the hypsometric integral increases with the advance in stage which is evaluated based on the change in mountain altitude it has a relatively good correlation with the stage however the sequence of change in the hypsometric integral is different according to the extent of the terrain examined whether the terrain is restricted to the interior of a mountain or pertains to the whole mountain and whether it includes newly emerged land the stage should be evaluated based on the course of change in the integral characteristics for the extent of the mountain examined

rapid porosity and permeability changes of calcareous sandstone due to co2 enriched brine injection reservoir injectivity and storage capacity are the main constraints for geologic co2 sequestration subject to safety and economic considerations brine acidification following co2 dissolution leads to fluid rock interactions that alter porosity and permeability thereby affecting reservoir storage capacity and injectivity thus we determined how efficiently co2 enriched brines could dissolve calcite in sandstone cores and how this affects the petrophysical properties during computerized tomography monitored flow through reactor experiments calcite dissolved at a rate largely determined by the rate of acid supply even at high flow velocities which would be typical near an injection well the porosity increase was accompanied by a significant increase in rock permeability larger than that predicted using classical porosity permeability models this chemically driven petrophysical change might be optimized using injection parameters to maximize injectivity and storage

chronology of motion in a complete thrust belt the precordillera 30 31 s andes mountains in the precordillera thrust belt of west central argentina faulted rotated and onlapping relations of piggyback basin units and foreland basin units yield an accurate but imprecise chronology of thrust motion addition of data from provenance history strata accumulation rates and presence of thick conglomerate units in the bermejo foreland basin results in a thrust chronology that is more precise but not entirely independent of assumptions about foreland basin dynamics seven new radiometric dates allow substantial revision of the interpreted age of first deformation in the precordillera at about 30 south units previously assigned to the paleozoic and mesozoic are of oligocene and miocene ages a redbed unit that began before 21 6 pm 0 8 ma appears to have pre dated thrusting deposits in the early bermejo foreland basin were dominated by eolian sandstones unlike the younger fluvial and alluvial units an andesitic volcanic center within the miocene foreland basin had long term effects on sub

crustal motion in the southern andes 26 36 s do the andes behave like a microplate 1 a new global positioning system gps derived velocity field for the andes mountains 26 36 s allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen s opposing sides adding an andes microplate to the traditional description of nazca south america plate convergence provides the kinematic framework for nearly complete explanation of the observed velocity field the results suggest the oceanic nazca boundary is fully locked while the continental backarc boundary creeps continuously at 4 5 mm yr the excellent fit of model to data 1 7 mm yr rms velocity misfit and the relative aseismicity of the upper crust in the interior andean region in comparison with its boundaries supports the notion that the mountains are not currently accruing significant permanent strains additionally the model implies permanent deformation is not accumulating throughout the backarc contractional wedge but rather that the deformation is accommodated only within a narrow deformational zone in the backarc

bay sedimentation as controlled by regional crustal behaviour local tectonics and eustatic sea level changes coquimbo formation miocene pliocene bay of tongoy central chile abstract the north facing bay of tongoy in central chile is flanked by topographic highs in the west and east during the miocene and pliocene the bay extended inland at least 30 km farther south than a present it was filled with muds sands coquinas and gravel during a series of transgressions and regressions related to regional and local tectonic movements combined with global sea level variations 87sr 86sr and microfossil dating indicates transgressions between 11 9 11 2 ma 10 1 9 5 ma 9 0 7 3 ma 6 3 5 3 ma 4 3 2 2 ma and 1 7 1 4 ma the regional tectonic behaviour of the crust shows general uplifting from 10 5 ma to 6 9 ma associated with subduction of the juan fernandez ridge jfr beneath this part of the continent subsidence followed between 6 9 and 2 1 ma in the wake of the southeastward migrating jfr the subsequent subduction of an oceanic plateau similar to the jfr caused rapid uplift that led to the final emergence of the bay above sea level the puerto aldea normal fault along the western limit of the study area was reactivated during the regional uplift and subsidence events with reverse faulting occurring during the latter phase sporadic fault reactivation probably triggered the rapid changes in water depth reflected in the recorded vertical succession of facies

holocene coseismic and aseismic uplift of isla mocha south central chile abstract during the past 6000 years isla mocha a 12 km long island 30 km off the coast of south central chile experienced a 38 m fall of relative sea level caused primarily by rapid tectonic uplift of the island as many as 18 raised shorelines strandlines record this uplift historic accounts of uplift during the great earthquakes m 8 of 1835 and 1960 suggest some of the more prominent prehistoric strandlines also emerged during great earthquakes on the interface between the nazca and south america plates but the close elevational spacing of strandlines subdued morphology of strandline beaches scarcity of exposed bedrock wave cut platforms and the extremely high rates of aseismic uplift ca 70 mm yr of the island since the last great earthquake suggest that many strandlines were raised by aseismic rather than coseismic uplift strandline heights and 14 new radiocarbon ages on marine shells show that the present day uplift rate is more than three times the net rate ca 20 mm yr of the past 1000 years the recent high rate probably reflects increased aseismic slip on an inferred thrust fault in the overriding south america plate isla mocha overlies an area of high stress concentration between two major segments of the chilean subduction zone the inferred high rate of slip on the thrust fault may be a response to stress changes on the plate interface near the boundary between the segments

kinematic constraints on intra arc shear and strain partitioning in the southern andes between 38 s and 42 s latitude 1 on the basis of structural field work fault kinematic analysis and the analysis of digital imagery we describe the northern part of the southern andean intra arc liquine ofqui fault zone lofz as an sc like fault zone system accommodating part of the nazca south american plate convergence obliquity kinematic modeling suggests that the lofz accommodated 124 24 21 km of dextral displacement between 40 s and 42 s and 67 13 11 km between 38 s and 40 s since the pliocene associated vertical axis rotations are 31 4 clockwise and 9 1 counterclockwise along synthetic and antithetic faults respectively mean pliocene to recent shear rates along the lofz decrease northward from 32 6 mm yr to 13 3 mm yr compatible with partitioning of half of the convergence obliquity into the intra arc zone north of 40 s and complete partitioning to the south the displacement gradient along the intra arc zone results in margin parallel shortening of the fore arc

from glacier facies to sar backscatter zones via gpr we present a comparison between data acquired with frequency modulated ground penetrating radar gpr and satellite synthetic aperture radar sar both radars are polarimetric and operate at a center frequency of 5 3 ghz the field site is the polythermal glacier kongsvegen svalbard along glacier gpr profiles cover the ablation area and the accumulation area where the latter consists of superimposed ice si and firn the glacier facies are clearly identifiable on the gpr profiles although we show that the copolarized response is better for distinguishing different ice zones whereas the si firn boundary is most obvious in the cross polarized response a calibrated backscatter coefficient is calculated for the gpr data and compared with the sar backscatter coefficient the sar zones are in very good agreement with the gpr derived glacier facies we show that in the ablation area the sar response is dominated by backscatter from the previous summer surface in the si and firn areas it is dominated by sources below the previous summer surface

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

southern westerlies during the holocene deduced from geomorphological and pedological studies in the norte chico northern chile 27 33 s abstract in the norte chico precipitation is controlled by atmospheric perturbations and frontal systems associated with the belt of westerly wind circulation the holocene climatic history of the region can be reconstructed from geomorphic and pedologic investigations in comparison to modern climatic conditions increased influence of the westerlies is deduced for the time periods prior to 7300 yr b p between 5000 3700 yr b p 3000 1800 yr b p and around 270 yr b p it remains uncertain whether the increased influence of the westerlies was the consequence of northward shifts of the westerlies as a whole of a meridional expansion of the westerly belt or only of intensity changes of the atmospheric dynamics almost synchronous with changes in the westerlies the coastal fogs in the region were apparently reduced or the fog belt in the coastal range was elevated probably due to a weakened upwelling and warmer water conditions in the eastern pacific in general the climate of the norte chico has become more variable since 5000 yr b p especially since 3000 yr b p with frequent changes of the geoecological conditions

a warm interglacial episode during oxygen isotope stage 11 in northern chile abstract combined paleontological morphostratigraphic and geochronologic data from emerged middle pleistocene coastal deposits in mejillones peninsula 23 s northern chile strongly suggest that climatic conditions were particularly warm during the particularly warm during the oxygen isotope stage 11 high seastand episode an anomalous warm water molluscan assemblage from localities assigned to that interglaciation included several extralimital species presently living only north of 6 s or 14 s that were not present in the area during subsequent middle and late pleistocene or holocene interglacial episodes only two of these extralimital species may be found nowadays at the 23 s latitude in a protected locality immediately after the occurrence of strong el nino events many of the species of the thermally anomalous molluscan assemblage tama are the same as those which lived in a closed shallow lagoon near santa north central peru 9 s during a brief mid holocene episode the new findings thus indicate that lagoonal and protected embayments were significantly warmer than the open marine environment ca 400 ka actually the co occurrence of cool water fauna in exposed sectors of the coastline at that time suggests that the coastal upwelling activity and the humboldt current effects were not strongly reduced the warm water conditions prevailing in lagoons and protected bays during the mid brunhes episode may reflect particularly warm air temperatures and distinct ocean atmosphere relationships than those prevalent nowadays these data support the hypothesis that the oxygen isotope stage 11 was the warmest interglaciation at least in the southern hemisphere

testing the tectonic significance of some parameters of longitudinal river profiles the case of the ardenne belgium nw europe the longitudinal profiles of 24 rivers of 3rd to 5th order have been analyzed in order to recognize the regional tectonic differentiation pattern of the ardenne a paleozoic massif of nw europe data collected exclusively from 1 25 000 topographic maps were used to define a set of parameters related to the geometry of the profile and proxies for river bedload and drainage area validation of the proxy defined for the bedload discharge ratio demonstrates its potential use for inter river comparison based on its value at the river mouth it is however inadequate to estimate the ratio changes along a given stream course this proxy has been computed to estimate the portion accounted for by hydrodynamic factors in the river bed profiling thus outliers to the correlation function linking it to the river bed gradient have been considered as undergoing other influences principally of lithologic or tectonic origin most indicative of the computed profile parameters are those related to the concavity of the profile four more or less regional longitudinal profile types are recognized which are partly determined by differential tectonic movement the combined analysis of all the parameters confirms the current uplift of the ne ardenne and points to a subsidence of the namur area with respect to its sw and se surroundings whether periglacial or tectonic in origin the upper pleistocene lowering of a local base level has also been identified in the famenne another conclusion of this study is that in order to evidence tectonic influences and to avoid any misinterpretation in a region of complex geologic and geomorphic history and moderate tectonic activity it is essential to consider a number of parameters and to consider their significance within the framework of detailed geologic setting and morphogenetic history

early to mid holocene aridity in central chile and the southern westerlies the laguna aculeo record 34 s abstract central chile 32 35 s lies at the northern border of strong westerly influence and thus exhibits a steep precipitation gradient therefore the palaeoclimatic archives in the region are suitable for detecting past moisture changes the study of laguna aculeo 33 50 s 70 54 w presents a multiproxy holocene lake record including sedimentology geochemistry mineralogy pollen diatoms and radiocarbon dating 17 dates results indicate an arid early to mid holocene period about 9500 5700 cal yr b p after 5700 cal yr b p effective moisture increased progressively and around 3200 cal yr b p modern humid conditions were established numerous intercalated clastic layers reflect flood deposition during rainy winters a fluvial unit was deposited shortly before 9000 cal yr b p subsequently flood events were absent until 5700 but have become frequent since 3200 cal yr b p the frequency of flood layers possibly points to weak or no el nino activity during the early and mid holocene with a subsequent increase during the late holocene during the early and mid holocene the westerlies were probably blocked and hence deflected southward by the subtropical high pressure cell higher precipitation during the last 3200 yr seems strongly related to a weakened subtropical high pressure cell with intensified westerlies and possibly increased el nino activity

the topographic imprint of a transient climate episode the western andean flank between 15 5 and 41 5 s mountain range topography is determined by the complex interplay between tectonics and climate however often it is not clear to what extent climate forces topographic evolution and how past climatic episodes are reflected in present day relief the andes are a tectonically active mountain belt encompassing various climatic zones with pronounced differences in rainfall erosion and glacier extent under similar plate boundary conditions in the central to south western andes climatic zones range from hyperarid desert with mean annual rainfall of 5 mm a 22 5 s to year round humidity with 2500 mm a 40 s the andes thus provide a unique setting for investigating the relationship between tectonics climate and topography we present an analysis of 120 catchments along the western andean watersheds between 15 5 and 41 5 s which is based on srtmv3 90m data and new medium resolution rainfall tropical rainfall measurement mission trmm dataset for each basin we extracted geometry relief and climate parameters to test whether andean topography shows a climatic imprint and to analyze how climate influences relief our data document that elevation and relief decrease with increasing rainfall and descending snowline elevation furthermore we show that local relief reaches high values of 750 m in a zone between 28 s to 35 s during pleistocene glacial stages this region was affected by the northward shifting southern hemisphere westerlies which provided moisture for valley glacier formation and extended glacial coverage as well as glacial erosion in contrast the southern regions between 35 s to 40 s receive higher rainfall and have a lower local relief of 200 m probably related to an increased drainage density we distinguish two different climatically controlled mechanisms shaping topography 1 fluvial erosion by prolonged channel hillslope coupling which smoothes relief and 2 erosion by valley glaciers that generates relief finally our results suggests that the catchment scale relief of the andes between 28 s to 35 s is characterized by a pronounced transient component reflecting past climatic conditions copyright 2010 john wiley sons ltd

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

pore scale simulation of carbonate dissolution in micro ct images we present a particle based method to simulate carbonate dissolution at the pore scale directly on the voxels of three dimensional micro ct images the flow field is computed on the images by solving the incompressible navier stokes equations rock fluid interaction is modeled using a three step approach solute advection diffusion and reaction advection is simulated with a semianalytical pore scale streamline tracing algorithm diffusion by random walk is superimposed while the reaction rate is defined by the flux of particles through the pore solid interface we derive a relationship between the local particle flux and the independently measured batch calcite dissolution rate we validate our method against a dynamic imaging experiment where a ketton oolite is imaged during co2 saturated brine injection at reservoir conditions the image calculated increases in porosity and permeability are predicted accurately and the spatial distribution of the dissolution front is correctly replicated the experiments and simulations are performed at a high flow rate in the uniform dissolution regime pe 1 and peda 1 thus extending the reaction throughout the sample transport is advection dominated and dissolution is limited to regions with significant inflow of solute we show that the sample averaged reaction rate is 1 order of magnitude lower than that measured in batch reactors this decrease is the result of restrictions imposed on the flux of solute to the solid surface by the heterogeneous flow field at the millimeter scale

4d multi scale imaging of reactive flow in carbonates assessing the impact of heterogeneity on dissolution regimes using streamlines at multiple length scales abstract we have experimentally investigated the impact of heterogeneity on the dissolution of two limestones characterised by distinct degrees of flow heterogeneity at both the pore and core scales the two rocks were reacted with reservoir condition co2 saturated brine at both scales and scanned dynamically during dissolution first 1 cm long 4 mm diameter cores were scanned during reactive flow with a 4 m voxel size between 10 and 71 times using 4d x ray micro tomography ct over the course of 90 min second 3 8 cm diameter 8 cm long cores were reacted at the same conditions inside a reservoir condition flow apparatus and imaged using a medical grade x ray computed tomography scanner xct each sample was imaged 13 times over the course of 90 min at a 250 250 500 m resolution these larger cores were then scanned inside a ct at a 27 m voxel size to assess the alteration pore space heterogeneity after reaction both rock types exhibited channel widening at the mm scale and progressive high porosity pathway dissolution at the cm scale in the more heterogeneous rock dissolution was more focussed and progressed along the direction of flow additionally the dissolution pathways contained a distinct microstructure captured with the ct that was not visible at the resolution of the xct where the reactive fluid had not completely dissolved the internal pore structure this microstructure was further analyzed by performing a direct simulation of the flow field and streamline tracing on the image voxels we found that at the larger scales the interplay between flow and reaction significantly affects flow in the unreacted regions of the core when flow is focussed in large reacted channels this focusing is carried through to the unreacted parts of the rock where flow continues to be confined to preferential pathways after passing the reaction front this focussing effect is greater with increasing pore space heterogeneity indicating that the representative elementary volume rev for dissolution is far greater than the dissolution front itself this study of scale dependence using in situ 4d tomography provides insight into the mechanisms that control local reaction rates at the mm and cm scales furthermore this work suggests that under these conditions at larger scales it is likely to be structural heterogeneity that dominates the pattern of dissolution and therefore the evolution of high permeability pathways

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

orographic barriers high resolution trmm rainfall and relief variations along the eastern andes 1 quantifying the degree to which tectonic and erosive processes shape landscapes is key to understanding the evolution of tectonically active mountain belts here we explore the interplay of these two processes along the humid eastern flank of the south american andes we use high resolution tropical rainfall measurement mission trmm and srtm data to characterize elevation relief and hillslope angle of peak rainfall at orographic barriers over a distance of more than 3500 km along the eastern flanks we find that peak rainfall 3 5 m yr occurs at a mean elevation of 1 3 0 17 km a mean relief of 0 95 0 08 km and at moderate mean hillslope angles of 18 3 1 7 we suggest that topographic relief is the best first order rainfall predictor and we demonstrate how relief changes along strike south of the andean orocline alter rainfall distribution changes in climatic sedimentary and tectonic processes prevent the formation of high relief amounts at the mountain front and these areas are not characterized by pronounced rainfall peak

net late holocene emergence despite earthquake induced submergence south central chile abstract intertidal deposits show net late holocene emergence at three sites along the pacific coast near maullin and carelmapu chile latitude 41 6 41 7 s the maximum amount of net emergence is ca 1 m in the past 1500 years and ca 2 1 2 m in the past 4000 years emergence probably would have prevailed at a fourth site near maullin were the site not underlain by easily compacted deposits this site shows slight

an experimental study of co2 brine rock interaction at in situ pressure temperature reservoir conditions abstract a detailed investigation of co 2 brine rock interactions through a core flooding laboratory experiment was carried out under simulated reservoir conditions 100 c and 24 mpa changes in the ionic chemistry of the outlet solution combined with core scanning electron microscopy sem and bulk rock x ray diffraction xrd analysis of the core pre and post experiment reveal new insights into co 2 brine rock interactions minerals such as potassium k feldspar albite calcite and ankerite are variably dissolved after the experiments calcite is the mineral most affected by dissolution followed by ankerite whereas dissolution of feldspar minerals is minimal small amounts of kaolinite and solid phases were generated as a result of the experiment the solid phases are mainly comprised of c o na cl al and si and are presumed to be the transitional products in the formation of carbonate minerals the very low fluid penetration rate in the experiment resulted in significantly reduced contact area between the acidic co 2 fluid and minerals in the cores resulting in low rates of feldspar dissolution core permeability decreased substantially throughout the experiment although core porosity remained unchanged the permeability reduction is the result of precipitation of new mineral phases e g kaolinite and solid phases and potentially also the presence of clay particles released by the dissolution of carbonate cement which have then been transported in the fluid flow path and accumulated at pore throats the results provide new insights into co 2 trapping mechanisms in depleted oil and gas reservoirs and into the potential formation damage that may result from massive injections of co 2 into reservoirs during enhanced oil recovery programs

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

coastal neotectonics in southern central andes uplift and deformation of marine terraces in northern chile 27 s abstract neotectonic observations allow a new interpretation of the recent tectonic behaviour of the outer fore arc in the caldera area northern chile 27 s two periods of deformation are distinguished based on large scale neogene to quaternary features of the westernmost part of the coastal cordillera late miocene to early pliocene deformations characterized by a weak ne sw to e w extension is followed by uppermost pliocene nw se to e w compression the middle pleistocene to recent time is characterized by vertical uplift and nw se extension these deformations provide clear indications of the occurrence of moderate to large earthquakes microseismic observations however indicate a lack of shallow crustal seismicity in coastal zone we propose that both long term brittle deformation and uplift are linked to the subduction seismic cycle

active tectonics of the andes nearly 90 mm a 1 of relative plate convergence is absorbed in the andean plate boundary zone the pattern of active tectonics shows remarkable variations in the way in which the plate slip vector is partitioned into displacement and strain and the ways in which compatibility between different segments is solved along any traverse across the plate boundary zone the sum of relative velocities between points must equal the relative plate motion we have developed a kinematic synthesis of displacement and strain partitioning in the andes from 47 s to 5 n relevant for the last 5 ma based upon 1 relative plate motion deduced from oceanic circuits giving a roughly constant azimuth between 075 and 080 2 moment tensor solutions for over 120 crustal earthquakes since 1960 3 structural studies of deformed plio pleistocene rocks 4 topographic geomorphic studies 5 palaeomagnetic data and 6 geodetic data we recognize four neotectonic zones with subzones and boundary transfer zones that are partitioned in different ways these zones are not coincident with the classic zones defined by the presence or absence of a volcanic chain or differences in finite displacements and strains and tectonic form the long term segmentation and finite evolution of the andes may not occur in constantly defined segments in space and time in segment 1 47 39 s the slip vector is partitioned into roughly orthogonal benioff zone slip with large magnitude large slip surface earthquakes and both distributed dextral shear giving clockwise rotations of up to 50 and dextral slip in the curved liquine ofqui fault system giving 5 10 of anticlockwise fore arc rotation in segment 2 39 20 s the slip vector is partitioned into benioff zone slip roughly parallel with the slip vector andean crustal shortening and a very small component of dextral slip including that on the atacama fault system between 39 and 34 s a cross strike dextral transfer which deflects the chile trench and the volcanic arc absorbs the shortening contrast between segments 1 and 2 in segment 3 20 6 s the slip vector is partitioned into roughly orthogonal benioff zone slip crustal shortening sinistral trench parallel faulting and northeast southwest extension compatibility between segments 2 and 3 is maintained by the sinistral east southeast trending cochabamba shear zone and north trending dextral faults in segment 4 6 s to 5 n the slip vector is partitioned into roughly orthogonal benioff zone slip and dextral strike slip faulting in the fore arc and volcanic chain

morphotectonic segmentation of an active forearc 37 41 s chile abstract active forearc regions are characterized by seismo and morphotectonic segments that record recurrent seismic activity and subduction related tectonic deformation on different timescales however it is not well known on which timescales morphotectonic forearc segments retain their tectono geomorphic identity how they are related to earthquake rupture zones and what governs their long term evolution the forearc of the active convergent margin of south central chile 37 41 s is located within the rupture zone of the 1960 chile mw 9 6 megathrust earthquake in this region we combine geomorphological sedimentologic and morphometric dem analysis with compiled structural and geophysical data to reconstruct the morphotectonic evolution of the forearc the southern chile forearc comprises three segments nahuelbuta tolten and bueno segments that record a differential structural and geomorphic evolution whereas the tolten segment appears to be quasi stable the other two segments record pronounced ongoing quaternary uplift the nahuelbuta and bueno segments contain the n s oriented coastal cordillera characterized by numerous tectonically controlled drainage anomalies and evidence of sediment rerouting the morphotectonic segmentation appears to have persisted over timescales of 105 to 106 years importantly these segments do not correlate with earthquake rupture zones that exhibit a short term variability over 102 to 103 years thus earthquake rupture zones are transient second order phenomena which do not determine the long term morphotectonic forearc segmentation overall the differential forearc evolution and segmentation is influenced by a complex interplay of inherited upper plate structures and physical properties of the subducting oceanic nazca plate